Biology A Level Revision (AQA)
Paper 1 - Year 12 / AS Level
Biological Molecules
Cells
Organisms Exchanging Substances
Genetic Information, Variation
Paper 2 - Year 13 / A Level
Energy Transfers In and Between Organisms
Organisms Responses to their Environment
Genetics, Evolution and Ecosystems
The Control of Gene Expression
Some diagrams used in this document are sourced from Cognito (https://cognitoedu.org).
All rights to those diagrams belong to Cognito.
, Biology Revision A Level AQA
Energy Transfers In and Between Organisms
Photosynthesis
● What is it?
- Series of reactions using energy from The Sun to convert CO2 into carbohydrates.
- This takes place in chloroplasts of plants / algal cells.
- Converts light energy into chemical energy (stored as carbs or other molecules).
- This chemical energy can be transferred to an organism that consumes the plant.
- Carbon dioxide + water → oxygen + glucose
- 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆
● Stages of Photosynthesis:
- Light Dependent Reaction -
➢ First stage of photosynthesis.
➢ Initiated when light energy is absorbed by
chlorophyll.
- Light Independent Reaction -
➢ The second stage of photosynthesis.
➢ Does not require light energy to take place.
● Chloroplasts:
- Stroma is the space within chloroplasts
which contain starch grains (carbohydrates
produced are stored here).
- Thylakoids are fluid-filled sacs that are
stacked to form grana.
- These grana are linked by thylakoid
membranes to form lamellae.
- Lamellae contain photosynthetic pigments
that absorb specific wavelengths (colours) of
visible light.
- Examples of these photosynthetic pigments include:
➢ Chlorophyll a
➢ Chlorophyll b
➢ Carotene
● Photosystems
- Photosynthetic pigments are attached to proteins within thylakoid membranes and
together are called photosystems.
- There are two main types of photosystems:
➢ Photosystem I (PSI)
➢ Photosystem II (PSII)
- These both play an important role in Light Dependent Reactions.
Page 1
Paper 1 - Year 12 / AS Level
Biological Molecules
Cells
Organisms Exchanging Substances
Genetic Information, Variation
Paper 2 - Year 13 / A Level
Energy Transfers In and Between Organisms
Organisms Responses to their Environment
Genetics, Evolution and Ecosystems
The Control of Gene Expression
Some diagrams used in this document are sourced from Cognito (https://cognitoedu.org).
All rights to those diagrams belong to Cognito.
, Biology Revision A Level AQA
Energy Transfers In and Between Organisms
Photosynthesis
● What is it?
- Series of reactions using energy from The Sun to convert CO2 into carbohydrates.
- This takes place in chloroplasts of plants / algal cells.
- Converts light energy into chemical energy (stored as carbs or other molecules).
- This chemical energy can be transferred to an organism that consumes the plant.
- Carbon dioxide + water → oxygen + glucose
- 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆
● Stages of Photosynthesis:
- Light Dependent Reaction -
➢ First stage of photosynthesis.
➢ Initiated when light energy is absorbed by
chlorophyll.
- Light Independent Reaction -
➢ The second stage of photosynthesis.
➢ Does not require light energy to take place.
● Chloroplasts:
- Stroma is the space within chloroplasts
which contain starch grains (carbohydrates
produced are stored here).
- Thylakoids are fluid-filled sacs that are
stacked to form grana.
- These grana are linked by thylakoid
membranes to form lamellae.
- Lamellae contain photosynthetic pigments
that absorb specific wavelengths (colours) of
visible light.
- Examples of these photosynthetic pigments include:
➢ Chlorophyll a
➢ Chlorophyll b
➢ Carotene
● Photosystems
- Photosynthetic pigments are attached to proteins within thylakoid membranes and
together are called photosystems.
- There are two main types of photosystems:
➢ Photosystem I (PSI)
➢ Photosystem II (PSII)
- These both play an important role in Light Dependent Reactions.
Page 1
