CBSE Class 12 Biology Sexual Reproduction In Flowering Plants Worksheet Set B

Short Answer Type Questions

Question. (a) What are gametes ?
(b) In which sort of reproduction are gametes involved ?
(c) What is formed when two gametes fuse ?
(d) What is this act of fusion called ?
Answer : (c) (i) Male gametes (inside pollens) (ii) Female gametes (inside ovules)

Question. (a) Write the names of (a) male sex hormone, and (b) female sex hormones.
(b) What name is given to the fusion of sperm and ovum ?
(c) Name the tissue through which the foetus gets all the requirements from the mother’s body.
Answer : (c) Placenta

Question. (a) Draw a neat sketch of the stamen of a flower. Mark in it filament and anther.
(b) Draw a neat sketch of the carpel of a flower. Mark in it stigma, style and ovary.
(c) What is made in (i) anther, and (ii) ovary, of a flower ?
Answer : (c) (i) Male gametes (inside pollens) (ii) Female gametes (inside ovules)

Question. (a) Explain the terms ‘self pollination’ and ‘cross-pollination’ ?
(b) How do the insects help in cross-pollination ?
(c) How is the process of pollination different from fertilization ?
Answer : (c) In pollination, the pollens (containing male gametes) are transferred from anther to stigma of carpel ; In fertilisation, the male gamete fuses with the female gamete present in ovule inside the ovary of flower to form a fertilised egg or zygote

Question. (a) Explain the term ‘fertilisation’.
(b) Give some examples of different modes of fertilisation in nature ?
(c) What type of fertilisation takes place in (i) fish, and (ii) birds ?
Answer : (c) (i) External fertilisation (ii) Internal fertilisation

Question. (a) What are the male and female gonads in human beings ? Mention their functions.
(b) State the advantages of sexual reproduction over asexual reproduction.
Answer : (a) The male gonads are the testes and they produce sperms. The female gonad is the ovary and it produces eggs or ova.
(b) In sexual reproduction, there is a variation in the offsprings produced, which is impossible in case of asexual reproduction, as in the latter process, offsprings produced are identical to their parent.

Question. Describe the various steps involved in the sexual reproduction in animals. Draw labelled diagrams to show the fertilisation of an ovum (or egg) by a sperm to form a zygote.
Answer : The various steps involved in the sexual reproduction in animals are as follows:
Male gametes called sperms are produced by the male parent.
Female gametes called eggs are produced by the female parent.
The sperm fuses with the egg to form the zygote. This process is termed as fertilisation.
The zygote divides repeatedly to form a large number of cells. Ultimately it grows and develops into a baby.

Question. Why does menstruation occur ? Describe the menstrual cycle in human females (or women).
Answer : Menstruation occurs due to the rupture or removal of the inner, thick, and soft lining of the uterus when fertilization does not take place.
The menstrual cycle of a female is as follows:
After a female attains puberty, every month one of the ova of the ovary matures and gets released once every 28 days (on an average) by the process of ovulation.
The lining of the uterus becomes thick and spongy before ovulation in order to implant the fertilized egg. If the egg is not fertilized, this lining of the uterus breaks and comes out of the vagina along with the unfertilized egg which is known as menstrual flow.
This occurs on the 14thday of ovulation and lasts for 3-5 days.
After this flow stops, the uterus starts preparing itself again to receive fertilized egg. If it does not receive the fertilized egg, the same set of events is repeated.

Question. (a) Write the various steps involved in the sexual reproduction in plants.
(b) Name two plants which reproduce by sexual reproduction method and two plants which reproduce by asexual reproduction methods.
Answer : (b) Sexual reproduction : Wheat plant and Sunflower plant ; Asexual reproduction : Ferns and Mosses

Question. (a) What type of plants reproduce by sexual reproduction method ?
(b) What is a seed ? What are the parts of a seed ? Explain with the help of a labelled diagram.
Answer : (a) Flowering plants

Question. (a) What is puberty ? Who attains puberty at an earlier age in human beings : male or female (boy or girl) ?
(b) Mention two functions each of (i) human testes, and (ii) human ovaries.
Answer : (a) Puberty is the age at which males and females attain sexual maturity. In human beings, females attain puberty earlier than males.
(b) (i) Testes produce male gametes (sperms) and the hormone testosterone, responsible for secondary sexual changes in males.
(ii) Ovaries produce female gametes (ova or egg) and the hormone oestrogen, responsible for secondary sexual changes in females.

