AP BIOLOGY

Detailed explanation-1: -According to the endosymbiosis theory, the host cell engulfed the bacterium, and instead of digesting it as food, it negotiated a functional relationship that enabled the host cell/endosymbiont to utilize oxygen in energy metabolism.

Detailed explanation-2: -The host animal serves as a protected environment, providing the alga with a constant supply of nutrients in the form of nitrogen, phosphorus, and sulfur. In turn, the alga provides the host with glucose.

Detailed explanation-3: -The small cells (now called endosymbionts) benefited from the relationship by getting a safe home and nutrients. The large cells (now called hosts) benefited by getting some of the organic molecules or energy released by the endosymbionts.

Detailed explanation-4: -There are two major organelles in eukaryotic organisms that have resulted from endosymbiosis, mitochondria (common to most eukaryotes) and chloroplasts (found in plants and algae only), as well as a few less obvious examples.

Detailed explanation-5: -Abstract. The endosymbiotic theory posits that some eukaryotic cell organelles, such as mitochondria and plastids, evolved from free-living prokaryotes. Available data indicate that the mitochondrial endosymbiosis initiated the evolution of the eukaryotic cell, as suggested by Margulis.