This lesson describes the relationship between the size of an organism or structure and its surface to volume ratio. The PowerPoint and accompanying worksheets have been designed to cover point 3.1 of the AQA A-level Biology specification and also have been specifically planned to prepare the students for the upcoming lessons in topic 3 on gas exchange and absorption in the ileum.
The students are likely to have been introduced to the ratio at GCSE, but understanding of its relevance tends to be mixed. Therefore, real life examples are included throughout the lesson that emphasise the importance of the surface area to volume ratio in order to increase this relevance. A lot of students worry about the maths calculations that are associated with this topic so a step by step guide is included at the start of the lesson that walks them through the calculation of the surface area, the volume and then the ratio. Through worked examples and understanding checks, SA/V ratios are calculated for cubes of increasing side length and living organisms of different size. These comparative values will enable the students to conclude that the larger the organism or structure, the lower the surface area to volume ratio. A differentiated task is then used to challenge the students to explain the relationship between the ratio and the metabolic demands of an organism and this leads into the next part of the lesson, where the adaptations of larger organisms to increase the ratio at their exchange surfaces is covered. The students will calculate the SA/V ratio of a human alveolus (using the surface area and volume formulae for a sphere) and will see the significant increase that results from the folding of the membranes. This is further demonstrated by the villi and the microvilli on the enterocytes that form the epithelial lining of these folds in the ileum. The final part of the lesson introduces Fick’s law of diffusion so that students are reminded that the steepness of a concentration gradient and the thickness of a membrane also affect the rate of diffusion.
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This bundle contains 7 lessons which are highly detailed and cover the following points in the surface area to volume ratio, gas exchange and digestion and absorption topics of the AQA A-level Biology specification: * The relationship between the size of an organism or structure and its surface area to volume ratio * The development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces * Adaptations of gas exchange surfaces in single-celled organisms, insects, bony fish and in the leaf of a dicotyledonous plant * The gross structure of the human gas exchange system * The essential features of the alveolar epithelium over which gas exchange takes place * Ventilation and the exchange of gases in the lungs * Digestion in mammals of carbohydrates, proteins and lipids * Mechanisms for the absorption of the products of digestion by cells lining the ileum If you would like to sample the quality of lessons in this bundle, then download the alveolar epithelium and absorption in the ileum lessons as these have been uploaded for free
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