Six mark questions

Six mark questions are extended open response questions. These require longer answers than the structured questions with fewer marks. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

Six mark questions are marked using a levels-based mark scheme because they are open ended. To gain full marks, you need to:

  • support explanations using scientific knowledge and understanding
  • use appropriate scientific words and terms
  • write clearly, linking ideas in a logical way
  • maintain a sustained line of reasoning, rather than getting lost or bogged down

You are likely to see command words such as:

  • 'describe' - you need to give an account but no reason
  • 'explain' - you must give reasons or explanations
  • 'devise' - you must plan or invent a procedure using your scientific knowledge and understanding
  • 'evaluate' - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about atoms could include ideas about atomic structure, isotopes, radiation and nuclear reactions. Remember that the topics covered in the first paper are assumed knowledge for the second paper, so questions in the second paper may need knowledge and understanding of those topics too.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks, but you do need to write in full sentences, linking them logically and clearly.

Questions courtesy of Eduqas.

Sample question 1 - Foundation

Question

Radioactive substances are used in a wide variety of applications, which range from medical to industrial, commercial and research.

The list below shows information about some radioisotopes of cobalt and iodine.

  • Iodine-123 has a half-life of 13 hours and emits gamma.
  • Iodine-125 has a half-life of 59 days and emits gamma.
  • Iodine-127 is stable.
  • Iodine-129 has a half-life of 1.6 years and emits beta.
  • Cobalt-55 has a half-life of 17.3 hours and emits beta.
  • Cobalt-58 has a half-life of 70 days and emits beta.
  • Cobalt-59 is stable.
  • Cobalt-60 has a half-life of 5.3 years and emits both beta and gamma.

Radioactive isotopes are used widely in many medical applications. In treating brain tumours, patients are exposed to an external cobalt source of radiation to kill cancerous cells. To check the behaviour of the thyroid gland, patients swallow a liquid containing a radioactive tracer of iodine.

From the list above select one isotope that is suitable to be used for treating brain tumours and one that is to be used as a radioactive tracer. [6 marks]

Cobalt-60 is used in radiotherapy treating brain tumours [1]. It is a gamma emitter [1] which is necessary so the radiation can penetrate the skull to reach the tumour [1].

Iodine-123 is used to check thyroid function [1]. It has a relatively short half-life [1] which is important so that it decays quickly, minimising harm to the patient [1].

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • explain the reasoning for your choice of each
  • consider its half life
  • consider the emitted type of radiation and its suitability

Sample question 2 - Higher

Question

In 1986, a catastrophic event occurred in a nuclear reactor in Chernobyl in Ukraine that caused the reactor to explode, sending radioactive material into the atmosphere, causing nuclear fallout around the world.

Describe what happens in a fission reactor to enable a controlled chain reaction to occur and how uncontrolled reactions such as those that occurred in Chernobyl are prevented. [6 marks]

A fission reaction in a nuclear reactor occurs a when slow moving neutron is captured by a uranium atom with which it collides [1]. The uranium nucleus splits into two daughter nuclei [1], releasing two or three fast moving neutrons in addition to releasing energy [1]. These neutrons have to be slowed down in order to successfully fission with other uranium nuclei and this is achieved by a moderator (of graphite or water) [1].

The reactions are controlled by absorbing neutrons with control rods, thus allowing (on average) one neutron per fission to go on to achieve fission with another uranium nucleus [1]. In this way an uncontrolled series of fission reactions is avoided [1].

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • outline what happens in a chain reaction
  • explain how these reactions are kept under control