Biology 9700 · AS & A Level · Transport mechanisms
Transport mechanisms — practice question
Fig. 3.1 illustrates some fruits (grapes) from the grapevine, Vitis vinifera.
Sucrose is carried in the phloem of the grapevine to the fruits. Inside the fruits, sucrose is broken down by the enzyme sucrase, which is located in cell walls. The glucose and fructose formed by sucrose hydrolysis move through membrane proteins called hexose transporters into the cytoplasm of the fruit cells.
(a)[1]
State why membrane proteins are needed for molecules such as glucose to move across cell surface membranes into cells.
(b(i))[2]
The researchers concluded that VvHT1 is responsible for the facilitated diffusion of glucose into the cells. Explain how the results in Fig. 3.2 give evidence to support this conclusion.
(b(ii))[2]
The researchers thought that grapevines could be modified to have more hexose transporters to increase the size and quality of grapes. Explain why a greater number of hexose transporters could be commercially important to growers of grapevines.
(c(i))[1]
State what is meant by the term non-self antigen.
(c(ii))[4]
With reference to Fig. 3.3, explain how T-lymphocytes react to infection by a specific type of pathogen.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Polar / hydrophilic substances are unable to cross the hydrophobic core of the phospholipid bilayer” …