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OCR BIOLOGY (MODULE 5) > PLANT RESPONSES > Flashcards

PLANT RESPONSES Flashcards

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1
Q

Directional growth

A

=tropism

Controlled by plant hormones

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2
Q

Non-directional growth

A

=nastic response

Fast + controlled by temporary changes (e.g. plant turgidity- osmosis)

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3
Q

Example of non-directional growth response

A

Daisies:

Open during day for pollination, close during the night for protection

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4
Q

Physical responses to herbivores

A

Thorns
Spiny leaves
Tough fibrous tissue

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5
Q

Chemical responses to herbivores

A

Alkaloids- bitter + toxic (e.g. nicotine), increase production in response to damage
Tannins- bitter + bind to digestive enzymes of animals + inactivate them
Terpenoids- toxic + smell deters insects

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6
Q

Pheromones (response to herbivores)

A

Chemical produced by an individual to affect behaviour of another

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7
Q

Example of pheromone

A

When plant is damaged, release chemicals causing nearby plants to release chemicals
Chemicals attract parasites to kill attacker (e.g. caterpillar)

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8
Q

Thigmonasty (response to herbivores)

A

Response to touch

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9
Q

Responses to abiotic stress

A

Leaves fall off due to low temps (no photosynthesis, so wasting energy)
Antifreeze production- stops ice crystals forming in cytoplasm (e.g. carrots)
Stomatal closure to reduce transpiration (drought)

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10
Q

Types of tropisms

A

Geotropism (gravity)
Phototropism (light)
Chemotropism
Thigmotropism (touch)

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11
Q

State some roles of plant hormones

A

Produced in variety of tissue
Move via AT, diffusion + mass flow in phloem + xylem
Slow response
Permanent changes
Work synergistically + antagonistically with other hormones

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12
Q

Auxin effect

A

E.g. IAA
Promote cell elongation
Inhibits growth of side shoots
Inhibits leaf abscission

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13
Q

Cytokinins effect

A

Promote cell division

Works synergistically with auxin

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14
Q

Gibberellins effect

A

Stem elongation

Seed germination

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15
Q

Absicic acid effect

A

E.g. ABA
Seed dormancy
Stimulates stomatal closure (guard cells= flat + flaccid)
Stimulates anti-freeze production

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16
Q

Ethene effect

A

Promote fruit ripening

Leaf abscission

17
Q

Conclusions to plant hormone experiments

A

Shows shoots grow towards light
Tip is needed to grow + bend
Light sensors must be in tip of shoot
Auxin diffuses down shaded part of plant

18
Q

How does auxin work

A

Made in meristem cells near tips of roots + shoots
Causes cell elongation
Binds to receptors on cell surface membrane + promote AT of H+ into cell wall (=acidic)
Reduces pH= weakens cellulose bonds + activates enzymes to break cellulose bonds
Osmosis, elongation is permanent as cellulose cell wall is weakened
Plant ages + destroys auxin, cellulose cell wall; becomes rigid= permanent change

19
Q

Auxin + phototropism

A

Cells in tip contain phototropin in cell membrane
When hit by light they become phosphorylated
This causes auxin produced in shoot + tip to move to shaded side (via transporter proteins)
Cell elongates- shaded side bends

20
Q

Explain how roots are +ve geotropic + -ve phototrophic

A

Gravity causes auxin to move to lower side of roots + shoots

  • in root auxin inhibits cell elongation. Cells on lower side elongates less + root grows downwards
  • in stem auxin promotes elongation. Cells on lower side elongate + stem grows upwards
21
Q

Apical dominance

A

Region near top of terminal bud contains apical meristem = dominance over lateral buds= plants grow straight without wasting energy on side branches, allows them to compete for light (photosynthesis)
If tip of plant is cut off, lateral buds start growing + plant bushes out

22
Q

Control of apical dominance

A

Auxin made in aphical bud where it causes cell elongation

Auxin diffuses down lateral buds, where it inhibits them

23
Q

Why will lateral buds grow if plant is upside down?

A

Upside down= diffusion of auxin upwards against gravity, therefore auxin to lateral buds + growth

24
Q

Gibberellins + stem elongation

A

Produced in young leaves + seeds

Causes growth in cell internodes

25
Q

Auxin + Gibberellin can be…

A

Synergistic- grow tall

Antagonistic- gibberellins stimulate lateral shoots, auxin inhibits them

26
Q

Gibberellin + germination (Barley seed)

A

When seed absorbs water embryo releases gibberellins
Gibbs travel to aleurone layer (membrane) of endosperm (food store)
This switches on genes which code for amylase + protease (hydrolytic enzymes)
Stored starch hydrolysed to glucose (using enzymes)
This provides substrate for respiration so embryo can grow

27
Q

Why does leaf abscission occur

A

Less light in winter (shorter days, lower intensity) + lower temps reduces photosynthesis
Water lost through leaves, fungal infections + frost= damaged plant= leaf loss
Wastes energy

28
Q

Leaf abscission in deciduous plants

A

Auxin produced in young leaves, inhibits abscission
Reduce light= reduced auxin concentration
Ethene produced as leaves age
To balance shift between two hormones, leaf abscission starts (aux + eth= antagonistic)
Abscission layer of leaf have thin walls (weakened by enzymes), breaking cellulose bonds
At same time- Suberin develops underneath for protection
Vascular bundle sealed off
Leaf blown away with wind

29
Q

When is absicic acid produced

A

Under abiotic stress (e.g. temp)

Causes stomata to close, reducing transpiration

30
Q

Absicic acid + stomatal closure

A

ABA binds to receptors on cell surface membrane of guard cells
Ca2+ enters cell causing other ions to exit (e.g. K+ + Cl-)
Water potential of cell increases
Water leaves cell via osmosis
Guard cells= flaccid (straight)= closed stomata

31
Q

Commercial use of auxin

A

Selective weed killer
Rooting powder
Pathonocarpy fruit development without pollination

32
Q

Commercial use of gibberellins

A

Improve fruit shape
Delay fruit dropping
Bring forward seed production
Stopping= shorter plants= saves resources + reduces wind damage

33
Q

Commercial use of cytokinins

A

Promote cell division
Stops ageing (reduced waste)
Promote shoot growth in tissue culture

34
Q

Commercial use of ethene

A

Fruit ripening
Fruit dropping at same time (easier harvesting)
Speed up ripening
Promote growth of female flowers (for pollination)
Stopping increase CO2 which reduces ethene= delay fruit ripening

OCR BIOLOGY (MODULE 5) (7 decks)

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