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OCR Biology > 5.5 PLANT RESPONSE > Flashcards

5.5 PLANT RESPONSE Flashcards

1
Q

Describe the two types of response to external stimuli in plants

A

1) Tropism = a directional growth towards an external stimulus
2) Nastic response = a nondirectional response to external stimuli (usually chemical release)

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2
Q

Describe the five physical defences of plants

A

1) Cellulose cell wall - physical barrier
2) Ligin thickening of cell walls - waterproof and indigestible
3) Waxy cuticle - prevents water from collecting on surface so pathogens are not attracted
4) Callose - deposited in sieve tubes to block flow of pathogens

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3
Q

State the three chemicals released to prevent plants being eaten

A

1) Tannins
2) Alkaloids
3) Phermones

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4
Q

Describe the action of tannins

A
  • Toxic to microorganisms and larger herbivores
  • Taste bad
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5
Q

Describe the action of alkaloids

A
  • Taste bitter
  • Found in growing tips and flowers
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6
Q

Describe the action of pheromones

A
  • When released affect the behaviour of others
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7
Q

State the four types of tropism

A

1) Phototropism
2) Geotropism
3) Chemotropism
4) Thigmotropism

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8
Q

Define phototropism

A
  • Where shoots grow towards light (positive phototropism)
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9
Q

Define geotropism

A
  • Where roots grow towards gravity (positive geotropism)
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10
Q

Define chemotropism

A
  • On a flower, pollen tubes grow down the style (attracted by chemicals) towards the ovary where fertilization can take place
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11
Q

Define thigmotropism

A
  • Shoots of climbing plants wind around other plants or solid structures to gain support
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12
Q

Define photoperiod

A
  • The period of time in a day that an organism is exposed to light
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13
Q

State the five plant hormones

A

1) Auxins
2) Cytokinins
3) Gibberellins
4) Ethylene
5) Abscisic acid

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14
Q

Describe the location and four effects of cytokinin hormone

A

(ROOTS but transported from there)
1) Promote cell division
2) Delay leaf senescence (delays aging)
3) Promote cell expansion
4) Overcome apical dominance

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15
Q

Describe the location and two effects of abscisic acid hormone

A

(MATURE LEAVES/ROOTS)
1) Inhibits seed germination and growth
2) Causes stomatal closure when the plant is stressed by lower water availibility

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16
Q

Describe the location and three effects of auxin (IAA) hormone

A

(APICAL SHOOT TIP BUDS)
1) Promotes cell elongation
2) Inhibits growth of side shoots (from lateral buds)
3) Inhibits leaf fall

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17
Q

Describe the location and two effects of gibberellin hormone

A

(APICAL BUDS OF ROOTS AND SHOOTS)
1) Promotes seed germination
2) Promotes stem growth (via cell elongation by loosening cell walls) and (via cell division by stimulating the production of a protein that controls the cell cycle)

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18
Q

Describe the location and effect of ethene hormone

A

(LEAVES/STEMS/YOUNG FRUIT)
1) Promotes fruit ripening

19
Q

State the three ways in which hormones move around the plant

A

1) Active transport
2) Diffusion
3) Mass flow in the phloem sap or xylem vessel

20
Q

Explain what and where the apical and lateral bud is

A

Apical bud = on the top
Lateral bud = on the side
- (Bud = arise from meristems, a place that can grow into flower/stem/shoot)
- If the shoot tip (apical bud) is cut off, then plant starts to grow from lateral buds
- This is because inhibitory auxin levels drops in the shoots (as its gone now) so the lateral buds grow as they are no longer inhibited by auxins

21
Q

Define apical dominance

A
  • The inhibition of lateral bud growth (further down the shoot) due to auxins produced by the apical bud (at the tip of the plant shoot) that travel down to the lateral buds and thus prevent side shoot growth
22
Q

