Title Chapter - 1 The_Fundamental_Unit_of_Life.pdf ✅

The Fundamental Unit of Life Cells are the basic structural and functional unit of life. Cell was discovered by Robert Hooke. A number of cells can work together to form tissues and organs. History of Cell ● The cell is the basic structural and functional unit of all living organisms. It is the smallest part of the body of an organism which is capable of independent existence and is able to perform all the essential functions of life. ● The history of cell science began in 1665, with the observation of a thin section of bottle cork by the English scientist Robert Hooke. ● In 1838, Matthias Schleiden and Theodor Schwann proposed a basic cell theory. In 1858, another scientist, Virchow, made an addition to the existing cell theory. ● 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. ● Cells vary in number. Examples: Single-celled Amoeba, few-celled Spirogyra and multi- celled human being. They vary in size. Examples: Bacteria are the smallest, nerve cells are the longest and the ostrich egg is the largest. They vary in shape. Example: Columnar epithelial cells. Cellular respiration Cellular respiration is the process by which the food releases energy in the mitochondria. Cells absorb glucose from the food and burn it to produce energy. Structural Organization of Cells Prokaryotic & Eukaryotic cells Two types of cells Prokaryotic and Eukaryotic cells. Prokaryotic cells are primitive and lack well defined nucleus. Eukaryotic cells are more advanced and have well defined nucleus. Cell structure in Eukaryotic cells Eukaryotic cells have the most well-defined structure. These cells have cell membrane, membrane bound cell organelles and a well-defined nucleus. The nucleus has its own membrane called nuclear membrane.
ChemContent Cell membrane ● Cell membrane is the outer covering of a cell. ● It is made up of phospho-lipid bilayer membrane. ● It is selectively permeable in nature. ● The structure of a cell membrane is best described by the fluid mosaic model. Diffusion The movement of molecules from a region of their high concentration to a region of their lower concentration is known as diffusion. Osmosis in selectively permeable membrane Osmosis is the movement of water across a semi-permeable membrane. Osmosis is a selective process since the membrane does not allow all molecules to pass through it. Water is usually the only free flowing molecule across this membrane. Isotonic, hypotonic solutions, hypertonic solutions ● Isotonic solutions are those which have the same solute and pH concentration as the surrounding body fluid or the cytoplasm. ● Hypotonic solutions contain lesser amount of solute concentration compared to the surrounding fluid and can force the cell to rupture due to excess input of water into the cell. ● Hypertonic solutions contain higher concentration of solute compared to the surrounding fluid and thus push water out of cell, shrinking it. Types of Organisms Cell walls in plants Plant cells are different from animals cells due to the presence of a cell wall. The cell wall is made of cellulose and gives a rigid structure to the plant cell. Cell Organelles ● Endocytosis: Endocytosis is the invagination of cell membrane, followed by pinching off forming a membrane bound vesicle. This is commonly seen in Amoeba. ● Nucleus in cells: Nucleus is the processing unit of the cell. It is a double membrane bound organelle which contains the genetic material for inheritance. ● Chromosomes: During the growth phase of the cell, the chromatin condenses into a much thicker structure called chromosome.

ChemContent Differences between Prokaryotic and Eukaryotic Cells Eukaryotic Cell The term “Eukaryotes” is derived from the Greek word “eu“, (meaning: good) and “karyon” (meaning: kernel), therefore, translating to “good or true nuclei.” Eukaryotes are more complex and much larger than the prokaryotes. They include almost all the major kingdoms except kingdom monera. Structurally, eukaryotes possess a cell wall, which supports and protects the plasma membrane. The cell is surrounded by the plasma membrane and it controls the entry and exit of certain substances.