(i) We see eyes in planaria, insects, octopus and vertebrates. Can eyes be grouped together in case of the above-mentioned animals to establish a common evolutionary origin? Why? (ii) State one evidence to prove that birds have evolved from reptiles.

Q: (i) We see eyes in planaria, insects, octopus and vertebrates. Can eyes be grouped together in case of the above-mentioned animals to establish a common evolutionary origin? Why? (ii) State one evidence to prove that birds have evolved from reptiles.

(i) **No**, the eyes of planaria, insects, octopus and vertebrates **cannot be grouped together to establish a common evolutionary origin.** Reason: Although all of these organisms possess eyes and the function (vision) is similar, the *basic structural design* of their eyes is very different. • Planaria has simple eye-spots that can only detect light. • Insects have compound eyes made of many units (ommatidia). • Octopus and vertebrates have camera-type eyes, but the arrangement of retinal cells is reversed — in octopus the nerve fibres lie *in front* of the receptor cells, whereas in vertebrates they lie *behind* the receptor cells. Since the structures are anatomically different, they are **analogous organs** (similar function, different origin), and they suggest *independent* evolution rather than a single common evolutionary origin. (ii) **Evidence that birds evolved from reptiles:** The discovery of the fossil *Archaeopteryx* provides strong evidence. *Archaeopteryx* had features of both reptiles and birds — it possessed reptilian characters such as *teeth in the jaws, a long tail with caudal vertebrae, and clawed fingers*, along with avian (bird) characters such as *feathers and a beak*. Such a transitional/missing-link fossil shows that birds evolved from reptilian ancestors.

Heredity

Homologous vs analogous organs; evidences of evolution

Official Answer

(i) No, the eyes of planaria, insects, octopus and vertebrates cannot be grouped together to establish a common evolutionary origin.

Reason: Although all of these organisms possess eyes and the function (vision) is similar, the basic structural design of their eyes is very different.

• Planaria has simple eye-spots that can only detect light.

• Insects have compound eyes made of many units (ommatidia).

• Octopus and vertebrates have camera-type eyes, but the arrangement of retinal cells is reversed — in octopus the nerve fibres lie in front of the receptor cells, whereas in vertebrates they lie behind the receptor cells.

Since the structures are anatomically different, they are analogous organs (similar function, different origin), and they suggest independent evolution rather than a single common evolutionary origin.

(ii) Evidence that birds evolved from reptiles: The discovery of the fossil Archaeopteryx provides strong evidence. Archaeopteryx had features of both reptiles and birds — it possessed reptilian characters such as teeth in the jaws, a long tail with caudal vertebrae, and clawed fingers, along with avian (bird) characters such as feathers and a beak. Such a transitional/missing-link fossil shows that birds evolved from reptilian ancestors.

analogous organshomologous organsArchaeopteryxtransitional fossilconvergent evolutioncompound eyeinverted retina

Marking Scheme

11 mark (i): Stating 'No' and identifying them as analogous organs.
21 mark (i): Giving structural difference (e.g., compound vs. simple vs. inverted-retina eyes).
31 mark (ii): Naming Archaeopteryx and listing any one reptilian and one avian feature.

Hint

Part (i) — think analogous vs. homologous organs. Part (ii) — recall the missing-link fossil that has both teeth and feathers.

Quick Oral Answer

Eyes of these animals are analogous organs — they perform the same function (vision) but have different basic structural designs, so they cannot be used to show a common evolutionary origin. The fossil Archaeopteryx, with both reptilian (teeth, tail) and avian (feathers, beak) features, shows that birds evolved from reptiles.

Analysis & Explanation

The NCERT textbook classifies organs with similar function but different basic design as 'analogous organs', which indicate convergent evolution (different origins). Eyes in the listed groups differ in basic plan, so they are analogous, ruling out a common evolutionary origin. For (ii), the standard example cited in NCERT is Archaeopteryx — a transitional fossil showing reptilian and avian features, proving birds descended from reptiles.

Common Mistakes

1Calling the eyes 'homologous' — they are analogous because structure differs.
2Writing only feathers/Beak for Archaeopteryx and forgetting reptilian features such as teeth or tail.
3Confusing 'same function' with 'same origin'.

Interesting Facts

The octopus eye is often cited as the textbook case of convergent evolution with the vertebrate eye.

Archaeopteryx was about the size of a crow and lived around 150 million years ago in what is now Germany.

Despite having 'camera eyes' like us, the octopus evolved them completely independently.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2012?

This question carries 3 marks in the CBSE Class 10 Science 2012 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 "Homologous vs analogous organs; evidences of evolution" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2012 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.