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Home >>Biology Dictionary >> Cranial Nerves - Cycadales
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Coxa. The first segment, attached to the thorax, of an insect’s leg. See also femur, trochanter.
Cranial nerves. Ten to twelve pairs of nerves in vertebrates that emerge directly from the brain. They supply the sense organs and muscles of the head, neck, and viscera. Example of cranial nerves include the optic nerve (II) and the vagus nerve (X). With the spinal nerves, the cranial nerves form an important part of the peripheral nervous system.
Cranita Vertebrata.
Cranium. (brain case) The part of the vertebrate skull that encloses and protects the brain. It is formed by the fusion of several flattened bones, which have immovable joints (sutures) between them.
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Critical Group. Group of related organisms in which, though variations exist, it is difficult to detect and define units suitable for taxonomic recognition.
Crocodilia.
Alligators and crocodiles. An order of Reptilia, with internal openings of the nose far back in the mouth owing to the presence of a long bony far back in the mouth owing to the presence of a long bony false palate (as in mammals).
Crista.
The structure formed by folding of the inner mitochondrial membrane. The extent and nature of the folding varies, active cells having complex and closely packed crista, less active cells having fewer and less complex cristae. The surface of cristae is covered with stalked particles (respiratory granules) that contain the oxidative enzymes (e.g. ATPase and the cytochromes).
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Crop. An enlarged and modified part of the oesophagus where food may be kept for a time before passing on to the gizzard or stomach as for example in insects, leeches and birds, etc.
Cross. Act or product of cross-fertilization.
Cross-fertilization. Fusion of male and female gametes derived from different individuals of the same species.
Crossing over. The exchange of material between homologous chromatics by the formation of chiasmata, also chiasma.
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Crustacea. A class of arthropods with more than 4 pairs of legs; body divided into cephalothyorax and abdomena, compound eyes, respiration with gills; including prawsn, lobsters, shrimps, crabs, crayfish, barnacles and hermit crabs, etc.
Cryophytes. Plants growing on ice and snow; micro-plants, largely consisting of algae but including also some mosses, fungi, and bacteria.
Cusp. Projection on biting – surface of mammalian molar tooth.
Cross-over value (C.O.V).
Frequency of crossing over between tow genes in different parts of the same chromosome, expressed as percentage of gametes in which one of the two genes have been exchanged for an allele from the homologous chromosomes.
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Cuticle. It is the outer protective covering formed by epidermis.
Cuticle transpiration. The transpiration occurring through leaf is called cuticle transpiration.
Culture medium. It consists of a mixture of nutrients which may be used in liquid form or solidified with the help of agar. Such a medium is used to cultivate micro-organisms like bacteria.
Cybernetics. Self control and maintenance of living organisms.
Cycadales.
Order of Gymnispermate with fossil (Mesozic), and a few living representatives. Most primitive living seed plants. Indigenous to tropical and sub-tropical zones; living to a great age, up to 1000 years. Stem unbranched, tuberous or columnar, up to 20 metres in height, bearing a crown or fern-like leaves Dioecious. Microsporophylls distinct form vegetative leaves, arranged in a compact cone. Megasporophylls leaf-like structures, loosely grouped, or highly modified, grouped in a compact cone. Male gametes motile by cilia.
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Cycadofilicales. (Pteridospermae). Order of extinct, palaeozoic Gymnospermae that flourished particularly during the Carboniferous. Of great phylogenetic interest. Reproducing by seeds but possessing fern-like leaves and internal anatomy combining ferm like vascular system with development of secondary wood. Micro and Megasporophylls little different from ordinary vegetative fronds, not arranged in cones.
Cyclic AMP. A derivative of ATP that is widespread in animals cells as an intermediate messenger in many biochemical reactions induced by hormones. Upon reaching their target cells, the hormones activate the enzyme that catalyses cyclic AMP production. Cyclic AMP ultimately activates the enzymes of the reaction induced by the hormone concerned. Cyclic AMP is also involved in controlling gene expression and cell division, in immune responses, and in nervous transmission.
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