CBSE Class 10 Science How do Organisms Reproduce Assignment Set A

Which statement about the number of chromosomes in the cells and gametes is corrects.
(a) The number of chromosomes in P and Q are different
(b) The number of chromosomes in P and Q are same
(c) The number of chromosomes in S in one quarter of chromosomes in R
(d) The number of chromosomes in T is half the number of chromosomes in Q

(a) C
(b) A
(c) D

(d) B

Answer: After pollination, the pollen grains germinate n the stigma by producting pollen tube. This pollen tube is formed from inner wall of the pollen grain. It penetrates the stigma and passes through the style and enters the ovule through an opening called male gamete it releases two male gametes in the embryo sac. One male gamete fuses with egg cells and second fuses with two polar nuclei. The fusion of one male gamete with the egg cells is called syngamy. The fusion of second male gamete with two polar nuclei is called triple fusion. This process occurs in ovary.

 

 

 

h) Decrease in natural resources – More people will decrease the natural resources quickly.

 

 

Class 10 Science How Do Organisms Reproduce Notes and Questions

Short Answer Questions

Question. What are the different methods of contraception?
Answer: Various methods used for regulation of child birth can broadly categories as:
(i) Barrier methods: In this method, physical devices such as condom, diaphragm, cervical cap and copper-T are used.
(ii) Chemical method: use of spermicidal jelly by woman, oral pills and vaginal pills.
(iii) Surgical method: In surgical method, a small portion of vas deferens in male and the oviduct of female, is surgically removed or ligated. It is called vasectomy in male and Tubectomy in females.

Question. Can you think of reasons why more complex organism cannot give rise to new individuals through regeneration?
Answer: The reason is that complex organisms are not merely random collection of cells. Specialized cells are organized in them as tissues are organized in orgAnswer: These organs have to be placed at definite positions in the body. So, regeneration is not possible in multicellular organism.

Question. Draw a well labeled diagram of male reproductive system and describe its parts.

Answer: a) A pair of testes – Each testis produces sperms and male sex hormone called testosterone. Testes are present in small pouch called scrotum.
b) Epididymis – It is a long coiled tube. The head is connected with testis and tail is connected with vas deferens
c) Vas deferens – It is a long tube which begins from the tail of epididymis
Urethra – It receives the vas deferens from both the testes. It opens outside through penis. It carries both sperms and urine.

Question. Why is vegetative propagation practiced for growing some types of plants?
Answer: (i) Plants raised by vegetative propagation can bear flower and fruits earlier than those produced from seeds.
(ii) Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds.
(iii) All plants produced by this method are genetically similar enough to the parent plant to have its all characteristics.

Question. Explain vegetative reproduction through layering. Give examples.
Answer: It is a type of artificial vegetative reproduction in which a branch of the parent plant is buried in the soil. The portion of the branch which is in contact with the soil produces roots and this rooted branch is called layer. Layer is then detached form the parent plant which acts as a new plant. Example – Jasmine.

Question. Differentiate between asexual and sexual reproduction.
Answer:

Question. How does binary fission differ from multiple fissions?
Answer: Difference between binary fission and multiple fission:

Question. Why is DNA coping essential part of the process of reproduction?
Answer: DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are the information source for making protein. If information is different, different protein will be made that lead to altered body design.

Question. How does binary fission differ from multiple fissions?
Answer: Difference between binary fission and multiple fission:

Question. Draw a labeled diagram of the longitudinal section of a flower.
Answer:

Question. Why does menstruation occurs.
Answer: When in human female if the egg is not fertilized, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilized egg. Thus, its lining becomes thick and spongy. This would be required for nourishing the embryo if had fertilized. However, this lining is not required any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes roughly every month and is known as menstruation.

Question. What is the need of population control?
Answer: Overpopulation leads to a number of problems like –
a) Unemployment – More number of people means more jobs and if sufficient numbers of jobs are not available, it leads to unemployment.
b) Poverty – If there are more persons and the income is less, it becomes poorer with the addition of every child.
c) Food supply – If the population increases and the food production does not increase; this will lead to shortage of food supply.
d) Hygienic condition – more people in small area generally make the condition unhygienic for survival
e) Educational problem – It becomes difficult for the government to provide education to all
f) Housing problem – It also creates housing problem.
g) Pollution – More pollution with increasing population.
h) Decrease in natural resources – More people will decrease the natural resources quickly.

Question. Draw a flow chart showing various types of reproduction with examples.
Answer:

Question. Why is variation beneficial to the species but not necessarily for the individual?
Answer: Variations are useful for the survival of species in changed environment situations. If a population of reproducing organism were suited to a particular niche and if the niche is drastically altered the population could be wiped out. However, some variations are present some species will survive. Thus, variation is useful to species but not the individual.

