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a microscopic hair-like extension of the cell membrane of the epithelial cells forming the outer layer of the villus.
single-celled organisms with all life functions performed within the cell.
a ring of muscle that controls the passage of substances through a tube or body opening.
the process whereby certain substances are removed from a liquid and others retained, due to...
animals with two cellular body wall layers: the ectoderm and endoderm.
a hormone produced by the adrenal glands which helps to maintain the balance of sodium in the...