Chloroplasts, pigments and limiting factorsEdexcel International A Level Biology: Flashcards

Exam questions on Chloroplasts, pigments and limiting factors

1. A student extracts pigments from spinach leaves using propanone and applies a concentrated spot to a pencil line near the bottom of a strip of chromatography paper. The paper is placed in a solvent, which runs 9.0 cm from the pencil line to the solvent front. Four pigment spots separate. Their centres are 8.5 cm (carotene), 7.2 cm (xanthophyll), 6.3 cm (chlorophyll a) and 5.4 cm (chlorophyll b) from the pencil line.
   Explain why the pencil line must be above the level of the solvent in the container, and why the position of the solvent front must be marked as soon as the paper is removed.2 marks
2. A plant physiologist measures two spectra for a leaf. The absorption spectrum of extracted chlorophyll a shows strong absorption of blue light (about 430 nm) and red light (about 660 nm) and very little absorption of green light (about 550 nm). The action spectrum for photosynthesis in the leaf has peaks at similar wavelengths, but the rate of photosynthesis in green light is higher than the chlorophyll a absorption alone would predict.
   Use the information to explain why a plant lit only with green light photosynthesises slowly but not at zero rate.2 marks
3. An electron micrograph of a palisade mesophyll cell shows several chloroplasts. Each chloroplast is surrounded by a double membrane and contains stacks of flattened thylakoids joined by membranes called lamellae, a fluid stroma, small starch grains, and ribosomes and a loop of DNA.
   Describe how the structure of a chloroplast is adapted to its role in photosynthesis.3 marks