Describe the levels of cellular organization in an animal, and explain how organs work together as a system.

Humans—and other complex multicellular organisms—have systems of organs that work together, carrying out processes that keep us alive.

The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems.

The function of an organ system depends on the integrated activity of its organs. For instance, digestive system organs cooperate to process food.

The survival of the organism depends on the integrated activity of all the organ systems, often coordinated by the endocrine and nervous systems.

Explanation:

the truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey.

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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