Describe the experimental evidence for lateral bud inhibition

A

1) Apical bud/shoot tip is cut off and replaced with auxin paste
2) Lateral buds did not grow
3) Then an auxin transport inhibitor is apllied below the apex of the shoot to prevent the auxin from the auxin paste from travelling down to the lateral buds
4) Lateral buds grow
5) Therefore, its concluded that normal/high auxin hormone levels in the lateral buds inhibits its side shoot growth but low auxin hormone levels in the lateral buds promote its side shoot growth

23
Q

State and explain the three plant hormones invloved in bud growth

A

1) AUXINS = apical dominance

2) ABSCISIC ACID = abscisic acid simply inhibit bud growth
- High auxin levels keep abscisic acid levels high
- But when shoot tip/apical bud is cut off, the abscisic acid levels drop and the bud grows

3) CYTOKININS = cytokinins simply promote bud growth
- Directly applying cytokinins can overpower the effect of apical dominance
- High levels of auxin cause cytokinins to move to the shoot apex/tip/apical bud
- When the shoot apex/tip/apical bud is cut off, the cytokinins spread evenly around the plant so buds grow

24
Q

Explain how gibberellins cause seed germination

A
  • When the seed absorbs water, the embryo releases gibberellin
  • This stimulates the production of amylase which breaks down starch into glucose ready for respiration/protein synthesis
25
Q

State the genotypes of dwarf plants and tall plants

A
26
Q

Explain with diagrams how the presence and absence of the Le allele allows plants to be tall

A
  • Active gibberellin GA₁ is required for a plant to be tall
27
Q

Draw the experiment for grafting of plants to prove stem elongation is caused by gibberellins

A
28
Q

State where plant growth occurs

A

Meristems:
1) Apical buds (for length due to tem elongation)
2) Lateral buds (for width due to side shoots)

29
Q

State the four commercial uses of gibberellins

A

1) Fruit production
2) Brewing
3) Sugar production
4) Plant breeding

30
Q

State the three commercial uses of auxins

A

1) Herbicides
2) Seedless fruit
3) Plant cuttings

31
Q

State the commercial use of ethene

A

1) Fruit ripening

32
Q

State the twocommercial uses of cytokinins

A

1) Prevent leaf falling
2) Mass plant production

33
Q

Explain gibberillins in fruit production

A
  • Sprayed onto fruit to make their stems elongate causing them to grow bigger
  • Can act with cytokinins to maje apples a elongate/improve shape
34
Q

Explain gibberellins in brewing

A
  • During germination, the seed produces amylase which breaks down starch into maltose
  • Adding excess gibberellins can speed up the process
  • Maltose has malt for beer
35
Q

Explain gibberellins in sugar production

A
  • Gibberellins stimulate growth between nodes making the stems elongate
  • Sugar canes store sugar in these cells
  • So sugar yeild increases
36
Q

Explain gibberellins in plant breeding

A
  • Gibberellins can speed up the plant breeding by inducing seed formation on young plants
37
Q

Explain auxins in herbicides

A
  • Excess auxins promote rapid shoot growth so the stem cannot support itself, buckes and dies
38
Q

Explain auxins in seedless fruit

A
  • Excess auxins spayed onto unpollinated flowers can result in ovule growth
  • This triggers automatic auxin production
  • This helps the fruit in their developmental process
39
Q

Explain auxins in plant cuttings

A
  • Dipping the root/end of the plant cutting before plantation promotes root growth
  • Plants can be clones fast and cheap
40
Q

Explain ethene in fruit ripening

A
  • Ethene activated enzymes that help in the ripening process
41
Q

Explain cytokinins in delay of leaf falling

A
  • Delays leaf falling by the degradation of chloroplasts
42
Q

Explain cytokinins in mass production of plants

A
  • Can be used in tissue culture to help mass produce plants by encouraging cell division
43
Q

Explain the process and purpose of prevention of ripening

A

PROCESS:
- Storing fruit at low temperatures, little oxygen and high CO2 prevents ethene synthesis and therefore prevents ripening
- Silver salts are also ethene inhibitors

PURPOSE:
- So the fruit remains hard and easier for transport

OCR Biology (27 decks)

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