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Fields of interest
The assignment you have to write has a little bit to do with Biology and a little bit to do with Philosophy! The question of what is alive and what is not depends on the very definition of what is a living thing and this question is not of interest to biologists but only to philosopher.
How to nail this assignment
Therefore, for your assignment you will need to understand what a mitochondrion is (the Biology part) and to understand how do the different definitions of life apply to the mitochondrion (Philosophy part although you will need some knowledge in Biology to understand the relevance of these definitions).
What is a mitochondrion?
This question is too broad and cannot be answered here. Make sure to have a look at the wikipedia page. In short:
- mitochondrion contain DNA
- mitochondrion is the result of a bacteria that has somehow been internalized into a bigger cell (it is a symbiont). This is why today mitochondrion contain DNA. It is therefore not exactly an organelle like others. Note that plants, in addition to having mitochondrion, they have plasmids that are also consequences of a similar process of internalizing other form of life.
- mitochondrion DNA evolve (of course)
- mitochondrion are basically the energy factory of the cell.
- mitochondrion are not able to live by themselves outside a living cell (to my knowledge).
Definitions of life
It is important to understand that the definition of life has absolutely no impact on biology and is nothing but a question of nomenclature.
There are a lot of definitions and I can't cover all of them here. You might want to have a look at this wiki page. The previous link lists the most common properties we think about when thinking about the definition of life.
- Homeostasis: Regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.
Organization: Being structurally composed of one or more cells — the basic units of life.
- Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
- Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity, diet, and external factors.
Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
- Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms,"with an error rate below the sustainability threshold."
The question of whether viruses are alive is a very common one. Here are two Biology.SE posts on the subject: