Class 10 CBSE Notes | How Do Organisms Reproduce?

Keywords: Class 10 Science Notes, How do organisms reproduce, DNA copying, Variation in reproduction, Asexual reproduction, Vegetative propagation, Binary fission, Spore formation, Regeneration, CBSE Class 10 Biology

Introduction – Why Do Organisms Reproduce?

Reproduction is one of the most important characteristics of living organisms. Unlike nutrition, respiration, or excretion, reproduction is not essential for the survival of an individual organism, but it ensures the continuity of life on Earth.

• If organisms did not reproduce, species would disappear after the death of individuals.
• Reproduction allows organisms to create new individuals similar to themselves, maintaining the species population.
• It also leads to variations, which are essential for evolution and survival in changing environments.

Thus, reproduction plays a dual role: maintaining species stability and providing variation for adaptability.

Do Organisms Create Exact Copies of Themselves?

DNA Copying in Reproduction

• Organisms look similar because their body designs are similar.
• The blueprint of the body design is stored in DNA (Deoxyribo Nucleic Acid) inside the nucleus.
• During reproduction, organisms make copies of DNA so that new individuals inherit the same body design.

How DNA Copying Works

1. DNA undergoes replication inside the nucleus.
2. Two copies of DNA are formed.
3. Along with DNA, the cellular apparatus also divides.
4. As a result, one parent cell gives rise to two new cells.

However, DNA copying is not always perfect. Minor errors (variations) occur, leading to differences among individuals.

Importance of Variation

• Variations are small differences that arise during DNA copying.
• They are important for the long-term survival of species.

Example: If all bacteria in a pond need a fixed temperature to survive and global warming increases the temperature, most will die. But a few with variation (heat resistance) will survive and continue the species.

➡️ Hence, variation is not always beneficial for an individual but is essential for the survival of the species.

Modes of Reproduction in Organisms

Reproduction in organisms can be asexual or sexual. In this part, we study different asexual modes of reproduction.

Fission

Found in unicellular organisms. The parent cell divides into two or more individuals.

Binary Fission

• Parent cell divides into two equal halves.
• Example: Amoeba, Leishmania.
• In Amoeba, division can occur in any plane.
• In Leishmania, division occurs in a definite orientation.
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Multiple Fission

• The parent cell divides into many daughter cells simultaneously.
• Example: Plasmodium (malarial parasite).

• Multiple fission in Plasmodium

  
  
  

Fragmentation

Found in simple multicellular organisms like Spirogyra. The organism breaks into fragments, and each fragment grows into a new individual. Not possible in complex organisms because they have specialized cells, tissues, and organs.

Regeneration

Some organisms can regrow their body parts into complete organisms. Example: Planaria, Hydra. This occurs due to specialized regenerative cells. However, regeneration is not the main mode of reproduction in most organisms.

Regeneration in Planaria

Budding

A small outgrowth (bud) develops on the parent’s body. The bud grows and detaches to form a new individual. Example: Hydra, Yeast.

Budding in Hydra

Vegetative Propagation in Plants

• In plants, roots, stems, and leaves can give rise to new plants.
• Examples: Bryophyllum (buds on leaf margins), Potato (eyes), Sugarcane, Rose, Jasmine.

• Leaf of Bryophyllum with buds

  
  
  

Advantages of Vegetative Propagation

1. Plants bear flowers and fruits earlier.
2. Plants that do not produce viable seeds (banana, orange) can be grown.
3. New plants are genetically identical to the parent.
4. Tissue culture allows large-scale production of disease-free plants.

Spore Formation

Seen in fungi like Rhizopus (bread mould). Spores are produced inside sporangia (blob-like structures). Spores are covered with thick walls for protection. When they land in a moist environment, they germinate into new plants. ➡️ Spore formation helps survival in unfavourable conditions.

Questions and Answers

Q1. What is the importance of DNA copying in reproduction?

Answer: DNA copying ensures that the body design of organisms is passed on to the next generation. It maintains the stability of species while allowing minor variations for evolution.

Q2. Why is variation beneficial to the species but not necessarily for the individual?

Answer: Variations may not help an individual directly, but they provide some members of a population with the ability to survive under changing conditions. This ensures the long-term survival of the species.

Q3. How does binary fission differ from multiple fission?

Answer:
- Binary fission: Parent cell divides into two equal halves (e.g., Amoeba).
- Multiple fission: Parent cell divides into many daughter cells at once (e.g., Plasmodium).

Q4. How will an organism be benefited if it reproduces through spores?

Answer: Spores are light, protected by thick walls, and produced in large numbers. This increases survival chances, especially in unfavourable conditions.

Q5. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer: Complex organisms have specialized cells, tissues, and organs arranged in a specific order. Regeneration cannot recreate such complexity.

Q6. Why is vegetative propagation practised for growing some types of plants?

Answer: It allows faster, genetically identical reproduction of plants that cannot produce seeds (like banana and jasmine). It also helps in large-scale cultivation.

Q7. Why is DNA copying an essential part of the process of reproduction?

Answer: Without DNA copying, new individuals would not inherit the body design of the parent, and reproduction would fail to ensure species continuity.

FAQs on How Do Organisms Reproduce?

1. What are the two main types of reproduction?

Reproduction is of two types – Asexual reproduction (single parent, no gametes) and Sexual reproduction (two parents, gamete fusion).

2. What is the difference between budding and fragmentation?

Budding: New organism grows from a small outgrowth (Hydra).
Fragmentation: Parent breaks into parts, each growing into a new organism (Spirogyra).

3. Which organisms reproduce by regeneration?

Planaria, Hydra, and some starfish can reproduce through regeneration.

4. What is the advantage of vegetative propagation?

It helps in producing large numbers of identical plants quickly, useful in agriculture and horticulture.

5. Why is variation important in reproduction?

Variation ensures that some individuals survive environmental changes, leading to the evolution and survival of species.

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