Question. Producing individuals by parents consume a lot of energy. So, why should an individual organism waste energy in the process, it does not need to stay alive?
Answer: Reproduction, unlike other life processes is not essential to maintain the life of an individual organism. But it is essential for providing stability to the population of species. Maintaining the species is essential for maintaining balance in nature.

Question. How are spores produced in sporangium of Rhizopus?
Answer: a) A spore is a small microscopic structure with a thick wall.
b) Spores are generally formed in a structure called sporangium which reassembles formed in
a structure called sporangium which resemble blob on – a – stick.
c) Sporangia are formed at the tip of erect fungal hypha.
d) In each sporangium, a nucleus divides several times producing a large number of nuclei. Nuclei get surrounded by a little cytoplasm and develop into thick – walled cells or spores.
e) The wall of sporangium breaks to release the spores in air.
f) On germination in the presence of moist surface, each spore gives rise to a new organism.

Question. What is grafting? Why is it used in horticulture practices?
Answer: In grafting, cutting of a plant stem is attached to another rooted plant. The cutting of stem which is grafted on the other plant is scion and the rooted plant on which the cutting is grafted is called stock. The scion and stock are placed one over other and tied in such a way that there is no gap between them. The cambium activity takes place among them and they get joined. Grafting is used in plants which do not produce extensive roots.

Question. Why is variation beneficial to the species but not necessary for the individual?
Answer: Variation is beneficial to the species as it enables a species for its survival. A favourable variation makes an organism to live better in a changed environment and an unfavourable variation will not. So it is not necessarily true that a variation is beneficial to the individual

Question. Diagrammatically represent binary fission in amoeba
Answer:

 

 

Question. List two functions of ovary of human female reproductive system.
Answer: In human female, ovary contains thousands of eggs. One egg is produced every month one of the ovaries. Ovary also secretes estrogens hormone for development of sexual characteristics at puberty.

Question. How can the chromosomes be identified?
Answer: Chromosomes can be seen as thread like structure when cell is dividing.

Question. Name the life process of an organism that helps in the growth of its population.
Answer: Reproduction.

Question. Where is DNA found in a cell?
Answer: Genes/Chromosomes.

Question. List two functions performed by testis in human beings.
Answer: a. Testis produce sperms.
b. Produces male sex hormone, testosterone.

Question. Why is temperature of scrotal sac 2°C less than the body temperature?
Answer: Because testes require temperature 2°C less than the body temperature for the production of sperms.

Question. What is reproduction?
Answer: Reproduction is the process of producing individuals of its own kind.

Question. What is the effect of DNA copying which is not perfectly accurate on the reproduction process?
Answer: Leads to variation/ evolution.

Question. How can pregnancy be prevented surgically?
Answer: Pregnancy can be prevented surgically by adopting:
a. Vasectomy: When vas deferens in males are blocked surgically, sperm transfer will be prevented.
b. Tubectomy: When fallopian tubes are blocked, eggs will not be able to reach the uterus.

Question. ‘Regeneration is not reproduction’. Justify this statement with reason.
Answer: When a piece is cut from an organism, it grows into complete organisms. Regeneration is carried out by specialized cells. It is not reproduction since most organisms would not be able to grow through pieces.

Question. Draw a labelled diagram of
a. Regeneration in Planaria
b. Budding in Hydra
                 or
Explain budding in Hydra with the help of labelled diagrams only.
Answer:

Question. Draw a labelled diagram of (i) Binary fission in Amoeba (ii) leaf of Bryophyllum with buds.

Answer: 

 

Question. State one function each performed by the following organs in human beings: (a) Testes (b) Prostate gland
Answer: a. Formation of sperms takes place in testes.
b. Prostate gland contributes fluid to the semen.

Question. Why do we need to adopt contraceptive measures?
Answer: a. Contraceptive measures are needed to be adopted to prevent unwanted pregnancies.
b. To prevent sexually transmitted diseases.
c. Spacing between children.
d. For sound health of a mother.

Question. List any two reasons why the Government has banned prenatal sex determination by law.
Answer: a. People may get female foetus aborted.
b. Reckless female foeticide has disturbed malefemale ratio in society.

Question. Define the following processes of asexual reproduction:
a. Spore formation
b. Regeneration
c. Multiple fission
Answer: a. Reproduction seen in organisms by formation of spores.
b. Organisms are cut into any number of pieces and each piece grows into a complete organism.
c. Unicellular organisms divide into many daughter cells simultaneously.

Question. What happens when the following situations are initiated:
a. A Planaria is cut into three different pieces.
b. Leaf of the Bryophyllum with notches falls on the soil.
c. Testosterone is released in the male reproductive system.
Answer: a. Each piece grows into a complete organism.
b. Develops into new plants.
c. Changes occurs in the appearance at the time of puberty.

