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How Do Organisms Reproduce?: Class 10 Science answers, notes
Get summaries, questions, answers, solutions, notes, extras, PDF and guides for Chapter 7 How Do Organisms reproduce?: Class 10 Science textbook, which is part of the syllabus for students studying under SEBA (Assam Board), NBSE (Nagaland Board), TBSE (Tripura Board), CBSE (Central Board), MBOSE (Meghalaya Board), BSEM (Manipur Board), WBBSE (West Bengal Board), and all other boards following the NCERT books. These solutions, however, should only be treated as references and can be modified/changed.
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Summary
Organisms reproduce to create new individuals like themselves. This is not needed for an organism to stay alive, but it is how a species continues to exist. When organisms reproduce, they make copies of their “blueprints,” which are called DNA. DNA holds the instructions for building and running the body. Making copies of DNA is a very important first step in reproduction. Sometimes, small changes happen when DNA is copied. These changes are called variations.
Variations mean that the new individuals are not exact copies of their parents. They are similar, but a little different. These differences can be very important. If the world around an organism changes, like if it gets hotter, some individuals with helpful variations might survive better than others. So, variation helps a species survive over long periods.
There are different ways organisms reproduce. Single-celled organisms, like bacteria or Amoeba, often just split into two. This is called fission. Some, like yeast, grow a small bud that breaks off to become a new organism. Other simple organisms, like Spirogyra, can break into pieces, and each piece grows into a new one. This is fragmentation. Some animals, like Planaria, can regrow their whole body from a small part if they are cut. This is regeneration. Plants can also reproduce in special ways. Parts like stems or leaves can grow into new plants. This is vegetative propagation, and it’s how we get many fruit plants like bananas or roses. Some organisms, like bread mould, produce tiny spores. These spores are like seeds that can grow into new mould if they land in a good spot. All these methods use only one parent and are called asexual reproduction.
Sexual reproduction involves two parents. It mixes the DNA from both parents. This creates even more variation in the new individuals, which can be good for the species. In flowering plants, the flower has male parts (stamens) that make pollen and female parts (pistil) that have egg cells. Pollen needs to travel from a stamen to a pistil. Then, a male cell from the pollen joins with an egg cell to make a seed, which can grow into a new plant.
In humans, sexual reproduction also involves a male and a female. Boys and girls go through changes called puberty to become ready for reproduction. The male reproductive system makes sperm cells in the testes. The female reproductive system makes egg cells in the ovaries. During sex, sperm cells from the male can meet an egg cell from the female. If a sperm joins an egg, it forms a tiny new being called an embryo. The embryo grows inside the mother’s uterus for about nine months and then is born as a baby. If an egg is not joined by a sperm, it passes out of the woman’s body during menstruation. Sometimes, people choose to prevent pregnancy using methods like condoms or pills. These are called contraceptives. Understanding reproduction helps us understand life and how to stay healthy.
Textbook solutions
Intext Questions and Answers I
1. What is the importance of DNA copying in reproduction?
Answer: The importance of DNA copying in reproduction is that the consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species.
2. Why is variation beneficial to the species but not necessarily for the individual?
Answer: Variation is beneficial to the species because niches can change due to reasons beyond the control of the organisms. For example, temperatures on earth can go up or down, water levels can vary, or there could be meteorite hits. If a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.
However, variation is not necessarily beneficial for the individual because some variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die.
Intext Questions and Answers II
1. How does binary fission differ from multiple fission?
Answer: In binary fission, many bacteria and protozoa simply split into two equal halves during cell division. In contrast, other single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously by multiple fission.
2. How will an organism be benefited if it reproduces through spores?
Answer: An organism that reproduces through spores will be benefited because the spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer: More complex, multi-cellular organisms cannot simply divide cell-by-cell to give rise to new individuals through regeneration because many multi-cellular organisms are not simply a random collection of cells. Specialised cells are organised as tissues, and tissues are organised into organs, which then have to be placed at definite positions in the body. In such a carefully organised situation, cell-by-cell division would be impractical for creating a new individual. While regeneration of parts can occur, it is not the same as reproduction for most complex organisms, as they would not normally depend on being cut up to be able to reproduce.
4. Why is vegetative propagation practised for growing some types of plants?
Answer: Vegetative propagation is practised for growing some types of plants for several reasons:
(i) It is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes.
(ii) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
(iii) Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds.
(iv) Another advantage is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.
5. Why is DNA copying an essential part of the process of reproduction?
Answer: DNA copying is an essential part of the process of reproduction because reproduction at its most basic level involves making copies of the blueprints of body design. The DNA in the cell nucleus contains information for inheritance of features from parents to the next generation and is the information source for making proteins, which eventually lead to body designs. Therefore, a basic event in reproduction is the creation of a DNA copy to pass this information on. The consistency of DNA copying during reproduction is also important for the maintenance of body design features that allow the organism to use its particular niche, linking reproduction to the stability of populations of species.
Intext Questions and Answers III
1. How is the process of pollination different from fertilisation?
Answer: Pollination is different from fertilisation in that reproduction in flowering plants involves the transfer of pollen grains from the anther to the stigma, which is referred to as pollination. This is followed by fertilisation, which is the fusion of the male germ-cell produced by the pollen grain with the female gamete present in the ovule to give the zygote.
2. What is the role of the seminal vesicles and the prostate gland?
Answer: The role of glands like the prostate and the seminal vesicles is to add their secretions along the path of the vas deferens so that the sperms are now in a fluid. This fluid makes their transport easier and also provides nutrition.
3. What are the changes seen in girls at the time of puberty?
Answer: At the time of puberty, changes seen in girls include an increase in breast size, with darkening of the skin of the nipples at the tips of the breasts. Also, girls begin to menstruate at around this time.
4. How does the embryo get nourishment inside the mother’s body?
Answer: The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall and contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi, providing a large surface area for glucose and oxygen to pass from the mother to the embryo.
