NCERT Solutions Class 12 Biology Chapter 1 Reproduction in Organisms

Question : Why is reproduction essential for organisms?
Answer Reproduction is a fundamental feature of all living organisms. It is a biological process through which living organisms produce offspring’s similar to them. Reproduction ensures the continuance of various species on the Earth. In the absence of reproduction, the species will not be able to exist for a long time and may soon get extinct.

Question : Which is a better mode of reproduction sexual or asexual? Why?
Answer Sexual mode of reproduction is better because it is biparental reproduction and introduces variation among offsprings and their parents (in a population) due to crossing over and recombination during gamete formation by meiosis and thus helps in better adaptation to changing environment.

Question : Why is the offspring formed by asexual reproduction referred to as clone?
Answer In asexual reproduction, the offspring are morphologically and genetically identical to the parent and to each other. Hence they are called clones.

Question : Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Answer Offspring formed due to sexual reproduction have better chances of survival because:
(i) the offspring retains its hybrid vigour which may adapt better with the changing environment.
(ii) genetic variation is introduced among the offspring, which increases the range of tolerance or biological tolerance.
(iii) sexual reproduction occurs in adverse conditions in lower plant kingdom, so sexual spores survive in adverse conditions.
Sexual reproduction may not always show better chances of survival because the offspring may be inferior to the parents.

Question : How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Answer.  

S. No.	Progeny from asexual reproduction	Progeny from sexual reproduction
(i)	The progenies have similar genetic make up.	The progenies have different genetic makeup.
(ii)	The progenies are not only identical to one another but are exact copies of their parents, i.e., clone of the parent.	The progenies are different from each other and dissimilar to the parent.
(iii)	Variation is absent.	Variation is a common phenomenon.
(iv)	Variation may occur due to mutation.	Variation occurs due to mutation, crossing over and recombination.
(v)	Progenies are less adaptable to changes in environment.	Progenies are more adaptable to changes in environment.

 

Question : Distinguish between asexual and sexual reproduction. Why vegetative reproduction is also considered as a type of asexual reproduction?
Answer. The difference between asexual and sexual reproduction are as follows:

Asexual reproduction	Sexual reproduction
Asexual reproduction does not involve formation or fusion of gametes.	Sexual reproduction involves formation and fusion of gametes.
The offsprings formed by asexual reproduction are genetically identical to the parent and are referred to as clones.	The offsprings are neither identical to the parents nor to each other hence, it leads to variation in a population.
It is a simple and fast process.	It is an elaborate, complex and slow process.
It involves only mitosis.	It involves meiosis.
It is always uniparental (single parent).	It is usually biparental (two parents).
It helps in maintaining same characters for generations.	It plays a vital role in evolution process.
It is common among single-celled organisms, and in plants and animals with relatively simple organisation.	It is common in higher animals with complex organisation.

Vegetative reproduction is considered as a type of asexual reproduction because
(i) it is uniparental reproduction,
(ii) there is no involvement of gametes or sex cells, and
(iii) cell division is mitotic and no reductional division takes place,
(iv) vegetative propagules are somatic cells.
(v) there is no variation among the progenies.

Question : What is vegetative propagation? Give two suitable examples.
Answer. In plants, the vegetative propagules (runner, rhizome, sucker, etc.) are capable of producing new offsprings by the process called vegetative propagation. As the formation of these vegetative propagules does not involve both the parents, the process involved is asexual.
Examples: (i) Adventitious buds in the notches along the leaf margins of Bryophyllum grow to form new plants.
(ii) Potato tuber having buds when grown, develops into a new plant.

Question : Define
(a) Juvenile phase,
(b) Reproductive phase,
(c) Senescent phase.
Answer. 
(i) Juvenile phase: It is the pre-reproductive phase in which all organisms require a certain growth and maturity in the life before reproducing sexually.
(ii) Reproductive phase is the phase in the life cycle, where an organism possess all the capacity and potential to reproduce sexually. It is the end of juvenile phase or vegetative phase.
(iii) Senescent phase is the post-reproductive phase in the life cycle where an organism slowly loses the rate of metabolism, reproductive potential and shows deterioration of the physiological activity of the body.

Question : Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Answer. Higher organisms have resorted to sexual reproduction to
(i) get over the unfavourable condition,
(ii) introduce variation to enable better adaptive capacity, biological tolerance and competitive edge,
(iii) restore high gene pool in a population,
(iv) restore vigour and vitality of the race, and
(v) get proper parental care during vulnerable stage.

