Subject content

Introduction to Subject Content

Introduction to subject content

The subject content of this specification is presented in five sections:

  • How Science Works
  • the three sections of substantive content, Biology 2, Chemistry 2, Physics 2
  • the Controlled Assessment (Unit 4).

It is intended that the How Science Works content is integrated and delivered not only through the Controlled Assessment but also through the context of the content of Biology 2, Chemistry 2 and Physics 2.

The organisation of each sub-section of the substantive content is designed to facilitate this approach. Each of the sub-sections of Biology 2, Chemistry 2 and Physics 2 starts with the statement:

'Candidates should use their skills, knowledge and understanding to:'.

This introduces a number of activities, for example:

  • make informed judgements about the social and ethical issues concerning the use of stem cells from embryos in medical research and treatments.

These activities are intended to enable candidates to develop the skills, knowledge and understanding of How Science Works.

Other aspects of the skills, knowledge and understanding of How Science Works will be better developed through investigative work and it is expected that teachers will adopt a practical enquiry approach to the teaching of many topics.

The subject content is presented in two columns. The left-hand column lists the content that needs to be delivered. The right-hand column contains guidance and expansion of the content to aid teachers in delivering it and gives further details on what will be examined.

At the end of each section there is a list of ideas for investigative practical work that could be used to help candidates develop their practical enquiry skills to understand and engage with the content.

Opportunities to carry out practical work should be provided in the context of each section.

 These opportunities should allow candidates to:

  • use their knowledge and understanding to pose scientific questions and define scientific problems
  • plan and carry out investigative activities, including appropriate risk management, in a range of contexts
  • collect, select, process, analyse and interpret both primary and secondary data to provide evidence 
  • evaluate their methodology, evidence and data.

In the written papers, questions will be set that examine How Science Works in biology, chemistry and physics contexts. Examination questions will use examples that are both familiar and unfamiliar to candidates. All applications will use the knowledge and understanding developed through the substantive content.

Tiering of subject content

In this specification there is additional content for Higher Tier candidates. This is denoted in the subject content in bold type and annotated as HT only in Sections 3.3 to 3.5.

3.3 Unit 1: Biology 2

B2.1 Cells and simple cell transport

All living things are made up of cells. The structures of different types of cells are related to their functions. To get into or out of cells, dissolved substances have to cross the cell membranes.

Candidates should use their skills, knowledge and understanding to:

  • relate the structure of different types of cells to their function.

B2.1.1 Cells and cell structure

a) Most human and animal cells have the following parts:

  • a nucleus, which controls the activities of the cell
  • cytoplasm, in which most of the chemical reactions take place
  • a cell membrane, which controls the passage of substances into and out of the cell
  • mitochondria, which is where most energy is released in respiration
  • ribosomes, which is where protein synthesis occurs.

b) Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell. Plant cells often have:

  • chloroplasts, which absorb light energy to make food
  • a permanent vacuole filled with cell sap.

c) A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall; the genes are not in a distinct nucleus.

d) Yeast is a single-celled organism. Yeast cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.

e) Cells may be specialised to carry out a particular function.

B2.1.2 Dissolved substances

a) Dissolved substances can move into and out of cells by diffusion.

b) Diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration to a region with a lower concentration. The greater the difference in concentration, the faster the rate of diffusion.

c) Oxygen required for respiration passes through cell membranes by diffusion.

Suggested ideas for practical work to develop skills and understanding include the following:

  • observation of cells under a microscope, eg sprouting mung beans to show root hair cells
  • computer simulations to model the relative size of different cells, organelles and molecules
  • computer simulations to model the process of diffusion
  • making model cells
  • diffusion of ammonium hydroxide in a glass tube using litmus as the indicator
  • investigate how temperature affects the rate of diffusion of glucose through Visking tubing

B2.2 Tissues, organs and organ systems

The cells of multicellular organisms may differentiate and become adapted for specific functions. Tissues are aggregations of similar cells; organs are aggregations of tissues performing specific physiological functions. Organs are organised into organ systems, which work together to form organisms.

 B2.2.1 Animal Organs

a) Large multicellular organisms develop systems for exchanging materials. During the development of a multicellular organism, cells differentiate so that they can perform different functions.

Additional guidance:

Candidates should develop an understanding of size and scale in relation to cells, tissues, organs and organ systems.

b) A tissue is a group of cells with similar structure and function. Examples of tissues include:

  • muscular tissue, which can contract to bring about movement
  • glandular tissue, which can produce substances such as enzymes and hormones
  • epithelial tissue, which covers some parts of the body.

c) Organs are made of tissues. One organ may contain several tissues. The stomach is an organ that contains:

  • muscular tissue, to churn the contents
  • glandular tissue, to produce digestive juices
  • epithelial tissue, to cover the outside and the inside of the stomach.

d) Organ systems are groups of organs that perform a particular function. The digestive system is one example of a system in which humans and other mammals exchange substances with the environment.

The digestive system includes:

  • glands, such as the pancreas and salivary glands, which produce digestive juices
  • the stomach and small intestine, where digestion occurs
  • the liver, which produces bile
  • the small intestine, where the absorption of soluble food occurs
  • the large intestine, where water is absorbed from the undigested food, producing faeces.

Additional guidance:

Candidates should be able to recognise the organs of the digestive system on a diagram.

B2.2.2 Plant organs

a) Plant organs include stems, roots and leaves.

 Additional guidance:

Details of the internal structure of these organs are limited to the leaf.

b) Examples of plant tissues include:

  • epidermal tissues, which cover the plant
  • mesophyll, which carries out photosynthesis
  • xylem and phloem, which transport substances around the plant.

B2.3 Photosynthesis

Green plants and algae use light energy to make their own food. They obtain the raw materials they need to make this food from the air and the soil. The conditions in which plants are grown can be changed to promote growth.

Candidates should use their skills, knowledge and understanding to:

  • interpret data showing how factors affect the rate of photosynthesis
  • evaluate the benefits of artificially manipulating the environment in which plants are grown.

B2.3.1 Photosynthesis

a) Photosynthesis is summarised by the equation:

Photosynthesis equation

b) During photosynthesis:

  • light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and algae
  • this energy is used by converting carbon dioxide (from the air) and water (from the soil) into sugar (glucose)
  • oxygen is released as a by-product.

c) The rate of photosynthesis may be limited by:

  • shortage of light
  • low temperature
  • shortage of carbon dioxide.

d) Light, temperature and the availability of carbon dioxide interact and in practice any one of them may be the factor that limits photosynthesis.

Additional guidance:

Candidates should be able to relate the principle of limiting factors to the economics of enhancing the following conditions in greenhouses:

  • light intensity
  • temperature
  • carbon dioxide concentration.

e) The glucose produced in photosynthesis may be converted into insoluble starch for storage. Plant cells use some of the glucose produced during photosynthesis for respiration.

f) Some glucose in plants and algae is used:

  • to produce fat or oil for storage
  • to produce cellulose, which strengthens the cell wall
  • to produce proteins.

 g) To produce proteins, plants also use nitrate ions that are absorbed from the soil.

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigating the need for chlorophyll for photosynthesis with variegated leaves
  • taking thin slices of potato and apple and adding iodine to observe under the microscope
  • investigate the effects of light, temperature and carbon dioxide levels (using Cabomba, algal balls or leaf discs from brassicas) on the rate of photosynthesis
  • computer simulations to model the rate of photosynthesis in different conditions
  • the use of sensors to investigate the effect of carbon dioxide and light levels on the rate of photosynthesis and the release of oxygen.

B2.4 Organisms and their environment

Living organisms form communities, and we need to understand the relationships within and between these communities. These relationships are affected by external influences.

Candidates should use their skills, knowledge and understanding to:

  • suggest reasons for the distribution of living organisms in a particular habitat
  • evaluate methods used to collect environmental data, and consider the validity of the method and the reproducibility of the data as evidence for environmental change.

Additional guidance:

Candidates should understand:

  • the terms mean, median and mode
  • that sample size is related to both validity and reproducibility.

B2.4.1 Distribution of organisms

a) Physical factors that may affect organisms are:

  • temperature
  • availability of nutrients
  • amount of light
  • availability of water
  • availability of oxygen and carbon dioxide.

b) Quantitative data on the distribution of organisms can be obtained by:

  • random sampling with quadrats
  • sampling along a transect.

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigative fieldwork involving sampling techniques and the use of quadrats and transects; which might include, on a local scale, the:
    • patterns of grass growth under trees
    • distribution of daisy and dandelion plants in a field
    • distribution of lichens or moss on trees, walls and other surfaces
    • distribution of the alga Pleurococcus on trees, walls and other surfaces
    • leaf size in plants growing on or climbing against walls, including height and effect of aspect
  • analysing the measurement of specific abiotic factors in relation to the distribution of organisms
  • the study of hay infusions
  • the use of sensors to measure environmental conditions in a fieldwork context.

B2.5 Proteins – their functions and uses

Proteins have many functions, both inside and outside the cells of living organisms. Proteins, as enzymes, are now used widely in the home and in industry.

Candidates should use their skills, knowledge and understanding to:

  • evaluate the advantages and disadvantages of using enzymes in the home and in industry.

B2.5.1 Proteins

a) Protein molecules are made up of long chains of amino acids. These long chains are folded to produce a specific shape that enables other molecules to fit into the protein. Proteins act as:

  • structural components of tissues such as muscles
  • hormones
  • antibodies
  • catalysts.

b) Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes. Enzymes are proteins.

