10.4 Lesson 10.4: Plant Responses
Lesson Objectives
- List the major types of plant hormones and the main functions of each.
- Define tropism and explain examples of tropisms.
- Explain how plants detect the change of seasons.
Check Your Understanding
- Why do pants need sunlight?
Introduction
Plants may not move, but that does not mean they don’t respond to their environment.
Plants are constantly responding to their surroundings. Plants detect and respond to stimuli
such as gravity, light, touch, and seasonal changes. For example, you might have noticed how
a house plant bends towards a bright window. Plants must be able to detect and respond to
changes in the direction of light. You probably also have noticed that some trees lose their
leaves in the autumn, so plants must be able to detect the time of year. Plants are able to
respond to stimuli through the help of special chemical messengers, calledhormones. The
various ways that plants respond to their environment and the hormones that control these
responses will be the focus of this section.
Plant Hormones
In order for plants to respond to the environment, their cells must be able to communicate
with other cells. The chemical signals that travel through cells to help them communicate
are called hormones. You might be familiar with the term hormones since animals, including
humans, also depend on hormones, such as testosterone or estrogen, to carry messages from
cell to cell. Animal hormones will be discussed in theControlling the Body chapter. In
both plants and animals, hormones travel from cell to cell in response to a stimulus and also
activate a specific response.
Table 10.2:Each plant hormone has a specific function.Hormone Function
Ethylene Fruit ripening and abscission
Gibberellins Break the dormancy of seeds and buds; pro-
mote growth