Question : Explain why meiosis and gametogenesis are always interlinked?
Answer. Gametogenesis (formation of male and female gametes) is associated with reduction in chromosome number thus, the gamete formed contains half the chromosome set of the parental cell. So, gametogenesis is interlinked with meiosis because meiosis reduces the chromosome number to half, i.e., from 2n to ‘n’.

Question : Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(a) Ovary ———————————
(b) Anther ———————————
(c) Egg ———————————
(d) Pollen ———————————
(e) Male gamete ———————————
(f ) Zygote ———————————
Answer.
(i) Diploid (2n)
(ii) Diploid (2n)
(iii) Haploid (n)
(iv) Haploid (n)
(v) Haploid (n)
(vi) Diploid (2n)

Question : Define external fertilization. Mention its disadvantages.
Answer. The fusion of compatible gametes outside the body of the parent is called external fertilisation, e.g., in frog.
Disadvantages of external fertilisation:
(i) It requires a medium for fusion of gametes.
(ii) The young ones are often exposed to the predators and no parental care is provided.

Question : Differentiate between a zoospore and a zygote.
Answer. 

Zoospore	Zygote
These are endogenously, asexually produced,unicellular, naked and motile spores having one or two flagella.	Zygote is a diploid cell formed by fusion of male and female gametes.
It may be haploid or diploid.	It is always diploid.
Zoospore takes part in dispersal.	Zygote does not have significant role in dispersal.

Question : Differentiate between gametogenesis from embryogenesis.
Answer. 

Gametogenesis	Embryogenesis
It is the formation of gametes from meiocytes (gamete mother cells).	It is the formation of embryo from zygote.
This is a pre-fertilisation event.	This is a post-fertilisation event.
The cell division during gametogenesis is meiotic in diploid organisms.	The cell division during embryogenesis is mitotic in diploid organisms.
It occurs inside reproductive organs.	It occurs outside or inside the female body.
It produces haploid gamete.	It gives rise to diploid embryo

Question : Describe the post-fertilization changes in a flower.
Answer. The post-fertilisation changes that take place in a flower are as follows:
(i) The formation of zygote (inside ovule) which later develops into an embryo and primary endosperm cell which in turn develops into endosperm (provides nourishment to the growing embryo).
(ii) While the sepals, petals and stamens are shed, the pistil remains intact.
(iii) The fertilised ovule develops into seeds.
(iv) The ovary matures into a fruit that later develops a thick, protective wall called pericarp.
(v) Seeds after dispersal, germinate under favourable conditions, which later develop into a new plant.

Question : What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Answer. A flower which possess both the male and female reproductive structures, i.e., both stamen and carpel is called a bisexual flower.
List of some common bisexual flowers
S. No.   Common name                  Scientific name
(i)          China rose                         Hibiscus rosa-sinensis
(ii)         Chandni                            Tabernaemontana divaricata
(iii)        Makoi                                Solanum nigrum
(iv)       Sunflower                          Helianthus annuus
(v)        Mustard                             Brassica campestris

Question : Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Answer. A staminate or male flower has only stamens and no carpel. A pistillate flower has only carpel and no stamens. Plants that bear unisexual flowers are papaya and date palm.

Question : Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Answer. In viviparous animals, the young one develops inside the body of the female organism. As a result of this, the young one gets better protection and nourishment for proper development. In case of oviparous animals, they lay eggs and the young ones develop inside the calcareous shell,outside the body of the female. So, the young ones are not effectively protected and nourished and are vulnerable to predators. So, they are at a greater risk as compared to the offsprings of the viviparous animals.

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms MCQs

Choose and write the correct option in the following questions.

