CELL THEORY AND FUNCTION
The work of three Scientist botanist Mattias Scleiden, Theodor Schwann and Rudolph Virchow claimed
that plant and roots, animal are made of cells and that cells come only from other cells. Cells are the
smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and
reproducing. All living things are composed of cells. Their claims form the basic cell theory which is
made of three parts
a. All living things are made of one or more cells
b. Cells are the basic units of structure and function in organisms
c. All cells arise from existing cells
Protoplasm: This is the content of the cells including the nucleus, Cytoplasm is the cell content without
the nucleus. (cytoplasm + nucleus = protoplasm) cytoplasm= cytosol, organelles, vesicles & cytoskeleton
Cell is capable of surviving and replicating itself, the cell content differs in various ways from those
outside the cells. The cell content also mixes freely with the environment by diffusion and the differences
could not be maintained. The barrier is a very thin membrane.
Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a
single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells
working in concert. But whether it makes up an entire bacterium or is just one of trillions in a human
being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions
each minute and reproduce new cells that perpetuate life.
A Eukaryote is an organism whose cell has a nucleus. The nucleus is an internal compartment that houses
the cell’s DNA (Haeckel established that the nucleus was responsible for storing and transmitting
hereditary characters). Other internal compartments, or organelles, enable eukaryotic cells to function in
ways different from prokaryotes (single celled organism, cannot carry out specialized function, simple and
small, cause infection and food spoilage eg bacteria).
Cell size and Shape
Cells vary considerably in size. The smallest cell, a type of bacterium known as a mycoplasma, measures
0.0001 mm in diameter; 10,000 mycoplasmas in a row are only as wide as the diameter of a human hair.
Among the largest cells are the nerve cells that run down a giraffe’s neck; these cells can exceed 3 m in
length. Human cells also display a variety of sizes, from small red blood cells that measure 0.00076 mm to
liver cells that may be ten times larger. Along with their differences in size, cells present an array of
shapes. Some, such as the bacterium Escherichia coli, resemble rods. The paramecium, a type of
protozoan, is slipper shaped; and the amoeba, another protozoan, has an irregular form that changes shape
as it moves around. In humans, the outermost layers of skin cells are flat, while muscle cells are long and
thin. Some nerve cells, with their elongated, tentacle-like extensions, suggest an octopus.
In multicellular organisms, shape is typically tailored to the cell’s job. For example, flat skin cells pack
tightly into a layer that protects the underlying tissues from invasion by bacteria. Long, thin muscle cells
contract readily to move bones. The numerous extensions from a nerve cell enable it to connect to several
other nerve cells in order to send and receive messages rapidly and efficiently.
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, Functions: Each cell is a model of independence and self-containment. Cell carrys out the business of
living. Despite their individuality, however, cells also display a remarkable ability to join, communicate,
and coordinate with other cells. The human body, for example, consists of an estimated 20 to 30 trillion
cells. Dozens of different kinds of cells are organized into specialized groups called tissues. Tendons and
bones, for example, are composed of connective tissue, whereas skin and mucous membranes are built
from epithelial tissue. Different tissue types are assembled into organs, which are structures specialized to
perform particular functions. Examples of organs include the heart, stomach, and brain. Organs, in turn,
are organized into systems such as the circulatory, digestive, or nervous systems. All together, these
assembled organ systems form the human body.
Cell component: The components of cells are molecules, nonliving structures formed by the union of
atoms. Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids,
carbohydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell
structure and also participate in cell functions.
The organelles, membrane-bound compartments in cells, are built largely from proteins. Biochemical
reactions in cells are guided by enzymes, specialized proteins that speed up chemical reactions. The
nucleic acid deoxyribonucleic acid (DNA) contains the hereditary information for cells, and another
nucleic acid, ribonucleic acid (RNA), works with DNA to build the thousands of proteins the cell needs.
Organelle Structure and Function
Animal Cell
An animal cell typically contains several types of membrane-bound organs, or organelles. The nucleus
directs activities of the cell and carries genetic information from generation to generation. The
mitochondria generate energy for the cell. Proteins are manufactured by ribosomes, which are bound to
the rough endoplasmic reticulum or float free in the cytoplasm. The Golgi apparatus modifies, packages,
and distributes proteins while lysosomes store enzymes for digesting food. The entire cell is wrapped in a
lipid membrane that selectively permits materials to pass in and out of the cytoplasm.
Organisms are composed of cells, and these cells have specific structures within in them that allow them
to carry out their functions. These structures are called Organelles. Organelles perform different functions
within a cell, and this is called the Division of Labour.
Membrane Bound Organelles
An Organelle is a structure that carries out specific activities in the cell.
The Nucleus is the largest organelle in a cell. It contains a dense structure called the Nucleolus and is
surrounded by the Nuclear Envelope, a structure composed of two membranes, seperated by fluid, which
contain a number of nuclear pores that can allow relatively large molecules through. The nucleus contains
nearly all of the cell's genetic material. The Nucleolus creates Ribonucleic Acid and Ribosomes, which
then travel out of the nucleus, through the nuclear pores, to the cytoplasm where they are involved
in Protein Synthesis.
Lysosomes are membrane bound spherical sacs which contain digestive enzymes used to break down
materials, such as non-self microorganisms engulfed by Phagocytes.