Question. Mention any four ways of asexual reproduction.
Answer: a. Fission
b. Budding
c. Spore formation
d. Fragmentation
e. Regenerations

Question. Justify the following statements:
a. Variation is beneficial for the species over a period of time.
b. New offsprings produced are similar to their parents but not identical.
c. Binary fission is different in Amoeba and Leishmania.
Answer: a. Variations help a population in the process of natural selection and accumulation of adaptations in a population. It leads to evolution of a species.
b. Offspring, especially when produced sexually, have minor differences or variations among themselves hence they may not look identical. By virtue of them being from same species they look similar.
c. Binary fission in Amoeba is in any plane but in Leishmania it is in a fixed plane.

Question. a. What are sexually transmitted diseases? Name any one which is caused by bacteria and one caused by viral infection.
b. Mention any two methods to avoid such diseases.
Answer: a. Diseases that spread through the sexual contact are called sexually transmitted diseases.
(i) Gonorrhoea or syphilis is caused by bacteria.
(ii) Warts, HTV, AIDS is caused by virus.
b. (i) Use of condoms on penis.
(ii) Use covering on vagina.

Question. a. How do organisms reproduced by fission?
b. Write names of any two organisms which reproduce by this method.
c. Differentiate between the fission of Leishmania and Plasmodium.
Answer: a. Cell division takes place which leads to creation of new individuals.
b. Bacteria, Protozoa.
c. Leishmania — binary fission occurs in a definite orientation.
Plasmodium — undergoes multiple fission,

Question. Differentiate between the following:
a. Placenta and uterus
b. Unisexual and bisexual flowers
c. Fertilization and germination
Answer: a. Placenta and uterus : The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. After fertilization, embryo gets attached to
the walls of uterus.
b. Unisexual flowers contain either stamens or carpels. Bisexual flowers contain both stamens and carpels.
c. Fertilization and germination : The fusion of male gamete with female gamete leading to the formation of zygote is known as fertilization. The growth of embryo (present in the seed) into seedling under appropriate conditions is known as germination.

Question. a. Identify the asexual method of reproduction in each of the following organisms:
(i) Rose (ii) Yeast (iii) Planaria
b. What is fragmentation? Name a multicellular organism which reproduces by this method.
Answer: a. (i) Vegetative propagation by stem.
(ii) Budding
(iii) Regeneration
b. Fragmentation is a asexual method of reproduction in which an organism simply breaks up into smaller pieces/ fragments upon maturation. These pieces or fragments grow into new individuals. Spirogyra is the multicellular organism with relatively simple body organisation which reproduces through this simple method of reproduction, i.e., fragmentation.

Question. a. Give one example each of sexually transmitted diseases in each of following cases
(i) Bacterial infections (ii) Viral infections
b. How can spread of these diseases be prevented?
                                          or
Name one sexually transmitted disease each caused due to bacterial infection and viral infection. How can they be prevented?
Answer: a. Bacterial infections: Syphilis, Gonorrhoea.
Viral infections: Warts, AIDS, Hepatitis B, Herpes.
b. Spread of these diseases can be prevented by using physical barrier, avoiding sex with multiple partners.

Question. A part of the male reproductive system is shown below. Study the diagram and answer the questions that follow.

a. Two part have been incorrectly labelled. Identify them.
b. Give the function of urethra.
c. Which hormone is released by testis?
Answer: a. Testis, penis.
b. Urethra serves as a common passage for both sperms and urine.
c. Testosterone.

Question. a. Trace the path of sperms from where they are produced in human body to the exterior.
b. Write the functions of secretions of prostate gland and seminal vesicles in humAnswer:
Answer: a. The formation of sperms takes place in testes and delivered through the vas deferens which unites with a tube coming from urinary bladder to form urethra from where they are excreted out of the body.
b. Prostate gland and seminal vesicles add their secretions to make the sperms motile in a fluid which makes their transport easier and provides nutrition.

Question. Write scientific name for malarial parasite. How is fission in amoeba different from that of malarial parasite?
Answer: a. Plasmodium,
b. Fission in amoeba produces two daughter cells - binary fission. Fission in Plasmodium produce many daughter cells - multiple fission,

Question. a. Give the functions of the following:
1. Pollen tube
2. Ovary
b. List any two changes observed in the body of a female during puberty.
Answer: a. (i) Transfer of male gamete. (ii) Production of female gamete.
b. (i) Growth of mammary glands. (ii) Onset of menstrual cycle.

Question. What happens when:
a. APlanaria is cut into three different pieces,
b. Leaf of the Bryophyllum with notches fall on the soil.
c. Testosterone is released in the male reproductive system.
Answer: a. Three new Planaria will form due to regeneration.
b. New plantlets will form from these buds helping the plant to propagate vegetatively.
c. The male shows masculine features and attains fertility. Sperm starts forming in testis.

