What is a cell? A great quick overview.

Explore what each organelle does within various types of cells

In "Cell Anatomy Viewer," users can explore interactive illustrations of animal, plant, fungal, and bacterial cells. Clicking on an organelle, such as a lysosome, the nucleolus, or the Golgi complex, provides descriptions of its characteristics and functions.

Cells are categorized by the presence of contained genetic material and other organelles

While prokaryotes contain one or more cells with free-floating genetic material in a region called the nucleoid, eukaryotes possess a nucleus specialized for DNA storage. Plant cells possess cell walls—a reinforced structure surrounding their membrane—made of cellulose, while fungal cell walls contain chitin. Animal cells have lysosomes housing enzymes that break down biomolecules. (Some readers may experience a paywall.)

Explore the abundance of different types of cells in the human body

Lacking a nucleus and other organelles to maximize space for oxygen-carrying hemoglobin and enhance maneuverability through narrow capillaries, there are about four times as many red blood cells and platelets as all other cell types in the body combined. However, about half of the body's cell biomass consists of skeletal myocytes, or muscle fibers.

DNA carries the unique instructions that shape how each person grows and functions

The human genome contains over six billion DNA letters, organized into 46 chromosomes inherited from both parents. Genes—sections of DNA—serve as templates for making proteins, and variations in these sequences can affect how our bodies work or respond to the environment.

The inner life of a cell

White blood cells are responsible for protecting the human body from infection. This video uses biophysical data from Harvard researchers to accurately demonstrate what goes on inside one white blood cell as it works within the immune system.

View a gallery of images and videos of over 200 types of cells

Funded by the National Institute of General Medical Sciences of the National Institutes of Health, the Cell Image Library houses over 60,000 pieces of media, including microscopic photographs, time-lapse videos of cellular activity, and 3D reconstructions of organic processes.

What is the immune system? A quick 101

Your body’s immune system is designed to protect you from infection. Find out more about how the immune system works with this quick overview and set of diagrams.

Take a deep dive into the neuron

Neurons are the basic unit of the brain and nervous system—electrically excitable cells that sends signals throughout the body. They can communicate with each other, fire in sequence, and conspire to do everything from drive body movement to help form memories. Check out this intro-level overview to learn more about their structure and how they work.

How metabolism, when cells convert molecules into energy, works

Metabolism is when a cell’s internal network of chemical reactions breaks down food molecules and transforms them into pieces of the cell itself. Sometimes, cells build replacements for worn-out parts. Other times, they build energy molecules that power the cell’s activities.

Why don't we all have cancer?

The creation of a single cell produces 120,000 genetic mutations that can lead to cancer. This video investigates how our bodies proofread and autocorrect those mistakes.

A fascinating look at how our DNA is built and replicated

This easy-to-understand 13-minute video dives into the wondrous molecule deoxyribonucleic acid – also known as DNA – and explains how it replicates itself in our cells.

Cells can last in the human body from days to a person's entire life

Despite claims that a person's body replaces itself every seven to 10 years, the rate at which cells die and are replaced varies by cell type. Gastrointestinal cells that line the digestive tract and stomach last only a few days, while some heart muscle cells and most neurons are around from birth until death.

How do you sequence a genome?

If the genome is made up of microscopic chromosomes, how do scientists actually sequence it? Here's a 5-minute video explaining one of the most common processes.

Stem cells develop into a wide range of other specialized cells in the human body

Stem cells are different from other cells because they are capable of creating copies of themselves and producing other types of cells. For example, the ones found in our brains, bones, or muscles. Curious about stem cells? Here's a breakdown of how they work.

Cells create more organelles and duplicate their genetic material before dividing

As part of the cell cycle, this ensures that after mitosis—the process of cell division—the two resulting daughter cells possess the tools necessary to complete the functions of their parent cell, including accumulating energy and making proteins. During meiosis, four egg or sperm cells are created, each with half the parent cell's DNA.

What does blood do?

Blood's primary purpose is to ferry oxygen and nutrients to cells in need while collecting cell waste and byproducts for removal. It also enables the body's repair and immune systems to traverse our internal landscape to address cell damage or external invaders, such as viruses and parasites. Zooming out from the exact roles of blood's various cells, the fluid connective tissue also assists with maintaining homeostasis via temperature regulation and pH balance.

What is genetics?

What is a genome, and how are traits passed from generation to generation? Learn how pea plants helped launch the study of genetics and how the field of genetics research has evolved over time.

A simple explanation of semiconductors

Semiconductor chips are electronic devices that store and process information. Today they can contain billions of microscopic switches on a chip smaller than a fingernail. The article provides a quick overview of how the devices work and how they've provided the backbone of the computer age.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Before discovering cells, life was believed to emerge suddenly from inorganic matter

Popularized by Aristotle in the 4th century BCE, spontaneous generation was used to explain phenomena like mice appearing in seemingly sealed grain storage. The invention of the compound microscope in the late 16th century led to the identification of cells as the basic unit of life, but it was not until 1855 that their origin from preexisting cells was established.

Synthetic biology transforms cells into custom DNA foundries

At companies like Ginkgo Bioworks, researchers are reprogramming cells to act as workshops that can create custom molecules, such as medicines and fertilizers, by stitching together DNA sequences—often in novel combinations—before inserting them into an organism's genome.

Model organisms like yeast, mice, and flies help scientists decode the human body

Some species are used to quickly study the effects of human diseases and treatments because they are short-lived and have similar systems to those found in humans. Bacteria, like E. coli, have been used as human proxies given their rapid growth and ease of genetic manipulability.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

The biology of stress in your body

Stress is a normal human response that has evolved over millions of years to handle changes or threats in our environment. This article is a helpful overview of the biological basics of this response. While it is not harmful to our physiology in the acute setting, chronic stress can lead to damaging changes in the human body over many years.

View an illustrative journey of sperm cells navigating toward fertilization

In this series of comic-style panels, a "fellowship" of sperm cells travels through fictionalized versions of reproductive anatomy on their way to an egg cell. Each panel includes informative commentary on each step of the adventure, with research insights provided by a reproductive biologist, a biomedical scientist, and an andrologist.

Induced pluripotent stem cells are "reprogrammed" cells

Induced pluripotent stem cells are used in a great deal of stem cell research, but many people are still unfamiliar with exactly what “iPS” cells are. This video provides a clear (and short) explanation of iPS cells for non-experts, and offers insights into why scientists are interested in these cells.

Tracing the evolution of mobile phones

The first cell phone was created in 1973, with a 2.4-pound handset and a battery life of about 30 minutes. Since then, pretty much everything about it has drastically changed, with more than 5 billion cellphone users across the globe (that's more than half of the world population). Learn about the evolution of the mobile phone and where the technology may go in the future with this four minute video.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Watch what the Ebola virus does inside our cells and organs in order to spread and survive.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Read a deep dive on the 'all-purpose healing' peptide BPC-157.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

Learn how to read a prospectus, the juicy document that any company must file with the SEC before going public.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Some researchers have labeled nomophobia, the fear of being without your phone, as 'the phobia of the 21st century.'

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

A century of Billboard issues documenting the evolution of popular music.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

The name 'Silicon Valley' arose from the founding of Shockley Semiconductor Laboratory in Fairchild Semiconductor in 1956-57, founded near Stanford University in Palo Alto

The United States is one of only around two dozen countries with a fully federal system of government, in which power is divided between national and state governments.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.