Mark Scheme

Surface area is a principle concept related to many areas in biological functioning. Heat as well as substances can be transferred between and within the body and the environment. Explain the relationship between surface area and this transfer. [25 marks]

This essay is not open in its title – it says “Explain”. This means that you need to explain how surface area is related to whichever topic areas you write about.

This is the list of the MAIN POINTS that would be looked for in the essay:

• Principles: Diffusion and Fick’s law, size and surface area to volume ratio
• Substances: Blood and blood vessels, The exchange of respiratory gases in the lung, The structure and functions of the placenta, Absorption of the products of digestion
• Transfer of heat: The relationship between BMR, body mass and surface area, Temperature control

Examiners are also given instructions as follows: If the essay contains information from more than one area e.g. Diffusion & transfer of heat, two marks can be given; information from one area is awarded 1 mark generally. However, examiners are allowed some discretion in where information is drawn and this means that other study areas can be incorporated into the essay. For example, an examiner would be able to consider awarding marks for incorporating plant & microbial biology too as surface area: volume ratio principles are just as relevant to those areas of biology as Human Biology.

How marks are awarded

Each awarding body has slightly different values to how marks are awarded and / or where certain criteria fall.

This is a general idea of where marks for Essay 2 would be awarded.

• Scientific Content: maximum of 16 marks depending upon coverage of topic areas (in depth, superficial), occurrence of biological / scientific errors
• Breadth of Knowledge: maximum of 3 marks depending upon how many areas of the title have been covered (see Main Points above), if any topic areas essential to basic biological understanding have been omitted, if you have covered more than one area in the main points (little credit is given to writing about just one of the main areas)
• Relevance: this speaks for itself. If you start writing or drawing about something other than surface area and its linked topics, marks will be lost. The only occasion where you can put in something less relevant is the introduction but, better to keep to the topic rigidly.
• Quality of language: this also speaks for itself. This is all about good English, good scientific language (no terms like “great big thing” “huge” “amount” or other weak, vague language)