OCR Biology A - 5.1.5 - Plant and Animal Responses Part 1
Nastic responses are non-directional plant movements that occur in response to stimuli, such as light, temperature, or touch, but the direction of the response does not depend on the direction of the stimulus.
Nastic responses
Plant responses in which the direction of the plant response is independent of the stimulus
Key Terms
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 recieve unilateral gravitational stimulus (downwards)
Shoots are -vely geotropic and roots are +vely geotr...
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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 recieve 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 divison 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 abcission 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 addeed to normal seeds they dont 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 |
Research supporting geotropism in shoots | Plants are grown on a slowly rotating drum (clinostat) so gravitational stimulus is applied evenly Plants grow straight in both light and dark |
Research supporting geotropism in roots | Seeds are placed in petri dishes w/ moist cotton wool that are rotated 90 degrees as seedlings grow Cover lid w/ oil - ensure no light is coming in All petri dishes should be in same environment Geotropic response in the roots can be seen every 2 hours |
Investigating role of gibberellin in stem elongation | Plant 40 plants Water 20 plants normally Water other 20 w/ diluted solution of gibberellins Let all 40 grow for 28 days, measuring height every 7 Calculate rate at which plants grew |
IAA | Natural form of auxin responsible for +ve phototropism so plant bends towards light to phostosynthesise and grow taller and grows roots to reach water and nutrients Light stimulus detected by tip of plant |
Central nervous system | Brain and spinal cord Mostly relay neurones in brain Mostly non-myelinated in brain and myelinated in spinal cord |
Role of peripheral nervous system | Ensure rapid comm between the sensory receptors, CNS and effectors |
Divisions of PNS | Sensory nerous systems | Motor nervous system |
Sensory nervous system | Neurons conduct action potentials from the sensory receptor into the CNS |
Divisions of motor nervous system | Autonomic | Somatic |
Somatic nervous system | Motor neurones that conduct action potentials to effectors that are under voluntary control e.g. skeletal muscles Mostly myelinated neurones One single motor neuone connecting CNS to effector |
Autonomic nervous system | Motor neurones that conduct action potentials to effectors that arent under voluntary control e.g. cardiac muscles Mostly unmyelinated neurones At least two motor neurones involved - connected at ganglia |
Divisions of autonomic nervous system | Sympathetic | Parasympathetic |
Ganglia in sympathetic system | Outside CNS, near spinal cord |
Ganglia in parasympathetic system | Closer to effector tissue |
Neurones in sympathetic system | Short pre-ganglionic neurones | Long post-ganglionic neurones |
Neurones in parasympathetic system | Long pre-ganglionic neurones | Short post-ganglionic neurones |
Neurotransmitter in sympathetic system | Noradrenaline |
Neurotransmitter in parasympathetic system | Acetylcholine |
Four sections of the brain | Cerebrum Cerebellum Medulla Oblongata Hypothalamus and pituitary complex |
Cerebrum | Largest part of human brain Two hemispheres connected by corpus callosum Involved in control of speech and higher thought processes e.g. planning a task |
Cerebral cortex | Highly folded Outer part of cerebrum Involved in higher thought e.g. overriding reflexes, conscious thought, intelligence and reasoning |
What is the cerebral cortex divided into | Sensory areas - recieve impulses from sensory neurones Motor areas - send impulses out to effectors Association areas - link info and coordinate approriate respnse |
Cerebellum | Controls muscular movement and balance Connected to cerebrum by pons Coordination of posture |
Medulla oblongata | Controls involuntary processes e.g. heart rate and breathing rate Has specialised centres that recieve info from internal receptors and adjust breathing and heart rate accordingly |
Hypothalamus and pituitary complex | Organises homeostatic responses and controls various physiological processes Info is recieved from hypothalamus and hormones are released via the pituitary gland (controls endocrine system) |