Tuesday, 26 January 2016

TEXTBOOK ANSWERS AND SOLUTIONS CBSE CLASS X SCIENCE CHAPTER-9 Heredity And Evolution



      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

ANSWER :-(c) TtWW

      2)    An example of homologous organs is-
(a) our arm and a dog's fore- leg.
(b) our teeth and an elephant's tusks.
(c) potato and runners of grass.
(d) all of the above.

ANSWER:-(b) our teeth and an elephant's tusks.

3) In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.

ANSWER:-(a) a Chinese school-boy.

      3)    A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

ANSWER:-For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

5) How are the areas of study - evolution and classification - interlinked?

ANSWER:-Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.

6) Explain the terms analogous and homologous organs with examples.

ANSWER:-Homologous organs are those organs which have the same basic structural design and origin but have different functions.

Analogous organs are those organs which have the different basic structural design and origin but have similar functions.

7. Outline a project which aims to find the dominant coat colour in dogs.

ANSWER:-Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog. A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)


image credit : www.tutionteacher.in


  
8)Explain the importance of fossils in deciding evolutionary relationships.

ANSWER:-Fossil provides us evidence about:
The organisms that lived long ago such as the time period during which they lived, their structure etc.
Evolutionary development of species i.e. line of their development.
Connecting links between two groups.
Which organisms evolved earlier and which later.

9) What evidence do we have for the origin of life from inanimate matter?

ANSWER:-The evidence for the origin of life from inanimate matter, was provided through an experiment, conducted in 1953, by Stanley L. Miller and Harold C. Urey. In experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen, over water. This was similar to atmosphere that thought to exist on early earth.This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon from methane had been converted to simple compounds of carbon including amino acids which make up protein molecules and support the life in basic form. Thus, amply suggesting that life arose afresh on earth.

10)Explain how sexual reproduction gives rise to more viable variations than a sexual
reproduction. How does this affect the evolution of those organisms that reproduce sexually?

ANSWER:-In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations, whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate. Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus. However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable.

Variation and Evolution: Variants help the species to survive in all the conditions.
Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species.

11) How is the equal genetic contribution of male and female parents ensured in the progeny?

ANSWER:-In human beings, equal genetic contribution of male and a female parent is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes All human chromosomes are not paired.
Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome. During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of the diploid zygote. The zygote in the progeny receives an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X-chromosome.

12) Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

ANSWER:-We agree with the statement that only variations that confer an advantage to an individual organism will survive in a population. All the variations do not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations.

















Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.