The
Thymocyte progenitors enter the subcapsular region of the thymus as
double-negative cd3- t cells where the double negative refers to lack of
cluster determinants CD4 and CD8. Double-negative cd3- t cells exist as small population
that is 1%-5% of lymphocytes in the lymphoid organs and peripheral blood of
humans and normal rodents.
Answer: The water in the earth is older than earth itself.The water inside earth came out as steam from volcanic vents and the clouds rained down water..Comets also contain lot of water ice.Early period of solar system large amount of comets and asteroids hit the earth They also brought lot of water.
Explanation:
Answer: B
Explanation:
The T helper cell needs to acttivate the T cyctotoxic cell in order for the Tc cell to go do its work.
Once the TC cell is active it interacts with MHC-1 proteins on the surface of the infected host cell, this allows the Tc cell to recignise the host cell and begin secreting cytotoxins (perforins and granzymes) in order to degrade the infected cell and cause apoptosis (controlled cell death)
D is the correct answer to this question. Here is a chart of energy transfer.
