Photosynthesis
Introduced| English | Meaning |
|---|---|
| photosynthesis/ˌfəʊtəʊˈsɪnθəsɪs/ | The process by which plants and other organisms use light energy to make organic substances from carbon dioxide and water. |
| chlorophyll/ˌklɔːrəʊˈfɪl/ | A green pigment that absorbs light energy for photosynthesis. |
| Calvin cycle/ˈkælvɪn ˈsaɪkl/ | The cycle of reactions that uses ATP and reduced NADP to incorporate carbon dioxide into organic molecules. |
Turning light into food
- Plants do something almost magical: they build food out of thin air and sunlight.
- They take in carbon dioxide and water and capture the energy in light.
- From these they make glucose, storing the sun's energy in a sugar.
- This process — photosynthesis — feeds almost all life on Earth.
The overall reaction
- Photosynthesis 光合作用 combines carbon dioxide, water, and light energy.
- The products are glucose (sugar) and oxygen.
- $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.
- The green pigment chlorophyll 叶绿素 captures the light.
What does a plant use as raw materials for photosynthesis?
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Photosynthesis uses carbon dioxide + water + light energy to make glucose and oxygen.
Stage 1: the light reactions
- In the light reactions, chlorophyll absorbs sunlight.
- The energy splits water, releasing oxygen as a by-product.
- It also makes the energy carriers ATP and NADPH.
- These carriers power the next stage.
How photosynthesis works
Step through the two stages — light reactions capture energy, then the Calvin cycle builds sugar from CO₂.
The green pigment that absorbs light for photosynthesis is ____.
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Chlorophyll in the chloroplasts captures the light energy that drives the whole process.
Where does the oxygen released by photosynthesis come from?
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Light energy splits water, and the oxygen atoms are released as O₂.
Stage 2: the Calvin cycle
- The Calvin cycle 卡尔文循环 does not need light directly.
- It uses the ATP and NADPH to fix carbon dioxide into sugar.
- Carbon atoms from CO₂ are built up into glucose.
- So light energy ends up stored in a stable sugar.
The Calvin cycle captures light energy, and the light reactions build sugar from CO₂.
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False. It is the other way round: the light reactions capture energy as ATP and NADPH, and the Calvin cycle uses them to build sugar from CO₂.
Select all true statements about photosynthesis.
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Photosynthesis needs light, so it does not happen in the dark. The other three are correct.
Photosynthesis is two stages, not one. The light reactions capture energy; the Calvin cycle uses it to build sugar. The Calvin cycle needs the products of the light reactions, so it cannot run for long in the dark.
Why the world depends on a leaf:
- Almost every food chain starts with a photosynthesising plant.
- The oxygen you breathe was released by splitting water in a leaf.
- Even coal and oil are ancient sunlight, captured by photosynthesis long ago.
Photosynthesis turns carbon dioxide, water, and light into glucose and oxygen, using chlorophyll to capture the light. It has two stages: the light reactions make ATP and NADPH (and release oxygen), and the Calvin cycle uses them to build sugar from CO₂.
Write from 6 carbon dioxide molecules
- The Calvin cycle builds one glucose.
- Oxygen gas released by the light reactions comes from water.
How many carbon dioxide molecules are fixed for that glucose?
One glucose carbon skeleton needs six fixed carbons.
How many CO2 molecules make one glucose?
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Glucose has six carbons, each from CO2.