A correct keyword list names the right ideas but does not say which one causes which. “Explain” questions need the connections. This lesson turns the habit of listing into the habit of linking, and it uses everything from the earlier lessons in biological explanations and diagrams.
It appears in every topic that has a process with steps: exercise and breathing, water loss, enzyme action, eutrophication and more.
How do you repair a list?
Four steps.
- Find the starting change. What happens first? Write it as the first sentence.
- Put the keywords in time order. Ask what each one causes.
- Join each pair with a causal word: because, so, which leads to, therefore.
- Check the end. The last sentence must answer the question that was asked.
If you cannot join two keywords, a step is missing between them. Find it.
Worked example
Question: Explain why breathing rate increases during exercise.
Student’s keyword list: muscles, respiration, carbon dioxide, oxygen, brain, breathing rate.
All six terms are correct. No marks are given for the connections, because there are none.
Step 1, starting change: during exercise, muscle cells respire faster to release more energy.
Step 2, consequence: faster respiration uses more oxygen and produces more carbon dioxide.
Step 3, detection: the carbon dioxide concentration in the blood rises, and the brain detects this.
Step 4, response: the brain sends signals that increase the breathing rate.
Step 5, end: this brings in more oxygen and removes the extra carbon dioxide faster, so the muscles can keep respiring.
Repaired answer: “During exercise muscles respire faster, which uses more oxygen and produces more carbon dioxide. The rise in blood carbon dioxide is detected by the brain, so breathing rate increases. This supplies more oxygen and removes the extra carbon dioxide.”
The mistake to watch for
A common slip is to join the keywords with “and”, which adds ideas but does not cause anything.
Mistaken answer: “Muscles need oxygen and produce carbon dioxide and the brain and breathing rate increase.”
“And” joins the terms without saying that one thing leads to the next.
The correction swaps each “and” for a cause word and asks “does this really follow?”. “The brain detects it, so breathing rate increases” does follow. “Muscles and the brain” does not say anything.
Check yourself
1. Turn this list into a chain for “Explain why a plant wilts on a hot, dry day”: stomata, evaporation, water loss, roots, turgor, cells.
Show answer
“In hot, dry air, water evaporates faster from the leaf and leaves through the stomata. The roots cannot replace the water as fast as it is lost, so the cells lose water and lose turgor. The leaf loses its firmness and the plant wilts.”
2. Which link is missing? “More carbon dioxide in the blood, so breathing rate increases.”
Show answer
The detection step. The brain detects the higher carbon dioxide concentration, and then sends signals to increase the breathing rate.
3. Underline the causal word in: “The membrane is folded, which increases surface area, so more molecules cross.” How many are there?
Show answer
Two: which and so. Each joins a feature to a consequence: folded membrane to larger area, larger area to more molecules crossing.
Where this leads next
Try the mixed practice set, which asks you to repair, label and explain in one go. If answers keep losing the same link, record it in the mistake log and retest in a week.
A chain is quick to build when a teacher asks “and then what happens?” after each sentence you write. That is the kind of questioning that online one-to-one Biology tuition can give.