Please refer to How do the Organisms Reproduce Class 10 Science Important Questions given below. These solved questions for How do the Organisms Reproduce have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 10 Science all chapters.
Class 10 Science How do the Organisms Reproduce Important Questions
VERY SHORT ANSWER TYPE QUESTIONS
Question. How is the process of pollination different from fertilisation?
Answer.The process of transfer of pollens from anther to stigma is called pollination, which takes place only in plants.
Fertilisation is a process in which male sex cell and female sex cell join or fuse together to form zygote. It happens in all living organisms, in sexual reproduction.
Question. What is the role of seminal vesicles and prostate gland?
Write the functions of secretions of prostate gland and seminal vesicles in humans.
Answer.Seminal vesicle: It holds the liquid that mixes with sperm to form semen.
Prostate gland: It secretes fluid adding upto the semen and contains enzymes and other substances.
It also provides nutrition to the sperms, in the form of fructose and calcium. It protects sperms.
Question. List two preparations shown every month by the uterus in anticipation of pregnancy in the humans.
Answer.(i) The inner uterine wall becomes thick.
(ii) More blood vessels develop in its lining.
Question. Write the number of immature eggs present in the ovaries of newly born baby girl. Mention what happens to these immature eggs when the girl attains maturity.
Answer.Ovaries contain thousands of immature eggs at the time of birth. Some of these eggs start maturing when girls attain puberty. One egg is produced every month by one of the ovaries.
Question. Trace the path of sperms from where they are produced in human body to the exterior.
Testes → vas deferens → urethra → penis and then opens to outside.
Question. What is the main difference between sperms and eggs of humans? Write the importance of this difference.
Answer.Sperms are motile (movable) and have X or Y chromosomes whereas eggs are non-motile and have X chromosome only.
The sperms can reach to egg for fertilisation because these are motile. Chromosomes in them help in determination of sex of a new born child.
Question. The chromosomal number of the sexually producing parents and their offspring is the same. Justify this statement.
Answer.(i) In sexual reproduction, fusion of male and female gametes takes place, each of their germ cells or gametes contain half the number of chromosomes.
(ii) When male and female gametes fuse at the time of fertilisation it restores the original number of chromosomes of parent.
Question. Differentiate between plumule and radicle.
Question. Why do we need to adopt contraceptive measures?
Answer.(i) To prevent unwanted pregnancies.
(ii) To prevent STD (Sexually Transmitted Diseases).
(iii) To have proper gap between two children.
(iv) To control population.
(v) To have sound health.
Question. Give two differences between male gametes and female gametes.
Question. State one function each performed by 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. Differentiate between the following:
(i) Role of placenta and uterus in pregnancy (ii) Unisexual and bisexual flowers
Answer.(i) Placenta: The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta.
Uterus: After fertilisation, embryo gets attached to the walls of uterus.
(ii) Unisexual flowers: Flowers which contain either stamens or carpels.
Bisexual flowers: Flowers which contain both stamens and carpels.
Question. If a women is using copper-T, will it help in protecting against sexually transmitted diseases?
Answer.No, it can only prevent unwanted pregnancy. It will not be able to prevent contact of body fluids.
Question. Why is fertilisation not possible without pollination in plants?
Answer.Fertilisation is the process in which pollen grain and egg fuse to form zygote. Pollination is the process of transfer of pollen grains from stamen to the stigma of carpel. It means that fertilisation is not possible without pollination.
Question. List two unisexual flowers.
Answer.Watermelon, Cucumber and Willows (Any two)
Question. List two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer.(i) Special cell division involved in the process of gametes formation is the cause of variations.
(ii) Genetic material comes from two parents, which brings variations in offsprings.
Question. List two functions performed by testis in human beings.
(i) Testis produces sperms.
(ii) It produces testosterone hormone.
Question. Name the parts of a bisexual flower that are not directly involved in reproduction.
Answer.Sepals and petals are not directly involved in reproduction.
Question. What are those organisms called which bear both the sex organs in the same individual? Give one example of such organisms.
Answer.These are called hermaphrodites, e.g. earthworm and leech.
Question. List two functions of ovary of human female reproductive system.
(i) Ovary produces eggs for fertilisation.
(ii) They also produces hormones oestrogen and progestrone.
Question. Why is temperature of scrotal sac 2°C less than the body temperature?
Answer. Scrotal sac temperature is less by 2° because sperms are safe at a little lower temperature than body temperature. It is outside the body that is why it has lower temperature than body.
Question. Give one difference between zygote and embryo.
Answer.Zygote is a single celled fusion product of sperm and ovum whereas embryo is a multicellular product produced by mitotic divisions from zygote.
Question. Write the expanded form of AIDS.
Answer.Acquired Immuno Deficiency Syndrome.
Question.Give an example of a flower which contains both stamens and carpels.
Answer.Hibiscus, Mustard (Any one)
Question. Differentiate between pollen grain and ovule.
Answer. Pollen grains contain male gametes in plants and ovules contain female gametes.
Question. Differentiate between germination and fertilisation.
Germination: Involves development of embryo into a seedling.
Fertilisation: It involves fusion of male with female gametes.
Question.What are sexually transmitted diseases? Name a STDs which damages the immune system of human body.
Answer.Diseases that spread through the sexual contact are called STDs
AIDS damages the body’s immune system.
Question.What happens when egg is not fertilised?
Answer.When egg is not fertilised, blood and mucus comes out through vagina. This process is called menstruation.
Question. Why does the lining of uterus becomes thick and spongy during every month?
Answer. The lining of uterus becomes thick and spongy by the action of progesterone to receive and nurture the development of embryo.
Question. What is the role of scrotum?
Answer.Scrotum regulates the temperature of testes and maintains it at 35°C, two degree below the body temperature, so as to protect sperms from high temperature.
Question. How can the chromosomes be identified?
Answer.Chromosomes can be seen as thread like structure having specific shape when cell is dividing by which they can be identified.
Question. What happens when a Planaria gets cut into two pieces?
Answer.Each piece regenerates into new organism, planaria.
Question. How does binary fission differ from multiple fission?
Answer.In binary fission cell divides into two cells whereas in multiple fission a cell divide into many daughter cells.
Question. Select two plants from the following which are grown by vegetative propagation process:
Banana, Wheat, Mustard, Jasmine, Gram.
Answer.Banana and jasmine are grown by vegetative propagation, because they do not produce seeds.
Question. Name the part of Bryophyllum where the buds are produced for vegetative propagation.
Answer.Buds arise from the notches in the leaf margins of Bryophyllum.
Question. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual?
Answer.Under favourable conditions, spirogyra reproduces by a process known as fragmentation. This is an asexual method of reproduction.
Question. How does Planaria reproduce? Is this method sexual or asexual?
Answer.Planaria reproduces by a process known as regeneration. It is a type of asexual reproduction in which if Planaria can be cut into any number of pieces, each piece grows into a new individual organism.
