Specialized Cells and Tissues
A tour of the Studio's specimens in four groups (animal, plant, protist and fungus, and prokaryote), and how one genome builds cells with very different shapes and jobs.
Quick answer: Cells with the same DNA become different types through differentiation: each type switches on a different set of genes, so it makes different proteins and takes a shape that fits its job. Stem cells have not yet committed and can give rise to specialized cells.
What you will learn
- Explain how cells with the same DNA become different cell types.
- Match each specimen's key structure to its function.
- Name the four basic animal tissue types.
- Describe how stem cells differ from specialized cells.
Form follows function
A human body contains tens of trillions of cells of roughly 200 recognized types. A neuron looks nothing like a red blood cell, and neither looks like the cells in your skin. Yet nearly all of them carry the same DNA that was in the fertilized egg.
The answer is differentiationDifferentiationThe process by which a less specialized cell turns on a particular set of genes and becomes a specific cell type, such as a neuron or a muscle fiber.. As an embryo develops, cells switch on different sets of genesGeneA stretch of DNA that contains the instructions for making a particular RNA or protein. in response to signals from their neighbors. A cell that expresses the genes for myosin and actin becomes a muscle cell, and one that expresses neurotransmitter receptors and ion channels becomes a neuron. Once switched, the pattern is usually stable.
A stem cellStem cellA cell that can divide to make more of itself and can also give rise to one or more specialized cell types. is a cell that has not yet committed. It can divide to make more stem cells and can also give rise to specialized cells. Bone marrow stem cells, for instance, produce all the different cells in your blood.
Animal and human cells
Each cell in the Studio is a case study in structure and function. Pick out the feature that gives each one its job. We start with the animal and human cells, which share the standard eukaryotic toolkit but exaggerate different parts of it.
Animal cell: the general-purpose model
The animal cell has the standard eukaryotic toolkit: nucleus, mitochondria, ER, Golgi, lysosomes, and a flexible membrane. Specialized animal cells add or exaggerate parts of this basic plan.
Neuron: long and branched
The shape of a neuron is its function. Branching dendrites collect inputs, and a long axon delivers the output to other cells, sometimes more than a metre away.
Muscle fiber: packed with machinery
A skeletal muscle fiber is filled with myofibrils, and mitochondria sit between them to supply ATP. It is multinucleated, because it formed by fusion of many precursor cells.
Cardiac muscle cell: wired together
Heart cells are branched and joined end to end by intercalated discsIntercalated discThe specialized junction between two neighboring heart muscle cells. It contains gap junctions that pass electrical signals and anchoring junctions that transmit the force of contraction.. These contain gap junctions that pass electrical signals from cell to cell, and strong anchors that carry the force of each beat, so the heart contracts as one unit. Roughly a third of the cell's volume is mitochondria, because the heart never rests.
Epithelial cell: a living barrier
Epithelial cells line the skin, the gut, and the airways. They are joined side by side by tight junctionsTight junctionA seal between neighboring epithelial cells that blocks most substances from leaking between them. that seal the gaps between cells, and many carry microvilliMicrovilliTiny finger-like folds on the surface of a cell that greatly increase its surface area for absorption, as in the lining of the intestine. on the exposed surface to absorb nutrients.
White blood cell: a mobile defender
A white blood cell crawls through tissue, engulfs invaders, and digests them using lysosomes. Its lobed nucleus is flexible enough to squeeze through narrow gaps.
Red blood cell: an oxygen carrier
A mature red blood cell has thrown away its nucleus and most of its organelles to make room for hemoglobinHemoglobinThe iron-containing protein in red blood cells that binds oxygen in the lungs and releases it in the tissues. It gives blood its red colour., the iron-containing protein that carries oxygen. The biconcave shape gives a large surface area for gas exchange, and a protein skeleton under the membrane lets the cell fold its way through the narrowest capillaries.
Sperm cell: stripped down for one journey
A sperm cell keeps only what the trip needs. The head holds a compact nucleus capped by the acrosomeAcrosomeA cap-like sac of digestive enzymes at the front of a sperm head. The enzymes help the sperm penetrate the layers around the egg., a sac of enzymes that helps the cell penetrate the egg. A midpiece packed with mitochondria powers the long flagellumFlagellumA long, whip-like projection that moves a cell. Bacterial flagella spin like a propeller; eukaryotic flagella bend back and forth..
