Question

Select the homologous structure from the combinations given below:
i) Forelimbs of whales and bats
ii) Tuber of potato and sweet potato
iii) Eyes of octopus and mammals
iv) Thorns of Bougainvillea and tendrils of Cucurbita

Answer 1

Hint: Comparative anatomy is basically the study of the anatomy of two species and finding the similarities and differences between them. Homologous and analogous organs come under it.

Complete Answer:
Homologous structures support the idea that the different animals descend from a common ancestor and serve as evidence of evolution.
Eg: A dolphin's flipper, a bird's wing, a cat's leg, and a human arm are considered homologous structures.

(i) Forelimbs of whales help them to flip and swim in water, whereas bats help them to fly. The common bones such as the humerus, ulna and radius, carpals, metacarpals, and phalanges are present in both animals. Bats and whales have very similar homologous structures, demonstrating that these creatures all had a common ancestor. They show homologous structure.

(ii) Both Sweet potato and potato tubers are underground fleshy structures which perform the functions of storage of food and vegetative reproduction. Though they perform the same function they are different in origin i.e., sweet potato is an adventitious root and potato tuber is an underground stem. Therefore, both of these are an example of analogous organs.

(iii) Eyes of octopus and mammals show analogy, that is they are structurally different but functionally same. The Pax gene is a gene common to both humans and octopi as well they both have developed the "camera" eye. Their version of the camera eye was converging evolutionarily up until the point of their common ancestor of the bilateria group. Their eyes shared 1019 out of the 1052 ancestral sequences. This is the point at which the octopus eye and the human eye began to diverge and evolve independently and show analogous structure.

(iv) Thorns of Bougainvillea and tendrils of Cucurbita are examples for homologous organs as both of them arise from the axillary buds. But both of these different functions as thorns of Bougainvillea provide protection against gazing animals, whereas tendril of Cucurbita provide support in climbing.

So, the homologous structures are i) and iv).

Additional information: There are various evidences that support evolution
1. Comparative anatomy- Presence of analogous and homologous organs.
2. Development of embryo- The embryos of various organisms have a similarity until a certain period of gestation.
3. Fossils of plants and animals- It is the remains of non-degraded parts of the living plants and animals.

Note: It is very important that one does not get confused between homologous and analogous structures.
Homologous- Same ancestor, different function.
Analogous- Different ancestor, same function.