The basic structural and functional unit of an organism
The basic structural and functional unit of an organism is called cell. Cells are like bricks that are assembled to make a building. Similarly, cells are assembled to make the body of every organism. This is why cell are called the basic structural and functional unit of an organism. Discovery of cell:
Robert Hooke in 1665 observed slices of cork (a part of the bark of a tree) under a simple magnifying device. He Robert Hooke observed under a microscope there are many partitioned boxes or compartments like a honeycomb. Hooke coined the term ‘cell’ for each box.
A hen’s egg can be seen easily. Is it a cell or a group of cells?
It is a single cell. A white blood cell (WBC) in human blood is another example of a single cell.
How do scientists observe and study the living cells?
Scientists used microscopes which magnify objects. Stains (dyes) are used to colour parts of the cell to study the detailed structure.
Kinds of organism: Organisms which are made up of a single cell are called unicellular where as Organisms made up of more than one cell is called multicellular.
Cell Theory : Cell Theory was elaborated by a German botanist Schleiden and Zoologist Schwann
The Cell Theory states that:
1) All organisms are made up of one or more cells and the products of those cells.
2) All cells carry out life activities ( require energy, grow, have a limited size).
3) New cells arise only from other living cells by the process of cell division.
Tissue: The group of cells that are similar in structure and functions is called tissue. like nervous tissue in animal and Vascular tissue in plant.
Cells have different shape of Cells according to function they perform in body:
Generally, cells are round, spherical or elongated (red blood) . Some cells are long and pointed at both ends. They exhibit spindle shape (muscle cells) . Cells sometimes are quite long. Some are branched like the nerve cell or a neuron. Guard cell in leaves are kidney shaped. White blood cells change their shape and move like amoeba.
Which part of the cell gives it shape?
Cell membrane provides shape to the cells of plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to cells.
The size of cells in living organisms may vary . The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich. Nerve cell is the longest cell and blood cells are the smallest cell in our body
Protoplasm: The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.
Plasma membrane: The cytoplasm and nucleus are enclosed within the cell membrane together called the plasma membrane.
Cell membrane: The outer boundary of the cell is the cell membrane. It is composed of proteins and carbohydrates.
Functions of Cell membrane: The cell membrane gives shape to the cell. The cell membrane separates cells from one another and also the cell from the surrounding medium. The cell membrane is porous and allows the movement of substances or materials both inward and outward. This is why it is called selectively permeable membrane.
Cell wall: There is also another thick additional covering of animal cell called the cell wall. This is because plant cell need protection against variations in temperature, high wind speed, atmospheric moisture, etc.
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