"FUNDAMENTAL UNIT OF LIFE"
THE FUNDAMENTAL UNIT OF LIFE
Notes by:- Nagraj Sir
Cell:-it is
called the fundamental unit of life. It is capable of independent existence and
can carry out all the functions which are necessary for a living being. A cell
carries out nutrition, respiration, excretion, transportation and reproduction;
the way an individual organism does. Due to this, a cell is called the
fundamental and structural unit of life. All living beings are composed of the
basic unit of life, i.e. cell.
HISTORY OF DISCOVERY OF CELLS
• "Robert Hooke" was the first to discover cell(dead
cell) (1665).
• "Leeuwenhoek" was the first to discover free
living cells in pond water (1674).
• "Robert Brown" discovered the nucleus (1831).
• "Purkinje" coined the term ‘protoplasm (1839).
• "Schleiden" (1838) and "Schwann" (1839) proposed
the Cell Theory. "Virchow" (1855) made further addition to the cell theory.
• The discovery of electron microscope by "Max Knoll" and "Ernst Ruska" (1931)
made it possible to study the structures of cell organelles.
CELL THEORY
• All living organisms are composed of one or more cells.
• The cell is the basic unit of structure, function, and
organization in all organisms.
• All cells come from preexisting, living cells
Cell Membrane or Plasma Membrane:-Cell membrane is present in both plant and animal cells. Plasma membrane is a semi-permeable membrane.
It is living, elastic and made of proteins and lipids (fats). Its function is
to provide a mechanical barrier for the protection of the inner cell contents
from external environment and to regulate the movement of molecules in and out
of the cell by diffusion process.
Cell wall:-Cell wall is made of cellulose. it is rigid outer covering. It is
somewhat hard but permeable to most of the substances. Cell wall is available
in plant cells and in cells of bacteria and fungi.it provides shape for the
cell
Cytoplasm:-The part of the cell
between the cell membrane and the nuclear membrane is called the
cytoplasm. The cytoplasm consists of the matrix and the organelles. The
matrix is a transparent semi fluid substance. The organelles are found embedded
in the cytoplasm. They have definite shape, structure and function. All the
metabolic activities of the cell such as synthesis, secretion, digestion and
energy generation, are performed by the different cell organelles. Cell
organelles can be seen only with the help of an electron microscope
Nucleus:-This is a prominent,
spherical or oval structure found at the centre of the cell. It is the
controlling centre of all cell activities and has been described as the brain
of the cell. It regulates all metabolic and hereditary activities of the cell.
Nuclear Membrane: - This is a
double-layered membrane which separates the nucleoplasm from the cytoplasm.
Chromatin Network:- These are very
fine thread-like, coiled filaments uniformly distributed in the nucleoplasm. At
the time of cell division, the chromatin becomes thick and ribbon like and are
known as chromosomes. The chromosomes contain genes, which are composed of DNA
(deoxy-ribonucleicacid). Genes are responsible for storing and transmitting
hereditary characteristics from one generation to another. A gene is the
functional unit of a chromosome.
VARIOUS CELL ORGANELLES
ARE:-
Endoplasmic Reticulum: Endoplasmic reticulum is a mesh-like
structure which is composed of numerous tubes. It extends from the plasma
membrane to the nuclear membrane. There are two kinds of endoplasmic
reticulum,
(1)smooth ER(help in manufactured of fats molecules and lipids) and
rough ER.
(2)Rough ER has ribosomes(help in protein synthesis) on its surface which
give it the rough appearance.
Golgi Apparatus:-Also known as Golgi Complex or Golgi Bodies, they consist of
tiny, elongated, flattened sacs (cistern), which are stacked parallel to one
another along with some vacuoles and clusters of vesicles.The function of the
golgi body is to secrete certain hormones and enzymes and responsible for packaging of various
substances in the cell.. It also forms
lysosomes.The golgi body is usually found close to the nucleus.
Lysosomes:-These are tiny,
spherical, sac-like structures scattered all over the cytoplasm. Their main
function is digestion. They contain powerful destructive enzymes capable of
digesting all organic material, and hence called “digestive bags”. it present
in white blood cells are capable of digesting bacteria and viruses. During
starvation, lysosomes digest proteins, fats and glycogen in the cytoplasm, and
supply energy to the cell. They are also capable of digesting worn out cell
organelles, or even digesting the entire damaged cell containing them. Hence,it
is called as “suicide bag”.
Mitochondria:- it is a capsule-like structure. It is a double
membrane structure. Its inner membrane is projected into numerous finger-like
structures; called cristae.they are the sites of cellular respiration. After
cellular respiration, energy is stored in the form of ATP (Adenosine
triphosphate); in mitochondria). Hence, mitochondria
are termed as the “power house”of cell. Mitochondria have their own DNA and ribosomes
and hence mitochondria can produce their own protein.
Plastids:-These organelles are found only in plant cells. In 3 types:-
1)Chloroplasts- They are green and found in leaves. The green colour is due to
the presence of chlorophyll. The function of the chloroplast is to trap solar
energy for photosynthesis
2)Chromoplasts(Coloured Plastids)- They are yellow, orange and red, and found in flowers and
fruits. . Chromoplasts impart colour to flowers to attract insects for
pollination
3)Leucoplasts(Colour-less Plastids)-They are colourless and found in roots, seeds and underground
stem. Leucoplasts store food in the form of carbohydrates, fats and proteins.
Vacuoles: These are fluid filled
chambers and are often seen in many cells.They are very large in plant cells. A
plant cell usually has single but large vacuole. Vacuoles are much smaller and
very few in animal cell.
Ribosomes:-These are spherical,
granular particles which occur freely in the cytoplasm or remain attached to
the Rough ER. It contain RNA (ribonucleic acid) and proteins. Their
function is to provide the surface for protein synthesis.
Cell Division:-Cell division is the process by which a parent cell divides into two daughter cells.
Two Types :- Mitosis & Meiosis
