Important questions based on NCERT syllabus for Chapter 9 - Heredity and Evolution:
Question-1: Why are asexually reproducing organisms more capable of showing the hereditary features?
Solution: 1.Asexually reproducing organisms require only a single parent during the process of reproduction. So there is very less chance of occurrence of variation through DNA replication.
2.The asexually reproducing organisms are capable of showing the hereditary features more because in this mode of reproduction, mitotic or amitotic process is involved and the cell divides itself rapidly to new individuals which are identical (carbon copy) to their parents and have no variations.
Question-2: Why are human beings, who look so different from each other in terms of size, color and looks said to be of the same species?
Solution: 1. A species is a group of organisms that are capable of inter breeding to produce a fertile offspring. Skin color, looks and size are all variety of features present in human beings.
2. These features are generally environmentally controlled. Various human races are formed based on these features.
3. However, there is no biological basis to this concept of races. Therefore, all human beings are a single species as humans of different color, size and looks are capable of reproduction and can produce a fertile offspring
Question-3: Explain the importance of fossils in deciding evolutionary relationships.
Solution: 1. Fossils are the remains of organisms that once existed on earth. They represent the ancestors of the plants and animals that are alive today. They provide evidence of evolution by revealing the characteristics of the past organisms and the changes that have occurred in these organisms to give rise to the present organisms.
2. Let us explain the importance of fossils in deciding the evolutionary history with the help of the following examples. Around 100 million years ago, some invertebrates died and were buried in the soil in that area. More sediments accumulated on top of it turning it into sedimentary rock. At the same place, millions of years later, some dinosaurs died and their bodies were buried on top of the sedimentary rocks. The mud that contained dinosaurs also turned into rocks. Then, millions of years later, some house like creatures died in that area and got fossilized in rocks above the dinosaur fossils.
3. Some time later, due to soil erosion or floods in that area, the rocks containing horse-like fossils were exposed. If that area is excavated deeper, then the dinosaurs and the invertebrate’s fossils can also be found. Thus, by digging that area, scientists can easily predict that horse like animals evolved later than the dinosaurs and the invertebrates. Thus the above example suggests that the fossils found closer to the surface of the earth are more recent ones than the fossils present in deeper layers.