Eukaryote

Eukaryotes are a major group of living things whose cells have a special barrier called a membrane surrounding their nucleus. This means that unlike some other tiny life forms, eukaryotic cells keep their important control center safely protected. All animals, plants, fungi, seaweeds, and many tiny single-celled creatures are eukaryotes.

Eukaryotes first appeared a very long time ago during a time called the Paleoproterozoic, probably as cells that could wave around little tail-like parts called flagella. Scientists believe they came about through a process called symbiogenesis, where two different tiny life forms joined together. One was an ancient type of archaeon, and the other was a bacteria that could use oxygen. This joining created structures inside cells called mitochondria, which help provide energy.

Eukaryotic cells have many special parts called organelles, like the nucleus, and systems such as the endoplasmic reticulum and Golgi apparatus, all separated by membranes. These organisms can be single-celled or made up of many cells working together. When they reproduce, they can do so in two ways: without parents through mitosis, or with parents through meiosis and the joining of special cells called gametes, also known as fertilization.

Etymology

The word eukaryote comes from ancient Greek. It combines "eu" meaning "true" or "good" and "karyon" meaning "nut" or "kernel". Together, they refer to the nucleus found inside a cell. This name highlights an important part of these cells.

Diversity

Further information: Organism

Eukaryotes are a wide variety of living things, ranging from very tiny single cells like picozoans to enormous animals such as the blue whale, and tall plants like the coast redwood. Many eukaryotes are made of just one cell, but some, like animals, plants, and fungi, are made of many cells working together. Even though there are fewer types of eukaryotes compared to prokaryotes (such as bacteria and archaea), eukaryotes often grow much larger, making their total weight on Earth greater.

Eukaryotes have evolved to live in many different forms, with complex, multi-celled life developing separately in several groups including animals, symbiomycotan fungi, brown algae, red algae, green algae, and land plants. These organisms are grouped based on their genes, meaning they might not always look alike.

Distinguishing features

Further information: Cell (biology) § Eukaryotes

The main feature that sets eukaryotes apart is that their cells have a nucleus, a special part enclosed by a membrane that holds the cell's DNA. Unlike prokaryotes, which lack this nucleus, eukaryotic cells also contain many other tiny parts called organelles, each with its own job. These cells are much larger and more complex, and they use a process called mitosis to divide.

Eukaryotes also have unique ways of making and using energy, and many can perform photosynthesis to turn sunlight into food. They often have structures that help them move, like tiny hair-like projections called cilia or tail-like flagella. Some, like plants and fungi, have a tough outer layer called a cell wall that gives them shape and support. Many eukaryotes also have life cycles that include both sexual and asexual reproduction, combining genetic material in new ways.

Evolution

Further information: History of taxonomy

In ancient times, thinkers like Aristotle and Theophrastus recognized two main groups of living things: animals and plants. Later, scientists classified living things into kingdoms. Linnaeus in the 1700s placed fungi among plants, but we now know they are different enough to have their own kingdom. Single-celled organisms were grouped with plants or animals at first. In 1818, a scientist named Georg A. Goldfuss introduced the term Protozoa for certain single-celled creatures. By 1866, Ernst Haeckel proposed a whole kingdom for all single-celled eukaryotes, calling it Protista. This led to the idea of four main kingdoms of eukaryotes: Protista, Plantae, Fungi, and Animalia.

We now understand that all eukaryotes belong to a larger group called domains. In 1990, scientists suggested grouping them into a domain called "Eucarya." Today, we know that most eukaryotes fall into two big groups: Amorphea and Diphoda, which includes plants and many algae. The origin of eukaryotes is linked to a special event where a simple cell absorbed another cell, leading to the complex cells we see in plants, animals, and fungi today.

Main article: Eukaryogenesis

The origin of eukaryotic cells was a big step in life's history because these cells can become complex and form many kinds of organisms, including all animals and plants. Scientists think the last common ancestor of all eukaryotes had a nucleus and could perform basic life processes.

One major theory is that a special partnership between two different kinds of very simple cells led to the first eukaryotic cells. Later, another partnership helped create the cells that would become plants. Evidence from modern science supports the idea that eukaryotes have ancient roots, with possible fossil traces dating back over a billion years.