I have posted all my personal IB coursework (from the graduating class of 2011) on this website. Use page links below or on the right to navigate.
EE - extended essay
TOK essay
HL Biology (solid notes!)
HL History (Americas)
Sunday, 3 July 2011
Option E - Neurobiology and behaviour
E.1 Stimulus & response
E.1.1 Define the terms stimulus, response, and reflex in the context of animal behavior.
A stimulus is a change in the environment (internal or external) that is detected by a receptor and elicits a response. A reflex is a rapid, unconscious response.
● Stimulus - is a change in the environment (internal or external) that is detected by a receptor and elicits a response. E.g. a sound, increase in blood sugar, etc.
● Response - the activity of a cell or organism in response to a stimulus.
● Reflex - is a rapid, unconscious response.
E.1.2 Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses and effectors in the response of animals to stimuli.
● Receptors: detects a stimulus and converts it into an action potential ; receptors can be sensory cells or nerve endings from sensory cells.
● Sensory: receive messages across synapses from receptors and carry them to the central nervous system.
● Relay neurons: receive messages across synapses from sensory neurons and carry them to motor neurons that can cause an appropriate response.
● Motor neurons: receive messages across synapses from relay neurons and carry them to an effector.
● Effectors: carry out a response after receiving a message from a motor neuron; effectors can be muscles which respond by contracting, or glands which 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 effector.
Include white and grey matter, and ventral and dorsal roots.
withdrawl reflex: [1 max]
e.g. a hot/sharp object is touched and the hand withdrawn;
protects body from harm;
reflex arc: [3 max]
pain receptor/nociceptor in skin is stimulated;
impulse passed to sensory neuron;
passes impulse on to association neuron in spinal cord / grey matter;
motor neuron carries impulse to muscle/ effector which contracts;
Accept any of the above if clearly explained in a labelled diagram.
E.1.4 Explain how animal responses can be affected by natural selection, using two examples.
Use of local examples is encouraged.
The bird Sylvia atricapilla (blackcap) breeds during the summer in Germany and, until recently, migrated to Spain or other Mediterranean areas for winter. However, studies show that 10% of blackcaps now migrate to the UK instead. To test whether this change is genetically determined or not (and, therefore, whether it could have developed by natural selection or not), eggs were collected from parents who had migrated to the UK in the previous winter and from parents who had migrated to Spain. The young were reared and the direction in which they set off, when the time for migration came, was recorded. Birds whose parents had migrated to the UK tended to fly west, wherever they had been reared, and birds whose parents had migrated to Spain tended to fly south-west. Despite not being able to follow their parents at the time of migration, all the birds tended to fly in the direction that would take them on the same migration route as their parents.
This and other evidence suggests that blackcaps are genetically programmed to respond to stimuli when they migrate so that they fly in a particular direction. The increase in the numbers of blackcaps migrating to the UK for the winter may be due to warmer winters and greater survival rates in the UK.
● Natural selection effects animal responses only if the behaviour is heritable (controlled by a gene).
● There will be variation in the phenotypes for this behaviour within a population as a result of the differences in alleles that individuals have inherited.
● The presense of an allele in a population depends on how successful that allele is --alleles influencing more successful behavioral adaptations increase over time, and alleles influencing less successful behavioral adaptations decrease over time.
● Behavioral adaptions occur if the environment of an animal species changes, since natural selection might favour different alleles.
● Example: migration in blackcaps
○ Historically, populations of blackcaps from Germany migrated to Spain/other Mediterranean areas. Recent studies have shown that approximately 10% of the population migrates to the UK.
○ Experiments with eggs have shown that the direction of migration is genetically programmed and inherited.
○ Blackcaps whose parents migrated from Germany to the UK instinctively fly west, whereas those whose parents migrated to Spain tend to fly south west.
○ Offspring show this behaviour despite the location of where they were reared.
● Example: method of breeding in sockeye salmon
○ There are two genetically different populations of sockeye salmon in Washington -- beach-spawning salmon and river-spawning salmon.
