Starch, cellulose and plant fibresEdexcel International A Level Biology: Mind map

Exam questions on Starch, cellulose and plant fibres

1. A food technology student extracts two polysaccharides from plant material. Substance P is extracted from potato tuber cells, where the plant uses it as an energy store. Substance Q is extracted from the cell walls of flax stems, where it gives the stems their strength. Both substances are polymers of glucose.
   Explain two ways in which the structure of starch makes it suitable as an energy store in potato tuber cells.2 marks
2. Hemp stems contain bundles of long sclerenchyma fibres that are used to make rope. The wall of each fibre cell is made of cellulose microfibrils, and lignin is deposited in the wall during secondary thickening.
   Explain why sclerenchyma fibres have a high tensile strength.2 marks
3. A student compared the tensile strength of fibres from two plants, X and Y. A fibre sample was clamped at its upper end, masses were hung from its lower end, and more mass was added until the sample snapped. Sample X had a diameter of 0.60 mm and snapped at a mean mass of 2.5 kg. Sample Y had a diameter of 0.40 mm and snapped at a mean mass of 1.9 kg. Assume that each sample has a circular cross-section and use a gravitational field strength of 9.81 N kg⁻¹.
   Describe how the student should carry out this investigation so that the comparison between X and Y is valid and the results are reliable.3 marks