GCSE Science₈₄₆₅

Describe cellular respiration as an exothermic reaction which is continuously occurring in all living cells.

Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen).

Aerobic respiration is an exothermic reaction that can be represented by word and symbol equations.

$\mathsf{g}\mathsf{l}\mathsf{u}\mathsf{c}\mathsf{o}\mathsf{s}\mathsf{e}\mathsf{ }\mathsf{+}\mathsf{o}\mathsf{x}\mathsf{y}\mathsf{g}\mathsf{e}\mathsf{n}\mathsf{ }\mathsf{\to }\mathsf{c}\mathsf{a}\mathsf{r}\mathsf{b}\mathsf{o}\mathsf{n}\mathsf{ }\mathsf{d}\mathsf{i}\mathsf{o}\mathsf{x}\mathsf{i}\mathsf{d}\mathsf{e}\mathsf{ }\mathsf{+}\mathsf{w}\mathsf{a}\mathsf{t}\mathsf{e}\mathsf{r}$

An exothermic reaction is one that transfers energy to its surroundings.

• chemical reactions to build larger molecules
• movement
• keeping warm.

WS 1.2

(HT only) Write a balanced symbol equation for respiration, given the formula of glucose.

Compare the processes of aerobic and anaerobic respiration.

Anaerobic respiration in muscles is also exothermic but it gives out less energy. It is represented by the word equation:

$\mathsf{g}\mathsf{l}\mathsf{u}\mathsf{c}\mathsf{o}\mathsf{s}\mathsf{e}\mathsf{ }\mathsf{\to }\mathsf{l}\mathsf{a}\mathsf{c}\mathsf{t}\mathsf{i}\mathsf{c}\mathsf{ }\mathsf{a}\mathsf{c}\mathsf{i}\mathsf{d}$

Because the oxidation of glucose is incomplete in anaerobic respiration much less energy is given out than in aerobic respiration.

If insufficient oxygen is supplied, anaerobic respiration takes place in muscles. The incomplete oxidation of glucose causes a build-up of lactic acid and creates an oxygen debt. Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.

Explain the need for exchange surfaces and a transport system in multicellular organisms in terms of surface area:volume ratio.

A single-celled organism has a relatively large surface area:volume ratio.

The tissues of a multicellular organism consist of cells with a similar structure and function. Organs, such as the heart and lungs, are made of tissues. One organ may consist of several tissues. Organ systems, such as the circulatory system, are groups of organs that perform a particular function.

In multicellular organisms many organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by:

• having a large surface area
• a membrane that is thin, to provide a short diffusion path
• (in animals) having an efficient blood supply
• (in animals, for gaseous exchange) being ventilated.

MS 1c

Calculate and compare surface area:volume ratios.

Describe the human circulatory system, including the relationship with the gaseous exchange system, and explain how the structure of the heart and the blood vessels are adapted to their functions.

Describe some of the substances transported into and out of a range of organisms in terms of the requirements of those organisms, to include oxygen, carbon dioxide and dissolved food molecules.

The heart is a muscular organ that pumps blood around the body in a dual circulatory system.

The right ventricle pumps blood to the lungs, where gas exchange takes place. The left ventricle pumps blood around the rest of the body.

Valves prevent the blood from flowing back from the ventricles to the atria. Knowledge of the names of the heart valves is not required.

Blood vessels associated with the heart include the aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.

Gas exchange takes place in the lungs. Important features of the lungs are the trachea, bronchi, alveoli and the capillary network surrounding the alveoli. The alveoli have the specialised surfaces for gas exchange between air and the blood.

The natural resting heart rate is controlled by a group of cells that act as a pacemaker, located in the right atrium. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.

The body contains three different types of blood vessel:

• arteries
• veins
• capillaries.

MS 1a, 1c

Use simple compound measures such as rate.

MS 1a, 1c

Carry out rate calculations.

Explain how red blood cells, white blood cells, platelets and plasma are adapted to their functions in the blood.

• red blood cells
• white blood cells
• platelets.

WS 3.5

Identify different types of blood cells in a photograph or diagram.

