survival and response Flashcards
what is a stimulus?
change in the internal/external environment that results in a response.
what is an effector
muscle or gland that brings about the response.
what is a receptor?
cell that detects a stimulus.
What is taxis? Give detailed example
A directional movement in response to stimulus, eg earthworms move away from light
What is kinesis? Give a detailed example
A random movement in response to stimulus, organisms will increase movement in unfavourable conditions and decrease in favourable conditions. Eg woodlice move more quickly in dry environments.
Outline a method used to investigate how animals respond to changes in light.
A choice chamber. To investigate light – cover one half with black paper. Place 10 woodlice 5 mins record the number of woodlice in light in dark. Repeat/ share class results. Complete a chi square test
define phototropism
: shoots grow towards the light to increase the rate of photosynthesis
define gavitropism
shoots grow upwards and roots grow downwards towards the pull of gravity.
What is the role of IAA in phototropism
IAA is produced by the cell in the tip of the shoot, IAA diffuses down the shoot
IAA accumulates on the shaded side of the stem, causing cell elongation
Shoot bends towards the light
Explain gravitropism in flowering plants
The response of a horizontally growing root to gravity:
Cells in the tip of the root produce IAA, which is then transported along the root. Initially it is transported to all sides of the root.
Gravity influences the movement of IAA from the upper to lower side of the root.
A greater concentration of IAA builds up on the lower side of the root.
IAA inhibits cell elongation so the cells on this side elongate less and the root bends down.
Consider the following facts about IAA:
They are easily synthetically made
They are readily absorbed by plants
They are not easily broken down
They are lethal to some plants in low concentrations
Narrow-leaved plants are less easily killed than broad leaved plants
Suggest ways in which these facts might be relevant to agricultural practice
As they are easily synthetically made and readily absorbed by plants and lethal to some plants in low concentrations makes them useful as herbicides. Narrow-leaved plants are less easily killed than broad leaved plants means that they will kill weed but not crops as they are usually broad leaved. AS they are not easily broken down means that they will stay in the soil and act as a selective weed killer for some time. possible danger could be that as it is not broken down for some time the soil may not be suitable for growing crops for some time or it could pass through the food chain.
What is the autonomic nervous system and how does it work?
The autonomic nervous system is made up of the motor neurones which carry impulses to the involuntary muscles. Involuntary muscles are those over which we generally have no conscious control e.g. cardiac muscle, iris of the eye, gut muscles, muscles in arterioles.
There are two branches of the autonomic nervous system; the sympathetic and parasympathetic. The two branches are antagonistic which means they work in opposition to one another.
Under normal circumstances impulses travel along both branches simultaneously at a low rate but in times of stress the rate of impulses increases in the sympathetic branch and at times of relaxation the rate of impulses is higher in the parasympathetic.
State the difference in function between a sensory neurone and a motor neurone.
Sensory neurone transmits nerve impulse from a receptor to the CNS; Motor neurone transmits nerve impulse from CNS to an effector
What is an axon?
Axon carries the nerve impulse away from the cell body to an effector;
Why do membranes need special channels for the diffusion of charged ions?
Charged ions cannot dissolve in a phospholipids bilayer membrane like that of the axon. Therefore they cannot diffuse across the membrane. The ions need channel protein to produce a hydrophilic channel for diffusion or facilitated diffusion.
Explain why a neurone is active while it is said to be resting.
While the neurone is at rest, or not conducting an action potential, the membrane is actively transporting sodium ions out of the cell and potassium ions into the cell.
How is the resting potential of a neurone maintained?
Actively transporting 2x Potassium ions into and 3x Sodium ions out of the axon establishes the resting potential using a sodium-potassium ion pump;
the resting potential is maintained by the movement of potassium ions out of the axon via potassium ion leakage channels, by facilitated diffusion;
negatively charged proteins inside the axon
-70mV
List the events that results in an action potential
Voltage gated sodium channels open; sodium ions diffuse in down a diffusion gradient;
potential difference across the membrane is reversed +40mV gated sodium channels close and voltage gated potassium channels open and potassium diffuses out of the cell – the potential difference across the membrane reverses.
Distinguish between depolarisation and hyperpolarisation.