○ For the lake: females lay eggs in the sand and males have large bodies to hide in deep waters of the lake. In the river, males are too large to navigate in the fast moving current.
○ For the river: females lay eggs deep within the beds of the river so that they are not washed away by the current. Their bodies are thinner and narrow for increased maneuverability. Eggs of the river salmon are unable to hatch in the beaches of the lakes.
○ River and lake salmon cannot interbreed because their method of spawning is different, and this is determined genetically.
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.
Details of how each receptor functions are not required.
● Humans have a diversity of types of receptors and so can perceive a wide range of stimuli.
| Type of receptor | Type of stimulus | Example |
| Mechanoreceptor: transforms mechanical or movement stimulus into nerve impulses | 1. mechanical energy in the form of sound waves 2. movement due to pressure of gravity | 1. hair cells in the cochlea of the ear 2. pressure receptor cells in the skin |
| Chemoreceptors transforms chemical stimuli into a nerve impulse | 1. chemical substances dissolved in water (tongue) 2. chemical substances as vapours in the air (nose) | 1. receptor cells in the tongue 2. nerve endings in the nose |
| Thermoreceptors: detects changes in temperature and cause them to produce nerve impulses | 1. temperature | 1. nerve endings in the skin detect warm or cold |
| Photoreceptors transforms visible light into nerve impulses | 1. electromagnetic radiation, usually in the form of light | 1. rod and cone cells in the eye |
E.2.2 Label a diagram of the structure of the human eye.
The diagram should include the sclera, cornea, conjunctiva, eyelid, choroid, aqueous humour, pupil, lens, iris, vitreous humour, retina, fovea, optic nerve and blind spot.
E.2.3 Annotate a diagram of the retina to show the cell types and the direction in which light moves.
Include names of rod and cone cells, bipolar neurons and ganglion cells.
E.2.4 Compare rod and cone cells.
Include:
• use in dim light versus bright light
• one type sensitive to all visible wavelengths versus three types sensitive to red, blue and green light
• passage of impulses from a group of rod cells to a single nerve fibre in the optic nerve versus passage from a single cone cell to a single nerve fibre.
| Rods | Cones |
| sensitive to low light, therefore used in dim light | less sensitive to light, therefore used in bright light |
| there is only one type of rod and it is sensitive of all wavelengths of light | there are three types of cones: one is sensitive to red light, one is sensitive to blue light, and one is sensitive to green light |
| groups of rod cells pass impulses to a single nerve fibre in the optic nerve | a single cone cell passes an impulse to a single nerve fibre in the optic nerve |
E.2.5 Explain the processing of visual stimuli, including edge enhancement and contralateral processing.
Edge enhancement occurs within the retina and can be demonstrated with the Hermann grid illusion.
Contralateral processing is due to the optic chiasma, where the right brain processes information from the left visual field and vice versa. This can be illustrated by the abnormal perceptions of patients with brain lesions.
*Convergence
● Bipolar cells in the retina combine impulses from groups of rod or cone cells and pass them to ganglion cells of the optic nerve.
Edge enhancement :o
● Edge enhancement occurs in the retina.
● When light falls on a ganglion cell, the region of space that results as a response to the stimulus is called the ‘receptive field’.
● Ganglion cells of the optic nerve neurons respond differently, depending on where light stimulus falls on their receptive fields. There are two types of ganglion cells:
○ On-centre ganglion cells
■are stimulated when light falls on the centre of the receptive field (this occurs in the fovea)
■but stimulation is reduced if light also falls on the periphery.
○ Off-centre ganglion cells
■are stimulated when light falls on the periphery of the receptive field
■but stimulation is reduced if light falls on the centre
● Both types of ganglion cell experience increased stimulated if the edge of the light/dark is within the receptive field, and this results in edge enhancement.
● This can be observed with the Herman grid illusion, because white areas appear whiter if they are next to a black area. Grey areas are a result of peripheral vision, where receptive fields are larger and there is lower visual acuity as a result.
