Study of Cell

  1. A cell is basic structural and functional unit of life.

  2. The word Cell was first coined by British Scientist Robert Hook  in the year 1665

  3. The smallest Cell is Mycoplasma gallisepticum.

  4. The longest cell is Neuron.

  5. The biggest cell is egg of Ostrich.

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


Main Features of Cell theory

  1. All organisms are made up of at least one cell.

  2. A cell is the smallest unit that can carry out all the functions necessary for life.

  3. All cells arise from pre-existing cells.

Types of Cell


These are primitive cell having three basic structure of typical cell but lack of nuclear membrane.Nuclear material is present in a region of cytoplasm called nucleoid.other membrane bound organelles are absent such as mitochondria,ribosome.golgi bodies etc.Example:-Virus,bacteria and cynobacteria are Prokaryotes.

Prokaryotic organisms are asexual, meaning they do not need a partner to reproduce. Most reproduce through a process called binary fission where basically the cell just splits in half after copying its DNA. This means that without mutations within the DNA, offspring are identical to their parent.


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

Difference between Prokaryotes and Eukaryotes


  1. Size of Cell is generally small.

  2. Nucleus absent.

  3. It contain single chromosome.

  4. Membrane bound cell organelles.

  5. Cell division take place by fission or budding.


  1. Size of cell is generally large .

  2. Nucleus present.

  3. It contain more than one chromosome.

  4. Celll Organelles present.

  5. Cell division take place by mitosis and meiosis.

Structure  of  typical cell

A  cell have following structure

  1. Cell wall:- In Plant cell there is rigid cell wall which is non living and freely permeable.It is made up of cellulose and chitin.It provie shape and rigitdity to th cell.

  2. Cell Membrane :It is known as Plasma membrane which form the outer covering of animal cell.In plant it is found within is thin,elastic,living,double layer,permeable membrane.It is made up of phospholipid moleculs.

Function:-It regulates movement of molecules inside and outside of cell.

  1. Protoplasm:-The whole fluid present inside plasma membrane is protoplasm.The name protoplasm is given by purkenje in 1839.the protoplasm is made up of various chemical substances ike water ,ions,salt and organic is living part of the cell.Protoplasm is divided into two parts

  • Cytoplasm:-The fluid found outside the nuclear membrane.

  • Nucleoplasm:- The fluid found Inside the nuclear membrane.

  1. Mitrochondra:-It is discovered by Atman in the year 1886,these are cylindrical ,rod shaped or spherical strcture found in cytoplasm. It is surrounded by double layered membrane.Inner membrane has many fold called cristae.the pluid present inside mitrochondria is called matrix which contain mant enzyme and co enzyme.

Function:-Mitochondria is the respiratory site of cellular respiration. Mitochondria synthesize energy rich compound ATP,it is also known as Power House of cell.

  1. 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 it is called as dictyosomes.

Function:- it work as storage ,processing and packing of is involved in the synthesis of cell wall,plasma membrane and lysosomes.

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

Function:-Endoplasmic reticulum helps in the distribution of material. it forms supporting framework of cell.

  1. Ribosome:it is discovered by palade.Small granules like structure found attached to the endoplasmic reticulum or in freee is made up of ribonucleic.

Function:-Take part protein Synthesis.

  1. Lysosome:- it is 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 bag.

  1. Centosome:-It is discovered by Boveri. It is found in animal cell taking part in cell division.It is not bounded by membrane consist of two centriole.

Function:- It  helps in the  formation of spindle fibre during cell division.

  1. Plastid:- Only found in plant is of three type :-

  • Chloroplast:-These are green pigment found in green plant involved in photosynthesis.So it is called as Kitchen of the Cell.Choloroplast is bounded by two unit membrane having grana and stroma.gana is membrane bounded sac like structure found in stacks containing chlorophyll molecule.Stroma is the matrix npresent inside the choloroplast which contain photosynthesis enzyme and starch grain.Granum is the site of light reaction during photosynthesis while stroma is the site of dark reaction.

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

  • Chromoplast :-Provides Various colours to the plant.

  • Leucoplast:it is stores the food in the form of starch,fat and protein.

  1. Vacoule:-These are 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.

Function:-It helps in stores toxic metabolic waste.

  1. Nucleus:- the nucleus is spherical ,centrally located is a major structure found in plant it is shifted toward is bounded by double layer nuclear membrane having pore.within nucleoplasm nucleolus and chromatin material is 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 nuclei acid) and histone protein.during cell division Chromatic breaks into pieces and forms chromosomes.

Function:-It controls all the activity of cell,so it called as “ control room” of cell chromatin transmits hereditary characters from parents to their off springs.


Plant Cell


  1. Plant cell are larger in size.

  2. Cell wall present, made up of cellulose and chitin.

  3. Plastid present.

  4. Centrosome absent.

  5. Vacuoles are larger in size.

Animal Cell

  1. Animal Cell are generally smaller in Size

  2. Cell wall is absent.

  3. Plastid absent.

  4. Centrosome Present.

  5. Vacuoles are smaller in size.


In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.

Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.

Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.

Nucleid Acid:-Chromosomes are made up of nucleoprotein which constitute basic protein and nuclei acid.Two types nucei acids are recognized

  1. Deoxyribo nucleic Acid(DNA)

  2. Ribonucleic Acid(RNA)

Difference between DNA and RNA

Deoxyribo nucleic  Acid(DNA)

  1. It is usually occur inside nucleus and some cell organelles(Mitochondria and chloroplast in plant).

  2. It is double standard structure.

  3. DNA contain millions of nucleotides.

  4. The sugar portion of DNA Is 2- deoxyribo.

  5. Purine and pyrimidine bases are in equal in number.

  6. The base present in DNA are adenine (A),guanine(G),thymine(T) and cytosine(C).

  7. Hydrogen bonds are formed between complementary nitrogen bases of the opposite strands (A-T,C-G).

  8. DNA is spirally twisted to produce a regular helix.

  9. It replicates to form new DNA molecules.

  10. It occurs in the form of chromatin or chromosomes.

  11. The function of DNA is to transfer genetic information from one generation to the next.

  12. DNA transcribes genetic information to RNA its quantity is fixed for cell.

  13. Renaturation after meeting is slow.

  14. DNA is only two types Intra nuclear and extra nuclear.

  15. It is long lived.

Ribonucleic Acid(RNA)

  1. Very little RNA occurs inside the nucleus most of it is found in cytoplasm.

  2. I is single stranded.

  3. Depending upon type, RNA contain 70-12000 nucleotides.

  4. The sugar portion of RNA is ribose.

  5. There is no proportionality between numbers of purine and pyrimidine bases.

  6. The base present in DNA are adenine (A),guanine(G),uracil(U) and cytosine(C).

  7. Base pairing though hydrogen bonds,occurs in the coiled parts.

  8. The strand may get folded at places to produce a secondary helix or pseudohelix.

  9. It cannot normally replicate itself.

  10. it occurs in ribosomes or forms association with ribosome.

  11. The function of RNA is to direct synthesis of protein in the body.

  12. RNA translate the transcribed message for forming polypeptides. The quantity of RNA of cell is variable.

  13. It is quite fast.

  14. Three different Types of RNA –m-RNA,t-RNA and r-RNA.

  15. Some RNA are very short lived while others have somewhat longer life.