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In 1664, English scientist Robert Hooke viewed a thin slice of cork through an early microscope. To him, it looked like it was made of many tiny rectangular chambers.
He called them cells, from the Latin word cella. That means “small room.”
At first, scientists couldn’t see much in a cell. They thought it was just filled with jelly. They called that jelly protoplasm. But microscopes got better, and that view changed. We know now that each cell is a complex part of life.
Vacuole
Storage area for fat and other substances
DNA
or deoxyribonucleic acid (dee-ox-see-RYE-bo-new-CLAY-ic acid), contains coded information that describes every inherited trait. Traits are things like eye and hair color.
Nucleus
Cell’s control center, or brain
Ribosome (RI-buh-sohm)
Protein-producing factories: Proteins produce chemical messages that tell a cell what to do.
Golgi (GOL-jee)
Stores and carries newly made proteins until they can be released through the cell membrane
Lysosome
Where digestion of cell nutrients takes place
Cell membrane
Made up of a double layer of fatty material called lipids. It lets things pass into and out of a cell. They move through thousands of tiny openings on its surface. For example, it lets food pass into the cell. It also lets waste leave the cell.
Mitochondrion (mite-uh-CON-dree-on)
Breaks down substances to produce energy for the cell to use
Endoplasmic reticulum (en-duh-PLAZ-mik rih-TIH-cue-lum)
Smooth and rough tubes that move and store materials made by the cell
Cytoplasm
Jellylike fluid between cell membrane and nucleus. Most of the cell’s innards, or organelles, are found here. Organelles means “little organs.”
Ingredients of Cells
Water
Water makes up about 90 percent of a cell’s weight. Here’s what’s in the other 10 percent:
◀ Hair follicles and nails are made of proteins. About half the stuff in your body is made of protein. Every person has about 500,000 different proteins at work at any time. Most are like switches, turning chemical reactions on and off. Proteins are made by organelles. Organelles also perform other jobs. They turn food into energy and move molecules around.
Plant cells are very different from animal cells. Their outer covering is stiff, not fatty. Most plant cells also contain organelles called chloroplasts. Chloroplasts contain chlorophyll, a pigment that colors the plant green. Using light energy from the Sun, chlorophyll combines carbon dioxide and water to make sugar. This process is called photosynthesis. It gives plants energy. Plants in turn supply energy for all other forms of life. ▶
Check It Out!
How big is an average cell?
An average animal cell is about 1/1000 of an inch in diameter. The average plant cell is about three times larger than that. The average bacterial cell is about ten times smaller than that.
