CBSE Class 10 Science HOTs How Do Organisms Reproduce Set 03

Question. The ability to reproduce is lost in a female after
(a) fertilisation
(b) menstruation
(c) gamete formation
(d) menopause
Answer: (d) menopause

Question. When a sperm is deposited into the vagina which route does it travel?
(a) Vagina \( \to \) Oviduct \( \to \) Uterus \( \to \) Cervix
(b) Vagina \( \to \) Ovary \( \to \) Uterus \( \to \) Oviduct
(c) Vagina \( \to \) Cervix \( \to \) Uterus \( \to \) Oviduct
(d) Vagina \( \to \) Uterus \( \to \) Cervix \( \to \) Oviduct
Answer: (c) Vagina \( \to \) Cervix \( \to \) Uterus \( \to \) Oviduct

Question. In case the ova does not fertilise, which of the following events will take place?
(a) Menstruation
(b) Pregnancy
(c) Implantation
(d) Ovulation
Answer: (a) Menstruation

Question. When the foetus is growing inside the uterus it needs nutrients. Which part provides these nutrients?
(a) Placenta
(b) Amniotic sac
(c) Oviduct
(d) Uterus
Answer: (a) Placenta

Question. What marks the beginning of the reproductive life of a woman?
(a) Menopause
(b) Menarche
(c) Fertilisation
(d) Ovulation
Answer: (b) Menarche

Question. Where does fertilisation take place?
(a) Uterus
(b) Vagina
(c) Oviduct
(d) Cervix
Answer: (c) Oviduct

Very Short Answer Type Questions

Question. (a) Trace the path a male gamete takes to fertilise a female gamete after being released from the penis. (b) State the number of sets of chromosomes present in a zygote.
Answer: (a) Male gamete (sperm) travels in the female reproductive tract after being released. The path which it takes to fertilise the female gamete (egg) is vagina, uterus, fallopian tube resulting in a zygote.
(b) Zygote has 2 sets of chromosomes

Question. Justify the statement ‘Primary sex organs control the growth, function and maintenance of secondary sex organs’.
Answer: Primary sex organs produce the gametes and sex hormones - testes secretes testosterone and ovary secretes estrogen and progesterone.
Testosterone controls the growth, maintenance and functions of secondary sex organs like prostate gland, seminal vesicles and penis in a male.
Estrogen and progesterone controls the growth, maintenance and functions of secondary sex organs like uterus, fallopian tubes, etc.
Thus, we can justify that the primary sex organs control the growth and development of secondary sex organs.

Question. Why is it said that ‘sexual reproduction promotes, diversity of characters in the offsprings’? 
Answer: It is said that ‘sexual reproduction promotes diversity of characters in the offsprings’ because sexual reproduction results from the fusion of two gametes coming from two different and sexually distinct individuals. This leads to variation which is necessary for evolution.

Short Answer Type Questions

Question. What is placenta? Describe its role during pregnancy. 
Answer: A special tissue placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue and on mother’s side are blood spaces which surround the villi.
Role of placenta during pregnancy.
(i) Placenta provides a large surface area for glucose and oxygen to pass from the mother’s side to the embryo.
(ii) It also transports wastes generated by the developing embryo into mother’s blood.

Question. Describe ‘double fertilisation’ in plants. 
Answer: During fertilisation in plants, the following events take place:
(i) One of the male gametes fuses with the female gamete present in the embryo sac.
(ii) The other male gamete fuses with the two polar nuclei in the embryo sac.
The first fusion product gives rise to the zygote while the second one forms the endosperm. The process of fusion occurring twice in the embryo sac is called double fertilisaton.

Question. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. 
Answer: ‘Chromosomes’ are long thread-like structures which contain hereditary information of the individual and are thereby the carriers of genes. Chromosomes are located in the nucleus of a cell.
The parents are diploid \( (2n) \) as each of them has two sets of chromosomes. They form haploid \( (1n) \) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes. These two gametes fuse during fertilisation and the offspring become diploid \( (2n) \) which is same as parents chromosome number.

