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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Links and Resources
This activity pack gives an interesting context in which to discuss the topic of homeostasis. The resources provided are focused on thermoregulation in the context of an expedition to the South Pole.
Polly Hatchard was one of an all-women team who trekked to the South Pole. A range of audio clips describe the preparations and some of the problems she faced during her expedition to the pole. There is then an activity worksheet for students to complete.
It is not necessary to listen to all the audio clips and pages one and three of the activity sheet are the most relevant. The resource was originally aimed at 14-16 year olds, but would make a suitable starter activity for A level biology students. The audio clips could just simply be used as stimulus material and students could be asked to produce a flow diagram of the thermoregulation feedback mechanism.
Although originally designed for Key Stage Four students, there is material in this resource pack that would be useful for A level Biologists, but more importantly a lot of ideas for teaching activities that could easily be adapted.
The card sort for osmoregulation on page 84, for example, would make a useful starter activity with to see how much they remember from GCSE, or indeed if there are misconceptions that need to be addressed. Students could then be challenged to produce a similar set of cards for either thermoregulation or the control of blood sugar levels. If they do this in pairs, the pairs can then swap the cards produced to see if they can place them in the correct order.
Other ideas, such as making a jigsaw (page sixteen), could be adapted for example to a cross section of the kidney or of the loop of Henle counter current multiplier.
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.
This is a three page summary sheet on homeostasis. The resource provides details of the key mechanisms involved in homeostatic responses.
There is limited detail on these summary sheets. However they could be used as a quick recap, or students could be asked to translate the information provided in particular sections into another non-text format such as a flow diagram , presentation, poster etc.
This is another three page summary sheet, this time on the excretory system. The level of detail is just at the requirement for A level and there is a good concise and clear summary of the functions of the nephron.
This resource would be useful as a quick recap, perhaps with some additional questions to ensure all the detail required at A level was covered. Alternatively, as a pre-lesson read, with students preparing a two slide summary of these sheets, to be given at the start of the lesson.
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.
In this investigation produced by Science & Plants for Schools (SAPS), students look at the concentration of glucose in isotonic sports drinks. This enables students to see if the drinks are, in fact, isotonic with the blood.
This provides a good context for the study of homeostasis and is a context which many students will find appealing.
This investigation can be linked to an investigation to find out the glucose concentration in urine samples. The investigation could be altered so that students make up the glucose solutions to improve their skills in making serial dilutions.
The investigation is a good way to further understanding of the use of a standard curve in biology.