28. In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.
Answer: For a flower to produce fruits, it is necessary that pollination and fertilization take place. In the absence of stamens; as given here; cross pollination must have taken place to facilitate fertilization. The cross fertilization could be assisted by human or by some other agent of fertilization. This would have led to production of fruit.
29. Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Answer: Unicellular organisms reproduce asexually and often do that by binary fission. Binary fission is similar to mitosis; in which two daughter cells are produced after cell division. Hence, cell division can be considered as a type of reproduction in unicellular organisms.
30. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Answer: An exact copy of something is called a clone. During sexual reproduction, all the traits in an offspring are similar to the traits in the parent. Due to this, offspring formed after sexual reproduction exhibit remarkable similarity.
31. Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Answer: Gamete formation is the first step in sexual reproduction. Number of chromosomes is halved during gamete formation. As a result, the number of chromosomes in gamete is half the number of chromosomes in somatic cells. When male and female gametes fuse during fertilization, the number of chromosomes becomes equal to that in somatic cells. This explains how, offspring and parents of organisms reproducing sexually have the same number of chromosomes.
32. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Answer: Answer: When the colony of yeast is in water, it does not get nutrition; because water does not have nutrients. Sugar, on the other hand, provides nutrition. Once the yeast gets nutrition, it grows and begins producing buds. That is why, colonies of yeast fail to multiply in water, but multiply in sugar solution.
33. Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Answer: Water is necessary for all metabolic activities. On the moist bread the spores of bread mold get the much needed water; which is not available on the dry bread. Hence, bread mould grows profusely on a moist slice of bread rather than on a dry slice of bread.
34. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer: The first and foremost reason for the appearance of variations among the progeny formed by sexual reproduction is, gene pool of the progeny is contributed by two different individuals. The second reason is that variations also happen during DNA replication before cell division.
35. Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure ‘D’ and ‘E’ by indicating the regenerated regions.
36. From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.
(a) Do larger organisms have more number of chromosomes/cells?
(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?
(c) More the number of chromosomes/cells greater is the DNA content. Justify.
Answer: Number of chromosomes in somatic cells of some organisms:
|Organism||No. of Chromosomes|
Answer: (a) Number of chromosomes and size of an organism has no relationship. A smaller organism may have more chromosomes than a larger organism. The above table also shows number of chromosomes in kingfisher is significantly greater than that in dog; although kingfisher is much smaller in size.
Answer: (b) Ability to reproduce depends on a variety of factors; like availability of nutrients, water, conducive environment and suitable mate. Number of chromosomes has no bearing on the ease by which an organism reproduces.
Answer: (c) Chromosomes are composed of DNA. More chromosomes means, there will be more DNA. Hence, this statement is justified.
37. In tobacco plant, the male gametes have twenty four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote?
Answer: Answer: The number of chromosomes in the female gamete would be same as that in the male gamete, i.e. 24. The number of chromosomes in the zygote would be double the number in a gamete and hence it would be 48.
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