Contralateral processing
● *Convergence
● Sensory information from the left visual field is received at the right side of the visual cortex of the brain. Sensory information from the right visual field is received at the left side of the visual cortex of the brain.
● The left and right optic nerves meet at the optic chiasma.
● The action potentials from each side of the visual field switch to the opposing side of the optic nerve at the optic chiasma.
● “Seeing” occurs at the visual cortex of the brain. Messages from the action potentials of the left and right visual fields are processed and combined here to produce a single image.
● This is called contralateral processing.
E.2.6 Label a diagram of the ear.
Include pinna, eardrum, bones of the middle ear, oval window,round window, semicircular canals, auditory nerve and cochlea.
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 windows, and the hair cells of the cochlea.
The roles of the other parts of the ear are not expected.
● Vibrations from the eardrum enter the cochlea via bones of the middle ear.
○ Bones of the middle ear receive vibrations from the eardrums and amplify it [by approximately 20 times.]
● The stirrup of the middle ear strikes the oval window. This causes the oval window to vibrate and pass the vibrations along to the fluid of the cochlea, beginning at the upper compartment.
● As the vibrations travel along the fluid from the upper compartment to the lower compartment, the sensory hair cells in the middle ear are stimulate to vibrate from the pressure waves.
○ Hairs on the basilar membrane rub or pull against the inflexible membrane.
● The resulting movements of the sensory hair cells cause the production of an action potential, which is transmitted to the brain through a branch of the auditory nerve.
○ In different regions of the cochlea, different wavelengths of pressure waves cause the basilar membrane to vibrate.
● The waves in the fluid of the cochlea dissipate as they reach the round window.
E3 Innate and learned behaviour
E.3.1 Distinguish between innate and learned behaviour.
● Innate behaviour develops independently of the environmental context, whereas learned behaviour develops as a result of experience.
E.3.2 Design experiments to investigate innate behaviour in invertebrates, including either a taxis or a kinesis.
Examples include:
• taxis—Planaria move towards food (chemotaxis) and Euglena move towards light (phototaxis)
• kinesis—woodlice move about less in optimum (humid) conditions and more in an unfavourable (dry) atmosphere.
E.3.3 Analyse data from invertebrate behaviour experiments in terms of the effect on chances of survival and reproduction.
How innate behaviour increases chances of survival:
● Innate behaviours develop independently of the environment.
● The behaviour does not change with practise or repetition.
● Innate behaviour develops by natural selection because they increase reproductive success of the species since they are better adapted to the environment.
● Two types of innate behaviour are taxis and kinesis.
● Taxis is the movement to or away from a directional stimulus, such as the movement of fly larvae away from light because it helps protect from predators.
● Kinesis is response to non-directional stimulus, such as the movement of woodlice towards moist/dark areas to help avoid dehydration.
E.3.4 Discuss how the process of learning can improve the chance of survival.
● Learn behaviour is a result of experiences in response to the environmental.
● Natural selection will favour certain learned behaviours that increase reproductive success.
● Classical conditioning involves a conditioned response to a conditioned stimulus. For example, Pavlov’s experiment resulted in his dogs to salivate (conditioned response) when they heard the sound of a bell (conditioned stimulus) because it was associated with the serving of food.
● Operant conditioning involves trial and error learning. For example, foxes learn to avoid touching electric fences after receiving an electric shock.
● Conditioned behaviour based on response to rewards that increase survival;
● Imprinting involves learning a response during a receptive period. For example, ducklings follow the first thing they see that moves--their mother--when they are born and this helps them to avoid predators.
E.3.5 Outline Pavlov’s experiments into conditioning of dogs.
The terms unconditioned stimulus, conditioned stimulus, unconditioned response and conditioned response should be included.
● Pavlov investigated conditioning with the salivation reflex of dogs.
● He introduced the unconditioned stimulus of food accompanied by a bell ringing.
