CBSE Class 10 Science HOTs How Do Organisms Reproduce Set 04

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.

Reproductive Health and Contraception

Question. List three points of significance of reproductive health in a society.
Answer: (i) The mother carrying a child should be physically matured.
(ii) The mother should be mentally fit to take care of the child.
(iii) There should be at least 3 years gap between 2 children.
(iv) Nutritious food should be available to the mother during pregnancy and lactation period.

Question. List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males? How does the use of these techniques have a direct impact on the health and prosperity of a family? 
Answer: The techniques to prevent pregnancy include:
(i) Creation of mechanical barriers.
(ii) Changing the hormonal balance of the body.
(iii) Use of intra-uterine contraceptive devices.
(iv) Surgical methods.
Use of intra-uterine devices is not meant for males.
Impact of use of contraceptives:
(i) Use of mechanical barriers like condoms can prevent the spread of sexually-transmitted diseases.
(ii) Pregnancy will make major demands on the body and mind of the woman and if she is not ready for it, her health will be adversely affected; such a condition can be avoided.
(iii) By having a small family, the standard of living can be improved.

Question. List any four methods of contraceptions used by humans. How does their use have a direct effect on the health and prosperity of a family. 
Answer: Four methods of contraception used by humans are:
(i) Mechanical barrier such as condom.
(ii) Surgical method such as vasectomy for male and tubectomy for female.
(iii) Chemical method such as oral and vaginal pills.
(iv) Copper-T
Sexual act always has the potential to pregnancy. Pregnancy makes major demand on the body and mind of the woman, and if she is not ready for it, her health will be adversely affected. Contraceptive methods help in avoiding pregnancy and also help in keeping gap between two children, so that the woman’s body recovers. These methods help in limiting number of children to one or two. If family size is small, the family can save some amount after meeting the day to day expenditure. This will improve the economic condition of the family and the family will prosper.

Long Answer Type Questions 

Question. (a) What is pollination? Explain its significance. (b) Explain the process of fertilisation in flowers. Name the parts of the flower that develop after fertilisation into (i) seed, (ii) fruit.
Answer: (a) It is the transfer of pollen grain from the anther of a flower to the stigma of a carpel.
Significance of pollination:
(i) It is necessary for seed formation and thus, perpetuation of species.
(ii) It stimulates the development of fruits.
(b) • After the pollen lands on a suitable stigma, it has to reach the female germ cells in the ovary.
• The pollen tube grows out of the pollen grain through the style to reach the ovary.
• Male germ cell travels through the pollen tube to reach the female germ cell and fertilizes it.
• After fertilisation, the zygote divides several times to form an embryo within the ovule.
(i) Ovule becomes seed.
(ii) Ovary becomes fruit.

Question. (a) Name the human male reproductive organ that produces sperms and also secretes hormones. Write the functions of the hormone secreted. (b) Name the parts of the human female reproductive system where (i) fertilization and (ii) implantation occur respectively. Explain how the embryo gets nutrition inside the mother’s body. 
Answer: (a) The formation of sperms takes place in the testis. It secretes the hormone, called testosterone. In addition to regulating the formation of sperms, testosterone brings about changes in appearance seen in boys at the time of puberty.
(b) (i) The fertilisation takes place in the fallopian tubes. (ii) The implantation occurs in the uterus. 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. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. The development of the child inside the mother’s body takes approximately nine months. On completion of nine months, the child is born due to a rhythmic contractions of the muscles in the uterus.

Question. (a) Write the functions of the following parts in human female reproductive system: (i) Ovary (ii) Oviduct (iii) Uterus (b) Describe the structure and function of placenta. 
Answer: (a) (i) Ovary: It produces the female gametes or germ cells, called ova. It secretes the female sex hormones such as oestrogen and progesterone.
(ii) Oviduct: It transports the ova from the ovary to uterus/womb. Fertilisation occurs in the oviduct.
(iii) Uterus: Implantation of the embryo occurs in the lining of uterus and the complete development of foetus occurs here. The contractions of the muscles of uterus help in child birth.
(b) Structure of placenta: Placenta is a disc-like structure embedded in the uterine wall. It contains villi on the embryo’s side and on the mother’s side there are blood spaces, which surround the villi; this arrangement provides a large surface area for exchange of materials.
Functions of placenta: It transfers glucose and oxygen from the mother’s blood to the foetus. It also removes the wastes \( (CO_2 \) and nitrogenous wastes) generated by the foetus to the mother’s blood.

Question. (a) Why does fertilisation occur only once in a month in a human female? Explain. (b) Prenatal sex determination has been prohibited by law. State the necessity of enforcement of this law. (c) Where are human testis located and why? State their functions. 
Answer: (a) On attaining puberty, the eggs in the ovaries of a human female starts maturing. Only one egg is produced by one of the ovaries every month. Fertilisation can therefore occur only once in a month in a human female.
(b) The most ideal female, male sex ratio for a healthy society is 1000:1000. Because of reckless female foeticide, sex ratio is decreasing at an alarming rate in some sections of our society. It has therefore become necessary to ban detection of sex of the foetus.
(c) Testis are located outside the abdominal cavity inside the scrotum in a human male. The scrotum provides optimum temperature for the formation of sperms. Their function is to produce sperms and the male sex hormone testosterone.

