plant responses

Question 1

what is tropisms

Answer 1

the directional growth responses of plants

Question 2

what is phototropism

Answer 2

.growth response due to light
.shoots show positive phototropism(grow towards light)
.roots show negative phototropism(grow away from light)

Question 3

what is geotropism

Answer 3

.growth response due to gravity
.shoots show negative geotropism
.roots show positive geotropism

Question 4

what is chemotropism

Answer 4

growth response due to chemicals

Question 5

examples of plant growth regulators

Answer 5

.auxins
.gibberellins
.abscisic acid

Question 6

what do auxins promote

Answer 6

cell elongation

Question 7

what do gibberellins promote

Answer 7

seed germination and stem growth

Question 8

what do abscisic acid inhibit and cause

Answer 8

seed germination
.causes closing of stomata and ethene

Question 9

how do auxins cause cell elongation

Answer 9

.transport of hydrogen ion into cell walls
.results in lower pH of walls
.required for expansins which loosens the cellulose
.makes cell wall stretch to accommodate more water
.enabling expansion and growth of cells

Question 10

what happens when the shoot is illuminated from all sides

Answer 10

.auxins distributed equaly and move down the shoot tip causing elongation of cells
.shoot grows upwards

Question 11

what happens when the shoot is illuminated from one side only

Answer 11

.auxins move towards shaded part of shoot
.causing elongation of the shaded part only
.leads to the shoot bending towards the light

Question 12

what is leaf abscission and what is it controlled by

Answer 12

.dropping of leaves
.controlled by auxins, ethene and cytokinins

Question 13

what do cytokinins do

Answer 13

.produced by young leaves
.makes them suitable sink for transport in the phloem

Question 14

what do auxins do for the leaf

Answer 14

prevents leaves from aging

Question 15

what happens as the leaf ages

Answer 15

.levels of cytokinins and auxins fall
.causes levels of ethene to increase
.causes cellulose enzymes to be produce
.causes the breakdown of cell walls in the abscission layer weaking the leaves
.leaves break off branch

Question 16

what happens after the leaf falls off

Answer 16

a layer of suberin forms to prevent pathogens from entering

Question 17

what is apical dominance

Answer 17

.when the side shoot does not grow when the main shoot does
.when apex is removed the side shoot starts to grow

Question 18

what controls apical dominance

Answer 18

auxin, abscisic acid and cytokinins

Question 19

what does auxin do in apical dominance

Answer 19

.production in apex maintains high levels of abscisic acid
.inhibiting the growth of side shoots

Question 20

what does cytokinins do in apical dominance

Answer 20

.promotes bud growth
.concentrated near auxin reserve
.so when the bud is removed the cytokinins spread out more evenly causing the growth of lateral buds

Question 21

what are the commercial uses of plant hormones