AQA GCSE Homeostasis (Biology)
Homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
Homeostasis maintains optimum conditions for enzyme action and all cell functions.
Optimum conditions for enzyme action
Enzymes work best under certain conditions, their activity is affected by temperature and pH.
Each enzyme has an optimum temperature where it has the maximum rate of reaction.
If the temperature is too low, then the rate of reaction will be too slow to sustain life.
If the temperature is too high, then the enzyme is denatured and the reaction will stop, so life cannot be sustained.
Cell functions
Cell functions are the processes that happen inside cells that keep an organism alive. These processes are mostly controlled by enzymes, which is why homeostasis is important.
Examples of cell functions
| Cell Function | What happens in the cell | Link to homeostasis |
|---|---|---|
| Respiration | Glucose is broken down in cells to release energy | Needs the correct temperature, glucose concentration and water levels for enzymes to work efficiently |
| Enzyme controlled reaction | Enzymes speed up chemical reactions in cells | Enzymes only work at optimum temperature and pH. Extreme conditions will slow down reactions or denature enzymes |
| Cell growth and division | Cells grow and divide to make new cells | Requires enzymes and energy from respiration, which depend on stable internal conditions. |
| Transport of substances | Substances move in and out of cells by diffusion, osmosis and active transport | Water balance affects osmosis |
Examples of controlled conditions.
In the human body, conditions that are controlled include:
Blood glucose concentration
Core body temperature
Water levels
There are other examples of conditions that homeostasis will control.
Blood Glucose Concentration
Homestasis ensures that there is a steady supply of glucose for respiration and prevents the glucose levels being too high or too low.
Pancreas will monitor blood glucose concencentration. If the blood glucose concentration needs to be adjusted the pancreas will secrete either insulin or glucagon into the blood.
Core Body Temperature
Core body temperature is maintained at approximately 37°C.
This temperature is important for enzyme activity, see the notes earlier in the page for more detail.
The skin, blood vessels, sweat glands and thermoregulatory centre in the brain work together to help control core body temperature.
Water Levels.
Water levels need to be controlled to prevent cells losing or gaining too much water by osmosis.
Water levels are controlled by the kidneys in the body and a hormone called ADH.
Control Systems
Homeostasis involves automatic control systems. There are two types:
1.Nervous responses
2. Chemical (Hormonal) responses
| Nervous responses | Chemical (Hormonal) responses |
|---|---|
| Faster | Slower |
| Short lasting | Longer lasting |
| Use electrical impulses | Involve hormones in blood |
| Example: body temperature control | Example: blood glucose control |
Control System
All control systems include:
Receptors
Receptors are cells that detect stimuli.
Stimuli are changes in the external or internal environment such as change in light intensity, or change in temperature.
Examples of receptors include:
Temperature receptors in the skin, or glucose receptors in the pancreas.
Coordination centres
A coordination centre will receive and process information.
Once they have coordinated a response, a signal will be sent to an effector.
Examples of coordination centres include brain, spinal cord and pancreas.
The pancreas is a coordination centre because it detects changes in blood glucose and releases hormones that tell effectors how to respond.
Brain and spinal cord tend to use neurones, but pancreas using hormones.
Effectors
An effector will bring about a response, they are typically muscles or glands
In bringing about a response, they will restore optimum conditions.
When a muscle is stimulated it will contract to cause movement e.g. shivering.
When a gland is stimulated it will secrete hormones e.g. pancreas secreting the hormone insulin.
Practice Questions
1.Define the term homeostasis
2. Outline the importance of maintaining core body temperature
3. Name the three main parts to a control system.
Factors affecting the rate of photosynthesis
Measuring & calculating rates of photosynthesis
Inverse square law and photosynthesis
Economics of enhancing the conditions in greenhouses
Investigating the effect of light intensity on the rate of photosynthesis