Cell Size
Cell Size is how big or small the tiny building blocks are that make up every living thing.
Think of it this way
A big bowl holds a few large oranges with not much room left over. A small bowl the same depth holds dozens of grapes instead. Cells in the body are like those fruits. Smaller cells pack tight in large numbers, while bigger cells are fewer and fill more space each.
Explaining cell size by grade level
Every plant and animal is made of tiny parts called cells. You need a strong lens to see most of them. A big animal like a whale has more cells, not bigger ones. Most cells are about the same small size, no matter how large the whole creature is.