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OCR Biology Paper 1 > 5.5 - Plant Responses > Flashcards

5.5 - Plant Responses Flashcards

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1
Q

Explain why plants need to be able to respond to their environment

A
  • To cope with changing conditions
  • Avoid abiotic stress
  • To maximise photosynthesis
  • To obtain more light / water / minerals
  • Avoid herbivory
  • To ensure germination in suitable conditions
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2
Q

Give examples of abiotic stresses

A
  • Change of day length
  • Temperature
  • Water levels
  • Wind
  • pH
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3
Q

Summaries the physiological adaptations plants show to cope with abiotic stress

A
  • Thick waxy cuticles
  • Fine hairs on leaves
  • Sunken stomata
  • Wilting in hot, dry conditions
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4
Q

Name the type of plant that keeps their leaves all year round

A

Coniferous

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5
Q

Name the type of plant that lose their leaves in winter

A

Deciduous

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6
Q

Explain why deciduous trees lose their leaves in winter

A
  • Rate of photosynthesis decreases as day length reduces and temperatures fall
  • Amount of glucose produced by photosynthesis decreases
  • Amount of glucose needed increases
  • Needed for respiration to maintain leaves through winter and produce chemicals to
    prevent damage from freezing
  • More efficient to lose leaves and become dormant until days lengthen and temperatures
    increase in spring
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7
Q

What is photoperiodism?

A

Response of plant to lack of light (length of period of darkness)

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8
Q

What are phytochromes?

A
  • Pigments in leaves
  • Detect light levels
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9
Q

Describe the different types of phytochromes

A

Pr (inactive form)
Pfr (active form)
Pr abundant in darkness, Pfr abundant in light.
Ratio of Pr:Pfr enables plant to detect how long days are.

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10
Q

Give examples of plant responses affected by length of darkness

A
  • Dormancy of leaf bud
  • Timing of flowering
  • Tuber formation in preparation for winter
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11
Q

Define abscission

A
  • Leaf fall
  • Occurs in deciduous trees in autumn
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12
Q

Which plant hormones are involved in abscission?

A
  • Auxin
  • Ethene
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13
Q

Describe the process of abscission in deciduous trees

A
  • Triggered by falling light levels
  • Decreased concentration of auxin
  • Leaves produce ethene
  • Initiates gene switching in abscission zone at base of leaf stalk
  • Gene switching causes production of new enzymes
  • Enzymes weaken cell walls in outer layer of abscission zone (‘separation layer’)
  • Vascular bundles sealed off on stem side of separation layer
  • Layer forms protective scar when leaf falls preventing pathogen entry
  • Cells in separation zone retain water and swell
  • Puts more strain on outer layer
  • Further abiotic factors finish process (e.g. strong wind)
  • Strain too much and leaf separates from plant leaving waterproof scar
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14
Q

Explain how plant hormones protect plant cells in freezing conditions

A
  • Hormones (e.g. abscisic acid) trigger gene switching
  • Plants produce more sugars and proteins
  • Lower the freezing point of the cytoplasm
  • Protect cells against damage by ice crystals if they do freeze
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15
Q

How else can plants protect themselves from freezing?

A
  • Water in intercellular spaces freezes
  • Energy released raises temperature of cells
  • Solute concentration in cytoplasm and vacuoles maintains lower freezing point
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16
Q

How do stomata respond to abiotic stress?

A

They close

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17
Q

Name the hormone responsible for the closure of stomata

A

Abscisic acid (ABA)

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18
Q

Explain how ABA causes stomatal closure

A
  • ABA produced by roots
  • In response to low water levels
  • ABA transported to leaves
  • Binds to receptors on plasma membrane of guard cells
  • Causes ions to diffuse out guard cell
  • Water follows by osmosis
  • Guard cells become less turgid
  • Change in shape leads to closure of stomata
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19
Q

Define herbivory

A

Process by which herbivores eat plants

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20
Q

Outline the physical defences some plants have against herbivory

A
  • Thorns
  • Spiny leaves
  • Fibrous, inedible tissue
  • Stings
  • Hairy leaves
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21
Q

Summarise the various chemical defences plants have against herbivory

A
  • Tannins
  • Have bitter taste
  • Toxic to insects
  • Alkaloids
  • Affect metabolism of animals, acting as poison
  • Prevent germination in plants
  • Terpenoids
  • Act as toxin to insects and fungi
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22
Q

How can plant chemical defences be used by humans?

