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There are a lot of different
kinds of cells. Different cells can have different purposes, different
jobs, different shapes, and different characteristics. For example,
plant cells have a cell wall and animal cells don't.
Cells come in different shapes. They can be shaped like snowflakes, balls, cubes, saucers, rectangles, boxes, coils, or blobs of jelly. Animals cells are usually spherical or flat-sided. The amoeba, a one-celled organism that lives in water, has no regular shape. It is a jelly-like cell that changes shape to move around. Some muscle cells are long, thin, and pointed on both sides. Some nerve cells, with their long branches, look like trees.
The sizes of cells can be very different. Most cells are 1/1,000 of an inch (0.0025 centimeter) in diameter. Around 500 average sized cells could fit on a period at the end of a sentence. The bacterial cell is one of the smallest of all the cells, and the yolk of a ostrich egg is the biggest of all cells.
If you want to see actual pictures of all different kinds of cells, you can visit the Cells Alive picture gallery.
The reason plants and animals come in different sizes depends on their cells. The sizes of the cells aren't what matters. What matters is the total number of cells that make up the plant or animal. For example, an elephant is much bigger than a mouse because it is make of trillions more cells.