Home › Subjects › O-Level Pure Biology › Cell Structure and Organisation
O-Level Cell Structure and Organisation
What the O-Level syllabus expects for Cell Structure and Organisation, and how to practise it.
What the syllabus expects
- Draw comparisons between the make-up of a typical animal cell and a typical plant cell.
- Account for the way specialised cells have structures matched to what they do, for instance a muscle cell holding many mitochondria to deliver more energy, a root hair cell offering a large membrane surface area for stronger absorption, and a red blood cell lacking a nucleus so it can carry more oxygen.
How it's examined
Questions on this topic most often ask you to explain, outline. About 13% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (5 marks)
Outline, in order, the steps that lead to enzymes being made inside a cell and then released from it, naming clearly each organelle that takes part.
Show the worked answer
Enzymes are proteins, so their production follows the protein-secretion pathway. Steps in order: 1. The gene coding for the enzyme is transcribed in the nucleus to produce mRNA, which leaves through a nuclear pore. 2. The mRNA travels to ribosomes attached to the rough endoplasmic reticulum (rough ER), where the enzyme (polypeptide) is synthesised by translation. 3. The rough ER packages the enzyme into vesicles which bud off and carry it to the Golgi apparatus (Golgi body). 4. The Golgi apparatus modifies/processes and packages the enzyme, then buds off secretory vesicles. 5. The secretory vesicles move to and fuse with the cell surface membrane, releasing the enzyme out of the cell by exocytosis. (Mitochondria supply ATP for these processes.)
Example 2 (2 marks)
Explain why phospholipids can arrange themselves into a bilayer within the cell surface membrane.
Show the worked answer
Each phospholipid molecule has a hydrophilic (water-loving) phosphate head and two hydrophobic (water-hating) fatty-acid tails. Because there is a watery (aqueous) environment on both the inside and the outside of the cell, the molecules arrange so the hydrophilic heads point outward towards the water on both surfaces, while the hydrophobic tails point inward away from the water, facing each other. This produces a two-layer (bilayer) arrangement.
More O-Level Pure Biology topics
Movement of Substances · Biological Molecules · Nutrition in Humans · Transport in Humans · Respiration in Humans · Excretion in Humans · all of O-Level Pure Biology