Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Science Class 10

Class 10 : Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

The document Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev is a part of the Class 10 Course Science Class 10.
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SHORT ANSWER TYPE QUESTION

Q.1. Write one difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival - the one reproducing asexuaily or the one reproducing sexually? Give reason to justify your answer.    [CBSE 2018]
Ans.
Differences between asexual and sexual mode of reproduction.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
The species reproducing sexually will have better chances of survival because genetic variation is created during sexual reproduction; in case of an adverse environmental change, atleast some variants will survive and continue the race.

Q.2. 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?    [Al 2017]
Ans. 
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.

Q.3. State the changes that take place in the uterus when: 
(a) Implantation of embryo has occurred. 
(b) Female gamete/egg is not fertilised.    [Delhi 2017]
Ans. 
(a) After implantation, the cell divisions continue to occur.
Aplacenta 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 utems 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.

Q.4. State the basic requirement for sexual reproduction? Write the importance of such reproductions in nature.     [Delhi 2017]
Ans.
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.

Q.5. What is vegetative propagation? State two advantages and two disadvantages of this method.   [Al 2017]
Ans. Vegetative propagation refers to the development of new plants from vegetative parts (roots, stem or leaves) of an existing plant.
Advantages of vegetative propagation 
(i) Vegetative propagation is a cheaper, easier and more rapid method of propagation in plants than growing plants from their seeds.
(ii) Better quality of the plants can be maintained by this method.
(iii) lt results in propagation of those plants which do not produce viable seeds or produce seeds with prolonged period of dormancy.
(iv) The plants generated from vegetative means require less time to grow and have the advantage of being more uniform and genetically similar to the parent stock.
Disadvantages:
(a) No genetic variation is created.
(b) Continued vegetative propagation can lead to loss of vigour.

Q.6. What is regeneration ? Give one example of an organism that shows this process and one organism that does not. Why does regeneration not occur in the latter?    [Foreign 2017] 
Ans. Regeneration is defined as the ability of any small part of the body to give rise to a new individual e.g.
(a) Hydra and Planaria shows regeneration.
(b) Amphibians and human beings do not show regeneration.
- Regeneration is carried out by certain specialised cells, which can proliferate to make a large number of cells and different cells undergo development to become various cell types and tissues.
- Such regenerative cells are not found in amphibians and humans.

Q.7. What is asexual reproduction? Write the process of budding in Hydra.     [Delhi 2017(C)] 
Ans. Reproduction in Hydra:
• Hydra reproduces by budding using the regenerative cells.
• A bud develops as an outgrowth in Hydra due to repeated cell division at one specific site.
• When fully mature, the bud detaches itself from the parent body and develops into new independent individual.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.8. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement.    [AI 2017]
Ans. (a) Reproduction is necessary to maintain the continuity of species.
(b) Reproduction is linked to the stability of populations of species, which occupy well defined places called niches in the ecosystems.
(c) The variations created during reproduction are responsible for survival of a species in case of an adverse change in the environment and evolution.

Q.9. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual?    [Delhi 2017]
Ans. 
Spirogyra reproduces by fragmentation.
It is an asexual method of reproduction.

Q.10. Name the organs producing sperms and ova respectively in humans. [Foreign 2017] 
Ans. Testes produce sperms and ovary produces ova.

Q.11. What is meant by pollination ? Name and differentiate between the two modes of pollination in flowering plants.    [Delhi 2016]
Ans. 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.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.12. Name the three parts A, Band C of the flower shown in the following diagram and state one function of each.    [AI 2017(C); Delhi 2016]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans. A = Anther of stamen.
Function: Anther contains two pollen sacs within which numerous pollen grains are produced.
B = Carpel
Function: It is the female reproductive organ of a flower which receives pollen grains that moves through the style and causes fertilisation in the ovaries.
C = Ovule
Function: Ovule contains female gamete, egg.