B2.5.2 Enzymes

a) The shape of an enzyme is vital for the enzyme's function. High temperatures change the shape.

b) Different enzymes work best at different pH values.

c) Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules. They catalyse the breakdown of large molecules into smaller molecules.

d) The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine.

e) Protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and the small intestine.

f) Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine.

g) The stomach also produces hydrochloric acid. The enzymes in the stomach work most effectively in these acid conditions.

h) The liver produces bile, which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively.

i) Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry.

In the home:

  • biological detergents may contain protein-digesting and fat-digesting enzymes (proteases and lipases)
  • biological detergents are more effective at low temperatures than other types of detergents.

In industry:

  • proteases are used to 'pre-digest' the protein in some baby foods
  • carbohydrases are used to convert starch into sugar syrup
  • isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and therefore can be used in smaller quantities in slimming foods.

j) In industry, enzymes are used to bring about reactions at normal temperatures and pressures that would otherwise require expensive, energy-demanding equipment. However, most enzymes are denatured at high temperatures and many are costly to produce.

Suggested ideas for practical work to develop skills and understanding include the following:

  • design an investigation to find the optimum temperature for biological and non-biological washing powders to remove stains from cotton and other materials
  • investigate the action of enzymes using catalase at different concentrations and measuring the rate at which oxygen is given off from different foods, eg liver, potato, celery and apple
  • plan and carry out an investigation into enzyme action using the reaction between starch and amylase at different temperatures, pH and concentrations
  • using small pieces of cooked sausage, use 2% pepsin and 0.01M HCl in water baths at different temperatures to estimate the rate of digestion. This can also be carried out with 2% trypsin and 0.1M NaOH. The concentration of both enzymes can be varied
  • using computer simulations of enzymes to model their action in varying conditions of pH, temperature and concentration.

B2.6 Aerobic and anaerobic respiration

Respiration in cells can take place aerobically or anaerobically. The energy released is used in a variety of ways. The human body needs to react to the increased demand for energy during exercise.

Candidates should use their skills, knowledge and understanding to:

  • interpret the data relating to the effects of exercise on the human body.

B2.6.1 Aerobic respiration

a) The chemical reactions inside cells are controlled by enzymes.

b) During aerobic respiration (respiration that uses oxygen) chemical reactions occur that:

  • use glucose (a sugar) and oxygen
  • release energy.

c) Aerobic respiration takes place continuously in both plants and animals.

d) Most of the reactions in aerobic respiration take place inside mitochondria.

e) Aerobic respiration is summarised by the equation:

glucose + oxygen ➞ carbon dioxide + water (+ energy)

f) Energy that is released during respiration is used by the organism.

The energy may be used:

  • to build larger molecules from smaller ones
  • in animals, to enable muscles to contract
  • in mammals and birds, to maintain a steady body temperature in colder surroundings
  • in plants, to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins.

g) During exercise a number of changes take place:

  • the heart rate increases
  • the rate and depth of breathing increases.

h) These changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen and increase the rate of removal of carbon dioxide.

i) Muscles store glucose as glycogen, which can then be converted back to glucose for use during exercise.

B2.6.2 Anaerobic respiration

a) During exercise, if insufficient oxygen is reaching the muscles they use anaerobic respiration to obtain energy.

b) Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid.

c) Higher tier only:

As the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration. Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise lactic acid to carbon dioxide and water.

d) If muscles are subjected to long periods of vigorous activity they become fatigued, ie they stop contracting efficiently. One cause of muscle fatigue is the build-up of lactic acid in the muscles. Blood flowing through the muscles removes the lactic acid.

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigating the rate of respiration in yeast using carbon dioxide sensors and dataloggers
  • investigating the effect of exercise on pulse rate, either physically or using pulse sensors and dataloggers
  • investigating the link between exercise and breathing rate with a breathing sensor
  • investigating holding masses at arm's length and timing how long it takes the muscles to fatigue
  • designing an investigation using force meters and dataloggers to find the relationship between the amount of force exerted by a muscle and muscle fatigue

B2.7 Cell division and inheritance

Characteristics are passed on from one generation to the next in both plants and animals. Simple genetic diagrams can be used to show this. There are ethical considerations in treating genetic disorders.

Candidates should use their skills, knowledge and understanding to:

  • explain why Mendel proposed the idea of separately inherited factors and why the importance of this discovery was not recognised until after his death

Additional guidance:

Candidates should be familiar with principles used by Mendel in investigating monohybrid inheritance in peas. They should understand that Mendel's work preceded the work by other scientists which linked Mendel's 'inherited factors' with chromosomes.

  • interpret genetic diagrams, including family trees
  • higher tier only: construct genetic diagrams of monohybrid crosses and predict the outcomes of monohybrid crosses and be able to use the terms homozygous, heterozygous, phenotype and genotype

Addtional guidance:

Foundation Tier candidates should be able to interpret genetic diagrams of monohybrid inheritance and sex inheritance but will not be expected to construct genetic diagrams or use the terms homozygous, heterozygous, phenotype or genotype.

  • predict and/or explain the outcome of crosses between individuals for each possible combination of dominant and recessive alleles of the same gene
  • Make informed judgements about the social and ethical issues concerning the use of stem cells from embryos in medical research and treatments
  • Make informed judgements about the economic, social and ethical issues concerning embryo screening.

Additional guidance:

Data may be given for unfamiliar contexts.

B2.7.1 Cell Division

a) In body cells the chromosomes are normally found in pairs. Body cells divide by mitosis.

Additional guidance:

Knowledge and understanding of the stages in mitosis and meiosis is not required.

b) The chromosomes contain the genetic information.

c) When a body cell divides by mitosis:

  • copies of the genetic material are made
  • then the cell divides once to form two genetically identical body cells

Additional guidance:

Throughout section 2.7 candidates should develop an understanding of the relationship from the molecular level upwards between genes, chromosomes, nuclei and cells and to relate these to tissues, organs and systems (2.2 and 2.3).

d) Mitosis occurs during growth or to produce replacement cells.

e) Body cells have two sets of chromosomes; sex cells (gametes) have only one set.

f) Cells in reproductive organs – testes and ovaries in humans – divide to form gametes.

Additional guidance:

For Foundation Tier, knowledge of meiosis is restricted to where the process occurs and that gametes are produced by meiosis.

g) The type of cell division in which a cell divides to form gametes is called meiosis.

h) Higher Tier only: When a cell divides to form gametes:

  • copies of the genetic information are made
  • then the cell divides twice to form four gametes, each with a single set of chromosomes.

i) When gametes join at fertilisation, a single body cell with new pairs of chromosomes is formed. A new individual then develops by this cell repeatedly dividing by mitosis.

Additional guidance:

Candidates should understand that genetic diagrams are biological models which can be used to predict the outcomes of crosses.

j) Most types of animal cells differentiate at an early stage whereas many plant cells retain the ability to differentiate throughout life. In mature animals, cell division is mainly restricted to repair and replacement.

k) Cells from human embryos and adult bone marrow, called stem cells, can be made to differentiate into many different types of cells, eg nerve cells.

Additional guidance:

Knowledge and understanding of stem cell techniques is not required.

l) Human stem cells have the ability to develop into any kind of human cell.

m) Treatment with stem cells may be able to help conditions such as paralysis

n) The cells of the offspring produced by asexual reproduction are produced by mitosis from the parental cells. They contain the same alleles as the parents

B2.7.2 Genetic Variation

a) Sexual reproduction gives rise to variation because, when gametes fuse, one of each pair of alleles comes from each parent.

b) In human body cells, one of the 23 pairs of chromosomes carries the genes that determine sex. In females the sex chromosomes are the same (XX); in males the sex chromosomes are different (XY).

c) Some characteristics are controlled by a single gene. Each gene may have different forms called alleles.

d) An allele that controls the development of a characteristic when it is present on only one of the chromosomes is a dominant allele.

e) An allele that controls the development of characteristics only if the dominant allele is not present is a recessive allele.

f) Chromosomes are made up of large molecules of DNA (deoxyribo nucleic acid) which has a double helix structure.

Additional guidance:

Candidates are not expected to know the names of the four bases or how complementary pairs of bases enable DNA replication to take place.

g) A gene is a small section of DNA

h) Higher Tier only: Each gene codes for a particular combination of amino acids which make a specific protein.

i) Each person (apart from identical twins) has unique DNA. This can be used to identify individuals in a process known as DNA fingerprinting.

Additional guidance:

Knowledge and understanding of genetic fingerprinting techniques is not required.

B2.7.3 Genetic Disorders

a) Some disorders are inherited.

b) Polydactyly – having extra fingers or toes – is caused by a dominant allele of a gene and can therefore be passed on by only one parent who has the disorder.

Additional guidance:

Attention is drawn to the potential sensitivity needed in teaching about inherited disorders.

c) Cystic fibrosis (a disorder of cell membranes) must be inherited from both parents. The parents may be carriers of the disorder without actually having the disorder themselves. It is caused by a recessive allele of a gene and can therefore be passed on by parents, neither of whom has the disorder.

d) Embryos can be screened for the alleles that cause these and other genetic disorders.

Additional guidance:

Knowledge and understanding of embryo screening techniques is not required.

Suggested ideas for practical work to develop skills and understanding include the following:

  • observation or preparation and observation of root tip squashes to illustrate chromosomes and mitosis
  • using genetic beads to model mitosis and meiosis and genetic crosses
  • making models of DNA
  • extracting DNA from kiwi fruit.

B2.8 Speciation

Changes in the environment of plants and animals may cause them to die out. The fossil record shows that new organisms arise, flourish, and after a time become extinct. The record also shows changes that lead to the formation of new species.

Candidates should use their skills, knowledge and understanding to:

  • suggest reasons why scientists cannot be certain
    about how life began on Earth.

Addtional guidence:

The uncertainty arises from the lack of enough valid and reliable evidence.

