Download 4. Responding to environment Booklet [A2]

SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Responding to the environment: plant responses
Learning objectives:
 Explain why plants need to respond to their environment in terms of the need to avoid
predation and abiotic stress;
 Define the term tropism;
 Explain how plant responses to environmental changes are co-ordinated by hormones, with
reference to responding to changes in light direction;
 Evaluate the experimental evidence for the role of auxins in the control of apical dominance
and gibberellin in the control of stem elongation;
 Outline the role of hormones in leaf loss in deciduous plants;
 Describe how plant hormones are used commercially;
Key definitions:
Compile a glossary by writing your own definitions for the following key terms related to the
learning objectives above.
Key term
biotic
abiotic
tropisms
hormones
meristems
apical dominance
auxins
gibberellins
ethene
Definition
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Plant responses
Even though most plants are firmly rooted in the ground, they are still capable of responding and
making adjustments to changes in their external environment. This ability is manifested chiefly in
changing patterns of growth. These responses may involve relatively sudden physiological changes,
as occurs in flowering, or a steady growth response, such as a tropism. Other responses made by
plants include nastic movements, circadian rhythms, photoperiodism, dormancy, and vernalisation.
Tropisms: growth responses made by plants to directional external stimuli, where the
direction of the stimulus determines the direction of the growth response. A tropism may be
positive (towards the stimulus), or negative (away from the stimulus). Common stimuli for
plants include light, gravity, touch, and chemicals.
Life cycle responses: plants use seasonal changes in the environment as cues for the
commencement or ending of particular life cycle stages. Such changes are mediated by plant
growth factors, such as phytochrome and gibberellin. Examples include flowering and other
photoperiodic responses, dormancy and germination, and leaf fall.
Rapid responses to environmental stimuli: plants are quite capable of rapid responses.
Examples include the closing of stomata in response to water loss, opening and closing of
flowers in response to temperature, and nastic responses. These responses often follow a
circadian rhythm.
Plant competition and allelopathy: although plants are rooted in the ground, they can still
compete with other plants to gain access to resources. Some plants produce chemicals that
inhibit the growth of neighbouring plants. Such chemical inhibition is called allelopathy.
Plants also compete for light and may grow aggressively to shade out slower growing
competitors.
Plant responses to herbivory: many plant species have responded to grazing or browsing
pressure with evolutionary adaptations enabling them to survive constant cropping.
Examples include rapid growth to counteract the constant loss of biomass (grasses), sharp
spines or thorns to deter browsers (acacias, cacti), or toxins in the leaf tissues (eucalyptus).
In contrast to animal cells, the cell wall around a plant cell limits the cell’s ability to divide and
expand. Growth, therefore, only happens in particular places in the plant, where there are groups of
immature cells that are still capable of dividing. These places are called meristems.


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Apical meristems are located at the tips or apices of roots and shoots, and are responsible
for the roots and shoots getting longer.
Lateral bud meristems are found in the buds. These could give rise to side shoots.
Lateral meristems are found in a cylinder near the outside of roots and shoots and are
responsible for the roots and shoots getting wider.
In some plants, intercalary meristems are located between the nodes (where leaves and
buds branch off the stem). Growth between the nodes is responsible for the shoot getting
longer.
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Auxins, gibberellins, and ABA
Auxin was the first substance to be identified as a plant hormone. Charles Darwin and his son
Francis were first to recognise its role in stimulating cell elongation, while Frits W. Went isolated
this growth-regulating substance, which he called auxin. Indole-acetic acid (IAA) is the only known
naturally occurring auxin. Shortly after its discovery it was found to have a role in suppressing the
growth of lateral buds. This inhibitory influence of a shoot tip or apical bud on the lateral buds is
called apical dominance. Two Japanese scientists isolated gibberellin in 1934, eight years after the
isolation of auxin, and more than 78 gibberellins have now been identified.
Gibberellins are involved in stem and leaf elongation, as well as breaking dormancy in seeds.
Specifically, they stimulate cell division and cell elongation, allowing stems to ‘bolt’ and the root to
penetrate the testa in germination.
During the 1960s, Frederick T. Addicott discovered a substance apparently capable of accelerating
abscission in leaves and fruit, and which is now called abscisic acid (ABA). Although it now seems
that ABA has very little to do with leaf abscission, it is a growth inhibitor and also stimulates the
closing of stomata in most plant species. It is also involved in preventing premature germination
and development of seeds.
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Phototropism
In a phototrophic response, a shoot bends towards a light source. This happens because the shaded
side elongates faster than the illuminated side, which pushes the end of the shoot towards the light.
Evidence from experiments involving cereal seedlings in particular suggests that the light shining on
one side of the shoot causes the auxins to be transported to the shaded side, where they promote
an increase in the rate of elongation, making the shoot bend towards the light.
How the light causes redistribution of auxin is still uncertain. Two enzymes have been identified
(phototropin 1 and phototropin 2). Their activity is promoted by blue light wavelength (400-450nm).
