responding to the environment

Question 1

Why is it important that plants can respond to the environment?

Answer 1

To avoid predation
To reduce abiotic stress - water excess, air pollution, heat stress, drought stress
And therefore survive longer to reproduce.

Question 2

Define tropism

e.g.?

Answer 2

the directional growth response of plants to external stimuli. Positive - towards, negative- away.
Stimulus –> growth response
chemicals –> chemotropism (e.g. pollen grain grows pollen tube in direction towards chemicals produced by embryo in positive chemotropism)
light –> phototropism
gravity –> geotropism
touch –> thigmotropism e.g. vines/climbing plants

Question 3

How are plant responses to environmental changes coordinated? e.g. changes in light direction

Answer 3

By plant hormones.
e.g. when a shoot is illuminated from one side auxins produced in shoot tip move to the part of the plant that is in the shade via active transport and accumulates there. This is thought to be stimulated by blue light activating phototropins (protein carriers of auxin). The higher concentration of auxin on the shaded side of the shoot causes cells to take up more water and grow longer - thus bending towards the light source - as it binds to cell membrane receptors and stimulates enzymes that break cross-linkages between cellulose molecules = more stretch.

Question 4

What does the communication system of flowering plants involve?

Answer 4

sensor(receptor) –> plant hormone –> effector

Question 5

What is apical dominance?

How does it benefit the plant?

Answer 5

The fact that the shoot tip/apical bud is dominant over - controls the growth of - the lateral buds that can grow into side shoots/branches. This is because the high conc. auxin produced by the shoot tip inhibits the growth of the lateral buds.
Benefit: allows the plant to grow vertically to reach more light and prevents too many branches growing which would cause leaves to shade each other.

Question 6

What experimental evidence is there of the role of auxins in the control of apical dominance?

Answer 6

If a growing shoot is turned upside down, the lateral buds grow into side shoots - auxin is unable to diffuse to the lateral buds against gravity.
If a ring of auxin inhibitor is applied below the apical bud, the lateral buds grow into side shoots.
If an apical bud is cut off and IAA (a type of auxin) is applied to the shoot, the lateral buds do not grow into side shoots - IAA replaces the natural auxin and inhibits lateral bud growth accordingly.

Question 7

What experimental evidence is there of the role of gibberellin in stem elongation?

Answer 7

• plants that are genetically dwarf have been found to lack giberellin - but when giberellic acid (GA) is applied they grow tall.
• Some dwarf plants lack an enzyme for making giberellin. If stem sections from normal plants are grafted onto these dwarf plants, they grow tall - the plants are able to use the enzyme from the stem graft to make giberellin.
• stem grafts of dwarf plants have fewer, shorter cells. This shows that giberellin is meant to stimulate cell division by mitosis and cell elongation.

Question 8

outline the role of hormones in leaf loss in deciduous plants

Answer 8

Auxin levels fall - auxin is made in young leaves and inhibits leaf fall - and so ethene levels rise.
Abscisic acid (ABA) is a plant hormone that stimulates the production of ethene and senescence (ageing) of leaves in response to stress. In winter an abscission zone forms in the petiole at the base of the leaf stalk consisting of a separation layer and a waxy protective layer which seals the xylem and phloem and so prevents the loss of nutrients and water from the plant.
Ethene stimulates the fall of leaves or abscission by causing the enzyme cellulase to be produced in the separation layer, which digests cell walls.
Cytokinin levels fall meaning leaves receive fewer nutrients.

Question 9

Why is it important that abscission occurs?

Answer 9

Protects plants from excessive water loss by transpiration over the winter, and prevents frost damage. Deciduous plants cannot photosynthesise as much as the temperature and light intensity are low, so leaves are not needed and energy would be wasted maintaining them.

Question 10

Describe the commercial uses of plant hormones

Answer 10

• synthetic auxins are used as growth stimulants when rooting cuttings
• a synthetic auxin 2,4-D, used as a selective weedkiller kills broadleaved species (dicotyledons) but not grass or cereal crops (monocotyledons) at appropriate concentrations
• a form of abscisic acid that is not readily broken down by plants is used as an anti-transpirant as it closes stomata.
• ethene speeds up fruit-ripening in fruits
• gibberellins delay senescence (ageing) in citrus fruits so they can be left longer before being picked, extending their availability
• gibberellins stimulate stem elongation in bunches of grapes so each grape has space to grow larger.

Question 11

Why do animals need to be able to respond to their environment?

Answer 11

In order to respond rapidly and adaptively to changes in both external and internal environments:
to fine food, shelter a mate, and to avoid predators and adverse conditions

Question 12

How are animal responses coordinated?

Answer 12

by the nervous and endocrine systems

Question 13

How is the human nervous system organised?

