Ssc Biology Chapter 2 Hand Note Exclusive -

SSC Biology Chapter 2: Cells and Tissues (Hand Note) 1. The Cell (Introduction)

Definition: The cell is the structural and functional unit of life. It is the smallest living entity capable of carrying out all life processes. Discovery: Robert Hooke (1665) observed a thin slice of cork under a self-made microscope and coined the term "Cell" (meaning little room in Latin). Cell Theory: Proposed by Schleiden and Schwann (1839).

Main postulates:

All living organisms are composed of one or more cells. The cell is the basic unit of structure and organization in organisms. All cells arise from pre-existing cells (proposed by Rudolf Virchow). ssc biology chapter 2 hand note exclusive

2. Structure of a Typical Cell A cell consists of three main parts: Cell Membrane, Cytoplasm, and Nucleus. A. Cell Membrane (Plasma Membrane)

Definition: The thin, elastic, and semi-permeable outer covering of the cell that separates the cell content from the external environment. Structure: Composed of a Phospholipid Bilayer with embedded proteins (Fluid Mosaic Model). Function:

Gives shape to the cell. Controls the entry and exit of substances (Selective permeability). Protects the cell organelles. SSC Biology Chapter 2: Cells and Tissues (Hand Note) 1

B. Cytoplasm

Definition: The semi-fluid, transparent, jelly-like substance enclosed by the cell membrane, excluding the nucleus. Composition: 70-90% water, proteins, carbohydrates, lipids, and salts. Function: It houses the cell organelles and is the site of many metabolic reactions (glycolysis).

C. Cell Organelles (Key Organelles) 1. Mitochondria (The Powerhouse) Discovery: Robert Hooke (1665) observed a thin slice

Structure: Double membrane-bound; inner membrane forms folds called cristae (increases surface area). Contains its own DNA. Function: Produces energy (ATP) through cellular respiration. Known as the "Powerhouse of the cell."

2. Plastids (Found only in Plant Cells)