Hence, there is a lot of phototropin 1 activity on the light side, but progressively less activity
towards the dark side. This gradient is thought to cause the redistribution of auxins.
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1. Plant responses to environmental changes are co-ordinated by plant growth
substances (plant hormones).
(a) Explain why plants need to be able to respond to their environment.
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(b) The following investigation was carried out into the effects of plant growth
substances on germination:
 a large number of lettuce seeds was divided into eight equal batches
 each batch of seeds was placed on moist filter paper in a Petri dish
and given a different treatment
The different treatments are shown in Table 6.1. each tick represents one
of the eight batches of seeds.
The batches of seeds were left to germinate at 25°C in identical conditions
and the percentage germination was calculated.
Fig. 6.1 (on the next page) shows the results of this investigation.
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Describe, with reference to Fig. 6.1, the effects of the plant growth
substances on the germination of lettuce seeds.
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(c) Explain why all lettuce seeds were kept at 25°C.
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A2 BIOLOGY
(d) State three variables, other than temperature, that needed to be controlled
in the investigation.
1 ____________________________________________________________
2 ____________________________________________________________
3 _________________________________________________________ [3]
(e) State two commercial uses of plant growth substances.
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2. State the term used to describe:
(i) a directional growth response of a plant
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(ii) a signalling molecule that enables plants to respond to environmental
change
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(iii) plants that lose their leaves seasonally
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(iv) the process of managing an ecosystem sustainably to protect biodiversity
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(v) organisms that return inorganic minerals from the bodies of dead
organisms to the abiotic environment
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(vi) the conversion of nitrogen gas to ammonium compounds in the soil
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3. Plants are able to respond to changes in their environment.
(a) Describe two ways in which hormones may alter a plant’s growth in
response to overcrowding by other plants.
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(b) Suggest how hormones alter a plant’s growth if the top of the plant shoot is
eaten by an animal.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Responding to the environment: animal responses
Learning objectives:
 Discuss why animals need to respond to their environment;
 Outline the organisation of the nervous system in terms of central and peripheral systems in
humans;
 Outline the organisation and roles of the autonomic nervous system;
 Describe, with the aid of diagrams, the gross structure of the human brain, and outline the
functions of the cerebrum, cerebellum, medulla oblongata and hypothalamus;
 Describe the role of the brain and nervous system in the co-ordination of muscular
movement;
 Describe how co-ordinated movement requires the action of skeletal muscles about joints,
with reference to the movement of the elbow joint;
 Explain, with the aid of diagrams and photographs, the sliding filament model of muscular
contraction;
 Outline the role of ATP in muscular contraction, and how the supply of ATP is maintained in
muscles;
 Compare and contrast the action of synapses and neuromuscular junctions;
 Outline the structural and functional differences between voluntary, involuntary and cardiac
muscle;
 State that responses to environmental stimuli in mammals are co-ordinated by nervous and
endocrine systems;
 Explain how, in mammals, the ‘fight or flight’ response to environmental stimuli is coordinated by the nervous and endocrine systems;
Key definitions:
Compile a glossary by writing your own definitions for the following key terms related to the
learning objectives above.
Key term
cerebrum
cerebellum
hypothalamus
medulla oblongata
central nervous system
Definition
SACKVILLE SCIENCE DEPARTMENT
Key term
peripheral nervous
system
antagonistic
synovial joint
neuromuscular junction
gradation of response
actin
myosin
involuntary muscle
cardiac muscle
voluntary muscle
myogenic
sarcomere
cross-bridge
power stroke
‘fight or flight’ response
stressor
Definition
A2 BIOLOGY
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
The brain
The brain is one of the largest organs in the body. It is protected by the skull, the meninges
(membranous coverings), and the cerebrospinal fluid (CSF). The brain is the control centre for the
body. It receives a constant flow of information from the senses, but responds only to what is
important at the time. Some responses are very simple e.g. cranial reflexes, whilst others require
many levels of processing. The human brain is noted for its large, well developed cerebral region,
and the region responsible for complex thought and reasoning. Each cerebral hemisphere is divided
into four lobes by deep sulci or fissures. These lobes: temporal, frontal, occipital, and parietal,
correspond to the bones of the skull under which they lie.
Primary structural regions of the brain
Cerebrum: is divided into two cerebral hemispheres and has many, complex roles. It
contains sensory, motor, and association areas, and is involved in memory, emotion,
language, reasoning, and sensory processing.
Ventricles: cavities containing the CSF, which absorbs shocks and delivers nutritive
substances.
Thalamus: is the main relay centre for all sensory messages that enter the brain, before they
are transmitted to the cerebrum.
Hypothalamus: controls the autonomic nervous system and links nervous and endocrine
systems. Regulates appetite, thirst, body temperature, and sleep.
Brain stem: made up of the midbrain, pons and medulla – relay centre for impulses between
the rest of the brain and the spinal cord. Controls breathing, heartbeat, and the coughing
and vomiting reflexes.
