Structure of Volvox Colony, Sexual and Asexual Reproduction in Volvox (With Diagrams)

After reading this topic you will learn about Habitat, Structure of Colony, Sexual and Asexual Reproduction in Volvox


Volvox is found in both in freshwater and marine water. Its presence gives water green color. It appears both in spring and summer season but mostly grow in rainy season. Season also affect on Sexual and Asexual Reproduction in Volvox.


Volvox always live in colony.

The cells of volvox colony are always fixed so that is called coenobium.

Spherical in shape. The rang of each colony cells from 500-50,000.

The outside of the colony consists of mucilage.

Volvox cells have biflagellate. Flagellate found outside of colony.

The collective movement of the flagella help to move the colony.

The shape and structure of all cells of a colony have alike.

The cell is closely packed. They are organized to form polygonal shape in the volvox colony.

The mature cells wall is thick & mucilaginous.

Their cell looks like pear shaped. These cells make periphery around the colony.


The structure of volvox same as Chlaymydomonas.

 Every cell has Biflagellate and attached at the outer side of the cells.

Each cell has cup shaped chloroplast. Chloroplast have one pyrenoid.

They have two contractile vacuoles that help in maintain the water balance in cell.

A nucleus found in center of cell and connected with flagella by neuromotor.

It also has eyespot near the anterior surface of colony that help in swimming in light.

Structure of volvox Colony

REPRODUCTION (Sexual and Asexual Reproduction in Volvox):

In volvox both type of reproduction present such as asexual and sexual.


Asexual reproduction occurs when condition is favorable.

Already present colonies reproductive cells help to produce new colonies.

Only posterior side of cell take part to make new colony by asexual reproduction

The cells increase in size. They are larger in size. These are known as gonidia.

These Gonidia develop in to many pyrenoids.

There are 5 to 20 gonidia in each colony.

Each gonidia produce daughter colony.

Sexual and Asexual Reproduction in Volvox


The gonidia move towards interior side of the colony. The first step gonidium divide longitudinal and this forms two cells.

In second step of division cell also divide longitudinal at right angle to the first into four cells.

 The third step four cells divide longitudinal and make eight cells from four cells are central.

These eight cells arranged in curved like structure that structure is called plakea stage.

These eight cells future longitudinal divide and make 16 cells.

These arrangements look like hollow-sphere.

This hollow sphere open on exterior side as a small hole that’s called phialopore.

The cells continue divide until the cells reaches the distinctive of that species.

The last step is inversion of colony. The cells become opposite in direction, their anterior end must face the periphery of colony.

Thus, new colony comes out from paternal cells.

Sometimes it remains within the parent colony.


Sexual Reproduction Occur When Condition Are Unfavorable.

The Oogamous type of Sexual reproduction mostly present in volvox. Colony may be monoecious or dioicous.

Female gametes known as gyn gonidia and male gametes are called antheridia.

these reproductive cells commonly called gametangia.


The male part (gametangia) are called antheridium. The antheridium. protoplast of divides many times like asexual reproduction. It divides again and again and produces 16-128 cells. These cells named antherozoid.

When division was compete they develop new flagellum at ends point of cells.

Types of Antherozoids:

There are two types of  Antherozoids cycles:

a)       When cells are 128 or less after division. In this type, all the antherozoids colony are liberated in the form of mass, Mass swims and reaches to the oogonium. Then the cells of antherozoid gets detached.

b)       If cell divide more than 128. In this type, antherozoids call become arranged itself into a hollow sphere shape within the antheridium. These cells undergo inversion process. After inversion antherozoids cells separate from each other. Then they are liberated fertilization.


Then female reproduction organ is Gynogonidia or oogonia. Female sex part is larger than male sex part. The protoplast of female converts into single oosphere in rounded in shape.


