10)Tropism Flashcards
(12 cards)
Tropism
It is the ability of the plant parts, shoot and root, to detect a stimulus such as light or gravity and carry out a response by bending towards or away from the stimulus
Why shoot bends towards light showing +ve phototropism (importance of tropism for shoot)
- to reach light, exposing larger surface area for more light absorption for more photosynthesis for more growth
- To reach Co2 for photosynthesis
- To reach O2 for respiration
- So flower can be accessible to pollinators
Why root bends towards gravity showing +ve gravitropism
- To absorb more water and minerals from soil
- For more anchorage in soil
How shoot carries response to light
- Auxin produced at tip of root
- Tip of shoor detects light coming from one side
- Auxin diffuses down concentration gradient’
- Accumulates in the shaded side
- Cells in shaded side absorb more water by osmosis
- More cell elongation and growth in shaded side
- Un equal growth, so shoot grows and bends toward light
- Showing +ve phototropism
How root carries response to light
- Auxin produced at tip of root
- Tip of root detect light coming from one side
- Auxin diffuses down concentration gradient
- Accumulates in the shaded side
- Causing the cells in shaded side to absorb less water by osmosis
- Less cell elongation and growth in shaded side
- Unequal growth so root grows and bends away from light
- Showing -ve gravitropism
How shoot carries a response to gravity
1.Auxin produced at tip of shoot
2. Auxin diffuses down concentration gradient and accumulates in the LOWER side
3.Causing the lower side to absorb more water by osmosis
4. More cell elongation and growth in shaded side
5. unequal growth, so shoot grows and bends away from gravity
6. Showing -ve gravitropism
How root carries a response to gravity
- Auxin produced at the tip of root
- Auxin diffuses down the concentration gradient
- Auxin accumulate in the LOWER side
- Causing the cells in the lower side to absorb less water by osmosis
- Less cell elongation and growth in the lower side
- Unequal growth so root grows and bends downwards towards gravity
- Showing +ve gravitropism
Control experiment to plant grown in the light
Grow plant in dark for comparison
Control experiment for plant grown under effect of gravity
Eliminate the effect of gravity by using clinostat/ rotating motor
Features of etiolated plant
- Long thin stem
- Pale yellow leaves
- stunted growth
Why plant becomes etiolated
- Dark: so plant only respires and doesnt photosynthesize, Uses starch as energy source
- Lack of magnesium, no chlorophyll, no photosynthesis, pale yellow leaves and chlorosis
Selective 2,4-D weed killer
-Genetically modified crops that are resistant to herbicides have weeds grown within them.
-Weed must be killed to decrease the competition on light, water and minerals.
-To increase crop yield and quality
-Lawns are sprayed with synthetic auxin 2,4D
-Weed will absorb more auxin, and crops wont
-Weed will grow rapidly out of control and become etiolated
-root growth will be inhibited by high conc of auxin
-so weed will die