A
  • Tannins
  • Flavour tea and red wine
  • Alkaloids
  • Used in coffee (caffeine)
  • Contained in cigarettes (nicotine)
  • Terpenoids
  • Insect repellent
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23
Q

Define pheromone

A
  • Chemical made by an organism
  • Affects social behaviour of other members of same species
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24
Q

Why is it necessary for pheromones to be volatile?

A

Must travel through the air to carry message

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25
Q

Give an example of how plants use pheromones to defend themselves

A
  • Maple trees produce pheromone when attacked by insects
  • Absorbed by leaves on other branches and nearby trees
  • Leaves produce protective chemicals, e.g. callose
26
Q

Define volatile organic compound (VOC)

A
  • Chemical made by an organism
  • Affects social behaviour of other species
27
Q

Outline how some plants use VOCs to defend themselves

A
  • Apple tree attacked by spider mites produce VOCs that attract predatory mites
  • Predatory mites destroy spider mites attacking tree
  • Wheat seedlings produce VOCs when attacked by aphids
  • VOCs repel other aphids from the plant
28
Q

Define meristems

A
  • Regions of small, undifferentiated (totipotent) cells
  • Continue to divide and grow throughout lifetime of plant
29
Q

Where are apical meristems found in plants?

A
  • Tip of root
  • Tip of stem
  • Cause lengthening of plant
  • Produces new leaves and flower
30
Q

Where are lateral meristems found in plants?

A

Cambium (within the stem)
- Cause widening of plant
- Produces bark on trees

31
Q

List organs found in plants

A
  • Roots
  • Stems
  • Flowers
  • Bulb
32
Q

What does a shoot consist of?

A
  • Stems
  • Leaves
33
Q

Define tropism

A

A plant’s directional response to a stimulus

34
Q

Give three different tropisms

A
  • Geotropism - response to gravity
  • Phototropism - response to light
  • Thigmotropism - response to touch (e.g. climbing plants)
35
Q

Define apical dominance

A
  • Plant growth primarily occurs at tip of shoot
  • Horizontal growth (e.g. branches, leaf stems) inhibited
36
Q

How does auxin stimulate cell elongation in shoots?

A
  • Auxin activates proton pumps in plasma membrane
  • Causes H+ ions to be pumped from cytoplasm to cell wall
  • Low pH breaks bonds in cell wall fibres, loosening them
  • Provides optimum pH for enzymes that keep cell wall elastic
  • Alters gene expression patterns to increase growth rate
  • Inhibits lateral growth
  • Growth of horizontal branches/shoots prevented
37
Q

Outline how the stem of a plant may bend towards the light

A
  • Auxins (plant hormones) concentrate on the side furthest from light
  • Causes cell lengthening
  • Stem bends towards the light
38
Q

Explain auxin’s role in phototropism

A
  • Positive phototropism is growth towards light
  • Auxin is a plant hormone
  • Produced by shoot tip (apex)
  • Diffuses down shoot on shaded side of stem
  • Causes active transport of H+ from cytoplasm to cell wall
  • Decrease in pH breaks bonds between cell wall fibres
  • Softens cell walls
  • Provides optimum pH for enzymes that keep cell wall elastic
  • Gene expression altered by auxin to promote cell growth
  • Causes cells on darker side to elongate
  • Shoot bends towards light
39
Q

What effect does auxin have in roots?