Question. What happens when a mature Spirogyra filament attains considerable length?
Answer.A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new plant.This process of reproduction is called fragmentation.
Question. Name the method by which hydra reproduces. Is this method sexual or asexual?
Answer.Hydra reproduces by budding. It is an asexual mode of reproduction.
Question. Name the causative agent of the disease ‘kala-azar’ and its mode of asexual reproduction.
Answer.Leishmania causes ‘kala-azar’. It reproduces by binary fission in a definite orientation.
Question. Give the respective scientific term used for studying.
(i) The mechanism by which variation are created and inherited and
(ii) The development of new type of organism from the existing ones.
Answer.(i) Heredity, (ii) Evolution.
Question. Name two simple organisms which have ability of regeneration.
Answer.Planaria and Hydra
Question. Name the type of cells which undergo regeneration.
Answer.Specialised cells called regenerative cells which can make large number of new cells.
Question. Regeneration is not possible in all types of animals. Why?
Answer.Regeneration is carried out by specialised cells which are present in few animals which can reproduce by regeneration.
Question. What is the advantage of reproduction through spores?
How will organism be benefitted if it reproduces through spores?
Answer.Spore with a cell wall can survive even in adverse conditions. Large number of spores are produced in one sporangium. It is easily dispersed through wind as they are large in number and light in weight.
Question. How does Plasmodium reproduce? Is this method sexual or asexual?
Answer.Plasmodium is a single celled organism which reproduces by the process of multiple fission. Multiple fission (i.e. breaking up of a single cell into many daughter cells) is an asexual mode of reproduction.
Question. What is DNA?
Answer:DNA means deoxyribo nucleic acid. It lies in the cell nucleus, which is the source of information for making proteins and different proteins lead to different body designs.
Question. Where is DNA found in the cell?
Answer:DNA is found in the nucleus.
Question. Explain how do organisms create an exact copy of themselves.
Answer:The cell uses biochemical reactions to make exact copies of DNA or genetic material.
Question. Name the information source of making proteins in the cell. State two basic events in reproduction.
Answer:DNA in the nucleus of a cell is the source of information for making proteins. The two basic events in reproduction are:
(i) creation of copy of DNA
(ii) creation of an additional cellular apparatus by cell then the DNA copies separate, each with its own cellular apparatus.
Question. Name the life process of an organism which helps in the growth of its population.
Question. Organisms have a varied body design. Name the property which gives the basic difference in body design.
Answer:Errors in DNA copying.
Question. The mode of reproduction depends on which feature of the organism?
Answer:The mode of reproduction depends upon the body design of organism. Those with simple body design may reproduce asexually. Those with complex body design may form gametes and may undergo sexual reproduction.
Question. What is the effect of DNA copying which is not perfectly accurate in the reproduction process?
Answer:DNA copying will lead to variation in populations which helps in evolution of the species.
Question. Give the full form of DNA.
Answer : Deoxyribo Nucleic Acid.
Question. How do we know that two different individuals belong to the same species?
Answer : Members of same species are capable of interbreeding the same species by the similarity in their body design and other physical features.
Question. What is pollination?
Answer : The process of transfer of pollen grains from the stamen to the stigma of a flower is called pollination.
Question. Name the nucleic acids.
Answer : DNA and RNA are the two nucleic acids present in the living cells.
Question. How does the developing embryo get nourishment inside the mother’s body?
Answer : The embryo gets nourishment from the mother’s blood with the help of a special tissue called placenta.
Question. When does copying of DNA occur?
Answer : Copying of DNA occurs during cell division.
Question. The mode of reproduction depends on which feature of the organism.
Answer : The mode of reproduction depends on the body design of the organism.
Question. Why is variation beneficial to the species but not necessary for the individual?
Answer : Accumulation of variations after several generations results in new set of traits required for survival. As they show results after many generations so they are not important for individual.
Question. Why is DNA copying an essential part of the process of reproduction?
Answer : DNA copying is needed because information stored in DNA is used to make protein.
Synthesis of different proteins will lead to altered body design. Thus, reproduction at its most basic level involves making copies of the blueprints of body design.
Question. How does reproduction help in providing stability to populations of species?
Answer: Living organisms reproduce for the continuation of a particular species. It helps in providing stability to the population of species by producing a new individual that resembles the parents. This is the reason why cats give birth to only cats or dogs give birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats or any other species.
Question. How is the process of pollination different from fertilization ?
Answer : Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. These are transferred by agents such as insects, birds, wind or water.
Fertilization is defined as the fusion of a male gamete (sperm) with a female gamete (ovary) to form a zygote by sexual reproduction.
Question. How does binary fission differ from multiple fission?
Answer : Binary Fission: An organism is divided into two individuals. Mitotic division takes place resulting in two identical individuals or daughter cells. e.g., Amoeba.
Multiple Fission: Mitotic division takes place. The nucleus divides repeatedly to form a number of equal sized and similar individuals, e.g., Plasmodium.
Question. Why is vegetative propagation practised for growing some types of plants?
Answer : The process by which some plants can reproduce asexually by their vegetative parts like roots, stems and leaves is called vegetative propagation. It has many advantages.
Plants raised by this method can bear flowers and fruits earlier than those produced from seeds. Plants that have lost capability to produce seeds like banana, orange, rose and jasmine can be propagated. All plants produced are genetically similar to the parent plant.
Question. What is the role of seminal vesicles and prostate gland?
Answer : Seminal vesicles are a pair of thin-walled muscular and elongated sacs which secrete a fluid for nourishment of sperms.
Prostate glands also produce a fluid which is released in the urethra along with secretion of seminal vesicle. It affects the vaginal pH so that sperms move smoothly inside the vagina.
Question. If a woman is using a copper−T, will it help in protecting her from sexually transmitted diseases?
Answer: No. Using a copper-T will not provide a protection from sexually transmitted diseases, as it does not prevent the entry of semen. It only prevents the implantation of the embryo in the uterus.
Question. Why is DNA copying an essential part of the process of reproduction ?
Answer: DNA (Deoxyribonucleic acid) copying is an essential part of reproduction as it passes genetic information from parents to offspring. It determines the body design of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by division of a cell to form two cells.
Question. What are the changes seen in girls at the time of puberty?
Answer : At the time of puberty, breast size begins to increase, with darkening of the skin of the nipples. Also, girls begin to menstruate at around this time.
Question. What are the functions performed by the testis in human beings?
Answer: The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called scrotum.
Functions of testes:
1. Produce sperms
2. Produce a hormone called testosterone, which brings about secondary sexual characters in boys.
Question. How will an organism be benefited if it reproduces through spores ?
Answer: There are many advantages, if an organism reproduces through spores.
