Abdel Elniel – Option E

Option E: Neurobiology and Behaviour

E1 Stimulus and response

E.1.1. Define the terms stimulus, response and reflex in the context of animal behaviourStimulus: A realised change in the environment (internal/external) detected by a receptorResponse: A change in the organism produced by the stimulusReflex: A rapid, unconscious response to a stimulus.

E.1.2. Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses and effectors in the response of animals to stimuliReceptors: Detect the stimulus, can be sensory cells or nerve endings of sensory

neuronsSensory neurons: Convey information from receptors into the CNSRelay neurons: Connect neurons i.e. receives information from sensory neurons and relays

it to motor neuronsMotor neurons: transmit signals from relay neurons to the effectorsSynapses: functional connections between neurons, or neurons and other cells.

Neurons have thousands of synapses, most connect axons to dendrites, other types include; axon to cell-body, axon to axon, and dendrite to dendrite.

Effectors: Carry out a response after receiving a message from a motor neuron; can be muscles, respond by contracting, or glands, respond by secreting.

E.1.3. Draw and label a diagram of a reflex arc for a pain withdrawal reflex, including the spinal cord and its spinal nerves, the receptor cell, sensory neuron, relay neuron, motor neuron and effecter.

Information obtained from http://www.slideboom.com/presentations/250249/IB-Biology-Option-E&h=bd50a – Mr. Lajos Papp, The British International school, Budapest

A reflex is an automatic response following a sensory stimulus. It is not under conscious control and is therefore involuntary. The pathways involved are called the reflex arc.Pain withdrawal reflex: When a person comes into contact with something painful, a reflex occurs.

Neurons in the skin are activated, sending sensory impulses to the spinal cord. Relay neurons send the impulse to motor neurons, causing a muscle contraction and moving the affected limb away from harm. Certain neurons will send impulses to the brain, where the feeling of pain is processed. This reflex is extremely important; it prevents extreme tissue damage when in contact to danger.

E.1.4. Explain how animal response can be affected by natural selection, using two examples.Offspring inherit successful types of response from their parents. Sometimes the environment of an animal species changes and natural selection may favour a different type of response.

BlackcapBreed in summer across Europe. Until recently populations in Germany migrated to Spain for the winter, now 10% of the birds migrate to the UK. Egg experimentation has shown that the migration is a genetic development. The blackcaps that migrate to the UK tend to fly west; those travelling to Spain usually fly southwest. Even though they do not follow their parents, all the birds tend to fly in the same direction as their parents.

Great TitGreat tit breeds in spring and early summer in Europe. The timing of egg laying is genetically determined. The day length can determine the time of year. Recently the mean date of an egg laying has become earlier. Adults that breed earlier have a more successful reproduction. This is due to earlier openings of leaves on deciduous trees and earlier peak in the biomass of invertebrates feeding on tree leaves.

E2 Perception of stimuli

E.2.1. Outline the diversity of stimuli that can be detected by human sensory receptors, including mechanoreceptors, chemoreceptors, thermoreceptors and photoreceptors

Mechanoreceptors:Respond to mechanical stimuli; gravity, vibration (sound) and pressure. Touch and pressure receptors are found near the skin surface. The ear incorporate numerous mechanoreceptors, hair cells in the inner ear vibrate due to sound sending nerve impulses to the brain. Different hair cells respond to different frequencies of sound.

Chemoreceptors:Detect chemical substances, e.g. taste and smell. Taste receptors are found on the tongue, the cells are grouped together in taste buds. Hair-like extensions of the receptor cells are exposed on tongue surface and detect chemicals present. The olfactory receptors are on the back of the nose.

Thermoreceptors:Detect temperature changes: peripheral skin receptors (send messages to the brain or spinal cord at a rate determined by skin temperature) and internal, central receptors in the hypothalamus.

Photoreceptors:Detect light and some other electromagnetic radiation. Rods and cones in the eye send messages to the brain, when they absorb light

E.2.2. Label a diagram of the structure of the human eyeSclera – white protective covering of the eyeCornea – front of the sclera, curved surface that refracts light towards retinaConjunctiva – thin transparent layer continuous with the epithelium of the eyelidsChoroid – black layer which prevents reflection of light and contains blood vessels to supply the retinaAqueous humour – clear solution of saltsPupil – variable opening in the iris to allow light to enter the eyeLens – transparent, elastic bi-convex structure which focuses the light onto the retinaIris – coloured part of the eye,

circular and radial muscles which control the size of pupilVitreous humour – clear gel like substance which fills the eye ballRetina – contains rods and cones and nerve cells for visionFovea – yellow spot contains cones only, spot of most accurate vision

Optic nerve – carries impulses to the brainBlind spot – point where optic nerve leaves the eye, not light sensitive.

