Specifications that use this resource:

Using your existing textbook

To help you teach our new A-level Biology specification from September 2015, the following resource shows where you can continue to use content from your current Nelson Thornes AQA A-level Biology textbooks (AS-level ISBN 978-0748782758, A2 ISBN 978-0748798131).

Fully revised and updated versions of these books and the associated Kerboodle resources for the new specifications will be available from Oxford University Press. Please also check the glossary on our website as some words have had changes in meaning.

Further details of new print and digital publications from Oxford University Press, Hodder, and Collins to support the new specification can be found on our website

Specification references to existing textbook chapters

3.1 Biological molecules

3.1.1 Monomers and polymers

Specification topic Nelson Thornes reference Additional notes/comments

Monomers are the smaller units from which larger molecules are made.

Polymers are molecules made from a large number of monomers joined together.

Monosaccharides, amino acids and nucleotides are examples of monomers.

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

AS textbook, section 2.2

AS textbook, section 2.3/2.5

2.2 in context of carbohydrates and

2.5 in the context of proteins

3.1.2 Carbohydrates

Specification topic Nelson Thornes reference Additional notes/comments

Monosaccharides ar e the monomers from which carbohydrates a r e made. Glucose, galactose and fructose are common monosaccharides.

A condensation reaction between two monosaccharides forms a glycosidic bond.

Disaccharides are formed by the condensation of two monosaccharides:

  • maltose is a disaccharide formed by condensation of two glucose molecules
  • sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule
  • lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule

Benedict’s reagent used as a qualitative test and as a quantitative test for reducing sugars.

Qualitative test for non-reducing sugars.

Glucose has two isomers, α -glucose and β-glucose.

Polysaccharides are formed by the condensation of many glucose units.

  • Glycogen and starch are formed by the condensation of α-glucose
  • Cellulose is formed by the condensation of β-glucose

The basic structu r e and functions of glycogen, starch and cellulose. T he r elationship of structu r e to function of these substances in animal cells and plant cells.

AS: 2.2

AS: 2.3

AS: 10.3

α-glucose in 2.3 and β–glucose in 10.3

3.1.3 Lipids

Specification topic Nelson Thornes reference Additional notes/comments

Triglycerides and phospholipids are two groups of lipid.

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

The R-gr oup of a fatty acid may be saturated or unsaturated.

In phospholipids,one ofthefattyacidsofa triglycerideissubstitutedbyaphosphate-containing group.

AS: 3.4

AS: 3.5

3.1.4 Proteins

Specification topic Nelson Thornes reference Additional notes/comments

Proteins have a variety of functions within all living organisms. The general structure of an amino acid as:

where NH2 represents an amine group, COOH represents a carboxyl group and R represents a carbon-containing side chain. The twenty amino acids that are common in all organisms differ only in their side group.

A condensation reaction between two amino acids forms a peptide bond.

  • Dipeptides are formed by the condensation of two amino acids
  • Polypeptides are formed by the condensation of many amino acids

A protein may contain one or more polypeptides.

The relationship between primary , secondar y , tertiary and quater nary structu r e, and p r otein function.

The role of hydrogen bonds, ionic bonds and disulfide bridges in maintaining the structure of proteins.

AS: 2.5

Enzymes lower the activation energy of the reactions they catalyse.

Theinduced- fitmodel of enzyme action.

The properties of enzymes r elate to their tertiary structu r e of their active site and its ability to combine with complementary substrates to form an enzyme-substrate complex. E xplanation of:

  • the specificity of enzymes
  • the effects of the following factors on the rate of enzyme-controlled reactions - enzyme concentration, substrate concentration, pH, temperature, concentration of competitive inhibitors and concentration of non-competitive inhibitors

AS: 2.6

AS: 2.7

AS: 2.8

No reference to enzyme concentration as a factor

Inhibitors in 2.8

3.1.5 Nucleic acids are important information-carrying molecules

Specification topic Nelson Thornes reference Additional notes/comments

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information-carrying molecules. In all living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes.

Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from pentose, a nitrogen-containing organic base and a phosphate group:

  • The components of a DNA nucleotide are deoxyribose, phosphate and one of the bases adenine, cytosine, guanine or thymine
  • The components of an RNA nucleotide are ribose, phosphate and one of the bases adenine, cytosine, guanine or uracil
  • A condensation reaction between 2 nucleotides forms a photodiester bond.

A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.

An RNA molecule is a relatively short polynucleotide chain.

AS: 8.1

A2: 14.1

Split between AS chapter 8.1 and A2 chapter 14.1

The semi-conservative replication of DNA ensures genetic continuity between generations of cells.

