OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.4.6 Homeostasis and Negative Feedback Exam Questions
Free OxfordAQA International A Level Biology revision for 3.4.6 Homeostasis and Negative Feedback: what you need to know, common mistakes and exam-style questions with answers. Covers the principles of homeostasis, core temperature, blood pH, negative feedback with separate correction mechanisms, and positive feedback.
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About OxfordAQA International A Level Biology 3.4.6 Homeostasis and Negative Feedback
Homeostasis and negative feedback in Unit 4 sets out the principles used throughout the rest of the unit. You need to explain why it is important to keep core temperature and blood pH stable in relation to enzyme activity, and why blood glucose and water potential must be controlled. You need to explain negative feedback and why having separate mechanisms to correct departures in each direction gives a greater degree of control. You also need to explain positive feedback, for example the breakdown of temperature control, and interpret examples of both. This topic links directly to blood glucose control, heart rate and enzymes.
What you need to know
- Homeostasis Homeostasis is the maintenance of a stable internal environment within restricted limits, through physiological control systems. It allows cells to function despite external changes.
- Temperature and pH Enzymes work best within a narrow range of temperature and pH. Too high a temperature or a change in pH alters the tertiary structure of enzymes, reducing the rate of metabolic reactions.
- Negative feedback A change from the optimum is detected by receptors and effectors bring about a response that returns the factor to the optimum. Separate mechanisms for increases and decreases give a greater degree of control.
- Positive feedback A change triggers a response that increases the change further. An example is the breakdown of temperature control in hypothermia, where a fall in temperature slows metabolism and the temperature falls further.
- Interpreting feedback To identify the type of feedback, ask whether the response reverses the change (negative) or amplifies it (positive).
Common mistakes in 3.4.6 Homeostasis and Negative Feedback
- Saying homeostasis keeps conditions constant. Conditions fluctuate within narrow limits around an optimum.
- Describing positive feedback as feedback that is good for the body. Positive means it amplifies the change, which is often harmful.
- Saying enzymes die if body temperature rises. Enzymes denature; they are not alive.
- Forgetting why separate mechanisms matter. They allow a faster and more precise return to the optimum in either direction.
Try three 3.4.6 Homeostasis and Negative Feedback exam-style questions
1. Explain why it is important to keep blood pH within narrow limits. (3 marks)
Show the mark scheme answer
Changes in pH alter charges on R groups of enzymes; ionic and hydrogen bonds in the tertiary structure change so the active site changes shape; fewer enzyme-substrate complexes form and metabolic reactions slow.
2. Explain what is meant by negative feedback. (2 marks)
Show the mark scheme answer
A change from the normal level is detected; a response returns the level to normal / the optimum.
3. Explain why having separate mechanisms to raise and lower a factor gives more control. (2 marks)
Show the mark scheme answer
Each mechanism can respond to departures in one direction; so the factor can be returned to the optimum faster / more precisely.
3.4.6 Homeostasis and Negative Feedback FAQs
What does OxfordAQA International A Level Biology 3.4.6 Homeostasis and Negative Feedback cover?
It covers the principles of homeostasis, core temperature, blood pH, negative feedback with separate correction mechanisms, and positive feedback.
Which unit is 3.4.6 Homeostasis and Negative Feedback examined in?
It is part of Unit 4, Control, which is an International A2 paper. The Unit 5 synoptic paper can also draw on this content.
What is an example of positive feedback in this topic?
The specification gives the breakdown of temperature control as an example. When core temperature falls too low, metabolic rate drops, less heat is released and the temperature keeps falling.