Question. (a) What is gestation period ? How much is the gestation period in humans ?
(b) Name one method of contraception which also protects against sexually transmitted diseases.
(c) Name one sexually transmitted disease for which no definite cure has been found so far. What is the causative organism of this disease ?
Answer : (b) Use of condom (c) AIDS, Virus (HIV)

Question. What are the three types of methods used for birth control (or regulating child birth) ? Give one example of each type.
Answer : The three types of methods used for birth control are:
Barrier method, e.g., condom
Chemical method, e.g., oral pills
Surgical method, e.g., vasectomy

Question. (a) What is the name of surgical method of birth control in human males in which the sperm ducts are cut and ligated (tied) at both ends ?
(b) What is the name of surgical method of birth control in human females in which the oviducts are cut and ligated (tied) at both ends ?
(c) Name the contraceptive device used by the human males which acts as a sheath over the male organ and traps the sperms in it.
(d) Name the contraceptive device used by human females which is put over the cervix.
Answer : (a) Vasectomy (b) Tubectomy (c) Condom (d) Diaphragm (or Cap)

Question. (a) Describe the surgical methods of birth control (i) for men, and (ii) for women.
(b) Name two devices used in the barrier method of birth control.
Answer : (a) (i) The surgical method of birth control for men is called vasectomy in which a small portion of the vas deferens is cut and their ends are sealed to prevent sperms from coming out.
(ii) The surgical method of birth control for women is called tubectomy in which a portion of oviducts are cut and their ends are ligated to prevent the release of eggs.
(b) The two devices used in the barrier method of birth control are condoms and diaphragms.

Question. (a) What is meant by contraception ? What are the different methods of contraception ?
(b) What is done in the contraception method known as (i) vasectomy, and (ii) tubectomy ?
(c) If a woman is using copper-T for contraception, will it protect her from sexually transmitted diseases ?
Answer : (c) No

Question. (a) What are sexually transmitted diseases ? Give two examples of sexually transmitted diseases.
(b) Which method of contraception prevents fertilised egg from being implanted in the uterus ?
Answer : (b) IUCD (or Copper-T)

Question. (a) What substances are contained (i) in oral pills, and (ii) in vaginal pills, used as contraceptives ? How do they work ?
(b) How does copper-T prevent pregnancy ?
(c) Name the disease caused by HIV.
Answer : (c) AIDS

Question. (a) What is the name of surgical method of birth control (or preventing pregnancy) which is carried out (i) in men, and (ii) in women ?
(b) Name the part of a seed which
(i) contains stored food
(ii) grows into root, and
(iii) grows into shoot.
Answer : (a) (i) Vasectomy (ii) Tubectomy (b) (i) Cotyledons (ii) Radicle (iii) Plumule

Question. Explain how, offsprings and parents of organisms reproducing sexually have the same number of chromosomes.
Answer : Reduction division (meiosis) during gamete formation halves the number of chromosomes in both male and female gametes. Since male and female gametes fuse during fertilisastion, the original number of chromosomes (as in the parent) is restored in the offspring

Question. In tobacco plant, the male gametes have 24 chromosomes.
(i) What is the number of chromosomes in the female gamete ?
(ii) What is the number of chromosomes in the zygote ?
Answer : (i) 24 (ii) 48

Question. (a) What would be the ratio of chromosome number between an egg and its zygote ?
(b) Distinguish between a gamete and a zygote.
Answer : (a) 1 : 2 (b) Gamete represents the sex cell or germ cell in sexual reproduction and it is of two types : male gamete and female gamete ; Zygote is the product of fertilisation in which a male gamete and a female gamete fuse with each other