Advantages of spore formation
1. Large numbers of spores are produced in one sporangium.
2. Spores are distributed easily by air to far1off places to avoid competition at one place.
3. Spores are covered by thick walls to prevent dehydration under unfavourable conditions.
Question. How is the process of pollination different from fertilization?
Answer: Pollination is the process of transfer of pollens from anther to stigma. It occurs with the help of certain pollinators such as air, water, birds, or some insects. Fertilization, on the other hand, is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of zygote.
Question. What is the role of the seminal vesicles and the prostate gland?
Answer: The secretions from seminal vesicles and prostate glands lubricate the sperms and provide a fluid medium for easy transport of sperms. Their secretion also provides nutrient in the form of fructose, calcium, and some enzymes.
Question. How will an organism be benefited if it reproduces through spores?
Answer : During adverse circumstances spore remain coated with protective layer. This helps an organism survive adverse conditions. Spores are means to tide over bad phases.
Question. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer : More complex organisms cannot give rise to new individuals because:
1. Their body design is highly complicated.
2. There are specific organs to do specific functions.
3. There is a labour division in the body of complex organisms.
4. Exception is lizard, which can regenerate its tail.
Question. If a woman is using copper-T, will it help in protecting her from sexually transmitted diseases?
Answer : No, it will not protect the woman from sexually transmitted diseases as fluid to fluid contact occurs in the vagina.
Question. What is the importance of DNA copying in reproduction?
Answer : DNA copying is an important phenomenon of reproduction through which the organisms pass on their characteristics to their offspring. It maintains the characteristics in different generations of the species. It also produces variations which are useful for the survival of species for long time.
Question. What could be the reasons for adopting contraceptive methods?
Answer: Contraceptive methods are mainly adopted because of the following reasons:
1. To prevent unwanted pregnancies.
2. To control population rise or birth rate.
3. To prevent the transfer of sexually transmitted diseases.
Question. How does the embryo get nourished inside the mother’s body?
Answer : The embryo grows inside the mother’s womb and gets nourishment from its mother’s blood through placenta. Placenta contains villi which connects the embryo with the mother’s blood. These villi provides a large surface area for glucose and oxygen to pass from mother to the embryo.
Question. Why is variation beneficial to the species but not necessary for the individual?
Answer:If environmental conditions undergo drastic change, some member of a species having variations of tolerating changed temperature may be able to survive, e.g. suppose population of bacteria is living in temperate water. If temperature of water increases due to global warming, most of the bacteria will die. However, if few variants are resistant to heat, then they would survive and grow further. Thus variation is useful for the survival of species over time, but it is not necessary for the individual.
Question. What is the importance of DNA copying in reproduction?
Why is DNA copying an essential part of the process of reproduction?
Answer:Reproduction involves producing same kind of species from parents. The genetic information is passed to the offspring by DNA present in each cell. This DNA, which is replicated (copied) is responsible for the resemblance of parents with offsprings with same traits. New traits are passed on due to difference in copying, new variations may occur and new species may evolve.
Question. How does reproduction help in providing stability to the populations of species?
Answer:It is because reproduction is a process by which species increase their population. If the rate of birth is more than death, the size of population will increase and will be more stable.
Question. When a cell reproduces, what happens to its DNA?
Answer:During the process of reproduction, transmission of DNA from parents to offspring takes place. Before reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides into two, these two copies are distributed equally between the two daughter cells so that similar amount and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency in the amount and type of DNA in the living organism of a particular species.
Question. (a) What is the location of following: (i) DNA in a cell, (ii) Gene
(b) Expand DNA.
Answer:(a) (i) DNA is found in nucleus of cell, (ii) Genes are located on the chromosomes.
(b) Deoxyribonucleic acid.
SHORT ANSWER TYPE QUESTIONS
Question. What are the two roles of testosterone?
Answer.(i) Testosterone regulates formation of sperms.
(ii) The appearance of secondary sexual characteristics at puberty like beard, genital hair, change in voice is due to testosterone.
Question. Why are testes located outside the abdominal cavity? Mention the endocrine and exocrine functions of the testes.
Sperm formation takes place at a lower temperature than body temperature therefore testes are located outside the body and its temperature is 2°C below the body temperature.
Functions of Testes:
Endocrine Function: The production of testosterone hormone.
Exocrine Function: The production of sperms.
Question. List six specific characteristics of sexual reproduction.
(i) Two parents are involved
(ii) Two dissimilar gametes are formed
(iii) Variations are produced
(iv) Occurs in higher and some of lower organisms
(v) Fertilisation is needed for zygote formation
(vi) It is a slow process.
Question. List three techniques that have been developed to prevent pregnancy. Which one of these is not meant for males? How does the use of these techniques have a direct impact on health and prosperity of a family?
Answer. The three techniques which prevent pregnancy are:
(i) Barrier method, (ii) Chemical method (iii) Surgical method
Chemical methods are not for males.
The use of contraceptive have a direct effect on the health and prosperity of the family.
(i) To avoid unwanted pregnancy–if the woman is not physically or mentally prepared to bear a child her health gets adversely affected.
(ii) Contraception allows the parents to space the birth of two children and helps in family planning.
(iii) This way they can decide how many children to have and allows them to bring them up properly especially in case of limited resources. (or any other)
Question. What are changes seen in girls at the time of puberty?
Answer.(i) Change in voice.
(ii) Increase in size of breasts.
(iii) Appearance of hair in armpit and genital hair (pubic hair).
(iv) Widening of hips.
(v) Rapid physical growth.
(vi) Onset of menstruation.
Question. Foetus derives its nutrition from the mother.
(i) Identify the tissue used for above purpose. Explain its structure.
(ii) Explain how wastes generated by developing embryo are removed.
(iii) How does the birth of child take place?
Answer.(i) Placenta is a disc like special tissue connection between embryo and uterine wall. It acts as an
endocrine gland. It possesses villi that increases the surface area for absorption of nutrients.Facilitates passage of nutrition and oxygen to embryo from mother through blood.
(ii) Waste substances produced by embryo are removed through placenta into mother’s blood.
(iii) Birth of child takes place after the gestation period (9 months inside the womb of mother). When the contractions in muscles of the uterine walls is at highest then the birth of child takes place by the birth canal.
Question.6. Name the parts A, B and C shown in the following diagram and state one function of each.
‘A’ is anther. It contains pollen grains.
‘B’ is style. It allows growth in pollen tube up to the ovary from the stigma.
‘C’ is ovary. It contains ovules.
Question. Name the reproductive parts of an angiosperm. Where are these parts located? Explain in brief the structure of female reproductive parts.
The male reproductive part of an angiosperm is stamen. The female reproductive part is pistil/carpel,which consist of stigma, style and ovary.
Stigma: It is the site for deposition of pollen grains after pollination.
Style: It is a tube that allows growth of pollen tube to reach the ovary.
Ovary: It contains ovules that develops into seeds.
