NCERT Solutions for Class 12 Science Biology Chapter 1 Reproduction In Organisms are provided here with simple step-by-step explanations. These solutions for Reproduction In Organisms are extremely popular among Class 12 Science students for Biology Reproduction In Organisms Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 12 Science Biology Chapter 1 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 12 Science Biology are prepared by experts and are 100% accurate.
Page No 1:
Question 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:
Hence, the correct answer is option (c).
Page No 1:
Question 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:
Sexual reproduction involves the formation of gametes through reduction division or meiosis and fusion of male and female gametes from the same individual or different individuals of the opposite sex. The gametes show variation due to the occurrence of crossing over and independent segregation of homologous chromosomes during meiosis. Moreover, when male and female gametes fuse during sexual reproduction, the resulting zygote has a combination of genes different from either of the parent. Since the offspring resulting from sexual reproduction possesses DNA different from the parents, the term 'clone' cannot be applied to it.
Hence, the correct answer is option (a).
Page No 1:
Question 3:
Asexual method of reproduction by binary fission is common to which of the following?
i. Some eukaryotes
ii. All eukaryotes
iii. Some prokaryotes
iv. All prokaryotes
Choose the correct option from the following:
(a) i and ii; (b) ii and iii; (c) i and iii; (d) iii and iv.
Answer:
Binary fission is a method of asexual reproduction during which a single cell divides into two halves. This method occurs in single-celled organisms such as bacteria (prokaryote), Amoeba (eukaryote), and Paramoecium (eukaryote).
Hence, the correct answer is option (c).
Page No 1:
Question 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:
Hence, the correct answer is option (b).
Page No 2:
Question 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:
Since the meiotic division occurs after the formation of the zygote, the multicellular, filamentous alga is haploid. This alga bears the haploid gametangia.
Hence, the correct answer is option d.
Page No 2:
Question 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:
Hence, the correct answer is option c.
Page No 2:
Question 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 a 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:
Hence, the correct answer is option (b).
Page No 2:
Question 8:
The statements given below describe certain features that are observed in the pistil of flowers.
i. Pistil may produce more than one seed
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:
Pistil or gynoecium is the female reproductive organ in flowering plants. A pistil may have one or more than one free or fused carpel and each carpel may have one or more than one ovules. So, statements i. and ii. are true.
Hence, the correct answer is option (a).
Page No 2:
Question 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 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:
Hence, the correct answer is option (b).
Page No 3:
Question 10:
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:
In plants, meristematic cells have the capacity to divide and form new cells. So, the appearance of vegetative propagules from the nodes of plants such as Sugarcane and Ginger is due to the presence of meristematic cells at the nodes.
Hence, the correct answer is option b.
Page No 3:
Question 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 a 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:
Hence, the correct answer is option (c).
Page No 3:
Question 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.
Answer:
Hence, the correct answer is option b.
Page No 3:
Question 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:
Hence, the correct answer is option c.
Page No 3:
Question 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. The parental body is distributed among the offspring
d. They are microscopic
Answer:
Hence, the correct answer is option c.
Page No 4:
Question 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 makeup
Answer:
Hence, the correct answer is option d.
Page No 4:
Question 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:
Zoospores are motile, microscopic asexual reproductive structures produced in algae and fungi. So, except for option b, all other statements are correct.
Hence, the correct answer is option b.
Page No 4:
Question 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:
Post-fertilisation events occur after the formation of zygote and involve embryogenesis. Among the given events, transfer of pollen grains, formation of flower and formation of pollen grains are pre-fertilisation events.
Hence, the correct answer is option b.
Page No 4:
Question 18:
The number of chromosomes in the shoot tip cells of a maize plant is 20. The number of chromosomes in the microspore mother cells of the same plant shall be:
a. 20
b. 10
c. 40
d. 15
Answer:
Shoot tip cells and microspore mother cells both are diploid in a maize plant thus, both will have the same number of chromosomes, that is, 20.
Hence, the correct answer is option a.
Page No 4:
Question 1:
Mention two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually.
Answer:
The two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually are:
(a) simple body organization
(b) unicellularity.
Page No 4:
Question 2:
Why do we refer to offspring formed by asexual method of reproduction as clones?
