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OCR A Biology (advanced information only 2022) > 5.1.5 Plant responses > Flashcards

5.1.5 Plant responses Flashcards

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1
Q

Define the term abiotic factor

A

Abiotic factors are non-living factors e.g. wind, climate

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2
Q

Define the term Biotic factor

A

Biotic factors are living factors (organisms) e.g. plants, predators, prey

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3
Q

What is a Tropism?

A

TROPISM is a directional growth response which is determined by the direction of the external stimulus

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4
Q

What is a phototropism?

A

A plants response to LIGHT, an abiotic factor that ensures that as the plant grows, it gains maximum exposure to sunlight

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5
Q

What is a Geotropism?

A

A plants response to GRAVITY, an ABIOTIC factor which ensures that no matter the orientation of the seed, the shoots/stem will go in a negative-geotropism (upwards) and the roots will go in a positive-geotropism (down)

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6
Q

What is a Thigmotropism?

A

A plants response to TOUCH, a biotic or abiotic factor allowing for especially climbing plants to detect living or non-living support and curl around it, also allows it to access areas of more sunlight through this climbing

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7
Q

What is a Chemotropism?

A

A plants response to chemicals around it, such as pollen tubes growing towards the ovaries

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8
Q

How might a plant respond to touch? give an example

A

Leaves may fold inwards, shown in Mimosa pudica

  • caused by rapid water uptake of cells at the base of each leaf, causing them to fold
  • this is not a tropism as it is not caused by a directional stimulus, responses like these are called NASTIC movements
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9
Q

How might a plant respond to herbivory? (being eaten by herbivores)

A 
Plants combat/respond to herbivory via having physical adaptations like thorns or spines on the leaves and stems
Or
by releasing/containing special chemicals in response to stress
chemicals include:
-Tannins
-Alkaloids
-Pheromones
-terpenoids
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10
Q

What do Tannins do?

A

Water soluble chemicals stored in vacuole of plants, have a bitter taste that and can be poisonous. These factors can then deter animals from consuming them

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11
Q

What do plant Alkaloids do?

A

Alkaloids are nitrogenous chemicals in plants that are bitter tasting and can be toxic, particularly to herbivorous insects and some fungi

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12
Q

What do terpenoids do?

A

-They are toxic to insects and fungi s they are neurotoxins and repellants

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13
Q

What do plant pheromones do?

A

Chemicals released by one member of a species causing a physiological change in nearby same species, possible directly toxic to her herbivores and induce defensive changes in nearby plants

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14
Q

Give some examples of Abiotic stress factors

A

Freezing
Drought
Increased soil water salinity
Presence of heavy metals (e.g. lead, copper, zinc, mercury)

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15
Q

How may plants respond to abiotic stress?

A
  • Plants can respond to drought by shutting their stomata (reducing water loss through transpiration) or by dropping their leaves
  • Some plants can respond to temperatures below freezing by producing an antifreeze chemical in their cells, that decreases the formation of ice crystals that can destroy plant cells if allowed to form within them
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16
Q

what type of phototropism is displayed in plant shoots?

A

positive phototropism

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17
Q

Investigating tropism in plants:

What happens when the tip of a shoot is cut off or covered by an opaque cap?

A

It stopped having a phototrophic response to surrounding directional light sources, suggesting that the tip of the shoot is responsible for detecting light

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18
Q

Investigating tropism in plants:
What happens when the shoot tip is covered by a transparent cap or there is an opaque sheath protecting the base of the shoot?

A

The shoot responded to the directional light source and began to curve, meaning the base has does not assist in detecting direction light sources while the tip does

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19
Q

Investigating tropism in plants:

What happens when the tip of the shoot is separated from the res of the plant via an gelatine block?

A

The phototrophic response still happened in response to directional light, meaning that the stimulus for growth is hormonal, which can be transferred through the gelatine block

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20
Q

Investigating tropism in plants:

What happens when mica (impermeable to chemicals) is inserted as a barrier between the tip of the shoot and the stem?

A

Mica is impermeable to chemicals, this resulted in the shoot not having a phototrophic response as the hormones could not penetrate the barrier to stimulate growth

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21
Q

Name the main plant hormones

A
  • Auxins
  • Gibberellins
  • Cytokinin’s
  • Abscisic Acid
  • Ethene (the only gaseous hormone)
22
Q

What is the purpose of the plant hormone Auxin?

A

Promotes cell elongation, inhibits growth of side-shoots, inhibits leaf abscission (leaf-fall)

23
Q

What is the purpose of the plant hormone Cytokinin

A

promotes cell division

24
Q

What is the purpose of the plant hormone Gibberellins?

A

Promotes seed germination and growth of stems

25
Q

What is the purpose of the plant hormone Ethene?

A

To ripen fruit

26
Q

What is the purpose of the plant hormone abscisic acid?

A

Inhibits seed germination and growth, causes stomatal closure when plant stressed due to lack of water

27
Q

Where are auxins produced?

A

They are produced in the actively growing tips of shoots/roots in the meristematic cells

28
Q

How are plant hormones transported?

A

Plant hormones may be transported by mass flow in xylem vessels or phloem sieve tubes and then will go into target cells via diffusion or active transport

29
Q

What is an apical meristem?

A

the tips of roots and shoots

30
Q

What is a Lateral bud meristem?

A

side buds where shoots grow

31
Q

what is a lateral meristem?

