At a water-treatment laboratory, samples were taken from a filter that had become blocked. The table shows observations of four organisms under a microscope...
Question 1 Report
At a water-treatment laboratory, samples were taken from a filter that had become blocked. The table shows observations of four organisms under a microscope. Sample C was also tested by trying to grow it without host cells. This investigation helped the laboratory decide which organisms could cause disease in a water supply.
| sample | typical diameter / micrometres | nucleus present | cell wall present | chloroplasts present | other observation |
|---|---|---|---|---|---|
| A | 1.8 | no | yes | no | divides into two cells |
| B | 7.5 | yes | yes | no | new cells form as buds |
| C | 0.12 | no | no | no | only makes more particles inside living cells |
| D | 35 | yes | yes | yes | moves using a flagellum |
(a) Complete the following by naming the group for each sample: A, B, C and D. [4]
(b) Use Table 1 to explain why A is classified as a bacterium. [2]
(c) What evidence in Table 1 shows that C is a virus rather than a cellular organism? [2]
(d) Describe four actions the laboratory could use to reduce the risk of disease organisms entering drinking water from this filter. [3]
Answer Details
(a) Sample A is a bacterium. [1 mark] Sample B is a fungus, specifically yeast. [1 mark] Sample C is a virus. [1 mark] Sample D is a protoctist, or protist. [1 mark]
(b) A has no nucleus, so it is prokaryotic, as bacteria are. [1 mark] It has a cell wall and divides into two cells by binary fission, which is bacterial reproduction. [1 mark]
(c) C has no nucleus, cell wall, or chloroplasts, so it lacks cellular structures. [1 mark] It can make more particles only inside living host cells. [1 mark] This dependence on host cells is characteristic of viruses.
(d) Any three suitable actions are:
- clean or replace the blocked filter; [1 mark]
- disinfect water, for example with chlorine or ultraviolet light; [1 mark]
- use finer filtration; [1 mark]
- test water samples regularly for microorganisms; [1 mark]
- keep treatment equipment sealed from contamination; [1 mark]
- heat-treat water where appropriate. [1 mark]
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