Question. (a) Name the two types of germ-cells present in human beings. How do they structurally differ from each other? Give two differences. (b) Why are testes located outside the abdominal cavity of the body?
Answer: (a) The two types of germ cells present in human beings are sperm and ova. The sperm of human have either X or Y chromosome. The ova always carry X chromosome. The sperm is structurally long with a tail. Whereas the ova is round in structure.
(b) Testes are located outside the abdominal cavity because sperm formation requires a lower temperature in comparison to normal body temperature. Testes being outside the abdominal cavity, gets an optimal temperature for the production of sperms.

Question. (a) Describe why variations are observed in the offspring formed by sexual reproduction. (b) List two preparations shown every month by the uterus in anticipation of pregnancy in human. 
Answer: (a) Variations are observed in the offspring formed by sexual reproduction. During sexual reproduction, two types of gametes fuse. Even though the gametes contain the same number of chromosomes, their DNA is not identical. This causes variation among offsprings.
(b) The uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.

Question. (a) List the parts of human male reproductive system which contribute fluid to the semen. State two advantages semen offers to the sperms. (b) Describe the role of fallopian tubes in the female reproductive system.
Answer: (a) Prostate gland and seminal vesicles add fluid in the vas deferens. Semen makes transportation of sperms easier and also provides nutrition to the sperms.
(b) Fallopian tubes:
(i) They carry eggs from ovaries to uterus.
(ii) They allow sperm to travel to meet the egg.
(iii) Fertilisation takes place here.

Question. What is meant by pollination? Name and differentiate between the two modes of pollination in flowering plants. 
Answer: Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. The two modes of pollination are self pollination and cross pollination.
Self-pollination:
(i) Self-pollination occurs within a flower or between two flowers of the same plant.
(ii) Flowers do not depend on other agencies for pollination.
(iii) Pollen grains are produced in small numbers.

Cross-pollination:
(i) Cross-pollination occurs between two flowers borne on different plants of the same species.
(ii) Agents such as insects, water and wind are required for pollination.
(iii) Pollen grains are produced in large numbers.

Question. State the basic requirement for sexual reproduction? Write the importance of such reproductions in nature. 
Answer: Sexual reproduction requires male and female individuals of the species.
New genetic variations are created, where each variation would be novel, as sexual reproduction combines DNA (genetic material with accumulated variations) from two different individuals. Such genetic variations are useful in ensuring survival of species.

Question. List six specific characteristics of sexual reproduction. 
Answer: Specific characteristics of sexual mode of reproduction.
(i) Sexual reproduction promotes diversity of characters in the offsprings.
(ii) It results in new combinations of genes brought together in the gametes and this reshuffling increases genetic variation.
(iii) It plays a prominent role in the origin of new species.
(iv) The sexual mode of reproduction incorporates process of combining DNA from two different individuals during reproduction.
(v) It need two parents to produce an offspring.
(vi) Sex cells are used in sexual reproduction.

Question. Name the male and female gametes in animals. What is fertilization and where does it take place in human females? 
Answer: The male and female gametes in animals are sperm and ovum respectively.
Fertilization is defined as the fusion of a male gamete (sperm) with a female gamete (an ovum or egg) to form a zygote during sexual reproduction.
Fertilization takes place in the fallopian tube of a human female.

Question. State the changes that take place in the uterus when: (a) Implantation of embryo has occurred. (b) Female gamete/egg is not fertilised. 
Answer: (a) After implantation, the cell divisions continue to occur. A placenta develops and the embryo gets nutrition from the mother’s blood through placenta. The complete development of the foetus occurs in about nine months.
(b) When the female gamete is not fertilised, the thickened and spongy lining of the uterus is not required any more. Hence, the lining along with its blood vessels, breaks and comes out through the vagina as blood and mucus, in the process, called menstruation.

