B16

Question 1

Auxins

Answer 1

Cell elongation, prevent leaf abscission, tropisms, stim. ethene release, fruit ripening.

Question 2

Gibberellins

Answer 2

Stem elongation, mobilise food stores (germintation), stim. pollen tube growth (fertilisation).

Question 3

Ethene

Answer 3

Fruit ripening, promote abscission.

Question 4

Abscisic Acid (ABA)

Answer 4

Stim. stomata closing, maintain seed dormancy.

Question 5

Germination

Answer 5

1. Absorb water.
2. Embryo activates.
3. Prod. giberellins.
4. Stim. prod. of enzymes.
5. Break down food stores.
6. Embryo use stores for ATP prod.
7. Grow & break seed coat.

Question 6

Synergism

Answer 6

Different hormones working together (complementary), give an increased response. Achieves fine control over plant response.

Question 7

Antagonism

Answer 7

Hormones with opposite effects. E.g. growth & inhibition.
The balance between determines response.

Question 8

Commercial Uses: Control Ripening

Answer 8

Ethene ripen climacteric fruit (cont. ripen after harvest e.g. banana). Harvest when fully formed but not ripe, transport with less damage, expose to ethene gas, inc. selling time.

Question 9

Commercial Uses: Rooting Powders & Micropropagation

Answer 9

Auxin on cut shoots –> grows roots (propagates new plant). Agriculture & horticulture propagate large scale with micropropagation (hormones control thousands of new cell prod. and differentiation).

Question 10

Commercial Uses: Hormonal Weedkillers

Answer 10

Weeds compete with crops & interrupt metabolism. Synthetic dicot auxins absorbed by weeds, inc. growth rate, unsustainable, weeds die. (Crops - narrow leaved monocots, weeds - broad leaved dicots).

Question 11

Commercial Uses: Other Hormone Uses

Answer 11

Auxins (prod. seedless fruit).
Ethene (promote fruit dropping e.g. cotton).
Cytokinins (prevent ageing of ripened, control tissue development in micropropagation).
Giberellins (delay ripe/ageing, improve size/shape).

Question 12

Abiotic Stresses

Answer 12

High wind, excess H2O, temp. change, day length.

Question 13

Herbivore Stresses

Answer 13

Physical Defences - wax, above ground covered with cutin, subrin (walls), bark, thorns, hairy leaves.
Chemical Defences - if physical penetrated. Kill, ill , repel.

Question 14

Abiotic: Leaf loss

Answer 14

Cold winter = less pts.
More efficient to lose leaves.

Question 15

Abiotic: Daylight sensitivity

Answer 15

‘Photoperiodism’ = sensitivity to lack of daylight. Longer daylight hrs –> leaves bud/flowers bloom.

Question 16

Abiotic: Leaf abscission

Answer 16

Less light, ethene switches on genes which stimulate enzymes. Enzymes digest & weaken cell walls at abscission zone. Leaf separates, leaves waterproof scar to protect plant.

Question 17

Abiotic: Preventing freezing

Answer 17

Some plants with chemicals act as a natural antifreeze. Activated in winter, reversed by inc. temp.

Question 18

Abiotic: Stomatal control

Answer 18

ABA dec. water potential/tugidity of guard cells (close), less H2O lost. Open again to cool plant.

Question 19

Chemical defense: Tannins

Answer 19

Bitter, inactivate digestive enzymes in saliva of animals.

Question 20

Chemical defense: Alkaloids

Answer 20

Bitter, nitrogenous, poisonous. Toxic to insects (caffeine), release to soil to stop germination around it (protect other plants).

Question 21

Chemical defense: Terpenoids

Answer 21

Toxins & oils. Pyrethrin (insecticides) and Citronella (put insects off).

Question 22

Chemical defense: Pheromones

Answer 22

Warn others in species. Tree attacked –> release pheromones –> absorbed by leaves on other branches –> leaves make callose, helps protect if attacked.

Question 23

Auxin conc. in shoots

Answer 23

Apical Dominance.
High conc. = suppresses the growth of shoots.
Low conc. = lateral shoots inc. growth.

Question 24

Tropisms

Answer 24

Growth response to environmental cues/unidirectional stimulus.
+ve = towards stim. -ve = away from stim.

Question 25

Phototropism

Answer 25

Controlled by IAA (auxin).
Inc conc. = elongation in shoots and inhibit in roots.
Unilateral light = growth on dark side, IAA diffuse to shaded side, shoot bends towards light (+ve phototropism). Roots bend away from light (-ve phototropism).

Question 26

Geotropism

Answer 26

Controlled by IAA (auxin).
Gravity. Shoots -ve geotropism (grow upwards), roots +ve geotropism (towards stim).
Ensure shoots receive light and roots in soil.