UNIT 10 Flashcards
(35 cards)
Explain how melatonin plays a part in the control of circadian rhythms.
Controls sleep cycle;
Secreted by the pineal gland;
Production is controlled by hypothalamus;
Photoreceptors in the retina are sensitive to light;
Presence of light detected by photoreceptors adjusts melatonin production in pineal gland;
For diurnal animals melatonin levels are high at night / for nocturnal animals melatonin levels are high in day;
As light increases, melatonin levels drop and the animal becomes active/alert;
Helps synchronise circadian rhythms which affect other physiological processes;
E.g. mating/hibernation;
Distinguish between the nervous and endocrine systems.
Nervous system
Electrical signal
Signal carried by neurons
Fast
Specific
Short-lasting effect
Endocrine system
Chemical signal;
Signal carried by blood;
Slow;
Affects multiple targets;
Longer-lasting effect;
Describe the effects of epinephrine secretion.
Secreted by the adrenal gland;
Activates sympathetic nervous system;
Increases heart rate and breathing rate;
Pupils dilate;
Decreased blood flow to digestive system;
Increased blood flow to muscles;
Increases alertness to surroundings;
Increased blood glucose levels;
Faciliates intense muscle contractions in dangerous surroundings;
Describe how the respiratory centre detects and responds to strenuous exercise.
Respiratory centre in the medulla oblongata;
Strenuous exercise increases respiration by muscles;
Increases CO2 concentration;
Results in low blood pH;
Low blood pH detected by chemoreceptors
In carotid arteries and aorta;
Sends nerve impulses from sensory receptors to respiratory centre/medulla oblongata;
Respiratory centre in medulla oblongata sends nerve impulses via sympathetic nerve;
Increases breathing rate by increasing intercostal muscles/diaphragm contraction;
More oxygen supplied to tissues for respiration;
Cardiovascular centre in medulla oblongata sends nerve impulses via sympathetic nerve towards sinoatrial node;
Increases heart rate by increasing heart muscle contraction;
Baroreceptors and chemoreceptors play an important role in this control. Compare and contrast how these two types of receptors help with the regulation of heart rate.
BOTH
Both located at aorta and carotid arteries;
Both send information to medulla oblongata;
Stimulation can cause change in heart rate
BARORECEPTORS
Located inside aorta and carotid arteries
Sends action potential when blood pressure increases
Detect changes in blood pressure
Detect O2, CO2 levels and pH
CHEMORECEPTORS
Located in tissue outside aorta and carotid arteries;
Sends action potential when change deviates from the norm;
Detect changes in blood pH;
Detect stretching of walls of arteries;
Describe the processes controlled by CNS and ENS in the digestive system.
Swallowing of food and egestion of faeces by CNS;
Under voluntary control;
Peristalsis is a wave of rhythmic contraction of muscles;
Coordinated by ENS;
Under involuntary control;
Explain how auxin promotes cell growth.
Auxin is positively phototrophic / produced in shoot tip;
Light causes auxin to diffuse down cells on the shaded side / light causes auxin to be actively transported out of cells on the illuminated side;
Auxin accumulates on the shaded side;
Auxin stimulates activity of proton pumps in the plasma membrane;
Proton pumps actively transport H+ from cytoplasm into cell wall;
Acidifies cell wall / lowers pH;
Activates enzymes to break cross-links between cellulose microfibrils;
Cell wall becomes more flexible and water moves in by osmosis leading to cell elongation;
Auxin regulates gene expression to promote cell elongation on the shaded side;
State and explain the branch of the nervous system that controls a pain reflex arc.
Peripheral nervous system;
To prevent injury;
For rapid response;
Involuntary response / under unconscious control / automatic response;
Describe how the cerebellum exerts overall control over the voluntary movements of the body.
