cell

BIOLOGY

INTRODUCTION TO CELL!!

CELL…..CELLS are the fundamental structural units of living organisms and basic units of life. It performs all life functions like nutrition, excretion, metabolism, respiration, etc. It is atiny mass of protoplasm which is surrounded by a membrane and is capable of performing all functions of life.

DISCOVERY OF A CELL

LeeuwenhoekPurkinje

VirchowRobert H

ooke Schleiden

Schwann

In 1665, Robert Hooke-an English scientist ,saw cells for the first time in a thin slice of cork. He observed them as “Honey Comb” like structures and named them “cellulae” or “cells”(little room).

In 1674, A. Van Leeuwenhoek- a Dutch scientist, studied living cells(bacteria, protozoa, etc.) for the first time.

In 1831, a Scottish botanist, Robert Brown, discovered and named the nucleus in the cell.

J.E. Purkinje, in 1839, used the term protoplasm for the living substance present inside the cell.

The “Cell Theory” was formulatedby two German biologists, M.J. Schleidenin 1838, a botanist and T. Schwann, a zoologist in 1839. According to them, the cell is the structural and functional unit of all living beings.

In 1855, Rudolf Virchow, a German Pathologist established that all cells arisefrom pre-existing cells.

CELL THEORY…..

In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and alsothe basic unit of reproduction. With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells, also known as cell biology.

Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. Cell theory was eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor Schwann. However, many other scientists like Rudolf Virchow contributed to the theory. Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.

Cell Theory states…1) Bodies of the living beings are

made up of cells and their products.

2) Activities of an organism are the sum total of activities of its cells.

3) Cells develop from pre-existing cells.

(Viruses are an exception to cell theory.)

UNICELLULAR ORGANISMS….

The organisms which are made up of single cells are called Unicellular organisms. Examples are Amoeba, Paramoecium,bacteria,etc.

In unicellular organism:-Organism is represented by a single cell.A single cell performs all the functions.There is no division of labour.A single cell is consumed.The life span of the individual is short.

MULTICELLULAR ORGANISMS….

The organisms which are made up of a number of cells are called Multicellular Organisms. Examples are Fungi, plants, animals.

A large number of cells are present.Different tissues perform various functions of the body.There is division of labour and specialized Cells perform special functions.Some cells take part in reproduction.Life span is long.

In Multicellular organisms:

SHAPE AND SIZE OF CELLS..The shape and size

of cells vary considerably but all

of these are ultimately

determined by the specific function of the cell. Some cells

can change their shape like Amoeba

and WBC, While most of the plant cells and animal

cells have almost fixed shapes, eg. Liver cells, ovum,

smooth muscle cell, germ cell, bone cell,

Sperm, etc.

Human RBC’s are biconcave disc shaped. Nerve cells are elongated thread

like with branched terminals. In a multicellular organism, The shape of a cell depends

mainly on its functional adaptations and partly on the surface tension, viscosity of the

protoplasm mechanical action between adjoining cells and rigidity of the

cell covering.

A Typical Cell Is Formed

Of Three Parts:

Plasma Membrane…..The outermost extremely

delicate elastic membranous covering of the cell that separates its contents

from the external environment is called

PLASMA or CELL Membrane.

-Maintains the shape of the cell.-Protects the internal contents of the cell.-It is selectively permeable to allow entry of certain things only.-It has points on its surface to help in tissue formation, defends the cell, etc.-Osmosis occurs due to presence of tiny water channels.

CELL WALL:The ”CELL WALL” is a very tough, flexible, semi transparent and supportive and protective layer that surrounds the cells of fungi, some protists and prokaryotes. Cell Wall possesses many small pores through which adjacent cells remain connected. The connections between adjacent cells are made up of cytoplasmic strands called Plasmodesmata.

Plant cell wall is made up of cellulose, or chitin in fungi, it possess cell walls made of the glucosamine polymer chitin, and algae typically possess walls made of glycoproteins and polysaccharides. Unusually, diatoms have a cell wall composed of biogenic silica. Often, other accessory molecules are found anchored to the cell wall.

Extra deposition of lignin( for strength), suberin (for impermeability) and cutin (surface coating) may be present.

CELL NUCLEUS:-In cell biology, the NUCLEUS is a membrane enclosed organelle found in eukaryotic cells.

Nucleus is a dense protoplasmic body that contains hereditary information for controlling cell activities as well as for transfer to next generation. It is the largest cell structure which is oval or spherical in outline. It lies in the median or central position in animal and young plant cells.In mature cells, the nucleus lies towards the periphery due to formtion of a large central vacuole.