B2.8.1 Old and new species

a) Evidence for early forms of life comes from fossils.

b) Fossils are the 'remains' of organisms from many
years ago, which are found in rocks. Fossils may
be formed in various ways:

  • from the hard parts of animals that do not
    decay easily
  • from parts of organisms that have not decayed
    because one or more of the conditions needed
    for decay are absent
  • when parts of the organism are replaced by
    other materials as they decay
  • as preserved traces of organisms, eg footprints,
    burrows and rootlet traces.

c) Many early forms of life were soft-bodied, which
means that they have left few traces behind.
What traces there were have been mainly
destroyed by geological activity.

d) We can learn from fossils how much or how little
different organisms have changed as life developed
on Earth.

e) Extinction may be caused by:

  • changes to the environment over geological time
  • new predators
  • new diseases
  • new, more successful, competitors
  • a single catastrophic event, eg massive volcanic eruptions or collisions with asteroids
  • through the cyclical nature of speciation.

f) New species arise as a result of:

  • isolation – two populations of a species become separated, eg geographically

HT only:

  • genetic variation – each population has a wide range of alleles that control their characteristics
  • natural selection – in each population, the alleles that control the characteristics which help the organism to survive are selected
  • speciation – the populations become so different that successful interbreeding is no longer possible.

Additional Guidence:

For Foundation Tier, ideas are restricted to knowledge and understanding of isolation.

3.4 Unit 2: Chemistry 2

C2.1 Structure and bonding

Throughout this unit candidates will be expected to write word equations for reactions specified. Higher tier candidates will also be expected to write and balance symbol equations for reactions specified throughout the unit.

C2.1 Structure and bonding

Simple particle theory is developed in this unit to include atomic structure and bonding. The arrancgement of electrons in atoms can be used to explain what happens when elements react and how atoms join together to form different types of substances.

Candidates should use their skills, knowledge and understanding to:

  • write formulae for ionic compounds from given symbols and ionic charges
  • represent the electronic structure of the ions in sodium chloride, magnesium oxide and calcium chloride in the following form:
electronic structure for sodium ion 
for sodium ion (Na+)
  • represent the covalent bonds in molecules such as water, ammonia, hydrogen, hydrogen chloride, methane and oxygen, and in giant structures such as diamond and silicon dioxide, in the following forms
 representation of covalent bonds
  • Higher tier only: represent the bonding in metals in the following form: C2-1 Structure and Bonding Diagram 2

C2.1.1 Structure and bonding

a) Compounds are substances in which atoms of two or more elements are chemically combined.

b) Chemical bonding involves either transferring or sharing electrons in the highest occupied energy levels (shells) of atoms in order to achieve the electronic structure of a noble gas.

c) When atoms form chemical bonds by transferring electrons, they form ions. Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions. Ions have the electronic structure of a noble gas (Group 0).

Additional guidance:

Candidates should be able to relate the charge on simple ions to the group number of the element in the periodic table.

d) The elements in Group 1 of the periodic table, the alkali metals, all react with non-metal elements to form ionic compounds in which the metal ion has a single positive charge.

Additional guidance:

Knowledge of the chemical properties of alkali metals is limited to their reactions with non-metal elements.

e) The elements in Group 7 of the periodic table, the halogens, all react with the alkali metals to form ionic compounds in which the halide ions have a single negative charge.

Additional guidance:

Knowledge of the chemical properties of the halogens is limited to reactions with alkali metals.

f) An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.

Additional guidance:

Candidates should be familiar with the structure of sodium chloride but do not need to know the structures of other ionic compounds.

g) When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong. Some covalently bonded substances consist of simple molecules such as H2, Cl2, O2, HCl, H2O, NH3 and CH4. Others have giant covalent structures (macromolecules), such as diamond and silicon dioxide.

Additional guidance:

Candidates should know the bonding in the examples in the specification for this unit, and should be able to recognise simple molecules and giant structures from diagrams that show their bonding.

h) Metals consist of giant structures of atoms arranged in a regular pattern.

i) Higher tier only: The electrons in the highest occupied energy levels (outer shell) of metal atoms are delocalised and so free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions.

Suggested ideas for practical work to develop skills and understanding include the following:

  • molecular modelling
  • modelling electron transfer and electron sharing using computer simulations
  • Group 1 and Group 7 reactions, eg sodium with chlorine
  • the reactions of bromine, chlorine and iodine with iron wool
  • growing metal crystals by displacement reactions using metals and salts
  • modelling metal structures using polyspheres and bubble rafts.

C2.2 How structure influences the properties and uses of substances

C2.2 How structure influences the properties and uses of substances

Substances that have simple molecular, giant ionic and giant covalent structures have very different properties. Ionic, covalent and metallic bonds are strong. However, the forces between molecules are weaker, eg in carbon dioxide and iodine. Metals have many uses. When different metals are combined, alloys are formed. Shape memory alloys have a range of uses. There are different types of polymers with different uses. Nanomaterials have new properties because of their very small size.

Candidates should use their skills, knowledge and understanding to:

  • relate the properties of substances to their uses

Additional guidance:

Candidates may be provided with information about the properties of substances that are not specified in this unit to enable them to relate these to their uses.

  • suggest the type of structure of a substance given its properties
  • evaluate developments and applications of new materials, eg nanomaterials, fullerenes and shape memory materials.

Additional guidance:

Candidates should be familiar with some examples of new materials but do not need to know the properties or names of specific new materials.

C2.2.1 Molecules

a) Substances that consist of simple molecules are gases, liquids or solids that have relatively low melting points and boiling points.

b) Higher tier only: Substances that consist of simple molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

Additional guidance:

Candidates need to be able to explain that intermolecular forces are weak in comparison with covalent bonds.

c) Substances that consist of simple molecules do not conduct electricity because the molecules do not have an overall electric charge.

C2.2.2 Ionic compounds

a) Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces in all directions between oppositely charged ions. These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

Additional guidance:

Knowledge of the structures of specific ionic compounds other than sodium chloride is not required.

b) When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry the current.

C2.2.3 Covalent structures

a) Atoms that share electrons can also form giant structures or macromolecules. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures (lattices) of atoms. All the atoms in these structures are linked to other atoms by strong covalent bonds and so they have very high melting points.

Additional guidance:

Candidates should be able to recognise other giant structures or macromolecules from diagrams showing their bonding.

b) In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard.

c) In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery.

Additional guidance: Higher Tier candidates should be able to explain the properties of graphite in terms of weak intermolecular forces between the layers.

d) Higher tier only: In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity.

Additional guidance: Candidates should realise that graphite is similar to metals in that it has delocalised electrons.

e) Higher tier only: Carbon can also form fullerenes with different numbers of carbon atoms. Fullerenes can be used for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg in tennis rackets.

Additional guidance: Candidates' knowledge is limited to the fact that the structure of fullerenes is based on hexagonal rings of carbon atoms.

C2.2.4 Metals

a) Higher tier only: Metals conduct heat and electricity because of the delocalised electrons in their structures.

Additional guidance: Candidates should know that conduction depends on the ability of electrons to move throughout the metal.

b) The layers of atoms in metals are able to slide over each other and so metals can be bent and shaped.

c) Alloys are usually made from two or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other and so make alloys harder than pure metals.

d) Shape memory alloys can return to their original shape after being deformed, eg Nitinol used in dental braces.

C2.2.5 Polymers

a) The properties of polymers depend on what they are made from and the conditions under which they are made. For example, low density (LD) and high density (HD) poly(ethene) are produced using different catalysts and reaction conditions.

b) Thermosoftening polymers consist of individual, tangled polymer chains. Thermosetting polymers consist of polymer chains with cross-links between them so that they do not melt when they are heated.

Additional guidance: Higher Tier candidates should be able to explain the properties of thermosoftening polymers in terms of intermolecular forces.

C2.2.6 Nanoscience

a) Nanoscience refers to structures that are 1–100nm in size, of the order of a few hundred atoms. Nanoparticles show different properties to the same materials in bulk and have a high surface area to volume ratio, which may lead to the development of new computers, new catalysts, new coatings, highly selective sensors, stronger and lighter construction materials, and new cosmetics such as sun tan creams and deodorants.

Additional guidance:

Candidates should know what is meant by nanoscience and nanoparticles and should consider some of the applications of these materials, but do not need to know specific examples or properties.

Questions may be set on information that is provided about these materials and their uses.

Suggested ideas for practical work to develop skills and understanding include the following:

  • demonstration of heating sulfur and pouring it into cold water to produce plastic sulfur
  • investigating the properties of ionic compounds, eg NaCl:
    • melting point, conductivity, solubility, use of hand lens to study crystal structure
  • investigating the properties of covalent compounds:
    • simple molecules, eg wax, methane, hexane
    • macromolecules, eg SiO2 (sand)
  • investigating the properties of graphite
  • demonstrations involving shape memory alloys
  • investigating the properties of metals and alloys:
    • melting point and conductivity, hardness, tensile strength, flexibility
    • using models, for example using expanded polystyrene spheres or computer animations to show how layers of atoms slide
    • making metal crystals by displacement reactions, eg copper wire in silver nitrate solution
  • distinguishing between LD and HD poly(ethene) using 50:50 ethanol:water
  • making slime using different concentrations of poly(ethenol) and borax solutions
  • investigating the effect of heat on polymers to find which are thermosoftening and which are thermosetting.

C2.3 Atomic structure, analysis and quantitative chemistry

C2.3 Atomic structure, analysis and quantitative chemistry

The relative masses of atoms can be used to calculate how much to react and how much we can produce, because no atoms are gained or lost in chemical reactions. There are various methods used to analyse these substances.