Question. (a) Fertilisation in humans can occur only once in a month. Why ?
(b) What is the scientific name of
(i) womb, and
(ii) birth canal ?
Answer : (a) Because ovulation takes place once every month, that is, an egg is released once every month by ovary

Question. The diagram shows female reproductive system. Name the parts labelled A to D.
(a) In which part do the sperms enter ?
(b) Which part releases the egg ?
(c) In which part does fertilisation take place ?
(d) In which part does the foetus develop ?
Answer : A is oviduct (or fallopian tube) ; B is ovary ; C is uterus (or womb) ; D is vagina (a) Part D (vagina) (b) Part B (ovary) (c) Part A (oviduct) (d) Part C (uterus)

Question. Why is it an advantage for the testes to be situated in the scrotal sac outside Nthe main body cavity ? Can you think of one disadvantage ?
Answer : Because the formation of sperms requires a lower temperature than the normal body temperature which is possible due to testes being outside the main body cavity ; Being outside the main body cavity, testes are more prone to injury.

Question. Which structures in human female are equivalent to the following structures in the male ?
(a) testes
(b) vas deferens
(c) penis
In each case say in what respect the structures are equivalent ?
Answer : (a) Ovaries in female ; Both make gametes (b) Oviducts in female ; Both transport gametes (c) Vagina in female ; Penis discharges sperms and vagina receives sperms

Question. People who die from AIDS are not killed by the virus itself. Explain.
Answer : HIV affects the immune system of a person who has AIDS. This weakens the body making it unable to fight any infection. Therefore, people who die from AIDS are not killed by the virus itself but by other infections.

Question. (a) What is the life support system of a fetus ?
(b) How long does a human baby take to develop before birth ?
(c) What is the name of the narrow opening between the uterus and the vagina.
Answer : (a) Placenta (b) About nine months (c) Cervix

Long Answer Type Questions

Question. (a) What is meant by ‘unisexual flowers’ and ‘bisexual flowers’ ? Give two examples of each.
(b) What is pollination ? How does pollination occur ?
(c) Describe the process of fertilisation in a flower with the help of labelled diagrams.
(d) What changes take place in the flower after fertilisation which lead to the formation of seeds and fruit ?
Answer : (a) Unisexual flowers are the incomplete flowers where the male and female reproductive parts are present in different flowers. Example : papaya & date palm.
Bisexual flowers are the complete flowers where both the male and female reproductive parts are present in the same flower. Example : pea & sunflower.
(b) Pollination is the transfer of pollen grains from anther to stigma for fertilisation.
(c) shown in pic
(d) After fertilisation, the ovary becomes the fruit and the ovule becomes the seed.

Question. (a) Draw a neat diagram of a flower showing its various parts. In this diagram mark stem, receptacle, sepals, petals, stamen and carpel.
(b) What name is given to
(i) all the petals of a flower, and
(ii) all the sepals of a flower ?
(c) What are (i) stamen, and (ii) carpel, in a flower?
(d) What is the other name of carpel of a flower ?
(e) What is the name of yellow powdery substance present in the anther of a flower ?
Answer : (a) A flower
(b) (i) The corolla
(ii) The calyx
(c) (i) Stamen is the male reproductive organ in a flower.
(ii) The carpel is the female reproductive organ in a flower.
(d) The other name of carpel is pistil.
(e) The yellow powdery substance present in the anther of a flower is pollen grains.

Question. (a) What changes are seen in boys at the time of puberty ?
(b) Name the organs which produce sperms in human males.
(c) Draw a labelled diagram of the human male reproductive system. With the help of this diagram, describe the working of human male reproductive system ?
(d) What is the role of seminal vesicles and prostrate gland in human male reproductive system ?
Answer : (a) Physical changes that occur during puberty in boys
Broadening of chest and shoulders.
Deepening of voice and appearance of facial hair.
The appearance of body hair and pubic hair.
Increase in size of genitals.
Growth spurt.
Ability to ejaculate.
(b) The testis is an organ which produces sperms in human males.
(c) The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body and within the pelvis.

