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Summary AQA Biology A Level Revision - Homeostasis - Unit 16 $4.53   Add to cart

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Summary AQA Biology A Level Revision - Homeostasis - Unit 16

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These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification - Very comprehensive notes and enabled me to achieve an A* in my A Level Biology exams.

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  • Unit 16
  • May 24, 2019
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  • 2017/2018
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Biology revision – Homeostasis (16)
Principles of Homeostasis

- By maintaining a relatively constant internal environment for their cells, organisms can
limit the external changes these cells experience
- This maintenance of a constant internal environment is called homeostasis
- Internal environment is made up of tissue fluids that bathe each cell, supplying
nutrients and removing wastes
- Maintaining the features of this fluid at the optimum levels protects the cells from
changes in the external environment, thus giving organism degree of independence
What is homeostasis?

- Maintenance of internal environment within restricted limits in organisms
- Involves trying to maintain chemical make-up, volume and other features of blood and
tissue fluid within restricted limits
- Homeostasis ensures the cells of the body are in environment that meets their
requirements and allows them to function normally despite external change
- Continuous changes take place in temp, pH and WP
o Occur around an optimum point
- Homeostasis is the ability to return to that optimum point and thus maintain organisms
in a balance equilibrium
Importance of homeostasis

- Essential for proper functioning of organisms for following reasons:
o Enzymes that control biochemical reactions within cells and other proteins are
sensitive to change in pH and temp
 Any change reduces rate of reaction or may denature
 Even small change in temp or pH can impair ability of enzymes to carry
out their roles effectively
 Maintaining a fairly constant internal environment means reactions take
place at a suitable rate
o Changes to WP of blood and tissue fluids may cause shrink/ expansion of cells
 Cells thus cant operate normally
 Maintenance of constant blood glucose conc is essential in ensuring a
constant WP
 Constant blood glucose conc also ensures a reliable source of glucose
for respiration by cells
o Organisms with ability to maintain constant internal environment are more
independent of changes in external envrionment
 May have a wider geographical range and thus have a greater chance of
finding food, shelter, etc.
Control mechanisms

- Control of any self-regulating system involves a series of stages that feature:
o Optimum point – the point at which the system best operates
 Is monitored by a
o Receptor – detects any deviation from optimum
 Informs the
o Coordinator – coordinates information from receptors
 Sends instruction to an appropriate

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