Question. Suggest three contraceptive methods for birth control, which is essential for the health and prosperity of a country. State the basic principle involved in each.
(i) Barrier method: Condom is placed on the erect penis of male before sexual intercourse. In female,a thin rubber disc is placed in the vagina, which covers the opening of cervix.
(ii) Oral pills: Birth control pills can be taken to prevent pregnancy.
(iii) Surgical methods: Use of copper-T in females, surgically implanted at the opening of the cervix, prevents entry of sperms.
Vasectomy in males, tubectomy in females can also help in population control. In vasectomy, sperm ducts are cut. In tubectomy, oviducts are tied, blocked or cut. Sperms cannot reach the ova and thus pregnancy is avoided.
Question. Write one main 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.Any one of the following differences:
(i) In sexual reproduction two opposite sexes are involved whereas in asexual reproduction only one individual is involved.
(ii) In sexual reproduction male and female gametes formation take place whereas in asexual reproduction no gamete formation occurs.
• Sexually reproducing organisms have better chances of survival.
• This is because more variations are generated.
Question. (a) State in brief the functions of following female reproductive system
(i) Ovary, (ii) Fallopian tube, (iii) Uterus
(b) State in brief the functions of following male reproductive system
(i) Scrotum, (ii) Testes, (iii) Vas deferens
(a) (i) Ovary: It produces ova and female sex hormones.
(ii) Fallopian tube: It is the site of fertilisation and transfer of female gamete from the ovary.
(iii) Uterus: Implantation of zygote and it keeps foetus till complete development.
(b) (i) Scrotum: It protects testes.
(ii) Testes: It produces sperms.
(iii) Vas deferens: It delivers sperms from testes to urethra.
Question. Why must pollination occur before fertilisation? How is pollination different from fertilisation? What does a pollen contain inside?
Answer.Pollination must occur before fertilisation as it has to reach the male gametes present in pollen grain which will germinate to form a pollen tube and carry the male gametes to the ovum. Pollination is different from fertilisation because here the pollen grain with its male gametes just reaches the stigma, whereas fertilisation of male gamete to ovum results in formation of diploid zygote which is the foundation of new generation.
Question. Mention the changes observed in flower after fertilisation.
(i) Ovary ripens and developed into fruit.
(ii) Ovules develop into seed.
(iii) Petals and sepals wither and drop.
(iv) Stigma, style and stamens dry up and fall off.
Question. How do sperms reach the female genital tract? Where fertilisation and implantation of the embryo does take place? For how long does the embryo remain attached to uterine walls?
Answer.Sperms travel upwards through uterus to oviduct where they may meet an ovum and hence fertilise it. Fertilisation takes place in oviduct to give rise to single celled zygote. The zygote
divides to become multicellular embryo which gets fixed in uterus. The embryo remains attached to uterine walls throughout gestation period which is about 40 weeks in humans.
Question. Draw the diagram of a female reproductive system and label the part which:
(i) Produces egg in female germ cell (ii) Part where zygote is implanted.
(iii) Path for entry of sperms.
Answer.(i) Ovary produces eggs
(ii) Zygote is implanted in womb or uterus
(iii) Entry of sperms through vagina.
Question. State the basic requirements for sexual reproduction. Write the importance of such reproduction in nature.
Answer.The basic requirements for sexual reproduction to take place are involvement of two parents and fusion of their haploid gametes. In the sexual reproduction, a new individual is formed by the fusion of two haploid gametes, one from the male parent and the other from the female parent. Since the new individual formed is diploid in nature, the gametes must be formed by meiosis, so that chromosome number can be reduced to half. When fusion of gametes occurs, the two nuclei of these two gametes fuse and the chromosome number is restored to normal. The zygote, thus formed is diploid in nature.
Importance of sexual reproduction:
Sexual reproduction involves fusion of male and female gametes coming from both the parents. The fusion of these gametes results in genetic variations in the offsprings. This way sexual reproduction promotes diversity of characters in offsprings by providing genetic variations. These genetic variations, thus lead to evolution of species as well as allow the organisms to become better adapted in the changing environment.
Question. State the changes that take place in the uterus when:
(a) Implantation of embryo has occurred.
(b) Female gamete/egg is not fertilised.
(a) When the implantation has occurred in uterus of the mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.
(b) If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more required, it will slowly break down and come out through the vagina as blood and mucus known as menstruation which lasts for about two to eight days.
Question. Draw a labelled diagram of longitudinal section of pistil of flower showing germination of pollen grains on the stigma.
Question. List any four steps involved in sexual reproduction and write its two advantages.
The four main steps involved in sexual reproduction are:
(i) In the first stage of sexual reproduction, meiosis process occurs and the number of chromosomes reduces from diploid (2n = 46) to haploid (n = 23) for each gamete.
(ii) In the second stage, there is transfer of male gametes into the female body.
(iii) In the third stage, the two gametes will fuse together after fertilisation, a single male gamete will fuse with a female gamete. i.e. fertilisation process takes place.
(iv) After fusion of male and female gametes, they form a zygote, in which the number of chromosomes is restored to diploid (2n = 46).
The two main advantages of sexual reproduction are:
(i) There are more variations, which leads to better adaptability of the offsprings in the environment.
(ii) Promotes the diversity in the characteristics of offspring, because it results by fusion of gametes.
Question. List three distinguishing features between sexual and asexual types of reproduction in tabular form.
Question. Describe the structure and function of placenta.
Answer.Structure of placenta: It is a special disc like tissue embedded in mother’s uterine wall and connected to the foetus/embryo.
Functions of placenta: It provides a large surface area for glucose and oxygen/nutrients to pass from mother’s body to the developing/developed embryo/foetus and also helps in passing the waste from the foetus/embryo to the mother’s body.
Question. Differentiate between self pollination and cross pollination.
Question. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement.
Answer:Reproduction is an energy consuming process which is not essential for the survival of an individual.But it is the most important characteristic of all living beings, because of the following reasons:
(i) Reproduction helps in increasing the number of members of a population.
(ii) By replacing the dead members with the new ones, it minimises the risk of extinction of a species.
(iii) It brings about variations in species, thus leading to their evolution.
Question. (a) (i) Write full form of DNA.
(ii) State the role of DNA in the cell nucleus.
(iii) What will be the effect if the information of the DNA is changed?
(b) Explain the importance of DNA copying in reproduction.
(b) (i) Deoxy Ribonucleic Acid
(ii) It helps in synthesis of protein and transfer of genetic characteristics.
(iii) Proteins will be changed.
(b) Body designs are similar due to DNA copying.
DNA cell nucleus carry information for synthesis of protein.
If DNA copying will not take place then body design will change.
Question. What is STD? Name two STDs.
Answer : STD is Sexually Transmitted Disease. Two STDs are syphilis and gonorrhoea.
Question. How does binary fission differ from multiple fission ?
