Back to  How do Flowers grow?

The asnwer to your questions comes from Mark B.

Good biology question. I found an answer in the children's reference section of the Carlingwood Library. The New Book of Popular Science #4 explains plants use water to make their food. Plants like animals need food to grow. One main difference between plants and animals is that plants make their own food.

Photosynthesis is the starting point for plants to make their own food. The green pigment chlorophyll which is unique to plants is required for photosynthesis; so is sunlight or light of comparable wavelength. The raw materials required are water and carbon dioxide.

Water is drawn from the soil through surface cells on the roots of the plant. Carbon dioxide is obtained from the air through leaf pores called stomata. In the presence of chlorophyll and sunlight, water and carbon dioxide react chemically to form oxygen and a sugar known as glucose - a food element of the carbohydrate group and the basic food of plants. The name photosynthesis is a good one since the Greek meaning is "putting together in light."

  1. Very Brief Form of the Chemistry of Photosynthesis

    1. Light reaches the cells that contain chlorophyll (green stuff).

    2. The chlorophyll absorbs the light energy and changes it to chemical energy.

    3. Water molecules in the cells break up. The oxygen from the water is set free.

    4. The hydrogen from the water molecules combine with carbon dioxide from the air to form glucose, a simple sugar.

    5. The glucose molecule is held together by the chemical energy. In other words, the energy is trapped within the glucose molecule.

      There are two phases or parts to photosynthesis:

      1. Light Reaction - Light energy is trapped and converted into chemical energy.

      2. Dark Reaction - Chemical process - trapped energy used to make glucose.

      Here's the chemical equation:

    Energy + 6CO2 + 6H20 --> C6H12O6 + 6O2

    The letters C, H, and O stand for the elements carbon, hydrogen, and oxygen. The large numbers stand for the numbers of molecules. The lower numbers are the number of atoms in the molecules.

    Thus, H2O is a water molecule with two atoms of the element hydrogen and one atom of the element oxygen.

    If you read the photosynthesis equation backwards, right to left you get the chemical reaction for respiration. This is the chemical breakdown of food in an organism into energy. Typical respiration takes place when oxygen combines or "burns", sugar. Thus oxygen plus sugar (glucose) yields energy with water and carbon dioxide produced as waste. But remember carbon dioxide and water are also raw materials of photosynthesis. From them a green plant makes food and oxygen, that is to say it recycles these wastes into useful products.


    The New Book of Popular Science

    Volume 4

    Section: Plant Life

    pp 2-7 What is a Plant?

    pp 8-10 The Plant Kingdom

    pp 71-83Vital Processes of Plants

    pp 84-88Photosynthesis

    % % page \* arabic

    % % page \* arabic2

    Back to