Candidates should use their skills, knowledge and understanding to:

  • evaluate sustainable development issues relating the starting materials of an industrial process to the product yield and the energy requirements of the reactions involved.

Additional guidance:

Candidates may be given appropriate information from which to draw conclusions.

C2.3.1 Atomic structure

a) Atoms can be represented as shown in this example:

b) The relative masses of protons, neutrons and electrons are:

Name of particle    Mass

Proton          1

Neutron         1

Electron         Very small

c) The total number of protons and neutrons in an atom is called its mass number.

d) Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.

e) Higher tier only: The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element.

f) The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.

Additional guidance:

Candidates are expected to use relative atomic masses in the calculations specified in the subject content. Candidates should be able to calculate the relative formula mass (Mr) of a compound from its formula.

g) The relative formula mass of a substance, in grams, is known as one mole of that substance.

C2.3.2 Analysing substances

a) Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small.

b) Chemical analysis can be used to identify additives in foods. Artificial colours can be detected and identified by paper chromatography.

Additional guidance:

Knowledge of methods other than paper chromatography is not required, but questions may include information based on the results of chemical analysis.

c) Gas chromatography linked to mass spectroscopy (GC-MS) is an example of an instrumental method:

  • gas chromatography allows the separation of a mixture of compounds
  • the time taken for a substance to travel through the column can be used to help identify the substance
  • the output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column 
  • higher tier only: the mass spectrometer can also give the relative molecular mass of each of the substances separated in the column.

Additional guidance:

Candidates need only a basic understanding of how GC-MS works, limited to:

  • different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated
  • the number of peaks on the output of a gas chromatograph shows the number of compounds present
  • the position of the peaks on the output indicates the retention time
  • a mass spectrometer can identify substances very quickly and accurately and can detect very small quantities.

Higher tier only: The molecular mass is given by the molecular ion peak.

Knowledge of fragmentation patterns is not required.

C2.3.3 Quantitative chemistry

a) The percentage of an element in a compound can be calculated from the relative mass of the element in the formula and the relative formula mass of the compound.

Additional guidance:

Candidates should be able to calculate the percentage of an element in a compound, given its formula

b) Higher tier only: The empirical formula of a compound can be calculated from the masses or percentages of the elements in a compound.

Additional guidance:

Candidates should be able to calculate empirical formulae.

c) Higher tier only: The masses of reactants and products can be calculated from balanced symbol equations.

Additional guidance:

Candidates should be able to calculate the masses of individual products from a given mass of a reactant and the balanced symbol equation.

d) Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because:

  • the reaction may not go to completion because it is reversible
  • some of the product may be lost when it is separated from the reaction mixture
  • some of the reactants may react in ways different from the expected reaction.

e) The amount of a product obtained is known as the yield. When compared with the maximum theoretical amount as a percentage, it is called the percentage yield.

Additional guidance:

Higher Tier candidates will be expected to calculate percentage yields of reactions.

f) In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called reversible reactions and are represented:

For example:

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigating food colours using paper chromatography
  • working out the empirical formulae of copper oxide and magnesium oxide
  • calculating yields, for example magnesium burning to produce magnesium oxide or wire wool burning to produce iron oxide
  • there are opportunities in this section to build in the idea of instrumentation precision, eg for the collection of gases, the use of boiling tubes, gas jars or gas syringes
  • copper sulfate – hydration/dehydration
  • heating ammonium chloride in a test tube
  • adding alkali and acid alternately to bromine water or to potassium chromate solution
  • 'blue bottle' reaction (RSC Classic Chemistry Experiments no. 83)
  • oscillating reaction (RSC Classic Chemistry Experiments no. 140).

C2.4 Rates of reaction

C2.4 Rates of reaction

Being able to speed up or slow down chemical reactions is important in everyday life and in industry. Changes in temperature, concentration of solution, gas pressure, surface area of solids and the presence of catalysts all affect the rates of reactions. Catalysts can help to reduce the cost of some industrial processes.

Candidates should use their skills, knowledge and understanding to:

  • interpret graphs showing the amount of product formed (or reactant used up) with time, in terms of the rate of the reaction

 Additional guidance:

Knowledge of specific reactions other than those in the subject content for this unit is not expected, but candidates will be expected to have studied examples of chemical reactions and processes in developing their skills during their study of this section.

  • explain and evaluate the development, advantages and disadvantages of using catalysts in industrial processes.

Additional guidance:

Information may be given in examination questions so that candidates can make evaluations.

C2.4.1 Rates of reaction

a) The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time:

b) Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy. The minimum amount of energy particles must have to react is called the activation energy.

c) Increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically. This increases the rate of reaction.

d) Increasing the pressure of reacting gases increases the frequency of collisions and so increases the rate of reaction.

e) Increasing the concentration of reactants in solutions increases the frequency of collisions and so increases the rate of reaction.

f) Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.

g) Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.

Additional guidance:

Knowledge of named catalysts other than those specified in the subject content for this unit is not required, but candidates should be aware of some examples of chemical reactions and processes that use catalysts.

h) Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs.

Suggested ideas for practical work to develop skills and understanding include the following:

  • designing and carrying out investigations into factors such as:
    • temperature, eg magnesium with acids at different temperatures
    • surface area, eg different sizes of marble chips
    • catalysts, eg the decomposition of hydrogen peroxide using manganese(IV) oxide, potato and/or liver; the ignition of hydrogen using platinum; oxidation of ammonia using platinum; cracking liquid paraffin using broken pot
    • concentration, eg sodium thiosulfate solution and dilute hydrochloric acid.

There are opportunities here for measurements using sensors (eg carbon dioxide, oxygen, light, pH, gas pressure and temperature) to investigate reaction rates.

C2.5 Exothermic and endothermic reactions

C2.5> Exothermic and endothermic reactions

Chemical reactions involve energy transfers. Many chemical reactions involve the release of energy. For other chemical reactions to occur, energy must be supplied.

Candidates should use their skills, knowledge and understanding to:

  • evaluate everyday uses of exothermic and endothermic reactions.

Additional guidance:

Candidates may be given data from which to draw conclusions.

C2.5.1 Energy transfer in chemical reactions

a) When chemical reactions occur, energy is transferred to or from the surroundings.

Additional guidance:

Knowledge of delta H (H) conventions and enthalpy changes, including the use of positive values for endothermic reactions and negative values for exothermic reactions, is not required.

b) An exothermic reaction is one that transfers energy to the surroundings. Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation. Everyday uses of exothermic reactions include self-heating cans (eg for coffee) and hand warmers.

c) An endothermic reaction is one that takes in energy from the surroundings. Endothermic reactions include thermal decompositions. Some sports injury packs are based upon endothermic reactions.

d) If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case. For example:

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigating temperature changes of neutralisations and displacement reactions, eg zinc and copper sulfate
  • investigating temperature changes when dissolving ammonium nitrate, or reacting citric acid and sodium hydrogencarbonate
  • adding ammonium nitrate to barium hydroxide
  • demonstration of the addition of concentrated sulfuric acid to sugar
  • demonstration of the reaction between iodine and aluminium after activation by a drop of water
  • demonstration of the screaming jelly baby
  • demonstration of the thermite reaction, ie aluminium mixed with iron(III) oxide
  • investigation of hand warmers, self-warming cans, sports injury packs.

There are opportunities here for measurements using temperature sensors to investigate energy transfer.

C2.6 Acids, bases and salts

C2.6 Acids, bases and salts

Soluble salts can be made from acids and insoluble salts can be made from solutions of ions. When acids and alkalis react the result is a neutralisation reaction.

Candidates should use their skills, knowledge and understanding to:

  • select an appropriate method for making a salt, given appropriate information.

C2.6.1 Making salts

a) The state symbols in equations are (s), ( l ), (g) and (aq).

b) Soluble salts can be made from acids by reacting them with:

  • metals – not all metals are suitable; some are too reactive and others are not reactive enough
  • insoluble bases – the base is added to the acid until no more will react and the excess solid is filtered off
  • alkalis – an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution.

Additional guidance:

Candidates should be able to suggest methods to make a named soluble salt.

c) Salt solutions can be crystallised to produce solid salts.

d) Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed. Precipitation can be used to remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent.

Additional guidance:

Candidates should be able to name the substances needed to make a named insoluble salt.

C2.6.2 Acids and bases

a) Metal oxides and hydroxides are bases. Soluble hydroxides are called alkalis.

b) The particular salt produced in any reaction between an acid and a base or alkali depends on:

  • the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates)
  • the metal in the base or alkali.

c) Ammonia dissolves in water to produce an alkaline solution. It is used to produce ammonium salts. Ammonium salts are important as fertilisers.

d) Hydrogen ions, H+(aq), make solutions acidic and hydroxide ions, OH–(aq), make solutions alkaline. The pH scale is a measure of the acidity or alkalinity of a solution.

Additional guidance:

Candidates should be familiar with the pH scale from 0 to 14, and that pH 7 is a neutral solution.

e) In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation:

Suggested ideas for practical work to develop skills and understanding include the following:

  • the preparation of soluble salts:
    • copper sulfate by adding copper oxide to sulfuric acid
    • magnesium sulfate by adding magnesium oxide to sulfuric acid
    • copper chloride by adding copper oxide to hydrochloric acid
    • zinc nitrate by adding zinc oxide to nitric acid
    • sodium chloride by adding sodium hydroxide to hydrochloric acid
    • copper sulfate by adding copper carbonate to sulfuric acid
    • investigation of the effect of conditions on the yield of the salt
  • the preparation of insoluble salts:
    • lead iodide by mixing solutions of lead nitrate and potassium iodide
    • barium sulfate by mixing solutions of barium chloride and sodium sulfate
    • investigation of the effect of conditions on the formation of precipitates.