Answer: In binary fission, a single cell divides into two equal halves. Amoeba and Bacteria divide by binary fission.
Binary fission in Amoeba: In multiple fission, a single cell divides into many daughter cells simultaneously. Amoeba and Plasmodium divide by multiple fission.
Question. Why does menstruation occur ?
Answer: Menstruation is a process in which blood and mucous flows out every month through the vagina. This process occurs every month because one egg is released from the ovary every month and at the same time, the uterus (womb) prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo. If the egg does not get fertilised, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucous from the vagina.
Question. State the changes that occur in human males and females at puberty.
Answer : Puberty is the state of sexual maturiy in humAnswer : The changes that take place in males during puberty are growth of hair on the body, appearance of beard and moustache and the voice becomes hoarse. Females show development of breasts, and beginning of menstruation.
Question. List any two differences between pollination and fertilisation
|1. Transfer of pollen grain from anther to stigma of a flower.||Fusion of pollen nucleus and ovule in the ovary.|
|2. Its types are self pollination and cross pollination.||Its types are internal and external fertilisation.|
Question. Why is variation beneficial to the species but not necessarily for the individual?
Answer: Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, all variations are not necessarily beneficial for the individual organisms.
Question. What are the changes seen in girls at the time of puberty ?
Answer: Secondary sexual characteristics in girls:
1. Increase in breast size and darkening of skin of the nipples present at the tips of the breasts.
2. Appearance of hair in the genital area.
3. Appearance of hair in other areas of skin like underarms, face, hands, and legs.
4. Increase in the size of uterus and ovary.
5. Beginning of menstrual cycle.
6. More secretion of oil from the skin, which results in the appearance of pimples.
Question. What are the advantages of sexual reproduction over asexual reproduction ?
Answer: Advantages of sexual reproduction:
1. In sexual reproduction, more variations are produced. Thus, it ensures survival of species in a population.
2. The new formed individual has characteristics of both the parents.
3. Variations are more viable in sexual mode than in asexual one. This is because in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
Question. How does the embryo get nourishment inside the mother’s body?
Answer: The embryo develops inside the mother’s body for about nine months. Inside the uterus, the outer tissue surrounding the embryo develops finger1like projections called villi.
These villi are surrounded by uterine tissue and maternal blood. They provide a large surface area for exchange of oxygen and nutrients. Also, there is a special tissue called placenta, which is embedded in the uterine wall. The embryo receives the oxygen and nutrients from the mother’s blood via the placenta. The waste materials produced by the embryo are also removed through the placenta.
Question. Mention the information source of making proteins in the cell. What is the basic event in reproduction?
Answer : Cellular DNA is the information source of making proteins in the cell.
The basic event in reproduction is copying of DNA so that the cells can further divide.
Question. Name one sexually transmitted disease each caused due to bacterial infection and viral infection. How can these be prevented?
Answer : Bacterial infection: gonorrhoea
Viral infection: warts and HIV-AIDS
Prevention: Use of condoms by male.
Question. What is self and cross pollination?
Answer : Self Pollination: It is the transfer of pollen grains from the anther of a flower to the stigma of the same or another flower on the same plant.
Cross Pollination: It is the transfer of the pollen grains from the anther of a flower to the stigma of another flower on a different plant of the same species.
Question. How are the modes for reproduction different in unicellular and multicellular organisms?
Answer: In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc. whereas in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc. In more complex multicellular organisms such as human beings and plants, the mode of reproduction is sexual reproduction.
Question. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration ?
Answer: Simple organisms such as Hydra and Planaria are capable of producing new individuals through the process of regeneration. The process of regeneration involves the formation of new organisms from its body parts. Simple organisms can utilize this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth and development. However, complex organisms have organ 1system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.
Question. (a) In human body what is the role of
(i) Seminal vesicles (iii) Prostrate glands.
(b) List two functions performed by testes in human beings.
Answer : (a) Seminal vesicles: Produce a fluid which makes the transport of sperms easy.
Prostate glands: Produces a fluid which keeps sperms floating in it and provides nourishment.
(b) Two functions of testes:
(i) They secrete hormone: testosterone responsible for the male characteristics.
(ii) It helps in the formation of sperms.
Question. (a) Draw a diagram illustrating, fertilisation in a flowering plant and label it. Pollen grain, male germ cell, female germ cell, stigma.
(b) Describe the process of fertilisation in plants.
Answer : (a)
(b) Fertilisation in plants: It takes place after the pollination is done.
(i) The pollen grain develops a tube called pollen tube which carries male germ cells to the ovary.
(ii) The male germ cell fuses with the female germ cell in the ovary and forms zygote.
(iii) The zygote further forms embryo.
(iv) The embryo develops a protective coating and forms seed.
(v) The ovary forms a fruit with seed in it.
Question. (a) Draw a diagram showing longitudinal section of a flower and label on it: stigma, ovary, anther, filament.
(b) How is the process of pollination different from fertilisation?
Answer : (a)
Question. (a) Name the parts labelled A, B, C, D, and E
(b) Where do the following functions occurs? (Img 102)
(i) Production of an egg
(iii) Implantation of zygote
(c) What happens to the lining of uterus
(i) before release of fertilised egg.
(ii) if no fertilisation occurs.
Answer : (a) A ⎯→ Fallopion tube
B ⎯→ Ovary
C ⎯→ Uterus
D ⎯→ Cervix
E ⎯→ Vagina
(b) (i) Production of an egg — ovary
(ii) Fertilisation — fallopian tubes
(iii) Implantation of zygote — lining of the uterus
(c) (i) Before release of fertilized egg – the uterus wall becomes thick.
(ii) If no fertilisation occurs – the lining of uterus slowly breaks down and comes out in the form of bleeding.
Question. (a) Explain the terms:
(i) Implantation (ii) Placenta
(b) What is the average duration of human pregnancy? (CBSE 2009)
Answer : (a) (i) Implantation: The zygote when fixes itself on the inner thick wall of uterus for further development is called implantation.
(ii) Placenta: It is the special tissue in the form of a disc which is embedded in the uterus wall. It provides large surface area for glucose and oxygen to pass from mother to the embryo. The waste generated by the embryo also passes into the mother’s blood through this placenta (b) It takes nine months for the human pregnancy.
Question. What are sexually transmitted diseases? Name four such diseases. Which one of them damages the immune system of human body to complete?
Answer : The diseases that spread due to sexual contact from infected person to a healthy person are called sexually transmitted diseases.
(i) Gonorrhoea (ii) Syphilis (iii) Warts (iv) AIDS
AIDS: Acquired Immuno Deficiency Syndrome damages the immune system.
Question. What is the role of following in reproduction?
(i) DNA (ii) Ovulation (iii) Fertilisation
(iv) Puberty (v) Contraception
Answer : (i) Variation (ii) Egg production (iii) Zygote formation
(iv) Attainment of sexual maturity (v) Birth control
Question. What are the advantages of sexual reproduction over asexual reproduction?
