CBSE Tutorials

How do Organisms Reproduce?

Reproduction is the process by which living organism produce new individuals similar to themselves.

Reproduction ensured continuity of life on earth.

It involves continuation of characters from the parents to daughter cells by copying of DNA (deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell.

The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.

Therefore, a basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other.

Copying of DNA is also not a foolproof exercise, even a minute changes bring about Variation in the blue print of the offsprings.

The useful variations are retained while the harmful one does not go beyond.

REPRODUCTION

Asexual Reproduction:

Asexual Reproduction is extremely useful as a mean of rapid multiplication. It is common in lower plants and animals.

Asexual reproduction can be divided in following parts:

1. FISSION : When parent cell divides/split into two or more individuals.
   
   1. Binary Fission: when parent cell divides into two individuals it is termed as binary fission. e.g. Amoeba, Paramecium.
      

    

2. BUDDING : Some individual develops a small outgrowth from its body part known as bud, as the bud grows it detaches from the parent body and develops into a whole new individual.

Budding in yeast

1. Spore Formation : Spores are small, bulb like structure develops at the top of the erect hyphae of the fungus plant. They a light weight and produce numerous spores at same time, released into the air and germinate, into new individuals after landing into food or soil.
   

   
   

Spore formation in Bread Mould

4. FRAGMENTATION : It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. eg. fragmentation in spirogyra

Fragmentation in Spirogyra

5. REGENERATION : When the simple animals like Hydra, Planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialised cells which grow large numbers of cells.

VEGETATIVE PROPAGATION :

A mode of reproduction in which part like the stem, root, leaves develop into new plant under favourable conditions.

e.g.
Sugarcane, roses, Bougain-villea, Chrysanthemum etc

Vegetative propagation are of following types:

• Layering : The adventitious roots are produced in the branch of the stem before the plant is detached from the parent plant. The branch of stem is called a layer. This process is utilized in the propagation of plant and the phenomenon is called layering. Layering is used in the propagation of plants like Lemon, Guava, Hibiscus, Bougainvillea, Jasmine, Raspberry, Strawberry and many ornamental plants.
  

• Grafting : In this method of reproduction, two plants of closely related varieties are joined together so that they leave as one plant.
  

1. The portion of a plant that is grafted on the other plant is called scion, and the plant in which grafting is performed is called the stock.
   
2. This method is applied to improve variety of fruits like mango, apple, peas, citrus and guava.
   

Benefits

1. Plants can bear flowers, fruits earlier than those produced from seeds.

2. Growing Banana, orange, rose, jasmine that have lost the capacity to produce seeds.

3. Genetical similarity is maintained in the plants.

eg. Sugarcane, rose, grapes by layering or grafting.

Assignment

1. Which life process ensure that a plant or animal species will not disappear from the earth?                                        (1)
   

2. Define Asexual reproduction?                            (1)
   

3. Why is DNA copying an essential part of the reproduction?            (1)
   

4. Can you consider cell division as a typr of reproduction in unicellular organism? Give one reason.                                    (1)
   

5. What are the advantages of sexual reproduction over asexual reproduction?    (2)
   

6. Why more complex organisms cannot give rise to new individuals through regeneration?                                    (2)
   

7. How does reproduction help in providing stability to population of species?    (2)
   

8. Why does bread mould grow profusely on a moist slice of bread rather than on dry slice of bread?                                    (2)
   

9. (i) Which are the two main types of reproduction in lioving organisms?    (3)
   

   (ii) classify the following under these two types: Amoeba, frog, Earthworm. Yeast.
   

10. Explain vegetative propagation with the help of two examples. List two advantages of vegetative propagation.                            (3)
    

11. What is a sexual reproduction? How do potato and bryophyllum plants reproduce vegetatively?
    

12. Write three differences between asexual and sexual reproduction.        (3)
    

13. What are the various artificial methods of vegetative propagation in plants?    (5)
    

14. Define asexual mode of reproduction. What are the different methods of asexual mode of reproduction? Define regeneration with the help of diagram.        (5)