There are opportunities here for using pH sensors to investigate neutralisation.

C2.7 Electrolysis

C2.7 Electrolysis

Ionic compounds have many uses and can provide other substances. Electrolysis is used to produce alkalis and elements such as aluminium, chlorine and hydrogen. Oxidation–reduction reactions do not just involve oxygen.

Candidates should use their skills, knowledge and understanding to:

  • predict the products of electrolysing solutions of ions

    Additional guidance:

    Knowledge and understanding is limited to the methods indicated in the subject content.

  • explain and evaluate processes that use the principles described in this unit, including the use of electroplating.

C2.7.1 Electrolysis

a) When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution.

b) Passing an electric current through ionic substances that are molten, for example lead bromide, or in solution breaks them down into elements. This process is called electrolysis and the substance that is broken down is called the electrolyte.

c) During electrolysis, positively charged ions move to the negative electrode, and negatively charged ions move to the positive electrode.

d) Electrolysis is used to electroplate objects. This may be for a variety of reasons and includes copper plating and silver plating.

e) At the negative electrode, positively charged ions gain electrons (reduction) and at the positive electrode, negatively charged ions lose electrons (oxidation).

f) If there is a mixture of ions, the products formed depend on the reactivity of the elements involved.

g) Higher tier only: Reactions at electrodes can be represented by half equations, for example:


or

Additional guidance:

Candidates should be able to complete and balance half equations for the reactions occurring at the electrodes during electrolysis.

h) Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite. Aluminium forms at the negative electrode and oxygen at the positive electrode. The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide.

Additional guidance:

Candidates should understand why cryolite is used in this process.

i) The electrolysis of sodium chloride solution produces hydrogen and chlorine. Sodium hydroxide solution is also produced. These are important reagents for the chemical industry, eg sodium hydroxide for the production of soap and chlorine for the production of bleach and plastics.

Suggested ideas for practical work to develop skills and understanding include the following:

  • the electrolysis of molten lead bromide or zinc chloride
  • investigation of the electrolysis of any solutions of a soluble ionic compound, eg copper chloride, sodium chloride, zinc bromide, zinc iodide
  • a demonstration of the Hoffman voltameter
  • the electroplating of copper foil with nickel in a nickel sulfate solution
  • the movement of ions, eg by the electrolysis of a crystal of KMnO4 on filter paper dampened with sodium chloride solution, or the electrolysis of CuCrO4 in a saturated urea solution using a U-tube
  • using conductivity sensors to monitor conductivity and changes in conductivity.

3.5 Unit 3: Physics 2

P2.1 Forces and their effects

P2.1 Forces and their effects

Forces can cause changes to the shape or motion of an object. Objects can move in a straight line at a constant speed. They can also change their speed and/ or direction (accelerate or decelerate). Graphs can help us to describe the movement of an object. These may be distance-time graphs or velocity-time graphs.

Candidates should use their skills, knowledge and understanding to:

  • interpret data from tables and graphs relating to speed, velocity and acceleration
  • evaluate the effects of alcohol and drugs on stopping distances
  • evaluate how the shape and power of a vehicle can be altered to increase the vehicle's top speed
  • draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object.

P2.1.1 Resultant forces

a) Whenever two objects interact, the forces they exert on each other are equal and opposite.

b) A number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together. This single force is called the resultant force.

c) A resultant force acting on an object may cause a change in its state of rest or motion.

Additional guidance:

Candidates should be able to determine the resultant of opposite or parallel forces acting in a straight line.

d) If the resultant force acting on a stationary object is:

  • zero, the object will remain stationary
  • not zero, the object will accelerate in the direction of the resultant force.

e) If the resultant force acting on a moving object is:

  • zero, the object will continue to move at the same speed and in the same direction
  • not zero, the object will accelerate in the direction of the resultant force.

P2.1.2 Forces and motion

a) The acceleration of an object is determined by the resultant force acting on the object and the mass of the object.

Additional guidance:

  • F is the resultant force in newtons, N
  • m is the mass in kilograms, kg
  • a is the acceleration in metres per second squared, m/s2

b) The gradient of a distance–time graph represents speed.

Additional guidance:

Candidates should be able to construct distance–time graphs for an object moving in a straight line when the body is stationary or moving with a constant speed.

c) Higher Tier only: Calculation of the speed of an object from the gradient of a distance–time graph.

d) The velocity of an object is its speed in a given direction.

e) The acceleration of an object is given by the equation: The gradient of a velocity–time graph represents acceleration.

Additional guidance:

  • a is the acceleration in metres per second squared, m/s2
  • v is the final velocity in metres per second, m/s
  • u is the initial velocity in metres per second, m/s
  • t is the time taken in seconds, s

f) The gradient of a velocity–time graph represents acceleration.

g) Higher Tier only: Calculation of the acceleration of an object from the gradient of a velocity–time graph.

h) Higher Tier only: Calculation of the distance travelled by an object from a velocity–time graph.

P2.1.3 Forces and braking

a) When a vehicle travels at a steady speed the resistive forces balance the driving force.

Additional guidance:

Candidates should realise that most of the resistive forces are caused by air resistance.

b) The greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance.

Additional guidance:

Candidates should understand that for a given braking force the greater the speed, the greater the stopping distance.

c) The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver's reaction time (thinking distance) and the distance it travels under the braking force (braking distance).

d) A driver's reaction time can be affected by tiredness, drugs and alcohol.

Additional guidance:

Candidates should appreciate that distractions may affect a driver's ability to react.

e) When the brakes of a vehicle are applied, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increase.

f) A vehicle's braking distance can be affected by adverse road and weather conditions and poor condition of the vehicle.

Additional guidance:

Candidates should understand that 'adverse road conditions' includes wet or icy conditions. Poor condition of the car is limited to the car's brakes or tyres.

P2.1.4 Forces and terminal velocity

a) The faster an object moves through a fluid the greater the frictional force that acts on it.

b) An object falling through a fluid will initially accelerate due to the force of gravity. Eventually the resultant force will be zero and the object will move at its terminal velocity (steady speed).

Additional guidance:

Candidates should understand why the use of a parachute reduces the parachutist's terminal velocity.

c) Draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object.

d) Calculate the weight of an object using the force exerted on it by a gravitational force:

Additional guidance:

  • W is the weight in newtons, N
  • m is the mass in kilograms, kg
  • g is the gravitational field strength in newtons per kilogram, N/kg

P2.1.5 Forces and elasticity

a) A force acting on an object may cause a change in shape of the object.

b) A force applied to an elastic object such as a spring will result in the object stretching and storing elastic potential energy. 

Additional guidance:

Calculation of the energy stored when stretching an elastic material is not required.

c) For an object that is able to recover its original shape, elastic potential energy is stored in the object when work is done on the object to change its shape.

d) The extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded:

Additional guidance:

  • F is the force in newtons, N
  • k is the spring constant in newtons per metre, N/m
  • e is the extension in metres, m

Suggested ideas for practical work to develop skills and understanding include the following:

  • dropping a penny and a feather in a vacuum and through the air to show the effect of air resistance
  • plan and carry out an investigation into Hooke's law
  • catapult practicals to compare stored energy
  • measurement of acceleration of trolleys using known forces and masses
  • timing objects falling through a liquid, eg wallpaper paste or glycerine, using light gates or stop clocks
  • plan and carry out an investigation to measure the effects of air resistance on parachutes, paper spinners, cones or bun cases
  • measuring reaction time with and without distractions, eg iPod off and then on.

P2.2 The kinetic energy of objects speeding up or slowing down

P2.2 The kinetic energy of objects speeding up or slowing down

When an object speeds up or slows down, its kinetic energy increases or decreases. The forces which cause the change in speed do so by doing work. The momentum of an object is the product of the object's mass and velocity.

Candidates should use their skills, knowledge and understanding to:

  • evaluate the benefits of different types of braking system, such as regenerative braking
  • evaluate the benefits of air bags, crumple zones, seat belts and side impact bars in cars.

Additional guidance:

This should include ideas of both energy changes and momentum changes.

P2.2.1 Forces and energy

a) When a force causes an object to move through a distance work is done.

b) Work done, force and distance are related by the equation:

Additional guidance:

  • W is the work done in joules, J
  • F is the force applied in newtons, N
  • d is the distance moved in the direction of the force in metres, m

c) Energy is transferred when work is done.

Additional guidance:

Candidates should be able to discuss the transfer of kinetic energy in particular situations. Examples might include shuttle re-entry or meteorites burning up in the atmosphere.

d) Work done against frictional forces.

e) Power is the work done or energy transferred in a given time.

Additional guidance:

  • P is the power in watts, W
  • E is the energy transferred in joules, J
  • t is the time taken in seconds, s

f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.

Additional guidance:

Candidates should understand that when an object is raised vertically work is done against gravitational force and the object gains gravitational potential energy.

  • Ep is the change in gravitational potential energy in joules, J
  • m is the mass in kilograms, kg
  • g is the gravitational field strength in newtons per kilogram, N/kg
  • h is the change in height in metres, m

g) The kinetic energy of an object depends on its mass and its speed.

Additional guidance:

  • Ek is the kinetic energy in joules, J
  • m is the mass in kilograms, kg
  • v is the speed in metres per second, m/s

P2.2.2 Momentum

a) Momentum is a property of moving objects.

Additional guidance:

  • p is momentum in kilograms metres per second, kg m/s
  • m is the mass in kilograms, kg
  • v is the velocity in metres per second, m/s

b) In a closed system the total momentum before an event is equal to the total momentum after the event. This is called conservation of momentum.

Additional guidance:

Candidates may be required to complete calculations involving two objects. Examples of events are collisions and explosions.

