Non-Cellular Life: Definition & Examples

Non-Cellular Life: Definition & Examples
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  • 0:00 What Is Non-Cellular Life?
  • 0:48 Viruses
  • 1:23 The Mimivirus
  • 2:09 Virions and Viroids
  • 2:43 Lesson Summary
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Lesson Transcript
Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

The idea of non-cellular life has been confusing scientists for almost 100 years. Read on to learn more about what non-cellular life is and the major, recent discovery that has turned this century-old debate on its head.

What Is Non-Cellular Life?

You may believe that in order for something to be considered alive it must contain cells. Well, many scientists would agree with you. However, there are organisms that fall into the category of non-cellular life, and they are actually incredibly common. In fact, whenever you catch the common cold or flu, you are coming into contact with this highly contentious life form.

Non-cellular life refers to organisms, such as viruses, that exist without any cells, and it is a very controversial topic. The cell theory, which is one of the fundamental tenets of biology, states that all living things are composed of cells and that cells are the basic units of life. So the idea that something can be considered alive without having cells is an issue that is up for debate.

Viruses

Viruses are at the heart of this century-old debate. Viruses are parasites that infect plants, animals, fungi, and bacteria. They consist of genetic material surrounded by a protein coat and are unable to grow or reproduce without a host. The classification of viruses has confused scientists for nearly 100 years. Originally they were viewed as poisons. In fact, the word 'virus' is Latin for 'poison.' They have since been viewed as living creatures, then mere bio-chemical compounds, and, most recently, somewhere in between chemical compounds and life forms.

The Mimivirus

The discovery of the mimivirus in 2003 has added a new chapter to the debate. This giant virus, more than double the size of other large viruses, is capable of conducting certain life processes without a host cell, like making proteins. The name 'mimivirus' originated from the term 'mimic,' since scientists originally thought they were observing a new type of bacteria. In other words, the mimivirus mimics the bacteria.

Some scientists are now suggesting that the mimivirus represents a very ancient form of life, once capable of living without a host. It has since evolved into the current parasitic form of viruses that we see today. This idea is groundbreaking as it suggests that we may need to completely re-evaluate our definition of life.

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