Cell nuclei contain most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, to form chromosomes. The genes within these chromosomes are the cell's nucleagenome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression—the nucleus is, therefore, the control center of the cell.

NUCLEUS has the following parts:-NUCLEAR ENVELOPE- It is a double membrane covering, which separates the nucleus from the cytoplasm. It is connected to Endoplasmic Reticulum and bears Ribosomes.NUCLEOPLASM (Sap)- It is colorless, dense sap found inside the nucleus in which chromatin and nucleolus are suspended.NUCLEOLUS- It is nearly rounded structure found inside the nucleus. It is not bounded by a membrane. It is rich in RNA and protein. It is the site of ribosome formation.CHROMATIN MATERIAL- It is the form of an interwined mass of thread-like structures made of DNA and protein. During cell division, chromatin becomes highly condensed, thick, rod-like structures, known as chromosomes.

The protoplasmic mass of the cell inner to plasma membrane and excluding nucleus is called the CYTOPLASM.It comprises cytosol (the gel-like substance enclosed within the cell membrane) – and the organelles – the cell's internal sub-structures. All of the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm.

CYTOPLASM:

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PROKARYOTIC CELL...In PROKARYOTES(pro-primitive, karyote-nucleus), a true nucleus and membrane bound organelles are absent. They comprise of bacteria and cynobacteria (blue-green algae).They are devoid of a nuclear envelope and a nucleolus and are smaller in size(1-10 millimeter). Genetic material lies free in the cytoplasm. It is equal to a single chromosome and is thus, called a NUCLEOID.

EUKARYOTIC CELL...In EUKARYOTIC ( eu-true, karuote-nucleus) cell, there is a true nucleus and membrane bound cell organelles float in the cytoplasm. Plants, animals and protozoans are eukaryotes. Genetic material lies covered on the outside by nuclear envelope. Two or several chromosomes and a nucleolus are present in it.

PLANT CELL....

AN

IMA

L

CELL..

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Plant Cell...Animal cell...

CELL ORGANELLES...

CELL ORGANELLES are sub cellular, microscopic structures which have characteristic form, and function where certain life processes take place. They are bounded by a membrane to keep theircontents separate from the external environment . On the basis of their membranes, they are of three types, double membrane, single membrane, and no membrane.

ENDOPLASMIC RETICULUM...The endoplasmic reticulum (ER) is a type of organelle in the cells of eukaryotic organisms that forms an interconnected network of flattened, membrane-enclosed sacs or tubes known as Cisternae. The endoplasm is the inner core of the cytoplasm and the membranes of the ER are continuous with the outer membrane of the nuclear envelope. ER is present in all the cells except prokaryotes and mammalian erythrocytes.

They are of two types:-# Rough Endoplasmic Reticulum- It is characterized by the presence of ribosomes on its surface. It synthesizes lipids. It is formed of vescicles and tubules.

# Smooth Endoplasmic Reticulum-It is devoid of ribosomes on its surface. It synthesizes proteins. It is mainly formed of flat sacs or cisternae.

Functions of ER:-Rough ER is a site of protein synthesis.Smooth ER is a site of lipid synthesis.It helps in intracellular and intercellular transport of substances.It gives internal support to the cytoplasm.It provides a large surface area for synthesis of chemicals and physiological activities.In vertebrates, smooth ER of liver cells takes part in detoxifying many poisons and drugs.

GOLGI APPARATUS....The GOLGI APPARATUS , also known as the GOLGI COMPLEX, is an organelle found in most eukaryotic cells.  It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898.Golgi apparatus packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination. It resides at the intersection of the secretory, lysosomal, and endocytic pathways. It is of particular importance in processing proteins for secretion, containing a set of glycosylation enzymes that attach various sugar monomers to proteins as the proteins move through the apparatus. It is a single unit in animal cell, whereas it is made of two separate units, called dictyosomes, in the plant cell.

FUNCTIONS OF GOLGI APPARATUS:-

It is involved in repair and synthesis of cell membranes.They form lysosomes.It packs all the secreted or excreted substances in vescicles for passage to the outside.It takes part in storage, modification, and packaging of various biochemicals produced by different components of the cell.Components of cell wall( except cellulose) are synthesized by it.Complex and special sugars (e.g. galactose) are made by it.