Explain the importance of sugars, amino acids, fatty acids and glycerol in the synthesis and breakdown of carbohydrates, lipids and proteins.

Describe some of the substances transported into and out of a range of organisms in terms of the requirements of those organisms, to include dissolved food molecules and urea.

The digestive system uses enzymes to break down large molecules in food into small soluble molecules that can be absorbed into the blood through the walls of the gut. The blood carries the small molecules to the cells of the body where they can be used for respiration or to make the new large molecules that the cells need as reserves of energy or for growth and repair.

Starch is a carbohydrate. Its molecules consist of a long chain of glucose molecules. Digestion by carbohydrase enzymes breaks down insoluble starch to water-soluble glucose. Cells use glucose during respiration.

Lipids are fats and oils. Digestion by lipase enzymes breaks down lipids to glycerol and fatty acids. Cells reform fats from the fatty acids and glycerol molecules. Fats are stored as a source of energy because cells can break them down and use them in respiration.

Proteins are long-chain molecules made up of many amino acids linked together. Digestion by protease enzymes breaks down proteins to amino acids. Cells use amino acids to make new proteins.

The liver breaks down unwanted amino acids to urea, which is then carried by the blood to the kidneys. The kidneys excrete urea in solution as urine.

Explain how the structure of the nervous system (including the central nervous system, sensory and motor neurones and sensory receptors) is adapted to its functions.

The nervous system enables humans to react to their surroundings and to coordinate their behaviour.

Information from receptors passes along cells (neurones) as impulses to the central nervous system, or CNS (the brain or the spinal cord). The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.

$\mathsf{s}\mathsf{t}\mathsf{i}\mathsf{m}\mathsf{u}\mathsf{l}\mathsf{u}\mathsf{s}\mathsf{ }\mathsf{\to }\mathsf{r}\mathsf{e}\mathsf{c}\mathsf{e}\mathsf{p}\mathsf{t}\mathsf{o}\mathsf{r}\mathsf{ }\mathsf{\to }\mathsf{c}\mathsf{o}\mathsf{o}\mathsf{r}\mathsf{d}\mathsf{i}\mathsf{n}\mathsf{a}\mathsf{t}\mathsf{o}\mathsf{r}\mathsf{ }\mathsf{\to }\mathsf{e}\mathsf{f}\mathsf{f}\mathsf{e}\mathsf{c}\mathsf{t}\mathsf{o}\mathsf{r}\mathsf{ }\mathsf{\to }\mathsf{r}\mathsf{e}\mathsf{s}\mathsf{p}\mathsf{o}\mathsf{n}\mathsf{s}\mathsf{e}\mathsf{ }$

Explain how the structure of a reflex arc is related to its function.

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.

An example of a simple reflex action is the pain withdrawal reflex. This can be explained in terms of a reflex arc.

Sensory neurones carry impulses from receptors to the spinal cord and brain. Relay neurones carry impulses within the CNS. Motor neurones carry impulses from the CNS to effectors.

Where two neurones meet, there is a tiny gap called a synapse. Impulses cross this gap using chemicals.

Explain methods of measuring human reaction times and recall typical results.

Reaction times vary from person to person. Typical values range from 0.3s to 0.9s.

This topic links with Stopping distances .

Describe the principles of hormonal coordination and control by the human endocrine system.

The endocrine system is composed of glands that secrete hormones directly into the bloodstream. Hormones are large molecules. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer.

The pituitary gland in the brain is a ‘master gland’. It secretes several hormones that act on other glands to stimulate other hormones to be released.

(HT only) Explain the roles of thyroxine and adrenaline in the body including thyroxine as an example of a negative feedback system.

(HT only) Adrenaline is produced by the adrenal gland. It boosts the delivery of oxygen and glucose to the brain and muscles and prepares the body for ‘flight or fight’.

(HT only) Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.

(HT only) The control of thyroxine levels involves negative feedback . Negative feedback tends to stabilise a system. Any change in the system leads to a response that tends to reverse the change.

WS1.2, MS 2c

(HT only) Interpret and explain simple diagrams of negative feedback control.

Describe the function of meristems in plants.