 The male part (Antherozoids) enter oogonium through a pore. Only single antherozoid enter in female sex and zygote is formed. When Zygote formed it secretes a thick wall that become oospore. This wall consists of three layered. Oospore produces a secretion in large amount that called heamotochrome, due to this its color orange red. They release oospore and in favorable condition they germinate same as asexual reproduction.

Classification of Bacteria on the Basis Of Nutrition and Its Types

Classification of Bacteria

Classification of Bacteria on the basis of nutrition. Bacteria are classified into two main group. One is autotrophic bacteria and other is heterotrophic.

Autotrophic Bacteria:

In this type those bacteria are included that can synthesis own food for our survival. They convert compound organic into simple inorganic substance. They obtain carbon from carbon dioxide to synthesis their food.

Autotrophic bacteria further classified into two group.

  1. Photoautotrophs
  2. Chemoautotrophs


  1. In which those bacteria are included that’s energy source are light.
  2. These bacteria have chlorophyll for photosynthesis.
  3. They can synthesis their own food.
  4. These bacteria chlorophyll same as plants chlorophyll, but in which chloroplast are absent.
  5. They use sunlight as an energy source and for hydrogen they use hydrogen sulphide instead of water.
  6. This process releases Sulphur as a byproduct.

Photoautotrophs further classified based on Hydrogen source;

  1. Purple Sulphur bacteria
  2. Green Sulphur bacteria
  3. Purple Non-Sulphur bacteria

Purple Sulphur bacteria:

These bacteria use Sulphur compound as source of proton and electron, e.g. chromatiumokenii.

Green Sulphur bacteria:

These bacteria use H2S as source of Proton and electron, e.g.  Chlorobacterium

Purple Non-Sulphur bacteria:

These bacteria use organic compound as source of electron and proton such as Rhodospirullummrubrum.


Chemoautotrophs are those bacteria that get energy from oxidation of inorganic substance during respiration.

  1. They maintain the soil fertility.
  2. They also play vital role in biosphere.
  3. They also perform nitrogen cycle.

Types of chemoautotrophs bacteria:

  • Iron bacteria
  • Sulphur bacteria
  • Hydrogen bacteria
  • Methane bacteria

Nitrifying Bacteria:

  1. They live in soil and oxidize ammonia gas in to nitrites, e.g. Nitrosomonas.
  2. Some bacteria convert nitrites into nitrates for plants e.g. Nitrobacter
  3. In this process energy is released and this energy used by bacteria.

Iron Bacteria:

  1. These bacteria present in iron rich in water.
  2. They oxidize ferrous compound into ferric and get energy from this process. E.g. Leptothrix, Ferrobacillus and Cladothrix.

2Fe (HCO3)2 + H2O   →  2Fe(OH)3 + 4CO2 + 29Kcal

4FeCO3 +O2 +6H2O   →  2Fe(OH)3 + 4CO2 + 81Kcal

Sulphur Bacteria:

  1. These bacteria found in hot springs that contain hydrogen sulphide.
  2. They oxidize metallic Sulphur to Sulphur and get energy. e.g. Thiothrix

Hydrogen Bacteria:

They grow in organic medium that consist of hydrogen, CO2 , O2 and oxidise hydrogen. e.g. Bacillus panctotrophus

Heterotrophic Bacteria:

This type of bacteria get energy from organic compound. They are not able to prepare their food. They depend on another organism. Classification of Bacteria Given Below.

Types of Heterotrophic Bacteria:

  1. Saprotrophic Bacteria
  2. Parasitic Bacteria
  3. Symbiotic Bacteria

Saprotrophic Bacteria:

  1. These bacteria get their energy from dead organic matter.
  2. They decompose the dead organic matter and get food and convert it into hums.
  3. These bacteria also known as decomposer.
  4. These bacteria secret decomposition enzyme that digest the complex organic matter in simple matter.
  5. These matters observed by bacteria as source of energy.

