A. <span>Exposure to an antigen
Exposure to viruses and antigens led to the foundation of modern vaccination. Vaccination introduces an antigenic material that helps the ability of the immune system to adapt a specific pathogen, therefore leading to a long-term immunity.</span>
Domains are the highest ranking of organisms in taxonomy. They are notably Bacteria, Eukarya, and Archaea
If a burning splint is placed in a container and burns more brightly in the presence of some gas already in the cylinder, that gas would probably be Oxygen.
Oxygen is the main component of air that we need to breathe. It is the most commonly available oxidizer. Besides combustion, it plays many roles in our life such as; the food we eat requires oxygen which helps in digestion and absorption of nutrients by the cells.
Answer:
B
Explanation:
An undifferentiated cell is such as that in a blastocyte. They are multipotent and can differentiate into any type of cells. The cells of the mass begin to have their gene differentially expressed (due to differential silencing of particular genes) hence the cell become determined. They become well organized into tissue such as skin and other organs.