Cerebellum: coordinates body movements, posture and balance.
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Sensory and motor regions in the cerebrum
General sensory area: receives sensations from receptors in the skin, muscles and viscera.
Sensory information from receptors on one side of the body crosses over to the opposite
side of the cerebral cortex where conscious sensations are produced. The size of the sensory
region for different body parts depends on the number of receptors in that particular body
part.
Primary motor area: controls muscle movement. Stimulation of a point on one side of the
motor area results in muscular contraction on the opposite side of the body.
Primary gustatory area: interprets sensations related to taste.
Visual areas: within the occipital lobe receive, interpret, and evaluate visual stimuli. In
vision, each eye views both sides of the visual field but the brain receives impulses from left
and right visual fields separately. The visual cortex combines the images into a single
impression or perception of the image.
Auditory areas: interpret the basic characteristics and meanings of sounds.
Language areas: the motor speech area (Broca’s area) is concerned with speech production,
the sensory speech area (Wernicke’s area) is concerned with speech recognition and
coherence.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Organising the nervous system
The nervous system is the body’s control and communication centre. It has three broad functions:
detecting stimuli, interpreting them, and initiating appropriate responses.
The central nervous system
The CNS comprises the brain and spinal cord. The spinal cord is a cylinder of nervous tissue
extending from the base of the brain down the back, protected by the spinal column. It transmits
messages to and from the brain, and controls spinal reflexes.
The spinal cord has an H shaped central area of grey matter, comprising nerve cell bodies,
dendrites, and synapses around a central canal filled with cerebrospinal fluid. The area of white
matter contains the nerve fibres.
The peripheral nervous system
The PNS comprises all the nerves and sensory receptors outside the CNS. The PNS comprises
sensory and motor divisions. Peripheral nerves all enter or leave the CNS, either from the spinal
cord (the spinal nerves) or the brain (cranial nerves). They can be sensory (from sensory receptors),
motor (running to a muscle or gland), or mixed (containing sensory and motor neurones). Cranial
nerves are numbered in roman numerals, I-XII. They include the vagus (X), a mixed nerve with an
important role in regulating bodily functions, including heart rate and digestion.
Sensory division
Sensory nerves arise from sensory receptors and carry messages to the central nervous system for
processing. The sensory system keeps the CNS aware of the external and internal environments.
This division includes the familiar sense organs such as ears, eyes and taste buds as well as internal
receptors that monitor internal state e.g. thirst, hunger, body position, movement, pain.
Motor division
Motor nerves carry impulses from the CNS to effectors: muscles and glands. The motor division
comprises two parts:
somatic nervous system – the neurones that carry impulses to voluntary (skeletal) muscles;
autonomic nervous system – regulates visceral functions over which there is generally no
conscious control e.g. heart rate, gut peristalsis involving smooth muscle, pupil reflex, and
sweating;
The autonomic nervous system
The ANS regulates involuntary visceral functions by means of reflexes. Although most ANS activity is
beyond our conscious control, voluntary control over some basic reflexes such as bladder emptying
can be learned. Most visceral effectors have dual innervation, receiving fibres from both branches
of the ANS.
These two branches, the parasympathetic and sympathetic divisions, have broadly opposing
actions on the organs they control (excitatory or inhibitory). Nerves in the parasympathetic division
release acetylcholine. This neurotransmitter is rapidly deactivated at the synapse and its effects are
short lived and localised. Most sympathetic postganglionic nerves release noradrenaline, which
enters the bloodstream and is deactivated slowly. Hence, sympathetic stimulation tends to have
more widespread and long lasting effects than parasympathetic stimulation.
Aspects of ANS structure and function are illustrated on the next page.
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Parasympathetic division
Iris of eye, tear glands, salivary glands: constricts pupil, stimulates secretion of the glands.
Heart and lungs: slows heart rate, dilates coronary blood vessels, constricts bronchial
muscle.
Liver, stomach, small intestine, pancreas: increases peristalsis (motility), promotes sugar
storage, and insulin and enzyme secretion.
Large intestine, bladder, genital organs: increases peristalsis, causes contraction of bladder
wall, stimulates genital erection in both sexes and secretion in females.
Ganglia are in or near the organ: preganglionic nerves are long, postganglionic nerves are short.
Sympathetic division
Iris of eye, salivary glands: dilates pupil and decreases secretion of glands.
Heart and lungs: increases heart rate, constricts coronary blood vessels, dilates bronchial
muscle.
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Liver, stomach, small intestine, pancreas: decreases peristalsis (slows motility), promotes
sugar release from liver, inhibits insulin and enzyme secretion.
Large intestine: decreases peristalsis (slows motility).
Bladder, genital organs: causes relaxation of bladder wall, stimulates pregnant uterus to
contract, stimulates ejaculation.
Ganglia are close to spinal cord: preganglionic nerves are short, postganglionic nerves are long.
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Coordinated movement
Bones are too rigid to bend without damage. To allow movement, the skeletal system consists of
many bones held together at joints by flexible connective tissues called ligaments. All movements
of the skeleton occur at joints: points of contact between bones, or between cartilage and bones.