Question. (a) What changes are seen in girls at the time of puberty ?
(b) Name the organs which produce ova (or egg cells) in human females.
(c) Draw a labelled diagram of the human female reproductive system. With the help of this diagram, explain the working of human female reproductive system.
(d) Describe the process of fertilisation in humans and development of embryo briefly.
Answer : (a) In girls, the first sign of puberty is the development of breasts. Other characteristics observed in girls are growing hair in the pubic region and armpits, and initiation of the menstrual cycle.
(b) Ovaries are the organs that produce ova (or egg cells) in human females.
(c) The female reproductive system organs comprise the ovaries, fallopian tube (uterine tube), uterus, cervix, and vagina.  

Question. (a) What is ovulation ? How often does it happen in human females ?
(b) Where does fertilisation take place in human females ?
(c) Explain why, fertilisation is possible if mating takes place during the middle of menstrual cycle.
(d) What is meant by implantation ?
(e) What is placenta ? What is its function ?
(f) What joins embryo to placenta in mother’s body ?
Answer : (a) Ovulation is the process where an ovum is released from an ovary. In human females, the ovaries release an ovum (an egg cell) every 28 days after attaining the age of puberty.
(b) In human females, fertilization takes place in oviducts.
(c) Fertilization is possible if mating takes place in between menstrual cycles because, during the middle of the menstrual cycle, ovulation takes place. Thus, the ovum has been released from the ovary and remains in living condition for about 2 days. Thus, if mating takes place during this time, the sperm penetrate inside the female body and fuse with the released ovum so that fertilization can take place.
(d) Implantation, or attachment of an embryo in the thick lining of the uterus (endometrium), is known as implantation.
(e) Placenta is a complex, circular tissue organ that forms the connection between the uterus wall and an embryo after the implantation.
The placenta's main function is to exchange nutrients, oxygen, and waste products between an embryo and the mother.
(f) In a mother's body, the umbilical cord joins the embryo to the placenta.

Question. An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give any one reason. 
Answer : Tapetum is  the microsporangial  layer that provides nourishment to the developing microspores. In an anther with malfunctioning tapetum, microspores do not get sufficient nutrition and hence viable male gametophytes are often not produced.

Question. How do the pollen grains of Vallisneria protect themselves? 
Answer :  Vallisneria is a water pollinated plant. Pollen grains of Vallisneria have a protective mucilaginous coat that prevents the water from damaging the pollen grains.

Question.Write the function of tapetum in anthers.
Answer : 
(i) Tapetum  nourishes  the developing microspores.
(ii)   It produces lipid rich ubisch granules containing sporopollenin, pollenkitt, compatibility recognising proteins etc.
(iii) It secretes enzyme callase for the separation of microspores.

Question. Write the characteristic features of anther, pollen and stigma of wind pollinated flowers.
Answer :  In wind pollinated flowers, anthers are exserted and versatile. In some cases like Urtica, the anthers burst suddenly to throw the pollen grains (gun powder mechanism). Pollens of wind pollinated flowers are light, small, winged, dry, smooth, non-sticky, unwettable and are produced in very large number.
Stigma of wind pollinated flower is exserted, hairy, feathery or branched to catch the wind borne pollen grains. The large thread-like stigmas and styles of cob of maize hang in air to catch wind borne pollens.

Question. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes this anther can produce?
Answer : Dithecous anther has four microsporangia or pollen sacs. This anther will have 400 microspore mother cells. As each microspore mother cell forms
4 pollen grains, 400 microspore mother cells will form 1600 pollen grains (male gametophytes).

Question. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristic of the pollen grains that makes it happen.
Answer : Sporopollenin is a major component of the hard outer layer called exine of pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. Hence, pollen grains of the part are well preserved as fossils.

Question. Name the type of flower which favours cross pollination. 
Answer : Unisexual flowers favour cross pollination.

Question. Why is bagging of the emasculated flowers essential during hybridisation experiments?
Answer : Bagging of the emasculated flowers is essential to prevent the landing of unwanted pollen on the stigma of flowers during hybridisation experiments.