Answer : In asexual reproduction, the offspring is almost identical to the parent because they have the same gene as their parent. Thus, variation is not present.
Sexual reproduction involves fusion of male and female gametes. The offspring exhibits diversity of characters because they receive some genes from the mother and some from the father. The mixing of genes in different combinations; results in genetic variations. This variation leads to the continuous evolution of various species to produce various organisms.
Question. What are the functions performed by testis in human beings?
Answer : The function of testis is to produce sperms and male sex hormone called testosterone.
Question. Why does menstruation occur?
Answer : Menstruation occurs in females when the egg produced inside the cervix is not fertilized. Since the egg does not fuse with the male gamete, so the thick and soft lining of uterus having a lot of blood capillaries in it are not required. This unfertilized egg dies within a day and the lining breaks down shedding blood along with other tissues. This comes out of the vagina in the form of bleeding.
Question. Draw a labelled diagram of the longitudinal section of a flower.
Question. What are the different methods of contraception ?
Answer : Contraception is the method to avoid pregnancy. Various methods of contraception are as follows:
Physical Barrier Methods: Use of condoms, diaphragms, cervical caps can be used.
These prevent the entry of sperms into the female genital tract by acting as a barrier between them.
Chemical Methods: Oral pills can be used which change the hormonal balance and stop release of egg. Vaginal pills kill the sperms.
Surgical Methods: This includes vasectomy (sperm duct is removed) in males and tubectomy (removal of small portion of fallopian tube) in females.
Question. How are modes of reproduction different in unicellular and multicellular organisms?
Answer : Unicellular organisms have only one cell. There is no separate tissue for reproduction.
So, they can reproduce by the process of fission or budding. Multicellular organisms contain various cells and have separate system for reproduction. So, they can reproduce by both sexual and asexual methods.
Question.How does reproduction help in providing stability to the population of species?
Answer : Stability is provided by equalizing the birth and death ratio. Thus, the rate of birth should approximately be equal to the rate of death.
Question.What could be the reasons for adopting contraceptive methods?
Answer : The reasons for adopting contraceptive methods could be:
1. Protection from sexually transmitted diseases such as HIV-AIDS, gonorrhoea, syphilis, warts etc.
2. Restricting the number of children.
3. Sufficient gap between successive births.
4. Enjoying a good reproductive health.
5. Controlling population.
Question. Why is vegetative propagation practised for growing some types of plants?
Answer.(i) Vegetative propagation is used to grow plants in which seeds are not formed or very few seeds are formed, e.g. banana, pineapple, orange.
(ii) It helps to grow plants in conditions where seed germination fails due to change in environment.
(iii) It is a faster, easier and cheaper process.
(iv) The plants produced are genetically similar and good quality or variety can be preserved easily.
Question. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer.Those organisms which reproduce by regeneration have similar and non-differentiated cells throughout the body, therefore body parts of organism grows into new organism.
In multicellular complex organisms, the cells get differentiated and perform different functions. In such organisms, body parts like skin, muscles, i.e. tissues can be regenerated, but the whole organism cannot be reproduced by regeneration.
Question. “Cell division is a type of reproduction in unicellular organism”. Justify.
Answer.Cell division in a unicellular organism results in the formation of two or more daughter cells which means it produces more individual.
Question. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Answer.Clones are organisms which are exact genetics copies of their parents. Their DNA is exactly identical to their parents, which is the cause of remarkable similarity.
Question. Draw in sequence (showing the four stages), the process of binary fission in Amoeba.
Answer.Sequence (showing the four stages), the process of binary fission in Amoeba.
Question. List two advantages of growing grapes or banana plants through vegetative propagation.
Answer.(i) Characteristics of parent plants are preserved.
(ii) Since these plants do not have viable seeds, therefore vegetative propagation is advantageous.
Question. List three conditions favourable for spores to germinate and grow.
Answer.(i) Availability of nutrition (food), (ii) moist place, (iii) warmth, (iv) dark place. (Any three)
Question. Name the type of asexual reproduction in
(a) Planaria (b) Rhizopus
(c) Spirogyra (d) Hydra
Answer.(a) Regeneration (b) Spore formation
(c) Fragmentation (d) Budding
Question. Leaves of bryophyllum fallen on the ground produces new plants, why?
Answer.Leaves of bryophyllum has adventitious buds or plantlets in the notches along the leaf margin. When buds fall on the soil, they develop into new plant under favourable conditions.
Question. Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Write the first step from where such a type of reproduction begins. Draw first two stages of this reproduction.
Answer.Binary fission, e.g. Fission in Amoeba Elongation of cell and its nucleus is the first step.
Question. Explain the term ‘Regeneration’ as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra.
Answer.Regeneration is the ability to produce an organism from their body parts. Many fully differentiated organisms show ability to reproduce by regeneration. In hydra, if the body is cut into two or three pieces, the lower part will develop head while the upper part will develop rest of the body. If its cells are separated, hydra will reform its structure by regeneration.
Question. What is multiple fission? How does it occur in an organism? Explain briefly. Name an organism which exhibits this type of reproduction.
Answer.The process in which parent cell divides into several small and equal sized daughter cells, which grows into a new organism is called multiple fission.
The nucleus of a cell divides into large number of nuclei and cytoplasm separates, forming a membrane around it. All this occurs within a protective covering. Plasmodium exhibits multiple fission.
Question. What happens when
(i) Planaria gets cut into two pieces
(ii) A mature spirogyra filament attains considerable length
(iii) On maturation sporangia burst
Answer.(i) Each piece will regenerate into complete organism. Cells at the location of the site of cut or wound,forms a small ball of cells that will differentiate into new tissues and regenerate the missing parts of the cut piece of the planaria.
(ii) When spirogyra attains considerable length, it breaks into smaller fragments and each fragment grows into a new plant.
(iii) On maturation, sporangial wall breaks and spores are dispersed to grow into new individual. These spores are very light and easily dispersed by wind.
Question. What is vegetative propagation? State two advantages and two disadvantages of this method.
Answer.Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from vegetative parts of the plants. It does not involve the production of seeds or spores for the propagation of new plants.
Two advantages of vegetative propagation are:
(i) Plants which do not produce seeds are propagated by this method, for example sugarcane, potato, etc.
(ii) Vegetative propagation is a cheaper, easier, rapid method of propagation in plants than growing plants from their seeds. For example, lilies grow very slowly and take 4 to 7 years to develop flowers when grown through their seeds, but flowers are produced only after a year or two when grown vegetatively.
Two disadvantages of vegetative propagation are:
(i) As there is no genetic variation, there is no chance of development of new and better varieties.
(ii) The vegetatively propagated plants are more prone to diseases that are specific to the species. This can result in the destruction of an entire crop.
