Eukaryotic cell ultrastructureEdexcel International A Level Biology: Subtopic test

1. 1
   A student examines an electron micrograph of an acinar cell from the pancreas, which secretes the digestive enzyme amylase. The cell has a large amount of rough endoplasmic reticulum, a prominent Golgi apparatus and many small vesicles close to the cell surface membrane.

   (a)

   Which structure is the site of synthesis of the polypeptide chains of the enzyme?

   [1 mark]

   • AThe nucleolus
   • BLysosomes
   • CCentrioles
   • DRibosomes attached to the rough endoplasmic reticulum

   (b)

   Which description would allow the student to identify the Golgi apparatus in the micrograph?

   [1 mark]

   • AA stack of flattened membrane-bound sacs with small vesicles budding from the edges
   • BA double membrane containing pores and a dark-staining region
   • CA rod-shaped structure with a folded inner membrane
   • DFlattened sacs with small dark dots on their outer surface

   (c)

   Explain why this cell having a large amount of rough endoplasmic reticulum is an advantage.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Tay-Sachs disease is an inherited disorder in which a lysosomal enzyme that breaks down a lipid is missing. The lipid builds up inside nerve cells, which swell and become damaged.

   (a)

   Which statement about lysosomes is correct?

   [1 mark]

   • AThey have a double membrane with a folded inner membrane
   • BThey are formed from vesicles that bud off the Golgi apparatus and contain hydrolytic enzymes
   • CThey are made in the nucleolus and contain DNA
   • DThey release energy by aerobic respiration

   (b)

   Which cell process is most directly affected in the nerve cells of a patient with this disease?

   [1 mark]

   • AAssembly of ribosomal subunits
   • BFormation of spindle fibres in cell division
   • CBreakdown of unwanted material inside the cell by hydrolytic enzymes
   • DFolding of polypeptides in the rough endoplasmic reticulum

   (c)

   Explain why the lipid builds up inside the nerve cells.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Pancreatic cells were given a short pulse of a radioactively labelled amino acid and then transferred to a medium containing only unlabelled amino acids. After 3 minutes most radioactivity was in the rough endoplasmic reticulum. After 20 minutes most was in the Golgi apparatus. After 60 minutes most was in vesicles near the cell surface membrane and in the medium surrounding the cells.

   (a)

   Describe the pathway taken by the labelled protein, as shown by these results.

   [3 marks]

   (b)

   The experiment is repeated with a drug that stops vesicles budding from the rough endoplasmic reticulum. Predict where the radioactivity would be found after 60 minutes, and explain the effect on the secretion of an extracellular enzyme.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An electron micrograph of a human liver cell (hepatocyte) shows: a large nucleus with a double membrane containing pores and a dark-staining region; many rod-shaped structures with a double membrane, the inner membrane being folded into projections; a network of flattened sacs covered in small dark dots; a network of tubules with no dots; and a stack of curved, flattened sacs. Hepatocytes make plasma proteins such as albumin, detoxify alcohol and need large amounts of ATP. They are grouped with other tissues to form the liver, an organ of the digestive system.

   (a)

   Identify the organelles described and explain how the appearance of each is related to its function in the hepatocyte.

   [6 marks]

   (b)

   A toxin damages the mitochondria in hepatocytes. Predict and explain the effect on the ability of the cells to make and secrete albumin.

   [6 marks]

   Total for question 4: 12 marks

End of questions