Parasitic Bacteria:

  1. These bacteria are also heterotrophic and not have any enzyme for decomposition.
  2. They total depend on another organism.
  3. They use the host enzyme to prepare their energy for growth.
  4. Most of these bacteria cause disease in host.
  5. These bacteria also called pathogens.
  6. Example Pneumococcus cause Pneumonia.

Symbiotic Bacteria:

  1. These bacteria act as symbiotic way with host and live together.
  2. They prepare food for host and in return get energy from host.
  3. Mostly these bacteria live in root of leguminous plants.
  4. They fix nitrogen for plants in the form of nodules. \

Types Of Reproduction In Bacteria

What is Bacteriophage?

Study About Tobacco Mosaic VIrus

Method of Sexual Reproduction in Bacteria In Detail

Method of Sexual Reproduction in Bacteria

In bacteria sexual reproduction are common method to increase population. In sexual reproduction both male and female take part and different method use to exchange (DNA) genetic information. Method of Sexual Reproduction in Bacteria are given below.

Method of Bacterial Recombination:

 In bacteria three way to transfer gene for genetic recombination.

  1. Transformation
  2. Conjugation
  3. Transduction


First time exchange of hereditary material in bacteria was founded in 1928 by Griffith.

Experiment of Transforming Hereditary material:

 In 1928 Griffith working on a bacterium (Streptococcus Pneumonia) that cause fever. They found that two type of strains were found.

  1. One was capsulated and because infection make colonies when grow on ager. It’s called S type of colony.
  2. The second was non-capsulated and not cause diseases, that make a rough colony when grow on colonies. Its called R type of bacteria.
  3. Griffith inject R-cells in a mouse to test the affect and Killed S cell with Heat.
  4. The mouse death occurred after few days.
  5. When he studies the dead mouse blood, they found that S cell was living in blood.
  6. After study he said that S cell release a factor that develop capsules for R cell and become virulent.
  7. This type of transformation was creating to be heritable.
  8. This transformation is also called transforming principle.
Transformation Method in Bacteria
Transformation Method in Bacteria

Identification of transformation Principal:

McCarty and Macleod identified the transformation principal of DNA in 1994. According to him genetic material is transformed through agent.

During transformation a small piece of DNA is given by donor and taken by recipient. Same mechanism of transformation also observed in Azotobacterial and Bacillus.

Bacterial Conjugation:

Conjugation mean transfer of DNA form one organism to other through direct content method.

First time this process was explain by Joshua Lederberg and Edward Tatum in 1946 in E. coli bacteria.

  1. According to him E. coli can synthesis all kind of amino acid if glucose and slat are present in optimum
  2. For experiment purpose they induce mutation in bacteria.
  3. They obtain two type of mutation bacteria, in one type of bacteria they are not able to synthesis a vitamin (biotin) and methionine amino acid.
  4. In other type of mutation, they cannot synthesis an amino acid threonine and leucine.
  5. Both type of bacteria was mixed and grow in a culture.
  6. Theoretically none of cell should be grow in medium but few colonies grow in medium from a bacterium.
  7. The transformation was ruled out as no chemical was founded
  8. Electron microscope show that direct cells contact was occur in coli bacteria.

Sex Factors:

A scientist Francois Jacob and Wolman demonstrate the mechanism of conjugation in E. coli. According to him some bacteria have an extra chromosome of DNA that called Fertility factor or F factor.

  1. The cell having these factors are called Male donor cell.
  2. Those cells have not these factors called Female or recipient cell.
  3. E. coli have one pili from outside, but F factor have 3 additional pilli which are responsible for physical contact with cell.
  4. They make a tube-like structure that called conjugation tube.
  5. A single stand F factor cross to recipient cell through the sex pilus.
Bacterial Conjugation Method
Bacterial Conjugation Method


