CHAPTER 16 - PLANT RESPONSES Flashcards
1
Q
What are tropisms
A
Directional growth in response to environmental cues
eg. Light and gravity
2
Q
What are the key limitations of plants
A
They are rooted - hence not mobile
no rapid responding nervous system
3
Q
How to plants communicate (cells and with other individuals) and respond to their environment
A
Hormones
4
Q
Are most plant responses faster or slower than animal responses
A
Slower
5
Q
What are the roles of the Auxin hormone group?
A
Control cell elongation
Prevent leaf fall (abscission)
Maintain Apical Dominance
Involved in tropisms
Stimulates release of Ethene
6
Q
What are the roles of the Gibberellin hormone group?
A
Causes Stem elongation
Triggers mobilisation of food stores in a seed at germination
Stimulates pollen tube growth in fertilisation
7
Q
What are the roles of Ethene
A
Causes Fruit ripening
Promotes abscission in deciduous trees
8
Q
What are the roles of ABA (abscisic acid)
A
Maintains Dormancy of seeds and buds
Stimulates cold protective responses eg. Antifreeze production, stimulating stomatal closure
9
Q
What is growth of plants controlled by
A
Plant hormones
10
Q
Do plant hormones work at high or low concentrations?
A
Low
11
Q
Why is it difficult for researchers to isolate the role of a single chemical in a response in plants
A
Multiple interactions between different chemical control systems
Plant hormones work at low concentrations
12
Q
Describe the series of events in seed germination
A
Seed absorbs water, embryo is activated and produces gibberellins
Gibberellins stimulate the production of enzymes that break down the food stores found in the seed.
The food store is in the cotyledons in dicot seeds and the endosperm in monocot seeds
Embryo plant uses these food stores to produce ATP for building materials so it can grow and break out through the seed coat.
Evidence suggests that gibberellins switch on genes which code for amylase and proteases - the digestive enzymes required for germination
ABA acts as an antagonist to gibberellin to control rate of seed germination
13
Q
What is the experimental evidence supporting the role of gibberellins in seed germination
A
Mutant seed varieties have been Breed which lack the gene to make gibberellins, so the seeds dont germinate. If Gibberellins are applied externally, they germinate normally
If gibberellin biosynthesis inhibitors are applied to seeds, they dont germinate as they cannot make the gibberellins needed for them to break dormancy. If inhibition is removed, or gibberellins are applied, the seed germinates
14
Q
What is an example of an Auxin
A
Indoleacetic acid (IAA)
15
Q
What is the general role of Auxins
A
Stimulates growth in plants
16
Q
Where are Auxins made
A
Cells at tip of the shoots and roots, and in the meristems
17
Q
What direction do auxins move
A
Down the stem and up the roots in transport tissue
18
Q
What do Auxins stimulate the growth of
A
Main apical shoot
19
Q
What effect do Auxins have upon the cell wall
A
Plasticity - causes a more stretchy cell wall
20
Q
What affect do Auxins have upon the pH after binding to receptors?
A
Fall to about 5
21
Q
Why is the fall in pH to 5 as a result of auxins affect necessary?
A
To keep cell walls flexible and plastic, as it is the optimum pH for enzymes that carry out this function
22
Q
What happens to auxin as cells mature
A
It is destroyed
23
Q
What affect do the destruction of auxins have upon the pH and cell plasticity
A
pH rises so
Enzymes become inactive so
Cell walls become rigid
24
Q
What are the effects of auxins on plant growth
A
Stimulate growth of main apical shoot
Suppress growth of lateral shoots - prioritising apical shoot
Low concentrations promote root growth/High concs inhibit root growth
25
What do gibberellins do
Affect length of internodes - regions between the leaves on a stem
Involved in germination of seeds and important in elongation of plant stems during growth
26
What is the proof for gibberellin action
Seedlings infected from fungus in Gibberella genus grew tall and thin
Plants without gibberellins are short stemmed
27
What are the benefits of using gibberellins
Dwarf varieties of plants can be bred
Reduces waste, and makes plants less vulnerable to damage from weather and harvesting
28
What is synergism
Different hormones working together, complementing each other and giving greater response than they would on their own
29
What is antagonism
If the hormones have opposite effects eg. one for promoting root growth and one inhibiting it, the balance will determine the response of the plant
30
Why are chemicals so important in coordinating the growth of plants
Plants are multicellular and often large so need coordination
plants don’t appear to have nervous systems so no electrical coordination system
chemicals can be carried in plant transport systems and move from cell to cell to coordinate responses
31
Give three examples of plant hormones and for each give one function in the plant
Auxins - Control cell elongation etc...
