Rohan says a cactus cannot make its own food, because it has no leaves

Why

Rohan is correct that leaves are where most plants make their food, and a cactus really does look leafless. But two things are going on. First, a cactus's sharp spines ARE its leaves — shrunk down to needles so the plant loses far less water in the desert. Second, the food-making job did not disappear; it moved. A cactus's thick stem is green because it is full of chlorophyll, the same substance that makes leaves green, and the stem carries out photosynthesis in the leaves' place. Test it: scratch the surface of a cactus stem and it is green underneath, just like the inside of a leaf — a plant part that colour is doing photosynthesis. His sister is right: a cactus's green stem makes its food while the spines are really reduced leaves — looking leafless is not the same as being unable to make food.