Scheme of Work Cambridge International as & a level

KC2 KC3 KC5

16.2.7 Explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, and the recessive allele, le. 16.3.1 Describe the differences between structural genes and regulatory genes and the differences between repressible enzymes and inducible enzymes. 16.3.2 Explain genetic control of protein production in a prokaryote using the lac operon. 16.3.3 State that transcription factors are proteins that bind to DNA and are involved in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription. 16.3.4 Explain how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that promote transcription.

Write key terms on the board that learners will recall from their work on transcription (Topic 6). As you call out a word, ask learners to raise their hand to see who can remember it, and then ask learners to keep their hand raised if they would like to provide some information related to it. Ask learners questions such as ‘What do you think of that response?’ and ‘Is there anything further to add?’ to develop a discussion. (F) Learners take part in a role-play activity to show how the different DNA sequences and proteins interact during bacterial control of lactose metabolism. Learners should place pieces of paper, representing genes, along a piece of string or rope which has been placed on the floor. The repressor could be represented by one learner who holds a sign stating ‘stop’ to prevent RNA polymerase from transcribing the three structural genes. Give suggestions for items that represent lactose. Ask learners to suggest how this could be used to illustrate the response of bacteria when they encounter lactose. After this activity, help learners draw up a table to distinguish between structural and regulatory genes, and repressible and inducible enzymes. Review learners’ experience by comparing their actions with an online interactive demonstration, e.g.: https://phet.colorado.edu/en/simulation/legacy/gene-machine-lac-operon Place a long piece of string on the floor that spans the entire classroom. Provide each learner with a piece of paper and ask them to determine a list of events that occur when seed germination is initiated. Learners work together to write their agreed steps on the pieces of paper and attach these to the string. Discuss the decisions that the learners have made. Allow learners to take photographs of this ‘timeline’ using their mobile phones for future reference. Provide a writing frame to help learners write an account of the sequences of events in the control of transcription by the lac operon and by gibberellins. This must have a series of model sentences but with key words removed. Learners complete the sentences using their experiences during the lesson and wider research. (F)