Please refer to Reproduction In Organisms Class 12 Biology Important Questions given below. These solved questions for Reproduction In Organisms have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 12 Biology all chapters.
Class 12 Biology Reproduction In Organisms Important Questions
Very Short Answer Questions
Question. Mention two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually.
Answer. The characteristics that enable Amoeba and yeast to reproduce asexually, are as follows
(i) Unicellularity
(ii) Simple body organisation
(iii) Uniparental condition
Question. Why do we refer to offspring formed by asexual method of reproduction as clones?
Answer. The reproduction is called asexual, when offspring is produced by a single parent with or without the involvement of gamete formation.
As a result, the offspring that are produced are not only similar to one another, but are also exact copies of their parent. Such a group of morphologically and genetically similar individuals is called clone.
Question. Although potato tuber is an underground part, it is considered as a stem.
Give two reasons.
Answer. Potato tuber is considered as a stem because of the following reasons
(i) The tuber has nodes and internodes.
(ii) Leafy shoots appear from the nodes.
Question. Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.
Answer. In a lifespan, the organism has to grow and develop (the juvenile phase). After that the organism mature sexually and enter into the reproductive phase, before it undergoes
senescence followed by death.
Since, the entire life cycle of an annual plant is shorter and has to be completed in one growing season, its juvenile phase is shorter than that of a perennial plant.
Question. Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant embryogenesis, fertilisation, gametogenesis, pollination.
– Thinking Process
The gametes need to be formed first of all, pollination ensures their transfer, so that
fertilisation can take place. Fertilised zygote divides and differentiates during embryogenesis.
Answer. The correct sequence of events of sexual reproduction in a flowering plant are as follows gametogenesis, pollination, fertilisation, embryogenesis.
Question. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.
Answer. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant.
In self-pollinated bisexual plants transfer of pollen to stigma of flowers is easier than the dioecious plants. It is so because the anther and stigma lie close to each other and pollination is not effected even in the absence of pollinator. But in dioecious plants pollinator is necessary to bring about effective pollination as the anther and stigma lie away from each other.
Question. 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, presence of large number of chromosomes in an organism is not a hindrance to sexual reproduction. Ophioglossum (a fern) has chromosome number 1260, still it can reproduce sexually.
In higher organisms, the chromosomes are present in a compartment called nucleus, within the cell. Whether the number is small or large, the chromosomes are duplicated and then
segregated inside this compartment, during cell division. The basis of sexual reproduction is generation of haploid gametes.
Question. Is there a relationship between the size of an organism and its life span?
Give two examples in support of your answer.
Answer. There is no relationship between the size and life span of an organism. e.g.,
(i) The mango tree has a shorter life span as compared to a peepal tree though both are of the same size.
(ii) The size of crow and parrot is almost same but the life span is 15 years and 150 years respectively.
Question. 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. In the figure given below the plant bears folllowing two types of flowers
A—Chasmogamous flower (the flowers remain open, exposing anthers and stigmas).
B—Cleistogamous flowers (the flowers remain closed, so that anthers and stigmas are
never exposed) following are the types of pollination that will occur in these flowers.
(i) Autogamy (within same flower)
(ii) Geitonogamy (different flowers of same plant)
(iii) Xenogamy (different plants)
It is a case of cleistogamy (a type of autogamy) in which some plants, like, Commelina bengalensis possess both chasmogamous and cleistogamous flowers.
In chasmogamous flowers, the flowers may undergo self-pollination or cross-pollination,
while in cleistogamous flowers, the flowers undergo only self-pollination.
Question.10 Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.
Answer. In unicellular animals, cell division is the means of reproduction to increase their number while, in case of multicellular organisms, they have well developed reproductive organs
which help in reproduction.
Their whole body does not participate in reproduction like unicellular organisms.
Question. In the figure given below, mark the ovule and pericarp.
Answer. In flowering plants, the zygote is formed inside the ovule. After fertilisation the sepals, petals and stamens of the flower wither and fall off. The pistil however, remains attached to the plant.
The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into the fruit which develops a thick wall called pericarp that is protective in function.
Question. Why do gametes produced in large numbers in organisms exhibit external fertilisation?
– Thinking Process
In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy (fusion of gametes in sexual reproduction) occurs in the external medium (water) , i.e., outside the body of the organism. This type of genetic fusion is called external fertilisation.
Answer. Organisms that take part in such process produce large number of gametes because
(i) In external fertilisation, there is a great chance that the sperm and the eggs released by the organisms can be affected by factors present in the environment like dessication, predators, etc. So, to make up for the high fatality rate of the gametes, the organism produces a lot of gametes.
(ii) Producing large number of gametes increase the chance for at least some eggs and sperms to meet in the environment ensuring that atleast a stable number of offspring are able to survive and carry on.
Question. Which of the following are monoecious and dioecious organisms?
(a) Earthworm …………. (b) Chara ……….
(c) Marchantia ……….. (d) Cockroach ………..
