![]() ![]() The development of sexual reproduction is another defining feature in the evolution of eukaryotes. Some eukaryotes reproduce asexually, while others reproduce sexually. Yet another theory proposes that eukaryotic cells evolved when an archaeon and a bacterium merged to form one cell. Theories involving mitochondria appearing in a cell that was already almost eukaryotic, with a nucleus, are known as autogenous models. However, another theory is that small amounts of DNA already in the cell were simply infolded within the cell membrane and evolved into organelles such as mitochondria. Mitochondria have DNA that is separate from the chromosomal DNA found in a cell’s nucleus. Over time, these bacteria formed the organelles incorporated within eukaryotic cells that are seen today, and became a necessary part of the eukaryotic cell. Under this theory, bacteria and the cells had a symbiotic relationship, where each benefited from the presence of the other. Some organelles, such as mitochondria and chloroplasts, may have evolved when free-living bacteria were taken up into cells. These organelles include mitochondria, which make energy, chloroplasts, which are found in plants and make food from light and carbon dioxide, and the endoplasmic reticulum, which sorts and packages proteins. Eukaryotes are more closely related to archaea, unicellular organisms sometimes found in extreme conditions such as hot springs, than to bacteria.Įukaryotic cells developed specific organelles, which are structures within the cell that perform a specific task. There are about 75 separate lineages of eukaryotes, most of which evolved into protists. Today, all complex organisms and most multicellular ones are eukaryotes, making this evolution a major event in the history of life on Earth. This picture depicts part of a eukaryotic cell with its enclosed nucleus and various organelles.Įukaryotic cells evolved from prokaryotic cells between 1.6 and 2.7 billion years ago. Unicellular eukaryotes perform many of the same actions as multicellular eukaryotes, such as locomotion, respiration, digestion, excretion, and reproduction. They move with the use of flagella, which are small thread-like appendages that extend from the cell membrane. Unicellular eukaryotes can reproduce sexually or asexually. Protists and fungi are usually unicellular, while animals and plants are multicellular. Protists are a group of organisms defined as being eukaryotic but not animals, plants, or fungi this group includes protozoa, slime molds, and some algae. There are four types of eukaryotes: animals, plants, fungi, and protists. The other two domains of life, Archaea and Bacteria, have prokaryotic cells, which are simpler and lack organelles except for ribosomes, which make proteins. Organisms with eukaryotic cells are grouped into the biological domain Eukaryota (also sometimes called Eukarya). Eukaryotic cells are cells that contain a nucleus and organelles, and are enclosed by a plasma membrane. Eukaryotes are organisms whose bodies are made up of eukaryotic cells, such as protists, fungi, plants and animals.
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