Flashcards in 5.5 - Plant and Animal Responses Deck (72):
Why do plants respond to stimuli?
To increase their chance of survival by responding to changes in their environment.
Give an example of plants responding to a biotic stress.
Herbivory – being eaten by plants.
Give an example of plants responding to an abiotic stress.
Anything that is non-living – drought, extreme cold.
Describe 3 chemical defences of plants to herbivory.
Tannins – both taste bitter & make the plant hard to digest.
Alkaloids - taste bitter, noxious smell & poisonous characteristics.
Pheromones - signalling chemicals that produce a response in other organisms.
Describe a physical defence of plants to herbivory & name a plant that does this.
Some plants fold up in response to being touched e.g. Mimosa pudica.
Why do plants fold up in response to herbivory?
May knock off the insect eating them or scare the organism eating them.
What is the name given to a plant responding to touch or contact?
What are tropisms?
A directional growth response to a stimulus.
What is geotropism, phototropism & hydrotropism?
A directional growth response to gravity, light or water.
Describe a positive and negative tropism.
Positive – grows towards the stimulus.
Negative – grows away from the stimulus.
Where are plant hormones produced? Where do they act?
Produced in growing regions & move to regions where they are needed. Specific hormones have specific shapes that only bind to complementary receptors on the plasma membrane of target cells.
Where does cell division take place in a plant?
Only in meristematic regions of the plant – tip of shoots & roots, cambium & pericycle.
How does growth occur elsewhere in the plant? What is this called?
Growth occurs by increasing the size of the cell by making cell walls loose & stretchy & absorbing water into the vacuole. This is called cell elongation.
What effect does Indoleacetic acid (IAA) have on the growth of shoots & roots?
Stimulates elongation in shoots. Inhibits elongation in roots.
Where is IAA produced?
Meristematic tissue – tips of shoots and roots.
How is IAA moved around the plant to control growth over short & long distances?
Over short distances - moves by diffusion & active transport.
Over long distances - moves via the phloem.
Where does IAA move to in shoots in response to light?
To the shaded areas to stimulate elongation in these cells.
Where does IAA move to in response to gravity?
It accumulates on the lower side & stimulates cell elongation in shoots or inhibits cell elongation in roots.
What are the roles of plant hormones?
Role in: Leaf loss. Stimulated by: Ethene. Inhibited by: Auxins.
Role in: Seed germination. Stimulated by: Gibberellins. Inhibited by: Abscisic acid.
Role in: Stomatal closure. Stimulated by: Abscisic acid. Inhibited by: Not inhibited, only stimulated.
Role in: Apical dominance. Stimulated by: Auxins stimulate the growth of the apical bud. Inhibited by: Auxins inhibit the growth of side shoots from the lateral buds.
Role in: Stem elongation. Stimulated by: Gibberellins. Inhibited by: Not inhibited, only stimulated.
What are the commercial uses of plant hormones?
Hormone: Ethene. Commercial use: Fruit ripening. Effect: Stimulates enzymes that - break down cell walls; break down chlorophyll; convert starch into sugars.
Hormone: IAA (auxin). Commercial use: Rooting powder. Effect: Stimulates cuttings to grow roots; lots of the same plant (cloning) can be grown quickly & cheaply.
Hormone: High levels of IAA. Commercial use: Selective weed killer. Effect: Stimulates the plant shoots of broad-leaved plants (dandelion) to grow so rapidly that it exhausts the plant & it dies. IAA has little effect on narrow leaved plants.
Explain the control of leaf loss by plant hormones.
Ethene stimulates abscission cells (layer of cells at the bottom of the leaf stalk) to expand, breaking cell walls & cause the leaf to fall.
Auxins are produced by young leaves & inhibit leaf loss.
Explain the control of seed germination by plant hormones.
Gibberellins are produced by the embryo. Gibberellic acid (GA) stimulates production of amylase (and other enzymes) by the aleurone layer. Amylase breaks down starch to maltose in the endosperm. Maltose is then broken down into glucose (by maltase) & used to provide energy for growing embryo.
Explain the control stomatal closure by plant hormones.
Abscisic acid binds to receptor on guard cell membrane. The receptors activate a cascade of events that result in specific ion channels opening. Ions move out of the guard cell, raising the water potential. Water leaves guard cells by osmosis. Guard cells become flaccid & stomata close.
What would trigger the stomata to close?
When there is too much water loss through transpiration or in response to detecting an invading pathogen.