Gibberellin - causes stem elongation
Ethene - fruit ripening
32
Why are hormones such as auxins and gibberellins described as plant hormones
Analogous to animal hormones
involved in coordination and control of the plant
made in one place
and carried through the transport system to another region where they have an effect
33
What are some abiotic stresses a plant faces
Day length, cold and heat, lack of water, excess water, high winds, and changes in salinity
34
How do deciduous trees deal with the lack of photosynthesis in colder months
Amount of glucose required for respiration to maintain the leaves, producing chemicals from chlorophyll may be too high
Drops leaves and remain dormant
35
What is photoperiodism
Plants that are sensitive to lack of light in their environment
36
How do plants deal with a lack of light in the environment
Some plants drop leaves
Make other pigments called phytochrome, each absorbing different levels of light
37
How does abcission occur
Falling light levels = fewer levels of auxins
Responds to less auxins by producing ethene, which creates an abcission zone, made up of two layers of cells sensitive to ethene
Initiate gene switching in these cells, resulting in production of enzymes, digesting and weakening cell walls in outer layer called the seperation zone
The vascular layer is sealed off, and fatty material is deposited to form a protective layer, finished my wind and low temps
(pg 446)
38
How to plants prevent freezing
Cytoplasm of plant cells and the sap in the vacuoles contain solutes which lower the freezing point
Some plants produce sugars, polysaccharides, amino acids and proteins which act as an anti-freeze to prevent cytoplasm from freezing
39
How and why do plants hormonally control their stomata
Either to cool down as water evaporates or to conserve water
opening and closing of stomata usually controlled by hormone ABA. Leaf cells release ABA under abiotic stress causing stomatal closure,
Plant roots give an indication to a level of soil water falling hence producing ABA, activating changes in concentration of compounds in guard cells, reducing water poteintial, and turgor, closing the stomata
40
Why is it important for plants to be able to respond to their surroundings
They are rooted to the ground so cannot move their bodies
therefore very important that they
are sensitive so they can grow in the right direction and make the best of the circumstances where they have germinated
41
Why do many trees in temperature climates lose all of their leaves in winter
The amount of photosynthesis that can take place decreases as day length is reduced and
temperatures fall
so the amount of glucose produced by photosynthesis falls
the amount of glucose needed for respiration to maintain leaves through the winter
and produce chemicals to prevent freezing damage increases
it becomes more efficient to lose the leaves and become
dormant until the days lengthen and temperatures increase again
42
Explain how plant hormones are involved in protecting the plant cells from damage in freezing conditions
Falling light levels decreased concentration of auxin leaves produce hormone ethene
ethene initiates gene switching in abscission zone at base of leaf stalk gene switching causes
production of new enzymes new enzymes digest and weaken cell walls in outer layer of abscission
zone (separation layer) vascular bundles sealed off, fatty material deposited in cells on stem side
of separation layer layer forms protective scar when lead falls preventing pathogen entry cells in
separation zone respond to hormonal cues by retaining water and swelling putting more strain on
outer layer further abiotic factors finish process strain is too much and leaf separates from plant
leaving neat waterproof scar
43
Give two more adaptions by which plant cells may be protected against damage by freezing during the winter
Chemicals such as abscisic acid
trigger gene switching
so plants make chemicals such as
sugars or proteins
which lower the freezing point of the cytoplasm
or protect the cells against
damage by ice crystals if they do freeze
44
If there is a sudden spell of freezing weather early in the autumn, many plants which can normally survive winter may be killed. Similarly, if there is a late frost several weeks after warm spring weather, plants that have already survived a harsh winter can die. Explain the difference in the response of the plants in these circumstances compared with the winter months
Protection mechanisms include leaf loss, production of chemicals to act as antifreeze or ice
protection depend on gene switching, and production of new compounds in response to triggers of day length and temperature which take place over several weeks (2);
sudden early frost – cold
protection mechanisms not in place so cells damaged and plant may be killed
late frost – reverse gene switching has occurred as plants move into summer mode
so levels of protection have fallen
and can’t respond to freezing temperatures so cells destroyed
45
What are some physical defences of plants
Thorns, barbs, spikes, spiny leaves, fibrous and inedible tissue, hairy leaves and stings
46
What are some chemical defences of plants to herbivory
Tannins - bitter taste to put animals off eating the leaves, toxic to insects, binding to digestive enzymes produced in saliva and inactivating them eg. phenols
Alkaloids - Affecting metabolisms and poisoning them, or acting as toxins in animals. Prevents seed germination in plants eg. tobacco, nicotine, morphine and cocaine
Terpenoids - Essential oils for a plant but often act as (neuro) toxins to insects and fungi that might attack the plant, or repellant eg. pyrethrin
