NCERT Exemplar Problems Class 12 Biology Chapter 1 Reproduction in Organisms

Multiple Choice Questions
Single Correct Answer Type
1. A few statements describing certain features of reproduction are given below
i. Gametic fusion takes place
ii. Transfer of genetic material takes place
iii. Reduction division takes place
iv. Progeny have some resemblance with parents
Select the options that are true for both asexual and sexual reproduction from the options given below:
(a) i and ii (b) ii and iii
(c) ii and iv (d) i and iii
Answer. (c) Transfer of genetic material and progeny have some resemblance with parents are the phenomenon common in’both asexual and sexual reproduction while gametic fusion and reduction division takes place in sexual reproduction only.

2. The term ‘ clone ’ cannot be applied to offspring formed by sexual reproduction because
(a) Offspring do not possess exact copies of parental DNA
(b) DNA of only one parent is copied and passed on to the offspring
(c) Offspring are formed at different times
(d) DNA of parent and offspring are completely different
Answer. (a)
• In asexual reproduction, a single individual (parent) is capable of producing offspring which are not only identical to one another but are also exact copies of their parent. The term clone is used to describe such morphologically and genetically similar individuals.
• In sexual reproduction because of the fusion of male and female gametes (either by same individual or by different individual of the opposite sex), sexual reproduction results in offspring that are not identical to the parents or amongst themselves.

3. Amoeba and Yeast reproduce asexually by fission and budding respectively, because they are
(a) Microscopic organisms
(b) Heterotrophic organisms
(c) Unicellular organisms
(d) Uninucleate organisms
Answer. (c) Many single-celled organisms reproduce by binary fission (e.g., Amoeba, Paramecium), where a cell divides into two halves and each rapidly grows into an adult.
In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which eventually gets separated and mature into new yeast organism (cells). Budding is also found in Hydra.

4. A few statements with regard to sexual reproduction are given below
i. Sexual reproduction does not always require two individuals
ii. Sexual reproduction generally involves gametic fusion
iii. Meiosis never occurs during sexual reproduction
iv. External fertilisation is a rule during sexual reproduction
Choose the correct statements from the options below:
(a) i and iv , (b) i and ii
(c) ii and iii (d) i and iv
Answer. (b)
• Sexual reproduction requires male and female gametes (either by same individual or by different individual of the opposite sex).
• Sexual reproduction generally involves gametic fusion.
• Meiosis occurs during sexual reproduction in dipoloid organisms.
• External fertilisation is not a rule during sexual reproduction, internal fertilization also takes place

5. A multicellular, filamentous alga exhibits a type of sexual life cycle in which the meiotic division occurs after the formation of zygote. The adult filament of this alga has
(a) Haploid vegetative cells and diploid gametangia
(b) Diploid vegetative cells and diploid gametangia
(c) Diploid vegetative cells and haploid gametangia
(d) Haploid vegetative cells and haploid gametangia
Answer. (d) Adult filament of a multicellular, filamentous alga have haplontic life cycle in which the meiotic division occurs after the formation of zygote. So, the filament of this alga have haploid vegetative cells and haploid gametangia.

6. The male gametes of rice plant have 12 chromosomes in their nucleus. The chromosome number in the female gamete, zygote and the cells of the seedling will be, respectively,
(a) 12,24,12 . (b) 24,12,12
(c) 12,24,24 (d) 24,12,24
Answer. (c) Gametophytic structure (n) of rice plant contain 12 chromosomes and sporophytic structure (2n) of rice contain 24 chromosomes.
Female gamete (n) =12,
Zygote (2n) = 24,
The cells of the seedling (2n) = 24.

7. Given below are a few statements related to external fertilization. Choose the correct statements.
i. The male and female gametes are formed and released simultaneously.
ii. Only a few gametes are released into the medium.
iii. Water is the medium in a majority of organisms exhibiting external fertilization.
iv. Offspring formed as a result of external fertilization have better chance of survival than those formed inside an organism.
(a) iii and iv (b) i and iii
(c) ii and iv (d) i and iv .
Answer. (b) In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. Organisms exhibiting external fertilisation show great synchrony between the sexes and release a number of gametes into the surrounding medium (water) in order to enhance the chances of syngamy. This happens in the bony fishes and frogs where a large number of offspring are produced. A major disadvantage is that the offspring are extremely vulnerable to predators threatening their survival up to adulthood.