E.2.3. Annotate a diagram of the retina to show the cell types and the direction in which light moves.

E.2.4. Compare rod and cone cellsThe two types of photoreceptor cells are the rod and cone. The cells are partly embedded in the pigmented epithelial cells of choroid. Their basic structure is very similar, but they have structural and functional differences. Each rod posses up to a thousand vesicles in its outer segment. These contain photosensitive pigment rhodopsin. Rhodopsin is made up of the protein opsin and a derivative of vitamin A, retinal. Retinal usually exists as a cis-isomer but light causes it convert to a trans-isomer. This change leads to the splitting of rhodopsin into opsin and retinal – i.e. bleaching. This splitting leads to the creation of a generator potential in the rod cell which if large enough generates an action potential along the neurons leading form the cell to the brain. Before the rid cell can be activated in the same way, the opsin and retinal must be resynthesised into rhodopsin. The resynthesis is carried out by the mitochondria in the rod cell, providing ATP for the process. Resynthesis takes longer that splitting but it faster the lower the light intensity is.There is similar process in cone cells, except the pigment here is iodopsin. This is less sensitive to light and so greater intensity is required to cause a breakdown.

E.2.5. Explain the processing of visual stimuli, including edge enhancement and contra lateral processing.

Contralateral processingBipolar cells in retina combine impulses from rod and cone sells and pass them to sensory neurons of the optic nerve, ganglion cells. The left and right optic nerves meet at a structure called the optic chiasma. Here, all the neurons that are carrying impulses from the half of the retina nearest the noses cross over to the opposite optic nerve. In consequence, the left optic nerve carries information from the right half of the field of vision and vice versa. Beyond the optic chiasma, neurons continue to the thalamus, where information is processed. It is then carried to the visual cortex at the back of the brain, where further processing leads to formation of images. This process allows the brain to deduce distances and sizes.

Edge enhancement:This occurs within the retina, two types of ganglion cells, each stimulated when light falls on the receptive field (small circular area of the retina)On-centre ganglion cells

Stimulated if light falls on the centre of the receptive field Stimulation is reduced if light falls on the periphery

Off-centre ganglion cells Stimulated if light falls on the periphery of the receptive field Stimulation is reduced if light falls on the centre of receptive field

Ganglion cells are stimulated greatest when the dark/light edge is within the receptive field. The edge effect can be shown through a Hermann grid.

E.2.6. Label a diagram of the ear.

E.2.7. Explain how sound is perceived by the ear, including the roles of the eardrum, bones of the middle ear, oval and round window, and the hair cells of the cochlea.

E3 Innate and learned behaviour

E.3.1. Distinguish between innate and learned behaviourInnate: behaviour shown in all normal members of a species despite variationLearned: behaviour that is developed as a result of experience

E.3.2. Design experiments to investigate innate and learned behaviour in invertebrates including either taxis or kinesis.Taxis: locomotion of an organism in a particular directional response to an external stimulus. E.g. flatworms moving towards food (positive chemotaxis); earthworms move away from light (negative phototaxis), euglena moving towards light (positive phototaxis)

Kinesis: movement of an organism or cell in response to a stimulus (like relieving oneself in the presence of a visual stimulus… well not really). The rate of kinesis is dependant on amount of movement not the direction. Observations can consist of the type of movement, speed of movement or direction of movement. The greater the intensity the faster it moves and the more often it changes direction. E.g. woodlice prefer moist habitats; their gas exchange system will dehydrate in dry areas. Kinesis ensures that woodlice spend greater time in humid areas than dry areas if areas are available. In dry areas they will be more active without direction until they are dehydrated. In humid areas they become quiet.

E.3.3. Analyse data from invertebrate behaviour experiments in terms of the effect of chances of survival and reproduction(You can do that on your own losers)

E.3.4. Discuss how the process of learning can improve the chances of survival

Moths – Classical conditioningMoths can learn by classical conditioning. The ability of some moths is greater than others. Moths that are better at classical conditioning will eventually associate black and orange caterpillars with a noxious taste and avoid getting sick, increasing their chance of survival. Alleles allowing classical conditioning are passed on to offspring at a higher rate than alleles without classical conditioning ability, therefore classical conditioning alleles accumulate and trait becomes common.

