Bio 152 | Spring 2024
Tropisms 1: Introduction and Experimental Design
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1. Complete the table below with information about three additional tropism types. The example of phototropism has been completed for you. Some tropisms might involve multiple factors within a plant. Use your textbook and at least one other reliable source to complete the table. Tropism type
Stimulus
Factors in plant that react
to the stimulus (e.g., cell
types, chemicals,
structures, etc.)
Location of each factor in
the plant
Phototropism
Light
- Auxin
- Photoreceptors
- Tip of shoot and then
along the shaded side of
shoot
- Throughout the shoot
Gravitropism
Gravity
-Auxin
-Lower side of roots and
stem
Thigmotropism
Touch
-Mechanoreceptors
-Auxin
-Throughout the plant,
contact with external
surfaces
-Auxin to the side opposite
of contact
Hydrotropism
Water
-Moisture sensitive cells
-Auxin -root tips
-root with higher water
concentration
2. Select one of the factors you listed above and develop a hypothesis concerning the mechanisms involved in a tropic response of the hypocotyl in Brassica
. Note: We are asking you to look at only one factor (or a very few closely related factors) to determine what effect the factor(s) may have on tropism in the hypocotyl. We are not asking you to determine
ALL the factors which may affect tropism in the hypocotyl of Brassica. Below, write a hypothesis you could test in our lab. Be sure to include a brief biological rationale that describes the mechanisms underpinning your hypothesis
(2-3 sentences total). Factor: auxin
In Brassica, uneven light distribution on the hypocotyl will lead to differential growth rates, causing the hypocotyl to bend towards the light source. 3. What kinds of equipment or supplies would you need to conduct an experiment to test the hypothesis you proposed in #2 above?
Brassica seeds, microscope, light source, soil
