12.1
Learning Objectives




Define homeostasis
Explain the importance of homeostasis
Describe how control mechanisms work
Explain how control mechanisms are co-ordinated
Success Criteria
 You can define homeostasis and suggest what things need to
be maintained in the body
 You can create a mind map of ideas for why homeostasis is
important
 You can take notes on control mechanisms
 You can answer an exam question on homeostasis
Starter
What is homeostasis?
 The maintenance of a constant internal environment
What things need to be maintained?
 Temperature
 Oxygen levels
 Water levels
 Tissue Fluid
 Composition of blood
Independence: Stops
organisms being reliant
on the external
environment (wider
choices of where to live
etc.)
Enzymes: sensitive to pH and
temperature changes. Big changes
could cause denaturation and stop
reactions occurring.
Why is
homeostasis
important?
Blood glucose:
essential to maintain
this to maintain water
potential and also
give cells a constant
supply of glucose for
respiration.
Water Potential: changing this in
blood/tissue fluid could make
cells shrink or even burst. Would
prevent cells operating normally.
Control Mechanisms
Stages of Homeostatic Control
 The Set Point (the norm)
 Receptor (detects variations)
 Controller (co-ordinates info and sends
instructions)
 Effector (brings about changes)
 Feedback Loop (tells receptor about the
changes)
Control Mechanisms
Input
Fall in
some
parameter
Receptors
Detect the
change
Control
Centre
Coordination
Effector
Have an
effect on the
system
Output
Rise in
some
parameter
Analysing Info from Receptors
 Changes can be detected by a number of different
receptors
 This gives the brain a better picture of what is being
altered
 Allows a more informed response to be made
Plenary – Exam Q
How does maintaining a constant body temperature allow
metabolic reactions in cells to proceed with maximum
efficiency?
(5)
Plenary – Exam Q ANSWERS
1. Body temp./37°C is optimum temp for enzymes;
2. excess heat denatures enzymes/alters tertiary
structure/alters
shape of active site/enzyme;
3. substrate cannot bind/eq,;
4. reactions cease/slowed;
5. too little reduces kinetic energy of molecules / molecules
move more slowly;
6. fewer collisions/fewer ES complexes formed’ max 5
Learning Objectives




Define homeostasis
Explain the importance of homeostasis
Describe how control mechanisms work
Explain how control mechanisms are co-ordinated
Success Criteria
 You can define homeostasis and suggest what things need to
be maintained in the body
 You can create a mind map of ideas for why homeostasis is
important
 You can take notes on control mechanisms
 You can answer an exam question on homeostasis