Q.13. List any four modes of asexual reproduction.    [CBSE 2016-17 C] 
Ans. Four modes of asexual reproduction are : 
(a) Fission - Parent cell divides to form two or more daughter cells.
(b) Fragmentation - Multicellular organism breaks into pieces and each undergoes cell division to develop into complete organisms.
(c) Regeneration - Multicellular organism breaks into piece and each undergoes cell division and differentiation (by specialised cells) to form complete organisms.
(d) Budding - A small outgrowth on the parent body detaches when mature and develops into a new individual.

Q.14. Name the three parts A, B and C of the flower shown in the figure and state one function of each.    [CBSE 2016-17 C]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.15. (a)  Write the functions of the following parts of human male reproductive system : 
(i) Testis ; (ii) Vas deferens ; (iii) Urethra ; (iv) Prostate. 
(b) List any two common pubertal changes that appear in human males.    [CBSE 2016-17 C]
Ans. (a) Functions of the following in human male reproductive system -
(i) Testis - Production of male hormone i.e., testosterone and male game test.e., sperms.
(ii) Vas deferens - Delivers sperms.
(iii) Urethra - Helps in transporting sperm out of the m ale reproductive tract, is common passage for both sperms and urine.
(iv) Prostate - Adds its secretion to the sperm so that they are in fluid medium which provides them with nutrition and makes the transport easier.
(b) Two changes in males during puberty -
(i) Appearance of facial hair.
(ii) Voice begins to crack.
(iii) Occasional enlargement of penis.
(iv) Muscular body.

Q.16. In the given figure label the concerned with 
(а) production of egg 
(b) site of fertilisation
(c) site of implantation 
(d) site of entry of sperm.     [CBSE 2017]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.17. In the given figure label the parts numbered 1 to 6.    [CBSE 2011,2016-17 C]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans. 
1. Pollen grain
2. Stigma
3. Pollen tube
4. Style
5. Ovaiy
6. Synergids

Q.18. Explain how spirogyra reproduces ? [CBSE 2013,2017] 
Ans. Spirogyra breaks up into smaller pieces upon maturation. These fragments grow into new individuals. Hence, it reproduces by fragmentation.

Q.19. List two reasons for the appearance of variations among the progeny formed by sexual reproduction.    [CBSE 2016]
Ans.
Sexual reproduction involves gametes from two different individuals. Thus their genetic make up is different and hence gametes carry different alleles.
It leads to formation of greater variation, so better adaptability and evolution.

Q.20. What happens when 
(a) Planaria gets cut into two pieces? 
(b) A mature Spirogyra filament attains considerable length? 
(c) On maturation sporangia burst?    [Foreign 2016] 
Ans. (a) When Planaria gets cut into two pieces, each piece grows into a complete organism.
(b) A mature Spirogyra on attaining considerable length breaks up into two or more small pieces. Each piece then grows into a new individual.
(c) When sporangia bursts, spores are released, each one of which develop into new individual.

Q.21. What changes are observed in the uterus if fertilisation does not occur ? [CBSE 2016]
Ans. If fertilisation fails to take place the thick and spongy lining of uterus which is formed to receive the fertilised ovum breaks and comes out through the vagina as blood and mucous. This cycle takes place every month and is known as menstrual cycle.

Q.22. In which part of the female reproductive organs of human female does fertilisation take place and what happens to the fertilisedegg ?    [CBSE 2017]
Ans. In human female, fertilisation takes place in the fallopian tube. After fertilisation, the fertilised ovum travels to uterus and gets attached to the wall of uterus for further development. This is called implantation.

Q.23. What happens when a mature Spirogyra filament attains considerable length ?    [CBSE 2016]
Ans. Its filament breaks up into smaller fragments or pieces, and each fragment grows into a new filament/individual.