The process of semi-conservative replication of DNA in terms of:

  • unwinding of the double helix
  • breaking of hydrogen bonds between polynucleotide strands
  • the role of DNA helicase in unwinding DNA and breaking its hydrogen bonds
  • attraction of new DNA nucleotides to exposed bases on template strands and base pairing
  • the role of DNA polymerase in the condensation reaction that joins adjacent nucleotides
A2: 11.1

Not in current AS or A2 books / spec.

3.1.6 ATP

Specification topic Nelson Thornes reference Additional notes/comments

A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative and consists of a molecule of ribose, a molecule of adenine and three phosphate groups.

Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase.

  • The hydrolysis of ATP can be coupled to energy-requiring reactions within cells
  • The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive

ATP is resynthesised by the condensation of ADP and P1. This reaction is catalysed by the enzyme ATP synthase during photosynthesis, or during respiration.

A2: 2.1

A2:3.2 / 4

ATP in: photosynthesis A2: 3.2

Respiration A2: chapter 4

3.1.7 Water

Specification topic Nelson Thornes reference Additional notes/comments

Water is a major component of cells. It has several properties that are important in biology. In particular, water:

  • is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
  • is an important solvent in which metabolic reactions occur
  • has a relatively high heat capacity, buffering changes in temperature
  • has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
  • has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air

AS: 13.8

Not in current AS / A2 books / spec in this format

3.2 Cells

3.2.1.1 Structure of eukaryotic cells

Specification topic Nelson Thornes reference Additional notes/comments

The structure of eukaryotic cells, restricted to the structure and function of:

  • cell-surface membrane
  • nucleus (containing chromosomes, consisting of protein-bound, linear DNA, and one or more nucleoli)
  • mitochondria
  • chloroplasts (in plants and algae)
  • Golgi apparatus and Golgi vesicles
  • lysosomes (a type of Golgi vesicle that releases lysozymes)
  • ribosomes
  • rough endoplasmic reticulum and smooth endoplasmic reticulum
  • cell wall (in plants, algae and fungi)
  • cell vacuole (in plants)

In complex multicellular organisms, eukaryotic cells become specialised for specific functions. Specialised cells are organised into tissues, tissues into organs and organs into systems.

AS: 3.3

AS: 3.5

AS: 10.4

Split currently in AS book between 3.5 and plant organelles in 10.4

3.2.1.2 Structure of prokaryotic cells and of viruses

Specification topic Nelson Thornes reference Additional notes/comments

Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in having:

  • cytoplasm that lacks membrane-bound organelles
  • smaller ribosomes
  • no nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins
  • a cell wall that contains murein, a glycoprotein.
  • In addition, many prokaryotic cells have:
  • one or more plasmids
  • a capsule surrounding the cell
  • one or more flagella

Details of these structural differences are notrequired.

Viruses are acellular and non-living. The structure of virus particles to include genetic material, capsid and attachment protein.

AS: 3.10 cholera

3.2.1.3 Methods of studying cells

Specification topic Nelson Thornes reference Additional notes/comments

The principles and limitations of optical microscopes, transmission electron microscopes and scanning electron microscopes.

Measuring the size of an object viewed with an optical microscope.

The difference between magnification and resolution.

Use of the formula: magnification = size of image /size of real object

Principles of cell fractionation and ultracentrifugation as used to separate cell components.

AS: 3.2

AS: 3.1

3.2.2 All cells arise from other cells

Specification topic Nelson Thornes reference Additional notes/comments

Within multicellular organisms, not all cells retain the ability to divide.

Eukaryotic cells that do retain the ability to divide show a cell cycle.

  • DNA replication occurs during the interphase of the cell cycle
  • Mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication

The behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis. The role of spindle fibres attached to centromeres in the separation of chromatids.

Division of the cytoplasm (cytokinesis) usually occurs, producing two new cells. Meiosis is covered in section 3.4.3

Mitosis is a controlled process. Uncontrolled cell division can lead to the formation of tumours and of cancers. Many cancer treatments are directed at controlling the rate of cell division.

Binary fission in prokaryotic cells involves:

  • replication of the circular DNA and of plasmids

division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids

AS: 11.2 and 11.3

AS: 11.3

Not specifically within book

3.2.3 Transport across cell membranes

Specification topic Nelson Thornes reference Additional notes/comments

The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes, is the same.

The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model of membrane structure. Cholesterol may also be present in cell membranes where it restricts the movement of other molecules making up the membrane.

