O-LevelBiologyCell Biology5090/21 · Oct/Nov 2023 · Q312 Marks

The bar chart in Fig. 3.1 shows the percentage of total human body mass for the five most common elements found in the human body. [Figure 3.1]

(a)(i)Calculate the percentage of the total human body mass made up from the three most common elements. total = %[2]
(a)(ii)Name two types of substance found in the human body that contain only carbon, hydrogen and oxygen.[2]
(b)(i)Water contains the elements hydrogen and oxygen and makes up a large percentage of an adult's total body mass. Discuss why water makes up such a high percentage of an adult's total body mass.[3]
(b)(ii)Explain why a cell from human tissue will burst when it is placed in water.[3]
(c)Human tissues contain different percentage masses of the elements shown in Fig. 3.1. Suggest one tissue that contains a relatively high percentage mass of nitrogen and explain your answer.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[2] 3(a)(i) 93.0 ; ; A 65, 18.5 & 9.5 for 1 mark
[2] 3(a)(ii) carbohydrates ; fats / lipids;
[3] 3(b)(i) any three from: solvent; named dissolved substance; cytoplasm is mostly water ; in blood / plasma + transport ; in urine + excretion; in sweat or evaporation cools body;
[3] 3(b)(ii) any three from: water enters + osmosis ; higher water potential in water / lower water potential in tissue / cells ; across selectively / partially / differentially / semi permeable membrane; cell swells up / expands / cytoplasm volume increases ; bursts due to lack of a cell wall ;
[2] 3(c) muscle; protein;

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