B and C)
They often obtain most of their nutrients through the cell membrane as diffusion is able to take place passively and so at no energy loss to the organism, this can be essential for a single celled organism as they are able to produce a lot less energy due to having fewer mitochondria in comparison to multicellular organisms.
They also require few resources as single celled organisms are very small and so require only a small amount of raw resources for respiration because they have a small energy demand to meet.
Epithelia are classified by the number of cell layers and the general shape of the cells
<span>because they have an enhanced sight due to the amount of magnification and objective lens</span>
One of the reasons for the success of the smallpox eradication campaign was that small pox only occurred in humans. Smallpox is an extremely contagious and deadly virus for which there is no known cure. it is caused by two variants, Variola major and Variola minor. it is a disease of the past that was eliminated by worldwide vaccination.