5.1.5 (a-f) Plant Responses

Question 1

Tropism

Answer 1

Plant directional growth towards an environmental stimulus.

Question 2

Nastic response

Answer 2

Rapid and reversible movement that is independent of a stimulus’ direction.

Question 3

Chemotropism and it’s importance.

Answer 3

Growth response towards a chemical stimulus.

Allows plant to obtain vital chemicals or the chemicals help to guide parts of the plant: such as pollen tubes growing towards calcium ions released by the ovule of a flower.

Question 4

Geotropism and it’s importance.

Answer 4

Growth response to the direction of gravity.

Positive geotropism allows a plant to be anchored for stability, allows roots to obtain more water/ nutrients.

Question 5

Hydrotropism and it’s importance.

Answer 5

Growth response towards water.

Positive hydrotropism especially in roots allows water to be obtained for photosynthesis.

Question 6

Phototropism and it’s importance

Answer 6

Growth response to light.

Positive phototropism allows plant to obtain maximum light as they are autotrophs that use light for photosynthesis.

Question 7

Thigmotropism and it’s importance

Answer 7

Growth response to touch/ pressure.

Allows support, especially tendrils that coil around supporting structures as they grow.

Question 8

Apical dominance

Answer 8

Auxins inhibit the growth of lateral shoots which enables plants to grow vertically.

Question 9

Auxin

Answer 9

Phytohormone responsible for many growth and developmental processes in a plant:

Apical dominance
Positive phototropism in stem
Positive geotropism in roots
Promotes cell elongation and enlargement

Auxins are made in the meristematic tissue.

Question 10

Describe how auxins are involved in phototropism.

Answer 10

In stems, a certain concentration of auxins promote cell elongation.

Auxin concentration increases on the shaded side of a stem, which promotes cell enlargement and elongation.

This is done by allowing the secretion of H+ into cell walls which loosen cellulose and allows cell expansion.

This causes the stem to bend towards the direction of light.

Question 11

Describe auxins in gravitropism. (4)

Answer 11

Certain concentration of auxins in roots inhibits it’s growth.

Auxin concentration increases on the bottom of a horizontal radical and inhibits the growth of bottom cells.

This causes the top cells to grow faster and bend downwards.

Whereas in stems, this causes an upward growth as the growth of cells at the bottom are promoted by auxins.

Question 12

Gibberellins

Answer 12

Plant hormone that stimulates cell elongation and division.

Promotes seed germination:
stimulates production of amylase, which breaks down starch into glucose in the endosperm.

Also promotes leaf and fruit senescence.

Question 13

Ethene in plants

Answer 13

Hormone that encourages fruit ripening and is involved in abscission in deciduous trees.

Ethene works in synergy with auxins to cause the degrading of the petioles, thus causing abscission.

Question 14

Name commercial uses of plant hormones

Answer 14

Promoting rooting of cuttings

Weed killers

Fruit ripening

Seedless fruit

Question 15

Describe how plant hormones are used to promote rooting of cuttings

Answer 15

Dipping the end of a shoot cutting into a powder containing auxin promotes root formation.

Question 16

Describe the use of plant hormones in weed killers.

Answer 16

Auxins are sprayed on broad leaved plants, which causes them to grown uncontrollably and die.

This does not affect grasses such as cereal crops.

Question 17

Describe how plant hormones are used in fruit ripening

Answer 17

Ethene is produced by ripening fruits.

When sprayed on other fruits, it stimulates ripening to occur for ideal times.

Question 18

Describe how plant hormones are used to produce seedless fruits.

Answer 18

Auxins or gibberellins are used to stimulate fruit development when pollination has failed.

Question 19

What is the need for plants to respond to their environment?

Answer 19

Allows them to cope with changes in conditions.

This avoids abiotic stress.

Responding ensures that photosynthesis is maximised

Question 20

Stimuli that plants respond to. (5)

Answer 20

Light

Temperature

Water

Thouch

Chemicals

Question 21

Abscisic acid (4)

Answer 21

Plant growth regulator that promotes seed dormancy by inhibiting germination.

Reduces enzyme production in seeds so starch is not broken down.

Causes stomata to close when there is low water content in the soil. This decreases transpiration and here it is produced in the roots.

Inhibits fruit ripening.