Seedlings grown in the light and in the dark are a favourite 0610 practical context: measuring with a ruler, spotting the odd one out, recording what you can see and explaining it with the biology of light. By hand, lift the cardboard box off tray D, then carry the ruler to each of the ten seedlings and read the length of its shoot from the soil surface to the tip, to the nearest millimetre. Find the anomaly, calculate the means, record three observable differences, plot both trays’ daily means on one grid and calculate a growth rate. Every attempt grows a different set of seedlings. Allow about 30 minutes.
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A heading with quantity / unit, every length read to the nearest millimetre with the ruler standing beside that seedling (within 1 mm), the anomalous seedling identified by comparing it with the rest of its tray, the mean for tray L from all five readings and the mean for tray D with the anomaly left out, and three differences that can actually be seen: colour, stem length and thickness, leaf size. Examiner reports on 0610 practical papers stress that observations must be visible features, not explanations.
Time on the x-axis and mean length on the y-axis with units, a y-scale that fits the tallest value and uses more than half the grid, all sixteen points within half a small square and in the right series, and a growth rate from Table 1.2 as change in length divided by time, to 2 significant figures.
Dark-grown shoots are longer because the seedling spends its seed store on rapid elongation towards light; they are yellow because chlorophyll is made only in light; only the green seedlings can photosynthesise and keep growing once the store is used up.
Two control variables (temperature, water, seed type and planting depth), a real source of error in measuring (where the soil surface and the tip are), an improvement that adds reliability (more seedlings, every shoot measured the same way), and why several seedlings are grown in each tray.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.