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In the United Kingdom, an unseen examination is an essay test in school or college, where the student does not know what questions are going to be asked in advance. [ 1 ] [ 2 ] The student is required to answer questions based upon what they have learned over the course of their academic study.
The definition of life has long been a challenge for scientists and philosophers. [ 2 ] [ 3 ] [ 4 ] This is partially because life is a process, not a substance. [ 5 ] [ 6 ] [ 7 ] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth.
Life appears to have adapted to the universe, and not vice versa. Some applications of the anthropic principle have been criticized as an argument by lack of imagination, for tacitly assuming that carbon compounds and water are the only possible chemistry of life (sometimes called "carbon chauvinism"; see also alternative biochemistry). [76]
Biology is the overall natural science that studies life, with the other life sciences as its sub-disciplines. Some life sciences focus on a specific type of organism. For example, zoology is the study of animals, while botany is the study of plants. Other life sciences focus on aspects common to all or many life forms, such as anatomy and ...
Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acid DNA and RNA for the mechanisms of heredity. Any successful theory of abiogenesis must explain the origins and ...
Like water and ammonia, liquid hydrogen fluoride supports an acid–base chemistry. Using a solvent system definition of acidity and basicity, nitric acid functions as a base when it is added to liquid HF. [70] However, hydrogen fluoride is cosmically rare, unlike water, ammonia, and methane. [71]
Chemistry is the scientific study of the properties and behavior of matter. [1] It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances.
Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. [1] A sub-discipline of both chemistry and biology , biochemistry may be divided into three fields: structural biology , enzymology , and metabolism .