What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer.
What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer.
- Homologous Structures: Homologous structures are organs or body parts in different species that share a similar basic structural design and developmental origin, but may perform different functions in their respective environments.
- Example: The forelimbs of a human, a bird, and a frog. They all share a similar basic bone design, but they are modified to perform different functions (grasping, flying, and propping/leaping respectively).
- Is a common ancestor necessary?: Yes, it is necessary.
Justification: According to the principles of heredity, "inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation." The similarity in the fundamental skeletal or structural design of homologous organs exists because they have been inherited from a shared common ancestor. Over succeeding generations, environmental selection and the accumulation of variations lead to subtle modifications in these structures to suit different functional needs, but the underlying basic design remains conserved, proving their common ancestral origin.
Marking Scheme
- 1Definition of homologous structures with emphasis on similar basic design but different functions (1 mark)
- 2Suitable example (e.g., forelimbs of human/bird/frog) (1 mark)
- 3Justification of common ancestry based on inheritance of basic body design and accumulation of variations (1 mark)
Hint
Think about how a basic body design is inherited from previous generations and how variations modify it for different functions over time.
Quick Oral Answer
Homologous structures are organs in different organisms that have a similar basic structural design but perform different functions, such as the forelimbs of a human and a bird. Yes, they must share a common ancestor because this basic design is inherited from a common ancestral group and modified over generations.
Analysis & Explanation
Homologous structures provide strong evidence for evolution and shared ancestry. The core concept is that a 'common basic body design' is inherited from a previous generation (ancestor). When populations of a species split and adapt to different environmental niches, natural selection acts on the variations generated during reproduction. This leads to modifications in the functions of these structures (divergent evolution), while the fundamental anatomical design remains the same because it is encoded in the inherited genetic framework.
Common Mistakes
- 1Confusing homologous structures with analogous structures (which have different basic designs but similar functions).
- 2Stating that homologous structures do not require a common ancestor.
Interesting Facts
Though the forelimbs of humans, cats, whales, and bats look completely different from the outside and perform vastly different tasks, they share the exact same basic arrangement of bones, inherited from an ancient lobe-finned fish ancestor.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2020?
This question carries 3 marks in the CBSE Class 10 Science 2020 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Heredity" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Inherited Traits and Body Design" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2020 paper?
This is a Short Answer question from Section B in the CBSE Class 10 Science 2020 paper.