DP Biology (last assessment 2024)

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Question 23M.2.HL.TZ1.4

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Date May 2023 Marks available [Maximum mark: 6] Reference code 23M.2.HL.TZ1.4
Level HL Paper 2 Time zone TZ1
Command term Explain, Identify, Outline, State Question number 4 Adapted from N/A
4.
[Maximum mark: 6]
23M.2.HL.TZ1.4

The diagram shows water molecules as they might be arranged in liquid water and the interactions between them.

(a.i)

State how many water molecules are shown in the diagram. 

[1]

Markscheme

10;

Examiners report

SL:

Candidates were very successful answering (a). 

HL:

Nearly all candidates were able to recognise the water molecules in the diagram and count the correct number.

(a.ii)

Identify the interactions that are shown between the water molecules.

[1]

Markscheme

hydrogen bonds/H bond;

Examiners report

SL:

Candidates were very successful answering 4(a).

HL:

60% of candidates stated that there are hydrogen bonds between water molecules. The commonest error was to think that these bonds are covalent.

(b.i)

With reference to the diagram, explain how water in sweat evaporates.

[2]

Markscheme
  1. heat increases molecular motion/vibration;
  2. (hydrogen) bonds break/bonds between water molecules break;
  3. water evaporation is separation of water molecules/water changes from liquid to gas/vapour;
  4. heat removed from skin surface/body;

 

Examiners report

SL:

In answering (b)(i) some seemed to think that water separates into hydrogen and oxygen atoms when it changes from liquid to gas.

HL:

The mean score here was less than 1 mark out of two, showing that the process of evaporation was not universally understood. Few answers included the idea that in changing from liquid to gas, molecules become separated from each other.

(b.ii)

Outline the reasons for secretion of sweat in humans.

[2]

Markscheme
  1. cooling/removal of heat/lowering body temperature;
  2. to prevent overheating
    OR
    to help maintain body temperature/for temperature homeostasis/for thermoregulation
    OR
    to keep temperature at 37 °C;

 

Examiners report

SL:

Most candidates answered (b)(ii) correctly with "coolant" and some mentioned "water homeostasis".

HL:

Most candidates knew that sweating causes cooling, but fewer were able to state clearly what is achieved by this.

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