Question. The period of growth from birth till attainment of sexual maturity is called
(a) Asexual phase
(b) Immature phase
(c) Maturation phase
(d) Juvenile phase
Answer. D

Question. 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

Question. 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

Question. A few statements with regard to sexual reproduction are given below. [NCERT Exemplar]
(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

Question. In Bryophyllum adventitious buds arise from
(a) leaves
(b) root
(c) stems
(d) flowers
Answer. A

Question. A gamete from a diploid parent is haploid, then from a haploid parent will be
(a) Ooploid
(b) Haploid
(c) 1/4n
(d) Tetraploid
Answer. B

Question. During formation of zygote
(a) fertilisation of male gamete occurs
(b) fertilisation of both gametes occurs
(c) fertilisation of female gamete occurs
(d) either (a) or (c)
Answer. C

Question. 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

Question. 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

Question. 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

Question. 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

Question. Given below are a few statements related to external fertilisation. 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 fertilisation.
(iv) Offspring formed as a result of external fertilisation 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

Question. 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) and (iii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (ii) and (iii)
Answer. C

Question. The most common asexual reproductive structure of algae and fungi are
(a) agygospore
(b) zoospore
(c) buds
(d) conidia
Answer. B

Question. Meiosis takes place in
(a) gemmule
(b) megaspore
(c) meiocyte
(d) conidia
Answer. C

Question. Vegetative propagation in mint occurs by
(a) stolon
(b) offset
(c) runner
(d) sucker
Answer. D

Question. 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

Question. Homothallism represents
(a) asexual condition
(b) unisexual condition
(c) bisexual condition
(d) none of these
Answer. C

Question. Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because.
(a) nodes are shorter than internodes
(b) nodes have meristematic cells
(c) nodes are located near the soil
(d) nodes have non-photosynthetic cells
Answer. B

Question. 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.
Answer. B

Question. 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 makeup
Answer. D

Question. 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

Question. 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

Question. 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

Question. 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 mobile
(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

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Assertion-Reason Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : Earthworm is monoecious.
Reason : Hermaphrodites bear both the sexes.
Answer. D

Question. Assertion : Grafting is not usually possible in monocots.
Reason : Successful grafting requires that cambia of both Stock and Scion fuse to form new vascular tissues.
Answer. A

Question. Assertion : Zygote is the only cell that gives a vital link between two generations of an organism.
Reason : The two gametes fuse to form a single zygote.
Answer. B

Question. Assertion : The offsprings of asexual reproduction are clones.
Reason : There is no fertilisation in asexual reproduction.
Answer. A

Question. Assertion : Large number of both male and female gametes enhance chances of syngamy.
Reason : In lizards female gametes develops directly into an individual.
Answer. B

Question. Assertion : Viviparous animals give better protection to their offsprings.
Reason : They lay their eggs in safer places in the environment.
Answer. C

Question. Assertion : In angiosperms, the ovule develops into a seed after fertilisation.
Reason : Fertilisation is not essential for the development of fruit.
Answer. B

Question. Assertion : Chances of survival of young one is more.
Reason : Mother’s body provides proper embryonic care and protection.
Answer. A

Question. Assertion : Binary fission occurs in single-celled animals.
Reason : Offsprings show variation.
Answer. C

Question. Assertion : Parthenogenesis is a kind of variation of sexual reproduction.
Reason : In parthenogenesis, a young one develops from an ovum but without fertilisation.
Answer. A

 

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Case-based/Source-based Question

1. Study the diagram given below and answer the questions that follow:

Question. Name an alga that reproduces asexually through zoospores. Why are these reproductive units so called?
Answer. Chlamydomonas reproduces through zoospores. The reproductive units are called zoospores because they are motile.

Question. Mention a characteristic feature and a function of zoospores in some algae.
Answer. Zoospores are microscopic motile structures. These are special structures by which algae reproduce asexually.

Question. How does Penicillium reproduce asexually?
Answer. Penicillium reproduces asexually by spore formation called conidia on conidiophores.

2. Given below is the diagram of a ginger rhizome. Answer the questions given below based on the diagram.

Question. Why do vegetative propagules in sugarcane and ginger appear from the nodes?
Answer. This is because the nodes have meristematic cells.

Question. Name the vegetative propagules in (a) Potato, and (b) Pistia.
Answer. The vegetative propagules of potato is tuber and that of Pistia is offsets.

Question. How does potato multiply?
Answer. Potato multiplies by buds (eyes) of the tuber (vegetative propagation).

3. Observe the diagram showing binary fission in Amoeba and answer the questions that follow.

Question. 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.

Question. How is the continuity of species maintained generation after generations?
Answer. Continuity of species is maintained generation after generations by the process of reproduction.

Question. Why are no variations seen in clones? State two reasons.
Answer. 
(a) Clones are produced from one parent only by mitosis.
(b) No fusion of gametes or syngamy takes place. Also, there is no recombination.

