PLANT RESPONSES OCR A LEVEL BIOLOGY 5.1.5

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  • Created by: Davina1st
  • Created on: 03-05-22 18:13
What is the difference between abiotic and biotic stress?
Biotic - living abiotic - non living e.g. drought extreme temp
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Where in a plant does growth occur?
In the meristem, where groups of immature cells, still capable of dividing are found.
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What are the meristems found at the tips of roots and shoots called?
Apical
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Meristems that give rise to side shoots and branches?
Lateral bud meristems
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What are lateral meristmes?
Cylinders of meristem tissue near the outside of roots/shoots responsible for them getting wider
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What are intercalary meristems?
Between the nodes where leaves and buds branch off the stem, responsible for the shot getting longer between the nodes.
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What s the definition of tropisms/tropic response?
A directional growth response to an external environmental stimulus. Either towards (positive) or away (negative) from that stimulus. Brought about by plant 'hormones'/'growth factors'
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Much of the work on tropisms involves using seeds and very young seedlings, why?
Easier to work with/manipulate, grow/respond quickly, the response to the environment shows up quickly, in adult plants, different parts of the plant respond differently.
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Give three examples of tropic responses.
Phototropism, geotropism, hydrotropism
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What is a nastic response?
The tropic response is not directional, they do not move away or towards a stimulus. E.g. Mimosa pudica
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What are the four main plant hormones?
Auxins, gibberellins, cytokinin, abscisic acid (ABA), and ethene (gas).
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What is the key role of auxin?
Control cell elongation, prevent leaf fall abscission, maintains apical dominance 9inhibits side shoots)
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What is the key role of gibberellins?
Cause stem elongation, trigger mobilisation of food stores in a seed at germination.
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Abscisic acid stimulates cold protective responses e.g. antifreeze/stomatal closing. True or false?
True.
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Fruit ripening and abscission is the role of which plant hormone?
Ethene
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What is the key role of cytokinins?
Stimulate cell division, regulate shoot meristem size, leaf/shoot growth
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How does a seed germinate?
Seed absorbs water, embryo plant activated, gibberellin produced, proteases break protein into a.a, used to make amylase, amylase breaks down starch=glucose=ATP, energy for cell division, causes embryo to burst out of seed coat.
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Describe some experimental evidence for the role of gibberellins in seed germination
Mutant varieties of seeds are bred which lack the gene for them to make gibberellins, so the seeds do not germinate. If gibberellins are applied externally, they germinate normally.
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Where is auxin made?
In shoot tip and root tip, they then diffuse/actively transported to where they're needed.
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How does auxin work?
Binds to specific receptors on plant cell walls, causes release of H+ into cell wall, lowers the pH, cellulose made more flexible, expansin enzyme activated, allow cell to elongate. Once cell ,matures, the auxin is destroyed.
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What is the distribution of auxin affected by? Explain why/how
Light intensity, if auxin is distributed equally, the shoot grows straight up, if unequal, the side with a higher concentration grows more than the other casing it to bend. Shoots positively phototropic bend towards light.
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Why wont a shoot show positive phototropism if the shoot tip is cut off?
Auxin is produced in the shoot tip
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Generally with shoots, the higher the auxin concentration...?
The faster they grow (until high conc are reached and then growth is inhibited).
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With roots, very low concentrations of auxin stimulate growth. True or false?
True, but then as conc increases, growth of roots is inhibited.
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What is the term given to the suppression of side shoot growth?
Apical dominance
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What are the advantages of apical dominance?
Allows plants to grow tall quickly, meaning they can get more light for phs and outcompete neighbours. Survival advantage
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Crop breeders sometimes breed plants with fewer gibberellins to have shorter stems. Why is this useful?
Shorter plants=less likely to be damaged by strong winds/heavy rainfall. Sometimes only grains are eaten, not the stem, giving a financial benefit to the farmer. Stems which are low value can be used as animal beddings.
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What is synergism?
When plant hormones work together, complimenting each other - giving a greater response than they would on their own.
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What is antagonism?
When plant hormones have opposite effects to each other e.g. one promotes growth while the other inhibits it. The balance between the two=plant response.
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What is the name given to plants grown in the dark?
Etiolation
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Why are plants that are grown in the dark pale in colour?
They are deprived of light, so they have little chlorophyll, without chlorophyll they're pale.
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Which crop plants are forced to grow in the dark?
Rhubarb - we eat the stem so want it to grow quick.
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Why is it useful for deciduous plants to lose their leaves in the winter?
Shorter days/lower light intensity=less photosynthesis possibel unable to produce much glucose. Becomes inefficient to keep leaves as they are using glucose in respiration. Trees with leaves more likely to be damaged/blown over in high winds/rain.
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How doe plants lose their leaves?
Less auxin, more Ethene, switches on genes for new enzymes to be made, enzymes weaken cells in abscission layer, lipids deposited on other layer, abiotic factors put strain on leaf and it falls off. Lipid waterproof scar left.
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Why would it matter if plant cells freeze?
Disruption to membrane structure, ice crystals damage bi-layer structure, damage to enzyme function, cell death.
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How do some plants protect their cells from freezing to death?
Cytoplasm and vacuole sap contains solutes, which lower freezing point. In winter, some plants produce extra sugars and amino acids to act as antifreeze.
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How do stomata work to reduce abiotic stress to a a plant?
Open - cool plant down. Closed - conserve water e.g. in times of drought or water stress.
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What hormone is involved in stomatal closure?
Abscisic acid (AbA)
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How does ABA work to close the stomata?
ABA binds to receptors on csm of guard cells, Ca2+ enter the pH of the cytoplasm increases (more alkaline). K+, NO3- and Cl- leave the cell, water potential decreases and water is moved by osmosis into surrounding cells=loss of turgor and stoma close
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As soil water potential increases/soil is less dry, ABA conc increases. True or false?
False - as soil water potential falls/soil is drying out ABA is released and increases with conc.
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What hormone is used in fruit ripening and why?
Ethene, used for fruit that ripen after they've been harvested e.g. bananas, tomatoes and avocados.
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What hormone is used in rooting powder and why?
Auxin - applied to cut shoots to stimulate production of root=easy propagation of plants. Essential in micropropagation.
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What hormone is used in weed killers and why?
Synthetic dicot auxins - absorbed by weeds which affect their metabolism, need to be made as weeds interfere with crop plants for light, space, water and minerals.
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What is a physical defence to herbivore stress?
Thorns, spikes, spiny leaves, inedible tissue, hairy leaves, stings to protect themselves and discourage other animals from eating them.
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What is a chemical defence to herbivore stress?
Tannins - phenols, bitter taste, toxic to insects, bind to digestive enzymes produced in saliva and inactivate them. Alkaloids poisonous to animals e.g. caffeine produced by coffee bush and niccotine from tobacco plants.
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What is a pheromone?
A chemical made by an organism which affects the social behaviour of other members of the same species. e.g. If a a maple tree is attacked by insects it sends pheromones so that other plants can make Callose for protection.
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Other cards in this set

Card 2

Front

Where in a plant does growth occur?

Back

In the meristem, where groups of immature cells, still capable of dividing are found.

Card 3

Front

What are the meristems found at the tips of roots and shoots called?

Back

Preview of the front of card 3

Card 4

Front

Meristems that give rise to side shoots and branches?

Back

Preview of the front of card 4

Card 5

Front

What are lateral meristmes?

Back

Preview of the front of card 5
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