You have probably seen the diagram: a round blob with a dark circle in the middle, a few bean shapes, some folded ribbons, and a dozen labels pointing in every direction. Maybe it was on a worksheet, maybe on a test review, maybe on a poster. The parts of the cell look like a lot to memorize, but there are fewer names than the diagram suggests, and each one has a plain job description. This guide walks through them in order, from the outside in.

In Google Trends data for the US over the past 7 days, related searches for the seed term "parts of a cell" were led by "parts of the cell" with a top score of 100, followed by "what is a cell" (62), "what are the parts of a cell" (52), "cell membrane" (24), "parts of a cell membrane" (24), "animal cell" (19), "nucleus" (17), "organelles" (12), "parts of a human cell" (10), and "mitochondria" (10). These top scores are relative interest, scaled so the most popular term in the set equals 100; they are not search counts. None of these terms was listed as rising, which would mean growth compared with the prior period, and none was marked "Breakout," the label for very large growth. The pattern is familiar: people start with the definition, then look up the names one by one.

What is a cell?

Start with the definition. OpenStax Biology 2e (section 4.1, "Studying Cells") puts it simply: a cell is the smallest unit of a living thing. The National Human Genome Research Institute (NHGRI) glossary calls a cell the basic building block of living things, and adds an estimate that an adult human body contains between 10 and 100 trillion cells.

The word itself has a history. Per OpenStax section 4.1, Robert Hooke coined the term "cell" in his 1665 publication Micrographia, for the box-like structures he saw when he looked at cork through a lens. Antony van Leeuwenhoek watched single-celled organisms move and called them "animalcules." The idea that ties it together is cell theory, which OpenStax credits to botanist Matthias Schleiden and zoologist Theodor Schwann: one or more cells make up all living things, the cell is the basic unit of life, and new cells arise from existing cells.

Cells do not stay solo in a body. Groups of similar cells form tissues, and anatomy books spend whole chapters naming those tissue types. If you want the next level up, our guide to the types of connective tissue picks up where this one stops.

The parts of the cell: a three-zone map

The easiest way to read any cell diagram is to sort every label into one of three zones:

• The boundary: the cell membrane, which wraps the whole cell.
• The interior: the cytoplasm, which holds the organelles in a fluid called cytosol.
• The control center: the nucleus, which OpenStax Anatomy and Physiology 2e (section 3.3) calls the largest and most prominent of a cell's organelles.

The NHGRI glossary sorts all cells into two groups, eukaryotes and prokaryotes. A eukaryote has a nucleus and membrane-bound organelles; a prokaryote does not. Plants and animals are made of eukaryotic cells, so everything below is eukaryotic vocabulary.

The cell membrane and its parts

The cell membrane, also called the plasma membrane, is the outer edge. The NHGRI glossary says it is found in all cells, separates the interior of the cell from the outside environment, consists of a lipid bilayer that is semipermeable, and regulates the transport of materials entering and exiting the cell.

If you searched "parts of a cell membrane," here is the list OpenStax Anatomy and Physiology 2e gives in section 3.1, "The Cell Membrane":

• Phospholipids: the membrane is built mostly from back-to-back phospholipids. Each has a head that OpenStax describes as polar and hydrophilic ("water loving") and lipid tails that are nonpolar and hydrophobic ("water fearing"). The heads face the water on both sides; the tails tuck into the middle. That two-layer arrangement is the bilayer.
• Integral proteins: proteins embedded in the membrane.
• Peripheral proteins: proteins typically found on the inner or outer surface of the bilayer.
• Glycoproteins: proteins with carbohydrate molecules attached.
• Glycocalyx: what OpenStax calls a fuzzy-appearing coating around the cell, formed by those attached carbohydrates.

Organelles in the cytoplasm

OpenStax section 3.2, "The Cytoplasm and Cellular Organelles," defines the cytoplasm as the organelles and cytosol taken together, and describes cytosol as the jelly-like substance within the cell. The NHGRI glossary defines an organelle as a subcellular structure with one or more specific jobs to perform in the cell, much like an organ does in the body. Here are the organelles most diagrams label, with the textbook job description for each.

