Lesson 58: Seedling Growth and Plant Responses
Growing plants respond to gravity and light. Seedlings show how roots and shoots change direction and how uneven growth can bend a stem toward a light source.
Key Ideas
- Plants can grow toward or away from things around them. This kind of growth response is called a tropism.
- Gravity helps guide plant growth. Young roots usually grow downward, while young shoots grow upward.
- A young shoot may bend toward light. This helps its leaves reach the light they need to make food.
- A shoot bends when one side grows longer than the other. Plant chemicals called hormones help control this growth.
Vocabulary
- Tropism: Plant growth toward or away from something, such as light or gravity.
- Gravitropism: Plant growth guided by gravity. Young roots usually grow down and shoots grow up.
- Phototropism: Plant growth in response to light, such as a shoot bending toward a window.
- Auxin: A plant hormone, or chemical messenger, that helps control growth.
Discussion Questions
- A houseplant on a windowsill often leans hard toward the glass. Using today's lesson, why does turning the pot around each week keep it growing straight?
- Astronauts grow seedlings in orbital microgravity. How might weaker gravity cues change root direction? What other cues could guide growth?
- Could a curved stem become straighter through later growth? What would have to change on its two sides?
Supplies
- A potted seedling or a bag of already-germinating beans, tape, and a marker