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May 17, 2024 · metabolism, the sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material. Living organisms are unique in that they can extract energy from their environments and use it to carry out activities such as movement, growth and development ...
May 6, 2024 · carbohydrate, class of naturally occurring compounds and derivatives formed from them. In the early part of the 19th century, substances such as wood, starch, and linen were found to be composed mainly of molecules containing atoms of carbon (C), hydrogen (H), and oxygen (O) and to have the general formula C 6 H 12 O 6; other organic molecules ...
Apr 23, 2024 · algae, members of a group of predominantly aquatic photosynthetic organisms of the kingdom Protista. Algae have many types of life cycles, and they range in size from microscopic Micromonas species to giant kelps that reach 60 metres (200 feet) in length. Their photosynthetic pigments are more varied than those of plants, and their cells have ...
5 days ago · Cancer, group of numerous distinct diseases that are characterized by the uncontrolled multiplication of abnormal cells in the body. Cancer is a major cause of sickness and death worldwide. Learn more about the history of cancer, cancer rates and trends, and the causes, diagnosis, and treatment of cancer.
May 18, 2024 · Sleep, a normal, reversible, recurrent state of reduced responsiveness to external stimulation that is accompanied by complex and predictable changes in physiology. Sleep contrasts with wakefulness, in which state there is an enhanced potential for sensitivity and an efficient responsiveness to external stimuli.
May 10, 2024 · tree, woody plant that regularly renews its growth ( perennial ). Most plants classified as trees have a single self-supporting trunk containing woody tissues, and in most species the trunk produces secondary limbs, called branches. To many, the word tree evokes images of such ancient, powerful, and majestic structures as oaks and sequoias, the ...
Apr 29, 2024 · mammal, (class Mammalia), any member of the group of vertebrate animals in which the young are nourished with milk from special mammary glands of the mother. In addition to these characteristic milk glands, mammals are distinguished by several other unique features. Hair is a typical mammalian feature, although in many whales it has disappeared ...