A

The width of the shoot and roots

32
Q

How do auxins promote cell elongation? (long answer)

A

-Auxins diffuse down the lateral meristems, diffusing into the plant cells and promoting H+ ions to be diffused into the cellulose cell walls creating the perfect pH for expansin
-Expansin hydrolyse hydrogen and glyosidic bond in the cellulose cell wall,
making it less rigid
-This allows new cells to absorb water and expand forming permanent vacuoles thus elongating the stem
-enzymes then break down the auxins, so expansin denatures and the stem in no longer very flexible

33
Q

simply explain how auxin effects a shoots in all round lighting

A
  • Auxin produced in meristem shoot tips
  • Auxins diffuse down the stem, attaching to receptors on plant cells
  • activates H+ ion pumps decreasing the pH, making the zone of elongation more flexible
  • new cells form vacuoles and expand, elongating the stem on all sides
  • Auxin is destroyed by enzymes, cell walls become more rigid and elongation is no longer possible
34
Q

simply explain how auxin effects a shoots subjected to unidirectional lighting

A

-Auxin is produced in the meristem tips of the shoot
-Auxin moves laterally from the light to dark side of the tips, so a higher auxin
conc is on the darker side as they diffuse down the stem
-more auxin on the darker side means that the darker side stays flexible for longer
-This means that the dark side elongates more than the lighter side, so the plant
turn towards the light source

35
Q

How would you be able to investigate geotropic response?

A

Use a clinostat ,a device that hold the plant sideways and rotates it at intervals so that gravity can act on all sides of the plant

36
Q

How does auxin work in roots?

A

In roots, most auxin goes to the bottom of the root and INHIBITS cell elongation while the upper side continues to grow causing the roots to grow downwards

37
Q

Define Apical dominance

A

This is when the Apical bud at the highest tip of the shoot, inhibits growth of lateral buds further down the shoot

38
Q

what will happen if the apical shoot is cut?

A

shoots will begin to grow from pre-existing lateral shoots

39
Q

What is the experimental evidence for apical dominance

A

Applying auxin paste to a cut in the side stem it did not promote side shoot growth, only when removing the apical shoot did side shoots begin to grow, which caused an increase in auxin levels in the lateral buds

40
Q

What are the other hormones involved in apical dominance?

A
  • Abscisic acid: inhibits the growth of lateral buds when there is high levels of auxin in the apical bud, when the bud is broken/cut apical auxin is no longer produced, so Abscisic acid concentration is no longer maintained in lateral buds, so they grow
  • Cytokinins: promotes the growth of lateral buds. the presence of Auxin in the apical bud acts as a sink for cytokinins, so it is concentrated there, when the apical bud is cut, cytokinins are more evenly distributed around the plant, simulating lateral bud growth
41
Q

define leaf senescence

A

The aging of leaves, their changing colour as chlorophyll

42
Q

Define leaf abscission

A

This is when leaves are shed from the plant

43
Q

How is leaf senescence avoided in plants?

A

Leave senescence is prevented via cytokinins, they maintain a nutrient supply to the leaves

44
Q

what is the process of leaf abscission?

A
  • Auxin that is produced in the tips of leaves, prevents leaf abscission, and is maintained by the presence of cytokinins
  • cytokinin levels drop, thus lowering levels of Auxin produced
  • a decrease of auxin = an increase of ethene production
  • increased ethene causes the development of a abscission layer at the base of the stalk
  • ethene stimulates cellulase to hydrolyse the abscission layer, so the leaf falls of
45
Q

what is the process of leaf abscission?

A
  • Auxin that is produced in the tips of leaves, prevents leaf abscission, and is maintained by the presence of cytokinins
  • cytokinin levels drop, thus lowering levels of Auxin produced
  • a decrease of auxin = an increase of ethene production
  • increased ethene causes the development of a abscission layer at the base of the stalk
  • ethene stimulates cellulase to hydrolyse the abscission layer, so the leaf falls of
46
Q

How does a tree protect its self when a leaf falls?

A

below the abscission layer, cell walls will contain suberin, which creates scar tissue when the leaf falls down, protecting it from pathogens

47
Q

What is the experimental evidence for gibberellins effect on cell elongation?

A

-Scientists analysed the gibberellic acid (G) concentrations within the stem cells of
tall pea plants
-Some with homozygous recessive alleles can produce G20 but not have
enzymes to make it into G1 so do not grow
-A mutant plant that cannot produce G20 is grafted onto the dwarf recessive
plant and the shoot grew!
-This is because the Dwarf plant produced the G20 while the grafted one produced
the enzyme to convert it to G1 and so it began to grow, showing that gibberellins
are necessary for cell elongation.

48
Q

What are some commercial uses of Auxins?

A

-Root tip powder, Used to make cuttings grow new shoots for a new plant
-Producing seedless fruit, Spraying auxin onto plants stimulates growth of fruit but
since thy are not fertilised, ovaries are not developed
-Weed-killer, artificial auxins cause so much extra growth that plants cant support themselves so they die
-stops abscission of leaves and fruits, so that they can remain on the plant until
harvested

49
Q

What are some commercial uses of Gibberellins

A
  • Fruit production
  • brewing
  • sugar production
50
Q

What are some commercial uses of cytokinins

A
  • Used to mass produce genetically identical plants

- delays yellowing of leaves by preserving chloroplasts

51
Q

What are some commercial uses of Ethene

A
  • stimulates the ripening of fruits, e.g. apples tomatoes citrus
  • promotes fruit dropping
  • promotes female sex expression in cucumber flowers
52
Q

what are some ways to prevent ethene production?

A
  • Low temperature, low O2 concentrations and high CO2 concentrations
  • helps keep fruit hard when transporting

OCR A Biology (advanced information only 2022) (17 decks)

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