5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Answer: A copper-T is a contraceptive device placed in the uterus to prevent pregnancy. The document states that using a covering, called a condom, for the penis during sex helps to prevent the transmission of many sexually transmitted infections to some extent; however, it does not state that a copper-T offers this protection against sexually transmitted diseases.
Exercise Questions and Answers
1. Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodtum.
(d) Leishmania
Answer: (b) Yeast.
2. Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Falloplan tube
Answer: (c) Vas deferens.
3. The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
Answer: (d) pollen grains.
4. What are the advantages of sexual reproduction over asexual reproduction?
Answer: The DNA copying mechanisms, while precise enough, are not absolutely accurate, and the resultant errors are a source of variations in populations of organisms. Sexual reproduction incorporates a process of combining DNA from two different individuals during reproduction. Combining variations from two or more individuals creates new combinations of variants, and each combination would be novel. Modes of sexual reproduction, therefore, allow for more and more variation to be generated, which is useful for ensuring the survival of the species.
5. What are the functions performed by the testis in human beings?
Answer: The functions performed by the testis in human beings are:
(i) The formation of germ-cells or sperms takes place in the testes.
(ii) The testes secrete the hormone, testosterone, which in addition to regulating the formation of sperms, brings about changes in appearance seen in boys at the time of puberty.
6. Why does menstruation occur?
Answer: Menstruation occurs if the egg is not fertilised. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg, and its lining becomes thick and spongy. If fertilisation does not occur, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle, known as menstruation, takes place roughly every month.
7. Draw a labelled diagram of the longitudinal section of a flower.
Answer:
8. What are the different methods of contraception?
Answer: The different methods of contraception fall into a number of categories:
(i) Mechanical barriers, such as condoms on the penis or similar coverings worn in the vagina, prevent sperm from reaching the egg.
(ii) Hormonal methods, commonly taken orally as pills, act by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur.
(iii) Intrauterine devices, such as the loop or the copper-T, are placed in the uterus to prevent pregnancy.
(iv) Surgical methods can create blocks to prevent gamete transfer. If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus, and in both cases, fertilisation will not take place.
9. How are the modes for reproduction different in unicellular and multicellular organisms?
Answer: For unicellular organisms, cell division, or fission, leads to the creation of new individuals; many bacteria and protozoa simply split into two equal halves during cell division.
In multi-cellular organisms with relatively simple body organisation, simple reproductive methods like fragmentation can still work. However, many multi-cellular organisms are not simply a random collection of cells; specialised cells are organised as tissues, and tissues into organs, placed at definite positions. In such a carefully organised situation, cell-by-cell division would be impractical. Multi-cellular organisms, therefore, need to use more complex ways of reproduction. Reproduction in such organisms is often the function of a specific cell type, and they may employ asexual methods like budding or vegetative propagation, or sexual reproduction involving two individuals. Complex multicellular organisms often rely on sexual reproduction, which involves specialised germ-cells from two individuals.
10. How does reproduction help in providing stability to populations of species?
Answer: Reproduction helps in providing stability to populations of species because the consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use its particular niche. Reproduction is therefore linked to the stability of populations of species. Furthermore, the variations that can arise during reproduction, especially sexual reproduction, can be present in a few individuals in these populations. If the niche were drastically altered, these variations would offer some chance for them to survive, which is useful for the survival of species over time and thus contributes to the long-term stability of the population.
11. What could be the reasons for adopting contraceptive methods?
Answer: The reasons for adopting contraceptive methods could be:
(i) To avoid pregnancy, as pregnancy makes major demands on the body and mind of the woman, and if she is not ready for it, her health can be adversely affected.
(ii) To prevent the transmission of sexually transmitted diseases, as some methods like condoms can help prevent transmission of many of these infections to some extent.
(iii) To manage the size of the human population, as an expanding population can make it harder to improve everybody’s standard of living.
Extras
Additional MCQs (Knowledge Based)
1. The information source for making proteins in the cell nucleus is:
A. RNA
B. DNA
C. Chromosome
D. Cytoplasm
Answer: B. DNA
2. The process by which organisms create new individuals similar to themselves is known as:
A. Respiration
B. Nutrition
C. Reproduction
D. Excretion
Answer: C. Reproduction
3. If a population of bacteria living in temperate waters experiences a significant increase in water temperature due to global warming, what is a likely outcome for the population if some variations exist?
A. All bacteria will die
B. All bacteria will adapt immediately
C. Most will die, heat-resistant variants may survive
D. The bacteria will migrate to cooler waters
Answer: C. Most will die, heat-resistant variants may survive
4. Identify the mode of asexual reproduction where a new individual develops as an outgrowth from the parent body.
A. Fission
B. Fragmentation
C. Budding
D. Spore formation
Answer: C. Budding
5. An organism that reproduces by forming a bud which develops into a tiny individual and then detaches from the parent body is:
A. Amoeba
B. Spirogyra
C. Hydra
D. Planaria
Answer: C. Hydra
6. Which of the following is NOT an advantage of vegetative propagation?
A. Plants bear fruits earlier
B. All plants are genetically similar
C. Propagation of seedless plants
D. Increased genetic diversity
Answer: D. Increased genetic diversity
7. Identify the parts of the male reproductive system in humans:
P. Testes
Q. Ovary
R. Vas deferens
S. Uterus
A. P and Q
B. Q and S
C. P and R
D. R and S
Answer: C. P and R
8. A student observes a unicellular organism under a microscope that splits into two equal halves. The plane of division can occur in any direction. This organism is most likely:
A. Leishmania
B. Yeast
C. Amoeba
D. Plasmodium
Answer: C. Amoeba
9. Binary fission in Amoeba : Splitting into two :: Regeneration in Planaria : ____________.
A. Forming an outgrowth
B. Growing from body parts
C. Releasing specialized cells
D. Fusion of gametes
Answer: B. Growing from body parts
10. The male gamete in flowering plants is contained within:
A. Ovules
B. Pollen grains
C. Sepals
D. Petals
Answer: B. Pollen grains
11. The fusion of male and female gametes is termed:
A. Pollination
B. Germination
C. Fertilisation
D. Variation
Answer: C. Fertilisation
12. In humans, sperm formation requires a temperature that is:
A. Higher than body temp
B. Same as body temp
C. Lower than body temp
D. Unaffected by temp
Answer: C. Lower than body temp
13. The structure that provides nutrition to the developing embryo from the mother’s blood is the:
A. Uterus
B. Ovary
C. Placenta
D. Fallopian tube
Answer: C. Placenta
14. If an egg in a human female is not fertilised, what typically happens?
A. It implants in the uterus
B. It develops into a foetus
C. The uterine lining breaks down
D. It is reabsorbed by the ovary
Answer: C. The uterine lining breaks down
15. Which of the following is NOT a method of contraception?
A. Condoms
B. Oral pills
C. Fertilisation
D. Copper-T
Answer: C. Fertilisation
16. Identify the sexually transmitted disease that is caused by a virus.
A. Gonorrhoea
B. Syphilis
C. HIV-AIDS
D. Kala-azar
Answer: C. HIV-AIDS
17. The process of cell division that reduces the number of chromosomes to half in germ cells is called:
A. Mitosis
B. Meiosis
C. Fission
D. Budding
Answer: B. Meiosis
18. The period during adolescence when reproductive tissues begin to mature is known as:
A. Gestation
B. Menstruation
C. Puberty
D. Germination
Answer: C. Puberty
19. A plant like Bryophyllum can be propagated from which part?
A. Root
B. Stem
C. Leaf
D. Flower
Answer: C. Leaf
20. Which of these are changes commonly observed in boys during puberty?
P. Breast development
Q. Voice cracking
R. Menstruation
S. Growth of facial hair
A. P and R
B. Q and S
C. P and Q
D. R and S
Answer: B. Q and S
21. Stamen : Male reproductive part :: Pistil : ____________.
A. Pollen grain
B. Female reproductive part
C. Ovule
D. Sepal
Answer: B. Female reproductive part
22. The definite orientation of binary fission in Leishmania is related to its:
A. Nutritional intake
B. Excretory system
C. Whip-like structure
D. Cell wall composition
Answer: C. Whip-like structure
23. The transfer of pollen grains from the anther to the stigma is known as:
A. Fertilisation
B. Germination
C. Pollination
D. Ovulation
Answer: C. Pollination
24. If the vas deferens in a male is blocked, what will be prevented?
A. Sperm production
B. Testosterone production
C. Sperm transfer
D. Urine flow
Answer: C. Sperm transfer
25. An organism like Planaria, if cut into pieces, can grow into complete individuals through:
A. Budding
B. Fragmentation
C. Regeneration
D. Spore formation
Answer: C. Regeneration
26. Which of the following is NOT a part of the female reproductive system in humans?
A. Ovary
B. Uterus
C. Vas deferens
D. Oviduct
Answer: C. Vas deferens
27. Which of the following organisms reproduces by multiple fission?
A. Amoeba
B. Yeast
C. Plasmodium
D. Spirogyra
Answer: C. Plasmodium
28. A farmer wants to grow sugarcane plants that will bear fruit earlier and be genetically similar to the parent plant. Which method of reproduction would be most suitable?
A. Growing from seeds
B. Vegetative propagation
C. Spore formation
D. Cross-pollination
Answer: B. Vegetative propagation
29. The part of a flower that develops into a fruit after fertilisation is the:
A. Ovule
B. Stigma
C. Ovary
D. Petal
Answer: C. Ovary
30. The inbuilt tendency for variation during DNA copying is the basis for:
A. Stability
B. Growth
C. Evolution
D. Respiration
Answer: C. Evolution
31. What are the primary functions of the testes in human males?
P. Production of eggs
Q. Production of sperms
R. Secretion of oestrogen
S. Secretion of testosterone
A. P and R
B. Q and S
C. P and Q
D. R and S
Answer: B. Q and S
32. DNA copying : Reproduction :: Blueprint copying : ____________.
A. Protein synthesis
B. Body design replication
C. Energy production
D. Cell division
Answer: B. Body design replication
33. The tiny blob-on-a-stick structures in Rhizopus that contain spores are called:
A. Hyphae
B. Buds
C. Sporangia
D. Gametes
Answer: C. Sporangia
34. If a cell simply pushed out a copy of its DNA without an organized cellular apparatus, the process would likely:
A. Form two new cells
B. Allow the new DNA to function
C. Not work for life processes
D. Divide by binary fission
Answer: C. Not work for life processes
35. The female gamete in humans is also known as the:
A. Sperm
B. Zygote
C. Egg
D. Embryo
Answer: C. Egg
36. Which of these is NOT a primary reason why reproduction is important for organisms, even if not for individual survival?
A. Continuation of species
B. Creation of variations
C. Maintaining individual life
D. Filling ecological niches
Answer: C. Maintaining individual life
37. Which of the following is a mechanical barrier method of contraception?
A. Oral pills
B. Copper-T
C. Condom
D. Vasectomy
Answer: C. Condom
38. A multicellular organism with a relatively simple body organisation, like Spirogyra, can reproduce by:
A. Regeneration only
B. Budding only
C. Fragmentation
D. Complex sexual means
Answer: C. Fragmentation
39. The part of the pistil that receives pollen grains is the:
A. Ovary
B. Style
C. Stigma
D. Anther
Answer: C. Stigma
40. The approximate duration of human pregnancy is:
A. Six months
B. Nine months
C. Twelve months
D. Three months
Answer: B. Nine months
41. Which of the following are essential for sexual reproduction in flowering plants?
P. Stamens
Q. Spores
R. Pistil
S. Hyphae
A. P and Q
B. Q and S
C. P and R
D. R and S
Answer: C. P and R
42. Testes : Sperms :: Ovaries : ____________.
A. Pollen
B. Eggs
C. Zygotes
D. Testosterone
Answer: B. Eggs
43. The hormone primarily responsible for the development of secondary sexual characteristics in boys during puberty is:
A. Oestrogen
B. Progesterone
C. Testosterone
D. Insulin
Answer: C. Testosterone
44. If the fallopian tube in a female is blocked, which process will be directly prevented from occurring within that tube?