Joints may be classified according to the amount of movement they permit: none (sutures), slight
movement (symphyses), and free movement in one or more planes e.g. synovial joints. Bones are
made to move about a joint by the force of muscles acting upon them. The muscles are attached to
bone by tendons. Many muscles act in antagonistic pairs, one set causing the joint to move one
way, the other set causing its return.
The skeleton of an animal works as a system of levers. The joint acts as a fulcrum, he muscles exert
the force, and the weight of the bone being moved represents the load. Contraction causes a
muscle to shorten and this shortening moves attached bones. When only a few fibres in a muscle
contract, the muscle will tighten but not produce movement. This partly contracted muscle state is
responsible for muscle tone and is important in maintaining posture. The amount of muscle
contraction is monitored by sensory receptors in the muscle called muscle spindle organs. These
provide the sensory information necessary to adjust movement as require.
The action of antagonistic muscles
The flexion (bending) and extension (unbending) of limbs is caused by the action of antagonistic
muscles; muscles that work in pairs and whose actions oppose each other. Every coordinated
movement in the body requires the application of muscle force. This is accomplished by the action
of agonists, antagonists, and synergists. The opposing action of agonists and antagonists also
produces muscle tone. Note that either muscle in an antagonistic pair can act as the prime mover,
depending on the movement (flexion or extension).
Agonists or prime movers: muscles that are primarily responsible for the movement and
produce most of the force required.
Antagonists: muscles that oppose the prime mover. They may also play a protective role by
preventing overstretching of the prime mover.
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Synergists: muscles that assist the prime movers and may be involved in fine-tuning the
direction of movement.
During flexion of the forearm at the elbow, the biceps brachii acts as the prime mover, and the
antagonist, the triceps brachii at the back of the arm, is relaxing. During extension, their roles are
reversed.
Movement of the leg is accomplished through the action of several large groups of muscles,
collectively called the quadriceps and the hamstrings. The hamstrings are actually a collection of
three muscles, which act together to flex the leg. The quadriceps at the front of the thigh (a
collection of four large muscles) opposes the motion of the hamstrings and extends the leg. When
the prime mover contracts very forcefully, the antagonist also contracts very slightly. This prevents
any overstretching and allows greater control over thigh movement.
The role of the muscle spindle
Changes in the length of a muscle are monitored by the muscle spindle organ, a stretch receptor
located within skeletal muscle, parallel to the muscle fibres themselves. The muscle spindle is
stimulated in response to sustained or sudden stretch on the central region of its specialised
intrafusal fibres. Sensory information from the muscle spindle is relayed to the spinal cord. The
motor response brings about adjustments to the degree of stretch in the muscle. These adjustments
help in the coordination and efficiency of muscle contraction. Muscle spindles are important in the
maintenance of muscle tone, postural reflexes, and movement control, and are concentrated in
muscles that exert fine control over movement.
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1. Impulses arriving at the neuromuscular junction cause vesicles to fuse with the pre-synaptic
membrane and release acetylcholine into the gap.
2. Acetylcholine binds to receptors on the muscle fibre membrane (sarcolemma) causing
depolarisation.
3. Depolarisation wave travels down tubules (T system).
4. T system depolarisation leads to Ca2+ release from stores in sarcoplasmic reticulum
(specialised endoplasmic reticulum).
5. Ca2+ binds to proteins in the muscle, which leads to contraction.
6. Acetylcholinesterase in the gap rapidly breaks down acetylcholine so that contraction only
occurs when impulses arrive continuously.
Three types of muscle
There are three kinds of muscle: skeletal, cardiac and smooth muscle, each with a distinct
structure. The muscles used for posture and locomotion are skeletal (striated) muscles. Their
distinct striped appearance is the result of the regular arrangement of contractile elements with the
muscle cells. Muscle cells are innervated by motor neurones, each of which terminates in a
specialised cholinergic synapse called the motor end plate. A motor neurone and all the fibres it
innervates is called a motor unit.
Skeletal muscle, also called striated or striped muscle has a
banded appearance under high power microscopy.
Sometimes called voluntary muscle because it is under
conscious control. The cells are large with many nuclei at the
edge of each cell.
Cardiac muscle is specialised striated muscle that does not
fatigue. Cells branch and connect with each other to assist
the passage of nerve impulses through the muscle. Cardiac
muscle is not under conscious control (it is involuntary).
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Smooth muscle is also called involuntary muscle because it is
not under conscious control. Contractile filaments are
irregularly arranged so the contraction is not in one direction
as in skeletal muscle. Cells are spindle shaped with one
central nucleus.
Structure of skeletal muscle
Skeletal muscle is organised into bundles of muscle cells or fibres. Each fibre is a single cell with
many nuclei and each fibre is itself a bundle of smaller myofibrils arranged lengthwise. Each
myofibril is in turn composed of two kinds of myofilaments (thick and thin), which overlap to form
light and dark bands. It is the alternation of these light and dark bands which gives skeletal muscle
its striated or striped appearance. The sarcomere, bounded by the dark Z lines, forms one complete
contractile unit.
