GK gneral knowledge general science Biology introduction
GK gneral knowledge general science Biology introduction Biology is the branch of science which is based on the study of the life . Biology gives the information of evolution of life and their facts.
BIOLOGY (bios=life, logos=study) is a science related to the study of living oraganisms. Today there are numerous branches of biology.
BRANCHES OF BIOLOGY- Botany, Zoology, Microbiology, Biochemistry, Genetics, Physiology, Anatomy
Cell Concept cell was discovered by Robert Hooke (1665),cell theory was proposed by Schleiden and Schwann(1838-1839)according to which all living organism are composed of cell and new cell is formed from pre-existing cells.
Cells– Tissues – organs – organ system – individual
Cell Shape There are various types of shapes in cell. For instance some bacteria are rod-shaped, spirals or even comma-shaped. Muscles cells are cylindrical and long. Some cells like Amoeba and leucytes change their shapes frequently hence, do not have exact shape.
Cell size Cell size (diameter) varies greatly in various plants and animals.
The smallest cells are found as mycplasma (cell diameter 0.2-5.0 u). The largest cell is the egg of an ostrich (6 inches in diameter around the outside).
Cell Number The Cell number also varies from a single cell in a unicellular organism to 60 thousand billion cells in a human being weighing about 80kg.
Prokaryotic Cells and Eukaryotic Cells The terms Prokaryote and Eukaryote refer to differences in the location of the genetic material with in the cell. In prokaryotes, the nucleus is not enclosed by nuclear membrances and lies free in the cytoplasm. These cells, therefore , lack true nucleus. The cells of Eukaryotes, however do contain true(well organized)nucleus.
Prokaryotes, e.g.- Bacteria , blue-green algae.
Eukaryotes, e.g. -Higher plants and animals.
The cell is absent but cell is enclosed by a plasma membrane. Centriole is present. Plastids is absent. Vacuoles are either small or absent. Lysosomes are present more in number. Cytoplasm during cell division divides by furrowing or cleavage method.
Cell wall is present. Centriole is absent. Plastids are present. A mature cell has a large central vacuole. Lysosomes are present less number. Cytoplasm usually divides by cell plate method.