Question. Describe in brief the role of (a) testis (b) seminal vesicle, (c) vas deferens, (d) ureter and (e) prostate gland in human male reproductive system.
Answer: (a) Testis: Testis are oval-shaped primary reproductive organs in men. The function of testes is to produce sperms and male sex hormone testosterone. The scrotum provides optimal temperature for the formation of sperms.
(b) Seminal vesicle: Seminal vesicles are a pair of thin-walled muscular elongated sac which secrete fluid for nourishment of sperms.
(c) Vas deferens: The sperms are carried by a long tube called vas deferens to organs called seminal vesicles where the sperms get nourishment, and stored.
(d) Ureter: It is the tube that carries urine from kidney to the urinary bladder. In humans, there are two ureters, one attached to each kidney.
(e) Prostate gland: Prostate gland produce a fluid which is released in the urethra along with the secretion of seminal vesicles for nourishment and transportation of sperms.

Question. (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions. (b) Name the parts of the human female reproductive system where fertilisation occurs. (c) Explain how the developing embryo gets nourishment inside the mother’s body.
Answer: (a) The male organ is testis. It secretes the hormone testosterone and regulates the formation of sperms. It brings about changes in the appearance of boys at the time of puberty.
(b) Fertilisation occurs in the oviduct.
(c) The developing embryo gets nourishment from the mother’s blood with the help of a special tissue, called placenta. The placenta provides a large surface area for the passage of glucose and oxygen from the mother’s blood to the embryo.

Question. List two sexually transmitted diseases in each of the following cases: (a) Bacterial infections (b) Viral infections (c) State the role of placenta in the development of embryo. (d) What happens when the egg is not fertilized?
Answer: (a) Bacterial infections: Gonorrhoea, Syphilis
(b) Viral infections: Warts, AIDS (Acquired Immuno Deficiency Syndrome)
(c) Role of placenta: After implantation, a disc like special tissue develops between the uterus wall and the embryo called placenta. The exchange of nutrients, oxygen and waste products between the embryo and the mother takes place through the placenta.
(d) If the egg does not get fertilised (due to non-availability of sperms in the female body) then the thick and soft inner lining of uterus along with the blood vessels and the dead egg comes out of the vagina in the form of bleeding called menstruation.

PRACTICE QUESTIONS

Question. What provides oxygen and nutrition to the developing embryo in the female body? 
(a) Fallopian tube
(b) Ovary
(c) Uterus
(d) Placenta

Answer: (d) Placenta

Question. Which of the following is caused by Virus?
(a) AIDS
(b) Gonorrhoea
(c) Syphilis
(d) All of the options

Answer: (a) AIDS

Question. The time period for the development of fetus inside the mother’s body is called: 
(a) Gestation
(b) Ovulation
(c) Menarche
(d) Menopause

Answer: (a) Gestation

Question. A pair of duct arising from testis, which carry sperms are
(a) fallopian tube
(b) vas deferens
(c) oviduct
(d) urethra

Answer: (b) vas deferens

Question. “DNA copies generated will be similar, but may not be identical to the original.” Explain. 
Answer: DNA copying is a biochemical process. No biochemical process is 100% accurate. During the process of DNA replication, some minor errors occur in the sequence of nucleotides. These subtle errors lead to small variations, making the DNA copies similar but not exactly identical to the original.

Question. What is a seed? How does it help in reproduction in plants?
Answer: A seed is a fertilized ovule containing an embryo and stored food. It helps in reproduction by protecting the embryo and allowing for its dispersal to new locations, where it can germinate under favorable conditions to grow into a new plant.

Question. Fertilisation is possible if ovulation has taken place during middle of the menstrual cycle. Give reasons.
Answer: Ovulation usually occurs around the 14th day of a 28-day menstrual cycle. Since an egg survives for about 24 hours and sperm can survive in the female reproductive tract for up to 3-5 days, the fertile window is in the middle of the cycle. Fertilisation can only occur if live sperm meet the released egg in the fallopian tube during this period.

Question. What changes are noticed on sexual maturity of human beings?
Answer: Changes include the development of secondary sexual characteristics such as pubic hair growth, armpit hair, breast development in females, deepening of voice and facial hair growth in males, and the onset of gamete production (menstruation in females and sperm production in males).

Question. How does the embryo get nourishment inside the mother’s body? 
Answer: The embryo receives nourishment from the mother's blood through the placenta. The placenta has villi on the embryo side that provide a large surface area for glucose, oxygen, and other nutrients to diffuse from the mother's blood spaces into the embryo's bloodstream.

Question. Name two bacterial diseases which are sexually transmitted. Name their causal organisms, symptoms and preventive measures.
Answer: (1) Gonorrhoea caused by Neisseria gonorrhoeae and (2) Syphilis caused by Treponema pallidum. Symptoms include burning sensation during urination and sores/rashes. Prevention involves using condoms during intercourse and avoiding contact with infected persons.

