NCERT Class 10: Science-Exercise Solutions

Chapter 09-Heridity and Evolution-Exercise Solutions

NCERT Book Page Number- 159
1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Ans. (c) TtWW
2. Example of homologous organs is
(a) our arm and a dog’s foreleg
(b) our teeth and an elephant’s tusks
(c) potato and runners of grass
(d) all of these
Ans. (d) all of these
3. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee
(c) a spider
(d) a bacterium
Ans. (a) a Chinese school-boy
4. A study found that children with light-coloured eyes are likely to have parents with lightcol¬oured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Ans. We cannot say with certainty whether the light coloured eyes is a dominant or a recessive character. Since both the parents and children have light coloured eyes, it should be a recessive trait.
5. How are the areas of study – evolution and classification interlinked?
Ans. The living organisms are classified on the basis of similarities and differences amongst them. More similar characteristics indicate their evolution from a common ancestor. Similarly, more differences indicate their different adaptations and divergence from a common ancestor.
6. Explain the terms analogous and homologous organs with examples.
Ans. Analogous organs : — The organs which look alike and perform same functions but are quite different in basic structure and embryonic origin in different species are called analogous organs. For example, the wings of a bat and the wings of a bird are analogous organs. Though the basic design of these wings are completely different, they look similar because they have a common function.
Homologous organs : — The organs which are similar in basic structure and embryonic origin but perform different functions in different species are called homologous organs. For example, the forelimbs of a human, a bird, a lizard and a frog show similarity in basic structure.
7. Outline a project which aims to find the dominant coat colour in dogs.
Ans. We can organise a survey to find the dominant coat colour in dogs. It can be performed as follows :
(i) Observe a dog population in your locality. Note down the different colours of dogs and number of dogs of each colour. Then find the percentage of each colour of dogs.
(ii) Observe the pups where same coat colour is present in both parents and offspring.
(iii) Find the colour of F1 generation of these dogs.
(iv) Allow the dogs for test cross i.e. allow cross between F1 dogs and the one having the other recessive colour.
8. Explain the importance of fossils in deciding evolutionary relationships.
(a) What are fossils?
(b) Explain the importance of fossils in evolutionary relationship.
Ans. Fossils are the remains or traces and impressions of any organism that lived in the geological past. Fossils provide a direct evidence of evolution and are called written documents of evolution. A few such fossils are as follows : –
(i) Trilobite, a palaeozoic arthropode
(ii) Ammonite, a spirally coiled shelled mollusc
(iii) Rajasaurus, a dinosaur.
There are some other fossils which give a strong evidence of a common ancestor as well as evolution. Fossils indicate the path of evolution of different groups. They indicate the phylogeny of some organisms. Some fossils have characteristics intermediate between two groups indicating the evolution of one group from another.
9. What evidences do we have for the origin of life from inanimate matter?
Ans. Stanley Miller and Harold Urey in 1953, assembled an apparatus and maintained the atmospheric conditions similar to those that existed on early earth over water. The temperature was maintained just below 100°C and sparks were passed through the mixture of gases to stimulate lightning. At the end of the experiment after a week, they found that 15% of the carbon (from methane) was converted to simple carbon compounds including amino acids which forms protein molecules. It clearly proved that organic compounds of life developed from inanimate matter.
10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduc¬tion. How does this affect the evolution of those organisms that reproduce sexually?
Ans. The offspring produced as a result of sexual reproduction show more variations while the individuals produced asexually are often quite similar to their parents. Though no offspring can be the exact copy of its parents, very minor differences are observed in asexually produced offspring. Variations arise during sexual reproduction due to —
(i) Chance separation of homologous chromosomes during gametogenesis.
(ii) Crossing over between homologous chromosomes.
(iii) Mutations occur during DNA replication, etc.
(iv) The variations are quite viable. Change in DNA due to replication are fewer. Most of them are harmful. They may have some negative impact on evolution except when the changing environment finds them useful.
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans. The genetic material of diploid organisms consists of two sets of chromosomes. The gametes are haploid and consist of single set of chromosomes. Sexual reproduction involves the fusion of male and female gametes. Each gamete brings one set of chromosomes hence diploid chromosome complement is restored. As a result diploid organism consists of 50% chromosomes from male parent and 50% chromosomes from female parent. So both the parents contribute equal amount of genetic material to the offspring.
12. Only variations that confer an advantage to an individual organism will survive in a popula¬tion. Do you agree with this statement? Why or why not?
Ans. The variations generated in offspring do not have equal chances to survive and get inherited in the next generation. The inheritance of such characteristics or variations depends on a number of environmental factors as well as on the nature of variations. For example, a marinewater fish cannot survive in freshwater, a bacterium can survive even in extremely hot places and most of the amphibians hibernate during winter to survive. The disadvantageous variationswhich are either lethal or extremely harmful are eliminated.