A-LevelBiologyCell structure9700/23 · Oct/Nov 2020 · Q69 Marks

Fig. 6.1 shows Vorticella, which is a single-celled organism that lives in freshwater. Vorticella has many cilia which it uses for feeding. [Figure 6.1] The distance shown by X–Y on Fig. 6.1 is 150 μm. Calculate the magnification of Fig. 6.1. State the formula that you will use and show your working. Write your answer to the nearest whole number. formula

(a)Fig. 6.1 shows Vorticella, which is a single-celled organism that lives in freshwater. Vorticella has many cilia which it uses for feeding. [Figure 6.1] The distance shown by X–Y on Fig. 6.1 is 150 μm. Calculate the magnification of Fig. 6.1. State the formula that you will use and show your working. Write your answer to the nearest whole number. formula[3]
(b)(i)The food particles are taken into the gullet by a current of water created by movement of cilia. Any particles suspended in the water, such as bacteria, are taken into the cell as shown in Fig. 6.2. [Figure 6.2] State the name of the process which takes the bacteria into the cell at Z and describe the way in which it occurs. name description[3]
(b)(ii)Describe the role of lysosomes in intracellular digestion in Vorticella.[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[3] formula (magnification =) size of image ; actual size
A M = I/A or I = A × M
A magnification triangle
length of line X–Y = 30 mm (± 2 mm) / 30 000 μm = 3.0 × 10⁻² m
actual length = 150 µm / 0.15 mm = 150 × 10⁻⁶ m
working length of the image (in m, mm or cm) divided by the actual size (A ± 2 mm) ;
(x) 200 ; A answer in range 187 – 213
[3] 1 endocytosis / phagocytosis ;
two from 2 particles / bacteria, reach end of, gullet / AW ;
3 binding / fusion / attachment, (of bacteria / food particles) to, receptors / (cell surface) membrane ; I 'makes contact with'
4 membrane engulfs, bacteria / food particles ;
5 fusion of phospholipids / membrane fusion ;
6 (phagocytic) vacuole / vesicle, pinches off from, surface / membrane ;
[3] I bulk transport
1 fuse / bind, with, phagosome / food vacuole / phagocytic vacuole / phagocytic vesicle ; A food vacuole, etc. implied
2 contain / add, hydrolytic / digestive, enzymes ; A hydrolases A description of one type of breakdown reaction catalysed by a lysosomal enzyme
3 an example of hydrolase or enzyme ; e.g. protease / lipase / carbohydrase / nuclease / lysozyme

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