Lesson 5: Plant responses and growth

1. Lesson 5: Plant responses and growth What are three stimuli that produce plant responses? Tropisms, hormones, and Auxin

2. Tropisms • A Tropismis a response to a plant toward or away from a stimulus. If a plant grows toward the stimulus, it is said to show a positive tropism. If a plant grows away from a stimulus, it shows a negative tropism. Touch, gravity, and light are three important stimuli that trigger growth responses, or tropisms, in plants. An example of a stimulus is when a fly is flying near a Venus Flytrap, the flytrap’s response is to munch on the fly. A Venus Flytrap is a Carnivorous Plants.

3. . Hormones and Auxin A hormone, which is produced by a plant, is a chemical that affects how the plant grows and develops. One important plant hormone is called the auxin. (AWK sin) Auxin speeds up the rate at which a plant’s cells grow and controls a plant’s response to light. When light shrines on one side of a plant’s stem, auxin builds up in the shaded side of the stem. The cells on the shaded side begin to grow faster. The cells on the stem’s shaded side are longer than those on its sunny side. The stems bend toward the light.

4. How do Plants Respond to Seasonal Changes? Photoperiodism, Critical Night Length, Short-Day Plants, Long-Day Plants, Day Neutral Plants, and Dormancy

5. Photoperiodism and Critical Night Length • The amount of darkness a plant receives determines the time of flowering in many plants. A plant’s response to seasonal changes in the length of night and day is called photoperiodism. • Plants respond differently to the length of nights. Some plants will only bloom when the nights last a certain length of time. This length, called the critical night length, is the number of hours of darkness that determines whether or not a plant will flower. For example, if a plant has a critical night length of 11 hours, it will flower only when there is over 11 hours of darkness.

6. Short-Day Plants, Long-Day Plants, Day-Neutral Plants, and Dormancy • Short-day plants flower when the nights are longer than a critical length. They bloom in fall or winter. • Long-day plants flower when nights are shorter than a critical length. They bloom in the spring or summer. • Day-neutral plants have a flowering cycle that is not sensitive to periods of light and dark. They can bloom year-round depending on the weather. • Dormancy is a period when an organism’s growth or activity stops. Dormancy helps plants survive freezing temperatures and the lack of liquid water.

7. Trivia! 1. What is a plant’s growth response called? a. Auxin b. Hormone c. Tropism 2. What are short-day plants? a. When the nights are shorter than a critical length b. When the nights are longer than a critical length c. Has a flowering cycle that is not sensitive to periods of light and dark. 3. Plant’s responses to seasonal changes in the length of night and day is a. Critical night length b. Photoperiodism c. Dormancy

8. 4. A _______ is produced by a plant is a chemical that affects how the plant grows and develops. a. hormone b. auxin c. tropism 5. One important plant hormone is named a. dormancy b. tropism c. auxin 6. What are long-day plants? a. flower when the nights are longer than a critical length. b. have a flowering cycle that is not sensitive to periods of light and dark. c. flower when nights are shorter than a critical length. 7. What is the critical night length? a. a period when an organism’s growth or activity starts. b. when some plants only bloom for a certain length of time. c. a plant’s growth response toward or away from a stimulus.

9. 8. Day neutral plants: a. have a flowering cycle that is not sensitive to periods of light or dark. b. flower when nights are shorter than a critical length. c. flower when nights are longer than a critical length. 9. Dormancy is: a. produced by a plant is a chemical that affects how a plant grows. b. The period when an organism’s growth or activity stops. c. A plant’s response to seasonal changes in the length of night and day. 10. The name of lesson five is: a. Three Stimuli that produce plant responses b. Plants’ seasonal changes responses c. Plant responses and growth