Within a myofibril, thin filaments, held together by the Z lines, project in both directions. The arrival
of a nerve impulse sets in motion a series of events that cause the thick and thin filaments to slide
past each other. This contraction results in shortening of the muscle and is accompanied by visible
change in the appearance of the myofibril: the I band and the sarcomere shorten and H zone
shortens or disappears.
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The sliding filament hypothesis
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Muscle contraction requires calcium ions (Ca2+) and energy (in the form of ATP) in order for the
thick and thin filaments to slide past each other. The steps are:
1. The binding sites on the actin molecule (to which myosin ‘heads’ will locate) are blocked by
a complex of two molecules: tropomyosin and troponin.
2. Prior to muscle contraction, ATP binds to the heads of the myosin molecules, priming them
in an erect high energy state. Arrival of an action potential causes a release of Ca 2+ from the
sarcoplasmic reticulum. The Ca2+ binds to the troponin and causes the blocking molecules to
move so that the myosin binding sites on the actin filament become exposed.
3. The heads of the cross-bridging myosin molecules attach to the binding sites on the actin
filament. Release of energy from the hydrolysis of ATP accompanies the cross bridge
formation.
4. The energy released from ATP hydrolysis causes a change in shape of the myosin cross
bridge, resulting in a bending action (the power stroke). This causes the actin filaments to
slide past the myosin filaments towards the centre of the sarcomere.
5. Fresh ATP attaches to the myosin molecules, releasing them from the binding sites and
repriming them for a repeat movement. They become attached further along the actin chain
as long as ATP and Ca2+ are available.
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1. Fig. 4.1 shows a junction between two neurones where the neurotransmitter is
dopamine.
Fig. 4.2 shows a neuromuscular junction.
(a) Complete Table 4.1 below to compare the structure and function of the
dopamine synapse and the neuromuscular junction.
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(b) The sequence of events at a dopamine synapse is given below:
 dopamine molecules bind to the protein receptors on the
postsynaptic membrane and trigger a response;
 dopamine leaves the receptors and moves back into the presynaptic
neurone;
 some dopamine is repackaged into vesicles;
 some dopamine is broken down by the enzyme monoamine oxidase
(MAO);
Table 4.2 summarises the action of some drugs that affect dopamine
synapses.
Use the information in Table 4.2 to suggest which drug molecule could have
a shape that differs from that of the dopamine molecules. Give a reason for
your answer.
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(c) Schizophrenia is a condition in which there is a higher than usual level of
dopamine in certain areas of the brain.
Suggest why phenothiazine is used to treat schizophrenia.
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(d) DRD4 is a dopamine receptor in humans. The DRD4 receptor gene has a
large number of alleles, of which a single individual can only have two.
Explain why one individual can only have two of the different alleles of the
DRD4 gene.
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(e) Name a technique that would reveal differences in the lengths of the
different forms of the DRD4 receptor gene.
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(f) Three alleles of DRD4 have the following alterations:
 a single base-pair substitution
 a 21 base-pair deletion
 a 13 base-pair deletion
Suggest which of the three mutations will have the most serious
consequences for the structure of the protein receptor. Give a reason for
your choice.
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(g) One allele of DRD4 has been found more frequently amongst individuals
whose personality is described as ‘novelty-seeking’ and whose behaviour
tends to be exploratory and impulsive. Suggest how this particular allele of
the DRD4 receptor could have become common in the human population.
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2. This question is about types of muscle and how the nervous system and
hormones control their activity.
(a) There are three types of muscle within the human body. These differ in
their cellular structure and in their function.
Complete Table 2.1 (below) to show how each type of muscle differs from
the other two types.
[6]
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(b) The human thorax is the area between the base of the neck and the base of
the rib cage. All three types of muscle can be found within this area.
For each type of muscle, identify where in the thorax this type of muscle
may be found.
voluntary _____________________________________________________
involuntary ___________________________________________________
cardiac ______________________________________________________
[3]
(c) Fig. 2.1 shows a vertical section through the human brain.
Use Fig. 2.1 to state the letter (B to E) of the part of the brain that would be
involved in the following:
adjusting the rate of contraction of cardiac muscle
________
clapping the hands together
________
automatically correcting balance when riding a bike
________
[3]
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(d) Movement disorders are conditions in which people lose the ability to
control their body movements.
Scientists have discovered that inserting electrodes to stimulate parts of the
brain can help to cure some movement disorders. This discovery has
resulted from experimental work with monkeys, which has made the
research controversial.
Suggest why monkeys rather than other laboratory animals, such as rats,
were used for this work and comment on whether their use in this way is
justified or not.
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(e) The ‘fight or flight’ response to threatening environmental stimuli is
coordinated by the nervous and endocrine systems.
