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Introduces how plants use sunlight to produce sugars.

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Photosynthesis (Process)

License: CC BY-NC 3.0


Oxygen - the oxygen that we breath - is just a waste product of plants!

Every split second that sunlight hits that leaf, photosynthesis is initiated, bringing energy into the ecosystem. It could be said that this is one of the most important - if not the absolutely most important - biochemical reaction. And it all starts with the leaf.

Vocabulary to know

  • chloroplast: Organelle that carries out photosynthesis in plants.
  • glucose: Simple sugar with the chemical formula C6H12O6; a product of photosynthesis.
  • photosynthesis: Process in plants that changes solar energy to chemical energy (carbohydrates).
  • producer: Organism that produces food (glucose) for itself and other organisms.
  • reactants: Subtances that enter a chemical reaction and "react" together.
  • products: Subtances that exit a chemical reaction that are "produced."
  • solar energy: Energy from the Sun.
  • chemical energy: Energy created and stored by plants, and used by plants and animals.

What is Photosynthesis?

Plants are producers, which means they are able to make, or produce, their own food.  This is done throught the process of photosynthesis.  Photosynthesis is the process in plants that changes solar energy to chemical energyAlmost all organisms obtain their energy either directly or indirectly from photosynthesis. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth.  Photosynthesis occurs in small organelles inside plant cells called chloroplasts. Only cells with chloroplasts can perform photosynthesis. Animal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms rely on other organisms to obtain their energy.

The process can be summarized as: in the presence of sunlight, carbon dioxide + water react to become glucose + oxygen.

Stating this in a chemical equation:

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

Glucose is a sugar that acts as the food source for plants. 

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. 

Oxygen formed during photosynthesis, which is necessary for animal life, is essentially a waste product of the photosynthesis process and get rid of it.

The Photosynthesis Song can be heard at http://www.youtube.com/watch?v=C1_uez5WX1o (1:52).

The Process of Photosynthesis

The Reactants

Reactants are subtances that ENTER a chemical reaction and "react" together.  The reactants of photosynthesis are carbon dioxide and water. These are the molecules necessary to begin the process. But one more item is necessary, and that is sunlight. All three components, carbon dioxide, water, and the sun's energy are necessary for photosynthesis to occur. These three components must meet in the chloroplast of the leaf cell for photosynthesis to occur.  Carbon dioxide enters the leaf from the air through special openings called stomata. Stomata are special pores that allow gases to enter and exit the leaf.  Water enters through the plants roots and move through veins to the plant cells in the leaves.  Once inside the plant's cells, carbon dioxide and water mix with chlorophyll.  Chlorophyll is the green pigment in leaves that captures energy from the sun

6CO2 + 6H2O + Light Energy →

The Products

What is produced by the plant cell during photosynthesis? The products of photosynthesis are glucose and oxygen. This means they are produced at the end of photosynthesis. Glucose, the food of plants, is used to store chemical energy. Glucose is a simple sugar molecule which can be combined with other glucose molecules to form large carbohydrates, such as starch. Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata of the leaves. As you know, animals need oxygen to live. Without photosynthetic organisms like plants, there would not be enough oxygen in the atmosphere for animals to survive.

→ C6H12O6 + 6O2

The Chemical Reaction

In summary, the REACTANTS "react" together, and the PRODUCTS are "produced."  Or, the REACTANTS of 6 molecules of carbon dioxide (CO2) and 6 molecules of water (H2O), with the addition of solar energy "react" to "produce" the PRODUCTS of 1 molecule of glucose (C6H12O6) and 6 molecules of oxygen (O2). Using chemical symbols, the equation is represented as follows:

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

Videos & Interactive Simulation

Open each resource in a new window. (right-mouse click and choose "Open link in new tab.")

Photosynthesis at http://www.youtube.com/watch?v=RNufj-64OO0 (7:08)

  • What do plants do with most of the sugar they produce during photosynthesis?
  • How do decreasing levels of CO2 affect plants? How do you think increasing levels of CO2 affect plants?

Photosynthesis at http://www.youtube.com/watch?v=mpPwmvtDjWw (2:41)

  • Where do plants get the raw materials for photosynthesis?
  • What do plants take up through their roots?  Which of these substances are used for photosynthesis?
  • Where does the chemical reactions of photosynthesis take place?



  • All the energy used by living things on earth came from the process of photosynthesis.
  • During photosynthesis, carbon dioxide and water combine with solar energy to create glucose (chemical energy) and oxygen.
  • Photosynthesis occurs in the chloroplast of the plant cell.
  • The reactants of photosynthesis are carbon dioxide and water and solar energy.  
  • The products of photosynthesis are glucose and oxygen.


  1. What would happen if the stomata of a plant leaf were glued shut? Would that plant be able to perform photosynthesis? Why or why not?
  2. What are the reactants needed to perform photosynthesis? The products?
  3. Where does the energy for photosynthesis come from?
  4. How is the process of photosynthesis central to sustaining life on Earth?

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