Homeostasis
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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Keeping Things Steady *suitable for home teaching*
This article provides an overview of homeostasis. It discusses examples of a range of homeostatic mechanisms and would be useful pre-reading for students before they begin the topic of homeostasis at A level.
A positive aspect of the article is the way it describes the effects of imbalances on the cells of the body. This is often an area that is failed to be emphasised. It is assumed that students will know why it is a good idea to maintain a constant body temperature. Reinforcing the link to enzyme optimum temperatures is often omitted at GCSE, but is a clear requirement at A level, similarly the link with stable pH.
Kidneys *suitable for home teaching*
This article describes the structure and function of the kidneys. There is a good diagram which shows the structure of the kidney tubule and how the various sections are involved in the processes of filtration and reabsorption.
Students could be given copies of this diagram and asked to add on the concentration levels at inside and outside of the tubules and therefore what net movement (or what) is seen where.
Students could also be asked to write a short report on the routes through the kidney of various molecules, such as a water molecule destined to be excreted or a sugar molecule.
One section of the article describes the control of urine production via ADH. Students could produce flow diagrams to illustrate the feedback control mechanism which operates when the body has too much, or too little water.
Interpreting Information About Sweating and Temperature
Homeostasis data questions that require students to analyse data in tables and graphs are popular with examiners. This resource provides both of these things, with some useful questions for the full ability range of students.
The first few questions could be completed in class, with the remainder set for homework. For the final question students could be asked to give a short presentation. Answers to the questions are provided, so it is important to remove this final page before using this with students. It would however be a useful sheet to use to allow students to first peer mark on their own and then use the answer sheet.