Cell structure and organisation

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   On an electron micrograph with a magnification of $\times 15\,000$, a mitochondrion measures $36\,\text{mm}$ long.

   Calculate the actual length of the mitochondrion. Give your answer in nanometres (nm).

   Mark scheme

   • Converts the image length to consistent units, e.g. $36\,\text{mm} = 36\,000\,\mu\text{m}$ (1)
   • Actual length $= 36\,000 \div 15\,000 = 2.4\,\mu\text{m}$ (1)
   • $= 2400\,\text{nm}$ (1)
2. Question 24 marks

   Cells in the pancreas make and secrete digestive enzymes.

   Describe the roles of organelles in the production and secretion of an extracellular enzyme.

   Mark scheme

   • The enzyme (polypeptide) is synthesised on ribosomes on the rough endoplasmic reticulum (1)
   • It is transported through the RER and moves to the Golgi apparatus in vesicles (1)
   • The Golgi apparatus modifies the protein (e.g. adds carbohydrate) and packages it into secretory vesicles (1)
   • Vesicles move to and fuse with the cell surface membrane, releasing the enzyme by exocytosis (1)