Answer 13

Into the central and peripheral nervous systems.
CNS = brain + spinal cord
periperal NS = nerves which run between CNS and rest of body - from receptors to effectors.
Receptors are specialised cells in the sense organs that detect specific stimuli and convert them into the electrical energy of nerve impulses
Effectors are parts of the body which produce a response.

Question 14

Describe the components of the peripheral nervous system

Answer 14

Has 2 components:

• the somatic nervous system, which includes all sensory neurones and the motor neurones that run to skeletal muscles
• the autonomic nervous system, which consists of two sets of motor neurones (sympathetic and parasympathetic) carrying impulses to effectors other than the skeletal muscles, e.g. to glands/muscles of the gut and heart. Sympathetic and parasympathetic nervous system use different neurotransmitters and so have different, often antagonistic, effects.

Question 15

Outline the roles of the sympathetic nervous system

Answer 15

the sympathetic nervous system speeds up body processes involved in stress, fight / flight. Neurotransmitter sometimes noradrenaline - very stimulatory.
Nerve pathways in this system pass through the ganglia near the spinal cord. Roles include:
- increased heart rate and force of contractions.
- increased breathing rate and depth of breath
- increased sweating and vasodilation of skin arterioles
- pupil dilation
Pre-ganglionic neurones vary in length.

Question 16

Outline the roles of the parasympathetic nervous system

Answer 16

This system allows rest, recovery and digestion. Nerve pathways in this system begin in the brain and the neurotransmitter is always ACh - inhibitory effect. Roles include:
- decreased heart rate and force of contractions
- decreased breathing rate and depth of breaths
- increased secretion of saliva and gastric juice
- pupil constriction
Pre-ganglionic neurones are very short.

Question 17

Describe the structure of the human brain (DIAGRAMS)

Answer 17

Made up of 4 main parts - cerebrum(largest part - 2 hemispheres), cerebellum(highly folded, at the back of the head, under cerebrum), hypothalamus(small area above pituitary gland) and medulla oblongata(swollen region at the top of the spinal cord).

Question 18

Outline the functions of the cerebrum

Answer 18

Outermost part = cerebral cortex, which is highly folded and made up of billions of relay neurones.
The conscious control centre of the voluntary nervous system, controls all higher order processes such as memory, language, conscious thoughts, reasoning, problem solving, emotional responses and the ability to overide some reflexes.

Question 19

Outline the functions of the cerebellum

Answer 19

control and coordination of movement, posture, hand-eye coordination

Question 20

Outline the functions of the medulla oblongata

Answer 20

• control of autonomic nervous system

- control of breathing, heart rate and smooth muscle of the gut

Question 21

Outline the functions of the hypothalamus

Answer 21

Involved in homeostatic control:

• body temperatures - thermoreceptors
• water potential of the blood - osmoreceptors
• the endocrine system is controlled via regulation of the pituitary gland

Question 22

How is muscular movement coordinated?

Answer 22

Sensory areas of the cerebrum send impulses to association areas. Impulses then pass to motor areas, and from there to effectors. In association areas the brain integrates these sensory inputs and motor outputs to ensure that muscular movement is coordinated and appropriate. This requires the controlled action of skeletal muscles about joints.

Question 23

Describe the function of joints.

What are synovial joints? two types?

Answer 23

joints allow movement between bones.
The most freely moveable joints are synovial joints, which have synovial fluid to lubricate the movement and cartilage over the bone surfaces.
There are 2 main types of synovial joints:
1. hinge joints that allow movement up and down e.g. the elbow
2. ball and socket joints that allow rotational movement e.g. the shoulder

Question 24

Describe an example of coordinated movement requiring the action of skeletal muscles about joints

Answer 24

Movement of muscles requires the coordinated action of voluntary muscles (skeletal) which can contract, but cannot elongate again without the action of an antagonistic muscle –> skeletal muscles therefore work in pairs, with movement achieved by the coordinated action of the antagonistic muscles: when one is contracted and shortened (the flexor), the other relaxes and is extended (the extensor).

e.g the elbow: to lift a weight, the bicep contracts (flexor) whilst the tricep relaxes
to put it down the bicep relaxes and the tricep contracts (extensor)

Question 25

outline the structural differences between voluntary, involuntary and cardiac muscle

Answer 25

Voluntary (skeletal)- striated due to overlapping actin and myosin filaments. Cylindrical cells. Multinucleate

involuntary(smooth) - unstriated, spindle-shaped cells, uninucleate.

Cardiac muscle - striated, branched uninucleate cells, intercalated discs joining cells

Question 26

outline the differences in function between voluntary, involuntary and cardiac muscle

Answer 26

Voluntary - to move bones. Contraction is quick and powerful, but muscles tire easily
Involuntary - found in the walls of the alimentary canal,bronchi, blood vessels (controls diameter) and the iris of the eye, for peristalsis, vasodilation/vasocontriction of arterioles to control blood flow, dilaton/contriction of the pupils. Contraction is fairly slow but tires slowly.
Cardiac - found in the heat, is myogenic, pumps blood. Contraction is quick and powerful and the muscle does not fatigue

Question 27

how is voluntary muscle movement controlled?

involuntary?