● Salivation was the unconditioned response by the dogs.
● Eventually the conditioned stimulus of a bell ringing without the unconditioned stimulus of of food resulted in salivation.
● Therefore salivation became the conditioned response to the bell ringing.
E.3.6 Outline the role of inheritance and learning in the development of birdsong in young birds.
● The development of birdsong is partly innate and partly learned.
● The chaffinch is an example.
● Male chaffinches use their song to keep other males out of their territory, and also to attract females. Since birdsong varies little between males, it is also used for identification of individuals of the same species.
● Chaffinches’ birdsong is partly innate because experiments have showed that when a young chaffinch is reared in isolation, the young bird demonstrates a ‘crude template’. The crude song is has some features of the normal birdsong (like length/number of notes), and is therefore innate/species-specific.
● It is also partly learned because some distinctive features (like narrower range of frequencies) of the adult song are missing. This must be learned from imitating adult chaffinches.
E4 Neurotransmitters and synapses
E.4.1 State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission.
● Some presynaptic neurons excite postsynaptic transmission.
● Some presynaptic neurons inhibit postsynatpic transmission.
E.4.2 Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses.
● Synapses are the sites of decision-making.
● The post-synaptic neuron has different receptor proteins; some bind to excitatory neurotransmitters while others bind to inhibitory neurotransmitters.
● Excitatory post-synaptic potentials depolarize post-synaptic neurons
○ Excitatory neurotransmitters (e.g. dopamine) cause the post-synaptic membrane to be more permeable to Na+, causing depolarization to move across the membrane.
● Inhibitory post-synaptic potentials hyper-polarize post-synaptic neurons
○ Inhibitory neurotransmitters (e.g. GABA) cause the post-synaptic membrane to be less permeable to Na+, or more permeable to Cl-, or causes K+ to diffuse out. This causes hyperpolarization, which moves across the membrane.
● Many pre-synaptic neurons can form synapses with a single post-synaptic neuron. Therefore the transmission of an action potential in a post-synaptic neuron is decided by the summation of input from pre-synaptic neurons.
● In this way, decisions can be made by the CNS.
E.4.3 Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.
Include ways in which synaptic transmission can be increased or decreased. Details of the organization and functioning of the entire brain, and theories of personality or explanations for personality, are not required.
● Psychoactive drugs affect the brain and personality.
● Excitatory drugs work by promoting transmission at excitatory synapses or inhibiting transmission at inhibitory synapses. Inhibitory drugs work by inhibiting transmission at excitatory synapses or promoting transmission at inhibitory synapses.
● Some psychoactive drugs enhance or block the release of neurotransmitters from the presynaptic membrane.
● Some psychoactive drugs act like neurotransmitters, blocking receptors at the postsynaptic membrane and preventing neurotransmitters from having its usual effect.
● Some psychoactive drugs act like neurotransmitters that bind to receptors at the postsynaptic membrane but are not broken down. Therefore their effect is much longer lasting.
● Some psychoactive drugs interfere with the breakdown of neurotransmitters, thus prolonging their effect.
● Examples of excitatory: nicotine, cocaine, amphetamines
● Examples of inhibitory: THC, alcohol, benzodiazepines
E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.
Use the following examples.
• Excitatory drugs: nicotine, cocaine and amphetamines
• Inhibitory 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.
Include the effects of these drugs on both mood and behaviour.
THC
● THC is the main psychoactive drug in marijuana.
● It mimics the neurotransmitter, anandamide.
● THC bonds to cannabinoid receptors, which are the receptors for anandamines.
● The effect is to inhibit the release of excitatory neurotransmitters and this hyperpolarizes the post-synaptic neuron.
● Therefore THC is an inhibitory psychoactive drug.
● Cannaboid receptors are found in synapses in the cerebellum, hippocampus and cerebral hemispheres. Therefore effects on behaviour and mood include: decreased ability to concentrate; loss of muscle control; impaired perception; memory loss; relaxed attitude; increased appetite; depression.
