Eukaryote

Eukaryotes are a big group of living things. Their cells have a special barrier called a membrane around a part called the nucleus. This keeps their control center safe. 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. Scientists think they started as cells that could move with tiny parts called flagella. 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. These help provide energy.

Eukaryotic cells have many special parts called organelles, like the nucleus. They also have systems such as the endoplasmic reticulum and Golgi apparatus, all separated by membranes. These organisms can be single-celled or made 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, these words describe the nucleus inside a cell. This name shows an important feature of these cells.

Diversity

Further information: Organism

Eukaryotes are many different kinds of living things. They can be very small, like single cells such as picozoans, or very large, like the blue whale or tall coast redwood trees. Some eukaryotes are made of just one cell, while others, like animals, plants, and fungi, are made of many cells working together. Though there are fewer types of eukaryotes than prokaryotes such as bacteria and archaea, eukaryotes can grow much bigger. Because of this, their total weight on Earth is often greater.

Eukaryotes have adapted to live in many different forms. Complex life with many cells evolved separately in several groups. These groups include animals, symbiomycotan fungi, brown algae, red algae, green algae, and land plants. These organisms are grouped by their genes, so they may not always look the same.

Distinguishing features

Further information: Cell (biology) § Eukaryotes

The main feature that sets eukaryotes apart is that their cells have a nucleus. This is 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. These organelles each have their own job.

Eukaryotic cells are much larger and more complex. They use a process called mitosis to divide.

Eukaryotes have unique ways of making and using energy. 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.

Evolution

Further information: History of taxonomy

Long ago, thinkers like Aristotle and Theophrastus saw two main groups of living things: animals and plants. Later, scientists sorted living things into groups called kingdoms. Linnaeus in the 1700s put fungi with plants, but we now know they are different enough to have their own kingdom. At first, tiny single-celled creatures were put with plants or animals. In 1818, a scientist named Georg A. Goldfuss named these creatures Protozoa. By 1866, Ernst Haeckel suggested a whole kingdom for all single-celled eukaryotes, calling it Protista. This helped create the idea of four main kingdoms of eukaryotes: Protista, Plantae, Fungi, and Animalia.

Today, we know that all eukaryotes belong to a bigger group called domains. In 1990, scientists suggested calling them "Eucarya." Now, we know most eukaryotes are in two big groups: Amorphea and Diphoda, which includes plants and many algae. Eukaryotes came from a special event where a simple cell took in another cell, leading to the complex cells in plants, animals, and fungi.

Main article: Eukaryogenesis

Eukaryotic cells were an important step in life's history because they 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 do basic life processes.

One big idea 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. Modern science shows that eukaryotes have very old roots, with possible fossil signs dating back over a billion years.