Question. The following statements (a), (b) and (c) seem to describe the water-pollinated submerged plants. Which one of these statements is incorrect?
(a) The flowers do not produce nectar.
(b) The pollen grains have mucilaginous covering.
(c) The brightly coloured female flowers have long stalk to reach the surface.
Answer : Statement (c) is incorrect. In submerged water- pollinated plants, the flowers are small, inconspicuous and generally dull coloured not brightly coloured.

Question. How can pollen grains of wheat and rice which tend to lose viability within 30 minutes of their release be made available months later for breeding programmes? 
Answer :  In some cereals such as wheat and rice, pollen grains lose viability within 30 minutes of their release. They can be made available months  later by means of cryopreservation i.e., storing them in liquid nitrogen at a very low temperature (–196°C).

Question. List the different types of pollination depending upon the source of pollen grain.
Answer : Based on the source of pollen grain, pollination can be of following three types:
(i) Autogamy : Autogamy (self pollination) is the transfer of pollen grains from anther to the stigma of the same flower.
(ii) Geitonogamy : It is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant. Geitonogamy is functionally cross-pollination involving a pollinating agent but genetically it is equivalent to autogamy since the pollen grains come from the same plant.
(iii) Xenogamy : It is the transfer of pollen grains from anther to the stigma of different plants of same species. It brings genetically different types of pollen grains to the stigma.

Question. Angiosperms bearing unisexual flowers are said to be either monoecious or dioecious. Explain with the help of one example of each.
Answer : Unisexual flowers are flowers bearing either male or female reproductive structures. Male flower is staminate, i.e., bearing stamens while female flower is pistillate i.e., bearing pistils.
In some flowering plants, both male and female flowers are present on same plant. Such plants are referred to as monoecious e.g., cucurbits. In some plants, unisexual male and female flowers are present on separate plants. Such plants are referred to as dioecious e.g., papaya.

Question. Name the organic materials exine and intine of an angiosperm pollen grain are made up of. Explain the role of exine. 
Answer : Exine is the outer tough and resistant layer of pollen grains made up of sporopollenin. Intine is thin continuous and inner wall of the pollen grain which is made up of cellulose and pectin.
Exine provides protection to pollen grain during its hazardous journey from anther of one flower to the stigma of another flower. Due to presence of sporopollenin in exine, pollens of past are will preserved as fossil in soil and sediments elabling the scientists to study pollen structure and pollination pattern of angiosperms of past.

Question. (a) How does cleistogamy ensure autogamy? (b) State one advantage and one disadvantage of cleistogamy to the plant.
Answer : (a) Cleistogamy is the condition where pollination occurs in closed flowers that do not open at all. In such flowers, the anthers and stigma lie close to each other. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
(b) One advantage of cleistogamy is that seed setting is assured even in the absence of pollinators as pollen on maturity will always reach the stigma due to their close placement.
One disadvantage of cleistogamy is that it does not allow cross pollination, thereby restricting chances of genetic variability

Question. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated. Justify. 
Answer : Geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same plant. It is functionally cross pollination involving pollinating agent but genetically it is similar to autogamy since the pollen grains come from the same plant.

Question. Name all the haploid cells present in an unfertilised mature embryo-sac of a flowering plant. Write the total number of cells in it.
Answer : In an unfertilised mature embryo sac of flowering plant,  six haploid  cells are present  i.e.,  two synergids, one egg, three antipodals. The total number  of cells in an unfertilised mature embryo sac is seven i.e., two haploid synergids, one haploid egg, three haploid antipodals and one central cell (containing two polar nuclei).

Question. Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm.
Answer : Two cells enclosed in a mature male gametophyte of an angiosperm are : a smaller generative cell and a much larger vegetative cell (or tube cell). Generative cell is spindle shaped to spherical in outline with thin dense cytoplasm surrounding a prominent nucleus. Vegetative cell has a lobed central nucleus that lies in vacuolated cytoplasm packed with, starch grains, lipids and proteins.

