The thick and waxy stem in cactus plant helps in:

1. Storing water

2. Absorbing water

3. Retaining water

4. Reducing loss of water

The correct option is C

Retaining water

The correct option is C:

Explanation of the correct option:

1. Desert plants like cactus have many adaptations to survive in the dry and hot climate of deserts.
2. Few of the adaptations cactus plant have are: fleshy stems, presence of spines, thick waxy layer etc.
3. Waxy stem means a wax-like coating on the stem which is present naturally.
4. The thick and waxy stem present in cactus plant help in retention of water inside the plant body.
5. As the climate is very dry and there is scanty rainfall in the deserts, it is necessary for the plant to conserve maximum water in their body.
6. The thick and waxy stem help them in doing so.

Explanation of the incorrect option:

Option A:

1. To store water the adaptation will be fleshy stem of cactus plant.

Option B:

1. For absorbing water roots are required.

Option D:

1. To reduce the loss of water leaves of cactus plant are modified into spines.

Final answer: The thick and waxy stem in cactus plant helps in retaining water.