Title CH 8_Cell_Structure_and_Functions Outdated.pdf ✅

SCIENCE Chapter 8: Cell – Structure and Functions
(1) CELL – STRUCTURE AND FUNCTIONS 08 Cell – Structure and Functions Cell as the Basic Unit of Life • The cell is the basic structural and functional unit of all living organisms. • It is the smallest part of the body of an organism, is capable of independent existence and is able to perform the essential functions of life. Discovery of the Cell • Robert Hooke observed cork cells under a simple microscope designed by him. • He observed compartments resembling honeycombs and each compartment was separated by a wall. • He termed each compartment as a ‘cell’. • It was the first indication that living organisms are made of cells. Cell Theory • In 1838, Matthias Schleiden and Theodor Schwann proposed the basic cell theory. In 1858, another scientist Virchow made an addition to the existing celltheory. • The postulates of the modern cell theory are ✓ The cell is the smallest unit of structure of all living things. ✓ The cell is the unit of function of all living things. ✓ All cells arise from pre-existing cells. Variety in Cells On the basis of the number of cells Single-celled Few-celled Multi-celled
(2) CELL – STRUCTURE AND FUNCTIONS 08 • Organisms made of a single cell. They are called unicellular organisms. • Examples: Bacteria, Yeast, Chlamydomonas, Amoeba, Paramoecium • Organisms made of a few hundred to few thousand cells. • Examples: Spirogyra, Volvox • Organisms made of millions to billions of cells. They are called multicellular organisms. • Examples: Man, cow, mango tree, crow On the basis of size of cells • Smallest cell: Examples: Bacteria (0.3–5.0 μm), red blood cells (7 μm) • Longest cell: Example: Nerve cell in the neck of a giraffe (˃3 mlong) • Largest cell: Example: Ostrich egg (170 mm × 130 mm) Smallest cell Longest cell Largest cell On the basis of shape of cells • Columnar: Epithelial cells • Spherical: Human ovum • Oval: Fat cells • Spherical, biconcave: Red blood cells • Rectangular: Spirogyra • Spiral: Sperm cell • Rod-shaped: Bacteria • C-shaped: Cartilage cells • Cylindrical: Striated muscle fibre cells • Branched: Nerve cells • Spindle-shaped: Smooth muscle cells
(3) CELL – STRUCTURE AND FUNCTIONS 08 Amoeba is irregular in shape. It changes its shape continuously due to the presence of pseudopodia. The change in shape helps Amoeba in movement and in capturing food. • Bean-shaped: Guard cell from a plantleaf • Irregular: Amoeba