Heredity and Evolution Class X Important Question and Answers

Science class 10 Heridity and Evolution

1.Why acquired characters are not inherited?
Ans.Acquired traits are those which are dev eloped in the organisms during their life time. They are not inherited to next generations. These traits are because of non- reproductive tissues, so cannot be passed.

2.How is the chromosome number restor ed in zygote?

Ans.Gametes (male and female) have N number o f chromosomes. During fertilization gametes fuse and forms zygote. Zygote retains 2N nu mber of chromosomes.

3.What are variations? Give their types.
Ans.Although offspring of the same parents re semble one another as to their parents, yet three are differences among them. These differe nces are called variations. It is of two types- (a) Reproductive- Passed from one generation to another . (b) None reproductive- Not passed from one generation t o another.

4.Write difference between Autosomes or Allosomes.
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5.State the evolutionary force which leads to origin of a new species.

Ans. Various elemental forces of evolution are- (a) Mutation (b) Recombination (Crossing over during meiosis, Random assortment of gene at the time of gamete formation). (c) Natural selection or survival of the fittest. (d) Genetic drift
6.What is a fossil? How do fossils tells us about the process of evolutions?
Ans. The dead remains of former living organ isms are called fossils. The branch of biology which deals with the study of fossils is ca lled paleontology. The study of fossils tells us that species arose from previously existing ones or that the evolution has occurred in nature and is still conti nuing.

7.Who disproved Lamarckism and how?
Ans. The concept of inheritance of acquired character of Lamark was disproved by August Weismann. He cuts the tail of rat at the tim e of birth and continued this for 21 generation. But tailless rats were never bor n. This trait do not change the DNA of germ cells so cannot be inherited. Hence, th e changes in non-reproductive tissue of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution.

8.Give the basic features of the mechanism of inheritance.
Ans. Basic features of mechanism of inherit ance- (a) Each character is controlled by a pair of factors. The factors may be similar or dissimilar. (b) When two dissimilar factors of a character are pres ent in an organism, only one expresses itself while other remains unexpresse d. (c) Two factors of a character are separated at the tim e of gamete formation and get only one factor for that character. (d) Inheritance of two or more pairs of contrasting tra its in such a way that one pair of contrasting traits is independent of the ot her pairs of contrasting traits.
9.Give difference between diploid and haploid

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10.Mention two sources of variation.
Ans. (1) Errors in DNA copying.
(2) Random fertilization.

11.What is monohybrid and dihybrid cross?
Ans. Monohybrid cross- It is the simplest cross in which inheritance of one character is studied. A cross is made between the pair of pla nts having one contrasting character such as tall or dwarf.
Dihybrid cross- A cross made be tween two plants having two pairs of contrasting character is called dihybrid cross. For ex. round a nd green seed crossed with yellow and wrinkled seed.

11.Why did Mendel choose pea plant for his experimentation?
Ans.Mendel selected garden pea for his ex periment for the following reasons- (a) The life span of this plant is very short so result s can be obtained and studied faster. (b) Garden pea has many characteristics which are in co ntrast to each other. (c) Moreover this plant is small, easy to grow and repr oduce large number of offsprings.

12.How does Archaeopteryx provide evidence for organic evolution?
Ans. Archeoptyrx has some features of repti les, characters of dinosaurs as well as some features of birds like wings. This shows that birds are closely related to reptiles. Birds could evolve from reptiles.

13.What is divergent evolution? Explain with the help of example
Ans. The formation of dissimilar looking or ganisms from common ancestors is called divergent evolution. This is also known as adaptive radiation which represents evolution of new forms in several directions from t he common ancestors type. The current example of such a process is the evolut ion of wild cabbage. For over more than 200 years, humans have cultivated wild ca bbage as a food plant and generated different vegetables (like cabbage, brocc oli, cauliflower, kohlrabi and kale etc) from it by different artificial selection s. Thus all these structures of different vegetables are descended from the same an cestor i.e. wild cabbage.
14.What is the difference between reproductive and non - reproductive variations ?
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15.Write similarities between Mendalian’s factors and gene.
Ans. Mendel proposed the inheritance of trait s from parents to offsprings by hereditary units called factors. Mendel suggested t hat every character is controlled by a pair of factors. Sutton and Boveri (1902) found striking similarities between the behaviours of Mendelian fa ctors and the chromosomes during meiosis and fertilization. Factor and chromo somes are present in paired condition in the parents, seprate during meiosis an d again get paired after fertilization.

16.What is emasculation? Why is it done?
Ans. Removal of anther to avoid pollination in experimental plant is called Emasculation.

17.What is gene? Where are genes located?
Ans.Segments of DNA are called gene. Genes are located on chromosomes.

18.How many contrasting characins did Mendel see in garden pea? Give any two of them.
Ans. Mendel observed seven contrasting charact ers is pea plant. For Ex- flower position- axial an d terminal. seed shape- round and wrinkled.

19.Give difference between homologous and analogous or gans.
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20.State three law s of Mendel.
Ans. Mendel’s law- (A) Law of dominance- when two dissimilar factors of a character are present in an organism only one expresses itself (dominant fac tor) while other remain unexpressed (recessive factor)
(B) Principle of segregation – two factors of a charact er are separated at the time of gamete formation and each gamete gets only one f actor for that character.
(C) Principle of independent assortment- this principle states that inheritance of two or more pair of contrasting traits is such a w ay that one pair of contrasting traits is independent of the other pair of contrasting traits.