Bears – trial and error/operant conditioningSome bears experiment with various methods to catch salmon, these bears obtain more resources than those that don’t experiment, increasing their survival chances. Alleles that allow them to

attempt operant conditioning are passed on to their offspring at a higher rate than alleles without operant conditioning; alleles will accumulate and becomes common in the population.

E.3.5. Outline Pavlov’s experiment into conditioning of dogs1. Dogs were presented the taste of powdered meat and the quantity of saliva was measured.

A fistula (hole) was present in the cheek, from salivary duct so that drops of saliva could fall through a funnel and counted. Pavlov found that there was a certain amount of saliva produced given a standard quantity of meat powder. This is the simple inborn reflex involving the meat powder.

2. The dogs heard the ticking of a metronome before having meat powder puffed into their mouths. At first there was no change in the quantity of saliva produced

3. After six demonstrations of the metronome ticking before meat powder being given, the saliva was produced as soon as the metronome started and before meat powder arrived. A conditioned reflex had been established.

4. The metronome ticking resulted in the production of saliva alone5. Repetition of the 4th stage led to a reduction of saliva produced until the stimulus no longer

elicited a response

E.3.6. Outline the role of inheritance and learning in the development of birdsong in young birds.In some species, birdsong is partly innate and partly learned. For example the male chaffinch uses song to attract females and keep males out of their territory. Males have different songs allowing identification of individual birds. All chaffinch songs are similar but they differ from each other, the type of song they sing is dependent on what they learn to be most effective.

E4 Neurotransmitters and synapses

E.4.1. State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission.

Excitatory synapsesThe neurotransmitter released the presynaptic neuron causes sodium ions or other positively charged ions to enter the postsynaptic neuron, helping to depolarise it and cause an action potential. Postsynaptic transmission is therefore excited

Inhibitory synapsesThe neurotransmitter released by the presynaptic neuron causes negatively charged chloride ions to move into the postsynaptic neuron, increasing its polarisation. This effect, called hyperpolarisation, makes it more difficult to depolarize a neuron sufficiently to cause an action potential. Postsynaptic transmission is therefore inhibited.

E.4.2. Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory pre-synaptic neurons at synapsesOne of the fundamental roles of the brain and spinal cord is decision-making. This can be a simple process, as in a reflex, or much more complicated, for example when choosing a partner. Synapses are the sites at which decisions are made. One pulse of excitatory neurotransmitter, released when an action potential reaches the end of a postsynaptic neuron, is unlikely to be enough to cause postsynaptic transmission. A rapid sequence of pulses of neurotransmitter is needed. These could come from the same presynaptic neuron, or more likely from a number of different ones.

This is possible because postsynaptic neurons have synapses with more than one presynaptic neuron. Where many presynaptic neurons form synapses with a postsynaptic neuron, some of these synapses will be excitatory and others will be inhibitory. The effects of excitatory neurotransmitters may be cancelled out if an inhibitory neurotransmitter is also being released. Whether an action potential is initiated in the postsynaptic neuron is therefore decided by the summation of messages from all of these synapses. In this way, decisions can be made by the central nervous system.

E.4.3. Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.Synapses are the sites of decision-making:A postsynaptic neuron's membrane potential is the summation of input from presynaptic neurons

Excitatory synapses depolarize postsynaptic neurons Inhibitory synapses hyper-polarize postsynaptic neurons

If the post-synaptic neuron reaches threshold potential at its axon hillock, it will produce an action potential; pre-synaptic neurons can vary in the frequency, but not intensity of their input, since action potentials are "all-or-none”

Drugs are chemical substances that are ingested, injected, inhaled or put into the body in some other way, to cause a change in the functioning of the body. Psychoactive drugs affect the brain and personality. Most psychoactive drugs affect the functioning of the brain by disrupting synaptic transmission. Excitatory drugs work either by promoting transmission at excitatory synapses or inhibiting transmission at inhibitory synapses. Inhibitory drugs do the opposite.

Psychoactive drugs can affect synaptic transmission in a variety of ways. Some psychoactive drugs have a chemical structure similar to a neurotransmitter and so bind to receptors for that neurotransmitter in postsynaptic membranes. They block the receptors, preventing the neurotransmitter from having its usual effect. Other psychoactive drugs with a chemical structure similar to a neurotransmitter have the same effect as the neurotransmitter. However, unlike the neurotransmitter, they are not broken down so when they bind to the receptor, the effect is much longer lasting. Some psychoactive drugs interfere with the breakdown of neurotransmitters in synapses or its reabsorption into the presynaptic neuron and so prolong the effect of neurotransmitters.