Movement across membranes occurs by:

  • simple diffusion (involving limitations imposed by the nature of the phospholipid bilayer)
  • facilitated diffusion (involving the roles of carrier proteins and channel proteins)
  • osmosis (explained in terms of water potential and using the terms ‘hypertonic’, ‘hypotonic’ and ‘isotonic’)
  • active transport (involving the role of carrier proteins and the importance of the hydrolysis of ATP)
  • co-transport (illustrated by the absorption of sodium ions and glucose by cells lining the mammalian ileum)

Cells may be adapted for rapid transport across their internal or external membranes by an increase in surface area of, or by an increase in the number of protein channels and carrier molecules in their membranes

AS: 3.5

AS: 3.6

AS: 3.7

AS: 3.8

AS: 3.9

3.2.4 Cell recognition and the immune system

Specification topic Nelson Thornes reference Additional notes/comments

Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify:

  • pathogens
  • cells from other organisms of the same species
  • abnormal body cells
  • toxins

Definition of antigen. The effect of antigen variability on disease and disease prevention.

Phagocytosis of pathogens. The subsequent destruction of ingested pathogens by lysozymes.

The response of T lymphocytes to a foreign antigen (the cellular response).

  • The role of antigen-presenting cells in the cellular response
  • The role of helper T cells (TH cells) in stimulating cytotoxic T cells (TC cells), B cells and phagocytes. The role of other T cells is notrequired

The response of B lymphocytes to a foreign antigen, clonal selection and the release of monoclonal antibodies (the humoral response).

  • Definition of antibody
  • Antibody structure
  • The formation of an antigen-antibody complex, leading to the destruction of the antigen, limited to agglutination and phagocytosis of bacterial cells
  • The roles of plasma cells and of memory cells in producing primary and secondary immune responses

The use of vaccines to provide protection for individuals and populations against disease. The concept of herd immunity.

The differences between active and passive immunity.

Structure of the human immunodeficiency virus (HIV) and its replication in helper T cells.

How HIV causes the symptoms of AIDS. Why antibiotics are ineffective against viruses.

The use of monoclonal antibodies in:

  • targeting medication to specific cell types by attaching a therapeutic drug to an antibody
  • medical diagnosis

Details of the production of monoclonal antibodies is notrequired.

Ethical issues associated with the use of vaccines and monoclonal antibodies.

The use of antibodies in the ELISA test.

AS: 6.3

AS: 6.2

AS: 6.3

AS: 6.5

AS: 6.4 / 6.5

AS: 6.6

AS: 6.5 but fairly brief

AS: 6.5

Not specifically on spec / in books

In AS book 6.1 / 6.2 / 6.3 / 6.4 but not specifically

Not in current AS / A2 books / spec in this format

3.3 Organisms exchange substances with their environment

3.3.1 Surface area to volume ratio

Specification topic Nelson Thornes reference Additional notes/comments

The relationship between the size of an organism or structure and its surface area to volume ratio.

Changes to body shape and the development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces.

AS: 13.1

3.3.2 Gas exchange

Specification topic Nelson Thornes reference Additional notes/comments

Adaptations of gas exchange surfaces, shown by gas exchange:

  • across the body surface of a single-celled organism
  • in the tracheal system of an insect (tracheae, tracheoles and spiracles)
  • across the gills of fish (gill lamellae and filaments including the counter-current principle)
  • by the leaves of dicotyledonous plants (mesophyll and stomata).

Structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects and xerophytic plants.

The gross structure of the human gas exchange system limited to the alveoli, bronchioles, bronchi, trachea and lungs.

The essential features of the alveolar epithelium as a surface over which gas exchange takes place.

Ventilation and the exchange of gases in the lungs. The mechanism of breathing to include the role of the diaphragm and the antagonistic interaction between the external and internal intercostal muscles in bringing about pressure changes in the thoracic cavity.

AS: 13.2

AS: 13.3

AS: 13.4

AS: 13.2 and 13.4

AS: 4.1

AS: 4.3

AS:: 4.2

AS: 4.5

3.3.3 Digestion and absorption

Specification topic Nelson Thornes reference Additional notes/comments

During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.

Digestion in mammals of:

  • carbohydrates by amylases and membrane-bound disaccharidases
  • lipids by lipase, including the action of bile salts
  • proteins by endopeptidases, exopeptidases and membrane bound dipeptidases

Mechanisms for the absorption of the products of digestion by cells lining the ileum of mammals, to include:

  • co-transport mechanisms for the absorption of amino acids and of monosaccharides

the role of micelles in the absorption of lipids

AS: 2.1

AS: 2.4

AS: 3.9 (only carbs)

Only carbohydrate digestion and absorption covered in any detail

Disaccharidases not specifically mentioned in text book.

3.3.4.1 Mass transport in animals

Specification topic Nelson Thornes reference Additional notes/comments

The haemoglobins are a group of chemically similar molecules found in many different organisms. Haemoglobin is a protein with a quaternary structure.