8. The statements given below describe certain features that are observed in the pistil of flowers.
i. Pistil may have many carpels
ii. Each carpel may have more than one ovule
iii. Each carpel has only one ovule
iv. Pistil have only one carpel
Choose the statements that are true from the options below:
(a) i and ii (b) i and iii
(c) ii and iv (d) iii and iv
Answer. (a)
• Pistil may have many carpels (multicapillary pistil like Papaver)
• Each carpel may have more than one ovule (like Watermelon,.Papaya etc.)

9. Which of the following situations correctly describe the similarity between an angiosperm egg and a human egg?
i. Eggs of both are formed only once in a lifetime
ii. Both the angiosperm egg and human egg are stationary
iii. Both the angiosperm egg and human egg are motile transported
iv. Syngamy in both results in the formation of zygote
Choose the correct answer from the options given below:
(a) ii and iv (b) iv only
(c) iii and iv (d) i and iv
Answer. (b) Syngamy in both results in the formation of zygote is similarity between an angiosperm egg and a human egg.

10. Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because
(a) Nodes are shorter than intemodes
(b) Nodes have meristematic cells
(c) Nodes are located near the soil
(d) Nodes have non-photosynthetic cells
Answer. (b) Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because nodes have meristematic cells. Examples of vegetative propagules: (i) Leaf buds of bryophyllum, (ii) Eyes of potato, (iii) Bulbifof Agave, (iv) Offset of water hyacinth, (v) Rhizome of ginger.

11. Which of the following statements, support the view that elaborate sexual reproductive process appeared much later in the organic evolution?
i. Lower groups of organisms have simpler body design
ii. Asexual reproduction is common in lower groups
iii. Asexual reproduction is common in higher groups of organisms
iv. The high incidence of sexual reproduction in angiosperms and vertebrates
Choose the correct answer from the options given below:
(a) i, ii and iii (b) i, iii and iv
(c) i, ii and iv (d) ii, iii and iv
Answer. (c) Elaborate sexual reproductive process appeared much later in the organic evolution because of
• Lower groups of organisms have simpler body design.
• Asexual reproduction is common in lower groups of organisms.
• High incidence of sexual reproduction in angiosperms and vertebrates.

12. Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because
(a) Sexual reproduction is a lengthy process
(b) Gametes of parents have qualitatively different genetic composition
(c) Genetic material comes from parents of two different species
(d) Greater amount of DNA is involved in sexual reproduction
Ans. (b)
• Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because gametes of parents have qualitatively different genetic composition.
• In asexual reproduction due to involvement of only one parent, so there is no chance of variation.

13. Choose the correct statement from amongst the following:
(a) Dioecious (hermaphrodite) organisms are seen only in animals.
(b) Dioecious organisms are seen only in plants.
(c) Dioecious organisms are seen in both plants and animals.
(d) Dioecious organisms are seen only in vertebrates.
Answer. (c) Dioecious organisms are seen in both plants (like papaya) and animals (like cockroach).

14. There is no natural death in single celled organisms like Amoeba and bacteria because
(a) They cannot reproduce sexually
(b) They reproduce by binary fission
(c) Parental body is distributed among the offspring
(d) They are microscopic
Answer. (c) There is no natural death in single celled organisms like Amoeba and bacteria because the parental body is distributed among the offspring.

15. There are various types of reproduction. The type of reproduction adopted by an organism depends on
(a) The habitat and morphology of the organism
(b) Morphology of the organism
(c) Morphology and physiology of the organism
(d) The organism’s habitat, physiology and genetic make up
Answer. (d) The organism’s habitat, its internal physiology and several other factors (genetic make up) are collectively responsible for how it reproduces. When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual.

16. Identify the incorrect statement.
(a) In asexual reproduction, the offspring produced are morphologically and genetically identical to the parent.
(b) Zoospores are sexual reproductive structures.
(c) In asexual reproduction, a single parent produces offspring with or without the formation of gametes.
(d) Conidia are asexual structures in Penicillium.
Answer. (b) Zoospores are asexual reproductive structures.

17.Which of the following is a post-fertilisation event in flowering plants?
(a) Transfer of pollen grains
(b) Embryo development
(c) Formation of flower
(d) Formation of pollen grains
Answer. (b)

18. The number of chromosomes in the shoot tip cells of a maize plant is 20. The number of chromosomes in the micro spore mother cells of the same plant shall be
(a) 20 (b) 10 (c) 40 (d) 15
Answer. (a) Shoot tip cells of a maize plant is a sporophytic structure (2n) and microspore mother cells of maize plant is also a sporophytic structure (2n). So, microspore mother cells (MMC) contain 20 chromosomes.