Meristem tissue contains the cells in a plant that divide as the plant grows. This type of tissue is found at the growing tips of shoots and roots. The cells differentiate into different types of plant cells depending on where they are in the plant.

WS 1.4

Describe and explain the use of stem cells from meristems to produce clones of plants quickly and economically.

Describe some of the substances transported into and out of a range of organisms, in terms of the requirements of those organisms, to include oxygen, carbon dioxide, water and mineral ions.

Plants, like other multicellular organisms, need specialised structures for transporting and exchanging materials. The roots, stem and leaves form a plant organ system for transport of substances around the plant.

Plants take in carbon dioxide from the atmosphere for photosynthesis and oxygen for respiration. Plants take in water from the soil with dissolved ions including nitrate ions to make proteins and magnesium ions to make chlorophyll.

Explain the need for exchange surfaces and a transport system in multicellular organisms.

Explain how water and mineral ions are taken up by plants, relating the structure of the root hair cells to their function.

Explain how the structure of xylem is adapted to its functions in the plant.

Describe the process of transpiration including the structure and function of the stomata.

Water is drawn into the roots of plants from the soil. Water moves into the root hairs by osmosis. Mineral ions move from the soil into the root hairs by active transport.

Water flows from the roots through xylem in its stems to its leaves. Xylem tissue is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream from the roots to the leaves.

Water evaporates in the leaves and the water vapour escapes through tiny holes in the surface of leaves called stomata. The stomata can open or close as conditions change because the guard cells can gain or lose water by osmosis.

Explain the effect of a variety of environmental factors on the rate of water uptake by a plant, to include light intensity, air movement and temperature.

The rate of transpiration varies with:

• light intensity, which affects the opening of stomata
• air movements, which affect the concentration of water vapour in the air around leaves
• temperature, which affects the rate at which water evaporates.

MS 1a, 1c

Understand and use simple compound measures such as the rate of a reaction.

MS 4a

Translate information between graphical and numerical form.

MS 4a, 4c

Plot and draw appropriate graphs, selecting appropriate scales for axes.

WS 3.3

Carry out and represent mathematical and statistical analysis.

MS 2c, 4a

Extract and interpret information from graphs, charts and tables.

Recall that chromatography involves a stationary and a mobile phase and that separation depends on the distribution between the phases.

Interpret chromatograms, including measuring R_f values.

Suggest chromatographic methods for distinguishing pure from impure substances.

The chlorophyll and other pigments in plant leaves can be separated and identified by chromatography. Chromatography can be used to separate mixtures and can give information to help identify substances.

The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent can be expressed as its R_f value:

${\mathsf{R}}_{\mathsf{f}}\mathsf{ }\mathsf{=}\mathsf{ }\frac{\mathsf{d}\mathsf{i}\mathsf{s}\mathsf{t}\mathsf{a}\mathsf{n}\mathsf{c}\mathsf{e}\mathsf{ }\mathsf{m}\mathsf{o}\mathsf{v}\mathsf{e}\mathsf{d}\mathsf{ }\mathsf{b}\mathsf{y}\mathsf{ }\mathsf{s}\mathsf{u}\mathsf{b}\mathsf{s}\mathsf{t}\mathsf{a}\mathsf{n}\mathsf{c}\mathsf{e}}{\mathsf{d}\mathsf{i}\mathsf{s}\mathsf{t}\mathsf{a}\mathsf{n}\mathsf{c}\mathsf{e}\mathsf{ }\mathsf{m}\mathsf{o}\mathsf{v}\mathsf{e}\mathsf{d}\mathsf{ }\mathsf{b}\mathsf{y}\mathsf{ }\mathsf{s}\mathsf{o}\mathsf{l}\mathsf{v}\mathsf{e}\mathsf{n}\mathsf{t}}$

Different compounds have different R_f values in different solvents, which can be used to help identify the compounds. The compounds in a mixture may separate into different spots depending on the solvent, but a pure compound produces a single spot in all solvents.

MS 1a

Recognise and use expressions in decimal form.

MS 1c

Use ratios and percentages.

WS 3.3

Carry out and represent mathematical and statistical analysis.