The MITOCHONDRIA is a rod shaped or sausage shaped membrane-bound organelle found in most aerobic  eukaryotic cells. These structures are sometimes described as "the powerhouse of the cell" because they contain enzymes necessary for the total oxidation of food an for release of high amount of energy in the form of Adenosine Triphosphate (ATP), used as a source of chemical energy. It is used for synthesis of new chemical compounds and for mechanical work. It is also known as the “energy currency of the cell”.

MITOCHONDRIA....

It is double membraned organelle.It contains cristae at the inner surface which occurs over tennis-racket shaped particles called Oxysomes. It encloses a matrix having DNA , ribosomes and enzymes. It is semi-autonomous as they have their own ribosomes and DNA due to which they are able to manufacture some o their own proteins and enzymes.

Functions of Mitochondria:-They are sites where aerobic part of respiration called Kreb's Cycle is performed.They provide energy for vital activities of living cells.They provide intermediates for synthesis of various chemicals like fatty acids, steroids, amino acids, chlorophyll, etc.

A LYSOSOME is a membrane-bound cell organelle found in most

animal cells (they are absent in red blood cells). Structurally and

chemically, they are spherical vesicles containing hydrolytic

enzymes for intracellular digestion and waste disposal. They are also

known as “Suicide or Digestive Bags”. Old organelles, germs, food

particle, etc. fuse with lysosomes for disposal by digestion. In

damaged cell, lysosomes burst to release enzymes for digestion of

cellular components. They are found in animal cells except mammalian

RBC’S.

LYSOSOME

Functions of lysosomes:-They help in the destruction of foreign particles.They help in intracellular digestion of food particles.They help in removing dead and worn out organelles by digesting them, so, they are called cellular scavengers or demolition squads.

The PLASTID  is a major double-membrane organelle found, among others, in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell. They often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell's color. They have a common origin and possess a double-stranded DNA molecule that is circular, like that of prokaryotes.).

PLASTID

Undifferentiated plastids may develop into any of the following variants:Chloroplasts:- green plastids: for photosynthesis. Bounded by two membranes. Known as the” kitchen of the cell’.Chromoplasts  colored plastids: for pigment synthesis and storage.Gerontoplasts: control the dismantling of the photosynthetic apparatus during senescence.Leucoplasts colorless plastids, storage of food materials. Leucoplasts sometimes differentiate into more specialized plastids:Amyloplasts: for starch storage and detecting gravity

Elaioplasts: for storing fatProteinoplasts: for storing and modifying protein

Tannosomes: for synthesizing and producing tannins and polyphenols

Functions of Plastid:-They provide color to fruits and flowers.They help in pollination.They store starch, protein and oil.Chloroplasts maintain the balance of the two gases by absorbing carbon dioxide and releasing oxygen in photosynthesis.

RIBOSOMES...RIBOSOMES are extremely small, roundedbodies found either in free state in the cytoplasm or attached to the surface of ER. They are composed of Ribonucleic Acid(RNA) and proteins. They are not boundedby a membrane. So, they are present in both prokaryotes and eukaryotes.But, they are absent in mammalian RBC’S.

They are the site of protein synthesis in the cell.They are therefore, also called “protein factories”.

CENTROSOME

CENTROSOME is a small naked organelle present near the nucleus in the cells of some animals and some lower plants. It has a sheath of specialized cytoplasm called Centrosphere. It encloses two micro-cylinders called centrioles, which lie at right angles to each other. Centrosome divides before cell division to form two centrosomes. They form astril spindle poles.

VACUOLES......VACUOLES are

membrane bound non-

cytoplasmic sacs that contain non-

living solid or liquid contents.

They are of three types----

•SAP vacuoles- fluid filled (cell sap), occur in both plants and animal cells, its covering is known as Tonoplast, stores salts, sugar, amino acids, organic acids.•FOOD vacuoles- formed by the fusion of ingested food particles sacs with lysosomes , digestion occurs inside it, found in unicellular organisms.•CONTRACTILE vacuoles- collect liquid from the cell, swell up, rise to the surface and burst to release its contents, takes part in osmoregulation and excretion, occurs in unicellular organisms.

FACTS RELATED TO CELL .....Smallest organelle– RIBOSOME

Largest organelle– PLASTID(plant) MITOCHONDRIA(animal)Largest cell structure—NUCLEUSVIRUSES are neither prokaryotic nor eukaryotic.MITOCHONDRIA and PLASTIDS can replicate themselves.

Made By the student ofTHE DOON GLOBAL SCHOOL:

ADITI SHARMACLASS 9A