Answer 27

voluntary: by the voluntary nervous system in the motor areas of the cerebrum.

Involuntary: controlled by autonomic nervous system in medulla oblongata.

Question 28

Describe the histology and ultrastructure of striated muscle

Answer 28

consists of many striped muscle fibres.
Each fibre contains man myofibrils , striped due to overlap of actin and myosin filaments.
Muscle fibres are multicellular.
Sarcolemma- specialised muscle cell membrane, forms neuromuscular juntion with the terminal dendrites of motor nerves. In between myofibrils are sarcoplasmic reticulum tubules.
Myosin filamnets are thick, made up of fibrous protein with globular heads.
Actin filaments are thin, with 6 surrounding each myosin filament.
Two additional proteins within the myofibrils, are involved in the control of contraction: tropomyosin and troponin.

Question 29

Describe the banding pattern created by actin and myosin filaments in a muscle myofibril

Answer 29

A bands (dark)- whole length of myosin + overlap of actin
H zones (less dark) - myosin only
I bands (light) - actin only
Z lines - dark vertical lines through the centre of each actin filament
A sarcomere: from 1 Z line to another- this forms a repeating unit in a muscle myofibril.

Question 30

how is the supply of ATP maintained in muscles?

Answer 30

ATP comes from three sources: 1. Aerobic respiration

• Requires Oxygen and respiratory substrate
• Produced rapidly in the many mitochondria
  2. Anaerobic respiration
• Produced quickly in the sarcoplasm
• Leads to a build up of lactic acid
• Leads to an increase of blood flow to the muscles
  3. Creatine phospphate
• Stored in the sarcoplasm, donates phosphate to phosphorylate ADP to ATP

Question 31

Explain, with the aid of diagrams and photographs, the sliding filament model of muscular contraction

Answer 31

 The skeletal muscle has contractile organelles called microfibrils
 These microfibrils contract by sliding filaments over each other
 Each microfibril is made up of many microfilaments of which there are two types - myosin and actin

Question 32

What are the similarities between synapses and neuromuscular junctions?

Answer 32

Both release neurotranmitter by exocytosis
Calcium ions cause vesicles to move and fuse with prejunction/presynaptic membrane
Neurotransmitter crosses synapse by diffusion
Both post junction membranes have sodium channels
Neurotransmitter binds to specific receptors on postsynaptic/sarcolemma membrane

Question 33

What are the differences between synapses and neuromuscular junctions?

Answer 33

Neuromusular:
Neurotransmitter is acetylcholine
Acetylcholinesterase breaks down neurotransmitter
Between neurone and muscle
Post junction membrane is clefted
Many receptors
Needs one action potentials to cause depolarisation on post synaptic membrane

Synapse:
Various neurotransmitters
Various enzymes breaks down the neurotranmitters
Between two neurones
Post synaptic membrane is smooth
Fewer receptors
Needs many action potentials to cause depolarisation on post synaptic membrane


Question 34

outline the role of ATP in muscular contraction

Answer 34

1. myosin head attaches to actin - cross-bridge
2. the power stroke: head tilts, causing thin filament to be pulled along and overlap with thick filament. ADP and Pi are released
3. cross-bridge is broken as new ATP attaches to myosin head
4. head moves back as ATP is hydrolysed to ADP + Pi and forms another cross bridge further on

Question 35

how are animal responses coordinated?

Answer 35

by nervous and endocrine systems

Question 36

describe the coordination of the fight or flight response in mammals?

Answer 36

fight or flight: the range of coordinated responses to the perception of danger.

1. sights/sounds of danger are detected by receptors in the eyes and ears, causing many impulses to be generated and sent to the cerebrum
2. Cerebrum association areas interpret the situation and activate the hypothalamus
3. The hypothalamus stimulates increased activity of the sympathetic system (nervous!) as well as triggering the release of adrenaline from the adrenal glands into the blood (endocrine!)
4. The sympathetic system and adrenaline cause the following responses:
   - pupil dilation
   - increased heart rate
   - increased breathing rate and depth
   - increased metabolic rate
   - vasoconstriction of arterioles to the digestive system and skin
   - vasodilation of arterioles to the muscle and liver
   - increased blood glucose
   - increased sweat production
   - release of endorphins in the brain

Question 37

Define innate behaviour

Answer 37

Behaviour that is instinctive and genetically determined.
Carried out in a fixed pattern - rigid, inflexible.
Is automatic, and stereotypical to a species.
Not influences by the environment.
includes, taxis, kinesis and escape reflexes.