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Very Short Answer Questions

Question. Name the phenomenon and one bird where the female gamete directly develops into a new organism.
Answer. The phenomenon is called parthenogenesis. Turkey is the name of the bird.

Question. Meiosis is an essential event in the sexual life cycle of any organism. Give two reasons.
Answer. (i) Meiosis helps in the formation of gametes by reductional division and maintains constant number of chromosomes.
(ii) Meiosis brings variation in offsprings by recombination of genes.

Question. Mention the unique feature with respect to flowering and fruiting in bamboo species.
Answer. Bamboo species flower once in its life time generally after 50–100 years of vegetative growth. It produces large number of fruits and then dies.

Question. Write the two pre-fertilisation events from the list given below:
Syngamy, Gametogenesis, Embryogenesis, Pollination
Answer. Gametogenesis, Embryogenesis, Pollination.

Question. Why is banana considered a good example of parthenocarpy? 
Answer. In banana, formation of fruit occurs without fertilisation, and thus there is no formation of seeds.
So, it is considered a good example of parthenocarpy.

Question. Name the group of organisms that produce non-motile gametes. How do they reach the female gamete for fertilisation? 
Answer. Angiosperms produce non-motile gametes. They reach the female gamete with the help of air or water.

Question. Cucurbits and papaya plants bear staminate and pistillate flowers. Mention the categories they are put under separately on the basis of the type of flowers they bear. 
Answer. Cucurbit is a monoecious plant having staminate and pistillate flowers on the same plant. Papaya has staminate and pistillate flowers on separate plants and hence it is dioecious.

Question. Give reasons for the following:
Some organisms like honey-bees are called parthenogenetic animals. 
Answer. Since drones/males develop from unfertilised eggs so they are called as parthenogenetic animals.

Question. At what state does the meiosis occur in an organism exhibiting haploidic life cycle and mention the fate of the products thus produced.
Answer. Organisms exhibiting haploidic life cycle undergo meiosis during zygote formation. The products thus formed are haploid gametophyte.

Question. State the fate of a pair of autosomes during gamete formation. 
Answer. During gamete formation a pair of autosomes segregate from each other.

Question. Mention the unique flowering phenomenon exhibited by Strobilanthus kunthiana (Neelakuranji). 
Answer. Strobilanthus kunthiana flowers once in 12 years.

Question. Name two animals that exhibit oestrus cycle. 
Answer. Cow, sheep and rat (Any two).

Question. 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.

Question. In yeast and Amoeba the parent cell divides to give rise to two new individual cells. How does the cell division differ in these two organisms? 
Answer. In Amoeba, binary fission takes place whereas in yeast cell division occurs by budding.

Question. Is Marchantia monoecious or dioecious? Where are the sex organs borne in this plant? 
Answer. Marchantia is dioecious. The male sex organs, antheridia, are borne on the antheridiophores and female sex organs, called as archegonia are borne on archegoniophores.

Question. Name an organism where cell division is itself a mode of reproduction.
Answer. Protists/Monerans/Amoeba/Paramecium (any unicellular organism).

Question. How is it possible in Oxalis and Viola plants to produce assured seed-sets even in the absence of pollinators? 
Answer. By presence of cleistogamous flowers, hence anthers and stigma lie close to each other ensuring self-pollination.

Question. Mention the site where syngamy occurs in amphibians and reptiles, respectively.
Answer. In amphibians, external fertilisation occurs hence, syngamy occurs in the medium of water. In reptiles, internal fertilisation occurs hence, syngamy occurs within the body of female parent.

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Short Answer Questions

Question. (a) State the difference between meiocyte and gamete with respect to chromosome number.
(b) Why is a whiptail lizard referred to as parthenogenetic? 
Answer. (a) Meiocytes contain diploid sets of chromosomes whereas gametes contain haploid sets of chromosomes.
(b) Whiptail lizard reproduces without fertilisation, i.e., an unfertilised egg develops into a new individual. Therefore, they are referred to as parthenogenetic.

Question. Name the relationship between the first two words and suggest a suitable word 
(a) Doob grass : Runner : : Potato : …………
(b) Endogamy : Self-fertilisation : : Exogamy : …………
Answer. (a) Tuber (b) Cross-fertilisation.

