Scheme of Work Cambridge International as & a level

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bio scheme of work

Syllabus ref. and Key Concepts (KC) Learning outcomes

Extension activity: Learners prepare a series of five statements that can be classified as ‘always true,’ ‘sometimes true’ or ‘never true.’ Examples include ‘All cells have a surface membrane’ (always true), ‘Eukaryotic cells contain a nucleus’ (sometimes true – not red blood cells), and ‘Viruses and prokaryotic cells have membrane-bound organelles’ (never true). (F)

Past and specimen papers
Past/specimen papers and mark schemes are available to download at www.cambridgeinternational.org/support (F)

2: Biological molecules

Syllabus ref. and Key Concepts (KC)

Learning outcomes

Suggested teaching activities

2.1 Testing for biological molecules

KC2

KC6

2.1.1 Describe and carry out the Benedict’s test for reducing sugars, the iodine test for starch, the emulsion test for lipids and the biuret test for proteins.

2.1.2 Describe and carry out a semi-quantitative Benedict’s test on a reducing sugar solution by standardising the test and using the results (time to first colour change or comparison to colour standards) to estimate the concentration.

2.1.3 Describe and carry out a test to identify the presence of non-reducing sugars, using acid hydrolysis and Benedict’s solution.

Display a list of key terms that learners must know in the form of a ‘word board.’ These include the types of biological molecule and their key functions in organisms. As you call out a word, ask for a show of hands to see who has heard of it, then ask learners to keep their hand raised if they would like to link at least two of the words together. An example could be ‘carbohydrates and lipids contain the elements carbon, hydrogen and oxygen.’ (F)

Learners carry out some of the biochemical tests for different types of molecule. These may include simple laboratory techniques to confirm the presence of reducing sugars, starch, lipids and proteins. Demonstrate how dialysis tubing can be filled with starch solution and placed in a boiling tube of iodine solution. Invert the boiling tube (with bung) a few times and learners watch the contents of the dialysis tubing change colour. Ask learners to explain their observations.

Learners develop their practical skills further by preparing a range of dilutions of glucose by serial dilution and use the Benedict’s, iodine or biuret tests to estimate the unknown concentration of a solution of a given biological molecule. This exercise helps learners to form an understanding of the process of preparing solutions by serial dilution, and distinguish between qualitative, quantitative and semi-quantitative tests.

Learners review their knowledge by constructing a table to list the biological molecules, test reagent, negative result and positive result in separate columns. (I)

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