Biology Now: Core Edition - download pdf or read online

By Anne Houtman

ISBN-10: 0393938344

ISBN-13: 9780393938340

Written by way of a technological know-how journalist and academics with over thirty years event within the school room, Biology Now skillfully blends center biology ideas with well known technological know-how tales of genuine humans doing technology at the present time. those tales catch the human face of biology, highlighting the paintings of researchers and doctors who're making new discoveries each day. The textual content is followed through a wealth of rigorously crafted pedagogy that teaches scholars easy methods to research technology within the information, interpret facts, ask questions, and distinguish among technological know-how and pseudoscience.

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In this membrane, fibrils about 150 A thick are embedded in two crossing directions; they show no cross striation. Fibroblasts and pigment cells lie on the outside of the membrane. Micropodia of oocytes and follicle cells penetrate deeply into the basal membrane (Recourt, 1961). The substance of the basal membrane is strongly PAS-positive (Recourt, 1961). It further gives a strong reaction for tryptophan with p-dimethylaminobenzaldehyde. With toluidine blue and azure A, a metachromatic staining of the basal membrane adjacent to the oocytes occurs.

The basol2hilic staining is apparently attributable to the presence of large amounts of ribonucleoprotein. The presence of basic protein in it is indicated by an intense histidine reaction. When vitellogenesis begins, this region remains free of yolk. Its connection with the perinuclear cytoplasm becomes progressively narrower, while its peripheral part gradually extends along the surface. At the same time, many small metachromatic granules appear in it. Finally, the connection with the nucleus is broken and a layer of yolk-free cytoplasm spreads along the surface of the oocyte in apicobasal direction, but only as far as the follicular cavity reaches; it does not extend along the basal surface of the oocyte applied against the basal membrane.

The granules they contain are, on an average, somewhat smaller than the p granules in the pole plasm. In all eggs there are six SCA. They are distributed unevenly, four of them lying on one side and two on the other side of the egg; moreover, their distances from the poles of the egg differ. Together with the obliquity of the position of the vegetative pole plasm, the distribution of the SCA indicates a certain dorsoventrality of the egg structure (Raven, 1963). zdea EGG 25 visible (Fig. 7). Apparently they arise, just as the vegetative pole plasm does, during the passage of the eggs through the genital duct of the parent by a local accumulation of certain cytoplasmic constituents beneath definite parts of the cortex.

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Biology Now: Core Edition by Anne Houtman

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