Epicotyl
bryos, during which the region occupied by cells of the animal half of the blastula expands over the vegetal half. In amphibians the cells migrate and roll under through the BLASTOPORE, the vegetal cells remaining as just a plug filling the blastopore. EpiCOTYL. Upper portion of the axis of an embryo or seedling, above the cotyledons and below the 'next leaf or leaves. Compare hypocotyl Epidemic. Large-scale temporary increase in prevalence of a disease due to a parasite or some health-related...
Active Transport
trical potential between the inside and outside of a nerve or muscle cell or fibre which marks the position of an impulse as it travels alongthecell. See impulse, activation. Action spectrum. Plot of the quanta of different wavelengths required for a photochemical response against the wavelength of light used. Its reciprocal indicates photochemical efficiency. Activated sludge. Material consisting largely of bacteria and protozoa, used in and produced by one method of sewage disposal. Sewage is...
Cell Division
Extracellular maxtrix glycocalyx Extracellular maxtrix glycocalyx Free ribosomes .Ce w Tonoplast Capsule Cell wall Cytoplasmic Cytoplasm with membrane ribosomes Inclusion body lipid, starch, metapolyphosphate, or sulphur Capsule Cell wall Cytoplasmic Cytoplasm with membrane ribosomes Inclusion body lipid, starch, metapolyphosphate, or sulphur Nucleoid Mesosome Periplasmic no membrane space Granule of poly-j8-hydroxybutyric acid Fig. 3a amp b. Generalized eukaryotic structure a of animal cell...
Development Of Cleidoic Eggs In Amoeba
membranes occur within it during development. See cleidoic Amoeba. Genus of sarcodine protozoans. Single-celled animals of irregular and protean shape, moving and feeding by use of p se u d o -pod i a. Some slime mould cells are also loosely termed 'amoebae', , while any cell locomotion resembling an amoeba's is termed 'amoeboid'. 1 Amoebocyte. Cell haemocyte capable of active amoeboid locomotion found in blood and other body fluids of invertebrates in sponges, an amoeboid cell type implicated...
Cyclostomes
Cyanophycean starch. A storage polysaccharide found in cells of the cyan oBacter ia considered to be amylopectin. Cyanophycin granule. A protein storage body found in the cells Cycadofilicales Pteridospermae . Order of extinct, palaeozoic gymnophytes that flourished mainly during the Carboniferous. Of great phylogenetic interest. Reproduced by seeds, but with fern-like leaves internal .anatomy combined fern-like vascular system with development of secondary wood. Micro- and mega-sporophylls...
Plankton
bergmann'S rule., States. that in geographically variable species of HOMQIOTHERMI c animals, body size tends to be larger in cooler regions of a species range. See ALLEN s R u LE BErry. Many-seeded ' succulent fruit, in 'which the wall pericarp consists of an outer skin epicarp enclosing a thick fleshy mesocarp and inner membranous endocarp, as in gooseberry, currant, tomato. Compare drupe. Beta-blocker. Substance, such as the drug propanolol, selectively blocking beta receptors. Clinical use...
Corm
waste products from cells. Dinofiagellates have a similar but more complex structure, called a pusule, which may have a similar function. control, controlled experiment. see experiment. Convergence convergent evqlution . The increasing resemblance over time of distinct evolutionary lineages, in one or perhaps several phenotypic respects, increasing their phenetic similarity but generally without associated genetic convergence. Usually interpreted as indicating similar selection pressures in...
Info Ngd
Beta receptor. adrenergic receptor sites associated with adenylate cyclase in appropriate postsynaptic membranes, but not identical with it binding preferentially to adrenaline rather than noradrenaline. Heart muscle has beta receptors predominantly which result in 'increased heart rate and blood pressure when stimulated other beta effects include dilation of arterioles supplying skeletal muscle, bronchial relaxation and relaxation of the uterus. All these effects are mimicked by the synthetic...
Cell Wall
Cell theory. The theory, first proposed by Schwann in 1839, that organic structure originates through formation and differentiation of units, the cells, by whose divisions and associations the complex bodies of organisms are formed. Much of the original theory is now untenable. Schleiden's name is also associated with the theory. See VtfcCHOW. Cellular jmmuwty And CELLULAR RESPONSE. See IMMUNITY. Cellulose. The most abundant organic polymer. A polysaccharide, occurring as the major structural...
Binomial Nomenclature
germination to seed production and death. In the first season, biennials store up food which is used in the second season to produce flowers and seed. Examples include carrot and cabbage. Compare Bilateralcleavage. Old term for radial cleavage. See cleavage. Bilateral symmetry. Property of most metazoans, having just one plane in which they can be separated into two halves, approximately mirror images of one' another. This is usually the antero-posterior and dorso-ventral plane, separating left...
Info Gmr
by the occurrence of one or more evolutionary novelties apomor-phies . Any character found in two or more taxa is homologous in them if their most recent common ancestor also had it. Such a shared homologue may be symplesiomorphous or -morphic in these taxa if it is believed to have originated as a novelty in a common ancestor earlier than the most recent common ancestor, but synupomorphous -morphic if not. homoplasy occurs between characters that share structural aspects but are thought to...