E.4.4. List three examples of excitatory and three examples of inhibitory psychoactive drugs.Excitatory drugs: nicotine, cocaine and amphetaminesInhibitory drugs: benzodiazepines, alcohol and tetrahydrocannabinol (THC).

E.4.5. Explain the effects of THC and cocaine in terms of their action at synapses in the brain.

Cocaine Cocaine is an excitatory psychoactive drug. It stimulates transmission at synapses in the brain that use dopamine as a neurotransmitter. Cocaine binds to membrane proteins that pump dopamine back into the presynaptic neuron. It blocks these transporters, causing a build-up of dopamine in the synapse. The synapses that use dopamine as a neurotransmitter are responsible for pleasurable feelings that we get during certain activities, for example eating or having sex. Because cocaine causes continuous transmission at these synapses, it gives feelings of euphoria that are not related to any particular activity. It also causes users to have increased energy, alertness and talkativeness. Cocaine is highly addictive and is a widely abused drug. Tissue taken from the brains of cocaine users after death had lowered levels of dopamine, suggesting that the body adapts to cocaine use by

reducing secretion. This would explain cocaine-induced depression.

THC THC affects transmission at an unusual type of synapse, where the postsynaptic neuron can release a signalling chemical that binds to receptors in the membrane of the presynaptic neuron. It is not yet certain what these signalling chemicals are. THC binds cannabinoid receptors. When THC binds to cannabinoid receptors, it blocks the release of excitatory neurotransmitter. THC is therefore an inhibitory psychoactive drug. Cannabinoid receptors are found in synapses in various parts of the brain, including the cerebellum, hippocampus and cerebral hemispheres

cerebellum: THC thus impairs motor functions hippocampus: THC thus impairs short-term memory functions, cerebral cortex: THC thus affects higher order thinking

Users make various claims about the effects of THC, most of which are not backed up by any evidence. There is good evidence for disruption of psychomotor behaviour so it is not safe to drive vehicles or operate machinery. Short-term memory impairment, intoxication and stimulation of appetite are other effects.

E.4.6. Discuss the causes of addiction including genetic predisposition, social factors and dopamine secretion.The causes of addiction to psychoactive drugs have been widely studied, because of the physical and social damage that additions can cause. Three factors increase levels of addiction, especially when they are combined.

Dopamine secretion Some drugs are addictive and some are not. A feature of many addictive drugs is that transmission is stimulated at synapses using dopamine as a neurotransmitter. These synapses are involved in the reward pathway, which gives us feelings of well-being and pleasure. Users of addictive drugs find it very difficult to stop, because they have become dependent on the feelings that dopamine promotes.

Genetic predisposition Even with many drugs that are potentially addictive, not everyone becomes an addict. Addictions, especially alcoholism, are much commoner in some families than others. This suggests that genes can make some people predisposed.

Social factors Social factors can either prevent or encourage an addiction. Cultural traditions, peer pressure, poverty and social deprivation, traumatic life experiences and mental health problems all increase the chances of an addiction developing.

E5 The human brain (HL)

E.5.1. Label on a diagram of the brain, the medulla oblongata, cerebellum, hypothalamus, pituitary gland and cerebral hemispheres.

E.5.2. outline the functions of each of the parts of the brain listed E.5.1Medulla oblongata: controls automatic and homeostatic activities, such as swallowing, digestion

and vomiting, and breathing and heart activity.Cerebellum: coordinates unconscious functions, such as movement and balance.Hypothalamus: maintains homeostasis, coordinating the nervous and endocrine systems,

secreting hormones of the posterior pituitary, and releasing factors regulating the anterior pituitary.

Pituitary gland: The posterior lobe stores and releases hormone produced by the hypothalamus and the anterior lobe, and produces and secretes hormones regulating many body functions.

Cerebral hemispheres: act as the integrating centre for high complex functions such as learning, memory and emotions.

E.5.3. Explain how animal experiments, lesions and fMRI scanning can be used in the identification of the brain part involved in specific functions.

Animal experiments Many experiments have been performed on animals, including primates, often involving surgical procedures – parts of the skull have to be removed to get access to the brain. The animal must be kept alive so that the brain is still functioning. Experimental procedures are carried out on the brain and the effects on the animal are then observed, either during the operation or afterwards. Many scientists have ethical objections to these experiments as the animals may experience some suffering and are often sacrificed.

