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Home >>Biology Dictionary >> Protostele - Pterodactyla Pterosauria
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Protonema.
Branched multicellular, filamentous or less commonly thalloid structure on germination of spore in member of Bryophyta from which new plants develop as buds.
Protonephridium.
Organ thought to be excretory, present in Plathyelminthes, Nemertea, Rotifera, some trochophore larvae and amphioxus; consisting of one or more flame cells, at the inner end of tubes which open to the exterior.
Protoplasm.
Substance within and including plasma membrane of a cell or protoplast but often taken to exclude large vacuoles , or masses of section, or ingested material. In animal and plants differentiated into nucles and cytoplasm.
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Protoplast.
(Bot.) The actively metabolizing part (i.e. the protoplasm) of a cell as distinct from the cell-wall. Equivalent to what zoologist means by a cell.
Protopterus.
African lung-fish (dipnoan).
Protostele.
Most simple, primitive type of stele, consisting of central core of xylem surrounded by cylinder of phloem. Includes haplostele, simplest form with xylem in form of a rod; actinostele, with xylem ribbed, appearing star-shaped in transverse section; and plectostele, with xylem in form of several longitudinal parallel strips embedded in pholem. Present in stems of certain ferns, club mosses ; almost universally in roots.
Prototherian.
Any mammal of the sub-class prototheria including the Monotremes.
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Proventricules.
(1) Anterior part of stomach of birds, where digestive enzymes are secreted: the posterior part of stomach being the gizzard.
(2) Of some invertebrates (Crustacea, Insecta) the gizzard.
Proximal.
Situated relatively near to a point of attachment or of origin.
Psued.
Denoting either false or closely resembling.
Pseudo-alleles
Alleles in the sense that they affect the same process in the organism, and involve homologous cistrons as judged by the cis-trans effect; but nevertheless, because they have originated as mutations in different parts of the cistern, show recombination by crossing-over within the cistern.
Pseudogamy.
Development of the ovum into new individual as a result of stimulation by a male gamete, whose nucleus however does not fuse with that of ovum, and contributes nothing to hereditary constitution of embryo. Occurs in some nematodes, and in some higher plants.
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Pseudopodium.
Temporary protrusion of the cell, associated with flowing movement of protoplasm, occuring in rhizopod and other protozoa, white blood cells, etc. Serves locomotion and feeding (phagocytosis). Physiology of such movement is not understood.
Psoriasis.
A non-contagious disease of the skin marked by scaly red patches, due probably to a disorder of the immune system.
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Psychrophilic.
(Of a micro-organism), with optimum temperature for growth below 20°C.
Pterodactyla (Pterosauria)
Fossil order of gliding or flying reptiles. Lived during Jurrassic and Cretaceous Membranous wings supported manily by greatly elongated fourth finger, and also by rest of arm. Many analogies in structure with birds, but independently developed, though both birds and pterodactyls evolved from the same group of non-flying reptiles.
Pteropsida.
A sub-division of the Tracheophyta including the ferns, conifers and flowering plants.
Ptyalin.
A starch-splitting enzyme of the saliva, salivary amylase of man.
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Ptyxis.
(vernation) The way in which young leaves are folded or rolled in the bud.
Puberty.
Period at which an individual begins to become sexually mature. Age between 12-15 in girls and 13-16 in boys. Secondary sexual characters appear at this age that is facial hair in boys and breast development in girls.
Pubescent.
Covered With fine hair.
Pubis
(Pubic bone). One of a pair of bones forming the anterior ventral portion of the tetrapod pelvic girdle. They are sometimes joined to form the public symphyses.
Pubic symphysis.
Joint formed mid-ventrally by the fusion between pubic bones of two halves of pelvic girdle. In most mammals, Archaeopteryx, ostrich and reptile.
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