I. VERY SHORT ANSWER TYPE QUESTIONS (1 Mark)
Q1. Define heredity.
Ans. Heredity deals with the inheritance of characters from one generation to the next.
Q2. Define variations.
Ans. Variations are differences that occur between the organisms of the same species in spite of the same basic feature.
Q3. How does the creation of variations in a species promote survival?
Ans. Variations increases the adaptability of an organism to its changing environmental conditions.
Q4. What is a trait?
Ans. A characteristics feature is called a trait.
Q5. Name two human traits that show variations.
Ans. Colours of eyes and shape of external ears.
Q6. What is adaptation?
Ans. An adaptation is characteristics feature which helps an organism to survive in its habitat in a better way.
Q7. Which of the two sperm or egg–decides the sex of the child?
Ans. The sperm decides the sex of the child.
Q8. The forelimbs of frog, reptiles, birds and arms of man show the same basic design. What kind of organs are these?
Ans. Homologous organs.
Q9. What is microevolutions?
Ans. Microevolutions is the evolution that takes place on a relatively small scale at the population level and can change the common characteristics of particular species.
Q10. What is speciation?
Ans. Speciation is the process of formation of a new species from the already existing species by accumulation of variations, natural selection, gene flow, genetic drift, etc.
Q11. What is a gene?
Ans. Gene is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary characteristics.
Q12. Who is known as the ‘‘father of Genetics’’?
Ans. G.J. Mendel is called the ‘‘father of Genetics’’.
Q13. What is evolution?
Ans. Evolution is the sequence of gradual changes which take place in living organisms over millions of years to give rise to new species.
Q14. What type of reproduction gives rise to more number of successful variations?
Ans. Sexual reproduction.
Q15. What are fossils?
Ans. Fossils are preserved traces or remains of living organisms of geological past.
Q16. What are the uses of fossils?
Ans. 1. Fossils helps to trace the racial history of organisms.
2. They help to analyse the past climatic conditions.
3. They help to measure the geological time.
Q17. Name the scientist who put forth the theory of natural selection.
Ans. Charles Darwin.
Q18. What is artificial selection?
Ans. It is the process of modification of a species by selective breeding. Animals and plants with desirable characters are selected and propagated. Artificial selection by farmers has resulted in the formation of cauliflowers, cabbage, broccoli and kohlrabi from the wild cabbage.
II. SHORT ANSWER TYPE QUESTIONS (2 or 3 Marks)
Q1. How can we trace evolutionary relationships?
Ans. Evolutionary relationships can be traced by studying fossils, by studying homologous and analogous organs, by comparing the embryos of different animals and by comparing the DNA’s of different species.
Q2. What is phylogeny and molecular phylogeny?
Ans. Phylogeny is the evolutionary history of an organism.
Molecular phylogeny traces the evolutionary relationships by comparing the differences in the DNA of different organisms.
Q3. Why evolution should not be equated with progress?
Ans. Evolution cannot be equated with progress because it seems to have just given rise to more complex body designs. For example bacteria still flourish in spite of a very simple body design while dinosaurs did not survive in spite of complex design. Thus evolution is simply the generation of diversity and shaping of diversity by environmental selection.
Q4. What is environmental selection?
Ans. It is the selection within a population resulting from the influence exerted by the environment. It leads to a change in the composition of genes within a population.
Q5. What term did Mendel use for genes? Where are the genes located?
Ans. Mendel used the term ‘factors’ for genes. Genes are portions of DNA which code for a single protein.
Q6. How many pairs of chromosomes do human beings have, specify the types of chromosomes also?
Ans. Human beings have 23 pairs of chromosomes the first 22 pairs are called autosomes are similar in males and females. The 23rd pair is called the sex chromosome. In males it is XY and in females it is XX.
Q7. What are homologous organs? Explain with an example.
Ans. Homologous organs are those organs in different plants or animals which have the same basic structural design and origin but may have different functions.
Example., hand of human and fore-limb of frog.
Q8. What are analogous organs? Explain with an example.
Ans. Analogous organs have the same function but have different structural design and origin. For example, wings of birds and insects have the same function but have different structural design and origin.
Q9. State the importance of variations.
Ans. Variations are the differences in the characters among the individuals of a species. Variations enable the organisms to adapt themselves in the changing environmental conditions. Variations form the raw materials for evolution and formation of new species.
Q10. What is the significance of studying homologous and analogous organs?
Ans. Organisms that have homologous organs show relatedness and a common ancestory.
Q11. Which of the following combinations of sex chromosomes produces a male or a female child—XX or XY?
Ans. XX combination produces a female child while the XY combination produces a male child.
Q12. Which of the following are homologous and analogous organs?
(a) Wings of birds and insects.
(b) Flippers of whale and fins of fish.
(c) Flippers of whale and wings of bat.
(d) Our teeth and elephants tusks.
(e) Potato and runners of grass.
Ans. (a) — Analogous organs
(b) — Analogous organs
(c) — Homologous organs
(d) — Homologous organs
(e) — Homologous organs.
Q13. How do traits or characters get expressed?
Ans. Genes control the expression of a trait or a character in an organism. Genes produces proteins. The proteins act as enzymes which can directly control a character or help in the formation of a hormone which can control the expression of a particular character.
Q14. A true breeding tall plant is crossed with a true breeding short plant. All the offsprings of the F1 generation are tall. Of these two characters which one is dominant and which is recessive.
