Plant Responses - Module 5

Question 1

What are 3 main uses of commercial plant hormones?

Answer 1

1. Control of ripening
2. Hormone rooting powder and micropropagation
3. Hormonal weedkillers

Question 2

How are plant hormones used to control the ripening of fruit?

Answer 2

Plants will be harvested prior to ripening so they are hard and less likely to be damaged during transport

Once ready to be sold they are exposed to ethene - the hormones that makes them ripe

Question 3

How are plant hormones used commercially for micropropagation?

Answer 3

Adding auxins to cut shoots promotes the growth of new shoots, thus enhancing the success of propagation of new plants from cuttings

Question 4

How are plant hormones used commercially in hormonal weedkillers?

Answer 4

As interactions between plant hormones are balanced to prevent growth, the interruption of this balance may disturb the metabolism of the plant and subsequently kill it

Question 5

What hormones are used in weedkillers and what effect do they have on the plant?

Answer 5

Synthetic dicot auxins, impact the metabolism of a plant and they die

Question 6

What is a tropism?

Answer 6

Plant growth response to a stimuli from one direction

Question 7

What is a phototropism?

Answer 7

Plant growth response to light

Question 8

How do phototropism’s occur?

Answer 8

Occur as a result of the movement of auxins across the shoot or root (if the root is exposed to light) that is stronger on one side than the other

Question 9

What way will shoots grow in regard to light?

Answer 9

Shoots are positively phototropic and will grow towards light

Question 10

What way will roots grow in regard to light?

Answer 10

Roots are negatively phototropic and will grow away from the light

Question 11

What plant hormones controls stomata control?

Answer 11

ABA hormone causing stomata to close

Question 12

Why do plant hormones control the stomata?

Answer 12

To open the stomata to cool the plant and close the stomata in order to conserve water

Question 13

What is a specific response of the mimosa pudica?

Answer 13

Plants folding in response to touch
- potassium ion movement and osmotic water movement allow the leaves to curl and unfold scaring herbivores and dislodging insects

Question 14

What do tannins do as a plant chemical defence?

Answer 14

Tannins are toxic to insects as well as contain a phenol compound which is bitter

Question 15

What do alkaloids do as a plant defence chemical?

Answer 15

Contain bitter nitrogenous compounds and are toxic to animals acting as poison

Question 16

What do terpenoids do as a chemical plant defence?

Answer 16

Toxic to insects and fungi

Question 17

List some physical defences a plant may have to protect itself [4]

Answer 17

1. Thorns
2. Barbs
3. Spikes
4. Stings

Question 18

What is a pheromone? And give an example in plants

Answer 18

A chemical made by an organism affecting the social behaviour or other organisms in the same species

E.g maple trees release pheromones when under attack telling leaves on other branches to deposit callouses as a defence

Question 19

What are VOC’s in plants?

Answer 19

VOC’s are volatile organic compounds which act in a similar way to pheromones but interact with insects rather than other plants

Question 20

Where are auxins made?

Answer 20

Auxins are made in the roots, shoots and meristems of a plant

Question 21

Why do plants grow in the dark more rapidly?

Answer 21

Because they are trying to reach light in order to photosynthesise

Question 22

What is geotropism?

Answer 22

Plant growth response in regard to gravity?

Question 23

How do shoots response to gravity?

Answer 23

Shoots are negatively geotropic and will grow upwards

Question 24

How do roots respond to gravity?

Answer 24

Roots are positively geotropic and will always grow downwards

Question 25

How do gibberellins affect elongation of plant stems?

Answer 25

Gibberellins affect the length of the internodes - regions between leaves on a stem

Question 26

How are gibberellins involved in seed germination?

Answer 26

Evidence suggests gibberellins switch on genes that produce amylases and proteases - digestive enzymes required in germination breaking down the food stores in the seed

Question 27

What are the two pieces of experimental evidence that proves gibberellins are involved in seed germination?

Answer 27

1. Scientists breed mutant seeds which lack the gene to make gibberellins - the seeds do not germinate. If gibberellins are then applied externally they will germinate
2. If gibberellin inhibitors are applied the seed will not germinate, if taken away the seed will germinate

Question 28

What are auxins?

Answer 28

Growth stimulant hormones produced in plants

Question 29

How do auxins affect the main apical shoot of a plant?

Answer 29

Auxins affect the plasticity of the cell wall, meaning it will stretch more easily

They do this by binding to receptors on cell membrane causing pH to drop to the optimum 5, for enzymes to keep cell wall flexible

Question 30

What effect do high concentrations of auxins have on a plant?

Answer 30

High concentrations of auxin suppress lateral growth of shoots resulting in apical dominance

Question 31

What is apical dominance?

Answer 31

Apical dominance is the occurrence of auxins preventing lateral shoot grown

Question 32

What experimental evidence is there to show that auxins have an impact on apical dominance?

Answer 32

If the apical shoot is removed, lateral shoots will grow faster and if auxins are reapplied to apical shoot the growth of lateral shoots will decrease again

Question 33

What do low concentrations of auxins promote?

Answer 33

Root growth

Question 34

What is a synergism?

Answer 34

When different plant hormones work together resulting in a greater response than the one provided when the hormone acts alone

Question 35

What is an antagonism?

Answer 35

When plant hormones have the opposite affect and the balance of the hormones determines the effect on the plant

Question 36

Which hormones are involved in the falling of leaves on trees?

Answer 36

Auxins and ethene

Question 37

How do auxins and ethene cause plants to drop their leaves? [5]

Answer 37

1. As light levels fall, concentration of auxins fall
2. Leaves response to fall in auxin by producing ethene
3. Ethene stimulates production of digestive enzymes
4. Digestive enzymes weaken cell wall at ABSCISSION ZONE
5. Vascular bundles seal, Leaf falls

Question 38

How does a decrease in temperature affect plants?

Answer 38

If cells freeze membranes are disrupted and the plant will die

Question 39

How have plants adapted to prevent freezing?

Answer 39

Cytoplasm of plant cells contain solutes that lower the freezing point e.g sugars, amino acids and proteins