Back to AI Flashcard MakerBiology /LGS A-Level OCR Biology - Unit 5 - Plant and Animal Responses Part 1
LGS A-Level OCR Biology - Unit 5 - Plant and Animal Responses Part 1
This deck covers key concepts from Unit 5 of the OCR Biology syllabus, focusing on plant and animal responses, including tropisms, plant hormones, and mechanisms of growth and adaptation.
Nastic responses
Plant responses in which the direction of the plant response is independent of the stimulus
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Key Terms
Term
Definition
Nastic responses
Plant responses in which the direction of the plant response is independent of the stimulus
Herbivory
Consumption of plants
Abiotic
Physical
Tropisms
Directional growth responses in plants
Phototropisms
Influenced by light e.g. plants grow towards light to photosynthesise due to auxin moving unilaterally
Geotropism
Influenced by gravity; Plants receive unilateral gravitational stimulus (downwards); Shoots are -vely geotropic and roots are +vely geotropic
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| Term | Definition |
|---|---|
Nastic responses | Plant responses in which the direction of the plant response is independent of the stimulus |
Herbivory | Consumption of plants |
Abiotic | Physical |
Tropisms | Directional growth responses in plants |
Phototropisms | Influenced by light e.g. plants grow towards light to photosynthesise due to auxin moving unilaterally |
Geotropism | Influenced by gravity; Plants receive unilateral gravitational stimulus (downwards); Shoots are -vely geotropic and roots are +vely geotropic |
Thigmotropism | Influenced by touch; Shoots of climbing plants e.g. ivy winding around other plants or solid structures for support |
Chemotropism | Influenced by chemicals; Pollen tubes grow down the style of a plant towards the ovary where fertilisation takes place |
Plant hormones | Cytokinins; Abscisic acid (ABA); Auxins; Giberellins; Ethene |
Effects of cytokinins | Promote cell division; Delay leaf senescence - increases shelf life; Overcome apical dominance - lateral growth; Promote cell expansion |
ABA | Inhibit seed germination and growth; Stimulate cold protective responses; Cause stomatal closure when the plant is stressed by low water availability |
Effect of auxins | Promote cell elongation in roots - low conc; Promote shoot growth/ demote root growth - high conc; Inhibit growth of side shoots; Inhibit leaf abscission; Selective weedkiller; Promote cell division in cambium |
Effect of gibberellins | Promote seed germination - break bud dormancy (works against ABA); Promote growth of stems - elongation of internodes; Develop seedless fruit and fruit setting; Acts synergistically w/ auxin |
Effect of ethene | Promote fruit ripening - starch to sugar and breaks down chlorophyll and cell wall; Stimulates cells in abscission zone to expand and breaks cell wall causing leaf to fall off; Opp to auxin |
How do plants avoid herbivores | Tannins - phenolic compounds; toxic to herbivores and microorganisms; Alkaloids - make plants taste bitter; Mimosa leaves fold up in response to touch - scares insects |
Abscission in deciduous plants | Decreases production of auxin; More sensitive to ethene; Gene expression of enzymes in abscission zone; Cellulase breaks down cell walls in separation layer of abscission zone; Vascular bundles sealed off, fatty materials for neat, waterproof scar |
Mechanism of seed germination | Seed absorbs H2O and activates embryo; Begins to produce gibberellins; Gene expression –> produces amylases and proteases to break down starch food stores; Glucose is used as a respiratory substrate and in protein synthesis |
Mechanism of stomatal closure | Levels of soil water falls; Roots produce ABA; Transported and binds to guard cells; Increases pH, charged particles move out; Increases wp, water moves out; Loss of turgor closes stoma |
Proof of gibberellins causing seed germination | Mutant varieties that lack gibberellin do not germinate but w/ external gibberellin they do; When gibberellin inhibitors are added to normal seeds they don't grow |
Apical Dominance Effect | Auxin produced at the apex, inhibits growth of lateral buds |
Experimental evidence for apical dominance | Removal of apical buds allows lateral bud to grow; Auxin/synthetic auxin placed on cut tip continues to inhibit the growth of side shoots; Plant 30 plants of same type, age, genotype and weight in same soil; Remove tip of 10 and apply auxin paste; Remove tip of another 10 and add paste w/out auxin; Leave last 10 as control; Sig. increase of no. of side shoots grown in first 10 |
Recent research on apical dominance | Auxin stimulates production of ABA (inhibits growth); When apex is removed as is the source of auxin, ABA levels decrease; Most cytokinins go to tip so when tip is removed cytokinins spread evenly around plant promoting growth |
Where does growth occur in plants | Apical meristems; Lateral bud meristems |
Mechanism of cell elongation by auxin | Tip produces auxins, diffuses down; Promotes active transport of H+ into cell walls; Lowers pH, optimum pH for expansins; Breaks H bonds within cellulose; Reduces rigidity and H2O enters |
Confirming auxin as the hormone that causes growth | Impregnated agar blocks w/ diff conc. of auxin; Placed them on cut shoot tips; Same effects as in reg. shoots; Curvature is directly proportional to conc of auxin used |