NCERT Solutions

Class 10 Science

heredity and evolution

Q1) 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

  1. TTWW
  2. TTww
  3. TtWW
  4. TtWw

Answer:

(c)TtWW

This is dihybrid cross of a plant involving two characters in the same plant. As the progeny bloomed with violet flowers, therefore, the tall plants have genotype WW. Again the plant is neither tall nor short, so the genotype is Tt.

Q2) An example of homologous organs is

  1. our arm and a dog's fore-leg.
  2. our teeth and an elephant's tusks.
  3. potato and runners of grass.
  4. all of the above.

Answer:

(d)All the above

Q3) To terms, we have more in common with

  1. a Chinese school-boy.
  2. our teeth and an elephant's tusks.
  3. potato and runners of grass.
  4. all of the above.

Answer:

(d)All the above

Q4) 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:

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

Q5) How are the areas of study - evolution and classification - interlinked?

Answer:

The field of evolution and classification are interlinked in the following manner:
(i) The more characteristics two species have in common, the more closely they are related. Classification of species is a reflection of their evolutionary relationship.
(ii) The more number of characteristics shared by two organisms more is the probability of them having common ancestor. Thus, classification of an organism is the reflection of its evolutionary path.

Q6) Explain the terms analogous and homologous organs with examples.

Answer:

Homologus organs are those organs which have the same basic structural design and origin but have different functions. For Example: The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.


Q7) Outline a project which aims to find the dominant coat colour in dogs.

Answer:


Q8) Explain the importance of fossils in deciding evolutionary relationships.

Answer:

Fossil provide 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. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.
? Which organisms evolved earlier and which later.
? Development of complex body designs from the simple body designs.

Q9) 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.

Q10) Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer:

Sexual reproduction causes more viable variations due to the following reasons:
? Error in copying of DNA, which are not highly significant.
? Random seggregation of paternal and maternal chromosome at the time of gamete formation.
? Exchange of genetic material between homologous chromosomes during formation of gametes.
? Accumulation of variations occured due to sexual reproduction over generation after generation and selection by nature created wide diversity.
In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.

Q11) 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 female parents 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 receive 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.

Q12) 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. Different individual would have different kind of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for revolutionary process.