The role of haemoglobin and red blood cells in the transport of oxygen. The loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve.

The cooperative nature of oxygen binding to show that the change in shape of haemoglobin caused by binding of the first oxygens makes the binding of further oxygens easier.

The effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin (the Bohr effect).

Many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties.

The general pattern of blood circulation in a mammal. Names are required only of the coronary arteries and of the blood vessels entering and leaving the heart, lungs and kidneys.

The gross structure of the human heart. Pressure and volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood.

The structure of arteries, arterioles and veins in relation to their function.

The structure of capillaries and the importance of capillary beds as exchange surfaces. The formation of tissue fluid and its return to the circulatory system.

AS: 10.1

AS: 10.2

AS: 5.1/5.2

AS: 13.6

3.3.4.2 Mass transport in plants

Specification topic Nelson Thornes reference Additional notes/comments

Xylem as the tissue that transports water in the stem and leaves of plants. The cohesion-tension theory of water transport in the xylem.

Phloem as the tissue that transports organic substances in plants.

The mass flow hypothesis for the mechanism of translocation in plants. The use of tracers and ringing experiments to investigate transport in plants.

AS: 13.8 Not in current AS/A2 books/spec in this format

3.4 Genetic information, variation and relationships between organisms

3.4.1 DNA, genes and chromosomes

Specification topic Nelson Thornes reference Additional notes/comments

In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.

In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones. Together a DNA molecule and its associated proteins form a chromosome.

The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.

A gene is a base sequence of DNA that codes for:

  • the amino acid sequence of a polypeptide
  • a functional RNA (including ribosomal RNA and tRNAs).

A gene occupies a fixed position, called a locus, on a particular DNA molecule.

A sequence of three DNA bases, called a triplet, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate.

In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes. Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.

AS: 8.3

AS: 8.1

AS: 8.2

AS: 8.4

AS: 8.2

A2: 14.2

3.4.2 DNA and protein synthesis

Specification topic Nelson Thornes reference Additional notes/comments

The concept of the genome as the complete set of genes in a cell and of the proteome as the full range of proteins that a cell is able to produce.

The structure of molecules of messenger RNA (mRNA) and of transfer RNA (tRNA).

Transcription as the production of mRNA from DNA. The role of RNA polymerase in joining mRNA nucleotides.

  • In prokaryotes, transcription results directly in the production of mRNA from DNA
  • In eukaryotes, transcription results in the production of premRNA; this is then spliced to form mRNA

Translation as the production of polypeptides from the sequence of codons carried by mRNA. The roles of ribosomes, tRNA and ATP.

A2: 14.1

A2: 14.2

A2: 14.3

A2: 14.2

A2: 14.3

3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

Specification topic Nelson Thornes reference Additional notes/comments

Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation.

Mutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis.

Meiosis produces daughter cells that are genetically different from each other.

The process of meiosis only in sufficient detail to show how:

  • two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell
  • genetically different daughter cells result from the independent segregation of homologous chromosomes

crossing over between homologous chromosomes results in further genetic variation among daughter cells

A2: 14.4

AS: 8.4

No reference currently within textbooks

3.4.4 Genetic diversity and adaptation

Specification topic Nelson Thornes reference Additional notes/comments

Genetic diversity as the number of different alleles of genes in a population.

Genetic diversity is a factor enabling natural selection to occur.

The principles of natural selection in the evolution of populations.

  • Random mutation can result in new alleles of a gene
  • Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
  • The advantageous allele is inherited by members of the next generation
  • As a result, over many generations, the new allele increases in frequency in the population

Directional selection, exemplified by antibiotic resistance in bacteria, and stabilising selection, exemplified by human birth weights.

AS: 9.1

A2: 8.6

3.4.5 Species and taxonomy

Specification topic Nelson Thornes reference Additional notes/comments

Two organisms belong to the same species if they are able to produce fertile offspring.

A phylogenetic classification system attempts to arrange species into groups based on their evolutionary origins and relationships. It uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups. Each group is called a taxon (plural taxa).

One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species.

Each species is universally identified by a binomial consisting of the name of its genus and species, eg, Homo sapiens.

Recall of different taxonomic systems, such as the three domain or five kingdom systems, will not be required.

All in AS: 14.1

3.4.6 Biodiversity within a community

Specification topic Nelson Thornes reference Additional notes/comments

Biodiversity can relate to a range of habitats, from a small local habitat to the Earth.

Species richness is a measure of the number of different species in a community.

An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.

Calculation of an index of diversity ( d ) from the formula

where N = total number of organisms of all species and n = total number of organisms of each species.

