Cell Structure and Functions

Cell Structure and Functions

Introduction

• 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.
• 

Amoeba

• 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.

• 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 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.