CBSE Class 8 Science Chapter 8 Cell – Structure and Functions
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The cell can be described as the basic unit of life. Every organ, nerve, and bone in an organism is made up of groups of these cells. These cells decide how an organism looks, functions, and behaves. The word cell comes from the Latin word cella, which means a small room.
Features of cell:
▪ A cell is the smallest structural, functional and biological unit of life in all living organisms.
▪ All organisms are made of cells and cell products.
▪ Most of the cells are so small in size that they cannot be seen by naked eye.
▪ Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometers.
▪ The smallest cell is that of a PPLO (a bacterium).
▪ The egg of an ostrich is the largest cell on earth.
▪ The size and shape of a cell are different for different organisms.
▪ Organisms are classified as –
Unicellular – Consisting of a single cell. Example – bacteria.
Multicellular – Consisting of many cells that form complex structures. Example – plants, and animals.
▪ A cell can replicate independently i.e., it can divide itself into multiple new cells. This process is called cell division.
▪ Cells are made up of functional membrane-bound units called organelles.
▪ Cells of all organisms have the same kind of organelles.
▪ Amoeba is capable of changing shape with the help of pseudopodia.
▪ WBC’s in humans also show the same feature.
Cell Structure and Functions
Some of the cells have a simple structure and some are complex, but all cells essentially contain three basic parts. They are:
▪ Cell envelope, that contains:
▪ Cell membrane: It protects cell content and controls exit and entry of materials from the cell.
▪ Cell wall: It help plants to withstand changes in the outside environment without bursting
▪ It is the control center of a cell.
▪ It contains chromosomes made up of DNA and protein.
▪ It contains functional segments of DNA called genes, which are responsible for
the transmission of hereditary characters.
▪ The nucleolus is seen inside the nucleus.
▪ Nuclear membrane has pores for the exchange of material with the cytoplasm.
▪ It is the fluid content present inside the plasma membrane.
▪ Protoplasm + Cell organelles = Cytoplasm