Unit 6 - Organisms respond to changes in their internal and external environments
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Summary AQA A LEVEL BIOLOGY CHAPTER 16 HOMEOSTASIS NOTES
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Unit 6 - Organisms respond to changes in their internal and external environments
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AQA
I created these notes throughout y12&13 and used them for my A level 2022 exams. I got a grade 9 in GCSE and am awaiting for my a level biology result. These notes were made using the CGP revision guide, AQA Biology textbook and class notes in order to cover everything in the course. I have also ad...
Unit 6 - Organisms respond to changes in their internal and external environments
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16.1 PRINCIPLES OF HOMEOSTASIS
Wednesday, 2 March 2022
18:23
Homeostasis is the maintenance of a stable internal environment within restricted
limits.
● Involves physiological control symptoms.
Homeostasis ensures that body cells are in an environment which meets their
requirements, allowing them to function normally despite external changes and
prevent damage.
Maintaining the core body temperature and stable blood pH is essential for enzyme
activity:
● If body temperature is too high, enzymes can denature, and if too low,
enzyme activity is reduced, slowing the rate of metabolic reactions.
● If pH is too high or low, enzymes can denature. Enzymes work at their
optimum pH, often 7, but some enzymes work best in other pH levels.
The maintenance of a constant blood glucose level is also essential to ensure a
constant water potential.
● If concentration is too high, water moves out of cells by osmosis, so can
shrivel and die.
● If blood glucose is too low, water moves in and expands and may burst by
osmotic lysis.
● Constant blood glucose concentration ensures a reliable source of glucose for
respiration by cells to release energy.
The control of any self-regulating system involves a series of stages:
● The optimum point is monitored by receptors.
● These receptors detect any changes or deviations from the optimum point.
● Receptors inform the coordinator, which coordinates information from
receptor and sends instructions to an effector.
● The effector brings about the changes needed to return the system to the
optimum point.
● The return to normality creates a feedback mechanism, by which the receptor
responds to a stimulus created the change to the system due to the effector.
Negative feedback restores systems to their original level.
● The change produced by the control system leads to a change in the stimulus
which was detected by the receptors, turning the system off.
, ● Where a change triggers a response which reduces the effect of a change.
Positive feedback occurs when a deviation from an optimum point causes changes
which results in an even greater deviation from the normal.
Control systems usually have many receptors and effectors, allowing them to have
separate mechanisms.
Multiple negative feedback mechanisms give more control over changes in the
internal environment.
● Separate mechanisms can control deviations in different directions from the
original state.
If there is only one negative feedback mechanism, you'd only be able to actively
change a level in one direction so it turns to normal.
● One mechanism is slower and less controlled.
16.2 FEEDBACK MECHANISMS
Wednesday, 2 March 2022
21:44
Negative feedback is used to keep a stable internal environment.
● Allows for the survival of an organism.
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