Fig. 10.1 is an electron micrograph of a chloroplast. Two further chloroplasts, A and B, were measured from other micrographs. Fig. 10.1 Table 10.1 Chloropl...

(a) Complete Table 10.1 [3]

Magnification \(=\dfrac{\text{image length}}{\text{actual length}}\), with both lengths in the same unit. The image lengths are in mm and the actual lengths in \(\mu m\), so first convert: \(1\text{ mm}=1000\,\mu m\).

Worked example, chloroplast A: image length \(=30\text{ mm}=30\,000\,\mu m\), so magnification \(=\dfrac{30\,000}{5}=\times 6000\) [1 working, 1 answer]. Chloroplast B: \(20\text{ mm}=20\,000\,\mu m\), magnification \(=\dfrac{20\,000}{4}=\times 5000\) [1].

(b) How many chloroplasts help a palisade cell [3]

The palisade mesophyll is the main photosynthesising layer of the leaf. Having many chloroplasts lets the cell absorb more light energy [1]; this allows a higher rate of photosynthesis [1]; so more glucose / food is made [1]. The tall, closely packed palisade cells sit just under the upper surface where light is brightest, so the extra chloroplasts are put to full use.

(c) Why the stacked membranes need an electron microscope [3]

The internal membranes are extremely thin, far smaller than the wavelength of light can resolve [1]. An electron microscope has a much higher resolution (resolving power) [1], and this is possible because electrons have a much shorter wavelength than light [1]. Resolution is the ability to tell two very close structures apart; the shorter the wavelength used, the smaller the detail that can be separated, which is why the light microscope shows only a blur where the electron microscope shows distinct stacked membranes.