Info Veg
and in others retroviruses it is reverse-transcribed into DNA. tRNA molecules fold back upon themselves by complementary base-pairing to form double-stranded 'stems' and single-stranded 'loops'. A loop at one end bears a specific nucleotide triplet the anticodon while the 3'-end of the molecule carries a t RNA-specific amino acid both essential for protein synthesis to proceed by means of a GENETIC code. Ribosomal RNA subunits associate with protein molecules to form ribosomes. All tRNA and...
Crinoidea
emerge from the spinal cord, Dorsal and ventral roots of nerves from several segments are involved, but unlike those of spinal nerves these remain separate. Each root is numbered and named as a separate nerve numbering bears little 'relation to segmentation, but does to the relative posteriority of emergence. There are 10 pairs of cranial nerves in anamniotes 11 or 12 pairs in amniotes. Nerves I and II olfactory and optic nerves are largely sensory III oculomotor innervates four of the six eye...
Penguin Reference 3doks
Michael Abercrombie took a degree in Zoology at Oxford. and t heirbegan research work at CiBhiiiie Later he- taught in the Zoology Uepartmem. ffirm-_ ingnam University. He was Professor of ISibryoiogy and then Professor of Zoology a University Coileas London, and from 1970 TO 1979- was Director of the Strangewavs Research Laooraiory, Cambridge. He ' efeetect a_Fefe gt wia_f_the RovaLSocietyJ-a.-1958-Ljl and awarded an honorary doctorate-bv the Umver-shy of Uppsala in 1977. He died in May 1979-...
Cardioacceleratory And Cardioinhibitory Centres
Carboxylase. Enzyme fixing carbon - dioxide or transferring C00 groups. Important carboxylases occur in both respiration and photosynthesis. CARBOXYPEPTIDASE CARBOXYPOLYPEPTIDASE . Pancreatic enzyme, digesting peptides to-amino acids. Carboxysome. Structure in some bacteria e.g. chemoautotrophic Thiobacillus , housing the CO,-fixing enzyme ribulose-1,5, bisphosphate carboxylase. CARCINOGEN. Any factor' resulting in transformation of a normal cell into a CANCER cell. The ames test assesses...
Info Lav
with basal body . They occur at right angles to each other near the nucleus, separating at cell division amd organizing the spindle microtubules which arise from material surrounding the centriole, but possibly in turn organized by it . Centrioles generally arise at right angles to existing centrioles. Normally an animal obtains its centrioles from the sperm cell at fertilization rarely, an egg may form its own see parthenogenesis . Centrioles possess their own DNA and appear to be...
Carnivora
Carotene. Yellow or orange pigments found in the chloroplasts of plant cells. See carotenoids . Carotenoids. Group of yellow, orange and red plant pigments located in chloroplasts and plastids in parts of plant where chlorophyll is absent e.g. carrot roots, many flowers also in photosyn-thetic lamellae of blue-green algae Cyanobacteria , in some bacteria and some fungi. Increase in concentration in many ripening fruits, e.g. tomato. Not essential to photosynthesis, but serve as accessory...
Development Of Bisporic Embryo Sac
development of enzyme technology in industry and medicine, and of gene manipulation, often in the service of plant and animal breeding. Together, these constitute biomolecular engineering. Branches include fermentation technology, waste technology e.g. recovery of metals from mining waste and renewable resources technology, such as the use of lignocellulose to generate more usable energy sources. Organisms involved tend to be microorganisms, and their traditional involvement in the brewing,...
Penguin Books
Published by the Penguin Group Penguin Books Ltd, 27 Wrights Lane, London W85TZ, England Penguin Books USA Inc., 375 Hudson Street, New York, New York 10014, USA Penguin Books Australia Ltd, Ringwood, Victoria, Australia Penguin Books Canada Ltd, 2801 John Street Markham, Ontario, Canada L3R 1 B4 Penguin Books NZ Ltd, 182-190 Wairau Road, Auckland 10, New Zealand Penguin Books Ltd, Registered Offices Harmondsworth, Middlesex, England ' First published as The Penguin Dictionary of Biology, 1951...
Apparatus
Acid rain. Rainfall precipitation with a pH less than 5.6. Rain dissolves carbon dioxide, forming carbonic acid, giving it a normal pH of 5.6, but lower pHs result as it dissolves atmospheric pollutants such as oxides of nitrogen and sulphur dioxide. Some acid rain results from effects of atmospheric ozone production, some natural and some attributable to human activity. Its most serious consequence is the release of cations from the soil resulting in leaching. In the case of Mg ions this leads...
Aleuroplast
in contrast to metabolically inactive cells of most of the endosperm lt . containing aleurone grains, several hydrolytic enzymes and reserves of phytin releasing inorganic phosphate and inositol on digestion by phytase . During germination, aleurone cells secrete a-amylase into . the endosperm, initiating its digestion. Recent work suggests that the synthesis of enzymes by aleurone cells may not, be as specifically induced by gibberellins from the embryo axis as was once thought, although...