Categories:

• Earth and the Environment
  • Atmosphere and Weather
  • Biographies
  • Ecology and Environmentalism
  • Geography
  • Geology and Oceanography
  • Minerals, Mining, and Metallurgy
• History
  • Ancient Greece and Rome
  • Asia and Africa
  • Australia, New Zealand, and the Pacific
  • Biographies
  • Historians and Chronicles
  • Latin America and the Caribbean
  • Modern Europe
  • United States and Canada
• Literature and the Arts
  • Art and Architecture
  • Biographies
  • Classical Literature, Mythology, and Folklore
  • Fashion, Design, and Crafts
  • Journalism and Publishing
  • Language, Linguistics, and Literary Terms
  • Literature in English
  • Literature in Other Modern Languages
  • Performing Arts
  • Scholars and Historians
• Medicine
  • Anatomy and Physiology
  • Biographies
  • Diseases and Conditions
  • Divisions, Diagnostics, and Procedures
  • Drugs
  • Psychology
• People
  • History
  • Literature and the Arts
  • Medicine
  • Philosophy and Religion
  • Science and Technology
  • Social Sciences and the Law
  • Sports and Games
• Philosophy and Religion
  • Ancient Religions
  • Biographies
  • Christianity
  • Eastern Religions
  • Islam
  • Judaism
  • Other Religious Beliefs and General Terms
  • Philosophy
  • The Bible
• Places
  • Africa
  • Asia
  • Australia and Oceania
  • Britain, Ireland, France, and the Low Countries
  • Commonwealth of Independent States and the Baltic Nations
  • Germany, Scandinavia, and Central Europe
  • Latin America and the Caribbean
  • Oceans, Continents, and Polar Regions
  • Spain, Portugal, Italy, Greece, and the Balkans
  • United States and Canada
• Plants and Animals
  • Agriculture and Horticulture
  • Animals
  • Biographies
  • Botany
  • Microbes, Algae, and Fungi
  • Plants
  • Zoology and Veterinary Medicine
• Science and Technology
  • Astronomy and Space Exploration
  • Biochemistry
  • Biographies
  • Biology and Genetics
  • Chemistry
  • Computers and Electrical Engineering
  • Mathematics
  • Physics
  • Technology
• Social Sciences and the Law
  • Anthropology and Archaeology
  • Biographies
  • Economics, Business, and Labor
  • Education
  • Law
  • Political Science and Government
  • Sociology and Social Reform
• Sports and Everyday Life
  • Biographies
  • Crafts and Household Items
  • Days and Holidays
  • Fashion and Clothing
  • Food and Drink
  • Games
  • Manners and Customs
  • Social Organizations
  • Sports

Documents for "Cell Biology":

• cell in biology, the unit of structure and function of which all plants and animals are composed. The cell is the smallest unit in the living organism that is capable of integrating the essential life...

• cell division see cell ; mitosis ; meiosis.

• centriole see mitosis.

• cyclosis streaming of cytoplasm within a living cell without deformation of the external cell membrane. In some plant cells there is a rapid rotatory cytoplasmic movement, which is limited to the...

• cytokinesis see mitosis.

• cytology in biology, the study of the structure of all normal and abnormal components of cells and the changes, movements, and transformations of such components. The discipline includes cytogenics,...

• cytoplasm see protoplasm.

• ectoderm layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endoderm , or inner layer, is present in all early embryos. In the development of animals of the phyla Porifera , Ctenophora , and Cnidaria , these two primary layers give rise to all the tissues and organs of the animals, a process known as diploblastic development. In higher animals, such as those of the phyla Echinodermata and Chordata , a third, middle layer, the mesoderm , is formed between the ectoderm and endoderm during gastrulation, and the process is termed triploblastic development. In most embryos, differentiation of ectodermal tissue gives rise to epidermis...

• egg see ovum.

• embryo name for the developing young of an animal or plant. In its widest definition, the embryo is the young from the moment of fertilization until it has become structurally complete and able to survive as a separate organism. Embryology, the scientific study of embryonic development, deals with the period from fertilization until the...

• endocytosis in biology, process by which substances are taken into the cell. When the cell membrane comes into contact with a suitable food, a portion of the cell cytoplasm surges forward to meet and surround the material and a depression forms within the cell wall. The depression deepens and the...

• endoderm in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball. Cell...

• meiosis process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells ( ovum and sperm ), are being formed. Because fertilization consists of the fusion of two separate nuclei, one from each of the sex cells, meiosis is necessary to prevent the doubling of the chromosome number in each successive generation. An ordinary body...

• membrane structure composed mostly of lipid and protein that forms the external boundary of cells and of major structures within cells. Membrane organization is based on a sheet two molecules thick—a double layer of lipids aligned with their long hydrocarbon tails tucked inside—studded with...

• mesoderm in biology, middle layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball. Continued...

• mitochondria see cell.

• mitosis process of nuclear division in a living cell by which the carriers of hereditary information, or the chromosomes , are exactly replicated and the two copies distributed to identical daughter nuclei. Mitosis is almost always accompanied by cell division (cytokinesis), and the latter is sometimes considered a...

• molecular biology scientific study of the molecular basis of life processes, including cellular respiration, excretion, and reproduction. The term molecular biology was coined in 1938 by Warren Weaver, then director...

• nucleolus see cell.

• nucleus see cell , in biology.

• ovum in biology, specialized plant or animal sex cell, also called the egg, or egg cell. It is the female sex cell, or female gamete; the male gamete is the sperm. The study of the ovum is included in...

• phagocytosis see endocytosis.

• pinocytosis see endocytosis.

• protoplasm term once used for the fundamental material of which all living things were thought to be composed. It was studied by a number of early scientists, especially by Félix Dujardin, J. E. Purkinje, M...

• ribosome see cell ; nucleic acid.

• sperm or spermatozoon , in biology, the male gamete (sex cell), corresponding to the female ovum in organisms that reproduce sexually. In higher animals the sperm is produced in the testis of the male; it is much smaller than the ovum and consists primarily of a head, whose nucleus bears the...

• spermatozoon see sperm.

• tissue in biology, aggregation of cells that are similar in form and function and the intercellular substances produced by them. The fundamental tissues in animals are epithelial, nerve, connective, and...