Pheromones - Affect social behaviour of same species - ON ANOTHER FLASHCARD
47
What do pheromones do
Affects social behaviour of same species
Maple tree releases pheromone when attacked, leaves absorbed which producing callose to protect from attack, as well as warning other trees
Can tell neighbour it is under water stress
when Cabbages are attacked by capterpillars, it sends out a signal, attracting wasps to come and lays its eggs in the catepillars, which are then eaten alive, protecting the plant
If apple trees are attacked by spider mites, they produce VOCs attracting predatory mites which eat the pests
48
What does the minosa pudica do as well has having common defences (alkaloids and prickles) and how does it work
Leaves fold sown and collapse, frightening off herbivores and dislodging insects
Recovers over 10-12 minutes as a result of K+ movement into specific cells, followed by osmotic water movement
49
what is herbivory
Herbivory is the process by which herbivores eat plants
50
Describe two examples of chemical defences against herbivory by animals, explaining how they protect the plant and how they are used by people
Eg. tannins
bitter taste puts animals off eating leaves OR toxic to insects
flavour tea and red wine
Alkaloids
affect metabolism, often poison animals OR prevent
germination in plants OR stop roots of neighbouring plants spreading OR taste bitter
insecticide
terpenoids; toxic to insects OR repel insects; used as insect repellent
51
Why are the chemicals sometimes known as plant pheromones not strictly pheromones
A pheromone is a chemical made by an organism which affects the social behaviour of other members of the same species
plants are not mobile and do not behave socially so pheromones are not entirely appropriate
52
Why is it so important that these chemicals are volatile
They must travel through the air inside or outside of the plant to carry their message
so they must be in the form of a gas or vapour
52
52
Give two examples of how these chemicals may be used to protect a plant against herbivory, including a discussion as to whether your examples are pheromones or not
For example, pheromone produced by maple tree when attacked by insects that is absorbed by leaves on other branches and nearby trees
that make protective
chemicals such as callose (1); pheromone because acts between members of the same species to
affect their behaviour (1); OR not a pheromone as does not affect behaviour, only biochemistry.
Apple
tree attacked by spider mites produce chemicals that attract predatory mites (1); that come and
destroy the spider mites attacking the tree (1); NOT a pheromone as affects the social behaviour of a
different species (the predatory mites) not the same species (apple trees)
53
What is phototropism
The growth of plants in response to light which comes from one direction
54
What is gravitropism
The growth of plants in response to gravity
55
Why must the root grow upwards towards the light source
maximise photosynthesis
56
Why must a plants root grow downwards
To provide support, minerals and water
57
Why is most of the tropisms research conducted on young seedlings
Easy to work with, manipulate, and growing and responding rapidly - so changes show up quickly
58
Why are dicot seeds harder to manipulate than a monocot
Monocots emerge as the shoot is a single spike with no apparent leaves
59
What is the result of unilateral light from the side of a plant shoot, and an explanation
Shoot bends towards light
Shoot is positively photographic, bending occurs behind the tip
(pg 452)
60
What is the result of light from the side of a plant shoot with a shoot tip removed, and an explanation
No response
Tip must either detect the stimulus or produce the messenger as its removal prevents any response
(pg 452)
61
What is the result of light from the side of a plant shoot with a light proof cover placed over the intact tip of shoot, and an explanation
No response
The light stimulus must be detected by the tip
(pg 452)
62
What is the result of light from the side of a plant shoot with a thin, impermeable barrier of mica on the light side , and an explanation
Bends towards the light - movement of chemical down shaded side
Mica on illuminated Side of the shoot allows the hormone to pass, only down the shaded side where increases growth and causes, bending
(pg 452)
63
What is the result of light from the side of a plant shoot with mica inserted on shaded side, and an explanation
No response
Movement of chemical down shaded side is prevented by mica
Auxins travel up and down shaded side
(pg 452)
64
What is the result of light from the side of a plant shoot with tip removed, gelatine block inserted and tip replaced, and an explanation
Bends towards the light - movement of chemical down shaded side
Gelatin allows chemicals to pass through it, but not electrical messages, the bending which occurs must be due to a chemical passing from the tip
(pg 452)
65
Describe the result of the experiment where a shoot is split down the middle and one isn't, and their auxins responses to light
Describe following data
Kept in dark:
Intact shoot: 25.5
Split shoot: 24.1
Unilateral light:
I: 26.2
S: 23.4
Shoot in unilateral light but undivided:
I: 31.0 : 12.5
S: 23.0 : 24.7
(pg 453)
66
Why do plants grow quicker in the dark
In the dark, the biological imperative grow up was rapidly to reach the light to be able to photosynthesise. The seedlings that break through the soil first will not have to compete with the other seedlings for light
Evidence suggests that gibberellins are responsible for the extreme elongation of the internodes, where the plant is grown in the dark.
