What is an Obligate anaerobe? How do obligate anaerobes, like the bacteria C. Botulinum, get energy ?

See the answer below

Explanation:

Obligate anaerobes are microbes that can only survive in oxygen-deficient environments. They are killed by the normal atmospheric level of oxygen and will only thrive in environments whose oxygen levels are lower than that of normal atmospheric level.

Obligate bacteria such as Clostridium botulinum obtain their energy through anaerobic respiration processes such as fermentation and anaerobic respiration. During this process of fermentation, the lactic acid pathway is mostly used but other fermentation pathways such as propionic acid, mixed acid, acetogenesis, and methanogenesis pathways can be used.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!