Plant structures and functions - Linking questions

Linking questions span different topics. In linking questions, 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. Remember to write your answer in full sentences, not bullet points.

One way to answer linking questions is to follow these steps:

  1. identify exactly what the question is asking (perhaps by underlining key parts)
  2. identify what the link between the two parts of the question is
  3. make a short plan of these links (which will form the basis of your answer)
  4. include as much information as you can to obtain full marks (see below)

The number of marks per question part is given in this form '[4 marks]'. It is essential that you give four different answers if a question is worth four marks. Sometimes you can gain an additional mark by giving the units in a calculation or stating specific data points, eg after twenty-four hours the pH of the milk at room temperature had decreased by 1.2.

Linking questions will start with command words such as 'describe' or 'explain'. Some command words are easy to understand such as:

  • 'calculate' or 'determine' for maths questions
  • 'choose' for multiple-choice questions
  • 'complete' to fill in a gap in a table or graph
  • 'define' to give the meaning of an important word
  • 'suggest' where you use your knowledge in an unfamiliar situation

The command words 'describe' and 'explain' can be confused. 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 that the biodiversity is lower on the school field. This is because...

Explain how and why questions often have the word 'because' in their answer. Describe questions don't.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Foundation


Describe the similarities and differences between photosynthesis and respiration. [6 marks]

Six from:

  • respiration: glucose + oxygen → carbon dioxide + water (+ energy) - [1] for reactants and [1] for products
  • photosynthesis: carbon dioxide + water → glucose + oxygen - [1] mark for reactants and [1] for products
  • respiration occurs in all living cells
  • photosynthesis only occurs in chlorophyll in chloroplasts
  • respiration occurs at all times, whereas photosynthesis only occurs in the light
  • respiration is exothermic (it releases energy)
  • photosynthesis is endothermic (it requires energy)


Sample question 2 - Foundation


Describe the similarities and differences between plant and animal cells. [6 marks]

Six from:

  • they are both eukaryotic so have a nucleus

They both possess:

  • cell membranes to control what enters and exits a cell
  • cytoplasm where reactions occur
  • ribosomes where proteins are made
  • mitochondria where respiration occurs

Plant cells additionally have:

  • chloroplasts where photosynthesis occurs
  • a permanent vacuole filled with sap
  • a cell wall made of cellulose for support


Sample question 3 - Higher


Describe how to prepare a stained slide of onion epidermal tissue. [6 marks]

  1. take an onion bulb and remove one of the leaves [1]
  2. peel a piece of inner epidermis from the leaf using forceps [1]
  3. trim the piece of epidermis and place in one drop of water on a microscope slide [1]
  4. lower a coverslip on top, taking care not to trap any air bubbles [1]
  5. place one drop of iodine solution next to the coverslip [1]
  6. draw the iodine solution under the slide by placing a piece of filter paper on the other side of the coverslip [1]