A. true b. false in passive transport, molecules can only move with the net movement of molecules down their concentration gradient

This statement is true. Only active transport can move molecules up a concentration gradient using energy. Passive transport on the other hand, uses no energy and occurs naturally. Therefore molecules can only move a concentration gradient.

Passive transport requires no energy so moves with the gradient, not against it (active transport) so it is true

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.