Suggested ideas for practical work to develop skills and understanding include the following:

  • investigating the transfer of Ep to Ek by dropping a card through a light gate
  • plan and carry out an investigation to measure velocity using trolleys and ramps
  • running upstairs and calculating work done and power, lifting weights to measure power
  • a motor lifting a load to show how power changes with load
  • stretching different materials before using as catapults to show the different amounts of energy transferred, indicated by speed reached by the object or distance travelled.

P2.3 Currents in electrical circuits

P2.3 Currents in electrical circuits

The current in an electric circuit depends on the resistance of the components and the supply.

Candidates should use their skills, knowledge and understanding to:

  • apply the principles of basic electrical circuits to practical situations
  • evaluate the use of different forms of lighting, in terms of cost and energy efficiency.

Additional guidance:

Examples might include filament bulbs, fluorescent bulbs and light-emitting diodes (LEDs).

P2.3.1 Static electricity

a) When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and onto the other.

b) The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.

c) When two electrically charged objects are brought together they exert a force on each other.

d) Two objects that carry the same type of charge repel. Two objects that carry different types of charge attract.

e) Electrical charges can move easily through some substances, eg metals.

P2.3.2 Electrical circuits

a) Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric charge. The size of the current is given by the equation:

Additional guidance:

  • I is the current in amperes (amps), A
  • Q is the charge in coulombs, C
  • t is the time in seconds, s

b) The potential difference (voltage) between two points in an electric circuit is the work done (energy transferred) per coulomb of charge that passes between the points.

Additional guidance: Teachers can use either of the terms potential difference or voltage. Questions will be set using the term potential difference. Candidates will gain credit for the correct use of either term.

  • V is the potential difference in volts, V
  • W is the work done in joules, J
  • Q is the charge in coulombs, C

c) Circuit diagrams using standard symbols. The following standard symbols should be known:

circuit diagram standard symbols

Additional guidance:

Candidates will be required to interpret and draw circuit diagrams.

Knowledge and understanding of the use of thermistors in circuits, eg thermostats is required.

Knowledge and understanding of the applications of light-dependent resistors (LDRs) is required, eg switching lights on when it gets dark.

d) Current–potential difference graphs are used to show how the current through a component varies with the potential difference across it.

e) The current–potential difference graphs for a resistor at constant temperature.

current potential difference graph

f) The resistance of a component can be found by measuring the current through, and potential difference across, the component.

g) The current through a resistor (at a constant temperature) is directly proportional to the potential difference across the resistor.

h) Calculate current, potential difference or resistance using the equation:

Additional guidance:

  • V is the potential difference in volts, V
  • I is the current in amperes (amps), A
  • R is the resistance in ohms, Ω 

i) The current through a component depends on its resistance. The greater the resistance the smaller the current for a given potential difference across the component.

j) The potential difference provided by cells connected in series is the sum of the potential difference of each cell (depending on the direction in which they are connected).

k) For components connected in series:

  • the total resistance is the sum of the resistance of each component
  • there is the same current through each component
  • the total potential difference of the supply is shared between the components.

I) For components connected in parallel:

  • the potential difference across each component is the same
  • the total current through the whole circuit is the sum of the currents through the separate components.

m) The resistance of a filament bulb increases as the temperature of the filament increases.

resistance of a filament bulb

Additional guidance:

Higher Tier only: Candidates should be able to explain resistance change in terms of ions and electrons.

n) The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.

current through a diode

o) An LED emits light when a current flows through it in the forward direction.

Additional guidance:

Candidates should be aware that there is an increasing use of LEDs for lighting, as they use a much smaller current than other forms of lighting.

p) The resistance of a light-dependent resistor (LDR) decreases as light intensity increases.

q) The resistance of a thermistor decreases as the temperature increases.

Additional guidance:

Knowledge of a negative temperature coefficient thermistor only is required.

Suggested ideas for practical work to develop skills and understanding include the following:

  • using filament bulbs and resistors to investigate potential difference/current characteristics
  • investigating potential difference/current characteristics for LDRs and thermistors
  • setting up series and parallel circuits to investigate current and potential difference
  • plan and carry out an investigation to find the relationship between the resistance of thermistors and their temperature
  • investigating the change of resistance of LDRs with light intensity.

P2.4 Using mains electricity safely and the power of electrical appliances

P2.4 Using mains electricity safely and the power of electrical appliances

Mains electricity is useful but can be very dangerous. It is important to know how to use it safely.

Electrical appliances transfer energy. The power of an electrical appliance is the rate at which it transforms energy. Most appliances have their power and the potential difference of the supply they need printed on them. From this we can calculate their current and the fuse they need.

Candidates should use their skills, knowledge and understanding to:

  • understand the principles of safe practice and recognise dangerous practice in the use of mains electricity
  • compare the uses of fuses and circuit breakers
  • evaluate and explain the need to use different cables for different appliances
  • consider the factors involved when making a choice of electrical appliances.

Additional guidance:

Candidates should consider the efficiency and power of the appliance.

P2.4.1 Household electricity

a) Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

b) An alternating current (a.c.) is one that is constantly changing direction.

Additional guidance:

Candidates should be able to compare and calculate potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces.

Higher Tier candidates should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces.

c) Mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

d) Most electrical appliances are connected to the mains using cable and a three-pin plug.

e) The structure of electrical cable.

Additional guidance:

Candidates should be familiar with both two-core and three-core cable.

f) The structure and wiring of a three-pin plug.

Additional guidance:

Knowledge and understanding of the materials used in three-pin plugs is required, as is the colour coding of the covering of the three wires.

g) If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

h) When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit.

i) Some circuits are protected by Residual Current Circuit Breakers (RCCBs).

Additional guidance:

Candidates should realise that RCCBs operate by detecting a difference in the current between the live and neutral wires. Knowledge of how the devices do this is not required.

Candidates should be aware of the fact that this device operates much faster than a fuse.

j) Appliances with metal cases are usually earthed.

Additional guidance:

Candidates should be aware of the fact that this device operates much faster than a fuse. Candidates should be aware that some appliances are double insulated, and therefore have no earth wire connection.

k) The earth wire and fuse together protect the wiring of the circuit.

Additional guidance:

Candidates should have an understanding of the link between cable thickness and fuse value.

P2.4.2 Current, charge and power

a) When an electrical charge flows through a resistor, the resistor gets hot.

Additional guidance:

Candidates should understand that a lot of energy is wasted in filament bulbs by heating. Less energy is wasted in power saving lamps such as Compact Fluorescent Lamps (CFLs).

Candidates should understand that there is a choice when buying new appliances in how efficiently they transfer energy.

b) The rate at which energy is transferred by an appliance is called the power.

Additional guidance: 

  • P is power in watts, W
  • E is energy in joules, J
  • t is time in seconds, s

c) Power, potential difference and current are related by the equation:

Additional guidance:

Candidates should be able to calculate the current through an appliance from its power and the potential difference of the supply, and from this determine the size of fuse needed.

  • P is power in watts, W
  • I is current in amperes (amps), A
  • V is potential difference in volts, V

d) Higher Tier only: Energy transferred, potential difference and charge are related by the equation:

Additional guidance:

  • E is energy in joules, J
  • V is potential difference in volts, V
  • Q is charge in coulombs, C

Suggested ideas for practical work to develop skills and understanding include the following:

  • measuring oscilloscope traces
  • demonstrating the action of fuse wires
  • using fluctuations in light intensity measurements from filament bulbs to determine the frequency of a.c.
  • measuring the power of 12 V appliances by measuring energy transferred (using a joulemeter or ammeter and voltmeter) in a set time.

P2.5 What happens when radioactive substances decay, and the uses and dangers of their emissions

P2.5 What happens when radioactive substances decay, and the uses and dangers of their emissions

Radioactive substances emit radiation from the nuclei of their atoms all the time. These nuclear radiations can be very useful but may also be very dangerous. It is important to understand the properties of different types of nuclear radiation. To understand what happens to radioactive substances when they decay we need to understand the structure of the atoms from which they are made. The use of radioactive sources depends on their penetrating power and half-life.

Candidates should use their skills, knowledge and understanding to:

  • evaluate the effect of occupation and/or location on the level of background radiation and radiation dose
  • evaluate the possible hazards associated with the use of different types of nuclear radiation
  • evaluate measures that can be taken to reduce exposure to nuclear radiations
  • evaluate the appropriateness of radioactive sources for particular uses, including as tracers, in terms of the type(s) of radiation emitted and their half-lives
  • explain how results from the Rutherford and Marsden scattering experiments led to the 'plum pudding' model being replaced by the nuclear model.

Additional guidance:

Candidates should realise that new evidence can cause a theory to be re-evaluated.

Candidates should realise that, according to the nuclear model, most of the atom is empty space.

P2.5.1 Atomic structure

a) The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded by electrons.

Additional guidance:

Candidates should appreciate the relative size of the nucleus compared to the size of the atom.

b) The relative masses and relative electric charges of protons, neutrons and electrons.

c) In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no overall electrical charge.

d) Atoms may lose or gain electrons to form charged particles called ions.

e) The atoms of an element always have the same number of protons, but have a different number of neutrons for each isotope. The total number of protons in an atom is called its atomic number. The total number of protons and neutrons in an atom is called its mass number.

P2.5.2 Atoms and radiation

a) Some substances give out radiation from the nuclei of their atoms all the time, whatever is done to them. These substances are said to be radioactive.

Additional guidance:

Candidates should be aware of the random nature of radioactive decay.

b) The origins of background radiation.

