Phase Three: Stems, Leaves and Transpiration

All plants have stems. The main stem holds up the plant and carries water throughout the plant. Secondary stems grow out from the main stem. Leaves grow out of the secondary stems.

Green leaves are responsible for making most of the plant's food. Chlorophyll is the green substance in plants that works with energy from the sun to help carbon dioxide and water combine to make food for the plant. Plants pull water upward from the soil through xylem tubes in a process called transpiration.

Transpiration is controlled by the moisture content of the air and soil. Only 1 percent of the transpired water is used in the growth process. Transpiration also transports food from the soil into the roots and carries it to the different cells of the plant.

As the sun warms the water inside the plants leaves, transpiration occurs. This warming causes most of the water to turn into vapor and evaporate. The water vapor escapes into the air through the stomata. The water vapor absorbs heat as it escapes, which cools the inside of the leaves. The roots of the plant draw up more water to replace what was lost. The water travels up the stem and along the veins of the leaves through the xylem tubes.

Phase Three Vocabulary Definitions:

Transpiration - The flow of water through a plant.

Main Stem - Holds up the plant and carries water throughout the plant.

Secondary Stem - A stem that grows out from the main stem and holds the leaves.

Chlorophyll - The green matter that is needed to make food for the plant.

Xylem Tubes - The tubes that carry water and food to the plant.

Evaporation - The process by which a plant releases moisture.

Stomata - Tiny pores on the underside of the leaves in which carbon dioxide and oxygen enter and leave the plant.