  1. It refers as transmission of double stranded DNA from donor cell to recipient cell through a agent or third party. Mostly bacteriophage use for this purpose.
  2. First time in history of bacteria Zinder and Lederberg demonstrate the transduction mechanism in 1952 when they are study on typhoid causing virus (salmonella typhimurium).
  3. They mix two mutant bacteria that was unable to synthesis certain nutrient in a culture medium.
  4. They separated the Recombinant that was able to synthesis all essential nutrients.
  5. They said genetic material exchange through conjugation method.
  6. Later they carry an experiment are called U-tube experiment.
  7. They place the nutritional mutants in each arm of tube and keep separated with the help of filter that not allow the bacteria to passing in it.
  8. They fine out recombination was found even them.
  9. They say that some filterable agents are present in the bacteria that cross the non-filterable tube and recombine them to create next generation.
  10. Later told that bacteriophage or virus are these agents.

Transduction pattern:

 There are two patterns of transduction.

  1. Generalization
  2. Specialized Transduction

Generalization transduction:

  1. If all bacterial DNA part have chance to enter in transduction phage this process known as generalization transduction.
  2. Virus enzyme hydrolysis host chromosome in many small parts and any part of bacterial chromosome incorporated into the phage head in the process of phage assembly.
  3. It’s not attached on any viral DNA.
  4. A very large population transduction virus carries different part of bacteria chromosome.
  5. A small portion of bacteria DNA is carried through phages.
  6. They infect the bacterial DNA of recipient and become a part bacterium.

Specialization transduction:

  1. In which temperate phages transfer the restricted gene of bacterial chromosome to pro phage bacterial.
  2. This process is called restricted transduction.
  3. So this process occurs when a bacteriophage genome integrated as pro phage in host DNA.
  4. Then again become free upon induction and carry into the phage head.
  5. When they infect the bacteria and become the part of these bacteria DNA genome.
  6. This type of specialized transduction study in E. coli.

Types of reproduction in Bacteria

Types of Reproduction in bacteria and Growth Phases of Bacteria with Diagram

Growth and types of reproduction in Bacteria

Growth refer to change in population of bacteria. Bacteria have ability to reproduce very readily due to large surface area and get their food from environment by active transport and diffusion method. There are two type of reproduction in bacteria sexual and asexual.

  1. Growth of bacteria is affected by temperature, PH, nutrient and ion concentration.
  2. The optimum condition speed up of production of bacteria. in optimum condition cell division take place every 20 minutes.
  3. After division number of cells become double. This condition is called exponential growth. The time interval known as Generation time.

Bacteria Pass through different phases of growth.

  1. Lag Phase
  2. Log phase
  3. Stationary phase
  4. Death Phase

Lag Phase:

it is first stage of bacterial growth in which growth not start. In which bacteria only adopt themselves to new environment.

Log Phase (Exponential phase):

In this phase Bactria start their growth and become double if optimum condition available.

Stationary phase:

In this phase resource are limited and competition b/w bacteria increase. Bacteria growth slow down or stop. The number of cells remain constant this condition known as stationary phase.

Death Phase:

In this phase resource become exhausted and toxic waste product are produce and bacteria become start die.

Growth phases in Bacteria
Growth phases in Bacteria

Reproduction in Bacteria:

Both types of reproduction in bacteria present but mostly bacteria produce through Sexual reproduction method. In bacteria primitive type of reproduction.

Types of reproduction in Bacteria

  1. Asexual Reproduction
  2. Sexual reproduction

Asexual Reproduction:

Binary fission and endospore are most common asexual reproduction method in bacteria.

Binary Fission:

Fission occur when situation is good for growth. A cell grows into twice in size and then divide into to identical cell. Every daughter cell grows and then become a like parent cell. This process knows as a life cycle.

Mechanism of Binary division in Bacteria
Mechanism of Binary division in Bacteria

Mechanism of Binary division:

  1. When bacteria start division, they take nutrients from the environment, Synthesis cell part such as DNA, RNA, enzyme, protein and other important substance.
  2. The cell mass and cell size also increase.
  3. The DNA replicate and plasmic membrane start to grow inward at the center of bacteria cell.
  4. DNA attach with mesosoma and hold it position in replication and then inward growth was start that result development of septum start.
  5. Septum separated the into new daughter cell.