Question. How does the floral pattern of Mediterranean orchid Ophrys guarantee cross-pollination?
Answer. The orchid bears flowers which resemble the female wasp in colour, smell, as well as appearance.The male pollinators mistake them as their female counterparts. Therefore, in the process of their pseudocopulation they pollinate the flower.

Question. Explain the importance of syngamy and meiosis in a sexual life cycle of an organism.
Answer. In the sexual life cycle of an organism, meiosis results in formation of haploid gametes which fuse together by syngamy and the diploid nature of the organism is restored in the zygote.

Question. The cell division involved in gamete formation is not of the same type in different organisms. Justify.
Answer. The parents may be haploid or diploid but the gametes always have to be haploid. Diploid parents undergo meiosis to produce haploid gametes, whereas haploid parents undergo mitosis to produce haploid gametes.

Question. A list of three flowering plants is given below. Which ones out of them are
(i) monoecious and
(ii) bearing pistillate flowers?
List: Date palm, Cucurbits and Pea.
Answer. (i) Monoecious plant—Cucurbits
(ii) Bearing pistillate flowers—Date palm, Cucurbits.

Question. Angiosperms bearing unisexual flowers are said to be either monoecious or dioecious. Explain with the help of one example each.
Answer. In some flowering plants, both male and female flowers may be present on the same individual (monoecious) or on separate individuals (dioecious). Some examples of monoecious plants are Cucurbits and coconuts and of dioecious plants are papaya and date palm.

Question. Name any two organisms and the phenomenon involved where the female gamete undergoes development to form new organisms without fertilisation. 
Answer. The phenomenon of development of female gamete directly into an individual without fertilisation is called parthenogenesis, e.g., rotifers, honeybees, lizards and birds.

Question. It is said apomixis is a type of asexual reproduction. Justify. 
Answer. Apomixis is a type of asexual reproduction because :
(i) Apomixis is the formation of seeds or embryo without fusion of gametes or fertilisation.
(ii) Diploid egg cell is formed without reductional division and develops into the embryo without fertilisation.
(iii) Some cells of the nucellus start dividing and develop into embryo.

Question. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain. 
Answer. Flowers of pea plants are bisexual, hence can be self pollinated and produce pods with viable seeds. Papaya is a dioecious plant bearing male and female flower on separate plants. It is unable to produce viable seeds as there is no cross-pollination. It could be a male plant which is unable to produce fruit and seeds.

Question. The number of taxa exhibiting asexual reproduction is drastically reduced in the 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.

Question. Why dogs and cats have oestrus cycle but human beings have menstrual cycle, though all are mammals?
Answer. Dogs and cats are seasonal breeders . They have heat period during which ovulation takes place.Humans, on the other hand, have this cycle monthly.

Question. Which of the following are monoecious and dioecious organisms:
(a) Earthworm
(b) Chawra
(c) Marchantia
(d) Cockroach. 
Answer. (a) Monoecious (b) Monoecious
(c) Dioecious (d) Dioecious.

Question. A moss plant produces a large number of antherozoids but relatively only a few egg cells. Why?
OR 
Why do moss plants produce very large number of male gametes? Provide one reason. What are these gametes called? 
Answer. Antherozoids are motile male gametes which have to swim on the water surface to fertilise the immotile female gametes, i.e., egg. Since, during its transfer many antherozoids get destroyed, a large number of them are produced.

Question. A liverwort plant is unable to complete its lifecycle in a dry environment. State two reasons.
Answer. For sexual reproduction to take place in mosses and liverworts the motile male gametes, antherozoids, have to swim on the water surface to fertilise the immotile female gametes, egg.
In dry conditions, the antherozoids do not reach the egg and hence fertilisation cannot occur. So, the life cycle remains incomplete.

Question. Explain the significance of meiocytes in a diploid organism. 
Answer. In a diploid organism, meiocytes undergo meiosis to form haploid gametes. These help to restore diploidy (2n) through zygote formation or syngamy.

Question. Mosses and frogs both need water as a medium for fertilisation. Where does syngamy occur and how is it ensured in both these organisms?
OR
Write the basis of categorising animals as oviparous or viviparous, giving one example of each.
Answer. In frogs, external fertilisation takes place in water. The frogs release large number of motile gametes. There is synchronised maturation of ova and sperms.
In moss, internal fertilisation takes place. The male gametes are motile and are produced in large numbers.
OR
Oviparous animals are egg laying (fertilised or unfertilised). For example, reptiles, birds.
Viviparous animals give birth to young ones. For example, majority of mammals; humAnswer.

