Biology 9700 · AS & A Level · Transport mechanisms
Transport mechanisms — practice question
A range of substances can pass through cell surface membranes between the cytoplasm of animal cells and the extracellular environment. A student produced a sketch to show how substances move across the cell surface membranes of mammalian red blood cells. Fig. 1.1 presents the student’s sketch. Every arrow shows a substance moving across the membrane. The number on each of the 4 shapes shows the relative concentration of each substance in the cytoplasm and in the blood plasma. After doing research, the student compiled a list of some substances present in red blood cells, as shown in Fig. 1.2. Table 1.1 gives information about the 4 kinds of movement of substances across the cell surface membranes of red blood cells shown in Fig. 1.1.
(a)[5]
Fill in Table 1.1 using the evidence shown in Fig. 1.1 and Fig. 1.2.
(b)[2]
Some viruses infect plants via the surfaces of damaged leaves. These plant viruses can move from one leaf cell to another without needing to cross any cell surface membranes. Explain how some plant viruses can travel from one cell to another without passing through cell surface membranes.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “For letter A, an example substance is carbon dioxide / oxygen” …