A. Ovulation
B. Menstruation
C. Fertilisation
D. Implantation
Answer: C. Fertilisation
45. The technique of growing new plants from cells or tissues removed from the growing tip of a plant in an artificial medium is known as:
A. Grafting
B. Layering
C. Tissue culture
D. Spore culture
Answer: C. Tissue culture
46. Which of the following is NOT a characteristic of spores, such as those produced by Rhizopus?
A. They are reproductive cells
B. They are covered by thick walls
C. They require fusion of two gametes
D. They can develop into new individuals
Answer: C. They require fusion of two gametes
47. Which of these plants is commonly propagated using vegetative methods, partly because it may have lost the capacity to produce viable seeds?
A. Wheat
B. Pea
C. Banana
D. Mustard
Answer: C. Banana
48. A student observes yeast cells in a sugar solution. Which mode of asexual reproduction is most likely to be seen?
A. Fragmentation
B. Binary fission
C. Budding
D. Spore formation
Answer: C. Budding
49. The male reproductive part of a flower, responsible for producing pollen, is the:
A. Pistil
B. Sepal
C. Stamen
D. Petal
Answer: C. Stamen
50. The monthly discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina, in the absence of pregnancy, is known as:
A. Ovulation
B. Gestation
C. Menstruation
D. Fertilisation
Answer: C. Menstruation
51. In flowering plants, the ovule develops into a ________ after fertilisation.
A. Seed
B. Fruit
C. Flower
D. Leaf
Answer: A. Seed
52. The creation of an additional cellular apparatus accompanies _________ in cell division for reproduction.
A. DNA copying
B. Protein synthesis
C. Respiration
D. Excretion
Answer: A. DNA copying
53. If DNA copying mechanisms were less accurate, what would be a likely consequence for many of the resultant DNA copies?
A. They would work more efficiently
B. They would cause faster evolution
C. They would lead to larger organisms
D. They would not work with cellular apparatus
Answer: D. They would not work with cellular apparatus
54. Which of the following is NOT a component of the pistil in a flower?
A. Stigma
B. Style
C. Ovary
D. Anther
Answer: D. Anther
55. Identify the organism that does NOT primarily reproduce by fission.
A. Amoeba
B. Leishmania
C. Bacteria
D. Yeast
Answer: D. Yeast
56. A multicellular organism is broken into several pieces, and each piece grows into a new individual. This organism could be:
P. Planaria
Q. Spirogyra
R. Hydra
S. Amoeba
A. P and R
B. Q and S
C. P and S
D. Q and R
Answer: A. P and R
57. The process where an embryo gets embedded in the lining of the uterus is called:
A. Fertilisation
B. Ovulation
C. Implantation
D. Germination
Answer: C. Implantation
58. The common passage for both sperms and urine in the human male reproductive system is the:
A. Vas deferens
B. Ureter
C. Urethra
D. Seminal vesicle
Answer: C. Urethra
59. Changes in the body at puberty, such as increase in breast size in girls and new facial hair growth in boys, are signs of:
A. Sexual maturation
B. General body growth only
C. Disease onset
D. Nutritional deficiency
Answer: A. Sexual maturation
60. Contraceptive methods aim to prevent pregnancy. Which of these are recognized contraceptive approaches?
P. Mechanical barriers
Q. Hormonal balance changes
R. Surgical blocking of gamete transport
S. Increasing fertility
A. P, Q, and R
B. Q, R, and S
C. P, R, and S
D. P, Q, and S
Answer: A. P, Q, and R
61. Pollination : Transfer of pollen :: Germination : ____________.
A. Fusion of gametes
B. Development of embryo into seedling
C. Formation of fruit
D. Production of pollen
Answer: B. Development of embryo into seedling
62. The female germ-cell containing stored food is typically called the:
A. Male gamete
B. Sperm
C. Zygote
D. Female gamete
Answer: D. Female gamete
63. If a flower contains both stamens and pistil, it is described as:
A. Unisexual
B. Bisexual
C. Asexual
D. Incomplete
Answer: B. Bisexual
64. The motile germ-cell in sexual reproduction is conventionally called the:
A. Male gamete
B. Female gamete
C. Zygote
D. Ovule
Answer: A. Male gamete
65. Which of these is NOT a typical change observed in girls during puberty?
A. Breast size increase
B. Onset of menstruation
C. Darkening of nipple skin
D. Voice cracking
Answer: D. Voice cracking
66. Which of the following is NOT a bacterial sexually transmitted infection?
A. Gonorrhoea
B. Syphilis
C. Warts
D. Chlamydia
Answer: C. Warts
67. A person wishes to use a contraceptive method that also offers protection against some sexually transmitted infections. Which method would be suitable?
