One to two mark questions will start with command words such as 'describe' or 'explain'. Some command words are easy to understand such as:
The command words 'describe' and 'explain' can be confusing. If you are asked to describe a graph, you will be expected to write about its overall shape, whether it is linear or curved, the slope of gradients, etc. If you are asked to explain why a pattern or trend is seen in a graph, you will be expected to use your science knowledge, not just say what you see (which is a description), eg 'The graph shows a steep linear increase for the first three hours because…'.
‘Explain how’ and ‘why’ questions often have the word ‘because’ in their answer. 'Describe' questions don’t.
The number of marks per question part is given in this form ‘[2 marks]’. It is essential that you give two different answers if a question is worth two marks. Sometimes you can gain a second mark by giving the units in a calculation or stating specific data points, eg the speed of the object decreased by 8 m/s.
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Describe the differences between the voltage supplied by a cell and the voltage of the domestic mains supply [3 marks]
Describe how the resistance of a filament lamp changes as the current through it increases. [1 mark]
As current increases, the resistance of the filament lamp increases. 
When asked to describe relationships or patterns it is a good idea to clearly state how a particular change in one variable affects the other.
The figure shows the current-potential difference graph for three wires, A, B and C.
State which wire has the greatest resistance and give a reason why. [2 marks]
Wire C has the greatest resistance because the most potential difference is required to drive the same current through it compared to the other wires. OR for the same p.d. the current is the smallest.