5.4 Plant Responses

Question 1

What are auxins responsible for ?

Answer 1

They control cell elongation, prevents abscission and stimulates the release of ethene.

Question 2

What are gibberellins responsible for?

Answer 2

They cause stem elongation, trigger mobilisations of food stores at germination.

Question 3

What is ethene responsible for ?

Answer 3

Causes fruit ripening and promotes abscission in deciduous trees.

Question 4

What is ABA (abscisic acid) responsible for ?

Answer 4

Maintains dormancy of seeds and buds, stimulates cold protective responses and stomatal opening.

Question 5

How does seed germination occur ?

Answer 5

When seed absorbs water, embryo is activated and begins to produce gibberellins, which stimulates production is enzyme that breaks down food stores.

Question 6

Where are food stores in the plant ?

Answer 6

They are in the cotyledons in dicot seeds and endosperm in monocot seeds. It uses these to produce ATP.

Question 7

Where is auxin made in plants ?

Answer 7

Made in cells in shoots and roots and meristems, but less is produced as plant matures.

Question 8

What does high auxin levels do ?

Answer 8

High auxin suppresses growth of lateral shoots, resulting in apical dominance.

Question 9

What does low auxin levels do ?

Answer 9

Low auxin levels promotes root growth.

Question 10

What do gibberellins affect ?

Answer 10

They affect the length of internodes, space between leaves on a stem.

Question 11

What is synergism ?

Answer 11

When hormones work together to have a greater effect.

Question 12

What is antagonism ?

Answer 12

When substances have the opposite effects.

Question 13

What does auxin from apical buds prevent ?

Answer 13

Prevents growth of lateral buds. if apical bud is cut off, auxin levels drop and lateral buds being to grow.

Question 14

What is abiotic stress ?

Answer 14

Refers to non-living factors that affect/ cause harm to the plant. Eg., drought, temperature.

Question 15

What is abscission in a plant ?

Answer 15

Triggered by dark periods as less light results in falling concentrations of auxins by the production of ethene.

Question 16

How does the separation layer cause abscission ?

Answer 16

It is sensitive to ethene, which initiates gene switching which produces new enzymes. These digest and weaken cell, known as separation layer. Then a protective layer forms from fatty materials deposited when leaf falls.

Question 17

How is freezing prevented in cells ?

Answer 17

Cytoplasm of plant cells and sap in vacuoles contains solutes, which lower the freezing point.

Question 18

How is the stomata controlled in plants ?

Answer 18

They can open to cool plant or control water loss. Largely under the control of ABA. Under stress, ABA is released causing stomatal closure.

Question 19

How does ABA control stomatal opening ?

Answer 19

It activates the changes in ionic concentrations of guard cells, reducing water potential and turgor of cells. Guard cells close, which closes stomata and water loss is reduced.

Question 20

What are some common physical defences in plants ?

Answer 20

Common ones include, thorns, barbs, spikes or inedible tissues to prevent them from being eaten by plants.

Question 21

What are tannins ?

Answer 21

Part of compounds, phenols, that make up around 50% of dry weight of leaves. Has a bitter taste as they bind to digestive enzymes in saliva and inactivate them.

Question 22

What are alkaloids ?

Answer 22

Bitter, nitrogenous compounds that acts as drugs, affecting the metabolism of animals that have them, sometimes poisoning them.

Question 23

What are terpenoids ?

Answer 23

Large group of compounds that often form essential oils but often act as toxins to insects and fungi that might attack the plant. They interfere with the nervous system.

Question 24

What are pheromones ?

Answer 24

They affect the social behaviour of other members of the same species. Because plants do not behave socially they do not rely a lot on them. Some do however, such as maple trees.

Question 25

What are volatile organic compounds ?

Answer 25

They act like pheromones between themselves and other organisms, particularly insects. They are usually only made when the plant detects the attack by the pest insects saliva. They will attack predators of the pest as well as pheromones as a warning to other plants.

Question 26

What is geotropism ?

Answer 26

Response to gravity, where the roots are positively geotropic. This adaptation allows roots to grow downward and shoots to grow up to the light.

Question 27

What is phototropism ?

Answer 27

Response to light as a result of auxins across the shoot or root if exposed to light stronger on one side of the plant.

Question 28

What is chemotropism ?

Answer 28

Response to chemicals.

Question 29

What is figmotropism ?

Answer 29

Response to touch.

Question 30

How does a plant grow in the dark ?

Answer 30

If plant is in the dark, it grows quickly upward to reach the light to be able to photosynthesis. Gibberellins are responsible for the extreme elongation of internodes. Once exposed to light, resources can be used to grow leaves or strengthen the stem.

Question 31

How are plant hormones used to control ripening ?

Answer 31

Ethene is involved in ripening as ripening is linked to peak of ether production triggering a series of chemical reactions, such as increased respiration rate.

Question 32

How are plant hormones used in hormone rooting powders ?

Answer 32

Auxin affects shoots and roots. Dipping cut stems in rotten powder increases chances of roots forming and successful propagation takes place. Easier to develop cutting for sale.

Question 33

How are plant hormones used in weed killers ?

Answer 33

Plant hormones are balanced to enable plant to grow. If balance is lost, it can interrupt metabolism of whole plant and then lead to death. Weeds are plants that grown where they are unwanted. Weeds compete for light so are wide leaves. Auxin is absorbed on wide leaves and growth rate increases unsustainably.

Question 34

How are cytokines used ?

Answer 34

To prevent aging of ripened fruits and micropropagation to control tissue development.