Chapter 16: Plant Responses

Question 1

Commercial Use of Ethene:

Answer 1

Ripens climacteric fruits -> bananas, tomatoes, mangos

Question 2

How is ripening controlled? (Commercial)

Answer 2

Fruits harvested before ripe, cooled, stored and then transported. Then exposed to ethene in controlled conditions.

Question 3

Why is ripening controlled?

Answer 3

Prevents a lot of wastage during transport, increases the time available for sale

Question 4

Commercial use of Auxin:

Answer 4

Stimulate the growth of roots and shoots
Easier propagation of new plants from cuttings.
Increases chance of rooting
-Produce seedless fruit
-Weed killer

Question 5

Commercial use of gibberellins:

Answer 5

-Germination
-Delay ripening -> improve size and shape of fruits
-Speed up malting process of beer brewing
-

Question 6

Commercial Use of cytokinin:

Answer 6

Prevent/ delay ageing and ripening of fruit ->

Question 7

+ve’s of hormonal weed killers:

Answer 7

Simple and cheap
Low toxicity
Most crops are monocots and weeds are dicots. Synthetic dicot auxins are used as weedkiller to not affect the crop
Reduce competition in a monoculture

Question 8

How do hormonal weed killers kill weeds?

Answer 8

Disrupt hormone balance in weeds to reduce competition.

Disrupt metabolism of the plant.

Question 9

Role of Plant Hormones in Seed Germination:

Answer 9

Gibberellin produced when seed is in optimum conditions -> stimulate production of enzymes (amylase and proteases) to breakdown (hydrolyse) food stores
ABA is antagonistic to Gibberellin and-so their relative levels determine when germination occurs.

Question 10

Why do Plants rapidly grow upwards in the dark?

Answer 10

Attempt to quickly reach the light.

Once exposed to light the growth will slow down to prioritise resources used to synthesise leaves and strengthen stem.

Question 11

What are the two methods of investigating the effects of the hormones?

Answer 11

Growing seeds hydroponically using serial dilution of hormones or different concentrations on cut ends.

Question 12

Physical Defences of plants against herbivory:

Answer 12

Thorns, barbs, spikes, fibrous and inedible tissue, hairy leaves, stings, lignification of cell walls and stem, waxy cuticle

Question 13

Tannins:

Answer 13

Bitter tasting and toxic to insects (in parenchyma) by inhibiting their digestive enzymes

Question 14

Alkaloids:

Answer 14

Nitrogenous compounds that are bitter tasting and affect insect metabolism: - e.g nicotine or caffeine

Question 15

Terpenoids

Answer 15

Essential oils often acting as deterrents e.g citronella

Question 16

What are Pheromones:

Answer 16

Chemicals that affect the social behaviour of the same species to protect themselves

Question 17

Example of pheromones in plant defence against herbivory:

Answer 17

Maple trees attacked -> release pheromones -> absorbed into the leaves of plant -> stimulate the production of callose -> block plasmodesmata

Question 18

Volatile Organic Compounds:

Answer 18

Act like pheromones between different organisms of different species.
Diffuse into air surrounding the plant.
Produced when a plant detects an attack by an insect through chemicals in the insects saliva.

Question 19

Nastic Response:

Answer 19

Rapid non-directional response to a stimulus.

Question 20

Mimosa Pudica Depth;

Answer 20

The mechanical stimulus (touch) is converted into an electrochemical signal by causing the movement of ions across a partially permeable membrane. k+ and Cl- ions out of the extensor cells. The osmotic potential in the extensor increases and the flexor cells decrease. This cause water to enter the flexor cells, causing them to grow turgid, causing the leaflets to fold upwards.

Question 21

What is the benefit of the mimosa pudica’s nastic response?

Answer 21

Reduces water loss by transpiration at night, protects the plant from herbivorous insects, makes the plant appear to be ill, deterring herbivores

Question 22

How is the turgidity of the mimosa pudica restored:

Answer 22

The diffusion of ions followed by osmosis.

