WAEC Biology 2011 Theory — Question 2

Model answer

Demonstration of the effect of gravity on the roots of plants using a potted plant and Klinostat: Seeds of cowpea are sown in small pots (one seed per pot). After the appearance of the first foliage leaves, the pots are placed in the dark with the seedlings in a horizontal position. A klinostat with a seedling is also kept working in a horizontal position to serve as a control. The whole set-up is left for about 24 hours. After 24 hours, the shoot of the seedling in the pot curves and grows vertically upwards (away from gravity). If the soil is carefully washed off, it will be observed that the root has curved downwards (towards gravity). The shoot of the working klinostat remains in a horizontal position and does not curve.