Six mark questions are often the questions that people find the most difficult. In all longer answer questions, but especially the six mark ones, it is important that you plan your answer and not just rush into it. After all, you would plan an essay or short story before starting. Without a plan it is easy to stray away from the key point and lose marks, get steps in a process in the wrong order or forget key bits of information.
Six mark questions will start with command words such as ‘describe’ or ‘explain’. 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 the number of radioactive nuclei decreases as time increases. It does this 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 ‘[6 marks]’. It is essential that you give as many different points in your answer as possible, linking these together. Often, you will be asked to compare two things: make sure that you include both in your answer otherwise, you are likely to limit your score to two marks out of six marks.
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Scientists sometimes replace one scientific model with a different model.
For example, in the early 20th century the plum pudding model of the atom was replaced by the nuclear model of the atom.
Explain what led to the plum pudding model of the atom being replaced by the nuclear model of the atom. [6 marks]
An experiment was carried out to direct alpha particles at a thin gold foil . The plum pudding model suggested that mass and charge were evenly spread throughout the atom . It was expected that the particles would be scattered evenly by the atoms. It was found that most alpha particles passed straight through the foil  meaning most of the atom is empty space . A few alpha particles were deflected through large angles , meaning the atoms have a small, dense, positive nucleus .
The answer will need to be detailed, with scientific terms and easy for the examiner to follow. You could include the following ideas:
Explain how ionising radiation can have hazardous effects on the human body. [6 marks]
Ionising radiation turns atoms into ions  causing molecules to break up . The change in molecules can change DNA in the cell’s nucleus . If the DNA is sufficiently damaged, this may destroy the cell . Changes in the DNA can also cause mutations to genes  that can cause cancer .
Before starting a question of this type, it may be useful to list the scientific key terms to be included, eg ions, DNA, nucleus, mutations, cancer. These can then be used to structure the answer as a sentence by introducing and linking each term to the others.