Farming techniques reduce biodiversity. The balance between conservation and farming.

AS: 17.1

AS: 17.1

AS: 17.2

Species richness not used in current spec/ in text books

Different Index of Diversity in AS text book.

3.4.7 Investigating diversity

Specification topic Nelson Thornes reference Additional notes/comments

Genetic diversity within, or between species, can be made by comparing:

  • the frequency of measurable or observable characteristics
  • the base sequence of DNA
  • the base sequence of mRNA
  • the amino acid sequence of the proteins encoded by DNA and mRNA

Quantitative investigations of variation within a species involve:

  • collecting data from random samples
  • calculating a mean value of the collected data and the standard
  • deviation of that mean

interpreting mean values and their standard deviations

A2: 15.1

A2: 1.2

A2: 1.2

3.5 Energy transfers in and between organisms

3.5.1 Photosynthesis

Specification topic Nelson Thornes reference Additional notes/comments

The light-dependent reaction in such detail as to show that:

  • chlorophyll absorbs light, leading to photoionisation of chlorophyll
  • some of the energy from electrons released during
  • photoionisation is conserved in the production of ATP and reduced NADP
  • the production of ATP involves electron transfer associated with the transfer of electrons down the electron transfer chain and passage of protons across chloroplast membranes and is catalysed by ATP synthase embedded in these membranes
  • (chemiosomotic theory)
  • photolysis of water produces protons, electrons and oxygen

The light-independent reaction uses reduced NADP from the light-dependent reaction to form a simple sugar. The hydrolysis of ATP, also from the light-dependent reaction, provides the additional energy for this reaction.

The light-independent reaction in such detail as to show that:

  • carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). This reaction is catalysed by the enzyme rubisco
  • ATP and reduced NADP from the light-dependent reaction are used to reduce GP to triose phosphate
  • some of the triose phosphate is used to regenerate RuBP in the Calvin cycle

some of the triose phosphate is converted to useful organic substances

A2: 3.2

A2:3.3

All refs now from NT A2 text book unless otherwise indicated

No reference to chemiosmotic theory in photosynthesis currently

3.5.2 Respiration

Specification topic Nelson Thornes reference Additional notes/comments

Respiration produces ATP.

Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process.

Glycolysis involves the following stages:

  • phosphorylation of glucose to glucose phosphate, using ATP
  • production of triose phosphate
  • oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD

If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis.

If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport.

Aerobic respiration in such detail as to show that:

  • pyruvate is oxidised to acetate, producing reduced NAD in the process
  • acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A
  • acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-carbon molecule that enters the Krebs cycle
  • in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost
  • synthesis of ATP by oxidative phosphorylation is associated with the transfer of electrons down the electron transfer chain and passage of protons across inner mitochondrial membranes and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory)

other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle

A2: 4.1

A2: 4.2

A2: 4.3

Not clear in current book.

Referred to as protein channels in current book.

Not clear

3.5.3 Energy and ecosystems

Specification topic Nelson Thornes reference Additional notes/comments

In any ecosystem, plants synthesise organic compounds from atmospheric, or aquatic, carbon dioxide.

Most of the sugars synthesised by plants are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the biomass of the plants.

Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area per given time.

The chemical energy store in dry biomass can be estimated using calorimetry.

Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume, in a given time.

Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account, i.e. N PP = GPP – R where GPP represents gross productivity and R represents respiratory losses to the environment.

This net primary production is available for plant growth and reproduction. It is also available to other trophic levels in the ecosystem, such as herbivores and decomposers.

The net production of consumers (N), such as animals, can be calculated as:

N = I – F + R

where I represents the chemical energy store in ingested food, F represents the chemical energy lost to the environment in faeces and urine and R represents the respiratory losses to the environment.

A2: 5.2

A2: 5.3 within pyramids of biomass

A2: 5.4

A2: 5.4

A2: 5.2

No direct reference

Productivity in context of agricultural productivity

No direct reference to this in this format

3.5.4 Nutrient cycles

Specification topic Nelson Thornes reference Additional notes/comments

Nutrients are recycled within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle.

Microorganisms play a vital role in recycling chemical elements such as phosphorus and nitrogen.

  • The role of saprobionts in decomposition
  • The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants
  • The role of bacteria in the nitrogen cycle in sufficient detail to illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification

(The names of individual species of bacteria are not required).

The use of natural and artificial fertilisers to replace the nitrates and phosphates lost by harvesting plants and removing livestock.

The environmental issues arising from the use of fertilisers including leaching and eutrophication.