Question 23

What is the name of the joint-like structure containing extensor and flexor cells?

Answer 23

the pulvinus

Question 24

ABA roles:

Answer 24

Maintains seed and bud dormancy, stimulates cold protective responses e.g anti-freeze and stomatal closing.

Question 25

Why are seedlings used when investigating tropisms?

Answer 25

-Easy to manipulate -> respond quickly -> observable and easily measurable.

Question 26

Why are monocots used when investigating tropisms:

Answer 26

Shoot emerges as a singular shoot without leaves.

Question 27

2 methods of investigating Geotropism:

Answer 27

• Using a clinostat (rotating drum) -> rotate 4 times per hour -> root should grow in straight line.
• Seedlings in a petridish -> rotated at 90’ intervals. within 2 hours gravitropism observed.

Question 28

Methods of testing phototropism:

Answer 28

• Removing the tip -> np light detected -> no auxin production -> no response
• Light-proof cover -> No light detected -> auxins produced evenly -> no response
• Thin impermeable barrier of mica ——– 2 outcomes
• Placing tip on top of a gelatine block -> block is permeable to auxin -> allows for its diffusion and-so the plant will grow and bend.
• Splitting tip in half

Question 29

What are 3 things you should do when testing phototropism:

Answer 29

• A control where no changes to the plant show how it would usually grow.
• A unilateral light source should be used with seeds of the same variety.
• Use coleoptiles.

Question 30

What are the two outcomes of using an impermeable barrier of mica:

Answer 30

Light side -> Causes auxins to elongate tissue shaded side -> growth + bends towards light
Shaded side -> prevents auxins from diffusing to shaded side.

Question 31

Deciduous Trees Leaf abscission:

Answer 31

Lower rate of photosynthesis -> lower temps and shorter days -> rate of glucose uptake higher -> lose leaves to reduce glucose consumption.

Question 32

What are the two layers of the Abscission zone?

Answer 32

Separation layer and protective layer.

Question 33

What are the two pigments that cause photoperiodism ?

Answer 33

phytochrome, Pr and Pfr

Question 34

What are the two pigments that cause photoperiodism?

Answer 34

phytochrome, Pr and Pfr

Question 35

During Abscission how are the vascular bundles sealed off?

Answer 35

Fatty material is deposited on the stem side of the separation layer - > forms a protective scar.
Cells also respond to hormonal cues -> swell and retain water -> Strains outer separation layer.
Cellulase breaks down cell walls of plant cells.

Question 36

Abscission mechanisms:

Answer 36

Falling light levels lead to decreased auxin conc. -> Plants produce ethene in response -> initiates gene switching in abscission zone -> produces new enzymes -> digest and weaken cell walls of abscission zone. Abiotic factors (e.g wind) cause final breakage.

Question 37

What is a petiole?

Answer 37

A petiole is stem off of the main stem which precedes a fruit or leaf.

Question 38

Stomatal Control:

Answer 38

• > Controlled dependent on heat and water availability.
• Stomata opened to cool down -> Warm water absorbs heat and evaporates.
• Close to conserve water.

Question 39

When is ABA released by plants:

Answer 39

When roots in soil detect low water levels and when leaf cells are under abiotic stress to close the stomata.

Question 40

How does ABA control stomata opening/closing:

Answer 40

ABA binds to a receptor on the plasma membrane of a stomatal guard cell -> triggers a cascade reaction resulting in the ions moving into the cell, reducing their water potential -> causes the cell to become turgid, closing the stomata and reducing the water loss by transpiration.

Question 41

Methods of preventing freeze:

Answer 41

• Cytoplasm and sap in vacuoles decrease freezing point
• Solutes synthesises to act as antifreeze
• Most species only produce chemicals that make them frost resistant during the winter months. -> gene switching in response to prolonged decrease in temperature + reduction in day length
• Sustained spell of warmer weather can reverse changes.