Egg cell: a supply depot
The egg is one of the largest cells in the human body, and it is mostly a store of materials for the early embryo. It is wrapped in the zona pellucidaZona pellucidaThe glycoprotein coat surrounding a mammalian egg. Sperm must bind to it, and after fertilization it hardens to block other sperm., a glycoprotein coat that sperm must bind to. After fertilization, cortical granules release enzymes that harden this coat so that only one sperm gets in.
Stem cell: not yet committed
A stem cellStem cellA cell that can divide to make more of itself and can also give rise to one or more specialized cell types. looks plain on purpose. It has a relatively large nucleus with loosely packed chromatinChromatinDNA wrapped around proteins, as it appears in the nucleus when the cell is not dividing., so many genes can still be switched on, and few small mitochondria. When the right signals arrive it begins to specialize and its organelles change to match.
Osteocyte: the cell inside bone
Bone looks inert, but it is alive. Osteocytes sit in small chambers called lacunaeLacunaA small chamber in the bone matrix that houses one osteocyte. Thin canals called canaliculi link neighboring lacunae. inside the hard mineral matrix, and reach toward each other through thin canals. They sense the load on the skeleton and help decide where bone should be rebuilt.
Fat cell: built around a droplet
An adipocyte is built around one huge lipid dropletLipid dropletA storage body made of fats such as triglycerides, wrapped in a single layer of phospholipid. Fat cells hold one very large droplet. that stores energy as triglyceride. The droplet pushes the nucleus and a thin rim of cytoplasm against the membrane, so under the microscope the cell looks like a ring.
Rod cell: a sensor for dim light
Rod cells in the retina detect very dim light. Stacks of membrane discs in the outer segment are packed with the light-sensitive pigment rhodopsinRhodopsinThe light-sensitive pigment in rod cells of the retina. A single photon can change its shape and start the signal that we experience as vision in dim light., and even a single photon can start a signal. Mitochondria in the inner segment supply the energy, and the synaptic terminal passes the message on to the next neuron.
Plant cells
Plant cells share the eukaryotic toolkit, and add a wall, a large vacuole, and chloroplasts. Their specializations mostly serve two jobs: collecting light and managing water.
Plant cell: wall, vacuole, chloroplast
A plant cell is boxed in by a rigid cellulose cell wallCell wallA rigid layer outside the plasma membrane of plants, fungi, and most bacteria. It protects the cell and resists the pressure of water pushing outward.. A large central vacuoleVacuoleA fluid-filled, membrane-bound compartment. In mature plant cells a large central vacuole stores water and helps maintain turgor pressure. pushes water against that wall, creating turgor pressureTurgor pressureThe outward pressure of water against the cell wall in a plant cell. It keeps non-woody plant tissue firm; when it drops, the plant wilts. that keeps soft tissue firm. Chloroplasts make sugar from sunlight.
Guard cell: a living valve
A pair of guard cellsGuard cellOne of a pair of plant cells that surround a stoma. By taking up or losing water they change shape and so open or close the pore. surrounds each stomaStomaA tiny pore in the surface of a leaf, surrounded by two guard cells. Carbon dioxide enters and water vapour leaves through it (plural: stomata)., the tiny pore in a leaf where carbon dioxide enters and water vapour leaves. The wall is thicker on the pore side, so when the cells take up water they bow apart and the pore opens, and when they lose water it closes. Osmosis works the valve.
Root hair cell: more surface to absorb
A root hairRoot hairA long, thin outgrowth of a root surface cell. It greatly increases the surface area for absorbing water and minerals from soil. is a long outgrowth of a single root cell. It greatly increases the surface that takes in water and minerals, the same strategy that microvilli use in the gut.
Protists and fungi
Not every eukaryote is a plant or an animal. Many are single cells that do every job of life on their own.
