Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves.
Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Human cells contain the following major parts, listed in alphabetical order:
- Cytoplasm (illustration)
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The cytoplasm is fluid inside the cell that surrounds the organelles.
- Endoplasmic reticulum (ER) (illustration)
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This organelle helps process molecules created by the cell and transport them to their specific destinations either inside or outside the cell.
- Golgi apparatus (illustration)
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The golgi apparatus packages molecules processed by the endoplasmic reticulum to be transported out of the cell.
- Lysosomes and peroxisomes (illustration)
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These organelles are the recycling center of the cell. They digest foreign bacteria that invade the cell, rid the cell of toxic substances, and recycle worn-out cell components.
- Mitochondria (illustration)
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Mitochondria are complex organelles that convert energy from food into a form that the cell can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves.
- Nucleus (illustration)
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The nucleus serves as the cell’s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.
- Plasma membrane (illustration)
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The plasma membrane is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave the cell.
- Ribosomes (illustration)
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Ribosomes are organelles that process the cell’s genetic instructions to create proteins. These organelles can float freely in the cytoplasm or be connected to the endoplasmic reticulum (see above).
For more information about cells:
The NCBI Science Primer
offers additional information about the structure and function of cells under the headings “What is a Cell?” and “Cell Structures: The Basics.”
Next Topic: What is DNA?