Endospore Formation Method:

Endospore are oval, spherical, ellipsoidal and cylindrical mass of protoplast surrounded by with a multiple layer.

  1. Outermost wall layer is called exospore.
  2. Beneath the outer wall a spore coat composes by several layer of proteins.
  3. The spore coat followed by thick cortex made that made up of peptidoglycan.
  4. Protoplast compose by calcium and (DPA) Dipicolinic Acid which protect from heat resistance.

Sexual Reproduction:

Genetic recombination does the sexual reproduction in bacteria. New genotype is formed by recombination of gene and exchange of genetic material between homologous gene.

Sexual reproduction differs from the eukaryotic sexual reproduction. Gamete and fertilization process are absent in bacteria.

 Bacteria Recombination Method:

  1. Bacterial combination the cell does not fuse, usually a part of DNA from the donor cell to transfer to acceptor cell.
  2. After receiving the DNA part is positioned alongside the recipient DNA in that way homologous gene are adjacent.
  3. Enzyme act as recipient DNA.
  4. That cause nicks & and removal of fragment.
  5. The donor DNA is integrated into recipient DNA.
  6. Then recipient cell become recombinant DNA.
  7. Both donor and recipient DNA present in a same place.

Key Steps to remember Bacteria Recombination Method

Donor cell DNA >  Recipient cell >  position Both DNA Donor And Recipient >   Homologous Gene > Recipient Enzyme act >  cut and remove> integrated Donor DNA with recipient DNA >  Recombinant DNA

Study Morphology and structure of Bacteria

Bacteria, Morphology and structure of bacteria with Diagram In detail


Bacteria is a smallest living organism having a cellular structure in nature Bacteria is a smallest living organism having a cellular structure in nature . They are classified as microorganism due to unicellular prokaryotic. The study of Bacteria is called bacteriology.

  1. Bacteria found everywhere in environment, such as water, soil, air, dust partial, plants and in animals.
  2. They also present in hot water at 70 C or higher temperature.
  3. They found in large quantity, e.g. one gram of fertile soil contains more than hundred million and in fresh milk more than 3000 million bacteria found.

Morphology of Bacteria:

Morphology included size, shape, structure and arrangement of organism.

Size of bacteria:

Bacteria are very small and unicellular. It size is 0.5-1 um in diameter and 0.1-10 um in length.

Shape of Bacteria:

Bacteria have constant shape. They cover with a rigid cell wall. it,s present in varieties of shape due to this they are classified on the basic of according to shape.

  1. Cocci
  2. Bacilli
  3. Spirilla
  4. Spirochetes


Sphere in shape e.g. streptococcus pneumonia cause pneumonia.


Rod shape bacteria e.g. Lactobacillus present in milk.


There shape is curve with a twist or turn in shape. If curve in not complete so its called viriloid and more completed curve in called helical.


They can control their flexible shape and twist. These bacteria a ridge in nature.

Structure of Bacteria Call:

Bacteria contain many vital components. Some are outer component and some insider component of cell wall.

External component:

  • Flagella
  • Fimbriae or pili

These are vital component which are present in all types of bacteria, but some bacteria consist of some special component that only present in certain species.

Special component:

  1. Cell wall
  2. Cytoplasmic membrane
  3. Specialized membrane
  4. The Cytoplasm
  5. Plasmids
  6. Spores and Cysts
  7. Gas Vacuole
Structure of Bacteria

Capsule & slim layer:

Many bacteria secrete a stick fluid like substance that make a protective layer around the cell wall is called Capsule. Some time this layer diffuses then it’s called slim layers.

  1. Bacteria capsules are composing with polysaccharide material, but some bacteria capsule made up with polypeptide.
  2. Main function of capsule they help the bacteria to attach to substance and make colony.  Its also act as an antibiotic in bacteria to resist the diseases.


