Sample Material of Our Online Coaching Programme
Subject: General Science
What is Cell?
All living organisms on earth are divided in pieces called
cells. Cells are small compartments that hold all of the biolo-gical equipments
necessary to keep organisms. Cells carry out all the basic functions of life:
growth, metabolism and reproduction.
There are some organisms like amoeba consists of a single
cell. This single cell increase in size and when it attains a certain size, it
divides into two separates individuals. In case of multi cellular organisms, the
cell also divides into two parts, but the two parts remaining joined this
process is repeated crore of times so that body mass is built up. In this
process some cells become specialized to perform specific functions but other
retains their capacity for cell division throughout life.
Who Gave the Cell Theory?
The term cell was coined by Robert Hooke in 1665. In 1838
Matthias Schleiden, German botanist proposed the idea that all plants consists
of cells. In 1839, The Eodor Schwann a German zoologist asserted that all plant
and animals are made up of cells. This finding forms the basis of cell theory.
Components of Cell?
In the living organisms there are two types of cellular
organizations. If we look at very simple organisms like bacteria and blue-green
algae, We will discover cells that have no defined nucleus, these are
prokaryotes cells. The cells which have definite nucleus are known as eukaryote.
But the things which both have in common is that there are compartments
surrounded by some type of membranes. These are called cell membranes.
Cell membranes : It is like a plastic bag with some
tiny holes that bag holds all of the cell pieces and fluids inside the cell and
keeps foreign particles outside the cell. The holes are there to let some things
move in and out of the cell. Compounds called proteins and phospholipids make up
most of the cell membranes. the phospholipids make the basic bag. The proteins
are found around the holes and help move molecules in and out of the cell.
Substances like Co2 and O2 can move across the cell membranes by a process
called diffusion. Diffusion is a process of movements of substance from a region
of high concentration to a region where its concentration is low. Water also
obeys the law of diffusion. The movement of water molecules is called osmosis.
Cytoplasm : It is the fluid that fills a cell. Scientists
used to call the fluid proto plasm.cytoplasm contain many specialized cell
called organ cells. Each of these organ cells performs a specific function for