Part 2

Biology
Topic 12 ­ Control Systems in Plants
1. Define stimuli.
A change in the environment that causes a reaction by the organism
2. What is phototropism?
Directional plant growth in response to light
3. ‘Photo’ means light and ‘tropism’ refers to the movement towards by the plant.
4. Explain what kind of phototropism plant stems exhibit and why?
Positive phototropism because the plant stem grows towards the light
(needs light for photosynthesis)
5. Explain what kind of phototropism plant roots exhibit and why?
Negative phototropism because plant roots grow away from the light
(need water and nutrients and a stable base to grow from, all found in the soil)
6. What is gravitropism?
Directional plant growth response to gravity
7. Explain what kind of gravitropism plant stems exhibit and why?
Negative gravitropism because they grow against gravity
8. Explain what kind of gravitropism plant roots exhibit and why?
Positive gravitropism because plant roots grow with gravity (down)
9. Read ‘The Mechanisms of Gravitropism’ at the bottom of pg. 327 and explain how gravitropism works.
Heavy starch particles inside specialized cells detect the direction of the gravities pull
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10. Read ‘Other control mechanisms’ and list all the other types of control mechanisms.
Touch
Temperature
Chemicals
Water
Length of Darkness a plant is exposed to
­ some plants require long nights to produce flowers
Length of Daylight a plant is exposed to
­ some plants require certain hours of daylight to produce flowers
Scientists
Experiment
Contribution
Charles and Francis Darwin (1880)Which part of the plant detects and responds to light?
Peter Boysen­Jensen (1913)
What is the signal that initiates the phototropic response?
F.W. Went (1926)What is the specific substance for initiating the phototropic response?
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