primitive and non primitive unit cells

The enlargement of the blastodermic vesicle is followed by the detachment of some cells from the inner cell mass. The detached cells are pushed into the blastocoel to form the embryonal endoderm or hypoblast. These cells rapidly increase in number to constitu..

. Such type of unit cells in which particles are present only in the corners are called Simple Unit Cells . But it has been observed that the particles may also be present at some other special positions within the unit cell. Such uni..

. The five-kingdom classification gives a clear indication of cellular organization and modes of nutrition, the characters which appeared very early in the evolution of life. However, the five-kingdom classification has certain drawbacks also, particularly with reference to the lower forms of life...

has established fourteen different types of lattices called Bravais lattices according to the arrangement of the points in the different unit cells involved. These are listed below:..

Organic Evolution - Chemical evolution resulted in the formation of life on earth about 3.8 billion years ago. The primitive cells that resulted from this process gradually gave rise to primitive forms of organisms such as bacteria, algae, fungi and protozoan. These or..

The first photosynthetic organism probably appeared almost three billion years ago. With the evolution of photosynthesis, however, organisms began to change the face of our planet and, as a consequence, to exert strong influences on each other. Organisms have continued to change the environment, at..

show a primitive type of sexual reproduction called genetic recombination. Conjugating Bacteria In this process, the exchange of genetic materials takes place by a process called conjugation . Conjugating bacterial cells are in contact through a hollow tube called pilus. ..

According to the modified cell principle, new cells arise only from pre-existing cells. Cells transfer their genetic information only by way of cell division. The mode of cell division is largely the same in all living organisms in..

Summary - Earth is said to have been formed about4.8 billion years ago. Earliest earth was a hot revolving ball of gas. The formation of first cells in planet earth is explained by the theory of chemical evolution proposed by Oparin and Haldane, independently. According to this theory, th..

Pteridophytes - The division Pteridophyta includes a group of primitive vascular plants, commonly called pteridophytes. The adult plant body in these plants is a sporophyte. It shows differentiation into true roots, stem and leaves. The stem is mostly herbaceous . Leaves may be smaller or..