Q.24. Define reproduction. How does it help in providing stability to the population of species?     [DoE, AI 2016]
Ans. Reproduction: It is the process of producing new individuals of the same species by existing organisms of a species, i.e. parents.
Reproduction helps in providing stability to the population of species because reproduction is a process by which organism s in crease their populations. The rate of birth and death in a given population determine its size.

Q.25. What are those organisms called which bear both the sex organs in the same individual. Give one example of such organism.    [AI 2016]
Ans. 
Organisms which bear both the sex organs are called hermaphrodite/bisexual.
Example: Earthworm

Q.26. Name the part of Bryophyllum where the buds are produced for vegetative propagation.    [Delhi 2016] 
Ans. Vegetative part, leaf is used in the propagation of Bryophyllum.

Q.27. Name the method by which Hydra reproduces. Is this method sexual or asexual?    [Foreign 2016] 
Ans. Hydra reproduces by budding. It is an asexual method.

Q.28. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family ? [CBSE 2014,2015]
Or
Suggest three contraceptive methods to control the size of human population which is essential for the health and prosperity of a country. State the basic principle involved in each.    [CBSE 2016]
Ans. 
Four methods of contraception are :
(i) Mechanical barrier - So that sperm does not reach the egg. e.g., condom.
(ii) OCPs - Oral Contraceptive Pills act by changing hormonal balance so that eggs are not released.
(iii) IUD - Intra uterine device like copper-T to prevent pregnancy.
(iv) Surgical method - Blocking vas deferens or fallopian tube.
Since pregnancy makes major demands on body and mind of woman, so her health suffers. By contraceptive methods a woman is in better state of health to look after herself and her family Spacing children will result in healthier and happier children and will also be more economical for the family to look after, give good life, and education to fewer children.

Q.29. Draw diagrams to explain the regeneration that takes place in each of the body parts of Planaria when its body is cut into three pieces. Name any other organisms in which a similar process can be observed.    [CBSE 2014,2016]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans. See Fig. 8.9.
However, multicellular organisms with cell differentiation, when cut in small pieces, may regrow into complete organism with the help of specific cells, e.g., Planaria and Hydra. This process is known as regeneration.
Regeneration is also seen in Hydra.

Q.30. (a) Name an organism in which binary fission occurs in a definite orientation.
(b) Draw a neat diagram of a germinating seed and label on it the following : Cotyledon, Plumule, Radicle.
Or
Draw a germinated seed and label the future root, future shoot and structure that stores food.
Or
Draw diagram of a germinating seed and label the following parts of it :
(i) Part that gives rise to shoot system
(ii) Part that gives rise to root system.
(iii) Part that contains stored food.    [CBSE 2012,2016]
Ans.
(a) Leishmania.
(b)
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.31. ‘Different species use different strategies to determine sex of a newborn individual. It can be environmental cues or genetically determined/ Explain the statement by giving example for each strategy.    [CBSE 2016] 
Ans. Different species use very different strategies for this. Some rely entirely on environmental cues. Thus, in some animals, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female. In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined. However, in human beings, the sex of the individual is largely genetically determined. In other words, the genes inherited from our parents decide whether we will be boys or girls.

Q.32. Name the organ where ova are formed inside the body. Trace their pathway from their formation to fertilisation. Name the organ where they go after fertilisation.    [CBSE 2012,2013,2015]
Ans. 
Organ where ova are formed is ovary. Ova are released from ovary into the fallopian tube which lead into the uterus. The ovum gets fertilised in the fallopian tube, where sperms travel to fertilise the egg from cervix, through uterus, to fallopian tube.
The fertilised egg, i.e., zygote gets implanted in the uterus after fertilisation.

Q.33. State the changes that take place in the uterus subsequent to implantation of embryo ? How does this embryo get nourishment inside the mother’s body ?    [CBSE 2012,2015]
Ans. After implantation -The uterine wall thickens that is richly supplied with blood.
A special tissue called placenta develops which connects embryo to the uterine wall that provides nutrients and oxygen to it.
Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryonal side. On maternal side, are blood spaces, which surround the villi. This provides large surface area for glucose and oxygen to pass from the mother to the embryo.

