T cells. When HIV arrives in the lymph nodes – around 24 to 48 hours after exposure – they activate other immune cells, such as CD4 t-cells, HIV's primary target.
Answer:
it happens when 2 organisms jelp each other beneficial.
Explanation:
eg:algae and leguminous plants.the algae live on the roots and take in the nitrogen from the soil,which the plant cannot do and needs for growth.it takes in the nitrogen and pases it to the roots and even make the soil loose for the roots to move and they get a living space(algae on the roots).
If a pair of Organisms are capable of producing fertile offspring in nature they must belong to the same species
