3.6 - 3.6.4 - 3.6.4.1 Principles of homeostasis and negative feedback (A-level only) Flashcards
What is homeostasis?
The maintenance of an internal environment within restricted limits in organisms. It is also the ability to return to that optimum point and so maintain organisms in a balanced equilibrium.
Changes in your external environment can affect you …….. environment.
Internal (the blood and tissue fluid that surrounds your cells).
Why is homeostasis important?
It is important to maintain the right core body temperature and blood pH. This is because temperature and pH affect enzyme activity, and enzymes control the rate of metabolic reactions.
What happens if your body temperature is too high (e.g. 40 degrees centigrade)?
The enzymes become denatured. The enzymes molecules vibrate too much, which causes the H bonds that hold them together. The shape of the enzymes active site is changed and it no longer is able to catalyse reactions. Therefore metabolic reactions are less efficient.
What happens if your body temperature is too low?
Enzyme activity is reduced, slowing the rate of metabolic reactions.
What happens if your blood pH is too high or too low (highly alkaline or acidic)?
The enzymes become denatured. The H bonds are broken which means the shape of the enzymes active site is changed and no longer works as a catalyst. This means that metabolic reactions are less efficient.
Why is it important to maintain the right concentration of glucose in the blood?
Because cells need glucose for energy. Also, blood glucose concentration affects the water potential of blood.
What happens if blood glucose concentration is too high?
The water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis. This can cause the cells to shrivel up and die.
What happens if blood glucose concentration is too low?
Cells become unable to carry out normal activities because there is not enough glucose for respiration to provide energy.
What do homeostatic systems detect?
A change and respond by negative feedback.
What do homeostatic systems involve?
Receptors, a communication system and effectors.
In homeostasis what do receptors detect?
When a level is too high or too low, and the information is communicated via the nervous system or the hormonal system to effectors.
In homeostasis, what do effectors respond to?
Counteract the change by bringing the level back to normal.
What is the negative feedback mechanism?
The mechanism that restores the level to normal after it has been detected by receptors.
What is a downside of negative feedback?
Only works within certain limits. This means that is the change is too big then the effectors might not be able to counteract it.
How is multiple negative feedback mechanisms a positive?
It gives more control over changes in your internal environment.
What does having multiple negative feedback mechanisms allow?
It allows you to actively increase or decrease a level so it returns to normal.
What does only one negative feedback mechanism mean?
A slower response and less control.
What do positive feedback mechanisms amplify?
A change from the normal level.
Why is positive feedback useful?
To rapidly activate something e.g. a blood clot after an injury.
How is a blood clot forming after an injury an example of positive feedback?
- Platelets in the blood become activated and release a chemical.
- This chemical triggers more platelets to be activated.
- Platelets form a blood clot very quickly.
This process then ends with negative feedback which is when the body detects the that the blood clot had been formed.
When a homeostatic system breaks down, what can happen?
Positive Feedback.
How does hypothermia involve positive feedback?
- Hypothermia is low body temperature (below 35 degrees centigrade).
- It happens when heat is lost from the body quicker than it can be produced.
- As body temperature falls, the brain doesn’t work properly and shivering stops - this makes body temperature fall even more.
- Positive feedback takes body temperature further away from the normal level, and it continues to decrease unless action is taken.
Why is positive feedback not involved in homeostasis?
Because it does not keep your internal environment stable.