Yeast: a fungus in one cell
Yeast is a fungus that lives as one eukaryotic cell. It divides by buddingBuddingA form of reproduction in which a small daughter cell grows out of the parent, receives a copy of the nucleus, and then separates. Yeast divides this way.: a small daughter grows out of the mother, receives a nucleus, and separates. Because yeast is easy to grow and has a nucleus and organelles like ours, it is one of the workhorses of cell biology.
Paramecium: a whole organism in one cell
Thousands of ciliaCiliumA short, hair-like projection from the cell surface built around microtubules. Cilia beat to move fluid across a surface or to move the cell itself. propel a Paramecium and sweep bacteria into its oral groove. Because it lives in fresh water, osmosis keeps pushing water in, and two contractile vacuolesContractile vacuoleA vacuole in many freshwater protists that collects excess water and periodically pumps it out of the cell, which stops the cell from swelling and bursting. pump it back out.
Chlamydomonas: a swimming alga
Chlamydomonas has one cup-shaped chloroplast and two flagella. An eyespotEyespotA small, pigmented patch with light-sensitive proteins in some algae. It lets a swimming cell detect the direction of light and steer toward it. senses the direction of light, so the cell can steer toward the best place to photosynthesize.
Prokaryotes
Bacterium: small, sturdy, and fast
A bacterial cell has a peptidoglycanPeptidoglycanA mesh-like polymer of sugars and short peptides that forms the bacterial cell wall. wall, a nucleoid in place of a nucleus, and often a flagellum for swimming. Its small size gives a very high surface-area-to-volume ratio, so it can take in food and divide quickly.
Cyanobacterium: photosynthesis without chloroplasts
Cyanobacteria photosynthesize, but they have no chloroplasts. Their thylakoidThylakoidA flattened, membrane-bound sac that holds chlorophyll and carries out the light reactions of photosynthesis. In chloroplasts thylakoids are stacked; in cyanobacteria they lie free in the cell. membranes lie free in the cytoplasm, and protein-shelled carboxysomesCarboxysomeA polyhedral compartment with a protein shell, found in cyanobacteria. It packs the enzyme rubisco together with carbon dioxide so that carbon fixation works faster. concentrate the enzyme that fixes carbon dioxide. Chloroplasts are thought to descend from ancient cyanobacteria.
How can a neuron and a muscle cell have the same DNA but look so different?
From cells to tissues
A tissueTissueA group of similar cells that work together to perform a function, such as muscle tissue or epithelial tissue. is a group of similar cells that perform a shared function. Animal bodies are built from four basic types:
| Tissue | Main job | Example |
|---|---|---|
| Epithelial | Cover surfaces and line cavities; absorb and secrete | Skin, gut lining |
| Connective | Support, connect, and protect; includes blood and bone | Blood, cartilage, bone |
| Muscle | Contract to produce movement | Skeletal, heart, smooth muscle |
| Nervous | Sense, process, and send signals | Brain, nerves |
Plants have their own three tissue systems: dermal (the outer covering), vascular (the pipes that carry water and sugar), and ground (everything else, including photosynthesis and storage).
Tissues combine into organs, organs into organ systems, and these into an organism. At each level, the property of the whole depends on the cooperation of its specialized parts.
Which feature helps intestinal epithelial cells absorb nutrients efficiently?
Which of these is NOT one of the four basic types of animal tissue?
What to explore next
You have now covered the main structures, processes, and specializations of cells. Return to the Studio to rotate each specimen, take the quiz, or look up any term in the glossary.
Key takeaways
- A human body has roughly 200 recognized cell types, all built from one genome.
- Specialized cells keep all of their genes and simply use some of them.
- Animals have four basic tissues (epithelial, connective, muscle, nervous); plants have dermal, vascular and ground tissue systems.
- Structure matches function: microvilli absorb, axons conduct signals and chloroplasts photosynthesize.
Sources
- Biology 2e, Chapter 4: Cell Structure (OpenStax) Concepts adapted and rewritten; no text reproduced verbatim.
- Biology 2e, Chapter 15: Genes and Proteins (OpenStax) Used for gene expression and cell differentiation.
- NIH 3D: Gram-positive cell wall model
Last reviewed October 1, 2026