In 1966, american biologist lynn margulis proposed the theory of endosymbiosis, or the idea that mitochondria are the descendants of symbiotic, aerobic eubacteria. what does the theory of endosymbiosis explain?

Its explain why mitochondria in animals and plastids in plants have its own DNA and double membrane. The theory postulates that this is due to a symbiotic relationship that began with the history of life when protists probably engulfed bacteria (most probably by phagocytosis). The bacteria offered energy while it was sheltered. The relationship evolved to become facultative.

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.

It should be cryosphere and hydrosphere