A student estimated the surface area of a fresh leaf by placing it flat on a grid of squares, each square being 1 cm by 1 cm. She drew around the leaf, then...
Question 1 Report
A student estimated the surface area of a fresh leaf by placing it flat on a grid of squares, each square being 1 cm by 1 cm. She drew around the leaf, then counted the squares it covered. Fig. 4.1 shows the leaf on the grid with the midrib marked. She counted 24 squares that were completely covered and 10 squares that were at least half covered.
(a) Measure the length of the leaf midrib in Fig. 4.1, in cm, using the grid squares [1]
(b) State the rule the student should use to decide whether to count a partly covered square [1]
(c) Estimate the total area of the leaf, in square centimetres. Show your working [2]
(d) Convert this area to square millimetres [1]
(e) Suggest why the grid method only gives an estimate of the area [2]
(f) Name the type of venation shown and the plant group it indicates [2]
Answer Details
This question tests the grid method for leaf area, unit conversion, its limitations, and leaf venation.
(a) Counting whole squares along the midrib, its length is about 6 cm (accept 5 to 7) [1].
(b) The rule is to count a partly covered square only if half or more of it is covered by the leaf [1].
(c) Add the fully covered squares to the squares at least half covered: \[24 + 10 = 34\ \text{cm}^2\] Working [1], area 34 cm² [1]. [2]
(d) Convert cm² to mm² by multiplying by 100 (since \(1\ \text{cm}^2 = 100\ \text{mm}^2\)): \[34\times 100 = 3400\ \text{mm}^2\] so the area is 3400 mm² [1].
(e) The grid gives only an estimate because the curved leaf edge does not follow the square boundaries [1], so counting part-squares is only approximate [1]. [2]
(f) The leaf shows net / reticulate venation [1], which indicates a dicotyledon (dicot) [1]. [2]
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