After the stomach breaks down food, intestinal absorptive cells take in nutrients through their “microvilli." These tiny finger-like structures increase the total surface area of the cell membranes, making it easier to absorb lots of nutrients.

Nerve cells (or neurons) string together like wires to carry electrical signals very quickly throughout the body, especially the brain. The messages they carry include telling muscles to move and sensing (sight, sound, touch, temperature, pain, etc.). Branches at the ends of nerve cells create complex networks of multiple neurons connecting to each other.

The muscles that move your fingers, arms, legs, and so on are each made of millions of skeletal muscle cells all bundled together. These long, thin fibers become shorter and thicker when they contract. Most cells have just one nucleus. Not these! They have many.

A red blood cell has no nucleus. This lack of nucleus gives it room to carry more oxygen from the lungs to other cells all over the body. Unlike most cells that stick together to form large structures, red blood cells must flow through blood vessels, so they are round and stay separate.

A macrophage is a kind of white blood cell that crawls around inside your body hunting for germs. When it finds some, the macrophage reaches out and grabs it with a gooey arm called a “pseudopod” (which means “fake limb”).

Bone cells deposit hard, calcium-rich material around themselves. Thin tunnels allow bone cells to stay connected so that they can receive signals, oxygen, and nutrition.

Block-shaped palisade cells are full of chloroplasts. Their tall shape allows them to capture more light and carbon dioxide for photosynthesis.

Because they are round and don’t pack as closely together as other plant cells, spongy leaf cells are surrounded by plenty of air space where gases move in and out.

The walls of guard cells are thin on the outside and thick on the inside. This structure helps them open and close holes that allow water vapor and gases in and out of leaves.

Phloem cells form long, tall tubes through which sugar and other food is sent back and forth around the plant. Their walls have hole-filled ends called sieve plates. They have little cytoplasm and no nucleus.

Found near the tips of roots, root hair cells stick out into the soil. Water enters them easily through their thin walls. Because roots are underground and in the dark, they have no chloroplasts.

Xylem is made up of tube-shaped cells that bring water in one direction: up to the leaves from the roots. As they die, the thick walls become thin, woody tubes.