What is a plant as exposed to the light a slowing of upward growth is valuable resources can be used for synthesising leaves, extend an overall growth, hence the gibberellin level will fall
67
What is an etiolated plant and what are its key features
The rapid upward growth, which takes place in a plant grown in the dark
They are thin and pale, because the plant is deprived of little light chlorophyll that develops in the leaves
68
What are shoots and roots in respect to gravity
Shoots: negatively gravitropic
Roots: positively gravitropic
69
What is a tropism
Plant growth responses to a directional stimulus
70
Explain what is meant by phototropism and geotropisms
Phototropisms: Plant responses to unilateral light
Geotropisms: Plant responses to gravity
71
Describe the different phototropic and geotropic responses in shoots and roots
Shoots positively phototropic and negatively geotropic
roots negatively phototropic and positively geotropic
72
If a block of butter is used in auxin phototropisms experiment instead of the gelatine block, there is no response in the decapitated shoot. Explain how this informs scientists that the message is water soluble
Water soluble substances will pass through gelatin as it is made up of water
butter is a fat so water soluble substances will not pass through it, but fat soluble substances will
gelatine allows auxin to pass through it and so the response to unilateral light is maintained
butter prevents auxin moving through it so the response to unilateral light is lost
indicating that auxin is water soluble and not fat soluble
73
Originally scientists thought geotropisms were the result of auxin movements in response to gravity. Investigate current models of how do you tropisms occur and write a brief report
the importance of space flight in the investigation of geotropism should be mentioned for full marks (1);
the role of the root cap (1);
gravity perceiving cells (1);
amyloplasts and sedimentation under gravity
role of calcium ions
work in space to remove gravity
possibility of magnetic gradients
role of auxin
74
How are plant hormones used commercially
Auxins can produce seedless fruit
Ethene promotes fruit dropping
Cytokinins are used to prevent ageing of ripened fruit and products such as lettuces, and in micropropagation to control tissue development
Gibberellins can be used to delay ripening and ageing in fruit to improve the size and shape of fruits and in beer brewing to speed up the malting process
75
How are plant hormones used to control the ripening of fruit
Ethene involved in natural fruit ripening
used to ripen fruit such as bananas, mangos, tomatoes etc. at desired time
cytokinins and gibberellins can be used to delay fruit ripening
76
Why is it commercially important to be able to control fruit ripening
Ripe fruit is easily damaged in transport
once fruit is ripe it has a finite life before it goes off
If fruit is transported unripe and hard
much less likely to be damaged and doesn’t start to go off
controlled ripening when needed gives uniform product
and minimises waste
77
How do synthetic weedkillers work and why are they important
Weeds interfere with crop plants, competing for light, space, water and minerals, with low toxicity to animals
Hormone Imbalance can interrupt metabolism of the plant and lead to death.
If synthetic dicot auxins are applied as weedkiller, they are absorbed by broad leaved plants (weed), increasing growth so it is unsustainable so they die. Narrow leaved (monocot usually) crop plants (crop) are not affected and continue to grow normally
78
What are climacteric fruits
plants that continue to ripen after the are picked
79
How do hormone rooting powders propagate new plants from plant cuttings
A cutting is a small piece of stem with some leaves on
If this is placed in compost or soil, roots may appear
Dipping the cut stem into hormone rooting powder increases the chances of root forming
