Friday, 29 March 2019
Thursday, 28 March 2019
Wednesday, 13 March 2019
Saturday, 9 March 2019
Thursday, 28 February 2019
Chapter 1 Cell (class 8 NCERT science)
Cell was discovered by Robert hooke in 1665.
He observed slices of cork under a simple magnifying device. cork is a part of the bark of tree.
He took thin slices of cork and observe them under a microscope he noticed partitioned boxes or compartment in the cork slice.
Amoeba is a single cell that has no definite shape like other organisms , it keeps on changing its shape it is due to formation of pseudopodia which facilities movement and help in capturing food.
Pseudopodia means false feet.
For example -
WBC in human blood is a type of single cell which change its shape but amoeba is also a single cell but it is a full fledged organism capable of independent existence.
Membrane provides shape to the cell of plants and animals.
Cell wall is found in the plants which are made up of cellulose it gives shape and rigidity to these cells bacteria also have cell wall.
The smallest cell is 0.1 to 0.5 micrometre in bacteria.
The largest cell measuring 170 mm into 130 mm is the egg of an ostrich.
Cell membrane -
The basic component of cell or cell membrane, cytoplasm and nucleus the cytoplasm and nucleus are enclosed within the cell membrane also called plasma membrane. the membrane separates cell from one another and also the cell from the surrounding medium.
the plasma membrane is a porous and allows the movement of substance or materials both inward and outward.
Cytoplasm
it is the jelly like substance present between the cell membrane and nucleus various other components are organelles of cells are present in the cytoplasm these organelles are mitochondria Golgi bodies ribosomes lysosomes centrosome ribosome etc.
Nucleus
Nucleus is an important component of the cell it is also called brain of cell.
it is generally spherical and located in the centre of the cell it can be stained and seen easily with the help of microscope.
nucleus is separated from the cytoplasm by a membrane called nuclear membrane.
this membrane is also porus and allows the movement of materials between the cytoplasm and inside of nucleus.
with the microscope of higher magnification we can see a small spherical body in the nucleus it is called nucleolus.
in addition, nucleus contains thread like structure called chromosomes they carry genes and help in inheritance or transfer of character from parents to the offsprings.
The chromosome can be seen only when the cell divides.
The entire content of a cell is known as protoplasm it was discovered by purkinje.
It includes cytoplasm and nucleus protoplasm is called the living substance of cell.
Large vacuole is found in plants and smaller vacuoles is found in animal cells.
Coloured body is called plastids are found in the plant cells only green plastic container chlorophyll are called chloroplast.
He observed slices of cork under a simple magnifying device. cork is a part of the bark of tree.
He took thin slices of cork and observe them under a microscope he noticed partitioned boxes or compartment in the cork slice.
Amoeba is a single cell that has no definite shape like other organisms , it keeps on changing its shape it is due to formation of pseudopodia which facilities movement and help in capturing food.
Pseudopodia means false feet.
For example -
WBC in human blood is a type of single cell which change its shape but amoeba is also a single cell but it is a full fledged organism capable of independent existence.
Membrane provides shape to the cell of plants and animals.
Cell wall is found in the plants which are made up of cellulose it gives shape and rigidity to these cells bacteria also have cell wall.
The smallest cell is 0.1 to 0.5 micrometre in bacteria.
The largest cell measuring 170 mm into 130 mm is the egg of an ostrich.
Cell membrane -
The basic component of cell or cell membrane, cytoplasm and nucleus the cytoplasm and nucleus are enclosed within the cell membrane also called plasma membrane. the membrane separates cell from one another and also the cell from the surrounding medium.
the plasma membrane is a porous and allows the movement of substance or materials both inward and outward.
Cytoplasm
it is the jelly like substance present between the cell membrane and nucleus various other components are organelles of cells are present in the cytoplasm these organelles are mitochondria Golgi bodies ribosomes lysosomes centrosome ribosome etc.
Nucleus
Nucleus is an important component of the cell it is also called brain of cell.
it is generally spherical and located in the centre of the cell it can be stained and seen easily with the help of microscope.
nucleus is separated from the cytoplasm by a membrane called nuclear membrane.
this membrane is also porus and allows the movement of materials between the cytoplasm and inside of nucleus.
with the microscope of higher magnification we can see a small spherical body in the nucleus it is called nucleolus.
in addition, nucleus contains thread like structure called chromosomes they carry genes and help in inheritance or transfer of character from parents to the offsprings.
The chromosome can be seen only when the cell divides.
The entire content of a cell is known as protoplasm it was discovered by purkinje.
It includes cytoplasm and nucleus protoplasm is called the living substance of cell.
Large vacuole is found in plants and smaller vacuoles is found in animal cells.
Coloured body is called plastids are found in the plant cells only green plastic container chlorophyll are called chloroplast.
Subscribe to:
Posts (Atom)