Lesions Accidents, strokes and tumours can damage specific parts of the brain. The damaged areas are called lesions and from them, the location of particular brain functions can be deduced. For example,

lesions in Broca’s area in the left cerebral hemisphere cause dysphasia – inability to speak, but reading and writing are still possible.

FMRI It is a technique for determining which parts of the brain are activated by specific thought processes. Active parts of the brain receive increased blood flow, which FMRI records. The experimental subject is placed in the scanner and a high-resolution scan of the brain is taken. A series of low-resolution scans is then taken, while the subject is being given a stimulus. The scans show which parts of the brain are activated during the response to the stimulus.

E.5.4. Explain the sympathetic and parasympathetic control of heart rate movements in the iris and flow of blood to the gut

Heart rateIn controlling heart rate the parasympathetic nervous system slows down the heart and the sympathetic speeds it up. Chemoreceptors will pick up a stimulus like elevated CO2 levels in the blood. This information is processed by the medulla oblongata, from which sympathetic nerves stimulate the heart rate to increase. Conversely, if mechanoreceptors realise an elevated pressure in the aorta, parasympathetic nerves will decrease the heart rate.

Iris controlThe medulla oblongata processes information from chemoreceptors that pick up adrenaline. Adrenaline can be released when the body is stressed. Sympathetic nerves in the neck travel to motor neurons causing radial muscles in the iris to contract, dilating the pupil allowing more light to enter. Conversely if chemoreceptors pick up reduced stress hormones transferring a stimulus via neurons to the medulla oblongata, the neurotransmitter, acetyl choline, carry an impulse via parasympathetic nerves. Motor neurons in the brain behind the eye will causes circular muscles in the iris to contract, making the pupil constrict.

sympathetic system parasympathetic system

heart rate speeds up slows down

flow of blood to the gut

vessels are constricted, decreasing blood flow

vessels are dilated, increasing blood flow

movements of the iris

radial muscles contract, pupil dilates to give a better image

circular muscles contract, pupil constricts to protect the retina

E.5.5. Explain the pupil reflexThe pupil reflex: is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retina of the eye, thereby assisting in adaptation to various levels of darkness and light, in addition to retinal sensitivity. Greater intensity light causes the pupil to become smaller (allowing less light in), whereas lower intensity light causes the pupil to become larger (allowing more light in). Thus, the pupillary light reflex regulates the intensity of light entering the eye.Retina detects light intensity; impulses to brain in optic nerve; brain stem/medulla controls the reflex; causes dilation or constriction; polysynaptic reflex; no response => no brain stem control.

E.5.6. Discuss the concept of brain death and the use of the pupil reflex in testing for thisThe brain is considered dead when all parts of the brain are non-functional. This includes the brain stem and cerebrum. Pupil reflex can be used to determine of brain stem is functioning. If the pupil responds to light then the brain stem is functioning. Without the brain stem, homeostasis will stop,

and life cannot continue. Life can continue when cerebrum is non-functioning given the brain stem is functioning. However this would be a vegetative state. This can be considered ‘the higher brain standard of death’. Some may argue people in this state are dead, even if the cerebrum is functioning.

E.5.7. Outline how pain is perceived and how endorphins can act as painkillers

Pain receptors are located in the skin and other organs. They consist of free nerve endings, which perceive mechanical, thermal or chemical stimuli. Impulses are sent from these pain receptors to sensory areas of the cerebral cortex, causing feelings of pain. These feelings are necessary to allow us to know when our body is being damaged, so that we can take avoiding action – pain withdrawal reflex for example. However, pain sometimes becomes excessive or stops us from concentrating on important activities. In these situations, the pituitary gland releases endorphins.

The endorphins are carried in the blood to the brain. They bind to receptors in the membranes of neurons that send pain signals and block the release of a neurotransmitter that is used to transmit the pain signals within the brain. Endorphins are secreted during stressful times, after injuries and even during physical exercise such as running.

E6 Further studies of behaviour (HL)

E6.1 Describe the social organization of honey bee colonies and one other non-human example. 

Honey bee:Live in colonies of more than 60, 000. Most of the bees are workers, infertile females. There

consists one queen, a fertile female, whose job is to lay fertilised diploid eggs that will potentially hatch into larvae. The larvae will develop into queens, unless they are fed a particular diet, to produce a new queen. In one week the larvae will become a pupa, and after two weeks an adult honey bee.

