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In 1664, English scientist Robert Hooke viewed a thin slice of cork through an early microscope. Cork looked to him as if it were constructed of dozens of tiny rectangular compartments.
He called them cells, from the Latin word cella, meaning “small room.”
At first, scientists couldn’t see much within a cell and thought it was just filled with jelly. They called that jelly protoplasm. But improved microscopes slowly changed that view. We know now that each cell is really 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 cleverly coded information that passes on every inherited characteristic or trait.
Nucleus
Cell’s control center, or brain
Ribosome (RI-buh-sohm)
Protein-producing factories: Proteins produce chemical messages that run a cell.
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 some materials pass into and out of a cell through thousands of tiny openings on its surface. For example, it lets food pass into the cell and waste pass out of the cell.
Mitochondrion (mite-uh-CON-dree-on)
Produces energy for the cell to use by breaking down substance
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 working at any time. Most serve as switches that turn chemical reactions on and off when needed. Proteins are made by organelles. Organelles perform other jobs as well, such as turning food into energy and moving molecules around.
Plant cells differ greatly from animal cells. They have a stiff outer covering instead of a fatty one. Most plant cells also contain organelles called chloroplasts. Within each chloroplast, the green pigment (color) chlorophyll uses the Sun’s light energy to combine carbon dioxide and water to make sugar. This process—called photosynthesis—supplies plants with 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. But the average plant cell is about three times larger than an animal cell, and the average bacterial cell is about ten times smaller.