Cerebellum receives sensory input from sensory receptors when the body moves;
Provides information about current position of body/tension of muscles;
Cerebellum processes this information to form model of body’s position in space;
Compares the intended movement, instructed by the cerebral cortex, with the actual sensory feedback from the body / allows detection of errors in motor execution;
Sends corrective signals to the motor centres in the brainstem/cerebral cortex;
Controls timing and sequencing of movement/precise sequence of muscle contractions required for complex motor tasks;
Important for maintaining balance and posture;
Involved in motor learning and memory/muslce memory/improved motor performance through practice and repetition;
Compare and contrast the sources of the phytohormones cytokinin and auxin, and their roles in plant growth.
BOTH
Both control root and shoot growth;
Both positively affect each other’s production;
Both respond to environmental stresses;
AUXIN
Primarily produced in apical meristem in shoots
Transported to roots
Promotes cell elongation
Promotes main shoot growth
Transported in the xylem
Roles include promoting growth / regulating phototropism / regulating geotropism / promoting root initiation / promoting fruit development / inhibition of leaf and fruit abscission
CYTOKININ
Produced in the root;
Transported to shoots;
Promotes cell division;
Promotes lateral bud growth;
Transported in the phloem;
Roles include delaying senescence / mobilising nutrients from roots to shoots / influencing the opening and closing of stomata / promoting seed germination;
Describe how positive feedback is involved in synchronised and rapid fruit ripening.
Positive feedback is when the output of a system amplifies the system itself;
Ethylene is produced in ripening fruit;
Ethylene speeds up fruit ripening;
As fruit ripens further more ethylene is produced;
As nearby fruit detect ethylene they start to ripen;
Overall ethylene production increase;
Positive feedback synchronises timing of fruit ripening;
Explain how an impulse passes along the axon of a neuron.
Resting potential is -70mV;
Na+/K+ pumps maintain/re-establish the resting potential / 3Na+ out 2K+ in;
More sodium outside than inside at resting potential;
More potassium ions inside than outside at resting potential;
Nerve impulse is an action potential that stimulates a wave of depolarisation along the axon;
If the neuron is stimulated/threshold potential/-50mV reached, VGSC open;
Sodium ions move in at a rapid rate by facilitated diffusion;
Influx of Na+ causes depolarisation;
When membrane potential reaches +30mV, VGPC threshold is reached;
VGPC open and K+ ions diffuse/move out;
This causes repolarisation;
Active transport of K+ into neuron and Na+ out of neuron restores resting membrane potential;
Na+/K+ pumps restore resting potential;
Myelin sheath around the neuron insulates the axon;
Allows rapid transmission of nerve impulse;
Myelin sheath permits saltatory conduction;
Saltatory conduction is when nerve impulse jump from node to node;
Local current allows Na+ diffusion between depolarised region and adjacent region to depolarise;
Explain the principles of synaptic transmission.
Synapse is the gap between adjacent neurons;
Arriving action potential depolarises the pre-synaptic membrane;
Causes VGCC to open;
Influx of calcium ions by facilitated diffusion;
Causes synaptic vesicles to fuse with pre-synaptic membrane;
Vesicles release neutroansmitter into synaptic cleft by exocytosis;
Neurotransmitters diffuse across the synaptic cleft;
Neurotransmitters bind to receptors on post-synaptic membrane;
Causes sodium channels to open and sodium ions diffuse into the postsynaptic neuron;
Initiation of action potential/depolarisation in post-synaptic membrane;
Neurotransmitter broken down/removed by acetylcholinesterase;
Inactivated neurotransmitters reabsorbed into pre-synaptic neuron;
Explain the effect of neonicotinoid pesticides in insect synapses in the central nervous system.
Neonicotinoid has a similar chemical structure to acetylcholine;
Neonicotinoid binds irriversibly to acetylcholine receptors and trigger a sustained response;
Neonicotinoid cannot be broken down by acetylcholinesterase;
Prevents/blocks acetylcholine from binding;
Blocks transmission from CNS;
Blocks signals going to muscle;
Muscle contraction blocked;
Paralysis caused;
Resistance to neonicotinoid pesticides has been observed in some insects. Describe briefly how this resistance could have arisen in populations of insects.
