Origin and evolution of life Questions and Answers-5.


Q. 1. What is geological time scale ? How is it divided ?

(3 marks)

Ans. (1) Geological time scale is the arrangement of major divisions of geological time into eras. periods and epochs on the time scale.

(2) This division is based on the study of fossilized organisms obtained from the different strata of the earth.

(3) The characteristic significant events that occurred in the organization of organisms helped the geologists to understand the geological time scale.

(4) The major divisions of geological time are called eras.

(5) The eras are divided into periods and the periods into epochs.

(6) By studying fossils in the earth crust, the evolutionary changes in the organisms have been traced out.


USA History


Q. 2. What is meant by paleontological evidences ?

(2 marks)

Ans. (1) Paleontology means the study of fossils. Palaeontological evidences are the fossilized forms of various organisms which are obtained from different strata of the earth. They represent the dead remains of plants and animals that lived in the past in various geological layers.

(2) The older and more primitive forms of life are excavated from the lower strata of the soil whereas the recent ones are situated on the upper layers of the soil.

(3) Fossils are formed in variety of materials such as sedimentary rocks, amber, volcanic gas, ice, peat bogs, soil, etc.

(4) They provide the true, direct and reliable evidences of evolution.


Q. 3. What are the different types of fossils ? Describe them briefly.

(3 marks)

Ans. (1) Fossils are of three main types, viz. actual remains, moulds and casts.

(2) Actual remains are common types of fossils. They are seen in deep oceans where the dead bodies of plants and animals are buried deep down at the ocean bottom.

(3) Either the entire body or its hard parts are surrounded by minerals which form a fossil.

(4) In some cases, the entire body or part of the body is fossilized in ice.

(5) Mould is an impression of the body parts left on the soft mud of the oceanic floor.

(6) Cast is formed when the cavities of the mould are filled with minerals which later harden and form stony cast.


Q. 4. Describe the significance of the fossils.

(2 marks)

OR

Give the importance of fossils in support of organic evolution.                                                 (2 marks) (Oct. '13)

Ans. Significance of fossils : (1) Fossils are useful in reconstructing the phylogeny of organisms. Phylogeny is the evolutionary history and thus studying the fossil form helps in understanding the evolutionary pattern.

(2) Observing fossil helps in understanding the structure of extinct animals. Paleontology thus is a tool to study various body forms and their evolution

(3) From the fossils, one could understand the habit of extinct organisms.

(4) From the fossil record the connecting links between different groups could be understood.


Q. 5. What is a connecting link? Give suitable examples of connecting link.                                                 (2 marks)

Ans. (1) A connecting link is an intermediate or transitional state between two systematic groups of organisms.

(2) It bears characters common to both these groups on either side of its position. Thus it represents an evolutionary line.

(3) Connecting links are also called a missing link.

(4) E.g. Archaeopteryx, the extinct bird is a connecting link between Reptiles and Aves.

(5) Seymouria is a connecting link between Amphibia and Reptilia.

(6) Ichthyostega is a connecting link between Pisces and Amphibia.