Introduction
Variation refers to the differences in characteristics found among individuals of the same species. No two organisms are exactly alike, even if they belong to the same species or are offspring of the same parents.
According to NCERT, variations are important because they help organisms survive changing environmental conditions and play a key role in evolution.
Definition of Variation
Variation is the difference in traits or characteristics among individuals of the same species.
Examples of Variation
- Different heights among humans
- Variation in skin color
- Different eye colors
- Blood groups in humans
- Different flower colors in plants
- Variation in beak size among birds
Why Do Variations Occur?
Variations occur due to:
1. Genetic Changes
- Differences in genes inherited from parents
- Mixing of genes during reproduction
- Mutations in DNA
2. Environmental Factors
- Food habits
- Climate
- Lifestyle
- Physical activities
Example
Two identical twins may have different body weights if their diets and lifestyles differ.
Types of Variation
| Type | Description | Example |
|---|---|---|
| Genetic Variation | Caused by differences in genes | Blood groups |
| Environmental Variation | Caused by surroundings | Body weight |
| Continuous Variation | Shows a range of differences | Human height |
| Discontinuous Variation | Distinct categories | Blood group A, B, AB, O |
Importance of Variation
Variation is essential for the survival of species.
Major Importance
1. Helps in Adaptation
Organisms can adjust better to changing environmental conditions.
2. Ensures Survival
If environmental conditions change suddenly, some individuals with favorable variations may survive.
3. Basis of Evolution
Variations accumulate over generations and lead to the formation of new species.
4. Increases Biodiversity
Different characteristics create diversity among living organisms.
Sources of Variation
1. Sexual Reproduction
Sexual reproduction produces offspring with new combinations of genes.
Reasons
- Fusion of male and female gametes
- Crossing over during meiosis
- Random assortment of chromosomes
2. Mutations
Mutations are sudden changes in DNA that create new traits.
3. Genetic Recombination
Mixing of parental genes creates unique offspring.
Variation in Asexual Reproduction
- Asexual reproduction usually produces identical offspring.
- Small variations may occur due to copying errors during DNA replication.
Example
Bacteria reproducing by binary fission.
Variation and Evolution
Variation is the raw material for evolution.
Process
- Variations arise in organisms.
- Some variations provide survival advantages.
- Organisms with beneficial variations survive and reproduce.
- These traits are passed to future generations.
- Over time, evolution occurs.
Example
Long-necked giraffes survived better because they could reach higher leaves for food.
Difference Between Variation and Adaptation
| Variation | Adaptation |
|---|---|
| Differences among individuals | Special features helping survival |
| May or may not be useful | Always useful for survival |
| Occurs naturally | Develops through natural selection |
| Example: Different heights | Example: Camel’s hump |
Key NCERT Points
- Variation means differences among organisms of the same species.
- Variations arise due to genetic and environmental factors.
- Sexual reproduction produces more variation than asexual reproduction.
- Variations help organisms adapt to changing environments.
- Variation is essential for evolution and survival.
- Beneficial variations increase the chances of survival.
Practice Questions
Very Short Answer Questions
1. What is variation?
Answer: Variation is the difference in characteristics among individuals of the same species.
2. Why is variation important?
Answer: It helps organisms survive changing environmental conditions and supports evolution.
3. Name one source of variation.
Answer: Sexual reproduction.
4. What is a mutation?
Answer: A sudden change in DNA that creates new characteristics.
5. Which type of reproduction produces more variation?
Answer: Sexual reproduction.
Short Answer Questions
1. Explain the importance of variation.
Answer:
- Helps adaptation
- Increases survival chances
- Supports evolution
- Maintains biodiversity
2. How does sexual reproduction create variation?
Answer:
Sexual reproduction combines genetic material from two parents, producing offspring with unique gene combinations.
3. Give two examples of variation in humans.
Answer:
- Height
- Blood group
Fill in the Blanks
- Variation means differences among __________ of the same species.
Answer: individuals - Variation is important for __________.
Answer: survival - Sexual reproduction produces more __________.
Answer: variation - Sudden changes in DNA are called __________.
Answer: mutations - Variation is the basis of __________.
Answer: evolution
Multiple Choice Questions (MCQs)
1. Variation refers to:
A. Similarities among organisms
B. Differences among organisms
C. Reproduction
D. Growth
Answer: B. Differences among organisms
2. Which reproduction produces greater variation?
A. Binary fission
B. Budding
C. Sexual reproduction
D. Vegetative propagation
Answer: C. Sexual reproduction
3. Variation is important because it helps:
A. Digestion
B. Survival
C. Respiration
D. Excretion
Answer: B. Survival
4. Blood group is an example of:
A. Genetic variation
B. Environmental variation
C. Adaptation
D. Mutation
Answer: A. Genetic variation
5. Which is a source of variation?
A. Photosynthesis
B. Respiration
C. Mutation
D. Digestion
Answer: C. Mutation
6. Variation is necessary for:
A. Sleeping
B. Evolution
C. Excretion
D. Nutrition
Answer: B. Evolution
7. Which factor can cause environmental variation?
A. Genes
B. DNA
C. Climate
D. Chromosomes
Answer: C. Climate
8. Asexual reproduction generally produces:
A. Highly varied offspring
B. Identical offspring
C. New species immediately
D. Gametes
Answer: B. Identical offspring
9. Beneficial variations help organisms:
A. Become extinct
B. Survive better
C. Stop reproduction
D. Lose genes
Answer: B. Survive better
10. Variation is the raw material for:
A. Respiration
B. Photosynthesis
C. Evolution
D. Digestion
Answer: C. Evolution
Quick Revision Summary
✅ Variation means differences among individuals of the same species.
✅ Caused by genetic and environmental factors.
✅ Sexual reproduction creates maximum variation.
✅ Variation helps adaptation and survival.
✅ Variation is essential for evolution.
✅ Beneficial variations are passed to future generations.
