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Q1:
Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Solution :
1. Theoretical Foundation: Darwinian Selection in Microorganisms
According to Darwinian selection theory, evolution is driven by the differential survival and reproduction of individuals based on heritable variations. In bacterial populations, antibiotic resistance is not a product of the antibiotic itself, but rather a result of pre-existing genetic variations selected by the environment. [Ref: Darwin's Principle of Natural Selection]
2. Step-by-Step Mechanism of Selection
Step 1: Presence of Genetic Variation
In a large population of bacteria, mutations occur spontaneously during DNA replication. These mutations create genetic diversity, where some individuals possess genes (e.g., genes for efflux pumps, enzyme degradation of antibiotics, or modified target sites) that provide inherent resistance to specific chemical agents. [Per the Theory of Spontaneous Mutation and Random Variation]
Step 2: Environmental Pressure (Antibiotic Application)
When a population is exposed to an antibiotic, the drug acts as an environmental filter. Individuals lacking the resistance genes are eliminated due to metabolic disruption or cell death. [Per the Principle of 'Survival of the Fittest']
Step 3: Differential Reproduction
The resistant bacteria survive the selection pressure. Because they occupy the ecological niche previously held by the susceptible population and face less competition for resources, they multiply rapidly through binary fission. [Per the Principle of Geometric Population Growth]
Step 4: Inheritance and Population Shift
The resistance trait is passed on to the daughter cells. Over successive generations, the frequency of the resistance allele in the gene pool increases significantly, resulting in a bacterial population that is phenotypically resistant. [Per the Modern Synthesis of Evolution]
3. Schematic Representation of Selection
4. Comparative Analysis of Resistance Acquisition
| Factor | Description |
|---|---|
| Variation Origin | Spontaneous mutations or Horizontal Gene Transfer (HGT). |
| Selection Agent | Antibiotic concentration (Environmental constraint). |
| Result | Increased frequency of survival-conferring alleles. |
Final Solution: Antibiotic resistance in bacteria is a definitive example of Darwinian selection, where pre-existing variations in the bacterial population allow individuals with specific resistance traits to survive and proliferate in the presence of an antibiotic, while susceptible strains are eliminated, ultimately leading to the evolution of a resistant population through differential reproductive success.
More Questions from Class 12 Biology Evolution EXERCISES
- Q1: Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
- Q2: Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
- Q2: Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
- Q3: Attempt giving a clear definition of the term species.
- Q3: Attempt giving a clear definition of the term species.
- Q4: Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
- Q4: Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
- Q5: Find out through internet and popular science articles whether animals other than man has self-consciousness.
- Q5: Find out through internet and popular science articles whether animals other than man has self-consciousness.
- Q6: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
- Q6: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
- Q7: Practise drawing various animals and plants.
- Q7: Practise drawing various animals and plants.
- Q8: Describe one example of adaptive radiation.
- Q8: Describe one example of adaptive radiation.
- Q9: Can we call human evolution as adaptive radiation?
- Q9: Can we call human evolution as adaptive radiation?
- Q10: Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
- Q10: Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
CBSE Solutions for Class 12 Biology Evolution
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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