An unfamiliar diagram uses the same parts you already know. The task is to find those parts and say what the diagram shows, not to recall a picture.
This lesson belongs to transport in humans and animals. It works best after tracing circulation through the heart.
What is the reading method?
Follow the same five steps every time. The order stops you from jumping to a guess.
- Read the question first, and underline the command word: state, compare or explain.
- Identify what type of diagram it is: heart, vessel or flow.
- Name each labelled part using position, wall thickness and direction.
- Follow the arrows to see what moves where.
- Write one sentence per mark, each with a structure and its effect.
Worked example: a diagram described in words
A diagram shows two vessels side by side. Vessel M has a thick wall and a narrow lumen, and a pressure gauge reads high. Vessel N has a thin wall and valves, and the gauge reads low. A pointer between them shows a tiny vessel with a one-cell wall labelled K.
Question: explain how blood moves from M to N.
- M is an artery and N is a vein, from wall thickness and valves.
- K is a capillary, which joins them.
- Blood leaves the heart through M at high pressure, and passes through K where materials are exchanged.
- Pressure drops across K, so blood in N moves slowly, and valves stop it flowing backwards.
Answer: “Blood flows from artery M to vein N through capillary K. Pressure falls along the route, and valves in N keep the blood moving in one direction.”
Explaining without diagnosing
A diagram that shows a narrow vessel is asking about flow, not about a disease. Write what the diagram shows and its effect on the flow, nothing more.
| Answer style | Example | Suitable for SPM? |
|---|---|---|
| Describe | The vessel lumen is narrower, so less blood passes per second | Yes |
| Explain | A narrow lumen raises resistance, so pressure upstream is higher | Yes |
| Diagnose | The patient has a disease called … | No, it is outside the question |
Check yourself
A diagram shows a heart with the wall of chamber P drawn much thicker than chamber Q. Both chambers have arrows leaving them, P to the body and Q to the lungs. Identify P and Q and explain the difference in wall thickness.
Answer
P is the left ventricle and Q is the right ventricle. P pumps blood to the whole body, which needs higher pressure, so its wall is thicker. Q pumps only to the lungs, a shorter distance, so its wall is thinner.
What to study next
Test the method on new questions in the transport in humans and animals practice set. The biological data interpretation trainer gives more diagrams and tables.
For a teacher who supplies fresh diagrams and coaches the method, see online one-to-one Biology tuition.