Cocaine
● Cocaine is an excitatory psychoactive drug that increases activity in the post synaptic neuron.
● Cocaine blocks the recycling of dopamine at the pre-synaptic neuron. There is a buildup of dopamine and it remains active in the synapse.
● Dopamine is associated with feelings of pleasure and is part of the ‘reward pathway’.
● Cocaine also prevents removal of noradrenaline in the post-synaptic neuron.
● Effects on behaviour and mood include: increases alertness/energy levels; euphoria; sensation of force and power so reckless behaviour; sense of anxiety/hallucination; depression and depdendency.
E.4.6 Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion.
● Three factors that cause addiction include genetic predisposition, social factors and dopamine secretion.
Genetic predisposition
● Some are more vulnerable (genetically predisposed) to addiction than others. Studies have shown that there are genetic links to addiction demonstrated by specific alleles. E.g. addictions, especially alcoholism, are commoner in some families than others.
● Personality types that are more predisposed to unnecessary risk-taking may be more prone to addiction (speculation).
Social factors
● Social factors may prevent or encourage addiction. Some factors that encourage addiction include: cultural traditions; peer pressure; poverty; traumatic life experiences; poor mental health.
Dopamine secretion
● Dopamine is a neurotransmitter that is involved in the reward pathway.
● Many addictive drugs are associated with stimulation of dopamine, and these drugs create feelings of euphoria.Such drugs are addictive.
● Addiction results from the effect on dopamine metabolism in response to regular use: there is a reduction in the number of dopamine receptors in post-synaptic neurons.
● Tolerance develops, resulting in increased dosages to produce the same effect.
● As a result, dependence/addiction develops.
E5 The human brain
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 in E.5.1.
Medulla 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 hormones 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 (functional magneticresonance imaging) scanning can be used in the identification of the brain part involved in specific functions.
Include one specific example of each.
Animal experiments
● Experiments conducted on animals include surgical procedures.
● Healthy parts of the brain are removed or connections within the brain are severed in order to observe the resulting altered behaviour.
● Animals must be kept alive so that the brain is still functioning.
● For example, the severing of nerve fibres that cross over the centre of the brain below the two haves of the cerebral hemispheres gave clues to the interaction of the left and right halves of the brain. This experiment was done on cats.
● There are ethical issues related to suffering and sacrifice of animals.
Lesions
● Investigating patients with brain lesions allows for precise correlation between specific areas of the brain with the performance of a particular function.
● Damage may be a result of injury by accident, stroke, or tumours.
● For example, a bullet wound in the rear of a soldier’s skull resulted in blindness, indicating that the visual cortex at the rear of the cerebral hemispheres had a role in vision.
fMRI
● Functional magnetic resonance imagery (fMRI) is a technique used to observe which parts of the brain are activated by specific activities.
● Active parts of the brain receive increased blood flow and the fMRI detects this.
● For example, a subject placed in an fMRI scanner views an object moving across a screen and moves a cursor to track its movement. The fMRI indicates strong activation in the cerebellum because this part of the brain coordinates eye and hand movements.
E.5.4 Explain sympathetic and parasympathetic control of the heart rate, movements of the iris and flow of blood to the gut.
● The sympathetic and parasympathetic nervous system are part of the autonomic nervous system.
● The sympathetic prepares the body for action while the parasympathetic returns the body function to normal.
● Therefore they are antagonistic to each other.
Heart rate
● The sympathetic NS speeds up the heart rate so that more blood/energy is supplied to the muscles.
● The parasympathetic NS slows down heart rate since the body is relaxed and less blood is needed.
Movements of the iris
● The sympathetic NS make the radial muscles contract, causing dilation of the pupils to give better images.
● The parasympathetic NS makes the circular muscle fibres contract, so that pupils constrict to protect the retina from excess light.
Blood flow to the gut
● The sympathetic NS causes blood vessels to constrict, decreasing blood flow to the gut because digestion is not necessary in an emergency.
