UNIT – III ANIMAL DIVERSITY AND HUMAN NEEDS
ANIMAL CELL
An animal cell is a type of eukaryotic cell that lacks a cell wall and has a
true, membrane-bound nucleus along with other cellular organelles.
Animal cells range in size from a few microscopic microns to a few
millimetres. The largest known animal cell is the ostrich egg, which can
stretch over 5.1 inches across and weighs about 1.4 kilograms. This is in
stark contrast to the neuron in the human body, which is just 100
microns across.
The shape of animal cells also varies, with some being flat, others oval or
rod-shaped. There are also more intriguing shapes such as curved,
spherical, concave and rectangular. Most of the cells are microscopic in
size and can only be seen under the microscope.
As stated before, animal cells are eukaryotic cells with a membrane-
bound nucleus. Furthermore, these cells exhibit the presence of DNA
inside the nucleus. They also comprise other membrane-bound
organelles and cellular structures which carry out specific functions
necessary for a cell to function properly.
ANIMAL CELL DIAGRAM
, ANIMAL CELL STRUCTURE
Animal cells are generally smaller than plant cells. Another defining
characteristic is its irregular shape. This is due to the absence of a cell
wall. But animal cells share other cellular organelles with plant cells as
both have evolved from eukaryotic cells.
A typical animal cell comprises the following cell organelles:
Cell Membrane
A thin semipermeable membrane layer of lipids and proteins
surrounding the cell. Its primary role is to protect the cell from its
surrounding. Also, it controls the entry and exit of nutrients and other
microscopic entities into the cell. For this reason, cell membranes are
known as semi-permeable or selectively permeable membranes.
Nucleus
It is an organelle that contains several other sub-organelles such as
nucleolus, nucleosomes and chromatins. It also contains DNA and other
genetic materials.
Nuclear Membrane
It is a double-membrane structure that surrounds the nucleus. It is also
referred to as the nuclear envelope.
Centrosome
It is a small organelle found near the nucleus, which has a thick centre
with radiating tubules. The centrosomes are where microtubules are
produced.
Lysosome
They are round organelles surrounded by a membrane and comprising
digestive enzymes which help in digestion, excretion and in the cell
renewal process.
, Cytoplasm
A jelly-like material which contains all the cell organelles, enclosed
within the cell membrane. The substance found within the cell nucleus,
contained by the nuclear membrane is called the nucleoplasm.
Golgi Apparatus
A flat, smooth layered, sac-like organelle which is located near the
nucleus and involved in manufacturing, storing, packing and transporting
the particles throughout the cell.
Mitochondrion
They are spherical or rod-shaped organelles with a double membrane.
They are the powerhouse of a cell as they play an important role in
releasing energy.
Ribosome
They are small organelles made up of RNA-rich cytoplasmic granules,
and they are the sites of protein synthesis.
Endoplasmic Reticulum (ER)
This cellular organelle is composed of a thin, winding network of
membranous sacs originating from the nucleus.
Vacuole
A membrane-bound organelle present inside a cell involved in
maintaining shape and storing water, food, wastes, etc.
Nucleopore
They are tiny holes present in the nuclear membrane which are involved
in the movement of nucleic acids and proteins across the nuclear
membrane.
ANIMAL CELL
An animal cell is a type of eukaryotic cell that lacks a cell wall and has a
true, membrane-bound nucleus along with other cellular organelles.
Animal cells range in size from a few microscopic microns to a few
millimetres. The largest known animal cell is the ostrich egg, which can
stretch over 5.1 inches across and weighs about 1.4 kilograms. This is in
stark contrast to the neuron in the human body, which is just 100
microns across.
The shape of animal cells also varies, with some being flat, others oval or
rod-shaped. There are also more intriguing shapes such as curved,
spherical, concave and rectangular. Most of the cells are microscopic in
size and can only be seen under the microscope.
As stated before, animal cells are eukaryotic cells with a membrane-
bound nucleus. Furthermore, these cells exhibit the presence of DNA
inside the nucleus. They also comprise other membrane-bound
organelles and cellular structures which carry out specific functions
necessary for a cell to function properly.
ANIMAL CELL DIAGRAM
, ANIMAL CELL STRUCTURE
Animal cells are generally smaller than plant cells. Another defining
characteristic is its irregular shape. This is due to the absence of a cell
wall. But animal cells share other cellular organelles with plant cells as
both have evolved from eukaryotic cells.
A typical animal cell comprises the following cell organelles:
Cell Membrane
A thin semipermeable membrane layer of lipids and proteins
surrounding the cell. Its primary role is to protect the cell from its
surrounding. Also, it controls the entry and exit of nutrients and other
microscopic entities into the cell. For this reason, cell membranes are
known as semi-permeable or selectively permeable membranes.
Nucleus
It is an organelle that contains several other sub-organelles such as
nucleolus, nucleosomes and chromatins. It also contains DNA and other
genetic materials.
Nuclear Membrane
It is a double-membrane structure that surrounds the nucleus. It is also
referred to as the nuclear envelope.
Centrosome
It is a small organelle found near the nucleus, which has a thick centre
with radiating tubules. The centrosomes are where microtubules are
produced.
Lysosome
They are round organelles surrounded by a membrane and comprising
digestive enzymes which help in digestion, excretion and in the cell
renewal process.
, Cytoplasm
A jelly-like material which contains all the cell organelles, enclosed
within the cell membrane. The substance found within the cell nucleus,
contained by the nuclear membrane is called the nucleoplasm.
Golgi Apparatus
A flat, smooth layered, sac-like organelle which is located near the
nucleus and involved in manufacturing, storing, packing and transporting
the particles throughout the cell.
Mitochondrion
They are spherical or rod-shaped organelles with a double membrane.
They are the powerhouse of a cell as they play an important role in
releasing energy.
Ribosome
They are small organelles made up of RNA-rich cytoplasmic granules,
and they are the sites of protein synthesis.
Endoplasmic Reticulum (ER)
This cellular organelle is composed of a thin, winding network of
membranous sacs originating from the nucleus.
Vacuole
A membrane-bound organelle present inside a cell involved in
maintaining shape and storing water, food, wastes, etc.
Nucleopore
They are tiny holes present in the nuclear membrane which are involved
in the movement of nucleic acids and proteins across the nuclear
membrane.
