A population of mollusks are living in a stable ecosystem in the ocean. A rapid
drop in sea level causes the formation of a lake, which isolates a group of mollusks
from the rest. This quick environmental change causes rapid evolutionary change.
Due to the new small population, genetic drift occurs, and mollusks with larger
shells rapidly become the most common trait.

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.

From a high concentration to a low concentration.