An Overview of Cell
* Cell is the fundamental unit of life in all living organisms.
* Modern cell theory states that:
• Living organisms are composed of cells and products of cells.
• Cells arise from pre-existing cells.
* The plant cell is surrounded by a cell wall on the outside and a plasma membrane on the inside.
* Plant and animal cells contain a spherical structure called the nucleus, which contains thread-like structures called chromosomes.
* If the nucleus is membrane-bound, then the cell is called an eukaryotic cell.
* Cells without a membrane –bound nucleus are called prokaryotic cells.
* Eukaryotic cells contain membrane –bound organelles such as:
• Endoplasmic reticulum
• Golgi complex
• Lysosomes
• Mitochondira
• Microbodies
• Vacuoles
• Ribosomes
* The cytoplasm of prokaryotic cells is embedded only with ribosomes and plasmids.
* Cells can be disc-like, polygonal, columnar, cuboid or thread-like.
The Cell Membrane
* The cell membrane is composed of lipids, proteins and carbohydrates.
* Lipids are arranged in a bilayer, with the charged polar head of both layers pointing
* outward and the non-polar, hydrophobic tail made of saturated hydrocarbons pointing inward.
* The Fluid Mosaic Model put forth by Singer and Nicolsan states that lipids are found in the form of a fluid bilayer.
* Substances get transported across the cell membrane either through passive transport or through active transport.
* Cilia and flagella are hair-like structures projecting from the cell’s surface.
The Endomembrane System
* The Endoplasmic reticulum,Golgi apparatus , Lysosomes and Vacuoles are referred to as an endomembrane system.
* The Endoplasmic reticulum is a network or reticulum of tiny tubular structures.
* The Golgi apparatus consist of a series of flat, disc-shaped sacs or cisternae stacked one above the other.
* The Golgi apparatus acta as a packaging and forwarding centre and is an important site for the formation of glycoproteins and glycolipids.
* Lysosomes are single-membrane vesicular structures formed during the packaging process in the Golgi apparatus.
* Vacuoles are enveloped in a membrane called the tonoplast and contain water, sap, excretory products and other materials not useful for the cell.
Ribososmes, Mitochondria and Plastids
* Ribosomes are granular and non- membrane–bound structures composed of RNA and proteins.
* Mitochondria, called the “Powerhouse of the Cell” are sites of aerobic respiration and produce cellular energy in the form of ATP.
* The membranes of mitochondria divide its lumen into the outer compartment and the inner compartment called the matrix.
* Plastids, the largest double-membrane –bound cytoplasmic organelles, contain different pigments that impart specific colours to plants.
* On the basis of the pigments they possess, plastids can be classified as chloroplasts, chromoplasts and leucoplasts.
* Based on the type of nutrient stores, leuocoplasts can be classified as amyloplasts, elaioplasts and aleuroplasts.