Mitochondria. OpenStax describes a mitochondrion as a membranous, bean-shaped organelle and calls it the "energy transformer" of the cell, with an outer and an inner lipid bilayer membrane. Per OpenStax, mitochondria convert energy stored in nutrient molecules into adenosine triphosphate (ATP). The NHGRI glossary adds a detail many diagrams skip: mitochondria contain their own small chromosomes.

Ribosomes. OpenStax calls the ribosome the site of protein synthesis. The NHGRI glossary says it is made of both RNA and protein and reads the messenger RNA (mRNA) sequence to build a string of amino acids. OpenStax Biology 2e (section 4.3) notes that ribosomes can float freely in the cytoplasm or sit attached to the endoplasmic reticulum.

Endoplasmic reticulum (ER). OpenStax describes the ER as a system of channels continuous with the nuclear membrane. It comes in two versions. Rough ER gets its name because its membrane is dotted with ribosomes. Smooth ER lacks them.

Golgi apparatus. Per OpenStax, the Golgi apparatus is responsible for sorting, modifying, and shipping off the products that come from the rough ER. Think of it as the packing room downstream of the ER.

Lysosomes. OpenStax defines a lysosome as an organelle containing enzymes that break down and digest unneeded cellular components.

Peroxisomes. Like lysosomes, OpenStax says, a peroxisome is a membrane-bound organelle that contains mostly enzymes.

Cytoskeleton. Not a single organelle but a framework. OpenStax describes it as a group of fibrous proteins that give the cell its structure, built from three filament types: microfilaments (the thinnest), intermediate filaments, and microtubules (made of a protein called tubulin).

The nucleus, up close

The NHGRI glossary defines the nucleus as the membrane-enclosed organelle within a cell that contains the chromosomes. OpenStax section 3.3 names its parts:

• Nuclear envelope: two adjacent lipid bilayers with a thin fluid space between them.
• Nuclear pores: tiny passageways for proteins, RNA, and solutes between the nucleus and the cytoplasm.
• Nucleolus: the region that manufactures the RNA needed to build ribosomes.
• Chromatin: threads of DNA and associated proteins. A chromosome is the condensed form of chromatin.

OpenStax gives the numbers: humans have almost 22,000 genes distributed on 46 chromosomes. It also flags two exceptions to the one-cell, one-nucleus picture. Mature mammalian red blood cells do not contain nuclei at all, and some cells, such as muscle cells, contain more than one.

Parts of a human cell vs. an animal cell vs. a plant cell

A human cell is an animal cell, so the parts of a human cell are the same list you have just read. The comparison that matters on most worksheets is animal versus plant. OpenStax Biology 2e (section 4.3) spells it out: plant cells have a cell wall, chloroplasts and other specialized plastids, and a large central vacuole, while animal cells each have a centrosome and lysosomes and most plant cells do not.

Chloroplasts are the plant-side organelle people ask about most, and an animal cell has none. For that one, see our explainer on what a chloroplast is.

Our take

We think the cell is the best place to learn how science names things. Every label on that crowded diagram fits one of three zones: boundary, interior, or control center. Many of the names describe what you would see under a lens. The rough ER is rough because of what is stuck to it, and the smooth ER is smooth because those ribosomes are missing.

Once you have the map, you stop memorizing and start placing. That is a skill that carries well past biology class.

Why we carry it at PRSPR

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FAQ

What is a cell?

A cell is the smallest unit of a living thing, per OpenStax Biology 2e (section 4.1). The NHGRI glossary calls it the basic building block of living things.

What are the parts of a cell?

Most textbooks group them into three zones: the cell membrane, the cytoplasm (cytosol plus organelles such as mitochondria, ribosomes, the endoplasmic reticulum, the Golgi apparatus, and lysosomes), and the nucleus. These are the parts described in OpenStax Anatomy and Physiology 2e, sections 3.1 to 3.3.

What are organelles?

The NHGRI glossary defines an organelle as a subcellular structure with one or more specific jobs to perform in the cell, much like an organ does in the body.

Does an animal cell have chloroplasts?

No. OpenStax Biology 2e (section 4.3) lists chloroplasts, a cell wall, and a large central vacuole as plant cell structures, and centrosomes and lysosomes as structures animal cells have.