The symptom
You know the topic. You write a full paragraph. It comes back with one mark out of four, and the mark scheme seems to ask for the same thing in different words.
Usually it is not the same thing. Your answer said what happens. The mark scheme wanted the reasons it happens, written as a chain of links. Mark schemes usually credit the links separately, so a missing link usually means a missing mark.
The 0610 syllabus is clear on the difference. Describe means say what something is like or what happens. Explain means give the reasons: why or how, backed up with evidence.
Six reasons explain answers lose marks
Most weak explain answers have one or more of these faults. Check your last marked paper against the list.
The fix: build a chain, one link per mark
Use these steps on every question that starts with explain. They take less than a minute once they are a habit.
-
Find what you are explaining
Underline the command word and the thing to be explained. If there is data, the thing to explain is the pattern in the data.
-
Count the marks
Plan one separate idea for each mark. If you can think of one more, add it as a spare.
Tip. Two short sentences with two ideas beat one long sentence with one. -
Build the chain
Start with the cause, then say what happens at the level of molecules or cells, then give the result. That middle step is the one most often missing.
-
Join the links
Use “so”, “because” and “which means” between ideas. A list of true facts with no links does not show the relationship.
-
Use the syllabus terms
Swap every everyday word for the term in your notes: active site, denatured, water potential, partially permeable membrane.
-
Tie it to the question
Quote a value from the data, or name the organism, organ or experiment the question gives. Then delete any line that only repeats the question.
Before and after: the same answer, fixed
Here is an original Extended question on enzymes, first with a typical weak answer, then rebuilt as a chain.
This answer describes the pattern correctly, but it gives no reason for it. “Works better” is not a reason. “Dies” is wrong: enzymes are proteins, not living things, so they are denatured. Against the four mark points below, it earns little or nothing.
A student timed how long the enzyme amylase took to digest starch at five temperatures. The results are shown below. Explain these results.
Look at what changed. Each sentence leads to the next with “so”, and each one gives a reason. The terms come straight from the syllabus: kinetic energy, effective collisions, active site, denatured. And the answer uses the data: it quotes the times at 20 °C, 40 °C and 50 °C, and the result at 60 °C.
Check yourself
Use the six steps on this question. It is worth three marks, so plan three linked ideas before you write.
Strips of potato are left in pure water for 30 minutes. They become longer and firmer. Explain why.
Show a full-mark chain
So water moves into the cells by osmosis, from a higher to a lower water potential, through the partially permeable cell membrane.
The vacuole swells and pushes the cell membrane against the cell wall, so the cells become turgid. The strip is longer and firmer.
Read it from the end back: each sentence is answered by the one before it.