The answer is D. Most cells have a membrane but some dont
Because they do not have an immune system, don't have noses, don't have mouths, and just plain do not have the same functions as animals, insects, or humans. They don't have a heart or a brain, which means they can't catch a cold. They can get diseases however.
Clostridium, Bacteroides, and the methane-producing archaea (methanogens), are called obligate anaerobes because their energy-generating metabolic processes are not coupled with the consumption of oxygen.
