Home › Subjects › O-Level Pure Biology › Homeostasis, Co-ordination and Response in Humans
O-Level Homeostasis, Co-ordination and Response in Humans
What the O-Level syllabus expects for Homeostasis, Co-ordination and Response in Humans, and how to practise it.
What the syllabus expects
- Define homeostasis as keeping the internal environment constant.
- Account for the core principles of homeostasis, describing a stimulus that arises from an internal change, a corrective mechanism, and negative feedback.
- Set out how a steady body temperature is kept in humans through the roles of temperature receptors in the skin sensing changes, sweating, shivering, adjusting blood flow through vessels near the skin surface, and the co-ordinating work of the hypothalamus.
- Define a hormone as a chemical made by a gland and carried in the blood that changes how one or more particular target organs behave.
- Account for what an endocrine gland is, using the islets of Langerhans in the pancreas as the example.
- Account for how, as a homeostatic mechanism, the hormones insulin and glucagon keep blood glucose concentration under control.
- Set out type 2 diabetes mellitus as a blood glucose level that stays higher than normal because the body resists insulin or does not make enough of it.
- Recognise the risk factors for type 2 diabetes mellitus (such as poor diet and a sedentary lifestyle) and the ways it can be managed.
- Outline what anti-diuretic hormone (ADH) does in osmoregulation.
- Note that the nervous system, made up of the brain, spinal cord and nerves, co-ordinates and controls the body's functions.
- Outline how a co-ordinated reflex action arises in reply to a particular stimulus through the combined work of receptors, sensory neurones, relay neurones sited within the brain or spinal cord, motor neurones and effectors.
- Set out how the eye is built, as viewed from the front and in horizontal section.
- Give the main roles of the parts of the eye in forming a sharp image of near and far objects on the retina.
- Set out the pupil reflex as it responds to bright and to dim light.
How it's examined
Questions on this topic most often ask you to explain, outline.
Worked examples
Example 1 (5 marks)
Outline how signals are carried chemically across a synapse.
Show the worked answer
A nerve impulse arrives at the synaptic knob at the end of the presynaptic neurone. This causes vesicles containing neurotransmitter to move to and fuse with the presynaptic membrane, releasing the neurotransmitter into the synaptic cleft. The neurotransmitter diffuses across the cleft and binds to specific receptor molecules on the postsynaptic membrane. This triggers a new impulse in the postsynaptic neurone, so the signal is passed on.
Example 2 (4 marks)
When a rat caught sight of food set down in front of it, it began to produce saliva. Taking it that rats share nervous pathways broadly like those of people, trace the reflex arc in the rat responsible for this reaction.
Show the worked answer
The sight of food triggers salivation via a reflex arc. Tracing the pathway in order: 1. Receptor: light-sensitive receptor cells in the retina of the eye detect the sight of the food (stimulus). 2. Sensory neurone: carries the nerve impulse from the receptor to the central nervous system (brain). 3. Relay (intermediate) neurone: in the CNS (brain), passes the impulse from the sensory to the motor neurone. 4. Motor neurone: carries the impulse from the CNS to the effector. 5. Effector: the salivary gland, which responds by producing/secreting saliva (the response).
Example 3 (2 marks)
Explain why following a ketogenic diet might help people who have type II diabetes.
Show the worked answer
In type II diabetes the body cells respond poorly to insulin, so blood glucose rises after eating carbohydrates. A ketogenic diet is very low in carbohydrate. With little carbohydrate intake, less glucose is absorbed into the blood, so blood glucose levels rise much less and stay more stable, reducing the demand for insulin. The body instead breaks down fats for energy (producing ketones), so glucose control is easier to maintain despite the reduced insulin sensitivity.
More O-Level Pure Biology topics
Cell Structure and Organisation · Movement of Substances · Biological Molecules · Nutrition in Humans · Transport in Humans · Respiration in Humans · all of O-Level Pure Biology