● The parasympathetic NS causes blood vessels to dilate, increasing blood flow to the gut so that digestion may occur normally.
E.5.5 Explain the pupil reflex.
● When a bright light shines into one eye, the pupils of both eyes constrict. This is the pupil reflex.
● Photoreceptors in the retina detect light stimulus.
● Nerve impulses are sent into the brain by sensory neurons in the optic nerve.
● The medulla oblongata processes the impulse and sends impulses to the circular muscle fibres of the iris, causing them to contract and subsequently constrict the pupils.
E.5.6 Discuss the concept of brain death and the use of the pupil reflex in testing for this.
● The pupil reflex can be tested on comatose patients.
● A light is shone in an eye to see if the pupil constricts.
● Since the pupil reflex is reflex is an autonomic response, the patient is likely brain dead if the pupil reflex does not occur/pupils do not constrict.
○ Damage to the medulla oblongata means that recovery is very unlikely.
● If the pupil reflex is present and the pupils constrict, then the patient may be in a coma.
○ Damage may be restricted to the cerebral hemispheres, so recovery may be possible.
● Therefore the pupil reflex is diagnostic.
E.5.7 Outline how pain is perceived and how endorphins can act as painkillers
Limit this to:
• passage of impulses from pain receptors in the skin and other parts of the body to sensory areas of the cerebral cortex
• feelings of pain due to these areas of the cerebral cortex
• endorphins blocking transmission of impulses at synapses involved in pain perception.
● Pain receptors located in skin and other organs.
● Their nerve endings perceive mechanical, thermal and chemical stimulus.
● Pain receptors send signals to the cerebral cortex in brain/CNS for conscious pain sensation.
● Natural pain killers are endorphins.
● Endorphins are released by the pituitary gland and are carried in the blood.
● They bind to receptors of membranes of neurons that send the signal.
● This may block release of the neurotransmitters that are used to transmit the pain signal to the brain.
E6 Further studies of behaviour
E.6.1 Describe the social organization of honey bee colonies and one other non-human example.
Detailed structural differences and the life cycle of honey bees are not expected.
Honey bee colony
● Honey bee colonies are organized into a caste system, which includes the queen, the drone, and the worker.
● Colonies number up to 60 000 individuals.
● They cooperate to regulate the internal conditions of the hive and ensure survival of the colony. For example, worker bees may share information about the location of food to other bees.
● The queen is the fertile female. She lays eggs and also produces a pheromone to control the activities of the workers.
● The drones are fertile males. They mate with virgin females to spread the genes of the colony to new colonies, but otherwise do not contribute to the hive.
● The workers are infertile females. They collect nectar and pollen, convert pollen into honey, secrete wax and use it to build the comb, feed/look after larvae, and guard the hive.
● The colony can be considered as a ‘super-organism’. Either the colony as a whole survives and reproduce new colonies, or it does not. Therefore natural selection occurs at the level of the colony.
Naked mole rat colony
● Naked mole rats live in colonies of burrow systems in parts of East Africa.
● One dominant female mole rat is the queen. She is the only female in the community to reproduce, which she does with one male.
● There are three other castes of mole rats to help the queen:
○ ‘Frequent workers’ help dig tunnels and bring food.
○ ‘Infrequent workers’ are larger and occasionally help with heavier tasks.
○ ‘Non-workers’ live in the central nest, keeping the breeding female and her young offspring warm and defending the colony if it is attacked.
● Such complex burrow systems could not be maintained without extensive orgainzation, therefore the colony can be considered as a ‘super-organism’. Either the colony as a whole survives and reproduce new colonies, or it does not. Therefore natural selection occurs at the level of the colony.
E.6.2 Outline how natural selection may act at the level of the colony in the case of social organisms.
● The colony can be considered as a ‘super-organism’.
● Either the colony as a whole survives and reproduce new colonies, or it does not. Therefore natural selection occurs at the level of the colony.
● Therefore natural selection occurs at the level of the colony.