Describe and explain how the activation of the ‘fight or flight’ response
affects voluntary, involuntary and cardiac muscle.
In your answer, for each type of muscle, you should give a named structure
in which it is found and explain how the nervous and endocrine systems
affects its response.
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A2 BIOLOGY
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3. The autonomic nervous system has two divisions, each of which uses a
different neurotransmitter to bring about effects in the internal organs.
(a) In the table below, state which division of the autonomic nervous system
will be active in each case, and name the neurotransmitter that will be
secreted by neurones into the organs.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(b) State precisely where in the body adrenaline is produced.
___________________________________________________________ [9]
(c) The adrenaline molecule is not lipid-soluble, therefore it cannot pass
directly through the cell surface membrane. In order to bring about changes
inside the cell, adrenaline relies on a second messenger system.
Describe the events that occur after adrenaline reaches the cell surface
membrane that then result in metabolism inside the cell cytoplasm.
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(d) The second messenger system is a multi-step mechanism. It enables large
changes in cell metabolism to occur rapidly, although only relatively small
numbers of adrenaline molecules are involved.
Suggest how having a number of steps in the signalling pathway enables a
small number of adrenaline molecules to rapidly cause large effects.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
4. Fig. 2.1 is an electron micrograph showing a longitudinal section of contracted
striated muscle.
(a) Using Fig. 2.1, identify T, U and V.
T ____________________________________________________________
U ____________________________________________________________
V _________________________________________________________ [3]
(b) Using Fig. 2.1, name the structure between positions X and Y.
___________________________________________________________ [1]
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(c) Explain why glycogen granules are present in striated muscle.
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(d) Calculate the actual distance between positions X and Y on Fig. 2.1.
Show your working. Give your answer to the nearest 0.1 of a micrometre
(μm).
Answer = ____________________ μm [2]
(e) Fig. 2.2 below shows the arrangement of thick and thin filaments in striated
muscle.
State what happens to the lengths of the following when muscle contracts:
A band _______________________________________________________
H zone _______________________________________________________
I band _____________________________________________________ [3]
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(f) During strenuous exercise, the concentration of hydrogen ions in muscle
tissue increases. A high concentration of hydrogen ions reduces the ability
of calcium ions to bind to proteins in the myofibrils. This reduces the force
with which a muscle can contract.
Use this information and your own knowledge of the proteins in muscle
cells to explain how an increased concentration of hydrogen ions leads to a
reduction in the force of contraction of a muscle.
In your answer, you should make clear the link between the increased
concentration of hydrogen ions and the reduction in the force of contraction of
the muscle
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___________________________________________________________ [6]
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
5. Fig. 2.1 is a diagram showing a section through the human brain.
(a) Use Fig. 2.1 to identify a part of the brain, A, B, C, D or E, that is responsible
for:
coordination of the autonomic control of heart rate
________
coordination of osmoregulation by the kidney
________
coordination of the muscle involved in walking in an adult
________
coordination of muscles required to bend elbow joint deliberately ________
[4]
(b) Fig. 2.2, on the next page, shows the component of the human elbow joint.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Describe how three named components of the elbow joint interact to bring
about hinge movement (bending of the arm).
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(c) Outline the organisation and roles of the autonomic nervous system in
mammals.
In your answer, you should discuss the differences in physical arrangement,
and the differences in function of both parts of the autonomic nervous system
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
6. Animals and plants need to respond to changes in their environment.
(a) Give two reasons why both plants and animals need to be able to respond
to changes in their environment.
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(b) Plants coordinate their responses to environmental stimuli using hormones.
Mammals also coordinate responses to some stimuli using hormones.
State three differences in the ways in which plant and mammalian
hormones operate.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Responding to the environment: animal behaviour
Learning objectives:
 Explain the advantages to organisms of innate behaviour;
 Describe escape reflexes, taxes and kineses as examples of genetically-determined innate
behaviours;
 Explain the meaning of the term learned behaviour;
 Describe habituation, imprinting, classical and operant conditioning, latent and insight
learning as examples of learned behaviours;
 Describe, using one example, the advantages of social behaviour in primates;
 Discuss how the links between a range of human behaviours and the dopamine receptor
DRD4 may contribute to the understanding of human behaviour;
Key definitions:
Compile a glossary by writing your own definitions for the following key terms related to the
learning objectives above.
Key term
innate behaviour
learned behaviour
habituation
imprinting
classical conditioning
operant conditioning
social behaviours
psychosis
longitudinal study
Definition
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
The components of behaviour
Behaviour in animals can be attributed to two components: innate behaviour that has a genetic
basis, and learned behaviour, which results from the experiences of the animal. Together they
combine to produce the total behaviour exhibited by the animal. It should also be noted that
experience can modify innate behaviour. Animals behave in ‘automatic ways’ in many situations.
The innate behaviour follows a classical pathway called a fixed-action pattern (FAP) where an
innate behavioural programme is activated by a stimulus or releaser to direct some kind of
behavioural response. Innate behaviours are generally adaptive and are performed for a variety of
reasons. Learning, which involves the modification of behaviour by experience, occurs in various
ways.