21.Describe how the sex of the offspring is determined is the zygote is human beings?
Ans.The males can produce two types of game tes, either X-type or Y-type. The females produce only one type of gametes or ova, X-type. If X-type sperm fuses with the ovum, then the sex of the baby will be female. If Y -type sperm uses with the ovum, then the sex of the baby will be male. Sex of the b aby is decided at the time. Sex of the baby is decided at the time of fertilization.

22.Give a suitable explanation for “geographical isol ation of individual of a species lead to formation of a new species?
Ans. Reproduction barrier such as river (geogr aphical is olation) between the sub population leading to: a) Genetic drift or random changes in the gene frequen cy by chance alone e.g. selection of red or blue beetles instead of green i n presence of crows. b) Natural selection or selection of the fittest by na ture itself eg. Selection of green beetles instead of red ones in the presence o f crows.

23.( i ) Who provided the evidence of DNA as genetic materia l?
(ii) Why DNA is called polynucleotide. (iii) List three important features of double helic al model of DNA.
Ans.

(a) Mendel.
(b) DNA is made up many units o f nucleotides. (c) Important features- (1) Both the chains in helical runs anti-parallel.
 (2) There two nitrogenous base Purine (A, G) and pyrimidine (T, C).
 (3) A always bind with T an d C always binds with G.

24.Why acquired traits are not inherited?
Ans. Acquired traits are those which are devel oped in the organisms during their life time. These traits are because of non-reproductive tissue, so cannot be passed.

25.How evolution and classification are linked?
Ans. Classification is the arrangement of organi sms into groups on the basis of their characteristics. Characteristics are details of app earance or behaviour. Classification based on evolution is considered the most advanced and effective. The classification of organisms/ species into groups is a reflection o f their common ancestors and hence evolutionary relationship also.

26.What are coacervates?
Ans. First life molecules which are formed due to formation of membrane around amino acids, sugars and nitrogenous bases aggregates are called coacervates. Further development in coacervates leads to origin of life.

27.How do the two factors for a character, present in diploid cells, behave at the time gamete formation?

Ans. Two factors called X and Y, segregate durin g gamete formation. Hence gamete is either X or Y.
28.Only variations that confer an advantage to an indi vidual organism will survive in a population. Do you agree with this statement? Why or why not?

Ans.Variations that confer an advantage to an individual organism may or may not survive in the population depending upon the social behaviour of the organism. A variation in a social animal like ant may not survi ve in a population while a variation in an animal like a leopard may survive.

29.What are the different approach es to determine evolutionary history of man?
Ans. To construct evolutionary history of man , there are three approaches- (1) Historical method- It gives direct evidence in the form of fossil records. The age of fossils can be determined by carbon dati ng methods.
(2) Comparative method- By comparing several exis ting forms, we can makes ideas about their common ancestors and reconstruct their about possible history.
(3) Analytic method- By observing present day human be ing vestigial organs and by studying the development pattern from embryo to adult.

30.What is fossilization? How are fossils formed?
Ans.The process of fossils formation is calle d fossilization. Fossils are formed when organisms die; their bodies get decomposed and lost . Sometimes the body or a part of it may be in such an environment that it does no t let it decompose completely. The mud will eventually harden and retain the impre ssion of the body parts of the organism. This mud with the impression will be call ed fossil of the organism.

31.What are homo lo gous and analogous organ? Explain with the help of example.
Ans.Homologous organs are those which have si milar basic structure and origin but may have different functions. For example- Hands of human bein gs and wings of birds. Analogous organs- Organs which ha ve different basic structure and origin but have similar function are called analogous organs. For example- (1) wing of bat an d wing of bird. (2) wing of birds and wing of insect.

32.Give the pair of contrasting traits of the followin g characters in plant and mention which one is recessive and which is dominan t? (a) yellow seed (b) round seed

Ans. (a) Green seed- Dominant Yellow seed- Recessive (b) Wrinkled seed – Recessive Round seed- Dominant

33.Mention two important features of fossils which hel p in evolution.
Ans. (a) Fossils provide direct evidence o f evolution
 (b) Fossil records also provid e missing links between two groups of organisms, for example- Archaeopteryx.

34.What do you understand by the term natural selection?
Ans. According to theory of Natural selectio n, Nature select fittest animal for animal those who not fit, are eliminated by nature itself

35.Differentiate between convergent and divergent evol ution.
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36.What are the different ways in which individuals wi th a particular trait may increase in a population?
Ans.The factors which are responsible for rai sing a new species are selection of environmental conditions for survival of a particul ar species. If a variation occurs in a population and that variation results in bette r survival of the organism in the prevailing natural conditions, then the trait would be selected naturally and more in the population.

37.What are the different theories about origin of life?
Ans.(a) Theory of special creation- According to this theory the almighty god created life. (b) Theory of spontaneous generatio n- According to this theory, life originated from non-living materials by the process of a bioge nesis wring mud, decomposing matter, sun, air and water, etc. (c) Cosmozoic theory- It states tha t life came to Earth from some heavenly bodies in the form of spores or seeds. (d) Biogenesis- This theory states that life originated from pre-existing life. (e) Modern theory of origin of life - According to this, complex organic molecule was formed from simple inorganic molecules only in suitable condition.

38.What is the difference between chemical evolution and organic evolution?
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