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 movement of the particles of helium gas inside a balloon. [2 marks]
The particles move at a range of speeds  in different (random) directions .
It is important to include both the ideas of the particles having different speeds and different directions. This is what makes the overall motion of the particles random.
Write down the equation which links density, mass and volume. [1 mark]
density = mass ÷ volume 
Some questions in the exam will require you to recall and apply equations you have learned in class.
Other questions will ask you to use the ‘Physics Equation Sheet’. This is a set list of equations given to you in the exam. In this case you should find the correct equation and apply it in your working.
Make sure you read the question carefully so you understand what you are being asked to do. If an equation is given then use it, it’s not a trick.
The image shows particles of the same substance in three states of matter.
Use the image to explain why the solid has the highest density. [2 marks]
A solid has more particles than a liquid or a gas in a given volume. 
Density depends only on mass (the number of particles) and volume. 
Describe the direction of motion of the particles in a gas. [1 mark]
Particles in a gas move randomly in all different directions.