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Cell Structure and Organisation: Question 5

Syllabus 2.1

Structured Extended 7 marks

A food-safety officer takes a swab from each of three different surfaces in a kitchen and examines a single cell from each sample under a high-powered microscope. The structures visible in each cell are recorded below.

Sample 1: cell wall, cell membrane, cytoplasm, a large permanent vacuole, chloroplasts, a nucleus

Sample 2: cell wall, cell membrane, cytoplasm, ribosomes, one loop of circular DNA, several plasmids, no nucleus

Sample 3: cell membrane, cytoplasm, mitochondria, a nucleus, no cell wall

(a) Identify whether each sample is a plant cell, an animal cell or a bacterial cell. [3]

(b) Sample 2 lacks a structure that is present in both sample 1 and sample 3. Name this structure and state its function. [2]

(c) Name one structure present in sample 1 but absent from both samples 2 and 3, and give its function. [2]

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Worked solution

Part (a): Identifying each sample

Sample 1 has a cell wall, chloroplasts and a large permanent vacuole alongside a nucleus. Chloroplasts and a permanent vacuole are only found in plant cells, so sample 1 is a plant cell.

Sample 2 has a cell wall but no nucleus. Instead its genetic material is a loop of circular DNA, and it also has plasmids. A cell wall combined with circular DNA, plasmids and no nucleus is characteristic only of a bacterial cell, so sample 2 is a bacterial cell.

Sample 3 has a nucleus and mitochondria but no cell wall and no chloroplasts. A nucleus with no cell wall is characteristic of an animal cell, so sample 3 is an animal cell.

Part (b): A structure sample 2 lacks that samples 1 and 3 share

Samples 1 and 3 both have a nucleus, while sample 2 does not. The function of the nucleus is to control the cell’s activities: it contains the genetic material (DNA), organised into chromosomes, which carries the instructions for making proteins.

Part (c): A structure unique to sample 1

Sample 1 has chloroplasts, which are not present in sample 2 or sample 3. The function of chloroplasts is to absorb light energy and use it to carry out photosynthesis, producing carbohydrates for the cell.

(The large permanent vacuole is also unique to sample 1 and would be equally acceptable: it contains cell sap and helps to keep the cell turgid, providing support.)

Final answers

  • (a) Sample 1 = plant cell; Sample 2 = bacterial cell; Sample 3 = animal cell.
  • (b) Missing shared structure = nucleus; function = controls the cell’s activities and holds the genetic material.
  • (c) Structure unique to sample 1 = chloroplasts; function = absorb light energy for photosynthesis.