Cell: The Unit of Life
1. INTRODUCTION
What makes an organism living? The answer to this is the
presence of the basic unit of life the cell in all living organisms.
2. WHAT IS
• Cell is the fun
organisms. A
All organisms are composed of cells. not ensure in
• Anton Von Le
CELL THEORY
• In 1838, Matthias Schleiden, a German botanist, examined a large number of plants and • Rudolf Virchow explained that ne
observed that all plants are composed of different kinds of cells which form the tissues of the and finally modified the cell theo
plant. At the same time. Schwann (1839) a British Zoologist, reported that animal cells had a (i) All living organisms are compos
thin layer called plasma membrane. He concluded that plant cells have cell walls. Schleiden (ii) All cells arise from pre-existing
and Schwann together formulated the cell theory but this theory did not explain as to
how-new cell are formed ?
S I
AN OVERVIEW OF CELL
H Y
while egg of an ostrich is the largest isolated single cell. Nerve cells are some of the
P
• The cytoplasm is main arena of cellular activities in both plant and animal cells. • Animal cells contain another non-
• Ribosomes are non-membrane bound organelles found in both eukaryotic & prokaryotic helps in cell division.
cells. Apart from cytoplasm, they are also found in mitochondria, chloroplast and on rough ER. • Cells that have membrane bound
L
bound nucleus called prokaryotic
A L
PROKARYOTIC CELLS
W
• Lack membrane bound cell organelles. • In addition to genomic DNA. many bacteri
called plasmids. Plasmid DNA confers cert
• Are represented by bacteria, blue green algae. Mycoplasma or PPLO
such character is resistance to antibiotics
• All prokaryotes have a ceil wall surrounding the cell membrane (except Mycoplasma) with foreign DNA.
Cell envelope & its modifications Ribosomes and In
• Most prokaryotic cells have cell envelope. which is tightly bound three layered structure.
• Ribosomes are 70S, has subunits 50S
• The outermost glycocalyx followed by cell wall and then the plasma membrane
• Glycocalyx may be a loose sheath called slime layer or thick and tough called capsule. mRNA and form a chain called polyrib
• The cell wall prevents bacteria from bursting or collapsing. • Ribosomes are associated with plasm
• Extension of plasma membrane into the cell in the form of vesicles, tubules and lamellae
• The ribosomes of a polysome transla
are mesosomes. it helps in cell wall formation. DNA replication, distribution of daughter cells
respiration, secretion process and increase the surface area of plasma membrane • Reserve material is stored in the form
• In cyanobacteria, chromatophores contain pigments. Eg. phosphate granules, cyanophyce
• Each layer of cell envelope performs distinct function, they act together as a • Gas vacuoles are found in blue green
protective unit The plasma membrane is selectively permeable in nature and Interact with
the outside world. It is structurally similar to that of eukaryotes.
1. INTRODUCTION
What makes an organism living? The answer to this is the
presence of the basic unit of life the cell in all living organisms.
2. WHAT IS
• Cell is the fun
organisms. A
All organisms are composed of cells. not ensure in
• Anton Von Le
CELL THEORY
• In 1838, Matthias Schleiden, a German botanist, examined a large number of plants and • Rudolf Virchow explained that ne
observed that all plants are composed of different kinds of cells which form the tissues of the and finally modified the cell theo
plant. At the same time. Schwann (1839) a British Zoologist, reported that animal cells had a (i) All living organisms are compos
thin layer called plasma membrane. He concluded that plant cells have cell walls. Schleiden (ii) All cells arise from pre-existing
and Schwann together formulated the cell theory but this theory did not explain as to
how-new cell are formed ?
S I
AN OVERVIEW OF CELL
H Y
while egg of an ostrich is the largest isolated single cell. Nerve cells are some of the
P
• The cytoplasm is main arena of cellular activities in both plant and animal cells. • Animal cells contain another non-
• Ribosomes are non-membrane bound organelles found in both eukaryotic & prokaryotic helps in cell division.
cells. Apart from cytoplasm, they are also found in mitochondria, chloroplast and on rough ER. • Cells that have membrane bound
L
bound nucleus called prokaryotic
A L
PROKARYOTIC CELLS
W
• Lack membrane bound cell organelles. • In addition to genomic DNA. many bacteri
called plasmids. Plasmid DNA confers cert
• Are represented by bacteria, blue green algae. Mycoplasma or PPLO
such character is resistance to antibiotics
• All prokaryotes have a ceil wall surrounding the cell membrane (except Mycoplasma) with foreign DNA.
Cell envelope & its modifications Ribosomes and In
• Most prokaryotic cells have cell envelope. which is tightly bound three layered structure.
• Ribosomes are 70S, has subunits 50S
• The outermost glycocalyx followed by cell wall and then the plasma membrane
• Glycocalyx may be a loose sheath called slime layer or thick and tough called capsule. mRNA and form a chain called polyrib
• The cell wall prevents bacteria from bursting or collapsing. • Ribosomes are associated with plasm
• Extension of plasma membrane into the cell in the form of vesicles, tubules and lamellae
• The ribosomes of a polysome transla
are mesosomes. it helps in cell wall formation. DNA replication, distribution of daughter cells
respiration, secretion process and increase the surface area of plasma membrane • Reserve material is stored in the form
• In cyanobacteria, chromatophores contain pigments. Eg. phosphate granules, cyanophyce
• Each layer of cell envelope performs distinct function, they act together as a • Gas vacuoles are found in blue green
protective unit The plasma membrane is selectively permeable in nature and Interact with
the outside world. It is structurally similar to that of eukaryotes.