Question. In human females, what happens when (a) egg is fertilised (b) egg is not fertilised? 
Answer: The lining of uterus becomes thick and spongy before release of an egg.
(a) If the egg is fertilized, it moves upto uterus and gets implanted on uterus. The uterine wall thickens and richly supplied with blood. The region between embryo and uterine wall grows into placenta which provides nourishment and oxygen to the embryo. The child is borne as a result of rhythmic contraction of the uterine muscle.
(b) If the egg is not fertilized, the thick and nourishing lining of the uterus breaks and comes out through vagina as blood and mucus which is called menstruation.

Question. What are sexually transmitted diseases. List two example of each diseases caused due to (i) bacterial infection and (ii) viral infection. Which device or devices may be used to prevent the spread of such diseases. 
Answer: STDs are diseases which spread by sexual contact from an infected person to a healthy person.
(i) Gonorrhoea and Syphilis are STDs caused by bacterial infection.
(ii) AIDS and genital Warts are STDs caused by viral infection.
Spread of STDs can be prevented by—
(a) Avoiding sexual contact with infected persons.
(b) Using condom for penis during sexual act.

Question. What is AIDS? Which microbe is responsible for AIDS infection? State one mode of transmission of this disease. Explain in brief one measure for the prevention of AIDS.
Answer: AIDS is the Acquired Immuno Deficiency Syndrome. It is caused by a virus called Human Immunodeficiency Virus. AIDS is transmitted by sexual contact with an infected person. AIDS can be prevented by avoiding sexual contact with an infected person or by using condom during sex.

Question. What does HIV stand for? Is AIDS an infectious disease ? List any four modes of spreading AIDS.
Answer: HIV stands for Human Immunodeficiency Virus. Yes, AIDS is an infectious disease. Four modes of spreading AIDS are as follows:
(i) By having sexual contact with an infected person.
(ii) By the transfusion of blood from an infected person.
(iii) Through infected needles used for injection.
(iv) Through the placenta from the mother to child during pregnancy.

Question. Expand AIDS. List any four methods of prevention (control) of AIDS.
Answer: AIDS stands for Acquired Immuno Deficiency Syndrome. Four methods of prevention or control of AIDS are as follows:
(i) Using condom during sex.
(ii) Avoiding sharing of needles or use of disposable needles.
(iii) Testing blood for AIDS before transfusion.
(iv) Avoiding sexual contact with unknown person.

Question. List four categories of contraceptive methods. State in brief two advantages of adopting such preventive methods.
Answer: Four methods of contraception used by humans are:
(a) Mechanical barrier such as condom.
(b) Surgical method such as vasectomy or tubectomy.
(c) Chemical method such as oral or vaginal pill.
(d) Copper-T.
Advantages of using contraceptives.
(a) It helps in avoiding unwanted pregnancy.
(b) Condom helps in preventing transmission of STDs.

Question. The ability to reproduce is lost in a female after
(a) fertilisation
(b) menstruation
(c) gamete formation
(d) menopause
Answer: (d) menopause

Question. When a sperm is deposited into the vagina which route does it travel?
(a) Vagina \( \to \) Oviduct \( \to \) Uterus \( \to \) Cervix
(b) Vagina \( \to \) Ovary \( \to \) Uterus \( \to \) Oviduct
(c) Vagina \( \to \) Cervix \( \to \) Uterus \( \to \) Oviduct
(d) Vagina \( \to \) Uterus \( \to \) Cervix \( \to \) Oviduct
Answer: (c) Vagina \( \to \) Cervix \( \to \) Uterus \( \to \) Oviduct

Question. In case the ova does not fertilise, which of the following events will take place?
(a) Menstruation
(b) Pregnancy
(c) Implantation
(d) Ovulation
Answer: (a) Menstruation

Question. When the foetus is growing inside the uterus it needs nutrients. Which part provides these nutrients?
(a) Placenta
(b) Amniotic sac
(c) Oviduct
(d) Uterus
Answer: (a) Placenta

