Tropism

Question 1

What are the three types of tropism?

Answer 1

1. Phototropism
2. Gravitropism
3. Thigmotropism

Question 2

What is tropism?

Answer 2

a plants growth response to stimulil

Question 3

What is phototropism in response to?

Answer 3

light

Question 4

What is gravitropism in response to?

Answer 4

gravity

Question 5

What is thigmotropism in response to?

Answer 5

touch

Question 6

what is positive gravitropism?

Answer 6

Plants grow towards the center of the earth (ex. roots)

Question 7

what is negative gravitropism?

Answer 7

plant growth against gravity - away from the center of the earth (ex. stems growing up)

Question 8

what is the importance of gravitropism?

Answer 8

pulls roots down to anchor a plant so roots can get necessary water and minerals from the soil

Question 9

what is positive phototropism?

Answer 9

plant grows to maximize light source?

Question 10

what is the importance of phototropism?

Answer 10

enables leaves to be in the best position to receive adequate light for photosynthesis

Question 11

what was Charles Darwins experiment on phototropism?

Answer 11

Question: which part of the plant detects + responds to stimulus?

Experiment: seed germination -> study shoots in various conditions

Question 12

What did Charles Darwin find from his experiment?

Answer 12

-seeds with the tip covered did not respond to stimuli
> the tip of the stem is
responsible for
detecting light stimulus
but it is not where the
response is carried out
- the cells of the tip were somehow communicating with the cells in the area that was bending

Question 13

What was Boysen-Jensen’s experiment?

Answer 13

Question: what is the signal that initiates a phototropic response?

experiment: snipped of the tip of the grass seedling, then covered the stump with gelatin or mica

Question 14

what did Boysen-Jensen find from his experiment?

Answer 14

• Phototropism continued normally with the gelatin but not with mica
  > Whatever is responsible
  for communicating
  information from the tip
  area was able to diffuse
  through the gelatin but
  not the mica
• growth could only be accomplished because of a chemical moving from the tip to the area providing a change in growth

Question 15

What was F.W Went’s experiment?

Answer 15

Question: What specific substance is responsible for initiating the phototropic response?

Question 16

What did F.W Went find?

Answer 16

• in 1926 Went isolated the chemical substance which is called auxin

Question 17

What is auxin?

Answer 17

auxin is a growth hormone manufactured in one area and transported to another location to initiate cell elongation