Tropic movements
Growth that turns towards or away from a trigger.
Plants on a windowsill
A plant on a windowsill slowly leans in one direction. It is not moving like an animal. It is growing in a particular direction.
What do you think can change the direction in which a plant part grows?
What this lesson covers
The idea
Environmental triggers such as light or gravity change the direction in which plant parts grow; these directional, or tropic, movements can be towards the stimulus or away from it.
Plants on a windowsill
A plant on a windowsill slowly leans in one direction. It is not moving like an animal. It is growing in a particular direction.
What do you think can change the direction in which a plant part grows?
- Environmental triggers such as light or gravity
- The sound of people talking
- A message sent by a brain
Towards or away
Sort each movement by whether it is towards the stimulus or away from it.
Directional growth
These movements happen because the plant grows more on one side. Because the growth is directional, it looks as if the plant is moving.
Environmental triggers such as light or gravity change the direction in which plant parts grow. These directional movements are tropic movements, and they can be towards the stimulus or away from it.
Notes
Triggers such as light or gravity change the direction in which plant parts grow; these directional, or tropic, movements can be towards the stimulus or away from it.
Check yourself
What are tropic movements?
Which of these can change the direction in which plant parts grow?
A shoot bends towards light and a root bends away from it. What does this show?
- Quick movements that need no growth. Tropic movements are caused by growth. Quick movements that need no growth, such as the sensitive plant's, are the other kind.
- Movements controlled by a brain. Plants have no nervous system. Tropic movements are directional growth.
- Directional growth movements in response to a trigger such as light or gravity — correct. Yes!
- Light — correct. Yes!
- Salivation. Salivation is an involuntary action in animals, controlled by the medulla.
- A synapse. A synapse is the gap between neurons. Plants have no nervous system.
- Roots do not respond to light. Roots respond to light by bending away from it.
- Tropic movements can be towards or away from the stimulus — correct. Yes!
- Tropic movements are always towards the stimulus. These directional movements can be either towards the stimulus or away from it.