The Animal Cell All the tissues and organs of the body originate from a microscopic structure the fertilized ovumwhich consists of a soft jelly-like material enclosed in a membrane and containing a vesicle or small spherical body inside which are one or more denser spots. This may be regarded as a complete cell. All the solid tissues consist largely of cells essentially similar to it in nature but differing in external form.
Anatomy of the Human Body. The Ovum The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries. Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being.
The ovum is enclosed within a thick, transparent envelope, the zona striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata.
The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. See enlarged image Yolk.
In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourishing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout the whole period of incubation.
The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole.
A centrosome and centriole are present and lie in the immediate neighborhood of the nucleus.
Its structure is that of an ordinary cell-nucleus, viz. The nucleus is enclosed by a delicate nuclear membrane, and contains in its interior a well-defined nucleolus or germinal spot. It persists for some time after fertilization has occurred, and may serve for protection during the earlier stages of segmentation.
It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both. The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum.The cell is the fundamental structural unit of all living organisms.
Some cells are complete organisms, such as the unicellular bacteria and protozoa; others, such as nerve, liver, and muscle cells, are specialized components of multi-cellular organisms.
Cell theory Outline the cell theory.. The cell theory states that: All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of many cells while unicellular organisms (example: bacteria) are composed of only one cell. Shake Shack is coming to the Bay Area next month with new menu.
A comprehensive, coeducational Catholic High school Diocese of Wollongong - Albion Park Act Justly, love tenderly and walk humbly with your God Micah The Parts Of A Living Cell Biology Essay The karyon contains the cellular cistrons in the signifier of chromatin, which is a type of complex mixture made up of proteins and DNA.
Chromatin forms chromosomes during a procedure known as mitosis. Read this essay on The Living Cell Biology. Come browse our large digital warehouse of free sample essays.
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