B4 Specification

Module B4: The processes of life

B4.1 How do chemical reactions take place in living things?

1. understand that the basic processes of life carried out by all living things depend on chemical

reactions within cells that require energy released by respiration

2. understand the role of photosynthesis in making food molecules and energy available to

living organisms through food chains

3. describe photosynthesis as a series of chemical reactions that use energy from sunlight to

build large food molecules in plant cells and some microorganisms (e.g. phytoplankton)

4. describe respiration as a series of chemical reactions that release energy by breaking down

large food molecules in all living cells

5. recall that enzymes are proteins that speed up chemical reactions

6. recall that cells make enzymes according to the instructions carried in genes

7. understand that molecules have to be the correct shape to fit into the active site of the

enzyme (the lock and key model)

8. understand that enzymes need a specific constant temperature to work at their optimum,

and that they permanently stop working (denature) if the temperature is too high

9. explain that enzyme activity at different temperatures is a balance between:

a. increased rates of reaction as temperature increases

b. changes to the active site at higher temperatures, including denaturing

Candidates are not expected to explain why rates of reaction increase with

temperature

10. recall that an enzyme works at its optimum at a specific pH

11. explain the effect of pH on enzyme activity in terms of changes to the shape of the

active site.

B4.2 How do plants make food?

1. recall the names of the reactants and products of photosynthesis, and use the word

equation:

(light energy)

carbon dioxide + water → glucose + oxygen

2. recall the formulae of the reactants and products of photosynthesis, and use the

symbol equation:

(light energy)

6CO2 + 6H2O → C6H12O6 + 6O2

3. recall the main stages of photosynthesis:

a. light energy absorbed by the green chemical chlorophyll

b. energy used to bring about the reaction between carbon dioxide and water to

produce glucose (a sugar)

c. oxygen produced as a waste product

4. recall that glucose may be:

a. converted into chemicals needed for growth of plant cells, for example cellulose,

protein and chlorophyll

b. converted into starch for storage

c. used in respiration to release energy

5. recall the structure of a typical plant cell, limited to chloroplasts, cell membrane, nucleus,

cytoplasm, mitochondria, vacuole and cell wall

6. understand the functions of the structures in a typical plant cell that have a role in

photosynthesis, including:

a. chloroplasts contain chlorophyll and the enzymes for the reactions in photosynthesis

b. cell membrane allows gases and water to pass in and out of the cell freely while

presenting a barrier to other chemicals

c. nucleus contains DNA which carries the genetic code for making enzymes and other

proteins used in the chemical reactions of photosynthesis

d. cytoplasm where the enzymes and other proteins are made

7. recall that minerals taken up by plant roots are used to make some chemicals needed by

cells, including nitrogen from nitrates to make proteins

8. understand that diffusion is the passive overall movement of molecules from a region of their

higher concentration to a region of their lower concentration

9. recall that the movement of oxygen and carbon dioxide in and out of leaves during

photosynthesis occurs by diffusion

10. understand that osmosis (a specific case of diffusion) is the overall movement of water from

a dilute to a more concentrated solution through a partially permeable membrane

11. recall that the movement of water into plant roots occurs by osmosis

12. understand that active transport is the overall movement of chemicals across a cell

membrane requiring energy from respiration

13. recall that active transport is used in the absorption of nitrates by plant roots

B4.3 How do living organisms obtain energy?

1. understand that all living organisms require energy released by respiration for some

chemical reactions in cells, including chemical reactions involved in:

a. movement

b. synthesis of large molecules

c. active transport

2. understand that synthesis of large molecules includes:

a. synthesis of polymers required by plant cells such as starch and cellulose from

glucose in plant cells

b. synthesis of amino acids from glucose and nitrates, and then proteins from amino

acids in plant, animal and microbial cells

3. recall that aerobic respiration takes place in animal and plant cells and some

microorganisms, and requires oxygen

4. recall the names of the reactants and products of aerobic respiration and use the word

equation:

glucose + oxygen → carbon dioxide + water (+ energy released)

5. recall the formulae of the reactants and products of aerobic respiration and use the

symbol equation:

C6H12O6 + 6O2 → 6CO2 + 6H2O

6. recall that anaerobic respiration takes place in animal, plant and some microbial cells in

conditions of low oxygen or absence of oxygen, to include:

a. plant roots in waterlogged soil

b. bacteria in puncture wounds

c. human cells during vigorous exercise

7. recall the names of the reactants and products of anaerobic respiration in animal cells and

some bacteria, and use the word equation:

glucose → lactic acid (+ energy released)

8. recall the names of the reactants and products of anaerobic respiration in plant cells and

some microorganisms including yeast, and use the word equation:

glucose → ethanol + carbon dioxide (+ energy released)

9. understand that aerobic respiration releases more energy per glucose molecule than

anaerobic respiration

10. recall the structure of typical animal and microbial cells (bacteria and yeast) limited to:

a. nucleus

b. cytoplasm

c. cell membrane

d. mitochondria (for animal and yeast cells)

e. cell wall (for yeast and bacterial cells)

f. circular DNA molecule (for bacterial cells)

B4.3 How do living organisms obtain energy?

11. understand the functions of the structures in animal, plant, bacteria and yeast cells that have

a role in respiration, including:

a. mitochondria contain enzymes for the reactions in aerobic respiration (in animals,

plants and yeast)

b. cell membrane allows gases and water to pass in and out of the cell freely while

presenting a barrier to other chemicals

c. nucleus or circular DNA in bacteria contains DNA which carries the genetic code for

making enzymes used in the chemical reactions of respiration

d. cytoplasm where enzymes are made and which contains the enzymes used in

anaerobic respiration

12. describe examples of the applications of the anaerobic respiration of microorganisms,

including the production of biogas and fermentation in bread making and alcohol production.

© OCR 2011 GCSE Science A