Plant Adaptations & Responses

Big Picture

Plants have adapted to many different environments, including the water, the desert, and the air. All plants respond to stimuli such as light, gravity, seasonal changes, and disease. Since plants can’t move, they generally respond to stimuli by changing the way they grow.

Key Terms

Xerophytes: Plants adapted to dry environments.

Epiphytes: Plants that grow on other plants.

Tropism: When a plant grows toward or away from a

Phototropism: Plant’s response to light.

Gravitropism: Plant’s response to gravity.

Thigmotropism: Plant’s response to touch.

Photoperiodism: Plant’s response to changing sea-sons.

Dormancy: Period of little/no growth in plants.

Plant Adaptations

To Water

Aquatic plants are adapted to water:

  • No mechanisms needed for transporting or con-serving water
  • No root system, vascular tissues, or cuticles
  • Keep flowers above water so that pollination can happen
  • Have features, such as narrow leaves, that reduce resistance to moving water

To Dryness

Xerophytes are adapted to dryness:

  • Very large root system to absorb as much water as possible
  • Store water with thick stems
  • Reduce water loss: no leaves (leaves lose water by transpiration), thick/thorny skin to prevent animals from stealing water

To Air

Epiphytes grow on other plants (do not grow in soil) and are adapted to air:

  • Absorb water from the air
  • Leaves have special shapes to collect rain, fog
  • Examples include plants living in rainforests - they grow on other plants to get out of the shadows on the forest floor

Plant Responses

Plant responses are controlled by hormones (chemical messengers)

  • Plant tropisms: Phototropism, gravitropism (or geotropism), and thigmotropism are controlled by the hormone auxin, which makes cells on one side of the stem grow longer than the other side. This causes the plant to bend.
plants bend toward light
Image credit: CK-12 Foundation, CC-BY-NC-SA 3.0
Figure: Auxin makes plants bend toward light

Daily and seasonal responses include photoperiodism
and dormancy

  • Example: Responding to day and night by opening the leaves during the day to collect sunlight and closing the leaves at night to prevent water loss

Responses to disease:

  • Cells around infected tissues die to prevent disease from spreading
  • Chemicals are produced to kill pathogens