Depolarisation – the potential difference across the membrane becomes less negative inside compared with outside;
Hyperpolarisation makes the potential difference across the membrane more negative inside compared to outside.
Explain why it is impossible to stimulate another action potential in a cell membrane that is hyperpolarised.
The cell membrane has a greater potential difference across it than a normal resting potential (-80mV compared to -70mV). This makes it more difficult to depolarise the membrane. As sodium ions enter, the threshold that causes the sodium channels to open is not reached, therefore and action potential is not produced.
How are the sodium ion channels opened?
Each channel has a voltage-sensitive gate. A change in the potential around the gate causes it to move or change shape. This opens the channel.
Explain how diffusion gradients are created so that sodium ions can diffuse into the neurone.
The sodium/potassium ion pumps actively transport ions against their concentration gradients. Sodium ions are transported out of the neurone so that the concentration is low inside the neurone and high outside it. Potassium ions are transported into the neurone so that the potassium concentration is high inside the cell and low outside it.
State the importance of a myelin sheath to the transmission of a nerve impulse.
Myelin sheath speeds up the transmission of a nerve impulse
Explain how the myelin sheath causes saltatory conduction.
The myelin sheath is a fatty material bound to the neurone. The sodium and potassium ions cannot move through the sheath which is incomplete – the neurone membrane is exposed at the nodes of Ranvier, so the action potential jumps from one node to the next.
Explain how the presence of a myelin sheath speeds up the movement of an action potential.
Impulses jump from node to node – gaps in the myelin sheath
Explain how an action potential moves along a non myelinated neurone.
The membrane becomes depolarised ahead of the action potential.
Explain how information about the strength of a stimulus reaches the brain.
By the number of cells responding to the stimulus and the frequency of action potentials from those cells.
Explain what is meant by the term synapse and neurotransmitter.
A synapse is a functional contact between neurones; a neurotransmitter is a chemical that passes a signal from one neurone to another.
List the sequence of events as a nerve impulse is transmitted across a cholinergic synapse.
Action potential arrives at the axon of the synapse.
Ca+ channels open and Ca+ diffuse into the axon terminal.
Synaptic vesicles containing the neurotransmitter diffuse to the presynaptic membrane,
The vesicle fuses with the presynaptic membrane and releases neurotransmitter into the synaptic cleft.
Neurotransmitter Achetylcholine diffuses across the synaptic cleft and binds to the receptors on the post synaptic cleft.
This causes Na+ channels to open on the post synaptic membrane and sodium ions enter depolarising the post synaptic membrane.
This initiates an action potential.
The enzyme acetylcholine esterase breaks down the Ach, which is reabsorbed into the presynaptic knob – this requires energy in the form of ATP.
Explain why the calcium channels need to be voltage gated.
The calcium channels have gates that respond to the voltage change caused by the original action potential. If the calcium ion channels responded to any other stimulus, the synapse would release transmitter substance at the wrong time.
Why is it important that the synaptic cleft contains the enzyme acetylcholine esterase?
It must break down the neurotransmitter acetylcholine. If the Ach is left in the cleft it will continue to stimulate the postsynaptic neurone and cause action potentials.
Suggest why the presynaptic neurone ends in a synaptic knob.
Provides a large surface area which allows more vesicles of Ach to be released and allows the presynaptic neurone to stimulate more than one postsynaptic neurone.
List the roles played by synapses in the nervous system.
Allows the transmission of one direction only from presynaptic to post synaptic membrane.
May be excitatory or inhibitory.
Allow spatial and temporal summation.
Explain how a synapse can be inhibitory.
The neurotransmitter hyperpolarises the post synaptic membrane, so that the depolarisation is not sufficient to reach the firing threshold.
Explain what is meant by the term summation
Summation is the additive effect of impulses at a synapse
The cytoplasm in the synaptic knob has a high proportion of certain organelles. These include smooth endoplasmic reticulum, mitochondria and vesicles. Each organelle has a specific role to play in the functioning of the cell. Describe the role of these organelles and explain why they are found in relatively large numbers in the synaptic knob.
Smooth Endoplasmic reticulum – metabolism of neurotransmitter and with packaging it into vesicles.
Vesicles contain the neurotransmitter ready for exocytosis into the cleft.