Answer. (a) Earthworm- Monoecious animal (b) Chara- Monoecious plant
(c) Marchantia-Dioecious plant (d) Cockroach- Dioecious animal
Note In several fungi and plants, terms such as homothallic and monoecious are used to denote the bisexual condition (male and female reproductive structures in the same plant) and heterothallic and dioecious are the terms used to describe unisexual condition (male and female reproductive structures on different plants).
But in animals, individuals are either male or female (unisexual) or possess both the reproductive organs (bisexual).
Question. Match the organisms given in column I with the vegetative propagules given in column II.
Column I Column II
A. Bryophyllum 1. Offset
B. Agave 2. Eyes
C. Potato 3. Leaf buds
D. Water hyacinth 4. Bulbils
Answer. The correct matching is as follows
Column I Column II
(Plant Angiosperms) (Vegetative Propagules)
A. Bryophyllum Leaf buds
B. Agave Bulbils
C. Potato Eyes
D. Water hyacinth Offset
In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offsprings. These structures are called vegetative propagules.
Question. What do the following parts of a flower develop into after fertilisation?
(a) Ovary ……. (b) Ovules ……
Answer. (a) Ovary ……….. fruit (b) Ovules ………. seed
After fertilisation, the zygote develops into the embryo and the ovules develop into the seed.
The ovary develops into the fruit which develops a thick, protective wall called pericarp.
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. 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. 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. 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.
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.
Short Answer Questions
Question. In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer.
K Thinking Process
The requirement of meiosis is to reduce the number of chromosomes to half to maintain the ploidy. As the organism is haploid meiosis cannot occur during gametogenesis.
Answer. Meiosis can take place only in a diploid stage (post-zygotic stage) because the zygote is the only diploid cell in the life cycle of such organisms. This meiosis an case of haploid organisms will occur of the fertilisation.
Question. 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. Higher plants (angiosperms) and higher animals (vertebrates) have a more complex structural organisation as compared to the lower groups of plants and animals. They have evolved very efficient mechanism of sexual reproduction. These groups have resorted to reproduction by the sexual method for the following reasons
(i) To ensure healthy progeny
(ii) To produce genetically varied offsprings that adapt to changes in environment and surviveal in all climatic conditions.
(iii) It ensures the genetic recombination that results in variation which gives rise to evolution.
Question. 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. (i) Sterile diploid females as workers
(ii) One fertile diploid female as queen
(iii) Fertile haploid males as drones.
In case of honeybees, both haploid and diploid individuals formad as a result of incomplete (cyclic) parthenogenesis, i.e., both sexual reproduction and parthenogenesis. Fertilised eggs (zygote) give rise to queen and workers (both are females) by the process of sexual reproduction and unfertilised eggs (ova) develop into drones (males) by the process of parthenogenesis.
Question. 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 are
(i) Since, sexual reproduction involves the fusion of two types of gametes male and female), they must have haploid number of chromosomes.
(ii) 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.
(iii) Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.
Question. 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. The formation of new plants from vegetative units (vegetative propagules) such as buds,tubers, rhizomes. etc., is called vegetative propagation (vegetative reproduction). It can be considered as a type of asexual reproduction as it involves the production of new individuals.
(i) by a single parent
(ii) without the formation and fusion of gametes
(iii) without resulting in any genetic or morphological variations.
Question. ‘Fertilisation is not an obligatory event for fruit production in certain plants’. Explain the statement.
Answer. Fertilisation is not an obligatory event for fruit production in certain plants. Some fruits are developed from unfertilised ovary called parthenocarpic fruits.
These are seedless fruits, such as pomegranate, grapes, etc. 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.
Question. In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
– Thinking Process
The process of development of embryo from the zygote is referred as embryogenesis.
During embryogenesis, zygote undergoes cell division (mitosis) and cell differentiation.
Answer. Cell divisions increase the number of cells in the developing embryo, while cell differentiation helps group of cells to undergo certain modifications to form specialised tissues and organs to form an organism.
At many stages of embryogenesis, if cell differentiation does not occur, the embryo cannot develop into a new organism. It will only remain as a mass of cells.
Question. List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.
– Thinking Process
The changes that are subsequent to pollination and fertilisation can be categorised under post-fertilisation changes (events).
Answer. In an angiosperm flower, the post-fertilisation changes occur as follows
Question. 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 pea, fruit is legume. The pea pod is developed from monocarpellary, unilocular and half superior ovary. At maturity, the fruit splits along the dorsal and ventral sutures and
discharge its seeds.
In gynoecium with single carpel, ovules are always attached to the ventral suture. This results in the fruit with marginal placentation. Thus, the seeds are arranged in a row in legume (pea) pod.
In tomato, the fruit is berry. It is fleshy fruit develop from superior or inferior ovary. In this, the margins of the carpels grow inward to the centre of the ovary dividing the central chamber into compartments called locules.
So that, the ovules are arranged radially on the axis, attached by placenta that is called axial placentation. That’s the reason the seeds are embedded in the juicy pulp.
Question. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and atleast one feature common to both structures.
Answer. The feature common to zoospores and conidia is that both of these are the asexual reproductive structures, which facilitate the process of reproduction in asexually reproducing organisms.
Question. Justify the statement ‘vegetative reproduction is also a type of asexual reproduction’.