Q.34. State in brief the role of human male reproduction system. Why is it called the ‘urinogenital’ system ? [CBSE 2012,2015]
Ans.
The primary reproductive organ in males are testis. Testis produce male gamete and testosterone.
They are located in scrotum, outside the abdominal cavity, to maintain temperature 1-3 °C lower than body temperature. This is essential for production of sperms.
The sperms are formed and delivered through vas deferens which unites with ureter coming from urinary bladder.
The prostate glands and seminal vesicles release their secretions which are essential for sperms transport and nutrition.
This opens into urethra through which both urine and sperms are released.
Hence, human male reproductive system is also called urino-genital system as urine and semen are released from same tract.

Q.35. List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over the past 50 years in our country.    [CBSE 2015] 
Ans. Significance of reproductive health in a society :
(i) Reproductively healthy individuals will give rise to healthy new generation.
(ii) There will be fewer sexual transmitted diseases.
(iii) Healthy mothers mean happy households.
(iv) Healthy individuals mean more productive and prosperous families and society at

Q.36. List three distinguishing features between sexual and asexual types of reproduction, in tabular form.    [DoE; Al 2015]
Ans. Distinguishing features between sexual and asexual reproduction:
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.37. List four categories of contraceptive methods.
State in brief two advantages of adopting such preventive methods.    [Al 2015]
Ans. 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.

Q.38. List six specific characteristics of sexual reproduction.    [AI 2015] 
Ans. 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 gamete 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.

Q.39. Identify A, B and C in the given diagram and write one function of each.    [AI 2015]
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
Ans. A = Stigma
B = Pollen tube
C = Female germ cell
Function of stigma: Stigma helps in receiving the pollen grains from the anther of stamen during pollination.
Function of pollen tube: The pollen tube facilitates movement of male germ cell through it to reach female germ cell.
Function of female germ cell: It meets with the male germ cell to form zygote which divides many times to form an embryo.

Q.40. Name the two reproductive parts of a bisexual flower which contain the germ cells. State the location and function of its female reproductive part.    [Foreign 2015]
Ans. The two reproductive parts of a bisexual flower are stamen and carpel. Stamen is the male reproductive part of the plant. They are the little stalks with swollen tops just inside the rings of petals in a flower.
It is made up of two parts, i.e. a filament and an anther. Filament is the stalk of stamen and it bears anther and consists mainly of conducting tissue. Anther are sac-like structures which produce male garnets known as pollen.
The carpel is the female reproductive organ located at the centre of a flower. It consists of ovary, style and stigma. The ovary is the swollen part at the bottom of the carpel. The elongated part in the centre of the carpel is the style. The stigma is sticky so that it can trap pollen grains easily. Pollen tube that grows from the pollen grain to the ovary aids fertilisation.

Q.41. (a) Name the following:     [Delhi 2015] 
(i) Thread like non-reproductive structures present in Rhizopus. 
(ii) ‘Blobs’ that develop at the tips of the non-reproductive threads in Rhizopus, 
(b) Explain how these structures protect themselves and what is the function of the structures released from the ‘blobs’ in Rhizopus.
Ans. (a) (i) Hyphae (ii) Sporangium
(b) Spores are enclosed within sporangia which protects the spores.
Spores when released from sporangia develops into new Rhizopus.

Q.42. Explain the process of regeneration in Planaria. How is this process different from reproduction?    [Foreign 2015; Delhi 2013]
Ans.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
In regeneration, the organism need to be cut into pieces to get more organisms. In reproduction, the organism need not to be cut to multiply.

Q.43. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.    [AI 2015]
Ans. ‘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 (In) 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.

Q.44. Name the parts of a bisexual flower that are not directly involved in reproduction. [Foreign 2015] 
Ans. Parts of a bisexual flower which are not directly involved in reproduction are (i) Petal, (ii) Sepal and (iii) Stem.

