Scheme of Work Cambridge International as & a level

Extension activity: Learners prepare a glossary to include all of the words that begin with the letter ‘G’ in this topic (e.g. glucose, glycogen, glycogenolysis, glycogenesis and gluconeogenesis).

14.2 Homeostasis in plants KC2 KC5

14.2.1 Explain that stomata respond to changes in environmental conditions by opening and closing and that regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion with the need to minimise water loss by transpiration. 14.2.2 Explain that stomata have daily rhythms of opening and closing. 14.2.3 Describe the structure and function of guard cells and explain the mechanism by which they open and close stomata. 14.2.4 Describe the role of abscisic acid in the closure of stomata during times of water stress, including the role of calcium ions as a second messenger.

Refresh learners’ knowledge of key terms related to plant transport, which they encountered in Topic 7. Learners describe ‘a day in the life of a leaf’. Ask learners to consider what happens to the stomata on the underside of a leaf over 24 hours, beginning at midnight. Choose a learner to begin and then move to another to continue. Keep doing this until the description has reached the next midnight. Review this activity by hosting a brief quiz consisting of a series of multiple-choice questions taken from Paper 1. (F) Learners observe the opening and closing of stomata from freshly-obtained leaves from a well-watered plant that has been kept in the light. As soon as the epidermis is immersed in a solution of 15% urea and observed through a microscope, the stomata can be seen to close as the guard cells become plasmolysed. If the epidermis is immersed in a solution of dilute magnesium sulfate, then they will deplasmolyse and the stomata will open again. Learners use separate cards (around 10–12) to write out definitions and features of the terms stimulus, receptor, effector, control centre, response that are linked to homeostasis in plants. Learners swap with a partner, who can write down the relevant term that is being described. (I) Learners produce a ‘concept map’ to illustrate their learning during the lesson in a very visual way. Provide a series of words to help structure their work. (F)