Question. Explain the sequence of events in pollen-pistil interaction. 
Answer : Pollen pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule.
As soon as a pollen grain lands on the stigma, it is hydrated. As a result of hydration, the exine and intine proteins are released on the stigmatic surface. The pollen wall proteins bind to the stigma surface pellicle (receptor site for the pollen wall proteins) within few minutes of the contact.
When pollen is compatible, erosion of the cuticle of the stigma papilla begins beneath the emerging pollen tube. This is the essential preliminary requirement for the penetration of the pollen tube. In case of incompatible pollination, a callosic plug develops between the plasma membrane and pectocellulosic layer of the stigmatic papillae just below the point of contact with the pollen and the growth of pollen tube ceases.

Question. List the adaptive features of water pollinated flowers like Vallisneria. 
Answer : Vallisneria is a submerged dioecious aquatic plant in which pollination takes place by the agency of water. The adaptive features of water pollinated flowers of Vallisneria are as follows:
(i) The male plants produce a large number of male flowers. The male flowers abscise and rise to the surface where they float.
(ii) The male flowers have two fertile stamens. Two of their tepals form a boat-shaped structure while the third one functions as a sail.
(iii) The female plants bear long stalked solitary pistillate flowers. The mature female flowers are brought to the surface of water by the elongation of their stalks. They have large sticky trifid stigmas.
(iv) While floating, the male flowers are drawn in the depression surrounding each female flower. One anther of a male or staminate flower comes in contact with the stigma of the female flower. The anther bursts and pollination is performed.
(v) Pollen grains are covered by mucilage which helps them in sticking to stigma as well as protects them from wetting by water.
(vi) After pollination, the female flower is pulled inside water by the coiling of its stalk.

Question. Where is sporopollenin present in plants? State its significance with reference to its chemical nature.
Answer : Sporopollenin  is  present  in  exine  layer  of pollen grains. Sporopollenin is highly resistant fatty substance not degraded by any enzyme and not affected by high temperature, strong acid or strong alkali therefore pollen grains can be well preserved as microfossils.

Question. How does the study of different parts of a flower help in identifying wind as its pollinating agent? 
Answer : In a wind pollinated flower, following characteristics are present which help to identify that wind is its pollinating agent:
(i) Flowers are small and inconspicuous.
(ii) Non-essential parts are either absent or reduced.
(iii) The flowers are colourless, odourless and nectarless.
(iv) In case of unisexual flowers, the male flowers are more abundant. In bisexual flowers, the stamens are generally numerous.
(v) Flowers are produced above the foliage, before the appearance of new foliage or placed in hanging position.
(vi) Both the stigmas and anthers are exserted. Anthers are versatile.
(vii) Pollen grains are light, small, dusty, dry and unwettable.
(viii) Stigma is hairy, feathery or branched to catch the wind borne pollen grains.

Question. Trace pollen grain development from sporogenous tissue in the anther.
Answer : In an anther, each cell of the sporogenous tissue is a potential pollen or microspore mother cell (PMC). Each PMC divides by meiosis to form a microspore tetrad. This process is called microsporogenesis. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. The hard outer layer called the exine is made up of sporopollenin. The inner wall of the pollen grain is called the intine. When the pollen grain is mature it contains two cells, the vegetative cell and the generative cell. Different stages of microsporogenesis are shown below.

Question. Explain the process of artificial hybridisation to get improved crop variety in (a) plants bearing bisexual flowers (b) female parent producing unisexual flowers. 
Answer : Hybridisation is effective pollination between flowers of different species of the same genus, or even between flowers of different genera (as in the case of several orchids). It involves artificial pollination of the desired female parent with pollen from the desired male parent, taking all precautions to prevent contamination of the stigma with the pollen of any other type.
(a) In bisexual flowers, hybridisation involves emasculation i.e., removal of male reproductive parts (stamens) followed by artificial pollination.
(b) In unisexual flowers the procedure is rather simple. Unopened floral buds are covered with cellophane bags. When the stigma attains receptivity pollens from the male parent are dusted on it, and the pollinated flowers are rebagged.
 

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