Red Blood Cells
Red blood cells are flat and shaped like a disk. They carry oxygen around the body and are shaped that way so that gases can go in between them. They flow through blood veins and are part of the cardiovascular system.
White Blood Cells
White blood cells are round and can change their shape. They function like that because they need to envelop the germs that come into the body. They are part of the immune system.
Nerve cells can grow up to a meter long. They have an irregular shape that has tendrils so that the brain can communicate with the rest of the body. They are part of the nervous system.
Skin cells are rectangular, like bricks, to keep bacteria and germs out and moisture in. They are part of the skin system.
Muscle cells are long and stretchy so that you can move around without your arms breaking. Muscle cells are part of the muscular system.
Bone cells crisscross each other to make strong structures to support your body. They are part of the skeletal system.