Innate behaviours
Reflex behaviour is the simplest type of animal behaviour. A sudden stimulus induces an
automatic involuntary and stereotyped response. Many reflexes are protective.
Kinesis – random movement of an animal in which the rate of movement is related to the
intensity of the stimulus, but not to its direction.
Taxis – a movement in response to the direction of a stimulus. Movement towards a
stimulus are positive while those away from a stimulus are negative.
Stereotyped behaviour occurs when the same response is given to the same stimulus on
different occasions. This behaviour shows fixed patterns of coordinated movements called
fixed action patterns.
Learned behaviours
Classical conditioning: animals may associate one stimulus with another.
Habituation: response to a stimulus wanes when it is repeated with no apparent effect.
Insight behaviour: correct behaviour on the first attempt where the animal has no prior
experience.
Imprinting behaviour: during a critical period, an animal can adopt a behaviour by latching
onto its first stimulus.
Operant conditioning: also called trial and error learning, an animal is rewarded or punished
after chance behaviour.
Imprinting occurs when an animal learns to make a particular response only to one type of animal
or object. Imprinting differs from most other kinds of learned behaviour in that it normally can
occur only at a specific time during an animal’s life. This critical period is usually shortly after
hatching (about 12 hours) and can last for several days. While a critical period and the resulting
imprinted behaviour are normally irreversible, they are not considered rigidly fixed. There are
examples of animals that have had abnormal imprinted behaviours revert to the ‘wild type’. There
are two main types of imprinting using visual and auditory stimuli: filial and sexual imprinting.
Breeding ground imprinting uses olfactory (smell) stimuli.
Operant conditioning
Operant conditioning is used to describe a situation where an animal learns to associate a particular
behavioural act with a reward (as opposed to a stimulus in classical conditioning). This behaviour
determines whether or not the reward appears. Burrhus Skinner studied operant conditioning using
an apparatus he invented called a Skinner box. Skinner designed the box so that when an animal
(usually a pigeon or rat) pushed a particular button it was rewarded with food. The animals learned
to associate the pushing of the button with obtaining food (the reward).
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
The behavioural act that leads the animal to push the button in the first place is thought to be
generated spontaneously (by accident or curiosity). This type of learning is also called instrumental
learning because the spontaneous behaviour is instrumental in obtaining the reward. Operant
conditioning is the predominant learning process found in animals.
Classical (Pavlovian) conditioning
Classical conditioning, founded by Ivan Pavlov, describes a type of associative learning in which
behaviour that is normally triggered by a certain stimulus comes to be triggered by a substitute
stimulus that previously had no effect on the behaviour. Between 1890 and 1900, Pavlov noticed
that the dogs he was studying would salivate when they knew they were to be fed. It was
determined that the dogs were alerted by a bell that rung every time the door into the lab was
opened. Through experimentation, Pavlov discovered that the ringing of the bell initially brought
about no salivation, but the dogs could be conditioned to relate the ringing of the bell to the
presentation of food. Eventually the ringing of the bell elicited the same salivation response as the
presentation of food, indicating that the dog was conditioned to associate the two stimuli.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
1. Describe briefly one example of each of the following types of animal
behaviour:
(a) habituation
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(b) operant conditioning
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(c) social behaviour in primates and its importance
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___________________________________________________________ [3]
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
2. Animals behave in ways that enhance their survival and reproductive capacity.
This behaviour may be innate or learned.
(a) Describe what is meant by innate behaviour.
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(b) Describe what is meant by learned behaviour.
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(c) Describe the advantages to animals of innate and learned behaviour, with
reference to specific examples of each type of behaviour.
In your answer, you should include both types of behaviour and make clear the
advantages to the animals of your chosen examples
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
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3. Animals respond to frightening or stressful stimuli in their environment.
This question is about the ‘fight or flight’ response in mammals.
Fig. 2.1 below shows a husky dog in a calm state.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Fig. 2.2 below shows a different husky displaying external signs of the ‘fight or
flight’ response.
(a) Describe three features in the external appearance of the husky in Fig. 2.2
that are due to the ‘fight or flight’ response.
1 ____________________________________________________________
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2 ____________________________________________________________
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3 ____________________________________________________________
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(b) The ‘fight or flight’ response is brought about by the hormone adrenaline
and the autonomic nervous system working together. As well as causing
external differences in appearances, the ‘fight or flight’ response causes
numerous changes in the functioning of the internal organs. Complete Table
2.1 to describe how two internal organs would function differently in a calm
mammal compared to a frightened mammal.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
4. A long-term breeding experiment to investigate the genetic basis of tame
(friendly) behaviour was carried out in a population of silver foxes. The foxes
were bred each year and the resulting young foxes assessed each month
between the ages of 1 and 8 months to see how tame they were.
Table 6.1 shows how the foxes were put into categories according to their
tameness.
