Scheme of Work Cambridge International as & a level

Extension activity: Learners write an essay on the biological importance of water. Provide a writing frame (plan of ideas) for less confident learners. A good source of summary information is at: http://faculty.fmcc.edu/mcdarby/majors101book/chapter_03-chemistry/03-Water_Properties.htm(I)

Past and specimen papers

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

3: Enzymes

Syllabus ref. and Key Concepts (KC)	Learning outcomes	Suggested teaching activities
3.1 Mode of action of enzymes KC2 KC6	3.1.1 State that enzymes are globular proteins that catalyse reactions inside cells (intracellular enzymes) or are secreted to catalyse reactions outside cells (extracellular enzymes). 3.1.2 Explain the mode of action of enzymes in terms of an active site, enzyme–substrate complex, lowering of activation energy and enzyme specificity, including the lock-and-key hypothesis and the induced- fit hypothesis.	Learners should have learnt about enzymes as biological catalysts at Cambridge IGCSE (or equivalent). Write the names of several enzymes on the board, including amylase, protease, lipase, sucrase, maltase, and lactase. Point out that they usually end with the suffix ‘-ase’ and the first part of an enzyme’s name is derived from the substrate that they digest. Indicate that all the reactions catalysed by the enzymes listed have in common the addition of water in hydrolysis reactions. (F) Help learners to understand the role of enzymes using an analogy. Light a match and use this as an analogy for the purpose of an enzyme. Elicit from learners that a small input of energy (the act of striking the match) is required to start a reaction, but that once it begins, it progresses without any further input of energy. Learners work together to produce from memory a detailed graph showing the progress of an enzyme-catalysed reaction, complete with explanatory labels. Then display a graph on the board to help learners identify what they have missed and to learn from their mistakes. Hand out three very small pieces of modelling clay to each pair of learners. Challenge them to model the events that happen during the hydrolysis of a substrate. Learners describe and explain how their models illustrate the two modes of action and formatively assess their understanding. Learners may use animations of enzyme action available on the internet, such as: http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html https://learni.st/boards/15314/learnings/110380-lock-and-key-model-vs-induced-fit-model Learners prepare a ‘flipbook’ to convert a series of diagrams into a ‘moving picture’ showing the modes of enzyme action, or use paper cut-out models to show how enzymes can break up substrates into smaller molecules or can build up larger molecules from smaller ones. (I)