Additional guidance:

Knowledge and understanding should include both natural sources, such as rocks and cosmic rays from space, and man-made sources such as the fallout from nuclear weapons tests and nuclear accidents.

c) Identification of an alpha particle as two neutrons and two protons, the same as a helium nucleus, a beta particle as an electron from the nucleus and gamma radiation as electromagnetic radiation.

d) Higher Tier only: Nuclear equations to show single alpha and beta decay.

Additional guidance:

Candidates will be required to balance such equations, limited to the completion of atomic number and mass number. The identification of daughter elements from such decays is not required.

e) Properties of the alpha, beta and gamma radiations limited to their relative ionising power, their penetration through materials and their range in air.

f) Alpha and beta radiations are deflected by both electric and magnetic fields but gamma radiation is not.

Additional guidance:

All candidates should know that alpha particles are deflected less than beta particles and in an opposite direction.

Higher Tier candidates should be able to explain this in terms of the relative mass and charge of each particle.

g) The uses of and the dangers associated with each type of nuclear radiation.

h) The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level.

Suggested ideas for practical work to develop skills and understanding include the following:

  • using hot-cross buns to show the 'plum pudding' model
  • using dice to demonstrate probabilities involved in half-life
  • using Geiger counters to measure the penetration and range in air of the radiation from different sources.

P2.6 Nuclear fission and nuclear fusion

P2.6 Nuclear fission and nuclear fusion

During the process of nuclear fission atomic nuclei split. This process releases energy, which can be used to heat water and turn it into steam. The steam drives a turbine, which is connected to a generator and generates electricity.

Nuclear fusion is the joining together of atomic nuclei and is the process by which energy is released in stars.

Candidates should use their skills, knowledge and understanding to:

  • compare the uses of nuclear fusion and nuclear fission.

Additional guidance:

Limited to the generation of electricity.

P2.6.1 Nuclear fission

a) There are two fissionable substances in common use in nuclear reactors: uranium-235 and plutonium-239.

Additional guidance:

The majority of nuclear reactors use uranium-235.

b) Nuclear fission is the splitting of an atomic nucleus.

c) For fission to occur the uranium-235 or plutonium-239 nucleus must first absorb a neutron.

d) The nucleus undergoing fission splits into two smaller nuclei and two or three neutrons and energy is released.

e) The neutrons may go on to start a chain reaction.

Additional guidance:

Candidates should be able to sketch or complete a labelled diagram to illustrate how a chain reaction may occur.

P2.6.2 Nuclear fusion

a) Nuclear fusion is the joining of two atomic nuclei to form a larger one.

b) Nuclear fusion is the process by which energy is released in stars.

c) Stars form when enough dust and gas from space is pulled together by gravitational attraction. Smaller masses may also form and be attracted by a larger mass to become planets.

Additional guidance:

Candidates should be able to explain why the early Universe contained only hydrogen but now contains a large variety of different elements.

d) During the 'main sequence' period of its life cycle a star is stable because the forces within it are balanced.

Additional guidance: 

The term 'radiation pressure' will not be required.

e) A star goes through a life cycle. This life cycle is determined by the size of the star.

Additional guidance:

Candidates should be familiar with the chart on the next page that shows the life cycles of stars.

the life cycle of stars

f) Fusion processes in stars produce all of the naturally occurring elements. These elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life.

Additional guidance:

Candidates should be able to explain how stars are able to maintain their energy output for millions of years.

Candidates should know that elements up to iron are formed during the stable period of a star. Elements heavier than iron are formed in a supernova.

Suggested ideas for practical work to develop skills and understanding include the following:

  • using domino tracks for fission/chain reactions.

3.6 Unit 4 - Controlled Assessment

3.6.1 Introduction

This unit is assessed by Controlled Assessment. It is worth 25% of the total marks and consists of a minimum of one practical investigation based on topics in the specification.

Access arrangements (see sections 4.5 and 5.4) can enable candidates with special needs to undertake this assessment.

Teachers are encouraged to undertake a wide range of practical and investigative work, including fieldwork, with their candidates. We take the view that it is not good practice to do practical work only for the Controlled Assessment. As teachers know well, candidates enjoy and are motivated by practical work. Throughout this specification we have given many examples of practical work supporting the science content. Full details of this practical work are included in our resources package.

In this unit, candidates use a range of practical skills and knowledge in one investigation chosen from those supplied by AQA. The investigations are based on topics in the specification. Guidance for teachers will be given with each investigation. Every year, three Controlled Assessments will be available; one for Unit 2 and two for Unit 3. Each task assesses How Science Works skills, not candidates' knowledge and understanding of the science context.

The right-hand column of the tables below shows the Assessment Focus thread from National Strategies APP (Assessing Pupils' Progress). This will enable teachers to ensure progression from KS3 to KS4.

AS4.1 Plan practical ways to develop and test candidates' own scientific ideas

Candidates should be able to:

AS4.1.1 Develop hypothesis and plan practical ways to test them by:

Additional Guidance:

AF/thread

a) being able to develop a hypothesis

Candidates should be able to suggest the outcome of an investigation.

1/4

b) being able to test hypothesis

Candidates should be able to plan a fair test to investigate their hypothesis.

1/4

c) using appropriate technology.

Candidates should appreciate that technology such as data logging may provide a better means of obtaining data. They should be able to suggest appropriate technology for collecting data and explain why a technological method is the most appropriate. Candidates should use ICT whenever appropriate.

4/1

AS4.2 Assess and manage risks when carrying out practical work

Candidates should be able to:

AS4.2.1 assess and manage risks when carrying out practical work, by:

Additional Guidance:

AF/thread

a) identifying some possible hazards in practical situations

Candidates will be expected to independently recognise a range of familiar hazards and consult appropriate resources and expert advice.

4/4

b) suggesting ways of managing risks.

Candidates should assess risks to themselves and others and take action to reduce these risks by adapting their approaches to practical work in order to control risk.

4/4

AS4.3 Collect primary and secondary data

Candidates should be able to:

AS4.3.1 make observations, by:

Additional Guidance:

AF/thread

a) carrying out practical work and research, and using the data collected to develop hypotheses.

  4/3

 

 AS4.3.2 demonstrate an understanding of the need
to acquire high-quality data, by:

Additional Guidance:

AF/thread

a) appreciating that, unless certain variables are controlled, the results may not be valid

Candidates should be able to explain whether results can be considered valid and recognise when an instrument or technique might not be measuring the variable intended.

4/3

b) identifying when repeats are needed in order to improve reproducibility

Candidates should recognise that a second set of readings with another instrument or by a different observer could be used to cross check results.

4/3

c) recognising the value of further readings to establish repeatability and accuracy

Candidates should understand that accuracy is a measure of how close the measured value is to the true value.

4/3

d) considering the resolution of the measuring device

Candidates should be able to explain that resolution is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the indication (output).

4/3

e) considering the precision of the measured data where precision is indicated by the degree of scatter from the mean

Candidates should be able to distinguish between accuracy and precision when applied to an instrument's readings.

4/3

f) identifying the range of the measured data.

Candidates should be able to identify the upper and lower limits of the range and be able to identify which extra results, within or outside the range would be appropriate.

4/3

AS4.4 Select and process primary and secondary data

Candidates should be able to:

AS4.4.1 show an understanding of the value of means, by:

Additional Guidance:

AF/thread

a) appreciating when it is appropriate to calculate a mean

  5/1

b) calculating the mean of a set of at least three results.

Candidates should be able to recognise the need to exclude anomalies before calculating means to an appropriate number of decimal places.

5/1

AS4.4.2 demonstrate an understanding of how data may be displayed, by:

Additional Guidance:

AF/thread

a) drawing tables

Candidates should be able to draw up a table of two or more columns, with correct headings and units, adequately representing the data obtained.

3/2

b) drawing charts and graphs

Candidates should be able to construct an appropriate graphical representation of the data such as a bar chart or line graph and draw a line of best fit when appropriate. Candidates may use ICT to produce their graphs or charts.

3/2

c) choosing the most appropriate form of presentation.

Candidates should be able to identify the most appropriate method of display for any given set of data.

3/1

AS4.5 Analyse and interpret primary and secondary data

Candidates should be able to:

AS4.5.1 distinguish between a fact and an opinion, by:

Additional Guidance:

AF/thread

a) recognising that an opinion might be influenced by factors other than scientific fact

Candidates should recognise that the opinion may be influenced by economic, ethical, moral, social or cultural considerations.

2/1

b) identifying scientific evidence that supports an opinion.

  1/2

AS4.5.2 Review methodology to assess fitness for purpose, by:

Additional Guidance:

AF/thread

a) identifying causes of variation in data

Candidates should be able to identify from data whether there is any variation other than obvious anomalies, and identify a potential cause for variation or uncertainty.

 

5/2

b) recognising and identifying the cause of random errors. If a data set contains random errors, repeating the readings and calculating a new mean can reduce their effect.

Candidates should appreciate that human error might be the cause of inaccurate measurements and explain how human error might have influenced the accuracy of a measurement or might have introduced bias into a set of readings.

 

5/2

c) recognising and identifying the cause of anomalous results

Candidates should be able to identify anomalous results and suggest what should be done about them.

5/2

d) recognising and identifying the cause of systematic errors.

Candidates should be able to identify when a data set contains a systematic error and appreciate that repeat readings cannot reduce the effect of systematic errors.

Candidates should realise that a zero error is a type of systematic error. They should be able to identify if a scale has been incorrectly used and suggest how to compensate for a zero error.

5/2

AS4.5.3 identify patterns in data, by:

Additional Guidance:

AF/thread

a) describing the relationship between two variables and deciding whether the relationship is causal or by association.

Candidates should be able to use terms such as linear or directly proportional, or describe a complex relationship.

