One of adaptation of Cactus opuntia to conserve water is the reduction of

Analyze the question: It asks how the cactus (Opuntia) conserves water. The question wants the structure that is reduced as an adaptation to cut down water loss.

Explain the concept: Plants lose water mainly through transpiration, and most of it happens through the stomata on leaves. Xerophytes (desert plants) like cactus have developed features to reduce this loss:

• Leaves are reduced to spines, which cuts down the surface area for transpiration.
• The stem is fleshy and green, so it stores water and carries out photosynthesis.
• The stem has a thick, waxy cuticle.
• Roots are shallow and widespread, or very deep, to absorb water.

Solution:

• A. Internodes: these are not the main water-conservation adaptation.
• B. Stem to leaves: this is the wrong way round. The stem is not reduced to leaves. It is the leaves that are reduced, and the stem takes over photosynthesis.
• C. Leaves to spine: correct. The leaves are reduced to spines, so there is very little surface area for transpiration. The spines also protect the plant from herbivores.
• D. Flower size: this has nothing to do with water conservation.

Tip: Remember "cactus = spines for leaves, stem for food and water". If a question asks about xerophytes, look for the option that reduces leaf surface area, thickens the cuticle, or stores water.