Mutations for resistance in some insects;
Mutation causes breakdown of neonicotinoid/detoxification of pestivide/changes to receptor site;
Natural selection for resistance / resistant insect survive and reproduce / non-resistant killed leaving only resistant insects;
Distinguish between the types of signalling chemicals.
Hormones
Secreted directly into blood;
Transported by blood, slow;
Longer lasting effects;
Neurotransmitters
Secreted when a nerve impulse reaches the end of a presynaptic neuron;
Diffuse across synaptic cleft, rapid;
Short lasting effects;
Cytokines
Secreted by a wide range of cells;
Do not travel far;
Leads to changes in gene expression, multiple effects as one can bind to many;
Calcium ions
Pumped out of cells by calcium pumps in the plasma membrane;
Diffuse into cells through voltage or ligand-gated channels;
Used for cell signalling in neurons and muscle, cause muscle contraction;
Distinguish between hormones and neurotransmitters.
Hormones
Released by glands into bloodstream
From endocrine glands
Slow speed of action
Longer-lasting effects
Target multiple organs or tissues
Steroid, peptide and amine hormones
Neurotransmitters
Transmitted across synapse between neurons;
From neurons in nervous system;
Rapid speed of action;
Short-lasting effects;
Affect adjacent neurons or target cells;
Amino acids, peptides and monoamines;
Distinguish between transmembrane receptors and intracellular receptors, including the initiation of signal transduction pathways.
Transmembrane receptors
Embedded in plasma membrane
Bind ligands outside the cell
Composed of transmembrane proteins with hydrophobic and hydrophilic regions
Trigger conformational changes leading to secondary messenger production
Generally faster
Intracellular receptors
In cytoplasm or nucleus;
Bind ligands that can pass through plasma membrane;
Are hydrophilic and often consists of receptor protein that can interact with DNA;
Activate gene expression by binding directly to DNA;
Generally slower;
Describe the differences between regulation of cell signalling pathways by positive and negative feedback using examples.
Positive feedback enhances or amplifies the response;
Output of a pathway stimulates further activity in the same pathway;
E.g. uterine contractions during childbirth stimulate increased oxytocin release which further enhances contractions;
Negative feedback reduces or inhibits the response;
Output of a pathway inhibits its own production/activity;
E.g. high levels of thyroxine inhibit the release of TSH from the pituitary gland, reducing further thyroxine production;
Explain Quorum sensing bioluminescence.
Process where bacteria coordinate behavior based on cell population density through production and detection autoinducers;
Bacteria vibrio fischeri;
Produces autoinducer that is free to diffuse between cells;
Binds to LuxR receptor protein;
Causes gene expression for enzyme luciferase;
Catalyses conversion of luciferin to oxyluciferin which emits light in the process;
Mutualistic relationship between vibrio fischeri and bobtail squid (high population density of vibrio fischeri = high concentration of autoinducer);
Explain transmembrane receptors for neurotransmitters and changes to membrane potential.
Binding of acetylcholine to acetylcholine receptors causes conformational change and causes ion channels to open;
Allows sodium/calcium ions to flow into neuron;
Influx of ions causes depolarisation;
Explain how G protein-coupled receptors (CPCRs) work.
Epinephrine receptor is a transmembrane integral protein;
Binding of epinephrine causes conformational change in receptor;
Activates G-protein;
G-protein can interact with other intracellular signals or enzymes;
E.g. activates adenyl cyclase which converts ATP into cAMP;
cAMP acts as a second messenger and triggers a cascade of events activating protein kinase A;
PKA phosphorylates various target proteins which leads to increased heart rate/muscle contraction/glycogen breakdown/other metabolic effects typical of fight-or-flight response;
Explain transmembrane receptors with tyrosine kinase activity.
Insulin binds to tyrosine kinase;
Triggers dimerisation of tyrosine kinase;
Causes phosphorylation;
Initiates cascade of events;
Glucose transporters move to plasma membrane which increases glucose uptake;
