Scheme of Work Cambridge International as & a level

Resource Plus

Carry out the Investigating the effect of temperature on the permeability of plant cell membranes experiment referring to the Teaching Pack for lesson plans and resources.

Learners indirectly determine the integrity of cell membranes by measuring the loss of a coloured pigment from tissue at different temperatures. This investigation also offers an opportunity to revise the use of the colorimeter, which can provide quantitative data for further analysis, as well as exercises that distinguish between key experimental terms such as validity, reliability, accuracy, random error and systematic error.

Describe how the cell surface membrane has been likened to ‘protein icebergs floating in a sea of phospholipids.’ An animation that may help is:

www.wisc-online.com/learn/natural-science/life-science/ap1101/construction-of-the-cell-membrane

Learners model the arrangement of molecules in a fluid mosaic membrane. This helps them understand the idea that the different components are free to move. Provide a range of simple items, or cut-outs, and keep the models for reference in subsequent lessons as a visual aid. Ensure that learners have included all types of molecule, and ask them to use their model to explain the functions of phospholipids, cholesterol, glycolipids, proteins and glycoproteins. (I)

Learners use modelling clay to build models to show the events that occur during cell signalling. Two strips of paper can be used to represent the phospholipid bilayer. Use clay to represent ligands (small balls), receptor membrane proteins (shaped like a two-pronged fork) and intracellular enzymes (connected to the cytoplasmic region of the membrane receptors). (I)

Each learner writes a question about fluid mosaic membranes from the lesson on a coloured paper strip and the answer on differently-coloured paper strip. In groups of 6–8, hand out the strips so that each learner gets a question and an answer. One learner reads out their question, and the learner with the right answer then reads it out, followed by their question. (F)