Bioenergetics: GCSE Combined Science
Photosynthesis, limiting factors, aerobic and anaerobic respiration, exercise and metabolism
The short version
Write photosynthesis and respiration equations, explain limiting factors, describe exercise changes, and define metabolism.
Key idea
Needs light and chlorophyll. Symbol: 6CO2 + 6H2O → C6H12O6 + 6O2
Grade 2–3: Leaves take in carbon dioxide and water and make sugar and oxygen when it is light.
Grade 5–6: I can write the word equation and say chloroplasts / chlorophyll trap light.
Grade 9: I write the balanced symbol equation, name palisade cells as packed with chloroplasts, and I never say plants only photosynthesise and never respire — they respire all the time.
Go a bit deeper
The one you have not yet increased (or temperature denaturing enzymes) is
Grade 2–3: Plants need enough light and enough warmth.
Grade 5–6: I can name three limiting factors and sketch a rise-then-plateau graph.
Grade 9: Inverse square: move a lamp from 10 cm to 20 cm and intensity falls to 1/4. Pondweed RP: count bubbles or measure O2 volume; control temperature and CO2 (hydrogencarbonate).
Worked example
Worked example
Grade 2–3: Leaves take in carbon dioxide and water and make sugar and oxygen when it is light. Grade 5–6: I can write the word equation and say chloroplasts / chlorophyll trap light. Grade 9: I write the balanced symbol equation, name palisade cells as packed with chloroplasts, and I never say plants only photosynthesise and never respire — they respire all the time.
Lessons in this topic
- Photosynthesis
- Limiting factors
- Aerobic respiration
- Anaerobic respiration
- Response to exercise
- Metabolism
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
Give word and symbol equations, explain limiting-factor graphs, and use the inverse square law on Higher. Link oxygen debt to lactic acid.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
The word equation for photosynthesis is...
Photosynthesis is described as endothermic because...
In the pondweed practical, what is the independent variable when you move the lamp?
A photosynthesis graph levels off as light intensity increases. What does that mean?
Common mistakes
- Oxygen is a product, not a reactant. Mixing this with respiration’s equation is the classic Paper 1 dump.
- A bubble count assumes each bubble is the same size of oxygen. Say that assumption if they ask for a weakness.
- Plants photosynthesise and respire. At night, net gas exchange is CO2 out because photosynthesis stops.
- Anaerobic in animals is not ethanol. That mix-up is very common.
Answers and working
Frequently asked questions
Is GCSE Bioenergetics on Combined Science and Triple?
Bioenergetics is on Combined Science and on Triple Biology. Progress is shared in the ReviseEasy app.
Which exam board is this Bioenergetics page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Bioenergetics Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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