PREVIOUS YEAR QUESTION ‘+ Cell wall is found in the cells of plants, which is made vp of cellulose.(64" BPSC] ‘+ Mitochondria range from 0.5 to 1.0 u in diameter. ‘These structures are sometimes described as 'the powerhouse of the cell’ as they generate energy through respiration.{65”-67™ BPSC] NCERT FACTS ‘+ The basic structural unit of an organ is known as the cell. ‘+ In 1665, Robert Hooke discovered the cell. ‘© Acellisa living organism. ‘+A human body has trilions 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. ‘+ Example- Amoeba ‘+ Assingle-celled organism performs all the essential functions that a multicellular organism performs. ‘+ Unlike other organisms, Amosba 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 rouné, spherical, oF elongated. ‘+ Protoplasm is known as the living substance of the call, ‘+ The cells having nuclear substances without nuclear membrane are known as prokaryotic cells. Eg. 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 (as shown in the above image) is known as cytoplasm. ‘+ Different organelles of cells are also present in the cytoplasm such as Mitochondria, Golgt bodies, Ribosomes, etc. ‘+ Located in central part, nucleus is almost in spherical shape. + Nucleusis 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's @ fundamental unit of inheritance in living organisms. ‘+The entire constituents of a living cell are known asprotoplasm, which inchide 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.Animal cell spi ‘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 hasa 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. In 1674, Leeuwenhoek, with the help of developed microscope, discovered the free living cells in pond water In 1831, Robert Brown had discovered the nucleus in the cell, + In 1839, Purkinje used the term ‘protoplasm’ forthe fluid substance found in the cell + The cell theory was proposed by Schleiden (1838) and Schwann (1839), * According to the cell theory, all the plants and animals are composed of cells and that the cells the basic unit of life + In 1855, Virchow further expanded the cell theory and suggested that all cells arise from pre-existing calls. * In 1940, the discovery of electron microscope made possible to observe and understand the complex structure ofthe cell * The single cellular organisms, such as Amoeba, Chlamydomonas, Poramoecium, and bacteria, are known as unicellular organisms. The organisms consisting of many cells are known as multicellular organisms. Eg. human being, animals, birds, ete Significant Characteristics of Cells ‘Each living cell has the aptitude to perform certain basic functions that are characteristic of all living forms. © Each such cell has certain specific components within it known as cell organelles * Different types of cells have different function and each cell organelle performs a special function. © These organelles collectively constitute the basicunit. of life known as cell + Ail cells are found to have the same organelles, irrespective of their different functions and the ‘organism they found Structural Organization of Cell ‘* Following are the three basic features that every cell possesses ~ ‘Plasma Membrane/Cell Membrane © Nucleus © cytoplasm