MS 1d

Make estimates of the results of simple calculations.

WS 4.6, MS 2a

Use an appropriate number of significant figures.

MS 4a

Extract and interpret information from charts and tables.

Translate information between graphical and numeric form when calculating R_f values.

Describe the process of photosynthesis and describe photosynthesis as an endothermic reaction.

Photosynthesis takes place in the chloroplasts in the cells of the leaves of plants. The chloroplasts contain the chlorophyll, which absorbs sunlight.

Photosynthesis is an endothermic reaction that can be represented by word and symbol equations.

$\mathsf{c}\mathsf{a}\mathsf{r}\mathsf{b}\mathsf{o}\mathsf{n}\mathsf{ }\mathsf{d}\mathsf{i}\mathsf{o}\mathsf{x}\mathsf{i}\mathsf{d}\mathsf{e}\mathsf{ }\mathsf{+}\mathsf{w}\mathsf{a}\mathsf{t}\mathsf{e}\mathsf{r}\mathsf{ }\stackrel{\mathsf{l}\mathsf{i}\mathsf{g}\mathsf{h}\mathsf{t}}{\mathsf{\to }}\mathsf{ }\mathsf{ }\mathsf{g}\mathsf{l}\mathsf{u}\mathsf{c}\mathsf{o}\mathsf{s}\mathsf{e}\mathsf{ }\mathsf{+}\mathsf{o}\mathsf{x}\mathsf{y}\mathsf{g}\mathsf{e}\mathsf{n}$

Energy is transferred to the plant cells by light.

The glucose produced in photosynthesis may be:

• used for respiration
• converted into insoluble starch for storage
• used to produce fat or oil for storage
• used to produce cellulose, which strengthens the cell wall
• used to produce amino acids for protein synthesis.

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

WS 1.2

(HT only) Write a balanced symbol equation for photosynthesis given the formula of glucose.

Explain the effect of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.

The rate of photosynthesis depends on:

• the energy available from light
• the concentration of carbon dioxide in the air
• the temperature.

MS 1a, 1c

Carry out rate calculations for photosynthesis.

(HT only) Explain the interaction of these factors in limiting the rate of photosynthesis.

(HT only) The rate of photosynthesis may be limited by:

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

(HT only) Increasing any one of the factors speeds up photosynthesis until the rate is limited by the factor which is in shortest supply.

WS 1.4

(HT only) Use data to relate limiting factors to the cost effectiveness of adding heat, light or carbon dioxide to greenhouses.

MS 1a, 1c, 2c, 4a, 4c

Translate information between numerical and graphical forms and extract and interpret information from graphs, charts and tables.

WS 3.5

(HT only) Understand and use inverse proportion – the inverse square law – and light intensity in the context of factors affecting photosynthesis.

Describe the process of translocation.

Explain how the structure of phloem is adapted to its functions in the plant.

Phloem tissue is composed of tubes of elongated living cells adapted for translocation of sugars from where they are produced by photosynthesis in the leaves to other parts of the plant for immediate use or storage. Cell sap containing sugars and other nutrients is able to move easily from one phloem cell to the next as the end walls have pores.

Explain how communicable diseases are spread in plants.

Tobacco mosaic virus is a widespread plant pathogen affecting many species of plants, including tomatoes. It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves, which affects the growth of the plant due to lack of photosynthesis.

Rose black spot is a fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced. The disease is spread by spores of the fungus that are produced in the black spots.

Explain how the spread of communicable diseases may be reduced or prevented in plants, to include a minimum of one plant disease.

Common control methods for tobacco mosaic virus include:

• removing and destroying infected plants
• washing hands and tools after handling infected plants
• crop rotation to avoid planting in soil that has been infected for at least two years.

Methods to control black spot include:

• not planting roses too close together – to allow the air to flow freely around them
• avoiding wetting the leaves when watering – wet leaves encourage the fungal disease
• cleaning up any infected leaves from the ground round the roses – to avoid spores spreading
• using a fungicide to prevent infection – spraying, especially in advance of warm, wet weather.

WS 1.4

Explain applications of science to prevent the spread of plant diseases.