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Photosynthesis Reactions

The process used by plants and bacteria to generate sugars from carbon dioxide, water and light.

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Photosynthesis Reactions

Look at the amazing meat-eating plants pictured here! Called pitcher plants, they use their “pitchers” to capture and digest insects. But even these pitcher plants—like all other plants—make food by photosynthesis. They “eat” insects just to get extra nutrients.

Food from Light

Most of the energy used by living things comes either directly or indirectly from the sun. That’s because sunlight provides the energy for photosynthesis. This is the process in which plants and certain other organisms synthesize glucose (C6H12O6). The process uses carbon dioxide and water and also produces oxygen. The overall chemical equation for photosynthesis is:

6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose, in turn, is used for energy by the cells of almost all living things. Photosynthetic organisms such as plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants).

Q: How do living things get energy from glucose?

A: They break bonds in glucose and release the stored energy in the process of cellular respiration.

Photosynthetic Organisms

The organisms pictured in the Figures below, below, and below all use sunlight to make glucose in the process of photosynthesis. In addition to plants, they include bacteria and algae. All of these organisms contain the green pigment chlorophyll, which is needed to capture light energy.

A tremendous amount of photosynthesis takes place in the plants of this lush tropical rainforest.

The green streaks on this very blue lake are photosynthetic bacteria called cyanobacteria.

The green “scum” on this pond consists of photosynthetic algae.


  • Photosynthesis is the process in which certain living things use energy in sunlight to synthesize glucose from carbon dioxide and water. Oxygen is also produced in this process.
  • Chemical energy that is stored in the bonds of glucose molecules is used by the cells of almost all living things for energy.
  • Living things that undergo photosynthesis and produce glucose include plants, cyanobacteria, and algae.


  • photosynthesis: Process in which plants and certain other organisms use light energy to synthesize glucose from carbon dioxide and water and release oxygen.


Watch the video about photosynthesis at the following URL, and then answer the questions below.


  1. What structures in the leaves of plants are the keys to photosynthesis? Why are these structures green?
  2. In the video, how was the role of chlorophyll in photosynthesis demonstrated?
  3. Identify and briefly describe the two sets of reactions that take place during photosynthesis.


  1. What is photosynthesis?
  2. How is energy transformed in photosynthesis?
  3. Why are photosynthetic organisms green?

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