Mitochondria – supply the ATP needed to recycle the Ach, making the vesicles and move them towards the presynaptic membrane.
Demyelination is the loss of myelin from the neurones that are normally myelinated. Several degenerative diseases are due to the loss of myelin in certain neurones. The loss of muscle coordination faced by people with multiple sclerosis is due to the degeneration of the myelin sheath in neurones involved in the movement of muscles. The disease is suspected to be an autoimmune disorder – the immune system attacks the myelin sheath. The immune system may cause inflammation due to overproduction of cytokines or other factors such as interferon. What role do cytokines play in the immune system? Suggest how overproduction of cytokines could lead to inflammation and cell damage.
Cytokines are similar to hormones. They carry signals to certain cells in the immune system. They stimulate the action of macrophages, phagocytes, B lymphocytes and T kiler cells. If too much cytokine is released it may overstimulate the action of phagocytic cells and T killer cells which could cause damage too many body cells and produce inflammation
What is a transducer?
to convert the change in form of energy by the stimulus into another form.
Explain why sensory receptors are described as transducers.
They convert one form of energy into another.
What is the difference between the gated channels in the generator region and those further along the neurone?
The gated channels in the generator region have gates that are operated by energy coming from the stimulus. In the remainder of the neurone the gates are operated by potential difference changes. The gates would be opened by the movement of ions in the local circuit or by changes in potential difference s the membrane becomes depolarised.
List the different types of receptors found in mammals.
Photoreceptor; Electro receptor; mechanoreceptor; Thermoreceptor; chemoreceptor
Describe how a named receptor is able to act as a transducer.
Photoreceptors convert light energy into electrical energy; Mechanoreceptors such as pressure receptors convert touch pressure into electrical energy; chemoreceptors such as taste buds convert chemical energy into electrical energy
Describe the structure of a Pacinian corpuscle and explain how it works.
Pacinian corpuscle responds to mechanical pressure. The sensory neurone ending at the centre of the Pacinian corpuscle has a special type of sodium channel in its plasma membrane – stretch mediated sodium channel. These change the permeability of sodium ions when they are deformed. In its resting state, the stretch mediated sodium channels of the membrane are too narrow to allow sodium ions to pass through. When pressure is applied the Pacinian corpuscle becomes deformed and the membrane around the neurone becomes stretched. This stretching widens the sodium channels and allows sodium ions to diffuse into the neurone. This influx changes the potential and depolarises the membrane- producing a generator potential. Generator potential creates an action potential.
Explain why brightly coloured objects appear grey in dim light.
Only rod cells are stimulated by low intensity light. Rod cells cannot distinguish between different wavelengths/ colours of light, therefore the object is perceived as a mixture of boack and white-grey.
At night it is easier to see a star in the sky by looking slightly to the side of it rather than at it directly. Suggest why.
Light from star is low light intensity. Looking directly at the star, light gets focused on the fovea, where there are only cones. Cones respond to high light intensity. Looking at it from the side means that it gets focus on the retina where there are rod cells, these are stimulated at low light intensities so the star can be seen.
Outline the chemical mechanism controlling the heart rate
Sinoatrial node (SAN) initiates a wave of excitement (electrical impulses).
This spreads over the walls of the atria causing them to contract- atrial systole.
The electrical impulses reach the atrioventicular node (AVN). The wave of excitement is delayed through this node which allows the complete contraction of the atria before the ventricles start to contract.
The wave of excitement then travels down highly conductive tissue in the septum called the purkyne tissue/ bundle of His. As it reaches the base of the ventricles it causes the ventricles to contract from the bottom upwards. This is ventricular systole.
The heart then goes into a period of relaxation called diastole
Describe the function of the autonomic nervous system.
ANS controls the involuntary activities of internal muscles and glands
Distinguish between the functions of the sympathetic and parasympathetic nervous system
SNS stimulates effectors and so speeds up activity; prepares for stressful situations eg the flight or fight response PNS inhibits effectors and slows down activity; controls activity under resting conditions, conserving energy and replenishing body reserves. Eg rest and digest
Suppose the parasympathetic nerve connections from the medulla and oblongata to the SAN were cut. Suggest what might happen if a person’s blood pressure increases above normal.
