Plant Responses Flashcards
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 or to obtain more light / water / minerals
- Avoid herbivory
- To ensure germination in suitable conditions
2
Q
Give examples of abiotic stresses
A
- Change of day length
- Temperature
- Water levels
- Wind
- pH
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
4
Q
Name the type of plant that keeps their leaves all year round
A
Coniferous
5
Q
Name the type of plant that lose their leaves in winter
A
Deciduous
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
7
Q
What is photoperiodism?
A
Response of plant to lack of light (length of period of darkness)
8
Q
What are phytochromes?
A
- Pigments in leaves
- Detect light levels
9
Q
Describe the different types of phytochromes
A
Pr (inactive form)
- Pfr (active form)
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
11
Q
Define abscission
A
- Leaf fall
- Occurs in deciduous trees in autumn
12
Q
Which plant hormones are involved in abscission?
A
- Auxin
- Ethene
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
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
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
16
Q
How do stomata respond to abiotic stress?
A
They close
17
Q
Name the hormone responsible for the closure of stomata
A
Abscisic acid (ABA)
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
19
Q
Define herbivory
A
Process by which herbivores eat plants
20
Q
Outline the physical defences some plants have against herbivory
A
- Thorns
- Spiny leaves
- Fibrous, inedible tissue
- Stings
- Hairy leaves
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
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
23
Q
Define pheromone
A
- Chemical made by an organism
- Affects social behaviour of other members of same species
24
Q
Why is it necessary for pheromones to be volatile?
A
Must travel through the air to carry message
25
Give an example of how plants use pheromones to defend themselves
- 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
Define volatile organic compound (VOC)
- Chemical made by an organism
- Affects social behaviour of other species
27
Outline how some plants use VOCs to defend themselves
- 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
Define meristems
- Regions of small, undifferentiated (totipotent) cells
- Continue to divide and grow throughout lifetime of plant
29
Where are apical meristems found in plants?
- Tip of root
- Tip of stem
- Cause lengthening of plant
- Produces new leaves and flower
30
Where are lateral meristems found in plants?
Cambium (within the stem)
- Cause widening of plant
- Produces bark on trees
31
List organs found in plants
- Roots
- Stems
- Flowers
- Bulb
32
What does a shoot consist of?
- Stems
- Leaves
33
Define tropism
A plant’s directional response to a stimulus
34
Give three different tropisms
- Geotropism - response to gravity
- Phototropism - response to light
- Thigmotropism - response to touch (e.g. climbing plants)
35
Define apical dominance
- Plant growth primarily occurs at tip of shoot
- Horizontal growth (e.g. branches, leaf stems) inhibited
36
How does auxin stimulate cell elongation in shoots?
- 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
Outline how the stem of a plant may bend towards the light
- Auxins (plant hormones) concentrate on the side furthest from light
- Causes cell lengthening
- Stem bends towards the light
38
Explain auxin's role in phototropism
- 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
What effect does auxin have in roots?
- 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
Describe the ways in which a plant responds to overcrowding by other plants
- 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
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
42
Explain why most plants have more lateral shoots lower down the stem
- 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
Why is it beneficial for a plant to grow towards the light?
Maximises amount of photosynthesis
44
Define internode
Region between leaves on a stem
45
Explain how plants are able to grow in the dark
- Growth caused by gibberellin plant hormone
- Causes rapid cell elongation of internodes
- Results in fast upwards growth in dark conditions
46
Why is it important for plants to grow in the dark?
- Seedlings need to break through soil
- Compete with other seedlings and plants for light
47
Describe the structure of a seed
- Testa - seed coat that protects embryonic plant
- Cotyledon - food store for seed, forms embryonic leaves
- Plumule - embryonic shoot
- Radicle - embryonic root
48
Outline how and where energy is stored in plants
- Glucose from photosynthesis stored as starch
- Starch stored in chloroplasts and seeds/tubers
- Lipids stored in seeds
49
Describe the process of germination
- Food source used up
- Radicle grows down
- Shoot grows up
- Plant starts to photosynthesise
50
What conditions are needed for germination to occur? Use WOW to help you remember!
- 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
What are gibberellins?
- Plant hormones
- Required for germination
- Stimulate production of amylase and protease enzymes
52
Outline the metabolic processes that occur in starchy seeds during germination
- 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
How can the rate of germination be measured?
Measure rate of seed growth over a set period of time
54
Outline the experimental evidence for the role of gibberellins in seed germination
- 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
Describe the use of auxins in industry
- Rooting powder
- Selective weedkillers
- Development of seedless fruit
56
Describe the use of giberellins in industry
- Delays fruit ripening
- Increases fruit size
- Speeds up the brewing process
57
Describe the use of ethene in industry
- Controlled ripening
- Fruit dropping
- Leaf fall
58
Describe the use of cytokinins in industry
- Prevent ageing of ripened fruit
- Control tissue development in micropropagation
59
How are auxins used in propagation?
- Added to rooting powder
- Presence of auxin stimulates cut shoots to form roots
- Increases likelihood of successful propagation
60
How are auxins used as weedkillers?
- Artificial auxins created that are specific for weed plants
- Not taken up by crop plants
- Cause unsustainable growth in weeds
- Weeds die
61
Outline why both plants and animals need to be able to respond to changes in their environment
- To avoid abiotic stress
- To avoid being eaten
- To access resources
