tropisims

Question 1

what is the plant hormone that promotes elongation of shoot cells in high concentrations and inhibits root cell elongation in roots

Answer 1

Auxin

Question 2

where is auxin produces

Answer 2

growing tips of roots and shoots

Question 3

how does auxin work

Answer 3

It is soluble and so can diffuse across cells and can pass through agar (which is often used in experiments). It allows cells to elongate by releasing the tension in the cellulose that makes up the cell walls of plants.

Question 4

high conc of auxin in shoots

Answer 4

promotes elongation

Question 5

high conc of auxin in roots

Answer 5

inhibits elongation

Question 6

growth response of plants towards a light source coming from one direction only

Answer 6

postitive phototropism

Question 7

benifits of positive photropism

Answer 7

The benefits of this response to plants is that they receive a higher light intensity so they can photosynthesis at a faster rate. The plant therefore produces more glucose as a quicker rate. This glucose can be used as an energy source for greater growth or reproduction in the plant.

Question 8

what are the 6 steps that cause the plant to grow towards the light

Answer 8

1. A photoreceptor in the tip of the coleoptile (growing tip of a stem) detects light
2. Auxin is produced in the tip in response to the light being detected
3. The auxin diffuses across to the dark side of the stem (opposite to where the sun’s direction is)
4. It diffuses down the dark side and accumulates in higher concentrations there, higher than on the light side
5. The higher concentration of auxin causes cells on the dark side to elongate
   The growing tip bends towards the light

Question 9

a growth response of plants towards or away from the direction of gravity (downwards). Auxin is the hormone that controls this growth response

Answer 9

geotropism

Question 10

what is positive geotropism

Answer 10

he growth of plants (usually roots) downwards towards the direction of gravity

Question 11

what is the mechanism as to why the roots (radicles) display a positive geotropic response - 3 steps

Answer 11

1. Auxin accumulates in cells on the lower side of a root due to the pull of gravity
2. A high concentration of auxin in root cells on the lower side inhibits cell elongation but a low concentration of auxin in the cells on the upper side promotes elongation
3. The cells on the upper side elongate more causing the root to bends downwards

Question 12

what is Apical Dominance

Answer 12

the shoot apex inhibits the growth of lateral buds so that the plant may grow vertically. It is important for the plant to devote energy to growing upward so that it can get more light to undergo photosynthesis.