Question. What marks the beginning of the reproductive life of a woman?
(a) Menopause
(b) Menarche
(c) Fertilisation
(d) Ovulation
Answer: (b) Menarche

Question. Where does fertilisation take place?
(a) Uterus
(b) Vagina
(c) Oviduct
(d) Cervix
Answer: (c) Oviduct

Very Short Answer Type Questions

Question. (a) Trace the path a male gamete takes to fertilise a female gamete after being released from the penis. (b) State the number of sets of chromosomes present in a zygote. 
Answer: (a) Male gamete (sperm) travels in the female reproductive tract after being released. The path which it takes to fertilise the female gamete (egg) is vagina, uterus, fallopian tube resulting in a zygote.
(b) Zygote has 2 sets of chromosomes

Question. Justify the statement ‘Primary sex organs control the growth, function and maintenance of secondary sex organs’.
Answer: Primary sex organs produce the gametes and sex hormones - testes secretes testosterone and ovary secretes estrogen and progesterone.
Testosterone controls the growth, maintenance and functions of secondary sex organs like prostate gland, seminal vesicles and penis in a male.
Estrogen and progesterone controls the growth, maintenance and functions of secondary sex organs like uterus, fallopian tubes, etc.
Thus, we can justify that the primary sex organs control the growth and development of secondary sex organs.

Question. Why is it said that ‘sexual reproduction promotes, diversity of characters in the offsprings’? 
Answer: It is said that ‘sexual reproduction promotes diversity of characters in the offsprings’ because sexual reproduction results from the fusion of two gametes coming from two different and sexually distinct individuals. This leads to variation which is necessary for evolution.

Short Answer Type Questions 

Question. What is placenta? Describe its role during pregnancy. 
Answer: A special tissue placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue and on mother’s side are blood spaces which surround the villi.
Role of placenta during pregnancy.
(i) Placenta provides a large surface area for glucose and oxygen to pass from the mother’s side to the embryo.
(ii) It also transports wastes generated by the developing embryo into mother’s blood.

Question. Describe ‘double fertilisation’ in plants. 
Answer: During fertilisation in plants, the following events take place:
(i) One of the male gametes fuses with the female gamete present in the embryo sac.
(ii) The other male gamete fuses with the two polar nuclei in the embryo sac.
The first fusion product gives rise to the zygote while the second one forms the endosperm. The process of fusion occurring twice in the embryo sac is called double fertilisaton.

Question. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. 
Answer: ‘Chromosomes’ are long thread-like structures which contain hereditary information of the individual and are thereby the carriers of genes. Chromosomes are located in the nucleus of a cell.
The parents are diploid \( (2n) \) as each of them has two sets of chromosomes. They form haploid \( (1n) \) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes. These two gametes fuse during fertilisation and the offspring become diploid \( (2n) \) which is same as parents chromosome number.

Question. (a) Name the two types of germ-cells present in human beings. How do they structurally differ from each other? Give two differences.(b) Why are testes located outside the abdominal cavity of the body?
Answer: (a) The two types of germ cells present in human beings are sperm and ova. The sperm of human have either X or Y chromosome. The ova always carry X chromosome. The sperm is structurally long with a tail. Whereas the ova is round in structure.
(b) Testes are located outside the abdominal cavity because sperm formation requires a lower temperature in comparison to normal body temperature. Testes being outside the abdominal cavity, gets an optimal temperature for the production of sperms.

Question. (a) Describe why variations are observed in the offspring formed by sexual reproduction. (b) List two preparations shown every month by the uterus in anticipation of pregnancy in human. 
Answer: (a) Variations are observed in the offspring formed by sexual reproduction. During sexual reproduction, two types of gametes fuse. Even though the gametes contain the same number of chromosomes, their DNA is not identical. This causes variation among offsprings.
(b) The uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.