One- or 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.
The distance-time graph for a car is shown below:
Describe what the graph shows about the speed of the car as it travels the 80 m. [1 mark]
At first the car travels at a constant speed and then slows down .
There is a resultant force on a model rocket of 0.5 N upwards when it takes off. The arrow on the diagram shows the size and direction of the force of gravity acting on the rocket when it takes off.
Add another arrow to the diagram to show the thrust produced by the burning fuel at the time the rocket takes off. You should label the arrow with the size of the thrust. [2 marks]
For the best chance of gaining full marks, make sure that the arrow points upwards  and that you have labelled it with the size of the force .