Very Short Answer Type Questions
1. Mention two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually.
Answer. a. They are unicellular organisms.
b. They have a very simple body structure.

2. Why do we refer to’offspring formed by asexual method of reproduction as clones?
Answer. Offspring formed by asexual reproduction are called clones because they are morphologically and genetically similar to the parent.

3. Although potato tuber is an underground part, it is considered as a stem. Give two reasons.
Answer. a. The tuber has nodes and intemodes (as stem),
b. Leafy shoots appear from the nodes.

4. Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.
Answer. An annual has a shorter juvenile phase. Since its entire life cycle has to be completed in one growing season, its juvenile phase is shorter.

5. Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant: embryogenesis, fertilisation, gametogenesis, pollination.
Answer. Gametogenesis, Pollination, Fertilisation, Embryogenesis

6. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.
Answer. There is assured fruit set in self pollinated bisexual flower even in the absence of pollinators. In dioecious plants, there is male and female flowers present on different plants, so external pollinating agent is required for pollination.

7. Is the presence of large number of chromosomes in an organism a hindrance to sexual reproduction? Justify your answer by giving suitable reasons.
Answer. Presence of large number of chromosomes in an organism is not a hindrance to sexual reproduction. Butterfly has 380 chromosomes but it can reproduce sexually.

8. Is there a relationship between the size of an organism and its life span? Give two examples in support of your answer.
Answer. Life spans of organisms are not necessarily correlated with their sizes. The sizes of crows and parrots are not very different yet their life spans show a wide difference. Live span of crow is 15 year and of parrot is 140 years. A mango tree has a much shorter life span as compared to a peepal tree.

9. In the figure given below, the plant bears two different types of flowers marked ‘A’ and ‘B\ Identify the types of flowers and state the type of pollination that will occur in them.

Answer. ‘A’ is chasmogamous flower while ‘B’ is cleistogamous flower. A bisexual flower which normally open is called chasmogamous flower. Cleistogamous flowers do not open at all.
Cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
In a normal flower which opens and exposes the anthers and stigma complete autogamy is rather rare. Chasmogamous flower may show autogamy, geitonogamy or xenogamy.

10. Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.
Answer. Cell division cannot be a type of reproduction in multicellular organisms because cell division only increases the number of cells in an organism which leads to the growth of body.

11. In the figure given below, mark the ovule and pericarp.

Answer.

12. Why do gametes produced in large numbers in organisms exhibit external fertilisation?
Answer. Organisms exhibiting external fertilisation release a number of gametes into the surrounding medium (water) in order to enhance the chances of syngamy because there are few’ chances of fusion between male and female gametes.

13. Which of the followings are monoecious and dioecious organisms?
a. Earthworm ——————–
b. Chara ——————–
c. Marchantia ——————-
d. Cockroach ——————–
Answer. a. Earthworm—Monoecious
b. Chara—Monoecious
c. Marchantia—Dioecious
d. Cockroach—Dioecious

14. Match the organisms given in Column ‘A’ with the vegetative propagules given in column ‘B’.

Answer. Bryophyllum—leaf buds Agave—bulbils Potato—eyes
Water hyacinth—offset

15. What do the following parts of a flower develop into after fertilisation?
a. Ovary
b. Ovules
Answer. a. Ovary—Fruit
b. Ovules—Seeds

Short Answer Type Questions
1. In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer.
Answer. Meiosis takes place during its post-zygotic stage. Since the organism is haploid, meiosis cannot occur during gametogenesis.

2. The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants (angiosperms) and higher animals (vertebrates) as compared with lower groups of plants and animals. Analyse the possible reasons for this situation.
Answer. Both angiosperms and vertebrates have a more complex structural organisation. They have evolved very efficient mechanism of sexual reproduction. Since asexual reproduction does not create new genetic pools in the offspring and consequently hampers their adaptability to external conditions, these groups have resorted to reproduction by the sexual method.

