Notes #3 Tropisms & Plant environmental needs Unit 3 Horticulture

OBJECTIVE: Name & define 3 types of tropisms. Tropism is a change in a plant’s growth in response to a stimulus. There are several types of tropisms. The three most common tropisms are: phototropism geotropism (aka gravitropism) thigmotropism.

Phototropism A. Phototropism is a plant’s response to light. The stems and the leaves of plants grow toward the light. For example, a plant sitting in a window sill will bend toward the window or light. If the plant is turned around, it will bend toward the window again, if given enough time.

Geotropism B. Geotropism is a plant’s response to gravity. Roots grow downward because of geotropism. If you turn a seed upside down in its pot, it will still send its root downward and its shoot upward.

Thigmotropism C. Thigmotropism is a plant’s response to physical contact with another object. For example, a plant may wind around a pole or grow in a curving line once it touches a post or other solid object.

OBJECTIVE Explain the environmental requirements needed for plants to grow. In order for plants to grow, there are certain conditions that need to be met. The most important requirements are light, air, and water. Each of the requirements is necessary in plant growth, specifically the photosynthesis process. When all of these requirements are met, plants will thrive, but some plants may require different amounts of each. Example: a cactus requires sunlight but not a lot of water.

LIGHT Light can be either natural or artificial. Natural light comes from the sun. Artificial light sources: incandescent lights, fluorescent lights, metal halide lamps, low pressure sodium lamps, high pressure sodium lamps, etc.

AIR & Water B. Air is important because it carries the necessary carbon dioxide that plants need to make food. Air flows through the stomatas in the leaves of the plant. C. Water flows from the roots throughout the plants vascular system. It breaks down during the photosynthesis process to help the plant make food. Water is used in the transpiration process to help the plant stay at its healthiest temperature.