Answer:
In asexual reproduction, a single parent gives rise to an offspring. As a result, these asexually produced offspring are not only genetically and morphologically identical to one another but also to their parent. So, such morphologically and genetically similar offspring produced by asexual reproduction are referred to as clones.
Page No 4:
Question 3:
Although potato tuber is an underground part, it is considered as a stem. Give two reasons.
Answer:
A stem is characterised by the presence of nodes, internodes and scale leaves. The underground potato tuber possesses these characteristics so, it is considered a stem.
Page No 5:
Question 4:
Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.
Answer:
Annuals are the plants that produce flowers only once and die after flowers develop into fruits within the same growing season. In contrast, perennials are the plants that live for long years and flower year after year in the same season or throughout the year. Since annuals have to complete their life cycle in the same growing season, they have a shorter juvenile phase as compared to perennials.
Page No 5:
Question 5:
Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant:
embryogenesis, fertilisation, gametogenesis, pollination.
Answer:
The correct sequence in which the given events of sexual reproduction occur in a flowering plant is:
Page No 5:
Question 6:
The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.
Answer:
Page No 5:
Question 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:
No, the presence of a large number of chromosomes in an organism does not hinder sexual reproduction. Both plants and animals with a large number of chromosomes e.g. Ophioglossum, a fern (2n = 1,260) and hermit crab (2n = 254) can reproduce sexually. This is because chromosomes are present in pairs in the cells of eukaryotic organisms. For example, a hermit crab has 127 pairs of chromosomes in each body cell. Since gametes are produced by meiosis, they have only one chromosome of each pair. For example, male and female gametes of a hermit crab have 127 chromosomes. During sexual reproduction, haploid male and female gametes fuse to form a zygote with two pairs of each chromosome. So, the presence of chromosomes in large or small numbers in a cell does not affect sexual reproduction.
Page No 5:
Question 8:
Is there a relationship between the size of an organism and its life span? Give two examples in support of your answer.
Answer:
Page No 5:
Question 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:
The flower marked 'A' is an open flower with exposed anthers and stigma. Such a flower is called a chasmogamous flower. Self- or cross-pollination may occur in chasmogamous flowers. The flower marked as 'B' is a closed flower in which anthers and stigma are never exposed. Such a flower is called a cleistogamous flower. Self pollination will occur in cleistogamous flowers.
Page No 5:
Question 10:
Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.
Answer:
Cell division is a mode of asexual reproduction that occurs in organisms with a relatively simple organisation like algae and fungi. Multicellular organisms especially animals have complex body organisation (tissue and organ system level organisation). If such organisms reproduce through cell division, the number of cells will increase leading to the growth of the body but differentiation of these cells into specialised tissues and organs to form an organism will not occur. Hence, cell division cannot be a type of reproduction in multicellular organisms.
Page No 6:
Question 11:
In the figure given below, mark the ovule and pericarp.
Answer:
Page No 6:
Question 12:
Why do gametes produced in large numbers in organisms exhibit external fertilisation?
Answer:
In organisms exhibiting external fertilisation, syngamy or fusion of male and female gametes occur in external medium i.e. water. So, in order to increase the chances of the meeting of male and female gametes leading to syngamy, such organisms produce gametes in large numbers.
Page No 6:
Question 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
Page No 6:
Question 14:
Match the organisms given in Column- ‘A’ with the vegetative propagules given in column ‘B’.
Col. A Col. B
i. Bryophyllum a) offset
ii. Agave b) eyes
iii. Potato c) leaf buds
iv. Water hyacinth d) bulbils
Answer:
| Column A | Column B |
| i. Bryophyllum | c) leaf buds |
| ii. Agave | d) bulbils |
| iii. Potato | b) eyes |
| iv. Water hyacinth | a) offset |
Page No 6:
Question 15:
What do the following parts of a flower develop into after fertilisation?
a. Ovary ______________
b. Ovules ______________
Answer:
After fertilisation,
a. Ovary develops into a fruit.
b. Ovules develop into seeds.
Page No 6:
Question 1:
In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer.
Answer:
In haploid organisms, the parent body is haploid and the gametes are also haploid. So, in haploid organisms, gametes are produced through mitosis. Following fertilisation, a diploid zygote is formed. In order to restore haploidy, the zygote undergoes meiosis to form haploid organisms. So, meiosis occurs in the post-zygotic stage in haploid organisms undergoing sexual reproduction.
