A vaccine works by training the immune system to recognize and combat pathogens, either viruses or bacteria.
The root word of Unicellular already tells you the answer. Uni means only one cell. So the answer is one cell.
Tissue typing is a screening process in which cell markers in a donated organ or tissue are identified so that they can be matched to a recipient with similar cell markers. This has become more important in recent years because of the number of organ transplants
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46.