A
  • Accumulates on lower side of plant in response to gravity (geotropism)
  • Inhibits cell elongation
  • High concentrations limit growth
  • Lower side of root grows slower and roots turn downwards
40
Q

Describe the ways in which a plant responds to overcrowding by other plants

A
  • Positive phototropism
  • Auxin produced at shoot tip
  • Shoots bend towards light
  • Plants grow taller
  • Positive thigmotropism
  • Climbing plants climb other plants
  • Negative gravitropism
  • Grow roots towards water and minerals
    Suggest how hormones alter a plant’s growth if the top of the plant shoot is removed
  • Less auxin produced
  • Apical dominance stopped
  • Lateral buds develop
  • Plant becomes bushy
41
Q

Suggest how hormones alter a plant’s growth if the top of the plant shoot is removed

A
  • Less auxin produced
  • Apical dominance stopped
  • Lateral buds develop
  • Plant becomes bushy
42
Q

Explain why most plants have more lateral shoots lower down the stem

A
  • Auxin primarily produced at shoot tip
  • High concentration of auxin inhibits lateral growth
  • Causes apical dominance
  • Auxin diffuses down stem
  • Concentration of auxin lower towards bottom of stem
  • Lateral growth not inhibited
  • Lateral shoots grow more
43
Q

Why is it beneficial for a plant to grow towards the light?

A

Maximises amount of photosynthesis

44
Q

Define internode

A

Region between leaves on a stem

45
Q

Explain how plants are able to grow in the dark

A
  • Growth caused by gibberellin plant hormone
  • Causes rapid cell elongation of internodes
  • Results in fast upwards growth in dark conditions
46
Q

Why is it important for plants to grow in the dark?

A
  • Seedlings need to break through soil
  • Compete with other seedlings and plants for light
47
Q

Describe the structure of a seed

A
  • Testa - seed coat that protects embryonic plant
  • Cotyledon - food store for seed, forms embryonic leaves
  • Plumule - embryonic shoot
  • Radicle - embryonic root
48
Q

Outline how and where energy is stored in plants

A
  • Glucose from photosynthesis stored as starch
  • Starch stored in chloroplasts and seeds/tubers
  • Lipids stored in seeds
49
Q

Describe the process of germination

A
  • Food source used up
  • Radicle grows down
  • Shoot grows up
  • Plant starts to photosynthesise
50
Q

What conditions are needed for germination to occur? Use WOW to help you remember!

A
  • Water - rehydrates the seed and activates metabolic processes
  • Oxygen - required for aerobic respiration as seed germinates
  • Warmth - for enzyme activity
  • Each seed type has specific temperature requirements to ensure seeds germinate
    at the correct time of year
51
Q

What are gibberellins?

A
  • Plant hormones
  • Required for germination
  • Stimulate production of amylase and protease enzymes
52
Q

Outline the metabolic processes that occur in starchy seeds during germination

A
  • Water absorbed by the seed activates metabolism
  • Gibberellin synthesised
  • Stimulates production of amylase
  • Amylase digests starch (stored in cotyledon) to maltose
  • Maltose converted to glucose by maltase
  • Glucose used in aerobic respiration
  • Glucose used in synthesis of cellulose
53
Q

How can the rate of germination be measured?

A

Measure rate of seed growth over a set period of time

54
Q

Outline the experimental evidence for the role of gibberellins in seed germination

A
  • Mutant seeds that cannot produce gibberellins created
  • Seeds do not germinate
  • If gibberellins applied artificially, seed germinates
  • Gibberellin synthesis inhibitors applied to seed
  • Seed cannot produce gibberellins
  • Seed does not germinate
  • If inhibitor removed, seeds germinate
55
Q

Describe the use of auxins in industry

A
  • Rooting powder
  • Selective weedkillers
  • Development of seedless fruit
56
Q

Describe the use of giberellins in industry

A
  • Delays fruit ripening
  • Increases fruit size
  • Speeds up the brewing process
57
Q

Describe the use of ethene in industry

A
  • Controlled ripening
  • Fruit dropping
  • Leaf fall
58
Q

Describe the use of cytokinins in industry

A
  • Prevent ageing of ripened fruit
  • Control tissue development in micropropagation
59
Q

How are auxins used in propagation?

A
  • Added to rooting powder
  • Presence of auxin stimulates cut shoots to form roots
  • Increases likelihood of successful propagation
60
Q

How are auxins used as weedkillers?

A
  • Artificial auxins created that are specific for weed plants
  • Not taken up by crop plants
  • Cause unsustainable growth in weeds
  • Weeds die
61
Q

Outline why both plants and animals need to be able to respond to changes in their environment

A
  • To avoid abiotic stress
  • To avoid being eaten
  • To access resources

OCR Biology Paper 1 (20 decks)

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