Science in Focus: Shedding Light: Workshop 5

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Sunlight to Starch

In this program participants will explore how plants get their food. Starting with seeds, which have their own source of food, the program traces the growth of a plant, the development of chlorophyll in its leaves, and the production of sugar (and starch) in a process known as photosynthesis.


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Chlorophyll-containing organisms are able to absorb photons of light energy and use their energy to join carbon dioxide with hydrogen from water. As a result of a whole series of intermediate reactions sugar is made. Light energy is therefore transformed into chemical energy contained within sugar. As a by-product, oxygen is released into the atmosphere.

Sugar is used as the building block for plants. It is transported to all parts of the plant and used to make components of the cell as well as to provide the energy to drive the processes occurring in cells. When plentiful, sugar is converted to starch and stored.

Carbon dioxide is the main ingredient of sugar and consequently this gas is responsible for making the greatest contribution to the dry mass of a plant, be it the smallest daisy or the tallest tree. When asked where a plant gets its food, children will often answer that it comes from the soil. Even after instruction in photosynthesis, it is hard for students to believe that a gas can be the source of the stuff (matter) of which plants (including trees!) are made.

Not only is photosynthesis essential for the plant's growth, it is essential for maintaining life on Earth. Without plants, there would be an abundance of carbon dioxide in our atmosphere which would contribute to global warming. Additionally, the release of oxygen into the Earth's atmosphere during photosynthesis provided the conditions for evolution of a multitude of life forms.

Learning Objectives

Participants will gain:

  • An understanding of the process of photosynthesis, namely that chlorophyll in green plants absorbs light energy to combine carbon dioxide and water to make sugar and oxygen.
  • A recognition that light energy is absorbed and transformed into chemical energy within sugar

Standards

National Science Education Standards

K-4 Standards: http://bob.nap.edu/html/nses/html/6c.html#csck4

  • Organisms have basic needs. For example, animals need air, water, and food; plants require air, water, nutrients, and light. Organisms can survive only in environments in which their needs can be met. The world has many different environments, and distinct environments support the life of different types of organisms.

    Content Standards: K-4: Life Science: The Characteristics of Organisms

K-4 Standards: http://bob.nap.edu/html/nses/html/6c.html#csgk4

  • Although men and women using scientific inquiry have learned much about objects, events, and phenomena in nature, much more remains to be understood. Science will never be finished.

    Content Standards: K-4: History and Nature of Science: Science as a Human Endeavor

5-8 Standards: http://bob.nap.edu/html/nses/html/6d.html#csc58

  • For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. That energy then passes from organism to organism in food webs.

    Content Standards: 5-8: Life Science: Population and Ecosystems

5-8 Standards: http://bob.nap.edu/html/nses/html/6d.html#csg58

  • Scientists formulate and test their explanations of nature using observation, experiments, and theoretical and mathematical models.

    Content Standards: 5-8: History and Nature of Science: Nature of Science