Biology structure and functions

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Structure and Functions


· The basic structural unit of an organ is known as the cell.

· In 1665, Robert Hooke discovered the cell.

· A cell is a living organism.

· A human body has trillions of cells, which vary in shapes and sizes.

· The organism, which is made up of more than one cell, is known as multicellular organism.

· The single-celled organisms are known as unicellular organism. E.g. Amoeba.


· A single-celled organism performs all the essential functions that a multicellular organism performs.

· Unlike other organisms, Amoeba has no definite shape; so, it keeps on changing its shape.

· Amoeba has pseudopodia, which means – pseudo means false and podia means feet.

· Amoeba is a full-fledged organism capable of independent existence.

· Shape of the cells are normally round, spherical, or elongated.

· Protoplasm is known as the living substance of the cell.

· The cells having nuclear substances without nuclear membrane are known as prokaryotic cells. E.g. bacteria and blue green algae.

· The cells having well organized nucleus with a nuclear membrane are designated as eukaryotic cells. All multicellular organisms are eukaryotic cells.

Cell Structure and Function

· The basic parts of a cell are cell membrane, cytoplasm, and nucleus.

Human Cell

· Cell membrane is also known as the plasma membrane.

· The plasma membrane is porous and allows certain substances or materials move both inward and outward.

· The central dense round structure in the center is known as nucleus.

· The jelly-like substance between the nucleus and the cell membrane (as shown in the above image) is known as cytoplasm.

· Different organelles of cells are also present in the cytoplasm such as Mitochondria, Golgi bodies, Ribosomes, etc.

· Located in central part, nucleus is almost in spherical shape.

· Nucleus is separated from the cytoplasm by a porous membrane known as the nuclear membrane.

· The smaller and spherical structure, found inside the nucleus, is known as nucleolus.

· Nucleus contains thread-like structures known as chromosomes.

· Chromosomes carry genes and help in inheriting the characteristics of the parents to the offspring.

· Gene is a fundamental unit of inheritance in living organisms.

· The entire constituents of a living cell are known as protoplasm, which include nucleus and cytoplasm.

Plant Cell

· The cell membrane provides shape to the cells of plants and animals.

· In plant cell, cell wall is an additional covering over the cell membrane.

· An animal cell does not have cell wall.

· Cell wall gives shape and rigidity to plant cells.

· Cell wall gives protection, plant cells need protection against varying temperature, high wind speed, atmospheric moisture, etc.

· Bacterial cell also has a cell wall.

· Usually, most of the cells are microscopic in size and are not visible to the naked eye.

· The size of smallest cell is 0.1 to 0.5 micrometer found in bacteria.

· The size of largest cell is 170 mm × 130 mm, found in the egg of an ostrich.

· The size of the cells however has no relation with the size of the body of the animal or plant.

· Some small colored bodies in the cytoplasm of the cells of Tradescantia leaf are known as plastids.

· Plastids are found in different colors.

· Some plastids have green pigment and known as chlorophyll.

· Green colored plastids are known as chloroplasts.

· Chloroplasts give green color to the leaves.

· Chlorophyll is essential for the photosynthesis.