A. Oral pills
B. Copper-T
C. Condom
D. Surgical sterilisation
Answer: C. Condom
68. The process of reproduction that involves only a single parent is known as:
A. Asexual reproduction
B. Sexual reproduction
C. Gamete formation
D. Fertilisation
Answer: A. Asexual reproduction
69. The anther in a flower contains:
A. Sepals
B. Ovules
C. Pistil
D. Pollen grains
Answer: D. Pollen grains
70. Which of the following are parts of the human female reproductive system?
P. Ovaries
Q. Testes
R. Uterus
S. Vas deferens
A. P and R
B. Q and S
C. P and S
D. Q and R
Answer: A. P and R
71. The essential life processes for an individual organism include nutrition, respiration, and:
A. Excretion
B. Reproduction
C. Locomotion
D. Growth
Answer: A. Excretion
72. The blueprints for body designs are stored in the form of:
A. Proteins
B. DNA molecules
C. Carbohydrates
D. Lipids
Answer: B. DNA molecules
73. If a niche occupied by a population of organisms undergoes drastic alteration, and no variations exist within that population, the population could be:
A. Able to adapt quickly
B. Unaffected by the change
C. Guaranteed to survive
D. Wiped out
Answer: D. Wiped out
74. Which of the following is a key event in sexual reproduction but not in asexual reproduction?
A. DNA replication
B. Cell division
C. Growth of offspring
D. Fusion of gametes
Answer: D. Fusion of gametes
75. An organism that shows a whip-like structure at one end and reproduces by binary fission in a definite orientation is:
A. Leishmania
B. Amoeba
C. Yeast
D. Plasmodium
Answer: A. Leishmania
76. Identify the plant part NOT typically used for vegetative propagation as a primary method.
A. Root
B. Stem
C. Leaf
D. Flower
Answer: D. Flower
77. A student observes thread-like structures on a piece of moist bread that develop tiny blob-on-a-stick structures. These are indicative of:
A. Yeast budding
B. Rhizopus spore formation
C. Amoeba fission
D. Spirogyra fragmentation
Answer: B. Rhizopus spore formation
78. The creation of new combinations of variants from two or more individuals is a key feature of:
A. Asexual reproduction
B. Sexual reproduction
C. Regeneration
D. Binary fission
Answer: B. Sexual reproduction
79. In flowering plants, the female gamete or egg cell is present within the:
A. Anther
B. Ovule
C. Stigma
D. Petal
Answer: B. Ovule
80. If pollen from a hibiscus flower lands on the stigma of another hibiscus flower, this process is known as:
A. Self-pollination
B. Cross-pollination
C. Fertilisation
D. Germination
Answer: B. Cross-pollination
81. The testes are located outside the abdominal cavity in the scrotum because sperm formation requires:
A. A lower temperature
B. A higher temperature
C. Constant light
D. High pressure
Answer: A. A lower temperature
82. The hormone testosterone, secreted by the testes, regulates the formation of sperms and also brings about:
A. Changes in girls at puberty
B. Changes in boys at puberty
C. Onset of menstruation
D. Development of placenta
Answer: B. Changes in boys at puberty
83. The elastic bag-like structure in the female reproductive system where the embryo develops is the:
A. Ovary
B. Uterus
C. Vagina
D. Oviduct
Answer: B. Uterus
84. Which of the following is NOT a primary role of the placenta during pregnancy?
A. Passing glucose to embryo
B. Passing oxygen to embryo
C. Removing waste from embryo
D. Producing sperm cells
Answer: D. Producing sperm cells
85. Which of these contraceptive methods acts by changing the hormonal balance of the body?
A. Condoms
B. Oral pills
C. Copper-T
D. Diaphragm
Answer: B. Oral pills
86. A couple wishes to use a long-term contraceptive method that involves a minor surgical procedure to block gamete transport. Which of the following could they consider?
P. Vasectomy for male
Q. Oral pills for female
R. Tubectomy for female
S. Condom use
A. P or R
B. Q or S
C. P or Q
D. R or S
Answer: A. P or R
87. The process by which an individual organism creates more individuals, spending a lot of its energy, is:
A. Nutrition
B. Respiration
C. Reproduction
D. Excretion
Answer: C. Reproduction
88. The consistency of DNA copying during reproduction is important for the maintenance of:
A. Body design features
B. Rapid evolution
C. Energy levels
D. Individual survival
Answer: A. Body design features
89. If the information in DNA is changed, what will be the direct consequence?
A. Different proteins will be made
B. The cell will stop respiring
C. The organism will grow larger
D. No change will occur
Answer: A. Different proteins will be made
90. The malarial parasite, Plasmodium, reproduces asexually by:
A. Binary fission
B. Budding
C. Multiple fission
D. Fragmentation
Answer: C. Multiple fission
Additional MCQs (Competency Based)
1. Assertion (A): All multicellular organisms reproduce exclusively by cell-by-cell division of their entire body.
Reason (R): Specialised cells in multicellular organisms are organised into tissues and organs, making simple cell-by-cell division impractical for creating a new individual.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
2. Assertion (A): In flowering plants, the ovule develops into a seed after fertilisation.
Reason (R): Pollination is the transfer of pollen from anther to stigma.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true but R is not the correct explanation of A.
3. Assertion (A): Variation is beneficial for the survival of a species over time.
Reason (R): If a population of reproducing organisms is suited to a particular niche and the niche is drastically altered, individuals with variations may survive.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
4. Assertion (A): Sexual reproduction always results in offspring that are genetically identical to one of the parents.
Reason (R): Sexual reproduction involves the combination of DNA from two different individuals, leading to new combinations of traits.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
5. A student observes a filamentous green alga under a microscope. Over time, they notice that the filament breaks into several smaller pieces, and each piece grows into a new, complete filament. Which mode of reproduction is primarily being observed?
(a) Budding
(b) Binary fission
(c) Spore formation
(d) Fragmentation
Answer: (d) Fragmentation
6. A population of bacteria thrives in a pond with a stable temperature of 25°C. A sudden, prolonged heatwave raises the pond temperature to 35°C. Most bacteria die, but a few individuals survive and reproduce. What is the most likely reason for the survival of these few bacteria?
(a) They rapidly adapted to the new temperature during the heatwave.
(b) They had pre-existing genetic variations that made them heat-resistant.
(c) They were able to perform DNA copying more accurately at higher temperatures.
(d) They switched from asexual to sexual reproduction to increase diversity.
Answer: (b) They had pre-existing genetic variations that made them heat-resistant.
7. A couple wishes to prevent pregnancy and also reduce the risk of sexually transmitted infections. Which of the following contraceptive methods would best address both these concerns?
(a) Oral contraceptive pills
(b) Copper-T
(c) Condoms
(d) Surgical sterilisation
Answer: (c) Condoms
8. “No bio-chemical reaction is absolutely reliable. Therefore, it is only to be expected that the process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may not be identical to the original.”
