A level biology students need to be able to explain the principles of homeostasis through detailed understanding of feedback systems. Students need to understand the importance of maintaining the internal environment within restricted limits and the implications of these conditions not being met.

They need to be able to explain what is meant by both negative and positive feedback, be able to explain the general stages in negative feedback and clearly articulate the differences between positive and negative feedback systems.

Regulation of temperature, pH and blood sugar levels are particular examples that students will be expected to describe and explain in detail.

Kidney function is often included within this topic area, with students required to know about the processes of ultrafiltration and reabsorption and to be able to explain the role of the loop of Henle and the counter current multiplier mechanism. This is often a difficult concept for students and does rely on a prior understanding of water potential.

The process of osmoregulation, the role of ADH in this process and the way animals adapt to certain environments in respect of this process can also be included in this topic area.

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