c) The set-up was maintained at 37^ because this temperature is optimal for the metabolic activities of the living cells in the unripe pawpaw, ensuring their cell membranes remain f

c) The set-up was maintained at $37^\circ\text{C}$ because this temperature is optimal for the metabolic activities of the living cells in the unripe pawpaw, ensuring their cell membranes remain functional for osmosis. It also increases the rate of diffusion of sugar and the rate of osmosis of water, allowing the experiment to proceed at a reasonable speed.