Q.45. Name two simple organisms having the ability of regeneration.    [Al 2015]
Ans. Hydra and Planaria.

Q.46. Name the causative agent of the disease “Kalaazar” and its mode of asexual reproduction.    [Foreign 2015]
Ans. Leishmania causes kala-azar. It reproduces by binary fission.

Q.47. What is DNA copying?    [Delhi 2015] 
Ans. DNA in the cell nucleus is the information source for making proteins and different proteins lead to different body designs. During reproduction, similar copy of DNA is generated and the process is called DNA copying.

Q.48. Where is DNA found in a cell?    [DoE; AI 2015] 
Ans. DNA is found in the nucleus.

Q.49. What is DNA?   [Foreign 2015]
Ans. The full form of DNA is deoxyribonucleic acid. DNA lies in the cell nucleus which is the information source for making proteins, and different proteins lead to different designs.

Q.50. Name the life process of an organism that helps in the growth of its population.    [AI 2015] 
Ans. Reproduction

LONG ANSWER TYPE QUESTION 

Q.1. (a) Identify the given diagram. Name the parts 1 to 5.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
(b) What is contraception? List three advantages of adopting contraceptive measures.    [Delhi 2019]
Ans. (a) 1. Oviduct
2. Ovary
3. Uterus
4. Cervix
5. Vagina
(b) The prevention of pregnancy in women is called contraception.
(i) It helps in maintaining health of women as frequent pregnancies have adverse effect on the health of the mother.
(ii) It helps in preventing sexually transmitted diseases such as AIDS, syphilis, gonorrhoea, etc.
(iii) Is helps in birth control. If a family is small then each child will get proper resources like attention, education, food, clothes, etc.

Q.2. (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.    [CBSE 2018, AI 2017,17(C), Delhi 2016]
Ans. (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 7 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 rem oves the wastes (CO2 and nitrogenous wastes) generated by the foetus to the mother’s blood.

Q.3. (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.     [Delhi 2017]
Ans.
(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.

Q.4. (a) What is pollination ? Give its two types.
(b) Draw a longitudinal section of female reproductive part of a flower showing germination of pollen grain. Label on it the following :
(i) Stigma;
(ii) Pollen tube with a male germ cell;
(iii) Female germ cell.    [CBSE 2016-17 C]
Ans.
(a) Pollination is the process of transfer of pollen grains from anther of a flower to the stigma of a same flower or another flower of same species.
Depending on the flower, it is of two types :
(i) Self pollination - When pollen from the anther of the same flower lands on its stigma. (ii) Cross pollination - When pollen from one flower lands on stigma of another flower of same species, with the help of air, water, insects, birds or bats.
(b)
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev

Q.5. List and. explain briefly any three methods of contraception.    [CBSE 2016-17 Cl
Ans. Three methods of contraception :
(i) Mechanical Barrier - Condoms on penis or vagina is a covering worn so as to create a barrier such that sperms do not reach the egg.
(ii) Oral Contraceptive Pills - They change the hormonal balance o f the body so that eggs are not released and fertilisation does not take place.
(iii) Intra-Uterine Device - Devices like copper-T or loop are placed in the uterus which change the pH of uterus and hence sperms cannot survive, thereby preventing pregnancy.
(iv) Surgical Method - Blocking vas deferens in males and fallopian tube in females, would allow respective gametes to be released and hence act as contraceptive.