5/3

AS4.5.4 draw conclusions using scientific ideas and evidence, by:

Additional Guidance:

AF/thread

a) writing a conclusion, based on evidence that relates correctly to known facts

Candidates should be able to state simply what the evidence shows to justify a conclusion, and recognise the limitations of evidence. 

5/3

b) using secondary sources

Candidates should appreciate that secondary sources or alternative methods can confirm reproducibility.

5/3

c) identifying extra evidence that is required for a conclusion to be made

Candidates should be able to suggest that extra evidence might be required for a conclusion to be made, and be able to describe the extra evidence required.

5/4

d) evaluating methods of data collection.

Candidates should appreciate that the evidence obtained may not allow the conclusion to be made with confidence. Candidates should be able to explain why the evidence obtained does not allow the conclusion to be made with confidence.

5/4

AS4.6 Use of scientific models and evidence to develop hypotheses, arguments and explanations

Candidates should be able to:

AS4.6.1 review hypothesis in the light of outcomes, by:

Additional Guidance:

AF/thread

a) considering whether or not any hypothesis made is supported by the evidence

Candidates should be able to assess the extent to which the hypothesis is supported by the outcome.

1/2

b) developing scientific ideas as a result of observations and measurements.

Candidates should be able to suggest ways in which the hypothesis may need to be amended or whether it needs to be discarded in the light of the achieved outcome of an investigation.

1/2

Guidance on Managing Controlled Assessment

What is Controlled Assessment?

For each subject, Controlled Assessment regulations from Ofqual stipulate the level of control required for task setting, task taking and task marking. The 'task' is what the candidate has to do; the 'level of control' indicates the degree of freedom given to teachers and candidates for different aspects of the 'task'.

For GCSE Additional Science, the regulations state:

For this specification, this means:

Task setting – high control

  • We prepare equivalent Investigative Skills Assignments (ISAs) each year.

Task taking (research/data collection) – limited control

  • We require the practical work and data collection to be carried out under teacher supervision, during normal class contact time.
  • If more than one lesson is used, candidates' data and research work must be collected at the end of each lesson.
  • Candidates can work together during the investigation, but each candidate must contribute to the collection of the data and process the data individually.

Task taking (analysis and evaluation of findings) – high control

  • ISA tests should be taken under formal supervision, in silence without co-operation between candidates.
  • Candidates should be given their processed data for reference during the ISA test, and will also be provided with a data sheet of secondary data.
  • Teachers should not help candidates answer the questions.
  • Each ISA has a fixed time limit unless the candidate is entitled to access arrangements.
  • Candidates' processed data and their ISA tests are collected by the teacher at the end of each test.

Task marking – medium control

  • We provide 'marking guidelines'  for each ISA test.
  • We moderate your marking.

What is the Controlled Assessment like?

The Controlled Assessment comprises an ISA test which is assessed in two sections.

Prior to taking Section 1 of the ISA test, candidates independently develop their own hypothesis and research possible methods for carrying out an experiment to test their hypothesis. During this research, candidates need to do a risk assessment and prepare a table for their results.

Section 1 of the ISA test (45 minutes, 20 marks) consists of questions relating to the candidate's own research.

Following Section 1 candidates should carry out their investigation, and record and analyse their results.

If the candidate's plan is unworkable, unsafe or unmanageable in the laboratory then they may be provided with a method – an example of which will be provided by AQA. For plans that are otherwise good, but unworkable for a good reason (ie logistical) candidates should not lose any marks. However, where the plan is dangerous or unworkable (from a scientific perspective) this will be reflected in the marking.

Section 2 of the ISA test (50 minutes, 30 marks) consists of questions related to the experiment candidates have carried out. They are also provided with a data sheet of secondary data by AQA, from which they select appropriate data to analyse and compare with their own results.

Candidates will be asked to suggest how ideas from their investigation and research could be used within a new context.

Using ISAs

The documents provided by AQA for each ISA are:

  • a set of Teachers' Notes
  • the ISA – Section 1 and Section 2 which are to be copied for each candidate
  • the marking guidelines for the teacher to use.

The Teachers' Notes provide suggestions on how to incorporate ISAs into the scheme of work. About five lessons should be allowed for the ISA: one lesson for discussion, research and planning; one lesson for the completion of Section 1; one or two lessons for completing the experiment and processing their results and one lesson for completing Section 2 of the ISA.

Candidates will be expected to plan their investigation independently and should each draw up an appropriate table for recording their results.

While carrying out the investigation, candidates should make and record observations. They should make measurements with precision and accuracy. They should record data as it is obtained in a table. They should use ICT where appropriate. Candidates are also required to process the data into a graph or chart.

Candidates' tables of data and graphs or charts must be collected by the teacher at the end of each lesson. Candidates must not be allowed to work on the presentation or processing of their data between lessons, because marks are available for these skills.

The paper containing Section 2 of the ISA should be taken as soon as possible after completion of the investigation.

During the test, candidates should work on their own and in silence. When candidates have completed the test the scripts must be collected. Teachers are required to mark the tests, using the marking guidelines provided by AQA. Tests should be marked in red ink with subtotals placed in the margin.

Teachers are expected to use their professional judgement in applying the marking guidelines: for example, applying it sensibly where candidates have given unexpected answers. When teachers have marked the scripts, they may tell candidates their marks but they must not return the scripts. Completed ISAs must be kept under secure conditions while the ISA is valid.

Other guidance

Other guidance

Teachers' Notes will be put on to the AQA website prior to the ISAs becoming valid. ISA tests and marking guidelines will be published in advance.

If ISAs are to be used with different classes, centres must ensure security between sessions.

ISAs have specific submission dates. They may not be submitted in more than one year. The submission dates are stated on the front cover of each ISA.

Candidates may attempt any number of the ISAs supplied by AQA for a particular subject. The best mark they achieve from a complete ISA is submitted.

A candidate is only allowed to have one attempt at each ISA, and this may only be submitted for moderation on one occasion. It would constitute malpractice if the candidate is found to have submitted the same ISA more than once and they could be excluded from at least this qualification.

Specimen ISAs or ISAs that are no longer valid may be given to candidates so that they can practise the skills required. In these cases, candidates can be given back their completed and marked scripts. However, ISAs that are currently valid must not be given back to candidates.

3.7 Unit 5 - Additional Science 1

Additional Science 1

Additional Science 1 is half of Biology 2, half of Chemistry 2 and half of Physics 2, as follows: 

  • Biology 2 Sections B2.1 to B2.4
  • Chemistry 2 Sections C2.1 to C2.3
  • Physics 2 Sections P2.1 to P2.3 

See Sections 3.3, 3.4 and 3.5 above.

3.8 Unit 6 - Additional Science 2

Additional Science 2

Additional Science 2 is half of Biology 2, half of Chemistry 2 and half of Physics 2, as follows:

  • Biology 2 Sections B2.5 to B2.8
  • Chemistry 2 Sections C2.4 to C2.7
  • Physics 2 Sections P2.4 to P2.6 

See Sections 3.3, 3.4 and 3.5 above.

3.9 Mathematical and other requirements

Mathematical requirements

Mathematical requirements

One learning outcome of this specification is to provide learners with the opportunity to develop their skills in communication, mathematics and the use of technology in scientific contexts. In order to deliver the mathematical element of this outcome, assessment materials for this specification contain opportunities for candidates to demonstrate scientific knowledge using appropriate mathematical skills.

The areas of mathematics that arise naturally from the science content in science GCSEs are listed below. This is not a checklist for each question paper or Controlled Assessment, but assessments reflect these mathematical requirements, covering the full range of mathematical skills over a reasonable period of time.

Candidates are permitted to use calculators in all assessments.

Candidates are expected to use units appropriately. However, not all questions reward the appropriate use of units.

All candidates should be able to:

1. Understand number size and scale and the quantitative relationship between units.

2. Understand when and how to use estimation.

3. Carry out calculations involving +, – , x, ÷, either singly or in combination, decimals, fractions, percentages and positive whole number powers.

4. Provide answers to calculations to an appropriate number of significant figures.

5 Understand and use the symbols =, <, >, ~.

6. Understand and use direct proportion and simple ratios.

7. Calculate arithmetic means.

8. Understand and use common measures and simple compound measures such as speed.

9. Plot and draw graphs (line graphs, bar charts, pie charts, scatter graphs, histograms) selecting appropriate scales for the axes.

10. Substitute numerical values into simple formulae and equations using appropriate units.

11. Translate information between graphical and numeric form.

12. Extract and interpret information from charts, graphs and tables.

13. Understand the idea of probability.

14. Calculate area, perimeters and volumes of simple shapes.

In addition, Higher Tier candidates should be able to:

15. Interpret, order and calculate with numbers written in standard form.

16. Carry out calculations involving negative powers (only -1 for rate).

17. Change the subject of an equation.

18. Understand and use inverse proportion.

19. Understand and use percentiles and deciles.

Units, symbols and nomenclature

Units, symbols and nomenclature used in examination papers will normally conform to the recommendations contained in the following: 

The Language of Measurement: Terminology used in school science investigations. Association for Science Education (ASE), 2010. ISBN 978 0 86357 424 5. 

Signs, Symbols and Systematics: The ASE companion to 16–19 Science. Association for Science Education (ASE), 2000. ISBN 978 0 86357 312 5.

Signs, Symbols and Systematics – the ASE companion to 5–16 Science. Association for Science Education (ASE), 1995. ISBN 0 86357 232 4.

Equation sheet

We will provide an equation sheet for the physics unit and for the combined papers in Units 5 and 6. Candidates will be expected to select the appropriate equation to answer the question.

Data sheet

We will provide a data sheet for the chemistry unit and for the combined papers in Units 5 and 6. This includes a periodic table and other information. Candidates will be expected to select the appropriate information to answer the question.