Nineteen Out of Twenty-Eight Think Plants Eat Soil
A Grade 10 class of 28 students, nine of them EAL learners, completes a six-item quiz on plant nutrition. On the key item, 19 students choose 'plants take in their food from the soil' and only 6 choose the correct option. The scheme of work allows one 45-minute lesson before the unit test. The laboratory has eight working microscopes, dropper bottles of 0.05 mol/dm3 iodine solution and onion bulbs, and the risk assessment must be updated. The head of department wants evidence that the lesson changed students' thinking rather than that the content was simply covered.
1. Use the item data to plan the 45-minute lesson and justify each choice against what the misconception actually is.
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The distractor is not random guessing - 19 of 28 chose it, which suggests a stable alternative theory rather than a gap in recall: students think the soil supplies the plant's substance. Re-teaching the word equation will not dislodge it, so the lesson should create a discrepancy the students must resolve.
Plan: 5 minutes to collect predictions with a show-me board (which gains more mass, a plant in soil or one in distilled water with minerals?); 10 minutes on a short dataset - mass of soil before and after a plant grows, and mass of the plant - which shows the soil loses almost nothing; 15 minutes of guided reasoning in pairs with a claim–evidence–reasoning frame to explain where the carbon comes from; 10 minutes of independent writing of a two-sentence explanation; 5 minutes to re-poll. Use the pre-test item verbatim only as a comparison; the post-item must use a new context so recall of the lesson wording cannot masquerade as understanding.
2. The practical involves 28 students, 8 microscopes and 0.05 mol/dm3 iodine. Identify the resourcing and safety issues and say how you would organise the session.
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Eight microscopes do not mean eight workable stations: with 28 students the practical can run as seven groups of four, each with one microscope, which leaves one spare. So the real constraint is time and turn-taking, not equipment. Give each group a timed 12-minute microscope slot with named roles (one focuses, one holds the slide, one records, one reports) and rotate roles so every student focuses at least once; the remaining time is used for drawing and the mass data task at desks.
Iodine: 0.05 mol/dm3 is a stain and irritant, so the risk assessment must cover eye protection, dropper bottles rather than open pots, no eating or drinking, immediate rinsing of skin and eyes with water, and safe disposal. Check the students' health records for skin sensitivity, brief them before the bulbs are cut, and have a spill tray and paper towel ready. Cutting onion releases irritant vapour, so ventilate the room and limit cutting to a small number of bulbs.
3. How would you support the EAL learners and how would you gather evidence that the misconception, not just the vocabulary, has shifted?
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EAL support must attach to the reasoning, not just the words: pre-teach four or five terms with pictures and a bilingual glossary (soil, mineral, photosynthesis, glucose, mass), display sentence frames such as 'The plant's mass comes from ___ because ___', allow paired talk in first language before English writing, and model the explanation aloud. Otherwise a student may learn 'glucose' and still believe soil is the food.
Evidence: give the same pre-test item and a parallel post-test item set in a new context, and mark both against a rubric with three levels - names the source of carbon, links it to photosynthesis, and explains why soil mass does not account for plant mass. Look for change at whole-class level (from 6 of 28 to a target such as 20 of 28) and inspect the students who moved, using their written explanations as the audit trail. Ask two or three of the previously incorrect students to explain their new answer orally, and keep the scripts for the head of department.