A2: 6.1

A2: 6.3

A2: 6.4

A2:6.5

A2: 6.6

Phosphorous cycle not on current spec

Mycorrhiza not on current spec

3.6 Organisms respond to changes in their internal and external environments

3.6.1.1 Survival and response

Specification topic Nelson Thornes reference Additional notes/comments

Organisms increase their chance of survival by responding to changes in their environment.

In flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli.

The effect of different concentrations of indoleacetic acid (IAA) on cell elongation in the roots and shoots of flowering plants as an explanation of gravitropism and phototropism in flowering plants.

Taxes and kineses as simple responses that can maintain a mobile organism in a favourable environment.

Details of spinal cord and dorsal and ventral roots are not required.

A2: 9.1

A2: 10.1

A2: 9.1

Old spec refers to ‘gravitropism’ as ‘geotropism’

3.6.1.2 Receptors

Specification topic Nelson Thornes reference Additional notes/comments

The Pacinian corpuscle should be used as an example of a receptor to illustrate that:

  • receptors respond only to specific stimuli
  • stimulation of a receptor leads to the establishment of a generator potential

The basic structure of a Pacinian corpuscle.

Deformation of stretch-mediated sodium ion channels in a Pacinian corpuscle leads to the establishment of a generator potential.

The human retina in sufficient detail to show how differences in sensitivity to light, sensitivity to colour and visual acuity are explained by differences in the optical pigments of rods and cones and the connections rods and cones make in the optic nerve.

A2: 9.4

3.6.1.3 Control of heart rate

3.6.2.1 Nerve impulses

Specification topic Nelson Thornes reference Additional notes/comments

The structure of a myelinated motor neurone.

The establishment of a resting potential in terms of differential membrane permeability, electrochemical gradients and the movement of sodium ions and potassium ions.

Changes in membrane permeability lead to depolarisation and the generation of an action potential. The all-or-nothing principle.

The passage of an action potential along non-myelinated and myelinated axons, resulting in nerve impulses.

The nature and importance of the refractory period in producing discrete impulses and in limiting the frequency of impulse transmission.

Factors affecting the speed of conductance: myelination and saltatory conduction; axon diameter; temperature.

A2: 10.2

A2: 10.3

A2: 10.5

A2: 10.4

A2: 10.5

3.6.2.2 Synaptic transmission

Specification topic Nelson Thornes reference Additional notes/comments

The detailed structure of a synapse and of a neuromuscular junction.

The sequence of events involved in transmission across a cholinergic synapse in sufficient detail to explain:

  • unidirectionality
  • temporal and spatial summation
  • inhibition by inhibitory synapses

A comparison of transmission across a cholinergic synapse and across a neuromuscular junction.

A2: 10.6

A2: 10.7

3.6.3 Skeletal muscles are stimulated to contract by nerves and act as effectors

Specification topic Nelson Thornes reference Additional notes/comments

Muscles act in antagonistic pairs against an incompressible skeleton.

Gross and microscopic structure of skeletal muscle. The Ultrastructure of a myofibril.

The roles of actin, myosin, calcium ions and ATP in myofibril contraction.

The roles of calcium ions and tropomyosin in the cycle of actinomyosin bridge formation. (The role of troponin is not required.)

The roles of ATP and phosphocreatine in muscle contraction.

The structure, location and general properties of slow and fast skeletal muscle fibres.

A2: 11.1

A2:11.2

3.6.4.1 Principles of homeostasis and negative feedback

Specification topic Nelson Thornes reference Additional notes/comments

Homeostasis in mammals involves physiological control systems that maintain the internal environment within restricted limits.

The importance of maintaining a stable core temperature and stable blood pH in relation to enzyme activity.

The importance of maintaining a stable blood glucose concentration in terms of availability of respiratory substrate and of the water potential of blood.

Negative feedback restores systems to their original level.

The possession of separate mechanisms involving negative feedback controls departures in different directions from the original state, giving a greater degree of control.

A2: 12.1

A2: 12.2

A2: 13.1

3.6.4.2 Control of blood glucose concentration

Specification topic Nelson Thornes reference Additional notes/comments

The factors that influence blood glucose concentration.

The role of the liver in glycogenesis, glycogenolysis and gluconeogenesis.

The action of insulin by:

  • attaching to receptors on the surfaces of target cells
  • controlling the uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of target cells
  • activating enzymes involved in the conversion of glucose to glycogen

The action of glucagon by:

  • attaching to receptors on the surfaces of target cells
  • activating enzymes involved in the conversion of glycogen to glucose
  • activating enzymes involved in the conversion of glycerol and amino acids into glucose

The role of adrenaline by:

  • attaching to receptors on the surfaces of target cells
  • activating enzymes involved in the conversion of glycogen to glucose.