Question 38

Define learned behaviour

Answer 38

Behaviour that is altered by experience.
Dependent on memory/association/reinforcement/practice.
Variable in different members of a species.
Influenced by the environment/

Question 39

explain the advantages to organisms of innate behaviour?

examples with reference to escape reflexes, taxis and kinesis

Answer 39

• rapid, automatic response
• suits species with a short lifespan/with no parental care/with a solitary lifestyle
• only requires a simple nervous system
  e.g.
  Escape reflex: earthworms withdraw underground in response to vibrations on the ground helping them to avoid danger
  Taxis: nematode worm has chemoreceptors on its lips that sense the strength/direction of chemical signals in the air before moving its whole body up/down (directional) in positive/negative chemotaxis
  woodlice - negative phototaxis
  Kinesis: woodlice show an increase in activity - move faster and turn less - in dry conditions, helping them to leave these conditions and find moisture quicker

Question 40

What are examples of learned behaviours?

Answer 40

Habituation - ignore repeated stimuli if result in no reward/punishment
Imprinting - young animals recognise and follow another organism
Classical conditioning - animal learns to associate 2 different stimuli and responds to the first in anticipation of the second
Operant conditioning - animal learns to associate an action with an outcome in trial-and-error learning. Active and deliberate.
Latent learning - animals explore new surroundings and retain this information
Insight learning - animals work out solution to a problem by reasoning, based on past experience - the highest form of learning

Question 41

describe examples of each type of learned behaviour - advantage?

Answer 41

habituation: birds learn to ignore scarecrows. Avoids wasting energy responding to unimportant stimuli.
Imprinting: goslings follow the first moving object they see after hatching - allows them to access care and learn skills.
Classical conditioning: Pavlov’s dogs learn to associate bell with food and salivate in anticipation - prepared
Operant conditioning - Skinner’s rats learn by trial and error that pulling lever = food and eventually do so more quickly.
Latent learning - Rabbits explore surroundings of their burrow and learn the features of their environment - important for finding food, shelter and escaping predators.
Insight learning - chimpanzees stacked boxes to reach banana

Question 42

describe, using one example, the advantages of social behaviour in primates

Answer 42

Mountain gorillas live in a troop of about 10 inividuals - different tasks are shared between individuals

• group is more successful at finding food
• there are more individuals to look out for danger
• they can collectively defend a territory

Organisation in gorillas:

Grooming
pick parasites off another
Hygienic
Reinforces bonds

Clear-cut hierarchy
Prevents fighting which wastes energy
Males already know their rank order in the group

Care for the young
Mother looks after young -during this period the female protects the young gorilla as it learns the social and other skills necessary to live independently.
Further learning takes place after the age of 2.
The silverback is important in the development f young gorillas from the age of 3 to 6 years, both in terms of protection from older males within the group, and in play as a source of learning new skills.
Imitate adults for foraging etc

Question 43

discuss how the links between a range of human behaviours and the dopamine receptor DRD4 may contribute to the understanding of human behaviour

Answer 43

Some variations in human behaviour are linked to the possession of different DRD4 receptors in the brain for the neurotransmitter dopamine.
The different alleles appear to be responsible for individual differences in susceptibility to neuropsychiatric disease and in responsiveness to medication. e.g.:
- the allele with seven repeats, DRD4 7R, is associated with novelty-seeking behaviour as well as ADHD
- the DRD4 5R allele is associated with alcoholism and other drug abuse
- some studies have found links between DRD4 alleles and complex disorders such as schizophrenia - they have a higher density of receptors
Understanding the role of the DRD4 protein receptors and other neuroreceptors is helping the development of therapeutic drugs.
The link between the DRD4 receptor and abnormal behaviour helps us understand the role played by this receptor in normal behaviour

Question 44

Describe how an impulse in the motor neurone stimulates contraction of myofibril

Answer 44

Arrival of action potential at axon terminal causes entry of Ca2+, causes exocytosis of vesicles containing ACh.
ACh diffuses across gap and bonds to receptor site on sarcolemma.
Depolarisation of the sarcolemma occurs, spreading across sarcolemma to depolarise T tubules.
Sarcoplasmic reticulum releases calcium ions.
Calcium ions bond to troponin causing tropomyosin to move.
This reveals myosin binding sites on actin.
Myosin head binds to actin forming a cross bridge — contraction occurs!!

Question 45

describe the role of the brain and nervous system in the co-ordination of muscular movement

Answer 45

Areas os the cerebrum which receive sensory information (sensory areas) send impulses to association areas. Impulses then pass to motor areas, and from there to effectors.
In the association area (concerned with planning actions and movements) the brain integrates these sensory inputs and motor outputs to ensure that muscular movement is coordinated and appropriate