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The work of three Scientist botanist Mattias Scleiden, Theodor Schwann and Rudolph Virchow claimed
that plant and roots, animal are made of cells and that cells come only from other cells. Cells are the
smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and
reproducing. All living things are composed of cells. Their claims form the basic cell theory which is
made of three parts
a. All living things are made of one or more cells
b. Cells are the basic units of structure and function in organisms
c. All cells arise from existing cells
Protoplasm: This is the content of the cells including the nucleus, Cytoplasm is the cell content without
the nucleus. (cytoplasm + nucleus = protoplasm) cytoplasm= cytosol, organelles, vesicles & cytoskeleton
Cell is capable of surviving and replicating itself, the cell content differs in various ways from those
outside the cells. The cell content also mixes freely with the environment by diffusion and the differences
could not be maintained. The barrier is a very thin membrane.
Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a
single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells
working in concert. But whether it makes up an entire bacterium or is just one of trillions in a human
being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions
each minute and reproduce new cells that perpetuate life.
A Eukaryote is an organism whose cell has a nucleus. The nucleus is an internal compartment that houses
the cell’s DNA (Haeckel established that the nucleus was responsible for storing and transmitting
hereditary characters). Other internal compartments, or organelles, enable eukaryotic cells to function in
ways different from prokaryotes (single celled organism, cannot carry out specialized function, simple and
small, cause infection and food spoilage eg bacteria).
Cell size and Shape
Cells vary considerably in size. The smallest cell, a type of bacterium known as a mycoplasma, measures
0.0001 mm in diameter; 10,000 mycoplasmas in a row are only as wide as the diameter of a human hair.
Among the largest cells are the nerve cells that run down a giraffe’s neck; these cells can exceed 3 m in
length. Human cells also display a variety of sizes, from small red blood cells that measure 0.00076 mm to
liver cells that may be ten times larger. Along with their differences in size, cells present an array of
shapes. Some, such as the bacterium Escherichia coli, resemble rods. The paramecium, a type of
protozoan, is slipper shaped; and the amoeba, another protozoan, has an irregular form that changes shape
as it moves around. In humans, the outermost layers of skin cells are flat, while muscle cells are long and
thin. Some nerve cells, with their elongated, tentacle-like extensions, suggest an octopus.
In multicellular organisms, shape is typically tailored to the cell’s job. For example, flat skin cells pack
tightly into a layer that protects the underlying tissues from invasion by bacteria. Long, thin muscle cells
contract readily to move bones. The numerous extensions from a nerve cell enable it to connect to several
other nerve cells in order to send and receive messages rapidly and efficiently.
1
, Functions: Each cell is a model of independence and self-containment. Cell carrys out the business of
living. Despite their individuality, however, cells also display a remarkable ability to join, communicate,
and coordinate with other cells. The human body, for example, consists of an estimated 20 to 30 trillion
cells. Dozens of different kinds of cells are organized into specialized groups called tissues. Tendons and
bones, for example, are composed of connective tissue, whereas skin and mucous membranes are built
from epithelial tissue. Different tissue types are assembled into organs, which are structures specialized to
perform particular functions. Examples of organs include the heart, stomach, and brain. Organs, in turn,
are organized into systems such as the circulatory, digestive, or nervous systems. All together, these
assembled organ systems form the human body.
Cell component: The components of cells are molecules, nonliving structures formed by the union of
atoms. Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids,
carbohydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell
structure and also participate in cell functions.
The organelles, membrane-bound compartments in cells, are built largely from proteins. Biochemical
reactions in cells are guided by enzymes, specialized proteins that speed up chemical reactions. The
nucleic acid deoxyribonucleic acid (DNA) contains the hereditary information for cells, and another
nucleic acid, ribonucleic acid (RNA), works with DNA to build the thousands of proteins the cell needs.
Organelle Structure and Function
Animal Cell
An animal cell typically contains several types of membrane-bound organs, or organelles. The nucleus
directs activities of the cell and carries genetic information from generation to generation. The
mitochondria generate energy for the cell. Proteins are manufactured by ribosomes, which are bound to
the rough endoplasmic reticulum or float free in the cytoplasm. The Golgi apparatus modifies, packages,
and distributes proteins while lysosomes store enzymes for digesting food. The entire cell is wrapped in a
lipid membrane that selectively permits materials to pass in and out of the cytoplasm.
Organisms are composed of cells, and these cells have specific structures within in them that allow them
to carry out their functions. These structures are called Organelles. Organelles perform different functions
within a cell, and this is called the Division of Labour.
Membrane Bound Organelles
An Organelle is a structure that carries out specific activities in the cell.
The Nucleus is the largest organelle in a cell. It contains a dense structure called the Nucleolus and is
surrounded by the Nuclear Envelope, a structure composed of two membranes, seperated by fluid, which
contain a number of nuclear pores that can allow relatively large molecules through. The nucleus contains
nearly all of the cell's genetic material. The Nucleolus creates Ribonucleic Acid and Ribosomes, which
then travel out of the nucleus, through the nuclear pores, to the cytoplasm where they are involved
in Protein Synthesis.
Lysosomes are membrane bound spherical sacs which contain digestive enzymes used to break down
materials, such as non-self microorganisms engulfed by Phagocytes.
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