Biology Criterion A rewards explanation: linking a structure to its function, a process to its purpose, and a change in conditions to its effect on a living system.
You use correct terms and explain why something happens, not just that it happens.
You pick the right idea and use it on a situation you have not seen before.
You weigh data, claims or sources and reach a judgement you can support.
A little of the criterion is addressed. Ideas are basic, partly missing, or not linked to the task.
The main points are there but thin. Some explanations are correct; links to the task or evidence are incomplete.
Mostly accurate, well explained and consistently tied to the task, with only small gaps.
Detailed, precise and justified throughout, with ideas connected and applied to new situations or evidence.
A plain-language guide only. Your teacher marks against the official IB level descriptors.
Explain why a potato cylinder gains mass when placed in distilled water.
Because water goes into it.
The cells of the potato contain a solution that is more concentrated than distilled water. Water moves by osmosis, from the region of higher water concentration (outside) to lower (inside), across the partially permeable cell membrane. The cells take in water and the potato cylinder gains mass.
Criterion A is Knowing and understanding. It is marked out of 8 across 3 strands (A.i, A.ii, A.iii). Biology Criterion A rewards explanation: linking a structure to its function, a process to its purpose, and a change in conditions to its effect on a living system.
Link structure to function, such as thin walls and short diffusion distance in alveoli. Use terms precisely: diffusion, osmosis and active transport describe different processes. In data questions, quote values from the graph or table when you explain the trend.
Stating a function with no explanation of how the structure achieves it. Describing osmosis in terms of solutes moving rather than water. Using everyday words such as eats food instead of the process involved.
Written by CritABCD for study and revision, in our own words. The official MYP Biology guide and assessment criteria are published by the International Baccalaureate. Official IB guide ↗