Answer. In flowering plants, the units of vegetative reproduction such as runners, stolons, suckers,offsets, rhizome, corm, tuber, etc., are capable of giving rise to new offsprings. These
structures are called vegetative propagules.
In all these plants the formation of these structures does not involve two parents, the process involved is asexual. So, it can be said that vegetative reproduction is also a type of asexual reproduction.
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.
Question. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(i) Ovary (ii) Anther (iii) Egg
(iv) Pollen (v) Male gamete (vi) Zygote.
Answer. (i) Diploid (2n) (ii) Diploid (2n) (iii) Haploid (n)
(iv) Haploid (n) (v) Haploid (n) (vi) Diploid (2n)
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. 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. 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. What is vegetative propagation? Give two suitable examples.
Ans. 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. 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. 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.
Long Answer Questions
Question. Enumerate the differences between asexual and sexual reproduction.
Describe the types of asexual reproduction exhibited by unicellular organisms.
Answer. The differences between asexual and sexual reproduction are mentioned below
Asexual reproduction occurs usually in unicellular organisms, such as monerans and protists and in plants and certain animals.
It takes place in the following ways
(i) Binary Fission In this type of asexual reproduction, the parent organism divides into two halves, each half forming an independent daughter organism. e.g., Amoeba, Euglena, Paramecium.
(ii) Budding In this type of asexual reproduction, a daughter individual is formed from a small projection, the bud, arising from the parent body. e.g.,yeast, Hydra.
(iii) Fragmentation In this type of asexual reproduction, the parent body breaks into two or more fragment. Each body fragment develops into an organism. e.g., sponges, Selaginella.
(iv) Gemmule In this type of asexual reproduction, internal buds, called gemmules are involved. Gemmules are asexually reproduced mass of cells, that is capable of developing into a new organism. e.g., sponges.
(v) Sporulation In this type of asexual reproduction, dispersive structures called spores are released from the parent body that germinate under favourable conditions form new individuals.
(a) Motile spores are called zoospores and are found in aquatic animals. e.g., Albugo, Chlamydomonas.
(b) Non-motile spores are named as sporangiospores (e.g., Rhizopus, Mucor) and conidia e.g., Penicillium.
Question. 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. No, all the gametes formed from a parent organism do not have the same genetic composition.
It can be better understand with the help of the explanation given below Sexual reproduction in organisms generally involves the fusion of gametes from two different individuals. These gametes form by the process of gametogenesis. In the heterogametic species, gametes are of two types namely male and female. Gametes are haploid though the parent body from which they arise may be either haploid or diploid.
(a) A haploid parent like Monera, fungi, algae and bryophytes produce gametes by mitotic division. The number of chromosomes, i.e., the genetic composition remain same after such type of division.
(b) The diploid parent like pteridophytes, gymnosperms, angiosperms and most of the animals including human beings produces gametes by meiosis. In such organisms
(diploid), specialised cells called meiocytes (gamete mother cell) undergo meiosis.At the end of meiosis only one set of chromosomes gets incorporated into each gamete. It means the gametes formed contain a haploid number of chromosomes in contrast to the number of chromosomes in mother cells.
Question. 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. Follwing are the three reasons for the mode of sexual reproduction in higher group of organisms
(i) The sexual mode of reproduction ensures creation of new variants.
(ii) Genetically varied offsprings are produced that adapt to changes in environment and survive in all climatic conditions.
(iii) Sexual reproduction ensures the genetic recombination that results in variation which gives rise to evolution.
Question. Differentiate between (a) oestrus and menstrual cycles; (b) ovipary and vivipary. Give an example for each type.
Answer. The differences between oestrus and menstrual cycle are as follows
(b) The differences between ovipary and vivipary are as follows
Question. 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. Analyse the reasons for failure of fruit formation in rose.
– Thinking Process
Both these plants rose ai;l jnd tomato are 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. Rose plants produce large, attractive bisexual flowers, but they seldom produce fruits. The reasons for failure of fruit formation in rose are as follows
(i) Rose plants may not produce viable pollens, hence, no fertilisation can take place.
(ii) Rose plants may not have functional eggs.
(iii) Rose plants may have defective and non-functional ovule ,which is the female gametophyte generator.
(iv) There may be self-incompatibility.
(v) There may be internal barriers for pollen tube growth or fertilisation.
(vi) As rose plants are hybrids and reproduce vegetatively, there are chances for them to be sterile.
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.
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.
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. Differentiate between gametogenesis from embryogenesis.
Answer.
| S.No. | Gametogenesis | Embryogenesis |
| (i) | It is the formation of gametes from meiocytes (gamete mother cells). | It is the formation of embryo from zygote. |
| (ii) | This is a pre-fertilisation event. | This is a post-fertilisation event. |
| (iii) | The cell division during gametogenesis is meiotic in diploid organisms. | The cell division during embryogenesis is mitotic in diploid organisms. |
| (iv) | It occurs inside reproductive organs. | It occurs outside or inside the female body. |
| (v) | It produces haploid gamete. | It gives rise to diploid embryo. |