E.6.3 Discuss the evolution of altruistic behaviour using two non-human examples.
● Altruistic behaviour in an animal is potentially harmful to itself but beneficial to another animal.
● It is at the expense of the individual displaying the behaviour.
● Parental care is not altruism, and altruism decreases as genetic relationship between individuals increases. [meaning: beneficial actions for family members do not count]
● Altruistic behaviour might lead to an advantage for the individual displaying behaviour in the future.
● It is arguable that benefits for the individual demonstrating altruistic behaviour increases over time through survival of genes shared with recipient.
● For example, worker bees feed larva and protects the colony. A worker bee may die in defence of colony, however the queen bee / rest of colony are protected.
● For example, male non-breeding mole rats of a naked mole rat colony may defend their colony if it is attacked so that the breeding male and female may continue to reproduce successfully. Since mole rats in a colony are all genetically related, the non-breeding mole rats’ actions helps to ensure the survival of their own genes.
E.6.4 Outline two examples of how foraging behaviour optimizes food intake, including bluegill fish foraging for Daphnia.
Bluegill fish
● Bluegill fish live in ponds and feed on small invertebrates, including Daphnia.
● Their prey can be classified into small, medium, and larger sizes.
● When there is a low density of prey available, bluegills eat all possible prey sizes simply to obtain enough food.
● When there is a high density of prey available, bluegill will select larger prey in order to optimize energy intake per output of effort.
● When there is a medium density of prey, bluegills will use an intermediate strategy and favour larger prey over smaller prey.
● Therefore foraging is determined by the availability of prey.
Starling birds
● Parents feed crane fly larvae to their young, which they collect from soil by probing.
● With each larva held in the beak, foraging for additional larvae becomes increasingly inefficient.
● However, flying is energetically costly, so maximizing the number of larvae carried per journey is also favored.
● Thus, the maximum number of larvae carried is a function of the distance between the foraging area and the nest:
○ if close to nest, carry fewer larvae per journey,
○ if far from nest, carry more larvae per journey.
● Observational counts of numbers of larvae caught and carried to the nest closely matches theoretically expected values.
E.6.5 Explain how mate selection can lead to exaggerated traits.
An example of this is the peacock’s tail feathers.
● Sexual selection is the struggle between individuals of onesex (normally the males) for the possession of access to individuals of the opposite sex.
● The outcome for a loser of this struggle is few or no offspring.
● Victory in the struggle may depend on the use made of special features of structure or behaviour. These may serve as indicators of fitness factors such as health, size, and adaptive abilities.
● The successful male gains a greater representation of his genes in the next generation, including those associated with mate selection.
● The long-term outcome is the evolution of exaggerated traits that draw attention to a potential mate.
● For example, tail feathers of a peacock are associated with courtship and mate selection.
○ Males with more exaggerated tail feathers will be chosen for mating.
○ The characteristic can become exaggerated to a point that tail feathers become an encumbrance, hindering movement.
E.6.6 State that animals show rhythmical variations in activity.
E.6.7 Outline two examples illustrating the adaptive value of rhythmical behaviour patterns.
Examples could include the diurnal activity variation of hamsters, coordinated spawning in corals, or seasonal reproductive behaviour in deer.
Moonrats
● Moonrats are nocturnal mammals that live in the lowland forests of Asia.
● They forage at night with their strong sense of smell.
● Much of the prey (insects and other invertebrates) are active during night time.
● Moonrats are less vulnerable to predation at night.
● In the day they rest in holes among tree roots or hollow logs where they are unlikely to be discovered.
Red deer
● Red deer reproduce following an annual cycle.
● Males and females are sexually active only during the fall.
● Females form herds associating with a single dominant male, with whom they mate
● Gestation occurs over winter, offspring born in spring
● This system maximizes fitness for:
○ young: maximizing feeding time before 1st winter
○ females: mate only with highest quality male
○ males: large genetic payoff for dominant male, at cost of no genetic payoff for excluded males
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