Page No 6:
Question 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 higher plants and animals have a more complex body organisation than the lower plants and animals and are well adapted to diverse climatic conditions. Since asexual reproduction occurs in lower organisms with simple body organisation, higher plants and animals with complex body organisation have evolved efficient means of sexual reproduction based on their morphology and physiology. Also, sexual reproduction brings about variations in organisms required for their evolution and adaptation to the changing environment. Thus, the occurrence of asexual reproduction drastically reduces as we move from lower groups of plants and animals to higher groups of plants and animals.
Page No 7:
Question 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.
Answer:
The colony of honeybees has three types of individuals- queen (female), worker (female) and the drone (male). The queen and the workers are diploid with 32 chromosomes and the drone is haploid with 16 chromosomes. Diploid queen and worker bees develop from the fertilised eggs and haploid drones are developed from the unfertilised eggs through parthenogenesis.
Page No 7:
Question 4:
With which type of reproduction do we associate the reduction division? Analyse the reasons for it.
Answer:
Reduction division or meiosis is associated with sexual reproduction. Sexual reproduction involves the fusion of male and female gametes resulting in the formation of a zygote. Thus, in diploid organisms, the gametes must have half the number of chromosomes than the number of chromosomes present in the somatic cells so that the same diploid number of chromosomes is restored in the zygote. So, gametes are produced through meiosis in diploid organisms. In contrast, haploid organisms produce gametes through mitosis and meiosis occurs in the zygote to restore the haploid number of chromosomes in the organisms of the next generation. Thus, reduction division is associated with sexual reproduction to maintain the chromosome number constant over generations.
Page No 7:
Question 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:
In certain plants like Bryophyllum, water hyacinth, ginger, etc., specialised reproductive structures called vegetative propagules formed from the vegetative parts of a single parent are capable of producing new plants. These new plants are morphologically and genetically similar to each other and their parent plant. So, vegetative propagation is a type of asexual reproduction due to
(a) the involvement of a single parent.
(b) no involvement of meiosis and syngamy.
(c) the production of morphologically and genetically similar new plants.
Page No 7:
Question 6:
'Fertilisation is not an obligatory event for fruit production in certain plants'. Explain the statement.
Answer:
In plants such as Banana, the ovary develops into a fruit without fertilisation of ovules. Such a development of fruit without fertilisation is called parthenocarpy and such fruits are called parthenocarpic fruits. Since fertilisation does not occur, parthenocarpic fruits are seedless. So, fertilisation is not an obligatory event for fruit production in certain plants.
Page No 7:
Question 7:
In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
Answer:
Page No 7:
Question 8:
List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.
Answer:
- Calyx, corolla, stamens, style, and stigma become dry and weak. They wither away.
- The ovary develops into a fruit.
- The ovules develop into seeds.
- The zygote develops into an embryo.
- The primary endosperm nucleus develops into endosperm that provides nourishment to the developing embryo.
- The synergids and antipodals degenerate after fertilization.
- The funicle of the ovule changes into the stalk of the seed.
- The outer integument of the ovule changes into testa (outer seed coat).
- The inner integument changes into an inner seed coat (Tegmen).
- Micropyle changes into seed pore.
- Hilum changes into scar of the seed.
Page No 7:
Question 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 flowering plants, seeds develop from ovules and fruit develops from the ovary after fertilisation. So, the arrangement of seeds is the same as the arrangement of the ovules on the placenta inside the ovary, i.e. placentation. In pea, placentation is marginal i.e. placenta is formed as a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows. So, seeds are present in a row in a pea pod. In contrast, the tomato has axile placentation i.e. the placenta is axial and ovules are attached to it. So, after fertilisation, when the ovary develops into a fruit, seeds get scattered into the juicy pulp.
Page No 7:
Question 10:
Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and atleast one feature common to both structures.
Answer:
Zoospore Conidium
Dissimilarities between Zoospore and Conidium
| Zoospore | Conidium | |
| 1. | Zoospore is a motile asexual structure. | Conidium is a non-motile asexual structure. |
| 2. | Zoospore is produced inside the sporangium i.e. endogenous in origin. | Conidium is produced on the tip of the conidiophores i.e. exogenous in origin. |
Similarity between Zoospore and Conidium
Both zoospore and conidium are asexual reproductive structures.