The second messenger model of adrenaline and glucagon action, involving adenyl cyclate, cyclic AMP (cAMP) and protein kinase.

The causes of types I and II diabetes and their control by insulin and/or manipulation of the diet.

A2: 12.3

A2: 12.4

3.6.4.3 Control of blood water potential

Specification topic Nelson Thornes reference Additional notes/comments

Osmoregulation as control of the water potential of the blood.

The roles of the hypothalamus, posterior pituitary and antidiuretic hormone (ADH) in osmoregulation.

The structure of the nephron and its role in:

  • the formation of glomerular filtrate
  • reabsorption of glucose and water by the proximal convoluted tubule
  • maintaining a gradient of sodium ions in the medulla by the loop of Henle

reabsorption of water by the distal convoluted tubule and collecting ducts.

  Not on current spec / AS and A2 text books.

3.7 Genetics, populations, evolution and ecosystems

3.7.1 Inheritance

Specification topic Nelson Thornes reference Additional notes/comments

The genotype is the genetic constitution of an organism.

The phenotype is the expression of this genetic constitution and its interaction with the environment.

There may be many alleles of a single gene.

Alleles may be dominant, recessive or codominant.

In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous.

The use of fully labelled genetic diagrams to interpret, or predict, the results of:

  • monohybrid and dihybrid crosses involving dominant, recessive and codominant alleles
  • crosses involving sex-linkage, autosomal linkage, multiple alleles and epistasis

Use of the chi-squared ( X 2 ) test to compare the goodness of fit of observed phenotypic ratios with expected ratios.

A2: 8.1

A2: 8.2

A2: 8.4

A2: 8.3

A2: 8.4

No specific reference to the locus.

Dihybrid crosses new to this spec.

Epistasis and autosomal linkage not on current spec.

3.7.2 Populations

Specification topic Nelson Thornes reference Additional notes/comments

Species exist as one or more populations.

A population as a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.

The concepts of gene pool and allele frequency.

The Hardy–Weinberg principle provides a mathematical model, which predicts that allele frequencies will not change from generation to generation. The conditions under which the principle applies.

The frequency of alleles, genotypes and phenotypes in a population can be calculated using the Hardy–Weinberg equation:

p2 + 2 pq + q2 = 1

where p is the frequency of one (usually the dominant) allele and q is the frequency of the other (usually recessive) allele of the gene.

A2: 8.5

A2: 8.5

3.7.3 Evolution may lead to speciation

Specification topic Nelson Thornes reference Additional notes/comments

Individuals within a population of a species may show a wide range of variation in phenotype. This is due to genetic and environmental factors. The primary source of genetic variation is mutation.

Meiosis and the random fertilisation of gametes during sexual reproduction produce further genetic variation.

Predation, disease and competition for the means of survival result in differential survival and reproduction, ie natural selection.

Those organisms with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation. The effect of this differential reproductive success on the allele frequencies within a gene pool.

The effects of stabilising, directional and disruptive selection.

Evolution as a change in the allele frequencies in a population.

Reproductive separation of two populations can result in the accumulation of difference in their gene pools. New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring. In this way, new species arise from existing species.

Allopatric and sympatric speciation.

The importance of genetic drift in causing changes in allele frequency in small populations.

A2: 8.7

3.7.4 Populations in ecosystems

Specification topic Nelson Thornes reference Additional notes/comments

Populations of different species form a community.

Within a habitat, a species occupies a niche governed by adaptation to both abiotic and biotic conditions.

An ecosystem supports a certain size of population of a species, called the carrying capacity. This population size can vary as a result of:

  • the effect of abiotic factors
  • interactions between organisms: interspecific and intraspecific competition and predation

The size of a population can be estimated using:

  • randomly placed quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms
  • the mark-release-recapture method for motile organisms. The assumptions made when using the mark-release-recapture method

Ecosystems are dynamic systems.

Succession from pioneer species to climax community.

At each stage in succession, certain species may be recognised which change the environment so that it becomes more suitable for other species with different adaptations. The new species may change the environment in such a way that it becomes less suitable for the previous species.

Changes that organisms produce in their abiotic environment can result in a less hostile environment and change biodiversity. Conservation of habitats frequently involves management of succession.

A2: 1.1

A2: 1.3

A2: 1.4

A2: 1.5

A2: 7.1

A2: 7.2

3.8 The control of gene expression

3.8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins

Specification topic Nelson Thornes reference Additional notes/comments

Gene mutations might arise during DNA replication. They include addition, deletion, substitution, inversion, duplication and translocation of bases.

Gene mutations occur spontaneously. The mutation rate is increased by mutagenic agents.

Mutations can result in a different amino acid sequence in the encoded polypeptide.

