Many unicellular eukaryotes undergo mitosis for asexual reproduction. This is often called clonal reproduction, because offspring are identical to the parent cell. Because prokaryotes do not have a nucleus, they cannot undergo mitosis, but they can still do asexual reproduction.
How do prokaryotes reproduce asexually?
On the right is a colony of the cyanobacterium Nostoc. These unicellular organisms reproduce asexually to form colonies of individuals that live together in a secreted mucilaginous sheath (the bubble surrounding them). Much like Anabaena, some of these individuals are converted into heterocysts and are unable to feed themselves. How can we distinguish between a collaborative community of individuals and a multicellular organism?
The root tips you have been viewing are a small portion of the larger organism. How did life become multicellular from its unicellular origins? There are many theories about how this happened, but it is well-supported that multicellularity evolved multiple times in the tree of life. One theory for how multicellularity first occurred is through errors in cytokinesis, resulting in two identical cells that were still conjoined. This can be induced in yeasts (unicellular fungi), resulting in branching structures. These yeasts are referred to as snowflake yeasts. Investigate further here: http://www.snowflakeyeastlab.com/experimental%20evolution.htm