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PHYSIOLOGY OF THE CELL The cell is the basic fundamental, morphological and physiological unit of living beings.

It consists of protoplasm which is surrounded by a delicate membrane and consists of various microscopic and even smaller structures.

The protoplasm consists of a large amount of water and a large number of substances suspended in it.

A mass called a nucleus is present in the centre. The protoplasm inside the nucleus is called a nucleoplasm and the protoplasm outside the membrane is called as cytoplasm.

Various organelles present in cytoplasm are : I) Endoplasmic Reticulum II) Mitochondria III) Golgi Apparatus IV) Lysosomes V) Microtubules

CHARACTERISTICS OF A CELL a) Assimilation of nourishment b) Growth and repair c) Reproduction d) Excretion

PLASMA MEMBRANE This is a living membrane which forms the outermost layer of the cell that separates the cell from the external environment. STRUCTURE It consists of double layer of lipid molecules embedded with proteins in it. Two types of proteins• Lipoproteins (proteins containing lipids) • Glycoproteins (proteins containing carbohydrates) Each phosholipid is composed of two ends.

I. Hydrophilic II. Hydrophobic The hydrophilic ends of the phospholipids molecules face each other while the hydrophilic ends lie on the outer surface facing the proteins.

FUNCTIONS a) Protective – It forms a protective layer around the cell. b) It exists as barrier which separates the internal structures of cell from the external environment. c) Semipermeable membrane – It acts as a semipermeable membrane allowing selective passage of substances in and out of cell. d) It links adjacent cells. e) Digestive – It takes in food and excretes waste products.

GOLGI APPARATUS This exists as stack of flattened sacs of cisternae which is bounded by a membrane which has a smooth surface and these flattened cells are surrounded by vesicles of various shape and size. FUNCTIONS a) Storage b) Condensation c) Packaging d) Transfer of various materials. e) It is also involved in the formation of glycoprotein. f) Some enzymes are also located in golgi bodies. MITOCHONDRIA These exist as granular, rod shaped or filamentous bodies which remain disperse throughout the cytoplasm. STRUCTURE z It is surrounded by two membranes, the outer and inner membrane. z The inner membrane exists as folding called as cristae. z Outer membrane consists of enzymes z Inner membrane also consists of number of particles known as elementary particles. z MATRIX – is present inside of mitochondria and is concerned with citric acid cycle. FUNCTIONS a) Power house of the cell, as it supplies almost all of the energy. b) Most of the enzymes used in Krebs cycle are located in the inner membrane of mitochondria. c) Mitochondria produce energy rich ATP molecules.

LYSOSOMES Lysosomes are the cell inclusions which are surrounded by a membrane of lipoprotein and consist of a large number of digestive enzymes. CLASSIFICATION z z z z

Primary lysosomes – Produced by Golgi apparatus. Secondary lysosomes – Consists of material to be digested along with enzyme already present in it. Residual body – Consist of large number of digested and undigested particles. Autophagic vacoules – Consist of intracellular organs.

FUNCTIONS a) Vital role in intracellular and extracellular digestion. b) Under some conditions they provide nutrition by scavenging of intracellular organelles (Called as suicidal bags).

NUCLEUS Nucleus is the largest organelle present in the cell. STRUCTURE z Spherical structure z Separated from the cytoplasm with help of a double membrane called as nuclear-membrane. z Nuclear pores – Large number of openings in it called as nuclear pores. z Nucleoli – Structures made up of protein, DNA and RNA. z Made up of chromosomes FUNCTIONS a) Maintenance of cell. b) Replication of cell. c) Control the cytoplasmic activity.