Darkness / night time when no photosynthesis takes place so no need for gas exchange.
What is apical dominance?
The growth of the main, central stem of the plant is dominant over (i.e., grows more strongly than) other side stems. Apical dominance prevents side shoots from growing.
In what way does apical dominance help a plant to survive?
Allows a plant to grow very fast, past the smaller plants where there is competition for light. Saves energy as prevents the side shoots from the same plant competing with the shoot for light.
Why do side shoots grow when you remove the apical bud?
The apical bud produces auxins. If removed side shoot growth will no longer be inhibited and start growing by cell division & elongation.
Why do tall trees have large side shoots towards the base?
Auxins become less concentrated as they move away from the apical bud to the rest of the plant. At the base of the tree there is a very low auxin concentration and so side shoot growth is not inhibited.
Why are dwarf varieties of plants short?
A mutation will result in a non-functional gene for gibberellin. Without this hormone, stem elongation cannot be stimulated.
What happens when dwarf varieties of plant are treated with gibberellin?
Their stems elongate and they get taller.
What is the autonomic nervous system?
Part of the nervous system responsible for controlling involuntary motor activities.
What is the central nervous system?
Brain and spinal cord.
What is the peripheral nervous system?
Sensory and motor neurons connecting receptors and effectors.
What is the somatic nervous system?
Motor neurons under conscious control.
Describe the division of the nervous system.
CNS and PNS. PNS divided into sensory and motor systems. Motor system divided into somatic - neurones connecting muscles under conscious control, one neuron for each effector. Autonomic - neurones connecting muscles and glands under unconscious control - two or more neurones for each effector, neurones connected via ganglia.
Describe the subdivision of the autonomic nervous system.
Sympathetic. Stress - fight, flight, flirt, prepares body for activity. Effects: Increase in heart rate; pupils dilate; ventilation increases; reduced digestion; orgasm. Noradrenalin as neurotransmitter.
Parasympathetic. Relax - energy conservation. Effects: decrease in heart rate; pupils constrict; ventilation rate decreases; increased digestion; arousal. Acetylcholine as neurotransmitter.
Name the four main structures of the brains and outline their roles.
Cerebrum: Organises higher thought processes, conscious thought and memory, emotional responses.
Cerebellum: Coordinates movement and balance.
Hypothalamus and pituitary complex: Organises homeostatic responses.
Medulla oblongata: Coordinates autonomic responses.
What is the cerebral cortex?
Outermost layer of cerebrum. Thin layer of nerve cell bodies. Subdivided into areas with specific responsibilities:
Sensory - size and complexity linked to sensitivity of receptors.
Association - compares inputs with experiences to make judgements.
Motor - sends action potentials to effectors, size and complexity linked to the complexity of movements/parts of body; left hand side of cortex coordinates right hand side of body and vice versa.
What is the cerebellum?
Contains over half of all neurones in the brain. Coordinates balance and movement. Receives and interprets from many receptors including retina, inner ear and muscle spindle fibres.
How do the cerebral cortex and cerebellum coordinate movement?
Cerebral cortex processes conscious decision to contract muscle. Cerebellum coordinates complex responses. Connected by the pons. Coordination and balance require practice; skills are learnt. Programming of coordinated response strengthened through practice and is automatic.
What is the role of the hypothalamus?
Hypothalamus controls homeostatic responses. Temperature regulation. Osmoregulation. Contains sensory receptors. Acts by negative feedback.
What is the role of the pituitary gland?
Acts in conjunction with the hypothalamus. Posterior lobe linked to hypothalamus by neurosecretory cells. Hormones made in hypothalamus pass through neurosecretory cells to pituitary gland. Anterior lobe produces hormones which are released into blood by releasing factors.
What is the role of the medulla oblongata?
Controls non-skeletal muscle. Cardiac, smooth muscle. Regulates vital processes. Cardiac centre - heart rate. Vasomotor centre - circulation and blood pressure. Respiratory centre - rate and depth of breathing.
What is a reflex action?
A response to a change in environment that does not involve brain processing. The brain is informed of the reflex but does not coordinate it. Important for survival.
Outline the blink reflex.
Cranial reflex - passes through the brain but does not involve thought processes. Receptor and effector in same place - reflex arc. Stimulated by: Object in eye, bright light, loud sounds, sudden movement close to eye.
Outline the corneal reflex.
