CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 17(b)

Hydrotropism: the directional growth movement of a part of a plant in response to water. Roots grow towards water (positive hydrotropism). Experiment: (i) Soak a few seeds (such as gram or pea) in water overnight. (ii) Place a layer of moist cotton in a petri dish that has small holes (perforations) in its base. (iii) Put the soaked seeds on the moist cotton and place the dish on the mouth of an empty, dry beaker. Keep the cotton moist and leave the set-up for a few days. (iv) Observation: the roots of the germinating seeds first grow downwards and pass out through the holes into the dry air of the beaker. (v) After some time the roots bend and grow back upwards, towards the moist base of the petri dish. Conclusion: the roots grow towards the moisture, even against the pull of gravity; this demonstrates hydrotropism. (Any other relevant experiment earns credit, for example seedlings grown in dry soil in a trough with a porous pot of water buried on one side: after a few days their roots are found bent towards the pot.)