3. Honeybees produce their young ones only by sexual reproduction. Inspite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.
Solution.
• The colony of honey bees has three types of members: (i) Diploid queen are fertile females, (ii) Worker bees are sterile females and (iii) Drones are haploid males.
• An offspring formed from the union of a sperm and an egg develops as a female (queen or worker), and an unfertilized egg develops as a male (drone) by means of parthenogenesis. This means that the males have half the number of chromosomes than that of a female.

4. With which type of reproduction do we associate the reduction division? Analyse the reasons for it.
Answer. Reduction division (meiosis) is associated with sexual reproduction. The reasons for this are:
a. Since sexual reproduction involves the fusion of two types of gametes (male and female), they must have haploid number of chromosomes.
b. The cell (meiocyte) which gives rise to gametes often has diploid number of chromosomes and it is only by reducing the number by half that we can get haploid gametes.
c. Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.

5. Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger etc., as a type of asexual reproduction? Give two/three reasons.
Answer. Vegetative propagation is considered as a type of asexual reproduction because
(i) This is uniparental.
(ii) Clone formation takes place.
(iii) There is no fertilisation.

6. ‘Fertilisation is not an obligatory event for fruit production in certains plants’. Explain the statement.
Answer. Yes, it is observed in parthenocarpic fruits. The ‘seedless fruits’ that are available in the market such as pomegranate, grapes etc. are in fact good examples. Flowers of these plants are sprayed by a growth hormone that induces fruit development even though fertilisation has not occurred. The ovules of such fruits, however, fail to develop into seeds.

7. In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
Answer. During embryogenesis, zygote undergoes cell-division (mitosis) and cell differentiation. While cell divisions increase the number of cells in the developing embryo; Cell differentiation helps groups of cells to undergo certain modifications to form specialised tissues and organs to form an organism.
If cell divisions are not followed by cell differentiation then there will be no formation of tissues or organs, so a new organisms cannot be formed.

8. List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.
Answer. Post-fertilisation modifications

9. Suggest a possible explanation why the seeds in a pea pod are arranged in a row, whereas those in tomato are scattered in the juicy pulp.
Answer. In a fruit, seed arrangement depends on type of placentation. Pea and tomato shows different placentation. Pea shows marginal placentation while tomato shows axile placentation.

10. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and alt least one feature common to both structures.
Answer.

11. Justify the statement ‘Vegetative reproduction is also a type of asexual reproduction’.
Answer. Vegetative propagation is also a type of asexual reproduction because
(i) This is uniparental.
(ii) Clone formation takes place.
(iii) There is no fertilisation.
(iv) There is no gamete formation.

Long Answer Type Question
1. Enumerate the differences between asexual and sexual reproduction. Describe the types of asexual reproduction exhibited by unicellular organisms.
Answer.

The types of asexual reproduction exhibited by unicellular organisms:
• Many single-celled organisms reproduce by binary fission (e.g., Amoeba, Paramecium), where a cell divides into two halves and each rapidly grows into an adult.
• In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which eventually gets separated and mature into new yeast organism (cells).

2. Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give suitable explanation.
Answer. The gametes of a parent do not have the same genetic composition because they do not have identical copies of DNA. In the pachytene and diplotene stages of meiosis-I, the phenomenon of crossing over and chiasma formation take place between homologous chromosomes. This shifts segments of DNA from one chromatid to another (homologous chromosomes) in a random manner resulting in several new combinations of DNA sequences. As a result, when meiotic division is completed, gametes possess DNA with varying degree of variations.

3. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in Kingdom Animalia and Plantae prefer this mode of reproduction. Give at least three reasons for this.
Answer. a. Sexual reproduction brings about variation in the offspring.
b. Since gamete formation is preceded by meiosis, genetic recombination occurring during crossing over (meiosis-I), leads to a great deal of variation in the DNA of gametes.
c. The organism has better chances survival in a changing environment.

4. Differentiate between (a) oestrus arid menstrual cycles; (b) ovipary and vivipary. Cite an example for each type.
Answer. Differences between oestrus and menstrual cycles

5. Rose plants produce large, attractive bisexual flowers but they seldom produce Suits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons Tor failure of fruit formation in rose.
Answer. Failure of fruit formation in rose may be due to several reasons. Some of the likely reasons are
a. Rose plants may not produce viable pollen.
b. Rose plants may not have functional egg.
c. Rose plants may have abortive ovules.
d. Being hybrids, the meiotic process may be abnormal resulting in non-viable gametes. ‘
e. There may be self-incompatibility.
f. There may be internal barriers for pollen tube growth and/or fertilisation.