Life Cycle - Plants (4B)
Pre Lab 

  • Exploring photosynthesis.
  • Explaining how light is transformed into food.


  • carbon dioxide
  • chlorophyll
  • light
  • photosynthesis

Students will learn how plants transform light into food via photosynthesis.



The most important characteristic of plants is their ability to manufacture food . Typically this process, known as photosynthesis, occurs primarily in the green leaves of plants. Photosynthesis occurs only in the chloroplasts of plant cells because these are the organs that contain the green pigment chlorophyll. The rate of photosynthesis is dependent on light concentration, temperature, water, and organic and inorganic materials available to a plant. Three aspects of light are important for photosynthesis: intensity, quality, and duration. Intensity depends on the amount of sunlight falling on a given chloroplast per second. The rate of photosynthesis will increase if the light intensity is increased. The water available to a plant also influences the rate of photosynthesis.

Photosynthesis is the physical and chemical process involved in the trapping of the sun's energy and the use of this energy to manufacture food. Green plants utilize water and carbon dioxide and in the presence of sunlight and chlorophyll manufacture food. Food-making normally occurs in the leaf cells of a plant. Chlorophyll is the substance which gives leaves their green color, and is found within the chloroplasts (small green bodies in plant cells) of leaves. All the things needed by a plant to manufacture food are transported to the leaves through the roots and stems. The plant cells can convert sugar into starch for storage or combine it with other materials to build proteins, vitamins, or fats.

When the temperature gets cool it starts to shut down photosynthesis.  The chlorophyll needed for the process stops and the green color goes away.  The colors of orange and yellow which are masked by the chlorophyll come through.  The orange is from the pigment molecule called carotene and the yellow is from xanthophyll molecule.  Some leaves also turn red, but the is from the production of another molecule called anthocyanin.


  1. Read the poem The Colors of Fall.   This will give students a background of how leaves turn from green when it is producing food to the red, orange and yellow of fall (when photosynthesis shuts down. 
  2. The worksheet examines photosynthesis via chemical equations (with words) and has the students illustrate the equation in pictures using the symbols given. The key is for the students to see how you can easily write down what is happening in a simple equation.
  3. Point out to students to make a legend of each of the components so their diagram can be interpreted. You may want to give the following clues to help them out.  
carbon dioxide =

water =

sugar =

oxygen =

chlorophyll =

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