Which of the following best describes a response in which the roots show a positive tropic response and the shoots show a negative tropic response? 1 thigmotropism 2 hydrotropism 3 gravitropism 4 phototropism

3. gravitropism

The movement of plants in response to stimuli is called as tropism. Plants respond to different stimuli like light (phototropism), water present in the soil (hydrotropism), gravity (gravitropism) and touch (thigmotropism).

Gravitropism refers the growth and movement of plant parts with respect to the force of gravity exerted by earth. The roots shows positive gravitational tropism because they are growing towards earth gravity. The shoots or stems shows negative gravitational tropism because they are moving or growing against the gravity.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.