Question. Explain budding in hydra with the help of labelled diagrams only.
Answer.A bud is an outgrowth from the body part of parent due to repeated cell division at a specific site. These buds develop into new individuals, which detach from the parent body on maturation.
In hydra, the cells divide very fast at a specific site as an outgrowth called bud. These bud develops into a small individual, while remaining attached to the parent. When it matures, it detaches from the parent body to exist as an independent organism.
Question. What happens when:
(a) Accidently, Planaria gets cut into many pieces?
(b) Bryophyllum leaf falls on the wet soil?
(c) On maturation sporangia of Rhizopus bursts?
Answer.(a) When Planaria gets cut into many pieces, it will undergo a process known as regeneration due to which each piece will grow into a new planaria organism.
(b) When bryophyllum leaf falls on the wet soil, the buds that are produced in the notches along the
leaf will develop into new plants by the process known as vegetative propagation.
(c) When the sporangia of Rhizopus bursts upon maturation, the spores present inside it spread in the open environment. Then, with the help of different agents, they are carried to different places and when they land on a favourable surface, they start growing and produce new organism.
Question. Define the term pollination. Differentiate between self pollination and cross pollination. What is the significance of pollination?
Answer.Pollination: The process in which pollen is transferred from stamen to the stigma is called pollination.
Significance: After the pollen lands on suitable stigma, it needs to reach the female germ cells in the ovary where fertilisation takes place, zygot is formed. Zygot divides several times to form embryo with in ovule which develops a tough coat around it called seed coat and seed is formed. The ovary grows rapidly and ripens to form fruit.
Question. (a) List in tabular form two differences between binary fission and multiple fission.
(b) What happens when a mature spirogyra filament attains considerable length.
(b) A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new plant. This process of reproduction is called fragmentation.
Question. In the context of reproduction of species state the main difference between fission and fragmentation.Also give one example of each.
IV. LONG ANSWER TYPE QUESTIONS (5 Marks)
Question. List four points of significance of reproductive health in society. Name any two areas related to reproductive health which have improved over the past 50 years.
Answer. Significance of reproductive health in society are:
(i) Prevent STD (Sexually Transmitted Disease)
(ii) Advantages of small family
(iii) Less mortality among new borns
(iv) Reduces cases of maternal mortality
Two areas of Improvement are:
(i) Family planning. (ii) Decrease in STD cases.
Question. Explain what happens when:
(a) Testosterone is released in males. (b) Pollen grains falls on the stigma of flowers.
(c) Egg fuses with sperm cell. (d) Planaria is cut into many pieces.
(e) Buds are formed on notches of the bryophyllum leaf.
(a) (i) Formation of sperms and change in appearance.
(ii) Thick hair growth on face stet and pubic region and change in voice.
(b) A tube grows out of the pollen grain and travels through the style to the ovary.
(c) Zygote is formed i.e. fertilisation takes place.
(d) Each piece grows into new organism.
(e) Buds may fall on the soil and change into new organism.
Question. Write two causes of human population explosion. Explain with the help of a suitable examples how this explosion can be checked.
Two causes of human population explosion are:
(i) Reduced mortality rate due to better medical facilities.
(ii) Desire for male child.
(iii) Less awareness of birth control methods.
(iv) Illiteracy and poverty. (Any two)
Methods to check population explosion are:
(i) By using contraception methods.
(ii) Awareness among people of the advantage of small family.
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.
(a) The organ that produces sperms as well as secretes male hormone is testis. The hormone secreted by it is testosterone. Its important functions are as follows:
It stimulates sperm production.
It stimulates the development of secondary sexual characters in males like growth of beard hairs,low pitch voice, etc. It involves in the development, maturation and functioning of the male accessory sex organs like vas deferens and seminal vesicles
(b) In human female reproductive system, the process of fertilisation takes place in one of the fallopian tubes.
(c) The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. Placenta is a vascular membranous organ that connects the developing foetus to the uterine wall of the mother. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The placenta draws nutrients and oxygen, which it supplies to the foetus, from the maternal circulation. In turn, the placenta receives carbon dioxide and wastes of foetal metabolism and discharges them into the maternal circulation for disposal.
Question. (a) Draw the diagram of female reproductive system and match and mark the part (s):
(i) Where block is created surgically to prevent fertilisation.
(ii) Where CuT is inserted. (iii) Inside which condom can be placed.
(b) Why do more and more people prefer to use condoms? What is the principle behind use of condoms?
(a) (i) Fallopian Tube/Oviduct
(b) People prefer use of condoms as it prevents STDs/gives privacy to the user. Condoms help create a mechanical barrier preventing meeting of sperms and ovum.
Question. (i) Describe the role of prostate gland, seminal vesicle and testes in the human male reproductive system.
(ii) How is the surgical removal of unwanted pregnancies misused?
(iii) Explain the role of oral contraceptive pills in preventing conception.
(i) Prostate glands and seminal vesicle add their secretions so that the sperms are in a fluid state and it makes their transport easier and also provides nutrition to sperms. Testes secrete testosterone hormone which brings about changes in the appearance in the boys at the time of puberty.
(ii) Female foeticides/illegal sex selected abortion of female child.
(iii) Interfere in release of egg and eggs are not released.
Question. (a) List three different categories of contraception methods.
(b) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run.
(c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
(a) (i) Barrier method, (ii) Oral pills, (iii) Use of copper-T, (iv) Vasectomy in males, tubectomy in females.
(b) • It is because female foeticide is increasing.
• It leads to unbalanced sex ratio i.e., more males, less females.
On long run, it will help in maintaining healthier (equal) sex ratio.
It will save mothers from illegal medical termination of pregnancy and health issues.
(c) Gonorrhoea and syphilis are bacterial infections.
Warts and HIV-AIDS are viral infections.
Question. Trace the changes that take place in a flower from gamete formation to fruit formation.
Answer.[Diagram drawn and annotated with the following points will also be considered]
– Stamen is the male reproductive part and it produces pollen grains.
• The ovary contains ovules and each ovule has an egg cell.
• The pollen needs to be transferred from the stamen to the stigma.
• If this transfer of pollen occurs in the same flower, it is referred to as self-pollination./ On the other hand, if the pollen is transferred from one flower to another, it is known as crosspollination.
After the pollen lands on a suitable stigma, it has to reach the female germ-cells which are in the ovary. For this, a tube grows out of the pollen grain and travels through the style to reach the ovary/Figure
• The male germ-cell produced by pollen grain fuses with the female gamete present in the ovule.
• This fusion of the germ-cells or fertilisation gives the zygote.
• After fertilisation, the zygote divides several times to form an embryo within the ovule.
• The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit.
• Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off.
Question. (i) Draw a sectional view of human female reproductive system and label the part where (a) Egg develops, (b) fertilisation takes place, (c) fertilised egg gets implanted.
(ii) Describe in brief the changes that uterus undergoes (a) to receive the zygote (b) if zygote is not formed.