Contact with cornea distorts receptors. Sensory neurone enters via pons. Synapse connects sensory neurone to relay neurone, action potential passed to motor neurone. Eyelid blinks. Rapid (0.1s).
How is the corneal reflex overridden?
Myelinate neurone in pons pass action potential from sensory neurone to cerebral cortex. Thought processes can override reflex via inhibitory action potentials.
Outline the knee jerk reflex.
Spinal reflex, coordination of balance. Muscle in quadriceps (front of thigh) attaches to patella tendon. Patella tendon stretched over knee cap and connects lower leg bones to knee. When patella tendon is stretched spindle fibres detect increase in muscle length. Unexpected stretch causes reflex contraction of quadriceps. Leg straightens, balance regained.
Note reflex has no relay neurone, no synapse so quicker response, reflex cannot be inhibited.
Inhibitory action potentials are sent to synapse in the reflex arc to prevent contraction of opposing muscles during walking and running.
Describe the physiological changes associated with the fight or flight (and flirt!) response and their role in survival.
Change: Pupils dilate. Survival role: More light enters eye, retina more sensitive, vision enhanced.
Change: Heart rate and blood pressure increase. Survival role: More oxygen and glucose to muscles, increased removal of carbon dioxide and toxins.
Change: Arterioles to digestive system and skin constrict, arterioles to muscles and liver dilated. Survival role: Blood flow diverted to muscles and restricted to where it is not needed.
Change: Blood glucose levels increase, metabolic rate increases. Survival role: Increase in respiration in muscles, increase in energy for contraction.
Change: Ventilation rate and depth increases. Survival role: Increase in gas exchange, increase in oxygen needed for aerobic respiration.
Change: Erector pili muscles in skin contract. Survival role: Hairs stand up, increase in apparent size associated with aggression.
Change: Endorphins released from brain. Survival role: Natural painkillers, reduce impact of pain/wounding on activity.
Describe the coordination of the fight or flight response.
Receptors detect threat - eyes, ears, nose. Inputs fed to sensory centre in cerebrum. Cerebrum passes impulses to associated centres. If threat is recognised cerebrum stimulates hypothalamus.
Hypothalamus increases activity of sympathetic nervous system. Adrenal medulla secretes adrenaline. Glands and smooth muscle activated. Neural activity and hormones combine to form response
Hypothalamus increases release of hormones from anterior pituitary. CRH stimulates release of ACTH causing adrenal cortex to secrete corticoid hormones- increase in metabolism of carbohydrates needed for respiration. TRH stimulates release of TSH causing thyroid to secrete thyroxine- increase in metabolic rate, increase in synthesis of ATP.
Describe the role of adrenaline as a second messenger.
Adrenaline binds to cell surface receptor on plasma membrane of target cell. Receptor associated with G protein on inner plasma membrane. Activates adenyl cyclase. Adenyl cyclase cleaves ATP to form cyclic AMP. cAMP activates enzyme cascade. Effect of cascade determined by type of cell eg increase in rate of respiration in muscle cells, widening of pupil in eyes.
What does myogenic mean?
Cells initiate own beat at regular intervals. Atrial muscle has higher myogenic rate than ventricular.
Describe the roles of the cells that regulate the heart rate.
Cells of sinoatrial node, SAN. Region of tissue lying in upper wall of left atrium. Initiates action potential that travels as wave of excitation through atrial walls, causing contraction. Wave of excitation propagated via atrioventricular node, AVN, through Purkinje fibres to apex of heart. Wave of excitation passes through ventricular walls, causing contraction.
Which part of the brain regulates the frequency of excitation?
Cardiovascular centre. Lies in medulla oblongata.
Name the nervous system that regulates heart rate.
Describe the regulation of heart rate via the nervous system in response to stimuli from sensory receptors.
Action potential propagated from medulla oblongata down accelerans nerve to SAN. Causes release of noradrenalin at SAN. Heart rate increases. Action potential propagated from medulla oblongata down vagus nerve to SAN. Causes release of acetylcholine at SAN. Heart rate decreases.
Note that the nervous system does not initiate muscular contraction, it regulates the rate at which the heart beats.
Describe the role of stretch receptors in muscles heart rate regulation.
Stretch receptors in muscles detect movement. Impulses pass to cardiovascular centre. The greater the stretch, the higher the demand for oxygen due to increased movement. Heart rate increased via accelerans nerve. Decrease in stretch, decrease in heart rate via vagus nerve.
Describe the role of stretch receptors in the carotid heart rate regulation.