Blood pressure remains high because the parasympathetic system is unable to transmit nerve impulses to the SAN (which decreases HR and would lower BP)
The nerve connecting the carotid artery to the medulla oblongata of a person is cut. This person then undertakes some strenuous activity. Suggest and explain what might happen to the persons:
Heart rate – as the nerve is cut, no action potential can be sent to cardiovascular centre in medulla oblongata so HR remains the same as before exercise
Blood carbon dioxide concentration.
Blood CO2 concentration increases as a result of increased respiration- blood pH will lower and will be detected by chemoreceptors but as nerve is cut no action potential sent to cardiovascular centre in medulla oblongata so no increase in heart rate
Outline the sequence of event that take place at a neuromuscular junction.
Impulse depolarises the pre-synaptic membrane
Calcium channels open and calcium ions diffuse into the pre synaptic knob (motor end plate)
Vesicles fuse with the membrane and release acetylcholine into the synaptic cleft
Acetylcholine diffuses across the gap and binds to receptor proteins on the muscle cell membrane.
The membrane becomes depolarised; the wave of depolarisation passes along the membrane and down the T tubules.
Calcium ions are released from the sarcoplasmic reticulum
Calcium ions cause tropomyosin to move away from the actin binding sites allowing the myosin heads to bind.
List the similarities/differences between a synapse and neuromuscular junction.
Same: both have neurotransmitter in vesicles, which are released by exocytosis and which bind to receptor, this is then broken down in the synaptic cleft.
Different: post synaptic membrane in neuromuscular junction have lots of folds which form clefts. These store AChE. The post synaptic has more receptors than other synapses. It is always excitatory
What are antagonistic muscles? -
Pairs of muscles attached across a joint, which pull in opposite directions.
Distinguish between flexor and extensor muscles
flexor bends a joint; extensor muscles straighten
What muscular action is needed to flex the elbow? –
Contraction of the biceps and brachialis muscles, relaxation of the triceps.
Explain why the elbow is described as a hinge joint
The movement of the joint operates in one plane only, much as the opening of a door around a hinge.
Outline the mechanism of muscle contraction.
Action potential arrives at many neuromuscular junctions simultaneously, causing calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob
Ca2+. Cause synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic gap.
Acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle sarcolemma causing depolarisation.
Action potential travels down the T tubule and cause Ca2+ to be released from sarcoplasmic reticulum
Ca2+ causes tropomyosin molecules that were blocking the binding site on the actin filament to pull away, unblocks binding site on the actin allowing actin myosin cross bridge to form.
ADP molecules attached to the myosin head mean that they are in a state to bind to the actin filament and form a cross bridge
Once attached to the actin filament, the myosin heads change their angle, pulling the actin filament along as they do so and releasing ADP and Pi .This is called the power stroke..
An ATP molecule attaches to the myosin head, causing it to detach from the actin filament
The calcium ions then activate ATPase, which hydrolyses the ATD to ADP and Pi. The hydrolysis provides the energy for the myosin head to return to its original position.
The myosin head, once more with an attached ADP molecule then reattaches itself further along the actin filament and the cycle is repeated as long as the concentration of calcium ions remains high.
Explain how the shape of myosin molecule is adapted to its role.
Myosin has a globular head that is hinged, so can move back and forth. Each myosin head has a binding site for actin and a binding site for ATP
Sprinters have high levels of phosphocreatine in the muscles. Explain the advantage of this.
Phosphocreatine stores the phosphate that is used to generate ATP from ADP in anaerobic conditions. A sprinters muscles often work so strenuously that the oxygen supply cannot meet the demand. The supply of ATP from mitochondria during aerobic respiration therefore stops. Sprinters with the most phosphocreatine have an advantage because ATP can be supplied to their muscles for longer so they can perform better.
Dead dells can no longer produce ATP. Soon after death, muscles contract , making the body stiff- rigor mortis. From your knowledge of muscle contraction explain the reasons why rigor mortis occurs after death.
One role of ATP in muscle contration is to attach to the myosin heads, therefore causing them to detach from the actin filament and making the muscle relax. As no APT is produced after death, there is none to attach to the myosin, which therefore remains attached to actin, leaving the muscle in a contracted state- rigor mortis