Page No 7:
Question 11:
Justify the statement ‘Vegetative reproduction is also a type of asexual reproduction’.
Answer:
Page No 7:
Question 1:
Enumerate the differences between asexual and sexual reproduction. Describe the types of asexual reproduction exhibited by unicellular organisms.
Answer:
| Asexual Reproduction | Sexual Reproduction | |
| 1. | It involves single parents. | It involves either a single parent or two parents of opposite sex. |
| 2. | It does not involve the fusion of gametes. | It involves the fusion of male and female gametes. |
| 3. | It occurs in organisms with relatively simple body organisation. | It occurs in organisms with complex body organisation. |
| 4. | Offspring are morphologically and genetically similar to each other and their parents. | Offspring are not morphologically and genetically similar to each other and their parents. |
The different types of asexual reproduction exhibited by unicellular organisms are as follows:
Page No 7:
Question 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:
Page No 7:
Question 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 atleast three reasons for this.
Answer:
Though sexual reproduction is a long drawn, energy-intensive complex process, organisms of Kingdom Animalia and Plantae prefer this mode of reproduction for the following reasons:
a. Sexual reproduction generates variations that help the organisms to adapt to changing environments or new habitats and offer a survival advantage.
b. Offspring produced through sexual reproduction have characteristics of both the parents. This leads to an increase in genetic diversity.
c. Variations produced through sexual reproduction helps in evolution.
d. In sexual reproduction, different mutations are continually reshuffled from one generation to the next as a result, the disease is less likely to affect all the individuals.
Page No 7:
Question 4:
Differentiate between (a) oestrus and menstrual cycles; (b) ovipary and vivipary. Cite an example for each type.
Answer:
Differences between Oestrus and Menstrual Cycles:
| Oestrus Cycle | Menstrual Cycle | |
| 1. | The oestrous cycle is the changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase in non-primate mammals. | The menstrual cycle is the changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase in primate mammals. |
| 2. | Females show increased sex urge during an oestrous cycle. | Females do not show any increase in sex urge. |
| 3. | Heat is produced at the end of ovulation and copulation occurs only during this period. | No heat is produced during ovulation and copulation can occur any period of the cycle. |
| 4. | Endometrium is absorbed in the absence of conception. | Endometrium is shed as liquid discharge in the absence of conception. |
| 5. | The examples of animals having oestrous cycle are cow, sheep, rat, etc. | The examples of animals having menstrual cycle are monkeys, apes and humans. |
| Ovipary | Vivipary | |
| 1. | Ovipary is the phenomenon in which development of zygote takes place in the external environment. | Vivipary is the phenomenon in which the development of zygote occurs inside the body of the female organism. |
| 2. | Ovipary exhibiting animals or oviparous organisms lay fertilised or unfertilised eggs from which young ones hatch out. | Vivipary exhibiting organisms give birth to young ones. |
| 3. | The chances of survival of young ones are low due to vulnerability of eggs or young ones to predators. | The chances of survival of young ones are high due to proper care and protection offered to embryo during its development inside the body of the female organism. |
| 4. | The examples of oviparous organisms are fishes, amphibians, reptiles and birds. | The examples of viviparous organisms are mammals. |
Page No 8:
Question 5:
Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. On the other hand, a tomato plant produces plenty of fruits though they have small flowers. Analyze the reasons for the failure of fruit formation in rose.
Both these plants - rose and tomato - both selected by human beings for different characteristics, the rose for its flower and tomato for its fruit. Roses, being vegetatively propagated do not need to produce seeds.
Answer:
Artificial selection of rose plants by humans for its flower and its propagation by vegetative means had resulted in the production of no fruits or seeds in it. The possible reasons for the failure of fruit formation in rose could be:
a. Production of non-viable pollen grains required for pollination
b. Production of non-functional female gamete
c. Production of sterile ovules or anthers
d. Presence of defective tapetum
e. Self-incompatibility
f. Presence of internal barriers that prevent the entry or growth of pollen tubes or fertilization.
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