6.1.2Plant Nutrition
Chlorophyll — Cambridge IGCSE Co-ordinated Sciences 0654 - Biology Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 11
Part 1 of 4What chlorophyll is
A green pigment
- A green pigment Chlorophyll is a green pigment found inside plant cells.
- It reflects green light, which is why leaves and most plants look green.
Where it is found
- Where it is found Chlorophyll is contained in chloroplasts, the small organelles in the cytoplasm of leaf cells, especially palisade mesophyll cells.
- Chloroplasts can be seen as green discs under a light microscope.
Why leaves are green
- Why leaves are green The pigment absorbs mainly red and blue light and reflects green light, so green light reaches our eyes.
Part 2 of 4Role in photosynthesis (Extended)
1Light is absorbed
- Light is absorbed Chlorophyll absorbs light energy from the Sun.
2Energy is transferred
- Energy is transferred The light energy is transferred into chemical energy.
3Carbohydrates are made
- Carbohydrates are made The chemical energy is used to build carbohydrates from carbon dioxide and water.
4Energy is stored
- Energy is stored Glucose is a carbohydrate that holds this chemical energy in store until it is needed.
Part 3 of 4The overall reaction
| Item | Detail |
|---|---|
| Word equation | carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll) |
| Symbol equation | 6CO2 + 6H2O → C6H12O6 + 6O2 |
| Raw materials | Carbon dioxide from the air and water from the soil |
| Products | Glucose, used or stored by the plant, and oxygen, released as a by-product |
| Role of chlorophyll | It is not used up; it absorbs the light energy that drives the reaction |
Part 4 of 4Evidence that chlorophyll is needed
Variegated leaves
- Variegated leaves A variegated leaf has green areas containing chlorophyll and white areas without it.
- After a starch test, only the green areas turn blue-black, which shows that photosynthesis occurs only where chlorophyll is present.
Plants without light
- Plants without light A plant kept in the dark loses chlorophyll over time and turns pale yellow, because chlorophyll is not made without light.
Key terms
| Term | Meaning |
|---|---|
| Chlorophyll | The green pigment in chloroplasts that absorbs light energy for photosynthesis. |
| Chloroplast | An organelle in plant cells that contains chlorophyll and is the site of photosynthesis. |
| Pigment | A coloured substance that absorbs certain wavelengths of light. |
| Photosynthesis | The process by which plants use light energy to make glucose from carbon dioxide and water. |
| Chemical energy | Energy stored in the bonds of molecules such as glucose. |
Avoid these mistakes
1
Saying chlorophyll 'makes' energy — it absorbs light energy, which is transferred into chemical energy; energy is not created.
2
Writing that chlorophyll is found in all plant cells; root cells, for example, have no chloroplasts.
3
Saying chlorophyll absorbs green light; it reflects green light, which is why plants look green.
4
Writing that chlorophyll is a raw material or product of photosynthesis, when it is a pigment that is not used up.
5
Confusing chlorophyll with chloroplaststhe pigment is inside the organelle.
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