Study of Cell-Cytology

⇒ Study of cell is called cytology.

⇒ Cell Cell is the basic structural and functional unit of life.

⇒ The word ‘cell’ was first coined by British scientist Robert Hook in the year 1665.

⇒ Anton Van Leeuwenhook first described a living cell.

⇒ The smallest cell is Mycoplasma gallisepticum.

⇒ The longest cell in human body is Neuron.

⇒ The biggest cell is egg of Ostrich.

⇒ Schilden and Schwan established cell theory in the 1838-39. year

⇒ Germ plasm theory was proposed by August Weisman

1. All organism are composed of cell.

2. Body of every organism is made of

3. Each cell arises from pre-existing cell.

4. Every organism starts its life from single cell.

1. Prokaryotic cell: These are primitive cell having three basic structure of typical cell but lack nuclear membrane. Nuclear material is present in a region of cytoplasm called nucleoid. Other membrane bound organelles are absent such as mitochondria, lysosome, golgi bodies etc. Ex.-Bacteria and cynobacteria are Prokaryotes.

⇒ Number of Mitochondria in bacterial cell is zero.

⇒ The smallest known prokaryotic organism is Mycoplasma.

⇒ In photosynthetic prokaryotic bacteria chlorophyll is associated with membranous vesicles.

2. Eukaryotic cell: These are complete cell which contain membrane bound organelles and nucleus. Unicellular and multicellular plant and animal have Eukaryotic cell.

⇒ The biggest single celled organism is Acetabularia.

⇒ Nucleus contain chromatin made up of DNA and histone protein.

⇒ Nucleolus is present inside nucleus.

⇒ Structure of typical cell: A cell have following structure.

1. Cell wall: In plant cell there is a rigid cell wall which is non living and freely permeable. It is made up of cellulose or chitin. It provide shape and rigidity to the cell.

⇒ Cell wall of bacteria is made up of peptidoglycan.

2. Cell membrane: It is also known as plasma membrane which form the outer covering of animal cell. In plant cell it is found within cell wall. It is thin, elastic, living, double layer, permeable membrane.

⇒ Cell membrane is mainly composed of lipids and protein.

⇒ The major lipids are phospholipids arranged in a bilayer. Function: It regulates movement of molecules inside and outside of the cell.

⇒ The membrane is selectively permeable to some molecule present on either side of it.

3. Protoplasm: The whole fluid present inside plasma membrane is protoplasm. The name protoplasm is given by Purkenje in 1839. Protoplasm is made of up various chemical substances like water, ions, salt and organic molecule. It is the living part of cell.

A. Cytoplasm: The fluid found outside the nuclear membrane.

B. Nucleoplasm: The fluid found inside the nuclear membrane.

⇒ 99% of protoplasm is made up of oxygen (76%), carbon (10.5%), hydrogen (10%) and nitrogen (2.5%).

⇒ 80% of protoplasm is water.

⇒ The ratio of inorganic and organic compound found in protoplasm is 81: 19.

4. Mitochondria : Discovered by Altman in the year 1886. These are cylindrical, rod shaped or spherical structure found in cytoplasm. It is surrounded by double layered membrane. Inner membrane has many fold called cristae. The fluid presents inside mitochondria is called matrix, which contains many enzyme and co-enzyme.

⇒ Mitochondria is considered as prokaryotic cell inside eukaryotic.

Function Mitochondria is the respiratory site of cellular respiration. Mitochondria synthesize energy rich compound ATP. It is also known as ‘Power House’ of the cell. ATP is known as energy currency of cell.

5. Golgi bodies: Discovered by scientist Camilo Golgi. Golgi bodies are made up of group of tubes, vesicles and vacuoles. In plant it is more in number and here it is known as dictyosomes.

Function: It work as storage, processing and packaging of material. It also involved in the synthesis of cell wall, plasma membrane and lysosomes.

⇒ It help in the synthesis of carbohydrate from simple sugar which combine with protein made by ribosome forming glycoprotein.

6. Endoplasmic reticulum: Membranous network of tubules like structure found in cytoplasm is called endoplasmic reticulum. It is attached with the nucleus on one side and on other side it is joined with plasma membrane.

Function: Endoplasmic reticulum helps in the distribution of material. It form supporting framework of cell.

⇒ Rough endoplasmic reticulum is the site of protein synthesis due to presence of ribosome on it.

⇒ Smooth endoplasmic reticulum is the major site of lipid synthesis.

