Plant reponses

Question 1

What is a tropism

Answer 1

a plant that shows directional growth in response to environmental cues

Question 2

Key roles of auxins

Answer 2

• cell elongation
• prevent leaf fall
• fruit ripening
• involved in tropisms
• ethene release

Question 3

Key roles of gibberelins

Answer 3

• stem elongation
• trigger mobilisation in of food stores in seed germination
• stimulate pollen tube growth in fertilisation

Question 4

Key roles of ethene

Answer 4

• fruit ripening
• abscission in deciduous trees

Question 5

Key roles of abscisic acid (ABA)

Answer 5

• stimulate stomatal closing
• stimulate cold protective responses
• maintain seed and bud dormancy

Question 6

What is a cotyledon

Answer 6

a food store in a dicot seed

Question 7

How do gibberellins stimulate seed germination

Answer 7

• gibberellins begin to be produced when a seed absorbs water and the embryo is activated
• gibberellins stimulate the production of enzymes that break down food stored
• embryo uses food stores to produce ATP for building materials to break through seed coat

Question 8

Role of auxins in growth

Answer 8

Apical dominance- growth of the main branch only

Question 9

How do auxins affect cell wall plasticity

Answer 9

• auxin present means the wall stretches more easily
• auxin molecules bind to receptors in the plant cell membrane, causing the pH to fall to 5
• pH 5 is the optimum for enzymes to keep the walls stretchy
• as the cells mature, auxin is destroyed, causing pH to rise so enzymes maintaining plasticity are inactive
• walls become rigid so cells can no longer grow and expand

Question 10

What do high concentrations of auxins do

Answer 10

• suppress the growth of lateral shoots (branches)
• results in apical dominance
• shoots lower down aren’t affected so that lower lateral shoots grow better

Question 11

What is an internode

Answer 11

• regions between leaves on a stem

Question 12

What is synergism

Answer 12

• different hormones work together, complimenting each other
• give a response greater than they would individually

Question 13

What is antagonism

Answer 13

• substances have opposite effects, the balance between them determines the plants response
• give an effect smaller than they would individually

Question 14

Why do plants lose their leaves as a result of abiotic stress

Answer 14

• glucose required for respiration and to maintain leaves > glucose produced by photosynthesis

Question 15

What is photoperiodism

Answer 15

• the idea that plants are sensitive to lack of light in their environment

Question 16

What is phytochrome

Answer 16

-a light sensitive pigment, existing in 2 forms, Pr and Pfr
- each of the forms absorbs a different type of light

Question 17

What is the abscission zone

Answer 17

• made up of 2 layers of cells, sensitive to ethene
• at the base of the leaf stalk

Question 18

Process of leaf abscission

Answer 18

• falling light levels results in lower auxin concentrations
• leaves respond to low auxin by producing gaseous hormone ethene
• ethene initiates gene switching on in the abscission zone
  -gene switching on results in production of new enzymes which digest and weaken cell walls in the separation layer
• vascular bundles that carry materials in and out the leaf are sealed off
• fatty material is deposited into the cells on the stem side of the separation layer (forms protective scar later)
• cells in separation zone respond to hormonal cues by retaining water and swelling, straining the outer layer
• more abiotic stressors put to much strain on the leaf, it falls off leaving a scar

Question 19

What is the separation zone

Answer 19

cells in the outer layer of the abscission zone

Question 20

How do cells prevent freezing

Answer 20

• cytoplasm and sap in the vacuole contain solutes that lower the freezing point
• some solutes act as antifreeze- stop cytoplasm freezing
• different genes are suppressed and activated in response to change in daylength

Question 21

Role of ABA in stomatal control

Answer 21

• open and close stomata in response to abiotic stress
• leaf cells now appear to release ABA when under abiotic stress

Question 22

What is herbivory

Answer 22

• the process by which herbivores eat plants

Question 23

Physical defences against herbivory

Answer 23

thorns, spikes, hairy leaves, stings, inedible tissue

Question 24

Chemical defences against herbivory

Answer 24

• Tannins
• Alkaloids
• Terpenoids
• Pheromones
• VOC’s
  -Fold in response to touch

Question 25

Tannins

Answer 25

- have a bitter taste to animals - toxic to insects- bind and deactivate digestive enzymes in saliva

Question 26

Alkaloids

Answer 26

- bitter tasting, nitrogenous compounds - e.g. caffeine, nicotine, cocaine, morphine - Caffeine toxic to fungi and insects

Question 27

Terpenoids

Answer 27

- act as toxins to insects and fungi - e.g. phyrethin interferes with insect nervous system - some act as insect repellent

Question 28

Pheromones

Answer 28

- chemicals made by an organism that affect the social behaviours of other members of the same species - mainly animals only, e.g. maple trees

Question 29

VOC's

Answer 29

- volatile organic compounds - act as pheromones between plants and other organisms - e.g. attract herbivore predators

Question 30

Plants that respond in response to touch

Answer 30

- Venus fly trap - Mimosa Pudica= folds and collapses in seconds, removes herbivore, scares others, plants has prickles and toxic alkaloids

Question 31

Phototropism

Answer 31

- plant growth in response to light from 1 direction

Question 32

Geotropism

Answer 32

- plant growth in response to gravity

Question 33

Chemotropism

Answer 33

- plant growth in response to chemicals

Question 34

Thigmotropism

Answer 34

- plant growth in repsonse to touch

Question 35

How are plants phototropic

Answer 35

- results of auxin movement - if exposed to light brighter on 1 side (unilateral light), shoots grow towards light, roots grow away - shoots= phototropic, roots= negatively phototropic - enables maximum photosynthesis

Question 36

Effects of unilateral light on a plant

Answer 36

- causes auxin to move laterally, with a greater concentration on the unilluminated side - this stimulates cell elongation and growth towards the light - results in bend plant

Question 37

Growth of plants in the dark

Answer 37

- grow more rapidly in the dark- grow upwards to reach light ASAP - gibberellins responsible for extreme internode elongation in the dark

Question 38

Shoot and root geotropism

Answer 38

- shoots= negatively geotropic, grow against gravity - roots= positively geotropic, grow towards gravitational pull

Question 39

Hormones controlled in plant ripening

Answer 39

- ethene - fruit is harvested a long time before it is ripe so it can be transported easier - when time for sale, exposed to monitored levels of ethene to ripen

Question 40

Hormones affecting rooting powders and micropropagation

Answer 40

- auxin application to cut shoots stimulates production of new roots - cuttings can cause roots to appear - dipping the cut stem into hormone rooting powder increases chances of successful propagation occurring - easier to develop cuttings for people to sell

Question 41

Hormone weedkillers

Answer 41

- synthetic auxins used as weed killers= plants affected by weeds are often monocot, weeds are dicot - if synthetic dicot auxins are used, destroys weeds without harming plant

Question 42

Uses on plant hormones commercially

Answer 42

- fruit ripening - rooting powder/ micropropagation - weed killers - auxin involved in seedless food production - ethene promotes fruit dropping - cytokinin prevent aging of ripened fruit - gibberellins also delay ripening and aging, improve fruit shape and size