E1 Stimulus and Response

Assessment statementsE.1.1

Define the terms stimulus, response and reflex in the context of animal behaviour

E.1.2 Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses and effectors in the response of animals to stimuli.

E.1.3 Draw and label a diagram of a reflex arc for a pain withdrawal reflex.

E.1.4 Explain how animal responses can be affected by natural selection, using two examples.

E.1.1 Define the terms stimulus, response and reflex in the context of animal behaviourStimulus

Response

Reflex

A change in the environment (external or internal) detected by a receptore.g. movement, light, soundA change in an organism produced by a stimulus e.g. blinking, turning towards sound

A type of response that is rapid and unconscious e.g. knee jerk, blinking

E.1.2 Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses and effectors in the response of animals to stimuli.Structure Function

to detect a stimulus. Can be sensory cells or nerve endings on sensory neurons.

to receive messages across synapses, from receptors and carry them to the CNS.

to receive messages, across synapses, from sensory neurons and pass them to motor neurons.

to receive messages, across synapses, from relay neurons and carry them to an effector.

to carry out a response after receiving a message from a motor neuron. Can be muscles or glands.

a junction between two neurons. Synaptic transmission involves chemicals called neurotransmitters.

receptor

sensory neuron

relay neuron

motor neuron

effector

synapse

E.1.3 Draw and label a diagram of a reflex arc for a pain withdrawal reflex.

http://www.click4biology.info/c4b/E/E1.htm#3

Reflex Arc

E.1.4 Explain how animal responses can be affected by natural selection, using two examples.

● The ability of an animal to survive is directly affected by its behavioural choices.

● Individuals who make better choices are more likely to survive and produce offspring.

● Choices are determined by genes are inherited by the offspring.

● Changes in the environment that cause behavioural changes may cause change by natural selection.

Example 1 - Migration in Sylvia atricapilla

● Normally, Blackcap migrate south from its summer breeding grounds in Germany to over winter in Spain.

● Recently, some of the Blackcap population (10%) migrate in a westerly direction to the UK.

● The hypothesis is that this behaviour has a genetic basis and that there is an increased fitness value of migration to the west.

Experiment● The researcher collected un-hatched eggs from

parent birds that had visited the UK in the previous winter.

● The eggs are incubated away from the parents and have no contact with parent birds.

● Similarly un-hatched eggs from parent birds that overwintered in Spain the previous winter are collected, incubated and released as before.

Results● Birds of UK parentage flew west.● Birds of Spanish parentage flew south.

Conclusion● The direction of migration is genetically

determined and the population is diverging due to behaviour (not speciation yet).

What is the advantage of flying west to the UK?Less severe winters in the UK due to climate changeBirds going to the UK do not having to traverse the Alps in

their flight path.The UK is much closer meaning that birds returning to the

breeding grounds begin pair bonding much earlier.They will reproduce and pass on this heritable trait of ‘West

flying’ to their offspring.The ‘West flying’ behaviour will become more common.The population has changed with two types of behaviour

emerging ‘south flying’ and ‘west flying’, both are genetically determined.Ref: Stuart Bearhop et al have reported that the northern wintering birds (west flying) are also producing larger clutch sizes and more young.

Example 2 Rejection of Cuckoo Eggs

● Cuckoo lays single eggs in nests of other species

● Cuckoo hatches first and pushes other eggs out of nest

● Cuckoos have evolved various strategies for getting their egg into a host nest.

● Strategies based on host defensive strategies.● Female cuckoos lay eggs that closely

resemble the eggs of their chosen host. ● This has been produced by natural selection,

as some birds are able to distinguish cuckoo eggs from their own, leading to those eggs least like the host's being thrown out of the nest.[

● Cuckoos that show the highest levels of egg mimicry are those whose hosts exhibit high levels of egg rejection behavior.

Example 3 Timing of breeding in Parus major

● Parus major (Great Tit) breeds in spring or early summer throughout much of Europe

● Timing of egg laying is genetically influenced● Day length is used to determine the time of

year

Recent studies of birds in the Netherlands have shown:

● date of egg laying is becoming earlier● adults that breed earlier have greater

reproductive success

This is due to:● earlier opening of leaves on deciduous trees● earlier peak in biomass of invertebrates

feeding on tree leaves● invertebrates are the main food for offspring

(a) Define reflex (1)(b) Below is a diagram of a reflex arc for a pain

withdrawal reflex.

(i) Label the parts indicated by the letters I–IV (2)(ii) Explain the role of parts I and II in a pain

withdrawal reflex (2)

(a) rapid response that occurs automatically/involuntarily in response to a stimulus

(b) (i) Two correct labels for [1].I: sensory neuronII: motor neuronIII: dorsal root (of spinal nerve) NOT dorsal root ganglionIV: white matter (of spinal cord) (ii) Role of part I: [1 max]receptor cell detects stimulus and converts it to a nerve impulse;impulse travels along sensory neuron to (dorsal root of) spinal cord; Role of part II: [1 max]impulse travels along motor neuron to effector organ;causes muscle to contract removing contact with painful stimulus;

Evidence suggests that the behaviour of bees is often a response to odours. Scientists placed bees 200 cm away from an attractive odour source. An experimental group of bees had previous exposure to the odour, a control group had no previous exposure. Both the percentage of bees flying towards (orientated flight) and the percentage circling the odour source were measured.

(a) Calculate the percentage increase in orientated flight between the control group and the experimental group (1)

(b) Describe the effect of previous exposure to the

odour on the flight of bees (2) (c) Outline the type of behaviour that the

experimental group demonstrates (1) (d) Discuss the implications of this study for the

survival of bees (3)(Total 7 marks)

(a) 52-20/20 × 100 = 160% (units required)

(b) bees with previous exposure/experimental group fly around the

sourcemore than the control group;bees with previous exposure/experimental group fly towards the sourcemore than the control group;bees with previous exposure/experimental group circle more than thecontrol group;in bees with previous exposure, orientated flight is greater than circling;Accept vice versa statements. 2

max (c) the bees associate the odour with food, and this is learned/conditioningbehaviourDo not accept taxis or simply learned behaviour or conditioning. 1 (d) previous exposure leads bees to fly to food source more directly;giving them an advantage in finding food;increasing their chance of survival;and passing their genes to the next generation;less energy expended finding food;more direct flight/less flight time reduces chance of predation; 3

max