Q.6. (a) What is variation ? How is variation created in a population ? How does the creation of variation in a species promote survival ?
(b) Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes.    [CBSE 2017-18 C]
Ans. 
(a) Variation is occurrence of differences between organisms.
Variations are created in a population in different ways :
(i) There may be minor changes/errors during DNA copying mechanism which happens before any cell division. These variations may go on accumulating from previous generations, ultimately leading to visible changes.
(ii) In sexually reproducing organisms, the traits of two individuals combine and give rise to new combination in the progeny. This also leads to variation.
(iii) Thus combining variations from two or more individuals would thus create new combinations of variations.
Organisms with suitable variations will have better chances of survival. Depending on the nature of variation, different individuals would have different kind of advantages.
(b) In sexually reproducing organisms each cell has two copies of each chromosome, one each from the male and female parent. During gamete formation, one chromosome from each pair goes to a gamete. Hence, the gametes have half the number of chromosomes, but one chromosome of each pair. When two gametes combine, they restore the normal number of chromosome in the progeny

Q.7. What is placenta ? Describe its structure. State its functions in case of pregnant human female.    [CBSE 2012,2013,2016,2017]
Ans. 
For implantation of foetus, a special tissue called placenta develops from the maternal uterine wall. It is a disc shaped structure, in the uterine wall with villi on the embryonal side and large blood spaces on maternal side.
Functions :
(i) It provides large surface area for glucose and O2 to pass from mother’s blood to the embryo.
(ii) It also removes embryonal metabolic wastes.

Q.8. (a) Differentiate between pollen grains and ovule.
(b) State in brief the functions of the following parts of the human female reproductive system : 
(i) Ovary 
(ii) Fallopian tube 
(iii) Uterus.     [CBSE 2012,2015,2017 C]
Ans.
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
(b) (i) Ovary — Involved in production of ova and female sex hormone estrogen.
(ii) Fallopian tube - Receives ovum after ovulation and is the site of fertilisation.
(iii) Uterus - Embryo gets implanted and its development till child birth takes place here.

Q.9. (a) Mention the role of following organs of human male reproductive system :
(i) Testis
(ii) Scrotum
(iii) Vas deferens
(iv) Prostate glands
(b) State the reasons why testes are located outside the abdominal cavity.     [CBSE 2011,2012,2013,2015,2016-17 C]

Ans. (a) (i) Male gametes (sperms) and male hormone testosterone are produced by testis. (ii) Sperm formation requires a lower temperature than the normal body temperature. This temperature is 1-3°C lower than the temperature of the body. Testis are located outside the abdominal cavity, in the scrotum to provide right temperature.
(iii) The sperms formed are delivered through the vas-deferens which unites with a tube coming from the urinary bladder.
(iv) The prostate glands secrete the fluids which provides nutrition to the sperms and make their transport easier.
(b) They require a lower temperature than the human body temperature for the formation of sperms.

Q.10. (a) Draw a sectional view of human female reproductive system and label the following parts :
(i) where the development of egg occurs,
(ii) where fertilisation takes place,
(iii) where fertilised eggs get implanted.
(b) Describe the changes the uterus undergoes :
(i) to receive the zygote.
(ii) if zygote is not formed.     [CBSE 2013,2014,2015,2016-17 C]
Ans. (a)
Previous Year Questions - How do Organisms Reproduce? Class 10 Notes | EduRev
(b) (i) The zygote gets implanted in the uterus which thickens its walls and increases blood supply.
(ii) If zygote is not formed, the lining of the uterus slowly breaks and is shed alongwith blood and mucus and comes out through vagina in the form of menstrual flow.

Q.11. Discuss briefly the different types of reproduction.    [CBSE 2017-18 C]
Ans. 
Living organisms reproduce mainly by two methods :
(1) Asexual reproduction : In this mode of reproduction, the offspring arises from a single individual parent. Asexual type of reproduction takes place in unicellular organisms, some plants, and certain multicellular animals like sponges and Hydra.
Main types of asexual reproduction are :
(i) Fission.
(ii) Budding.
(iii) Spore formation.
(iv) Regeneration.
(v) Vegetative propagation.
(2) Sexual reproduction : For sexual reproduction, involvement of the two sexes, male and female, is essential. Sexual reproduction involves union of sperm (male gamete) and egg (female gamete). These gametes are produced by gonads testis in males and ovary in females.

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