Bacteria are considered organisms and are made up of one cell. They do not have a nuclear envelopeand membrane bound organelles. It has circular chromosomes and are diverse in the molecules they use for food/ habitats they occupy. They can be found at the bottom of the ocean, in boiling hot springs, and maybe even on other planets. Bacteria reproduce asexually. And when mutations are not an issue and no genetic material has been transferred from other bacteria or viruses, the daughter cells will be identical to the parent.
Viruses are not cells and are not made up of cells so they are not considered organisms. They are agents/particles that cannot make their own ATP/ carbon-containing compounds, so they rely on cells for energy and replication. Viruses are considered parasites because without other organisms viruses would just exist and would not be reproducing or catalyzing molecules. They have genome, so it is not determined iif it is alive or not. There are a lot more viruses in the world than any type of organism.
Protists do have a nuclear envelope and organelles. Their cytoskeleton gives them structure. It is common for protists to sexually reproduce but its not always. They undergo cell division through mitosis. Protists have DNA within their nucleus that is made with many parts with proteins called histones. Protists can be made up of several cells and are larger than bacteria. Due to their membrane bound organelles, each cell can specialize in a task. They can be parasitic, predatory or even photosynthetic in nature. They live in moist area.
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