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: 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. e number of chromosomes/cells? sm 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.
Number of chromosomes inNumber of chromosomes inNumber of chromosomes in somatic cells of some organisms
Ref: http://en.wikipedia.org/wiki/Chromosome#Number_of_chromosomes_in_various_organisms Accessed on 8th April 2013.
(a) Number of chromosomes and size of an organism has no relationship. A smaller organism may have more chromosomes than a larger organism.
(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.
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: 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.
38. Why cannot fertilisation take place in flowers if pollination does not occur?
Answer: For fertilization to occur, it is necessary that the male gamete reaches the female gamete. This can only happen when the pollen grains are transferred to the stigma through any means of pollination. So, fertilization cannot take place in flowers if pollination does not occur.
39. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?
Answer: The answer to the first part of this question is a definite yes. Meiosis is the cell division which happens during gametogenesis, i.e. during gamete formation. This results in number of chromosomes getting halved in gametes. When fertilization happens, the number of chromosomes becomes equal to that in somatic cells. After that, mitosis takes place during rest of the stages of life. And thus, the constancy of chromosomal number is maintained in all the three stages as mentioned in this question.
40. Where is the zygote located in the flower after fertilization?
Answer: After fertilization, zygote is located in the ovary.
41. Reproduction is linked to stability of population of a species. Justify the statement.
Answer: Every species has to constantly struggle for its survival. Natural predators and vagaries of nature keep on removing a large section of the population of a particular species. Moreover, the natural cycle of life and death also removes a section of the population. Reproduction is a way to replenish the lost section of population. Thus, it can be said that reproduction is linked to the stability of population of a species.
42. How are general growth and sexual maturation different from each other?
Answer: General growth and sexual maturation are different from each other in many senses. General growth is all about attaining physical maturity in which the organism undergoes through various stages to become an adult. Once the physical growth is complete, it lays the foundation for sexual maturity. Sexual maturity is related to preparing the body for physical and psychological responsibilities related to reproduction.
43. Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Answer: The path of sperm during ejaculation is as follows:
Vas deferens → Seminal Vesicle → Urethra
Glands associated with the male reproductive system and their functions are as follows: ss="Answer"> (a) Testis: Secretes the hormone testosterone.
(b) Prostate gland: Makes the medium of semen alkaline
(c) Seminal vesicle: Adds fluid content to the semen
(d) Cowper's gland: The secretion of this gland lubricates the urethra before ejaculation and neutralizes the acidic traces of urine in the urethra
44. What changes are observed in the uterus if fertilisation does not occur?
Answer: The uterus prepares during every ovulation cycle in anticipation of a possible pregnancy. The lining of the uterus thickens so that it can give support to the developing embryo. When fertilization does not occur, this lining disintegrates because it is no longer required. The fragments of the lining are shed along with blood and the discarded egg; through the vagina. The discharge of discarded tissues is called menstrual flow and the process is called menstruation.
45. What changes are observed in the uterus subsequent to implantation of young embryo?
Answer: Once the zygote is implanted in the uterine wall, several changes take place in the uterus. The uterine lining thickens so that it can give support to the growing embryo. It is richly supplied with blood so that it can provide nourishment to the embryo.
46. What are the benefits of using mechanical barriers during sexual act?
Answer: Mechanical barriers during sexual act provide two benefits. The first benefit is avoidance of unwanted pregnancy and the second benefit is prevention of sexually transmitted diseases.
47. In the given fig47. In the given figure, label the parts and mention their functions
(a) Production of egg
(b) Site of fertilization
(c) Site of implantation
(d) Entry of the sperms
48. What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Answer: The ratio of chromosome number between and egg and its zygote is 1 : 2. Sperm and eggs are genetically different in terms of the nature of the 23rd chromosome. The 23rd chromosome is an Y chromosome in sperm, while it is an X chromosome in egg.
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