Unit 5 - Plant & Animal Responses Flashcards
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)
Reflex reactions
Responds to changes in the environment but not involving the brain
Sensory –> relay –> motor
Brain may be informed but doesn’t coordinate
Survival; fast, involuntary and not learned (innate)
Cranial reflex
Nervous pathway passes through the brain
What makes something an reflex arc
Receptor and effector in same place
Blinking reflex
Cranial reflex
Corneal - object toucing eyes
Optical - Light hitting back of eye (retina)
Patnway for corneal blinking reflex
Receptor
Sensory neurone on cornea
Sensory centre on pons
Non-myelinated relay neuron passes action potential to motor neurone
Motor neurone passes out of brain to facial muscles
If the corneal blinking reflex is to be overridden
Sensory neurone on cornea
Myelinated relay neurones inform brain
Allows reflex to be overriden (inhibitory neurone) - faster so reflex can be overriden before it happens