Bacteria move from one place to other with the help of locomotion organ is called flagella.

  1. Flagella consist of hair like and helical cytoplasmic appendages structure.
  2. It may be present in both side or one side of the bacteria.

Fimbriae or pili:

  1. Pilli are rod like structure that composed of Pillin Protein.
  2. They help to cell to cell attachment.
  3. Basically, they act as sex organ in bacteria.
  4. it helps in mating of bacteria to generating new generation.

Cell wall:

  1. Cell wall present b/w the cytoplasmic membrane and capsule.
  2. It is rigid in nature and provide the shape to bacteria.
  3. Cell wall is compulsory component for bacterial growth.
  4. Those bacterial missing cell wall not complete their growth very well or stop.

On the basic of cell wall bacteria are divide into type.

  1. Gram Positive
  2. Gram Negative

Cytoplasmic membrane:

  1. It is present under the cell wall and cover the living matter of cell.
  2. Semi- permeable in nature.
  3. It composes of 60-70 % protein and 20-30% phospholipid.
  4. Protein are embedded between Bilayer of phospholipid.
  5. It is ATP producing site and attach with the DNA of bacteria.

Specialized membrane:

Infoldings are present in cytoplasmic membrane that make complex structure and increase surface area.

There are two types of Specialized membrane.

  1. Mesosomes membrane
  2. Photosynthetic membrane

Mesosomes membrane:

  1. They are infoldings in structure of cell membrane.
  2. They appear in cell division and attach with DNA.
  3. They help to separate the daughter cell after replication.
  4. They add the cross-wall b/w the bacterial daughter cell.

Photosynthetic membrane:

  1. Tubular like infoldings are produce by cytoplasmic membrane this is called Photosynthetic membrane.
  2. It is founded on photosynthetic bacteria only.
  3. They contain pigment and resemble in Blue green algae.


  1. The bacterial cell cover by a layer is called cytoplasmic membrane in cytoplasm.
  2. They differentiated into liquid part that called cytosol.
  3. This part is rich with ribosome and concentrated due to nuclear material.

Composition of Cytosol:

Cytosol is concentrated, complex solution of amino acid, inorganic acid, peptide, protein, nitrogenous bases, enzyme, vitamin, coenzyme that provide environment for metabolic process or activity.


  1. Ribosome is protein synthesis body that present in cytoplasm freely.
  2. They are dense in nature.
  3. Every ribosome consists of two subunits.
  4. One is 50S and second in 30S with equal amount of Protein and RNA.
  5. They are smaller than eukaryotic ribosome.


  1. Bacterial chromosome consists of 5*106 DNA molecule base pair and 1mm in length.
  2. Small part of protein is also present in it.
  3. DNA is primitive in nature.
  4. Most of bacteria have concentrated DNA and cytoplasmic region protect the DNA, that region is called nuclear body or nuclear region.
  5. Some bacteria have single stranded DNA, and some have double stranded DNA.


  1. Bacteria have smaller ring of DNA is called plasmid.
  2. Every plasmid has ability to self-replication due to presence own Gene.
  3. Some plasmid has ability to resist against the antibodies.
  4. They could produce enzyme that fight against the infection causing agent.
  5. Some plasmid integrating the bacterial DNA Chromosome.


  1. Bacteria produce endospore that act like a resistance bodies against the heat, desiccation and help to overcome the unfavorable growth situation.
  2. At favorable condition the spores germinate to make a new cell.


  1. In few bacteria complete cell developed into a thick walled that called cysts.
  2. Cysts also known as resistance body.
  3. They become new individual when condition is favorable.

Gas Vacuole:

  1. Gas vacuole provide buoyancy in some bacteria aquatic species.
  2. They are rigid, cylindrical and impermeable to water.
  3. They are protein in nature.
  4. Gas pass this membrane.