Q16. How is the sex of the child determined in human beings?
Ans. Human beings have 23 pairs of chromosomes. 22 pairs are autosomes and the 23rd pair is the sex chromosome. The males have XY and the females have XX. All the gametes formed in the females are of one type i.e., X. In males there are two types of sperms that are formed –X and Y. If the sperms having X fertilizes with the egg the zygote formed is XX. This will form female child. If the sperm having Y fertilizes with the egg then the zygote formed is XY and the offspring will be male child. So basically it’s the male gametes that decide the sex of the unborn child.
Q17. What is genetic drift?
Ans. Accidents in small populations can change the frequency of some genes in a population even if they give no survival advantage. This is genetic drift, which provides diversity without any adaptations. So, it is the random change in the frequency of alleles in a population over successive generation.
Q18. Which is gene flow?
Ans. It is the exchange of genetic material by interbreeding between populations of the same species. Gene flow increases the variations in a population.
Q19. What is classification?
Ans. It is the arrangement of organism into series of groups based on the similarity of characters on physiology, anatomy, morphology and other relationships.
Q20. How do we know how old fossils are?
Ans. We can find the relative of the fossil by the depth at which the fossil is found. The ones that are found near the surface are more recent than the fossils found in the deeper layer. The second way of dating fossils in detecting the ratios of different isotopes of the same element in the fossils material.
Q21. What is speciation? How does it occur?
Ans. Formation of new species from the existing ones over the period of time is called speciation. Speciation takes place due to gene flow, genetic drift, reproductive isolation and finally natural selection.
Q22. What is natural selection?
Ans. According to Darwin, natural selection is the process which brings about evolution of new species of plants and animals.
It consists of the following processes:
(i) He noted that the size of population tends to remain constant despite the fact that more offsprings are produced than needed.
(ii) Variations provide adaptations.
(iii) The best adopted survive in the changing environment (survival of the fittest).
(iv) Nature selects the best organisms with better adaptations and after many
generations new species are formed (natural selection).
Q23. Define Genetics. What did Mendel’s contribution to genetics?
Ans. The science of heredity and variation is called Genetics.
Mendel conducted breeding experiments in a plant called garden pea (pisum sativum) with contrasting pair of characters, found that only one character of the pairs appeared in the first generation but both the characters appeared in the subsequent generation. On the basis of these results of his experiments he put forth the various principals of inheritance. He also suggested that each character is controlled by a pair of factors which are now called as genes.
Q24. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits–blood group A or O is dominant? Why? (CBSE 2008)
Q25. Define variation in relation to a species: Why is variation beneficial is the species.
Ans. Variations are differences that occur between the organisms of the same species in spite of the same basic features.
Variation in species promotes survival of an organism in changing environment by
increasing the adaptability.
Q26. What is the effect of DNA copying which is not perfectly accurate on the reproduction process? (AI CBSE)
Ans. If DNA copying is not perfectly accurate then the variations occurs among the species of same organisms.
Q27. Describe briefly four ways in which individual with a particular trait may increase in population. (Foreign 2008)
Ans. Four ways in which individual with a particular trait may increase in population are:
(a) Variations that occur in species helps in the survival of individuals.
(b) Organisms when show genetic drift which cope them to survive in the given environment.
(c) Adaptation and natural selection.
(d) Sexual reproduction results in variation.
Q28. ‘‘Variations that confer an advantage to an individual organism only will survive in population’’. Justify. (Foreign 2008)
Ans. Variation is the difference in the characters or traits among the individuals of a species. Sexual reproduction of organisms produces variation. The variations produced in organisms during successive generations gets accumulated in the organism. The significance of variations shows up only if it continues to be inherited by the offspring for several generation.
Q29. What are fossils? What do they tell about the process of evolution? (AI CBSE. 2008)
Ans. Fossils are preserved traces or remains of living organism of geological past. Fossils help to trace the racial history of organisms. Fossils found closer to the surface are more recent than fossils found in the deepest layers.
III. LONG ANSWER TYPE QUESTIONS (5 Marks)
Q1. (i) What is genetics?
(ii) Give the common name of the plant on which Mendel performed its experiments.
(iii) What for did Mendel use the term factors and what are these factors called now?
(iv) What are genes? Where are the genes located?
(i) Science which deals with the study of heredity and variations is called genetic.
(ii) Pea plant.
(iii) Mendel used the term factors for ‘genes’.
(iv) Genes is the unit of inheritance. It is a part of the chromosome which controls
the appearance of a set of hereditary character.
Genes are located on the chromosome.
Q2. Define ‘evolution’. State Darwin’s theory of evolution.
Ans. Evolution is a change in the genetic composition of a population.
1. The size of population remains the same, constant despite the fact that more offsprings are produced than needed.
2. Variations provide adaptations.
3. The best adapted organism survive in the changing environment (survival of the fittest).
4. Nature selects the best organisms with better adaptations and after many generations new species are formed (natural selection).
Q3. What are various evidences in factors of evolution?
Ans. Evidences are:
(a) Homologous organs: Organs which have same structure but different function.
E.g., wings of a bat, hands of man and limbs of monkey.
(b) Analogous organ: Organs which perform similar function but are structurally different are called analogous organ. E.g., wings of bat, insects, birds.
(c) Vestigial organs: These organs are those which appear in an organism but are functionless e.g., vermiform appendix, nictitating membrane in eye is present in human beings but has no function.