Senin, 20 April 2015

#78 Question 1

(a) The diagram shows a small part of a cell, as seen using an electron microscope.




      (i) Name the parts labelled A to D.   (2 marks)
      (ii) Describe how part B is involved in the formation of extracellular enzymes. (3 marks)

(b) Give two reasons, other than the presence of part B, why the cell in the diagram cannot be a prokaryotic cell. (2 marks)
Total: 7 marks

Candidate A

(a) (i) A plasma membrane ü
          B  Golggi ü
         C nucleus û
         D phagocyte û

* C is the nuclear envelope (or membrane), not the nucleus itself. A phagocyte is a cell - perhaps the candidate is thinking of a phagocytic vesicle. 1/2

    (ii) First, the enzymes are made by protein synthesis on the ribosomes. Then they go into the endoplasmic reticulum. Then they are taken üto the Golgi where they are packaged. Then they go in vesicles üto the cell membrane where they are sent out byexocytosis.

* This candidate has not really thought about exactly what the question was asking, and has wasted time writing about events that take place before and after the involvement of the Golgi apparatus. There is, however, a mark for the idea that the Golgi apparatus receives proteins that have been in the RER, and another for packaging them into vesicles. 2/3

(b) It has a nucleus. ü And it has Golgi apparatus. û

* The Goigi apparatus is part B, and tilis has been excluded by the question. 1/2

Candidate B

(a) (i) A cell surface membrane ü
          B Golgi apparatus ü
          C nuclear envelope ü
          D vesicle ü

* All correct. 2/2

     (ii) Proteins made in the RER are transported to the convex face ü of the Golgi apparatus in vesicles. The vesicles fuse ü with the Golgi and the proteins inside are modified ü by adding sugars to make glycoproteins .ü  They are packaged inside membranes ü  and sent to the cell membrane.

* All correct. 3/3

(b) If it was a prokaryotic celi it wouldn't have a nucleus ü and it would have a cell wall. ü

* Correct. 2/2 .