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Biology · Grades 7–10

Photosynthesis and matter sources

Trace carbon as well as energy.

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Learn the idea

Process

Photosynthesis uses light energy to build energy-rich organic compounds from simpler starting materials.

Carbon

In the familiar plant model, carbon dioxide supplies carbon for sugar production.

Chloroplasts

Photosynthetic machinery is located in chloroplasts in many plant cells.

Whole plant

Plants also respire; photosynthesis is not their only energy-related process.

Worked examples

Where does much of the carbon in newly made plant sugar come from?

CO₂ supplies carbon in the photosynthesis model.

Carbon dioxide.

What is the role of light in photosynthesis?

Light energy powers the process rather than supplying carbon matter.

It provides energy.

Check your understanding

  1. Do plants also carry out cellular respiration?

    1. Only when every leaf falls off.
    2. No, only animals respire.
    3. Yes.

  2. A simplified equation uses 6 CO₂ to represent formation of one glucose molecule. How many carbon atoms are supplied?

  3. Why is saying plants get all their food from soil misleading?

Answers and marking notes

Answers and marking notes
  1. Yes.

    Plant cells use respiration as well as photosynthesis.

  2. 6

    Each CO₂ contains one carbon atom.

  3. Plants generally make sugars using carbon dioxide and water, while soil supplies water and mineral nutrients.

    Distinguish organic food molecules from mineral resources.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.