A Quick Breakdown

What is Photosynthesis?

Photosynthesis is the process by which plants make their own food.

The word photosynthesis can be separated to make two smaller words:

"photo" which means light

"synthesis" which means putting together

Plants need food but they do not have to wait on people or animals to provide for them. Most plants are able to make their own food whenever they need it. This is done using light and the process is called photosynthesis.

To make food, plants need:

- Carbon Dioxide

- Water

- Sunlight

Let’s take a look at how these are collected by plants.

  • Carbon dioxide from the air passes through small pores (holes) in the leaves. These pores are called stomata.
  • Water is absorbed by the roots and passes through vessels in the stem on its way to the leaves.
  • Sunlight is absorbed by a green chemical in the leaves.

The Process of Photosynthesis

Photosynthesis takes place in the leaves of plants. The leaves are made up of very small cells. Inside these cells are tiny structures called chloroplasts. Each chloroplast contains a green chemical called chlorophyll which gives leaves their green color.

  • Chlorophyll absorbs the sun’s energy.
  • It is this energy that is used to split water molecules into hydrogen and oxygen.
  • Oxygen is released from the leaves into the atmosphere.
  • Hydrogen and carbon dioxide are used to form glucose or food for plants.

Some of the glucose is used to provide energy for the growth and development of plants while the rest is stored in leaves, roots or fruits for later use by plants.

Here is the process in greater detail:

Photosynthesis occurs in two stages commonly known as Light dependent Reactions and the Calvin Cycle.

Light dependent Reactions

Light dependent reactions occur in the thylakoid membrane of the chloroplasts and take place only when light is available. During these reactions light energy is converted to chemical energy.

  • Chlorophyll and other pigments absorb energy from sunlight. This energy is transferred to the photosystems responsible for photosynthesis.
  • Water is used to provide electrons and hydrogen ions but also produces oxygen. Do you remember what happens to the oxygen?
  • The electrons and hydrogen ions are used to create ATP and NADPH. ATP is an energy storage molecule. NADPH is an electron carrier/donor molecule. Both ATP and NADPH will be used in the next stage of photosynthesis.

The Calvin Cycle

The Calvin Cycle reactions occur in the stroma of the chloroplasts. Although these reactions can take place without light, the process requires ATP and NADPH which were created using light in the first stage. Carbon dioxide and energy from ATP along with NADPH are used to form glucose.

Plants need carbon dioxide, water, and sunlight to make their food. They also make food called glucose. In addition to glucose, plants also produce oxygen.

This information can be written in a word equation as shown.

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This equation is the same as the written out version, but it shows the chemical formula for carbon dioxide, water, glucose, and oxygen.
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For extra practice, print out this diagram and fill it in to keep for personal use.
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Photosynthesis Poster


This will give you a quick, easy guide, to remembering the basic steps involved.

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Are You Lost?

If you are having trouble understanding photosynthesis through my words, try listening to someone else. This gives a good explanation and it will help you to visually understand photosynthesis.
Photosynthesis: Crash Course Biology #8

Fun Song!

This Photosynthesis song is written and sung to the tune of Michael Jackson's Thriller. It is a fun way to have students remember the basics of Photosynthesis.
Photosynthesis Song ("Thriller") - By Ben Leddy