How does the body keep its internal conditions steady, such as the level of glucose in the blood?
Define homeostasis and explain how blood glucose is controlled by insulin and the role of negative feedback
A scaffolded answer to the N(A)-Level Biology outcome on homeostasis. What homeostasis is, how insulin lowers blood glucose, the idea of negative feedback, and what happens in diabetes.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
This outcome wants a clear definition of homeostasis and an example worked through in detail: the control of blood glucose. You should be able to explain how the pancreas and the hormone insulin keep glucose steady, describe the idea of negative feedback in simple terms, and say what goes wrong in diabetes. The marks reward the definition, the named hormone and organ, and a clear cause-and-effect account of how the level is brought back to normal.
The answer
What homeostasis is
Homeostasis is the keeping of a steady internal environment inside the body, even when conditions outside change. Things kept steady include body temperature, the amount of water in the blood, and the amount of glucose in the blood. This matters because cells, and especially the enzymes inside them, only work well within a narrow range of conditions. If conditions swung too far, the enzymes would stop working and the body would be harmed.
Controlling blood glucose
Glucose is the sugar that cells use for respiration, so the body keeps its level in the blood fairly steady. The organ in charge is the pancreas, and the main hormone is insulin.
- After a meal, the blood glucose level rises.
- The pancreas detects this and releases more insulin into the blood.
- Insulin makes the liver and other cells take in glucose and store some of it.
- The blood glucose level falls back to normal.
Negative feedback
This is an example of negative feedback: when the level rises too high, the body acts to bring it back down; when it falls too low, the body acts to raise it. Each change triggers a response that reverses it, which keeps the level steady around a set point. (When glucose falls too low, the pancreas releases less insulin and the stored glucose can be released again.)
Diabetes
In diabetes, the body cannot control blood glucose properly, often because the pancreas does not make enough insulin. Without enough insulin, the blood glucose can rise dangerously high. People with diabetes may need to control their diet, exercise, or have insulin to keep their glucose steady. This shows how important the normal control system is.
Examples in context
Example 1. Why you sweat when you are hot. Keeping body temperature steady is another example of homeostasis. When you get too hot, you sweat, and as the sweat evaporates it cools the skin, bringing the temperature back down. This is negative feedback, the same reversing idea used for glucose.
Example 2. Why a person with diabetes checks their blood sugar. Because their body cannot control glucose well, a person with diabetes may test their blood and take insulin to keep the level steady, doing by hand what the pancreas normally does automatically. It shows how vital the normal control system is for health.
Try this
Q1. Define homeostasis. [2 marks]
- Cue. The keeping of a steady internal environment inside the body, despite changes in the conditions outside.
Q2. Name the hormone that lowers blood glucose and the organ that releases it. [2 marks]
- Cue. Insulin; released by the pancreas.
Q3. Explain why keeping a steady internal environment matters for the body's cells. [2 marks]
- Cue. Cells and their enzymes only work well in a narrow range of conditions, so if conditions changed too much the enzymes would stop working properly.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marksDefine homeostasis and explain why it is important for the body.Show worked answer →
Homeostasis is the keeping of a steady internal environment inside the body, despite changes outside. Examples of conditions that are kept steady are body temperature, the water content of the blood, and the level of glucose in the blood.
It is important because the cells, and especially the enzymes inside them, only work well within a narrow range of conditions. If the temperature, water level or glucose level changed too much, the enzymes would not work properly and the body could be harmed.
What markers reward: a clear definition (a steady internal environment despite outside changes), at least one example of a condition kept steady, and the reason (cells and enzymes need stable conditions to work). Just listing examples without the definition scores partly.
Original4 marksExplain how the body brings the blood glucose level back to normal after a large, sugary meal.Show worked answer →
After a sugary meal, the level of glucose in the blood rises. The pancreas detects this and releases more of the hormone insulin into the blood.
Insulin makes the liver and other body cells take in glucose from the blood and store some of it. This lowers the blood glucose level back towards normal. Once the level is back to normal, the pancreas releases less insulin. This is an example of negative feedback: a rise is detected and reversed.
What markers reward: glucose rises, the pancreas releases insulin, insulin makes the liver and cells take up and store glucose, and the level falls back to normal. Mentioning negative feedback (the change being reversed) is a good extra mark.
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