  • Some gene mutations change only one triplet code. Due to the degenerate nature of the genetic code, not all such mutations result in a change to the encoded amino acid

Some gene mutations change the nature of all base triplets downstream from the mutation, ie result in a frame shift

A2: 14.4

No reference to addition mutations in books

3.8.2.1 Most of a cell's DNA is not translated

Specification topic Nelson Thornes reference Additional notes/comments

Totipotent cells are cells that can mature into any type of body cell.

During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.

Totipotent cells occur only for a limited time in mammalian embryos. Pluripotent, multipotent and unipotent cells are found in mature mammals. They can divide to form a limited number of different cell types.

  • Pluripotent stem cells can divide in unlimited numbers and can be used in treating human disorders
  • Unipotent cells, exemplified by cardiomycetes

Induced pluripotent stem cells (iPS cells) can be produced from unipotent cells using appropriate protein transcription factors

A2: 15.1

New to specification - No reference in books

3.8.2.2 Regulation of transcription and translation

Specification topic Nelson Thornes reference Additional notes/comments

In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nucleus. The role of the steroid hormone, oestrogen, in initiating transcription.

Epigenetic control of gene expression in eukaryotes.

Epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA. These changes are caused by changes in the environment that inhibit transcription by:

  • increased methylation of the DNA or
  • decreased acetylation of associated histones

The relevance of epigenetics on the development and treatment of disease, especially cancer.

In eukaryotes and some prokaryotes, translation of the mRNA produced from target genes can be inhibited by RNA interference (RNAi).

A2: 15.2

15.2

New to specification - No reference in books

3.8.2.3 Gene expression and cancer

Specification topic Nelson Thornes reference Additional notes/comments

The main characteristics of benign and malignant tumours.

The role of the following in the development of tumours:

  • tumour suppressor genes and oncogenes
  • abnormal methylation of tumour suppressor genes and oncogenes

increased oestrogen concentrations in the development of some breast cancers

A2: 14.4/brief Most of this is new on the specification and not in the books

3.8.3 Using genome projects

Specification topic Nelson Thornes reference Additional notes/comments

Sequencing projects have read the genomes of a wide range of organisms, including humans.

Determining the genome of simpler organisms allows the sequences of the proteins that derive from the genetic code (the proteome) of the organism to be determined. This may have many applications, including the identification of potential antigens for use in vaccine production.

In more complex organisms, the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome.

Sequencing methods are continuously updated and have become automated.

  Most of this is new to the specification and not in the books

3.8.4.1 Recombinant DNA technology

Specification topic Nelson Thornes reference Additional notes/comments

Recombinant DNA technology involves the transfer of fragments of DNA from one organism, or species, to another. Since the genetic code is universal, as are transcription and translation mechanisms, the transferred DNA can be translated within cells of the recipient (transgenic) organism.

Fragments of DNA can be produced by several methods, including:

  • conversion of mRNA to complementary DNA (cDNA), using reverse transcriptase
  • using restriction enzymes to cut a fragment containing the desired gene from DNA
  • creating the gene in a ‘gene machine’

Fragments of DNA can be amplified by in vitro and in vivo techniques.

The principles of the polymerase chain reaction (PCR) as an in vitro method to amplify DNA fragments.

The culture of transformed host cells as an in vivo method to amplify DNA fragments.

  • The addition of promoter and terminator regions to the fragments of DNA
  • The use of restriction endonucleases and ligases to insert fragments of DNA into vectors. Transformation of host cells using these vectors

The use of marker genes to detect genetically modified (GM) cells or organisms. (Students will not be required to recall specific marker genes in a written paper)

A2: 16.1

A2:16.3

A2: 16.2

Brief and doesn’t actually say this.

3.8.4.2 Differences in DNA between individuals of the same species

Specification topic Nelson Thornes reference Additional notes/comments

The use of labelled DNA probes and DNA hybridisation to locate specific alleles of genes.

The use of labelled DNA probes that can be used to screen patients for heritable conditions, drug responses or health risks.

The use of this information in genetic counselling and personalised medicine.

A2: 16.6

A2: 16.7

3.8.4.3 Genetic fingerprinting

Specification topic Nelson Thornes reference Additional notes/comments

An organism’s genome contains many variable number tandem repeats (VNTRs). The probability of two individuals having the same VNTRs is very low.

The technique of genetic fingerprinting in analysing DNA fragments that have been cloned by PCR, and its use in determining genetic relationships and in determining the genetic variability within a population.

The use of genetic fingerprinting in the fields of forensic science, medical diagnosis, animal and plant breeding.

3.8.4.3

A2: 16.8

A2: 16.6 Application section

Specifications that use this resource: