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 the 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'.
Edexcel questions courtesy of Pearson Education Ltd.
A woman wants to check that a banknote is genuine. She is using a lamp which emits radiation which is part of the electromagnetic spectrum.
Explain how two different electromagnetic radiations enable the woman to check the banknote. [2 marks]
The banknote absorbs UV light  and re-emits visible light .
As the question is for two marks, make sure you mention at least two different types of electromagnetic waves.
Mobile phones emit microwaves.
Microwave ovens emit microwaves.
Explain why a mobile phone does not have the same heating effect as a microwave oven. [2 marks]
The heating effect for the oven and the phone depends on their power  and since the power of an oven is much greater than the power of a phone, the oven produces a greater heating effect .