I think the correct answer is c
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.
The answer is spicules. These
sharp-pointed structures are formed from calcium carbonate skeleton of
the organisms. They can also be formed from silica. They can be big (megascleres),
or microscopic (microscleres). Also dependent on the number of axis on the spicules, they are classified as monoaxon,
triaxon or polyaxon.
Diffusion occurs because of the movement of molecules from
the region of higher concentration to the region of lower concentration. This
movement of molecules occurs due to a thermal motion. Diffusion normally occurs
between two compartments having difference in concentration. In case of fluid
it moves from the region of higher concentration to the region of concentration
until a balance is reached. The process of diffusion is very important for the
humans as well. The oxygen that humans breathe in gets diffused with the blood.
I think the correct answer is A