The tamest 5% of the male foxes and the tamest 20% of the female foxes in
each generation were used for breeding to produce the next generation. This
was repeated for over forty generations.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(a) State the name given to the process in which only a certain percentage of
adult foxes were chosen by humans to breed in each generation.
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(b) Suggest why 20% of the female foxes were used for breeding but only 5% of
the male foxes.
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(c) Table 6.2 shows the number of foxes in the elite tameness class during the
long-term experiment.
Discuss what the results shown in Table 6,2 suggest about the causes of the
variation in tameness behaviour in silver foxes.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
______________________________________________________________
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(d) As tameness increased in the silver fox population over the years, it was
noticed that other phenotypic traits also became more common.
Table 6.3 compares the frequency of these traits in a control group of silver
foxes that had not been used in this long-term breeding experiment and in
the tame population of foxes.
Students were asked to suggest a variety of genetic hypotheses to explain
why these traits become more common in tame foxes. Their suggestions
were:
linkage
epistasis
inbreeding
genetic drift
Select one hypothesis from the list and explain how it could account for the
data in Table 6.3.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(e) Similar changes in tameness, colour and body shape are believed to have
occurred in the 11 000 year period during which the grey wolf species, Canis
lupus, evolved into the domesticated dog species, Canis familiaris.
Suggest how different types of isolating mechanism allowed dogs to evolve
separately to wolves.
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(f) Interbreeding between members of the wolf species and some dogs has
been reported.
However, there are some large breeds of dogs that cannot breed
successfully with small dog breeds.
Use this information and your own knowledge to explain the problems of
classifying wolves and different dog breeds according to:
 the biological species concept
and
 the phylogenetic species concept
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
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5. This question is about evolution, genetics, behaviour and physiology of cats.
Fig. 1.1. below shows a Scottish wildcat, Felis sylvestris.
Modern domestic cats evolved from a wild ancestor of similar appearance to
the Scottish wildcat.
Fig. 1.2 on the next page, shows a breed of domestic cat, Felis cattus. This
breed is called the Colourpoint Persian cat.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(a) State two phenotypic differences between the Scottish wildcat in Fig. 1.1
and the Colourpoint Persian cat in Fig. 1.2.
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(b) Name the process that:
has given rise to the modern domestic cat from its wild ancestor
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has given rise to coat colour variation in cats
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(c) In Colourpoint Persian cats, interaction between two genes, B/b and D/d,
causes the colour of the face, ears, paws and tail.
The dominant allele, B, gives a dark brown colour, known as ‘seal’.
The recessive allele, b, gives a light brown colour, known as ‘chocolate’.
The dominant allele, D, has no effect on coat colour.
However , the presence of two copes of the recessive allele, d, changes the
colour ‘seal’ to a colour known as ‘blue’, and ‘chocolate’ to a colour known
as ‘lilac’.
State the name given to this type of genetic interaction.
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Suggest the possible genotypes of a ‘seal’ Colourpoint Persian cat.
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[4]
(d) A ‘lilac’ Colourpoint Persian cat is homozygous at both the B/b and the D/d
gene locus.
What is meant by the terms homozygous and gene locus?
homozygous
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gene locus
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
(e) A cross was carried out between a ‘seal’ cat and a ‘lilac’ Colourpoint Persian
cat. A Punnett square of the expected genotypes of the offspring of this
cross is shown in Table 1.1.
Use Table 1.1 to state the phenotypes of the offspring and to predict the
phenotypic ratio.
phenotypes
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phenotypic ratio
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(f) Breeders of Colourpoint Persian cats are advised to be present at the birth
of the kittens. In this breed, the mother cat may not perform essential
maternal behaviour such as licking the newborn kitten to free it from its
amniotic sac (the membrane surrounding it at birth).
Wildcat mothers, even when they are first-time mothers, perform this
behaviour naturally.
State the type of behaviour shown by these wildcat mothers.
Give one characteristic of this type of behaviour.
type of behaviour ______________________________________________
characteristic __________________________________________________
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Over time, the frequency of domestic cat mothers who perform essential
maternal behaviour, such as licking the newborn kitten, had decreased.
SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
Suggest and explain a reason for this change in frequency over time.
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(g) Breeding pedigree cats, such as Colourpoint Persian cats, may involve
crossing closely related individuals in order to obtain desirable
characteristics.
Physiological problems are more common in pedigree animals than in wild
animals.
Suggest why physiological problems are more common in pedigree animals.
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(h) An example of a physiological problem in Colourpoint Persian cats is that
some of them cannot digest lactose sugar in milk. These cats can be fed
lactose-reduced milk which is made by a biotechnological process using
immobilised lactase enzyme.
State two methods of immobilising an enzyme.
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SACKVILLE SCIENCE DEPARTMENT
A2 BIOLOGY
6. A student who was interested in animal behaviour did a day’s work experience
at a zoo. He made these notes about some examples of animal behaviour that
he observed.
Match the examples A to H to the names of different types of behaviour by
writing the correct letter beside the name. One has been done for you.