Based on this information, what is a direct consequence of the inherent imprecision in DNA copying?
(a) All offspring are exact clones of their parents.
(b) Evolution cannot occur in asexually reproducing organisms.
(c) Genetic variation is introduced into populations.
(d) DNA copying always leads to lethal mutations.
Answer: (c) Genetic variation is introduced into populations.
9. “If the zygote is to grow and develop into an organism which has highly specialised tissues and organs, then it has to have sufficient stores of energy for doing this… But as the body designs become more complex, the germ-cells also specialise. One germ-cell is large and contains the food-stores while the other is smaller and likely to be motile.”
According to this, why do female gametes in complex organisms typically contain more food stores than male gametes?
(a) To ensure the male gamete can find the female gamete.
(b) To provide initial energy for the development of the zygote.
(c) Because female gametes are produced in larger numbers.
(d) To make the female gamete less motile.
Answer: (b) To provide initial energy for the development of the zygote.
10. Match the organism with its primary mode of asexual reproduction:
| Column A (Organism) | Column B (Mode of Reproduction) |
| (i) Amoeba | 1. Budding |
| (ii) Yeast | 2. Spore formation |
| (iii) Spirogyra | 3. Binary Fission |
| (iv) Rhizopus | 4. Fragmentation |
Codes:
(a) (i)–3, (ii)–1, (iii)–4, (iv)–2
(b) (i)–1, (ii)–3, (iii)–2, (iv)–4
(c) (i)–3, (ii)–4, (iii)–1, (iv)–2
(d) (i)–2, (ii)–1, (iii)–4, (iv)–3
Answer: (a) (i)–3, (ii)–1, (iii)–4, (iv)–2
11. Match the part of a flower with its primary reproductive function:
| Column A (Flower Part) | Column B (Function) |
| (i) Stamen | 1. Female reproductive part containing ovules |
| (ii) Pistil | 2. Produces male gametes (pollen) |
| (iii) Ovule | 3. Develops into a seed after fertilisation |
| (iv) Stigma | 4. Receptive tip for pollen grains |
Codes:
(a) (i)–2, (ii)–1, (iii)–3, (iv)–4
(b) (i)–1, (ii)–2, (iii)–4, (iv)–3
(c) (i)–2, (ii)–4, (iii)–1, (iv)–3
(d) (i)–4, (ii)–1, (iii)–3, (iv)–2
Answer: (a) (i)–2, (ii)–1, (iii)–3, (iv)–4
12. Arrange the following events in sexual reproduction of flowering plants in the correct sequence:
(i) Pollination
(ii) Fertilisation
(iii) Seed formation
(iv) Germination of pollen tube
(a) (i) → (iv) → (ii) → (iii)
(b) (iv) → (i) → (ii) → (iii)
(c) (i) → (ii) → (iv) → (iii)
(d) (ii) → (i) → (iii) → (iv)
Answer: (a) (i) → (iv) → (ii) → (iii)
13. Arrange the following events in human reproduction in the correct order after fertilisation:
(i) Implantation of embryo in uterine lining
(ii) Formation of zygote
(iii) Development of foetus
(iv) Division of zygote to form a ball of cells (embryo)
(a) (ii) → (i) → (iv) → (iii)
(b) (ii) → (iv) → (i) → (iii)
(c) (i) → (ii) → (iii) → (iv)
(d) (iv) → (ii) → (i) → (iii)
Answer: (b) (ii) → (iv) → (i) → (iii)
14. The menstrual cycle in human females typically occurs monthly, with menstruation itself lasting for a few days. If a woman’s menstrual cycle is consistently 28 days long, and her menstruation lasts for 5 days, for approximately how many days in one cycle is she not menstruating?
(a) 2 days
(b) 20 days
(c) 23 days
(d) 33 days
Answer: (c) 23 days
15. If a non-reproductive body cell of an organism has ‘2X’ amount of DNA, what will be the amount of DNA in its gamete (produced by meiosis) and in the zygote formed after fertilisation, respectively?
(a) Gamete: X, Zygote: 2X
(b) Gamete: 2X, Zygote: X
(c) Gamete: X, Zygote: X
(d) Gamete: 2X, Zygote: 4X
Answer: (a) Gamete: X, Zygote: 2X
Additional Questions and Answers
1. Do organisms create exact copies of themselves?
Answer: No, organisms do not create exact copies of themselves. While the cells produced during reproduction are similar, they are not likely to be absolutely identical. The process of copying DNA will have some variations each time, so the DNA copies generated will be similar, but may not be identical to the original.
2. What is the basic event in reproduction?
Answer: A basic event in reproduction is the creation of a DNA copy.
3. Why is variation said to be the basis for evolution?
Answer: The inbuilt tendency for variation during reproduction is the basis for evolution.
4. What is multiple fission?
Answer: Multiple fission is a process where single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously.
5. What is fragmentation?
Answer: Fragmentation is a reproductive method in multi-cellular organisms with relatively simple body organisation, like Spirogyra, where the organism simply breaks up into smaller pieces upon maturation, and these pieces or fragments grow into new individuals.
6. What is regeneration?
Answer: Regeneration is the ability of many fully differentiated organisms to give rise to new individual organisms from their body parts. If the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism.
7. What is budding?
Answer: Budding is a process of reproduction used by organisms such as Hydra, where regenerative cells are used. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
8. What is vegetative propagation?
Answer: Vegetative propagation is a mode of reproduction in many plants where parts like the root, stem, and leaves develop into new plants under appropriate conditions. This property is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes.
9. What is spore formation?
Answer: Spore formation is a reproductive process in many simple multi-cellular organisms, like the bread mould (Rhizopus). Tiny blob-on-a-stick structures called sporangia are involved in reproduction; these contain cells, or spores, that can eventually develop into new individuals. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
10. Name two modes of asexual reproduction in unicellular organisms.
Answer: Two modes of asexual reproduction in unicellular organisms are:
(i) Fission, where cell division leads to the creation of new individuals.
