Exam (elaborations)
OCR A Level Biology Plant and Animal Responses2023
OCR A Level Biology Plant and Animal Responses2023
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OCR A Level Biology: Plant and Animal Responses1. Abiotic stresses that plants respond to: Daylength, falling
temperatures, water availability
2. How plants respond to changes in day length: Deciduous plants lose
leaves, enter dormancy
3. How plants know when to respond to changes in day length: The ratio
of Pr and Pfr (Forms of phytochrome)
4. What are Pr and Pfr examples of?: Phytochromes
5. Photoperiodism: Sensitivity to lack of light in the environment
6. Plant responses that are affected by photoperiodism: Breaking
dormancy of leaf buds, timing of plant flowering, when tubers are
formed
7. Why do deciduous plants do leaf abscission?: The temperature is so
low that the amount of glucose required for respiration in the leaves
and to produce chemicals to prevent freezing is greater than the
amount produced by photosyn- thesis
8. How do plants do leaf abscission?: Falling light levels decrease the
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,concen- tration of auxin, more ethene produced, ethene initiates the
switching on of genes in the abscission zone to produce enzymes such
as cellulase, cellulase digests the cell wall in the separation zone,
vascular bundles sealed off, fatty material deposited into cells in
protective layer which forms scar, cells in separation zone retain
water, increases strain on separation zone, strain is too much, leaf
falls
9. How do plants respond to lower temperatures?: Cytoplasm and sap of
plant cells contain solutes to lower freezing point
10.How do plants respond to lower water availability?: Roots provide
early warning system by producing ABA when there is less water, ABA
transported to leaves, binds to receptors on plasma membrane of
guard cells, causes changes in ionic concentration of guard cells,
reduces water potential of cells, guard cells lose turgor, stomata
close
11.Type of plant responses to herbivory: Physical, chemical,
pheromones, folding in response to touch
12.Physical plant responses to herbivory: Thorns, barbs, spikes, spiny
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, leaves, fibrous tissue, inedible tissue, hairy leaves, stings
13.Chemical plant responses to herbivory: Tannins, alkaloids, terpenoids
14.How do tannins protect plants against herbivory?: Bitter tasting,
toxic to insects
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