⇒ Endoplasmic reticulum is responsible for the mechanical support, protein synthesis and enzyme transport.

7. Ribosome: Discovered by Palade. Small granules like structure found attached to the endoplasmic reticulum or in free state. It is made up of ribonucleic acid (RNA).

⇒ Ribosome is not surrounded by membrane.

Function: Take part in protein synthesis.

8. Lysosome: Discovered by De Duve. These are sac like structure bounded by single membrane and contain hydrolytic enzyme.

Function: It helps in intracellular digestion. The enzyme found in lysosome may digest the entire cell. So it is also known as ‘suicidal bags of the cell.’

⇒ Lysosome is not found in Red blood corpuscles of mammal.

9. Centrosome: Discovered by Boveri. It is only found in animal cell taking part in cell division. It is not bounded by membrane consist of two centriole.

Function: Centriole found in centrosome initiate the cell division forming spindle fiber between the pole.

10. Plastid: Only found in plant cell. It is of three type: (a) Chloroplast (b) Chromoplast (c) Leucoplast.

(a) Chloroplasts : These are green pigment found in green plant involve in photosynthesis. So, it is known as ‘Kitchen of the cell’. Chloroplast is bounded by two unit membrane having grana and stroma. Grana are made up of membrane bounded sac like structure known as thylakoid found in stack. It contain chlorophyll molecule. Stroma is the matrix present inside the chloroplast which contain photosynthetic enzymes and starch grain. A Granum is composed of 20 to 50 thylokoids. Granum is the site of light reaction during photosynthesis while stroma is the site of dark reaction.

Function : Chloroplast provides green colour to plant & take part in photosynthesis.

(b) Chromoplast provides various colours to the plant like flower, fruit etc.

⇒ Chromoplasts are of different kind.

Lycopene: In tomato it provide red colour.

Carotene Provide yellow or orange colour in plant. Example-Carrot.

Betanin: Found in sugar beet.

(c) Leucoplast is colourless. It stores the food in the form of starch, fat & protein, granules.

⇒ Leucoplast is found in root and underground stem.

11. Vacuole: It is fluid filled single membrane bounded, dead organelles of cell. In plant cell it is larger in size but in animal it is smaller in size.

⇒ The membrane which surrounds the vacoule called tonoplast.

Function: It helps in osmoregulation. It stores toxic metabolic waste.

⇒ In plant cell there is a large central vacuole that or may occupy 90% of total cell volume.

⇒ In plant cell, vacuoles provide turgidity and rigidity.

⇒ In Amoeba vacuole play role in osmoregulation and nutrition.

⇒ The membrane which surrounds the vacuoles is called tonoplast.

12. Nucleus: Nucleus is a spherical, centrally located major structure found in the cell. In plant cell it is shifted towards periphery. It is bounded by double layered nuclear membrane having pore. Within nucleoplasm nucleolus and chromatin material are present. Nucleolus is rich in protein and RNA. Chromatin material is thin thread like structure forming network. This is made up of genetic substance DNA (deoxyribo nucleic acid) and histone protein. During cell division chromatin breaks into pieces and form chromosome.

Function: It controls all the activity of cells. So it is also known as ‘control room’ of cell. Chromatin transmits

hereditary characters from parents to their offspring.

⇒ Other than nucleus DNA is also found in mitochondria and chloroplast.

⇒ Mitochondria is able to produce their own protein.

⇒ The movement of substance against diffusion gradient with the use of energy from respiration through cell membrane is called active transport.

⇒ Cell becomes turgid because of endosmosis.

⇒ The process of imbibition involves both diffusion and capillary action.

⇒ A cell increases in volume when it is placed in hypotonic solution.

⇒ When fresh egg place in salt water, it floats.

⇒ Chromosomes are thread like structure found in the nucleus as chromatin material. It becomes visible during cell division. Each chromosome is made up of two chromatids joined together at a point centromere. Bead like structure found on chromosome is called Genes are made up of DNA (deoxyribo nucleic gene. acid) which are the carrier of genetic information from generation to generation. In some viruses RNA is the genetic material called retrovirus. In prokaryotes there is only one chromosome, like bacteria and virus.

⇒ Chromosomes are made up of DNA and protein.

⇒ Chromosome was named by Waldeyer in 1888 capable of self replication, which transmit coded information from one generation to other.

⇒ Eukaryotic cell possess many chromosome. A particular kind of species have definite number of chromosome in their cell, which are in pair known as diploid. The set of unpaired chromosome is called haploid. Gametes have haploid set of chromosome.

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