Question

Why vacuoles are bigger in older cells than in younger cells?

Answer 1

Vacuoles in young plant cells are very small, but as the cells grow, vacuoles grow bigger, getting to join until they form one big vacuole that occupies almost the entire cytoplasm.
Plants need it to store \[H_{2}O\], salt and wastes, so they can use water in times of dryness to survive.