(ii) Budding, as seen in yeast, where small buds can separate and grow further.
11. What is sexual reproduction?
Answer: Sexual reproduction is a mode of reproduction that depends on the involvement of two individuals before a new generation can be created. It incorporates a process of combining DNA from two different individuals during reproduction.
12. What is self-pollination?
Answer: Self-pollination occurs if the transfer of pollen from the stamen to the stigma occurs in the same flower.
13. What is cross pollination?
Answer: Cross-pollination occurs if pollen is transferred from one flower to another.
14. Which part of a flower is the male reproductive part?
Answer: The stamen is the male reproductive part of a flower and it produces pollen grains.
15. Which part of a flower is the female reproductive part?
Answer: The pistil is present in the centre of a flower and is the female reproductive part.
16. What is a zygote?
Answer: A zygote is formed from the fusion of the male germ-cell (produced by pollen grain) with the female gamete (present in the ovule), a process also known as fertilisation. The zygote is capable of growing into a new plant.
17. What is germination?
Answer: Germination is the process by which the future plant or embryo contained within a seed develops into a seedling under appropriate conditions.
18. What is puberty?
Answer: Puberty is the period during adolescence when, as the rate of general body growth begins to slow down, reproductive tissues begin to mature.
19. Why are testes located outside the abdominal cavity?
Answer: Testes are located outside the abdominal cavity in the scrotum because sperm formation requires a lower temperature than the normal body temperature.
20. What is the function of the testes?
Answer: The functions of the testes include the formation of germ-cells or sperms, and the secretion of the hormone testosterone, which, in addition to regulating the formation of sperms, brings about changes in appearance seen in boys at the time of puberty.
21. What is the vas deferens?
Answer: The vas deferens is a tube through which the sperms formed in the testes are delivered. It unites with a tube coming from the urinary bladder. Along the path of the vas deferens, glands like the prostate and the seminal vesicles add their secretions so that the sperms are now in a fluid which makes their transport easier and this fluid also provides nutrition. If the vas deferens in the male is blocked, sperm transfer will be prevented. It is a part of the male reproductive system.
22. Which tube forms a common passage for sperms and urine?
Answer: The urethra forms a common passage for both the sperms and urine.
23. Where are eggs produced in the female reproductive system?
Answer: In the female reproductive system, the female germ-cells or eggs are made in the ovaries. When a girl is born, the ovaries already contain thousands of immature eggs, and on reaching puberty, some of these start maturing, with one egg being produced every month by one of the ovaries.
24. Through which tube does the egg travel from the ovary to the uterus?
Answer: The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube.
25. What is the function of the uterus?
Answer: The uterus is an elastic bag-like structure into which the two oviducts unite. The embryo is implanted in the lining of the uterus where it continues to grow and develop organs to become a foetus. The uterus prepares itself every month to receive and nurture the growing embryo; its lining thickens and is richly supplied with blood to nourish the growing embryo. The development of the child inside the mother’s body takes approximately nine months, and the child is born as a result of rhythmic contractions of the muscles in the uterus.
26. What is the placenta?
Answer: The placenta is a special tissue that helps the embryo get nutrition from the mother’s blood. It is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue, and on the mother’s side are blood spaces, which surround the villi. This structure provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta.
27. What is menstruation?
Answer: Menstruation is a cycle that takes place roughly every month if the egg is not fertilised. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg, and its lining becomes thick and spongy. If fertilisation does not occur, this lining is not needed any longer, so it slowly breaks and comes out through the vagina as blood and mucous. This process usually lasts for about two to eight days.
28. Name two bacterial sexually transmitted infections.
Answer: Two bacterial sexually transmitted infections are gonorrhoea and syphilis.
29. Name two viral sexually transmitted infections.
Answer: Two viral sexually transmitted infections are warts and HIV-AIDS.
30. Name one mechanical barrier method of contraception.
Answer: One mechanical barrier method of contraception is condoms on the penis.
31. Name one intrauterine device used for contraception.
Answer: One intrauterine device used for contraception is the loop or the copper-T, which are placed in the uterus to prevent pregnancy.
32. Which surgical method in males prevents sperm transfer?
Answer: The surgical method in males that prevents sperm transfer involves blocking the vas deferens.
33. Which surgical method in females prevents an egg from reaching the uterus?
Answer: The surgical method in females that prevents an egg from reaching the uterus involves blocking the fallopian tube.
34. Explain multiple fission in Plasmodium.
Answer: Other single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously by multiple fission.
35. Describe regeneration in Planaria.
Answer: Simple animals like Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as regeneration. Regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organised sequence referred to as development. However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able to reproduce.
36. Explain the process of budding in Hydra.
Answer: Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
37. Describe vegetative propagation in Bryophyllum.
Answer: In Bryophyllum, buds produced in the notches along the leaf margin fall on the soil and develop into new plants. This is a form of vegetative propagation, where parts like leaves develop into new plants under appropriate conditions. Vegetative propagation allows for the production of plants that are genetically similar enough to the parent plant to have all its characteristics.
38. Explain spore formation in Rhizopus.
Answer: In Rhizopus, the bread mould, tiny blob-on-a-stick structures are involved in reproduction. These blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow. The thread-like structures that develop on the bread are the hyphae and are not reproductive parts.
39. Discuss the importance of variation for the survival of species.
Answer: Variation is important for the survival of species over time. Niches, or well-defined places in the ecosystem that populations of organisms fill, can change due to reasons beyond the control of the organisms, such as changes in temperature or water levels. If a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. For example, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Thus, while every individual organism cannot be protected by variations, in a population, variations are useful for ensuring the survival of the species.
