1.4: Membrane transport
Teaching time: 3 hours
Practical time: 2 hours for practical 2 plus an additional 2 hours for HL students (beetroot membranes practical)
Key Vocabulary
prior learning & retrieval practice
Review 1.3 membrane structure
Review 2.4 proteins
Passive movement of molecules across the membrane
Essential idea: Membranes control the composition of cells by active and passive transport.
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Exercise 1: Answer these questions:
List and define the different types of passive transport. What does it mean for movement to be passive?
Exercise 2: Draw a phospholipid bilayer and add illustrations of the passive movement of molecules across it. Distinguish between diffusion and facilitated diffusion
A2: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Exercise 3: Read the relevant section of your textbook and connect-extend-challenge. Explain the importance of keeping organs bathed in isotonic solutions
Active Transport of molecules across the membrane
A1: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. We will examine this in topic 6.5
Exercise 4: Distinguish active from passive transport. List the ways in which membranes can use active transport.
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Exercise 5: Define Endocytosis and Exocytosis. List some examples of their uses in cells. Explain how the fluidity of membranes allow these processes to occur. Outline how vesicles transport materials within cells.
Practical 2
NoS: Experimental design—accurate quantitative measurement in osmosis experiments are essential. (3.1)
S2: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)
