Question

Short/Long answer type questions
The study of (i) Fossils of dinosaurs (ii) Forelimbs of the cheetah, bat, whale and human (lii) Thorns of Bougainvillea, and (iv) tendril of Cucurbita show that evolution of life forms has indeed taken place on Earth. Explain.

Answer 1

(i) Fossils of dinosaurs show how species, as we see them today, were not as such always. There has been a gradual change in species number, their distribution, forms and domination based on their ability to adapt. This also shows how changing environmental conditions and competition has been driving force for evolution.

(ii) Forelimbs of cheetah, bat, whale and human are built upon the same pattern as they all have the same bones namely humerus, radius, ulna carpels. These bones differ in different animals because they are modified and specialized according to different modes of life, such as swimming’ walking, jumping, flying, climbing, digging, etc. Such structures are said to be homologous organs. They show common ancestry i.e at some point of time these organisms shared a common ancestor which diverged into different species based on its environment and how it adapted for that environment.

(iii) Both the thorns of bougainvillaea and tendrils of Cucurbita origin from the stem and are modified from the axillary buds but their functions are different. It shows common ancestry. With time and their need for adaptation, these structures evolved to help these both species survive.