CURRAN SCIENCE
GCSE Biology Resources
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Read the passage about 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.
For example humans must maintain their core body temperature, blood glucose levels and water levels. This is important as enzyme action and cell function can be negatively affected by changes outside of optimum.
To prevent change, our body has several systems which it uses to maintain a constant internal environment.
Homeostatic mechanisms are so important for your survival that they are automatic. This means your body constantly adjusts without you having to consciously think about it. They all follow the same basic structure:
| Stimulus | Receptor | Co-ordination centre | Effector |
|---|---|---|---|
| a change in the environment e.g. light | cells that detect stimulus e.g. retina cells in eye | receive and process information e.g. brain and pancreas | bring about response to restore optimum e.g. muscles and glands |
Homeostatic control mechanisms come in two forms:
Read the passage and look at the diagram.
The nervous system allows humans to react to their surroundings and coordinate a response. The nervous system is rapid - the electrical impulses can travel at speeds of over 100 m/s - 220 mph - over three times the speed limit on a motorway!
The nervous system is made of specialised cells called neurones. Neurones can carry electrical impulses along their long thin cytoplasm, called an axon. Neurones come in 3 main forms: sensory neurone, relay neurone and motor neurone.
| Sensory neurone | These connect receptors to the coordinator |
| Relay neurones | These coordinate the correct response to the stimulus |
| Motor neurone | These send the signal from the coordinator to the effector |
The coordinators for the nervous system are the brain and the spinal cord. These are known collectively as the central nervous system (CNS). The CNS is responsible for coordinating all the sensory information around you, all your thoughts and maintaining all your internal systems (e.g. heart and breathing rate).
Read the passage and look at the diagram.
Reflex responses are rapid and automatic responses that protect organisms from damage. Reflexes are rapid and automatic because the electrical impulse does not travel to the brain and so the response is not conscious. In a reflex response the relay neurone is the spinal cord (part of the CNS but not the brain) - so you do not think about your response.
An example of a reflex response is touching a hot pan - you respond rapidly and automatically moving your hand away to prevent damage. The table below summarises the reflex response:
| Stimulus | Receptor | Neurone | Neurone | Neurone | Effector | Response |
|---|---|---|---|---|---|---|
| Hot pan | Receptor cells in fingers | sensory neurone | relay neurone (spinal cord) | motor neurone | muscle in arm | move hand away |
Read the passage about synapses.
Where a nerve ends and joins to another there is a gap. This gap is known as a synapse. At the synapse, the electrical signal is transferred into a chemical signal that diffuses across the gap. The synapse is important as it allows the nervous system to direct the signal to the right location. A good analogy is the switches on a railway line that move to ensure a train goes along the right track.
Read the method and look at the diagram.
The time it takes the body to recognise a change and react to it is called the reaction time. The reaction times of humans are all slightly different and can be affected by external factors. Some things can increase reaction time (make you slower to respond) e.g. alcohol and tiredness. Others decrease reaction time (make you faster) e.g. caffeine.
We can investigate reaction time using the ruler drop method:
To carry out the practical you need to identify your independent variable, which is the variable you are changing. For example dominant vs. non-dominant hand. You would then repeat the method above with your non-dominant hand.
There are lots of factors that affect reaction time so lots of variations of this method. It is essential you control all other factors that affect reaction time.
The ruler drop method has lots of human error in it so gives results that are not valid. An improved method would be to click a computer mouse when a colour changes on a screen as this removes human error and can measure in milliseconds.
| Test Number | Distance ruler dropped in mm |
|---|---|
| 1 | 117 |
| 2 | 120 |
| 3 | 115 |
| 4 | 106 |
| 5 | 123 |
| 6 | 125 |
| 7 | 106 |
| Attempt number | Student A (ms) | Student B (ms) | Student C (ms) |
|---|---|---|---|
| 1 | 275 | 260 | 272 |
| 2 | 259 | 268 | 268 |
| 3 | 251 | 251 | 275 |
| 4 | 261 | 256 | 266 |
| 5 | 260 | 244 | 270 |
| 6 | 263 | 280 | 283 |
| 7 | 259 | 468 | 274 |
| 8 | 256 | 258 | 278 |
| 9 | 255 | 255 | 286 |
| 10 | 248 | 277 | 275 |
| Mean | 259 | 282 | 275 |
Read the passage and look at the diagram.
The human brain is approximately 2% of your body mass. It is responsible for all coordination of complex behaviour as well as most of your homeostatic mechanisms. It is made of billions of interconnected neurones constantly sending and receiving electrical impulses to and from the rest of your body.
The medulla is responsible for controlling the unconscious control of heart rate, blood pressure and breathing rate.
The cerebral cortex (cerebrum) is the large folded area at the top of the brain; it is responsible for conscious co-ordination of intelligence, speech, memory and decision making.
The cerebellum ('little brain') sits at the back of the head above the neck. It is responsible for coordinating movement and balance.
The hypothalamus is a tiny cherry-size area situated behind your eyes; it plays a large role in homeostasis.
Read the passage about studying the brain.
The brain is a complex and delicate organ which makes understanding it and treating damage challenging.
Through examining people who have suffered brain injuries scientists have discovered that certain parts of the brain are specialised to perform certain tasks. For example the famous case of Phineas Gage helped scientists understand the role of the cerebral cortex.
Modern neuroscience allows scientists to map regions of the brain to particular functions. MRI scanning techniques allow scientists to measure activity when people carry out particular skills (e.g. translating text) or actions (moving their left arm).
Electrical stimulation allows neuroscientists to stimulate parts of the brain and record the response in a patient.
Read the passage and look at the diagram.
The eye is a complex sense organ that can not only detect the amount of light (brightness) but also the colours it has. This gives us the sense of vision. The receptor cells in the eye that detect light are found at the back of the eyeball in the retina. The structure of the eye is adapted to ensure the millions of cells found here can detect light to create an accurate image.
The brightness of your surroundings affects the size of your pupil. This ensures that in dark (dim) places more light can enter the eye and in bright spaces less light enters to prevent damage.
Read the passage about accommodation.
Accommodation is the word used to describe the process of focussing on near and far objects by changing the shape of the lens. The aim is to refract (bend) the light rays so that they focus on the retina.
Read the passage about eyesight problems.
There are two common eyesight problems in humans. They are Myopia (short sightedness) and Hyperopia (long sightedness). In both cases the problems are easily fixed by wearing glasses or contact lenses. More advanced treatments include laser eye surgery and lens replacement surgery.