Question. (a) How are variations useful for species if there is drastic alteration in the niches? (b) Explain how the uterus and placenta provide necessary conditions for proper growth and development of the embryo after implantation? 
Answer: (a) Variations allow some individuals in a population to survive extreme changes in the environment (niches), ensuring that the entire species does not go extinct. (b) The uterus thickens its lining and increases blood supply to provide a bed for the embryo. The placenta acts as a life-support system, facilitating the exchange of oxygen, nutrients, and waste between the mother and the developing embryo.

INTEGRATED (MIXED) QUESTIONS

Question. Differentiate between the following:  (a) Bud of Hydra and bud of Bryophyllum (b) Fragmentation and regeneration (c) Fertilization and germination
Answer: (a) Bud of Hydra is an outgrowth for asexual reproduction that detaches from the parent, whereas the bud of Bryophyllum is an adventitious bud on a leaf margin that grows into a plantlet. (b) Fragmentation is the breaking of a simple organism into pieces that grow into new individuals (e.g., Spirogyra), while regeneration is the ability to regrow lost body parts or entire organisms from fragments (e.g., Planaria). (c) Fertilization is the fusion of male and female gametes to form a zygote, while germination is the process by which a seed embryo begins to grow into a seedling.

Question. Define reproduction. How does it help in providing stability to the population of species? 
Answer: Reproduction is the biological process by which existing organisms produce new individuals of the same species. It provides stability by replacing deceased individuals, maintaining a balance between birth and death rates, and ensuring the continuity of the species over generations.

Question. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement.
Answer: (1) It ensures the continuity of life on Earth. (2) it leads to the inheritance of genetic material from parents to offspring. (3) it introduces variations through DNA copying errors and sexual reproduction, which are essential for evolution and adaptation.

Question. Write one difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival – the one reproducing asexually or the one reproducing sexually? Give reason to justify your answer. 
Answer: Asexual reproduction involves a single parent without gamete fusion, while sexual reproduction involves two parents and gamete fusion. Sexually reproducing species have better survival chances because sexual reproduction leads to greater genetic variation, which helps the population adapt to changing environmental conditions.

Question. (a) Which are the two main types of reproduction in living organisms? (b) Classify the following under these two types: Amoeba, Frog, Earthworm, Yeast 
Answer: (a) Asexual and Sexual reproduction. (b) Asexual: Amoeba, Yeast. Sexual: Frog, Earthworm.

Question. Planarians can regenerate lost body parts due to the presence of specialised cells called neoblasts. These specialised cells multiply and make a large mass of cells from which different cells undergo changes to become different types of cells and tissues. (a) In plants, in which type of tissue are cells that have a function similar to neoblasts found? (b) How do the characteristics of a planarium formed by regeneration compare with the characteristics of the original planarium? Justify your answer. 
Answer: (a) Meristematic tissue (specifically apical or lateral meristems). (b) The characteristics will be identical to the original planarium. Regeneration is a form of asexual reproduction where no genetic recombination occurs; therefore, the offspring is a clone of the parent.

Question. (a) Why is it not possible to reconstruct the whole organism from a fragment in complex multicellular organisms? (b) Sexual maturation of reproductive tissues and organs are necessary link for reproduction. Elucidate. 
Answer: (a) Complex organisms have highly specialized tissues and organs arranged in a complex hierarchy. They lack a uniform mass of undifferentiated regenerative cells throughout their body that can recreate all organ systems from a single piece. (b) Reproduction requires the production of viable gametes and the ability to nurture offspring. Sexual maturation (puberty) involves hormonal changes that trigger the development of primary and secondary sexual organs, enabling the organism to produce gametes and support fertilization and embryonic development.

ASSERTION AND REASON QUESTIONS

Question. In the following Questions, the Assertion (A) and Reason (R) have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Amoeba reproduces by fission.
Reason: All unicellular organisms reproduce by asexual method.
(a) A
(b) B
(c) C
(d) D

Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: In human beings, the female play a major role in determining the sex of the offspring.
Reason: Women have two X chromosomes.
(a) A
(b) B
(c) C
(d) D

Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: In male reproductive system, transport of sperm takes place in a fluid which also provide nutrition.
Reason: Prostate glands and seminal vesicles secrete in the vas deferens.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Plants raised by vegetative propagation can bear flower and seed earlier than those produced from seeds.
Reason: Plants which lost capacity to bear viable seeds, can propagate through vegetable propagation.
(a) A
(b) B
(c) C
(d) D

Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Ovary releases one egg every month.
Reason: The lining of uterus is always thick and spongy.
(a) A
(b) B
(c) C
(d) D

Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: In human beings the female produces two types of gametes.
Reason: Female has two X chromosomes. 
(a) A
(b) B
(c) C
(d) D

Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: A bisexual flower produces ova as well as the pollen.
Reason: Ova and pollen are produced in the carpel. 
(a) A
(b) B
(c) C
(d) D

Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Oral contraceptive pills and copper-T do not prevent sexually transmitted diseases.
Reason: Sexually transmitted disease are transmitted by contact with mucous membranes of infected organs.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.