Autotrophic, heterotrophic and saprophytic nutrition; the photosynthesis equation; leaf adaptations; limiting factors; nitrogen and magnesium.
6 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Every bite of food you have ever eaten started as sunlight caught by a leaf.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
Makes complex organic food from simple inorganic substances using light energy (photosynthesis).
Obtains ready-made organic food by eating other organisms.
Secretes enzymes onto dead organic matter and absorbs the products (fungi, bacteria).
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ in the presence of light and chlorophyll.
Large surface area; thin; palisade with many chloroplasts near top; air spaces; stomata; veins; transparent cuticle.
Light, CO₂, temperature. The one in shortest supply controls the rate.
Nitrogen → proteins/growth. Magnesium → chlorophyll.
Starch is insoluble (no osmotic effect), compact and unreactive.
Produces food for almost all food chains; releases O₂; removes CO₂ from the air.
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
| Light intensity (units) | 0 | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|---|
| Rate at 0.04% CO₂ | 0 | 10 | 18 | 22 | 23 | 23 |
| Rate at 0.10% CO₂ | 0 | 10 | 19 | 28 | 34 | 35 |
Try it in your notebook first, then reveal the solution one step at a time.
Try it in your notebook first, then reveal the solution one step at a time.
Glucose is not stored in the leaf as glucose: it is used straight away or converted into other substances.
The balanced equation is 6-6-1-6: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy, chlorophyll).
Magnesium is part of the chlorophyll molecule. Citrus and other crops short of magnesium develop yellow leaves (chlorosis) and grow poorly, so farmers add fertilisers containing magnesium and nitrogen.
Put a sprig of pondweed in water under a lamp and count the bubbles of oxygen per minute with the lamp at 10, 20 and 30 cm. What happens to the rate as the lamp moves away?
4 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Write full answers, then reveal the mark scheme and tick the points you earned (23 marks in total). Your answers are saved on this device.
Question 1 [13 marks]
Photosynthesis is important to all living things.
(a) Define the term “photosynthesis”. [2]
(b) Write a balanced chemical equation for photosynthesis. [2]
(c) Distinguish between the role of the intercellular air spaces and the stomatal pores. [2]
(d) Explain why the rate of photosynthesis decreases on a very hot day. [2]
(e) State ONE role of chlorophyll, and outline TWO ways photosynthesis is important to living things. [5]
Question 2 [10 marks]
Green plants make food by photosynthesis.
(a) Name the TWO raw materials and TWO conditions needed for photosynthesis. [4]
(b) Suggest THREE reasons why the glucose made is not stored in the leaves. [3]
(c) Describe the test to show that a green leaf contains starch. [3]
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.