Simple and facilitated diffusion are forms of passive transport and this lesson describes the factors that increase the rate of this movement across membranes. This fully-resourced lesson is the first in a series of two that have been designed to cover specification point 2.4 of the Pearson Edexcel A-level Biology A and the involvement of channel and carrier proteins is also described and discussed.
In a number of previous lessons that covered specification points 2.1 and 2.2, students were provided with the details of gas exchange surfaces and the structure and properties of cell membranes. This lesson continually refers back to the content of these lessons so that links can be made between the movement across a cell membrane with the concentration gradient, the parts of the membrane involved and any features that may increase the rate at which the molecules move. A series of questions about the alveoli is used to demonstrate how a large surface area, a short diffusion distance and the maintenance of a steep concentration gradient will increase the rate of simple diffusion. One of two quick quiz rounds is then used to introduce temperature and size of molecule as two further factors that can affect simple diffusion. The remainder of the lesson focuses on facilitated diffusion and describes how transmembrane proteins are needed to move small, polar or large molecules from a high concentration to a lower concentration across a partially permeable membrane.
The other lesson included in this series to cover specification point 2.4 describes active transport, endocytosis and exocytosis.
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