Question. Name the units of vegetative propagation in water hyacinth. Explain giving reasons why it has become the most invasive aquatic weed. 
Answer. Offsets are the unit of vegetative propagation in water hyacinth. Since the formation of hyacinth offsets does not involve two parents, the process involved is asexual, therefore they spread quickly.

Question. Name the vegetative propagules in the following:
(a) Agave
(b) Bryophyllum 
Answer. (a) Agave—Bulbil (b) Bryophyllum—leaf buds/adventitous buds.

Question.  Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions? 
Answer. Algae and fungi shift to sexual mode of reproduction for survival during unfavourable conditions.Fusion of gametes helps to pool their resources for survival. The zygote develops a thick wall that is resistant to dessication and damage which undergoes a period of rest before germination.

Question. If the chromosome numbers in meiocytes of human beings, rat, elephant, rice, butterfly and onion are 46, 42, 56, 24, 380 and 32, respectively. What will be the chromosome numbers in gametes of these species? 
Answer. The chromosome numbers in the gametes of these species will be
Human beings = 23, rat = 21, elephant = 28, rice = 12, butterfly = 190 and onion = 16.

Question. Zygote forms the major link between one generation and those of the next generation organism.
What is the fate of zygote in organisms which show: 
(i) haplontic life cycle and (ii) diplontic life cycle?
Answer. (i) Zygote of haplontic life cycle divides meiotically to form new organisms.
(ii) Zygote of diplontic life cycle divides mitotically during embryogenesis to form embryo and then individual.

Question. With which type of reproduction do we associate the reduction division? Analyse the reasons for it. 
Answer. Reduction division is associated with sexual reproduction because the diploid organisms undergo
meiosis to form haploid gametes.

Question. Mention two important characteristics in the sexual reproduction of frogs and bony fishes.
Answer. Both these release the mature gametes simultaneously. They also release a large number of gametes in the water to enhance the chances of syngamy (external fertilisation).

Question. Out of many papaya plants growing in your garden, only a few bear fruits. Give reason.
Answer. Papaya plant is dioecious, i.e., male and female flowers are borne on separate plants. Only plants bearing female flowers will bear fruits.

 

NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Long Answer Questions

Question. 

(a) (b) (c) (d)
(i) State the type of gametes shown in the diagram.
(ii) Identify the process taking place and the resultant structure.
(iii) Name an organism that reproduces in this manner.
(iv) Label (c) and (d). 
Answer. (i) Isogametes.
(ii) Fertilisation is taking place and zygote is the resultant structure.
(iii) Cladophora/Chlamydomonas.
(iv) (c) represents zygote; (d) represents new individual.

Question. Pollen banks are playing a very important role in promoting plant breeding programme the world over. How are pollens preserved in the pollen banks? Explain. How are such banks benefitting our farmer? Write any two ways. 
Answer. Cryopreservation/preserved in liquid nitrogen (–196°C).
(i) Availability of pollen of different genetic strains (for wider use).
(ii) Cryopreservation increases viability of pollens (which can be used in crop breeding programmes).
(iii) Can be preserved/stored for longer duration.
(iv) Conserve large number of species.
(v) To prevent complete extinction of any species.
(vi) Maintain biodiversity. (Any two)

Question. Differentiate between an annual and a biennial plant. Provide one example of each.
Answer.  Differences between annual plants and biennial plants

Annual plants	Biennial plants
These plants require a single season to complete their whole life cycle.	These plants require two seasons to complete their whole life cycle.
They grow, set seeds and die within one year.	In the first year, they grow a healthy root system and short stem, i.e., show vegetative growth and become dormant in winters. In second year, they grow quickly, flower, set seeds and die.
For example, rice, wheat, etc.	For example, onion, carrot, etc.

Question. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction,many groups of organism 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 chance of survival in a changing environment.

Question. What are vegetative propagules? Name any four of them along with an example for each.
Answer. The units of asexual vegetative structures of plants which are capable of giving rise to new individuals/plants are called vegetative propagules.
Example:
(i) Rhizome of ginger,
(ii) bulbil of Agave,
(iii) leaf buds of Bryophyllum,
(iv) bulbs of onion.