Biology 9700 · AS & A Level · Transport mechanisms

Transport mechanisms — practice question

Fig. 5.1 contains a transmission electron micrograph of portions of two plant cells. The middle lamella serves to hold neighbouring cells together. It is made of the polysaccharide pectin. Pectin interacts with the polysaccharides cellulose and hemicellulose in the cell walls of the plant cells, keeping the walls close together, as illustrated in Fig. 5.1.
(a)[2]

Cell structure X in Fig. 5.1 is a cytoplasmic channel through which strands of cytoplasm pass across the cell walls of the two cells. Name cell structure X and state one function of this cell structure.

(b(i))[1]

Suggest why researchers would not have considered ribosomes as the possible site for pectin synthesis.

(b(ii))[1]

Name the mechanism responsible for moving pectin out of the cell.

(c)[3]

Fig. 5.2 shows how cellulose concentration affects cellulase activity, and cellulase is used to make fruit juice less cloudy. Describe and explain the pattern in Fig. 5.2.

(d(i))[3]

In terms of how enzyme and substrate interact when ultrasound is applied, suggest explanations for the lower $K_m$ for pectinase and the higher $V_{\text{max}}$ for xylanase, as shown in Table 5.1.

(d(ii))[1]

Explain whether the information in Table 5.1 supports the recommendation that ultrasound can be used in the manufacture of fruit juices.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: plasmodesmata

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI