Answer
Reasons for the usage of agar in microbiology:
1) Powdered agar is easily soluble in water at 100° C which is not the case with most other nutrients.
2) Agar can be used as a culture medium for few hyperthermophiles since it does not melt below 100°C.
3) Agar is not digestible by most organisms, so it can remain solid even during the rapid growth of microorganisms.
4) Solidification of agar occurs a temperatures below 40°C. Hence, sterile nutrients such as blood and vitamins which are temperature sensitive can be added to cooling agar without any damage.
