Question 1
Multiple choiceMedium1 markBand X from a leaf extract is yellow-green. The solvent front travelled 8.0 cm and X travelled 3.6 cm. Reference chromatographic values and the absorption spectrum of X are shown.
| Reference pigment | Appearance | Rf |
|---|---|---|
| Chlorophyll a | Blue-green | 0.60 |
| Chlorophyll b | Yellow-green | 0.45 |
| Xanthophyll | Yellow | 0.70 |
| Carotene | Orange | 0.95 |
| Wavelength / nm (colour) | 450 (blue) | 550 (green) | 680 (red) |
|---|---|---|---|
| Relative absorption by X | 0.85 | 0.10 | 0.70 |
Which conclusion about X is supported by the results?
Show answer and explanation
Answer: B. The Rf value is distance travelled by the pigment divided by distance travelled by the solvent: 3.6/8.0 = 0.45. This matches chlorophyll b and is consistent with the yellow-green appearance. At 550 nm (green), X has its lowest relative absorption, so fewer electrons in X are excited and less light energy is available to support conversion to chemical energy.
A: reverses the spectrum reading; green light has the lowest, not the highest, absorption. C: reads the low green absorption correctly but assigns chlorophyll a, whose reference Rf is 0.60. D: mislabels 550 nm as red; the table identifies this wavelength as green.
Remember: wavelengths absorbed by a pigment can excite its electrons and contribute to photosynthesis.