(i) (a) Egg develops in ovary.
(b) Fertilisation takes place in fallopian tube.
(c) The fertilised egg gets implanted in uterus.
(ii) (a) The inner uterus lining becomes thick to receive the zygote and is supplied with blood and nutrients to nourish the embryo.
(b) The inner uterus lining breaks and released in the form of blood and mucus through vagina.
Question. (i) Identify A, B, C and D in the given figure. Write their names.
(ii) What is pollination? Explain its significance.
(iii) Explain the processes of fertilisation in flowers. Name the parts of the flower that develop after fertilisation into (a) seed (b) fruit.
(i) ‘A’ is stigma, ‘B’ is pollen tube, ‘C’ is ovary and ‘D’ is egg cell (female germ cell).
(ii) Pollination is a process of transfer of pollen grains from the anther of stamen to the stigma of carpel. It is necessary for fertilisation by sexual reproduction.
(iii) When male gamete and egg fuse together to form zygote, it is called fertilisation.
It takes place in ovule. After that the ovule develops a tough coat and is gradually converted into seed.
Fruit: The ovary grows rapidly and ripens to form a fruit after ovule has been fertilised.
Question. Identify the following methods and give one example of each:
(a) Process in which reproduction takes place by breaking up of parent into several fragments.
(b) Process of dividing of organisms into many cells simultaneously.
(c) Process of reproduction by formation of bud on the parent body.
(d) Process of reproduction by formation of spores.
(e) Process used by multi-cellular organisms to reproduce by cutting into many pieces and each piece forms a new individual.
Answer.(a) Fragmentation, Spirogyra (b) Multiple fission, Plasmodium
(c) Budding, Yeast/Hydra (d) Spore formation, Rhizopus
(e) Regeneration, Planaria
Question.(a) Identify the organism A, B and mode of asexual reproduction exhibited by them.
(b) How will an organism be benefitted if it reproduces through spores?
(c) Mention the two asexual methods by which hydra can reproduce. Explain briefly any one such method.
Answer.(a) ‘A’ is Bryophyllum–Vegetative propagation; ‘B’ is Plasmodium–Multiple fission
(b) Spores are covered with thick walls which protect them until they come into contact with a moist surface.
(c) Budding and regeneration
Budding: In this process hydra (or any other organism like yeast) use regenerative cells for reproduction. A bud develops as an outgrowth due to repeated cell division which develop into new individuals.
(a) Stem—Potato, Onion, Ginger (b) Roots—Banana, Asparagus
Question. What is binary fission in organisms? With the help of suitable diagrams, describe the mode of reproduction in amoeba.
Answer.Binary fission is a fission in which two daughter cells are formed of nearly equal size after replicating the genetic material of a single cell. Single-celled organisms like amoeba undergoes binary fission.
Question. (i) Describe the various steps involved in the process of binary fission with the help of a diagram.
(ii) Why do multicellular organisms use complex way of reproduction?
(ii) Multicellular organisms cannot reproduce by cell because they are not simple random collection of cells.
They have specialised cells, organised as tissues which are organised into organs.
Cell-by-cell division would be impractical (not practical).
Multicellular organisms require to use more complex ways of reproduction.
Question. Draw a well labelled diagram of the female reproductive system in humAnswer :
Question. State the functions of the following:
(a) testis (b) ovaries (c) vas deferens (d) stamen (e) pistil
Answer : (a) Testis: Form the male gametes the sperms and secrete the male sex hormone testosterone
(b) Ovaries: Form the female gamete ovum or the egg cell and secrete the female sex hormones estrogen and progesterone.
(c) Vas deferens: Transport the sperms from the testis to the exterior.
(d) Stamen: Form the pollen grains in flowers. The pollen grains bear the male gametes.
Question. Draw a labelled diagram of the longitudinal section of a flower .
Question. Give one term for the following:
(a) Beginning of menstrual cycle
(b) Release of ovum from the ovary
(c) Fusion of male and female eggs
(d) Prevention of unwanted pregnancy
(e) Time for development of offspring in female human.
Answer : (a) Menstruation (b) Ovulation (c) Fertilisation
(d) Contraception (e) Nine months
Question. Name the hormone the secretion of which is responsible for dramatic changes In appearance in girls when they approach 10–12 years of age.
Answer : Oestrogen and Progesterone.
(e) Pistil: The ovary forms the egg and the stigma helps in attracting the pollen grains for fertilisation.
Question. What are the various artificial methods of vegetative propagation in plants?
Answer : The various artificial methods of vegetative propagation in plants are:
(a) Cutting: In this any part of the plant like the stem root or leaf is cut and buried in the soil which gives rise to a new plant as in rose, guava, grapes etc.,
(b) Layering: In plants like jasmine and strawberry a branch from the plant is brought down too the ground and covered with damp soil. After few days new roots are formed and the branch is cut from the main plant.
(c) Grafting: In this the stem of a plant is given a cut and the other plant is fixed (with its stem) in it e.g., sugarcane, roses, grapes are grown for agricultural purposes.
(d) By Roots: Plants like sweet potato show the growth of more plants from a root.
(e) Stem: Plants like potato, ginger, onion, they show growth from their stems.
(f) By Buds: Plant like Bryophyllum and potato grow small buds on them and a growth of new plant takes place.
Question. Illustrate the following with the help of a suitable diagrams:
(i) Regeneration in Planaria
(ii) Budding in Hydra
Answer : (i) Regeneration in Planaria
Planaria: If it is divided into 3 parts a, b and c, each part grows as a new individual (IMG 105)
Question. With the help of diagrams explain the process of budding in Hydra and fission in Amoeba.
Answer : (i)
Question. Illustrate the following with the help of suitable diagram
(i) Spore formation in Rhizopus (ii) Multiple fission in Plasmodium
Answer : (i) Spore formation in Rhizopus
(ii) Multiple fission in Plasmodium
Question. Illustrate the following with the help of suitable diagram
(i) Binary fission in Amoeba
(ii) Leaf of Bryophyllum with buds
Answer : (i) Binary fission in Amoeba (ii) Bryophyllum leaf
Question. What are the different methods of contraception?
Answer: The contraceptive methods can be broadly divided into the following types:
1. Natural method: It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because during this period, ovulation is expected and therefore, the chances of fertilization are very high.
2. Barrier method: In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.
3. Oral contraceptives: In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.
4. Implants and surgical methods: Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Question. What is the importance of DNA copying in reproduction ?
Answer: DNA (Deoxyribonucleic acid) is the genetic material found in the chromosomes, which are present in the nucleus of a cell. The DNA is the information site for making proteins and each specific type of protein leads to a specific type of body design.
Thus, it is the DNA molecule that determines the body design of an individual. Therefore, it can be concluded that it is the DNA that gets transferred from parents to offsprings and makes them look similar.