Young workers act as nurses that take care of the larvae for two weeks. After the two weeks they begin cleaning and guarding the hive i.e. removing sick/dead bees. Eventually the workers will make trips to collect nectar. Workers communicate through pheromones and dances. When colony grows too large the queen will prepare her leave.

Some unfertilised eggs become drones, fertile males. Once the old has left with half her colony, a new queen will fly out with some drones, these drones will fertilise the new queen, who stores their sperm for the coming years. The new queen returns and begins laying eggs fertilised with the stored sperm. The drones have no further role; they are killed or driven out by the workers.

Naked Mole rat:Live in colonies of up to 80, in a burrow system in east Africa. One dominant female mole

will act as queen, like a queen bee. This female is the only that will reproduce, mating with a male from the colony. Frequent workers will dig the tunnels of the burrow system, and bring food to all.

Infrequent workers are large but will only occasionally work with the heavier tasks. Non-workers live the centre; they keep the breeding female and offspring warm and defend the colony in case of attack.

E6.2 Outline how natural selection may act at the level of the colony in the case of social organisms. A colony of a social organism can sometimes be considered one “super-organism”. The whole colony works together in order to survive and reproduce to form new colonies, or it fails. Natural selection, therefore, can only exist at the level of the colony.

E6.3 Discuss the evolution of altruistic behaviour using two non-human examples.Altruistic behaviour is that of an individual who helps other individuals, where it does not benefit the acting individual. Some altruistic acts can lead to the individual’s death.

Naked Mole rat:The non-breeding workers in a colony protect and help the reproducing male and female.

The evolution of this altruism is sometimes described as kin selection. The mole rats in the colony are all genetically related, although workers are helping rear offspring that is not their own, they are helping ensure the survival of their genes.

Vampire bats:They live in groups sucking blood from larger animals. If a bat fails to feed more than two

consecutive nights it may die of starvation. Bats that have fed successfully can regurgitate blood for a bat that has failed to feed. These occurs even the two bats are not genetically related. There is an advantage for the whole group in this pattern – reciprocal altruism. The bat that donates blood to a hungry bat may in the future receive blood when it is hungry. The benefits of receiving blood when starving is the greater than the cost of donating blood when well fed.

E.6.4. Outline two examples of how foraging behaviour optimizes food intake, including bluegill fish foraging for Daphnia

Bluegill sunfish These fish live in ponds, where they prey on small invertebrates. When there is a low density of prey, bluegill sunfish consume all sizes of them. At medium prey densities, bluegill sunfish consume only prey of moderate or larger sizes. At high prey densities they mostly consume large prey, plus some of medium size. Consuming small numbers of large prey takes less energy than large numbers of small prey, hence the preference for large prey. At low prey densities, smaller prey has to be eaten as well, to get enough food in total.

Starlings Starlings are birds that feed their young mainly on crane-fly larvae, which they obtain by probing into soil with their beak. Starlings become less efficient at probing for larvae, as the number of larvae they are holding in their beaks increases. The fewer journeys back to the nest, the less time and energy is used in transporting the larvae to the offspring. The optimum number of larvae for starlings to catch and carry back to the nest depends on the distance between the foraging area and the nest. As the distance increases, the optimum number of larvae also increases. When starlings have been observed, the number of larvae actually caught and transported has been found to be very close to the theoretical optimum.

E.6.5. Explain how mate selection can lead to exaggerated traits.Some species of animal have characteristics or behaviour patterns that seem to be developed excessively. The long and brightly coloured tail feathers of a peacock are an example. These are only used during courtship, to try to attract a female. At other times, the tail feathers will be an

encumbrance (burden), hindering rapid movement, especially during attacks by predators. This may be the explanation for the evolution of an exaggerated trait, must be well-adapted in other ways and so is a good mate to choose.

E.6.6. State that animals show rhythmical variations in activityAnimals show rhythmical variation in activity (quite a pointless syllabus point)

E.6.7.Outline two examples illustrating the adaptive value of rhythmical behaviour patterns

Moonrats Like many mammals, moonrats are nocturnal. Their excellent sense of smell helps them to forage at night when much of their prey is active – insects and other invertebrates. They are less vulnerable to predation at night and in the day they rest in holes among tree roots or in hollow logs, where they are unlikely to be discovered.

Red deer Reproduction follows an annual cycle in red deer. Males and females are only sexually active in the autumn. Males fight to establish dominance over groups of females with whom they mate. The advantage is that if the females start gestation in the autumn, the offspring are born in spring. Most food is available in spring and summer for feeding the offspring, so this type of season breeding gives the offspring the greatest chance of survival.