40. Explain why sexual reproduction generates greater variation than asexual reproduction.
Answer: The DNA copying mechanism, while precise, cannot be absolutely accurate, and the resultant errors are a source of variations. In asexual reproduction, variations accumulate slowly as each new variation is made in a DNA copy that already has variations accumulated from previous generations. Sexual reproduction, however, incorporates a process of combining DNA from two different individuals during reproduction. Since two different individuals in a population would have quite different patterns of accumulated variations, combining these variations creates new combinations of variants. Each combination would be novel, as it involves two different individuals. This allows for more and more variation to be generated, speeding up the process of making variants compared to asexual reproduction. Therefore, modes of sexual reproduction allow for greater variation to be generated.
41. Differentiate between self-pollination and cross pollination.
Answer: Pollen needs to be transferred from the stamen to the stigma for fertilisation to occur. If this transfer of pollen occurs in the same flower, it is referred to as self-pollination. On the other hand, if the pollen is transferred from one flower to another, it is known as cross-pollination. This transfer of pollen from one flower to another in cross-pollination is achieved by agents like wind, water or animals.
42. Describe the structure of a typical flower, highlighting its reproductive organs.
Answer: The reproductive parts of angiosperms are located in the flower. The different parts of a flower include sepals, petals, stamens and pistil. Stamens and pistil are the reproductive parts of a flower which contain the germ-cells.
The stamen is the male reproductive part and it produces pollen grains that are yellowish in colour. It consists of an anther and a filament.
The pistil is present in the centre of a flower and is the female reproductive part. It is made of three parts: the stigma, which is the terminal part and may be sticky; the style, which is the middle elongated part; and the ovary, which is the swollen bottom part. The ovary contains ovules, and each ovule has an egg cell.
A flower may be unisexual, like papaya or watermelon, when it contains either stamens or pistil, or bisexual, like Hibiscus or mustard, when it contains both stamens and pistil.
43. Explain the sequence of events from pollination to seed formation in flowering plants.
Answer: The sequence of events from pollination to seed formation in flowering plants begins with pollination, which is the transfer of pollen grains from the anther to the stigma. After the pollen lands on a suitable stigma, it has to reach the female germ-cells which are in the ovary. For this, a tube grows out of the pollen grain and travels through the style to reach the ovary.
The male germ-cell produced by the pollen grain then fuses with the female gamete present in the ovule. This fusion of the germ-cells, or fertilisation, gives us the zygote.
After fertilisation, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. Simultaneously, the ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off. The seed contains the future plant or embryo.
44. Explain the process of germination in seeds.
Answer: The seed contains the future plant or embryo which develops into a seedling under appropriate conditions. This process is known as germination. During germination, the embryo develops into a seedling, with the plumule forming the future shoot and the radicle forming the future root, using food stored in the cotyledon(s).
45. Describe the changes that occur in the male body during puberty.
Answer: During puberty, several changes occur in the male body. Some changes are common to both boys and girls, such as the growth of thick hair in new parts of the body like armpits and the genital area between the thighs, which can also become darker in colour. Thinner hair can also appear on legs and arms, as well as on the face. The skin frequently becomes oily, and pimples might begin to develop.
Specific changes in boys include new thick hair growth on the face, and their voices begin to crack. Further, the penis occasionally begins to become enlarged and erect, either in daydreams or at night. The growth of thick hair on the face in boys appears as a few scattered hairs first, and only slowly does the growth begin to become uniform. These changes are aspects of sexual maturation.
46. Describe the changes that occur in the female body during puberty.
Answer: During puberty, several changes occur in the female body. Some changes are common to both girls and boys, such as the growth of thick hair in new parts of the body like armpits and the genital area between the thighs, which can also become darker in colour. Thinner hair can also appear on legs and arms, as well as on the face. The skin frequently becomes oily, and pimples might begin to develop.
Specific changes in girls include an increase in breast size, with darkening of the skin of the nipples at the tips of the breasts. Also, girls begin to menstruate at around this time. These changes are signs of sexual maturation.
47. Explain the role of testosterone in male reproductive development.
Answer: Testosterone is a hormone secreted by the testes. In addition to regulating the formation of sperms, testosterone brings about changes in appearance seen in boys at the time of puberty.
48. Trace the path of sperm from production to fertilisation.
Answer: The formation of sperms takes place in the testes. From the testes, the sperms formed are delivered through the vas deferens, which unites with a tube coming from the urinary bladder. The urethra thus forms a common passage for both sperms and urine. Along the path of the vas deferens, glands like the prostate and the seminal vesicles add their secretions, forming a fluid that makes sperm transport easier and provides nutrition.
During sexual intercourse, sperms enter the female body through the vaginal passage. They travel upwards, through the uterus, and reach the oviduct (fallopian tube) where they may encounter the egg, leading to fertilisation.
49. Explain the structure and function of the placenta.
Answer: The placenta is a special tissue that helps the embryo get nutrition from the mother’s blood. It is a disc which is embedded in the uterine wall. The placenta contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi.
This structure provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The placenta also facilitates the removal of waste substances generated by the developing embryo by transferring them into the mother’s blood.
50. Discuss the different methods of contraception and their modes of action.
Answer: Contraceptive methods are used to avoid pregnancy and fall into a number of categories:
- Mechanical Barriers: These methods prevent sperm from reaching the egg. Condoms on the penis or similar coverings worn in the vagina can serve this purpose.
- Hormonal Methods: These contraceptives act by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur. These drugs commonly need to be taken orally as pills. However, they can cause side-effects due to hormonal changes.
- Intrauterine Devices (IUDs): Devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy. These can cause side effects due to irritation of the uterus.
- Surgical Methods (Sterilisation): These methods create blocks to prevent gamete transfer. If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus. In both cases, fertilisation will not take place.
51. Explain what happens when the egg is not fertilised and how menstruation occurs.
Answer: If the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Its lining becomes thick and spongy, which would be required for nourishing the embryo if fertilisation had taken place. However, if fertilisation does not occur, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle, known as menstruation, takes place roughly every month and usually lasts for about two to eight days.