Question. What is the effect of DNA copying, which is not perfectly ccurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer: a. DNA copying leads to more variations in the offspring.
b. Sexually reproducing organisms have special lineage of cells which have only half the number of chromosomes as the parent cell.
c. When such germ cells fused, a new individual is formed with the same amount of DNA as that of parent.

Question. Answer the following:
a. How is zygote formed?
b. State the function of placenta in the mother’s body.
c. At what interval the egg is formed in human female ovary?
d. Name two STDs caused by bacterial infection.
e. Why is prenatal sex determination prohibited?
Answer: a. Zygote is formed by the fusion of male and female gamete.
b. Placenta is a special tissue through which the developing embryo/foetus gets nutrition from mother’s blood. It also transports wastes of the embryo into mother’s blood.
c. Ovulation releases mature ovum from ‘ the ovary. It happens once during a menstrual cycle that is for roughly 28 days.
d. STDs caused by bacterial infection are Gonorrhoea and Syphilis.
e. Prenatal sex determination is misused and it may be the reason for female foeticide.

Question. a. Write the function of following parts in human female reproductive system:
(i) Ovary
(ii) Oviduct
(iii) Uterus
b. Describe in brief the structure and function of placenta.
                                                     or
Write the functions of the following in human female reproductive system: Ovary, oviduct, uterus How does the embryo get nourishment inside the mother’s body? Explain in brief.
Answer: a. Functions of Ovary, oviduct, uterus
Functions of Ovary
(i) Production of female hormone, oestrogen and progesterone.
(ii) Production of female gamete / egg /germ cell.
Functions of Oviduct:
(i) Transfer of female gamete from the ovary.
(ii) Site of fertilization.
Functions of Uterus:
(i) Implantation of Zygote/ embryo.
(ii) Nourishment of developing embryo.
b. Placenta is a special disc like tissue embedded in the mother’s uterine wall and connected to the foetus / embryo.
Placenta provides a large surface area for glucose and oxygen/nutrients to pass from the mother’s blood to the embryo/ foetus.

Question. a. Draw a sectional view of human female reproductive system and label the part where:
(i) Eggs develop
(ii) Fertilization takes place
(iii) Fertilized eggs get implanted.
b. Describe in brief, the changes the uterus undergoes:
(i) To receive the zygote
(ii) If zygote is not formed.
Answer: a. 

(i) Ovary
(ii) Oviduct or fallopian tube
(iii) Uterus or uterus wall
b. (i) It becomes thicker due to development of blood vessels and glands in it.
(ii) It gets peeled and shed off along with mucus, blood, dead ovum during menstruation

Question. Differentiate between:
a. Pollen tube and Style
b. Fission of Amoeba and Plasmodium
c. Fragmentation and regeneration
d. Bud of Hydra and bud of Bryophyllum
e. Vegetative propagation and spore formation.
Answer: a. Pollen tube forms and male gametes are carried by it to the ovule.
Style is part of female part- carpel through which pollen tube passes.
b. Amoeba shows binary fission where one cell splits into two equal halves.
Plasmodium (malarial parasite) shows multiple fission where one cell divides into many daughter cells simultaneously.
c. Fragmentation occurs in multi-cellular organisms with simple body organisation like Spirogyra (a filamentous alga). It involves breaking up of a filament into many fragments and each fragment growing into new individual.
Regeneration is the ability to give rise to new individuals from the body parts of the parent individual, e.g., Hydra and Planaria, if their bodies get broken into many pieces, each piece is capable of regrowing into a complete individual.
d. In Hydra, a bud is formed at a specific site by repeated cell division and develops into a tiny hydra.
In Bryophyllum, vegetative buds arise from the notches of its leaves and develops into a new plantlet.
e. Vegetative Propagation is the development of new plants from parts like root, leaf and stem under suitable conditions, e.g., Bryophyllum vegetative buds arise from the notches of its leaves. In potato, ginger, garlic etc. it occurs through stems. Spore formation: A spore is a special cell protected by thick coating. It is capable of germinating into a new plant when comes in contact with suitable and environment conditions and moist surface, e.g., in Rhizopus (bread mould), they are formed inside reproductive, bob¬like sacs called sporangia.

Question. What happens when
a. Testosterone is released in the male reproductive system.
b. Pollen grain falls on the stigma of flower.
c. Egg fuses with the sperm cell.
d. A Planaria is cut into three different pieces.
e. Buds are formed on the notches of leaf of the Bryophyllum.
Answer: a. The male shows masculine features and attains fertility/ sperm starts forming in testis.
b. Pollen tube forms and male gametes are carried by it to the ovule.
c. Fertilization occurs and a zygote forms.
d. Three new Planaria will form due to regeneration.
e. New plantlets will form from these buds helping the plant to propagate vegetatively.