F215 OCR A2 Biology Module 4 Responding to the Environment

This is module 4 of F215 OCR A2 Biology. It is very detailed answering every part of the specification just like the other modules which I have already put on here. 

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  • Created on: 12-06-11 19:47
Preview of F215 OCR A2 Biology Module 4 Responding to the Environment

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F215-Module 4-Responding to the Environment
5.4.1 Plant responses
a. Explain why plants need to respond to their environment in terms of the need to
avoid predators and abiotic stress
Phototropism-Plants grow towards like so they can get more light and
photosynthesise more.
Geotropism-Roots grow pulled down by gravity to anchor them into the soil to
take up water for support. More anchored into the ground means that it is less
likely to be fully pulled up by predators.
Chemotropism-On a flower where the pollen tube grows down the style because
it is attracted by chemicals towards the ovary so fertilisation can take place.
Thigmotropism-Shoots of climbing plants wind around solid structures to gain
b. Define the term tropism
Tropism-A directional growth response in which the direction of the response
varies by the direction of the external stimuli with positive being towards and
negative being away.
c. Explain how plant responses to environmental changes are co-ordinated by hormones
with reference to responding to changes in light direction
o Responding to change in light direction
o Positive tropic responses-shoot bends towards the light.
o Redistribution of auxin.
o Auxins move from the tip to the shaded area meaning that only the cells
on the shaded side elongate so this side is longer causing the shoot to
bend to the light.
Hormone Effect
Auxins Promotes cell elongation.
Inhibits growth of side shoots.
Inhibits leaf abscission (leaf fall).
Cytokinins Promotes cell division.
Gibberellins Promotes seed germination and
growth of stems.
Abscisic Acid Inhibits seed germination and
Causes stomatal closure when
there is low water availability.
Ethene Promotes fruit ripening.

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Evaluate the experimental evidence for the role in auxins in the control of apical
dominance and gibberellin in the control of cell elongation
Apical dominance
o It is when the growing apical bud at the tip of the shoot inhibits the
growth of lateral buds further down the shoot.
o When the tip which is the source of auxin is removed the auxin
concentration in the shoot drips and buds begin to grow.…read more

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Auxin inhibits abscission usually by acting on leaves in the abscission zone. But:
o Lead senescence causes auxin production at the tip to drop.
o So it makes cells in the abscission zone more sensitive to ethene whose
production is increased when there is a drop in auxin.
o So more of the enzyme cellulose is produced which digests the walls of
the cells in the abscission zone which separate the peptide from the
f.…read more

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Animal responses
a. Discuss why animals need to respond to their environment
Need to react to changes both internally and externally.
They need to be able to coordinate a set of different responses.
They need to respond to stay alive e.g. to run away from predators.
They need to regulate their temperature which may vary due to their
b.…read more

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o Most active in sleep and relaxation.
o Neurones linked at a ganglion close to the target tissue- longer
pre-ganglionic neurones.
o Post-ganglionic neurones secrete acetylcholine.
o Effects include decreased heart rate, pupil constriction and decreased
ventilation rate.
d. Describe, with the aid of diagrams, the gross structure of the human brain and
outline the functions of the cerebrum, cerebellum, medulla oblongata and the
o The largest part of the human brain.
o Divided into two hemispheres connected by the corpus callosum.…read more

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Describe how coordinated movement requires the action of skeletal muscles about
joints with reference to the movements of the elbow
1. Impulses arrive at the neuromuscular junction.
2. Vesicles fuse with the pre-synaptic membrane.
3. Acetylcholine is released.
4. The acetylcholine binds to receptors on the muscle fibre membrane
5. Depolarisation happens.
6. Depolarisation wave travels down t-tubules.
7. T-system depolarisation leads to Ca2+ being released from stores in the
sarcoplasmic reticulum.
8. Ca2+ binds to proteins in the muscle leading to contraction.
9.…read more

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Transfer from creatine phosphate in the muscle cell sarcoplasm. The
phosphate group from creatine phosphate can be added to ADP to make
ATP using the enzyme creatine phosphotransderase.
i. Compare and contrast the actions of synapses and neuromuscular junctions
Synapses Neuromuscular junction
Neurone to neurone. Neurone to sarcomere (muscle
Postsynaptic stimulation leads to cell).
action potential in postsynaptic Postsynaptic stimulation leads to
neurone. depolarisation of the sarcolemma
Synaptic knob tends to be smooth and muscle contraction.
and rounded.…read more

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State that responses to environmental stimuli in mammals are coordinated by
nervous and endocrine systems
Systems of both nervous and endocrine continuously monitor the external and
internal environments.
Coordination of responses to stimuli is needed for survival.
Mainly the result of brain activity to access the appropriate response and it
regulates a number of endocrine responses.
l. Explain how in mammals, the "fight or flight" response to environmental stimuli is
coordinated by the nervous and endocrine systems
1.…read more

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It can be positive where the reaction is towards the stimulus or negative
where the reaction is away from the stimulus.
o An orientation response where the rate of movement increases when the
organism is in unfavourable conditions.
o Non-directional response (not in any specific direction).
c. Explain the meaning of the term learned behaviour
Learned behaviour-It is a behaviour that changes or adapts with experience.
d.…read more

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The young are able to learn through observation and play, where they are
able to learn skills which are essential for when they are older.
o It can lead to the security of a group which leads to the survival and
learning of the young.
o The knowledge and protection of food sources can be shared within a
group giving them all a chance to survive and get enough food.…read more


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