Stretch receptors in wall of carotid sinus monitor blood pressure. Increase in exercise equals increase in blood pressure as heart beats harder and faster. If pressure rises too high stretch receptors send impulse to cardiovascular centre. Heart rate decreased via vagus nerve.
Describe the role of chemoreceptors in heart rate regulation.
Chemoreceptors in carotid arteries, brain and aorta monitor pH of blood. Increase in exercise causes increase in carbon dioxide dissolved in blood as carbonic acid. pH drops, affecting affinity of haemoglobin for oxygen. Change in pH detected by chemoreceptors, action potential propagated to cardiovascular centre. Usually heart rate increases via accelerator pathway to remove carbon dioxide form blood and raise pH. As pH returns to normal chemoreceptors detect change. Accelerator pathway reduced, heart rate slows.
Describe the action of an artificial pacemaker.
Electrical device fitted beneath skin and fat on chest or within chest cavity. Delivers electrical impulse either to SAN or directly to ventricle muscle. Rate responsive artificial pacemakers mimic biological responses. Sensors in arterial-venous system to detect changes in blood pH, oxygen/ carbon dioxide ratios and concentrations and ATP. Heart rate is modified accordingly.
Name the three types of muscle.
Cardiac - found in the heart
Involuntary - smooth muscle under autonomic regulation e.g. gut, iris.
Skeletal - striated, under voluntary control.
Describe the structure and function of involuntary muscle.
Individual tapered cells, 500μm x 5μm. Each cell contains a nucleus, actin and myosin bundles. Found in tubular structures- digestive system, circulatory system.
Describe the structure and function of cardiac muscle.
Cells form long fibres which branch to form cross bridges. Cross bridges ensure even spread of electrical stimulation across walls of heart. Cells joined by intercalated discs formed by fusion of cell surface membranes. Forms gap junctions for free diffusion of ions between cells. Action potential passes freely and easily through cardiac muscle. Purkinje fibres modified to carry electrical impulses.
Describe the structure and function of skeletal muscle.
Cells form fibres 100μm in diameter. Multinucleate fibres surrounded by sarcolemma. Specialised cytoplasm, sarcoplasm contains many mitochondria and extensive sarcoplasmic reticulum. Fibres arranged as contractile units, myofibrils. Myofibrils subdivided into sarcomeres. Sarcomeres contain actin and myosin. These give striated appearance.
Describe the sequence of events at the neuromuscular junction that lead to muscle contraction.
Action potential arrives at end of axon. Calcium ion channels open, calcium ions flood into axon. Vesicles containing acetylcholine move to and of axon and fuse with membrane. Acetylcholine molecules diffuse across junction and fuse with receptors on sarcolemma. Sodium ion channels open, sodium ions diffuse into muscle fibre. Sarcolemma is depolarised. Wave of depolarisation passes along sarcolemma and into transverse tubules.
Describe the structure of the thin filaments.
Two chains of actin subunits twisted together. Actin wrapped by tropomyosin to which troponin complex is bound. Troponin complex comprised of: one polypeptide to bind actin, one polypeptide to bind tropomyosin, one polypeptide to bind calcium ion.
Describe the structure of the thick filaments.
Bundles of myosin. Each molecule has two protruding heads at each end. Heads are mobile and can bind to actin.
Describe the structure of a myofibril.
Thin filaments make up the light band, I band, held at Z line. Thick filaments make up the dark band. Thick and thin filaments overlap except at midline. This is the H zone.
Describe the sliding filament hypothesis.
During contraction light band and H zone shorten. Z lines move closer together.Sarcomere shortens and thickens as actin and myosin slide past one another.
Describe the series of events as a muscle contracts.
Action potential passes along sarcomere and into t-tubules. Action potential carried to sarcoplasmic reticulum, calcium ions released into sarcoplasm. Calcium ions bind to troponin, shape alters. Tropomyosin moves and binding site on actin uncovered. Myosin heads attracted to actin, bind forming cross-bridges between filaments. Myosin head moves, pulling actin filament past myosin filament. Myosin head detaches from actin filament.
Describe the role of ATP in muscle contraction.
Myosin head acts as ATPase, hydrolyses ATP to ADP + Pi. Myosin head forms cross-bridge to actin filament. Myosin head tilts back, pulling actin filament, power stroke. ADP and Pi release from myosin filament. After powerstroke ATP attached to myosin and breaks crossbridge. ATP hydrolysed to ADP and Pi, energy released used to reset myosin head.