WBBSE 10th Class Science Solutions Science & Environment Chapter 2 Continuity of Life

SUB-TOPIC – 1.3

SUMMARY

• Mitotic cell division is mainly divided into two parts karyokinesis and cytokinesis. In karyokinesis, division of nucleus occurs in four stages-prophase, metaphase, anaphase and telophase and after completing karyokinesis, cytokinesis or cytoplasmic division takes place.
• As said earlier, karyokinesis occurs in four phases-prophase, metaphase, anaphase and telophase. In prophase, chromatins are getting packed densely to form chromosome along with spindle fibre. In metaphase, chromosomes become arranged in equatorial line. Chromatids move to opposite poles, during anaphase. And lastly during telophase two daughter nucleus are formed at two poles of the cell.
• The cytokinesis process is quite different in animal and plant cell. Incase of animal, cleavage method takes place to complete this process but incase of plant cell, cell plate formation is mandatory for cytokinesis.
• Along with mitosis, meiosis cell division also takes place. It is important for the formation of gamete. Meiosis is of two types-Meiosis. I also known as reductional division and meiosis II, which also known as equational division. Like mitosis, meiosis also divided into karyokinesis through prophase, metaphase, anaphase and telophase and cytokinesis.
• Though in mitotic division the number of chromosome stays constant, But in meiotic division the chromosome number reduce to half.
• During gamentogenesis by meiosis, crossing over occur between two non-sister chromatids of two homologous chromosome, help to produce variation.

Long Answer Type Questions

1. Prophase in plant cells: The events occurring during prophase in plant cells are as follows-[1] During this phase, the nucleus swells. [2] The chromatin reticula start coiling, get dehydrated and form chromosomes.
   
   [3] Each chromosome appears with two chromatids, which remain attached to each other by the centromere. [4] Chromatids undergo coiling or spiralisation to make the chromosome thick. [5] Nucleolus gradually diminishes in size. At the end of this phase, both nucleolus and nuclear membrane disappear. [6] Within the cytoplasm, microtubules grow, which form the anastral spindle during the later phases.
2. Prophase in animal cells: The above mentioned events also occur in animal cells except the development of microtubules for spindle formation. Other than these, certain typical events occur in animal cells during prophase. These are as follows- [1] The two centrosomes with paired centrioles, formed during interphase, start moving to two opposite poles of the cell during early prophase. [2] Astral rays radiate from the two centrosomes. Gradually, the rays grow in length, which in the later phase, prepare the astral spindle.
   

1. Metaphase in plant cells: The events occurring during metaphase in plant cells are as follows-[1] Nuclear membrane and nucleolus disappear completely. [2] Cytoplasmic microtubules arrange to form spindle. This spindle is formed without involvement of centrosome, therefore, it is called anastral spindle. This spindle comprises two types of fibres, which are-(i) chromosomal spindle fibres, which bind one pole of the spindle to centromere of chromosomes and (ii) continuous spindle fibres, which connect the two poles of the spindle. [3] All the chromosomes arrange along the equatorial plane of the dividing cell and the chromatids of each chromosome stay parallel to that plane. This typical distribution of the chromosomes forms the metaphase plate or equatorial plate across the cell. [4] Chromosomes become the densest and thickest. [5] At the end of this phase, the centromere of each chromosome starts to split longitudinally.
   
2. Metaphase in animal cells: All the above mentioned events occur in animal cells also, except the spindle formation. Here, the spindle is formed by the extension of astral rays from the centrioles, positioned at the two opposite poles of the dividing cell.

1. Anaphase in plant cells: The events occurring during anaphase, in plant cells, are as follows-[1] Centromere of each chromosome splits longitudinally, as a result two sister chromatids separate from each other with their own share of centromere and emerge as two daughter chromosomes. [2] Centromere of each daughter chromosome remains attached to chromosomal spindle fibre. [3] Inter-polar or continuous spindle fibres connect the two poles of the spindle. [4] Gradually, the chromosomal fibres contract to pull half of the daughter chromosomes towards one pole and remaining half to the opposite pole. This is called anaphasic movement. [5] During anaphasic movement, metacentric, sub-metacentric, acrocentric and telocentric chromosomes appear like the English letters ‘V’, ‘L’, ‘J’ and ‘T’ respectively, based on the position of centromere on the chromosome
2. Anaphase in animal cells: The above mentioned events also occur during anaphase in animal cells. Here, inter-zonal spindle fibres cluster in between separating chromosomes to form columnar stem bodies, which help in anaphasic movement.

1. Telophase in plant cells: The events occurring during telophase, in plant cells, are as follows- [1] At the start of telophase, equal number of chromosomes reach the two opposite poles of the spindle. [2] The chromosomes uncoil and rehydrate to become thin and long to form chromatin. [3] Nuclear membrane reappears around chromatin. [4] Nucleolus reappears within nucleus. [5] Finally, two equal number of chromosome-bearing and morphologically identical nuclei form within the dividing cell. [6] After formation of two daughter nuclei, during the end of telophase, cell plate formation starts by deposition of phragmoplast granules in the equatorial plane of the cell.
2. Telophase in animal cells: The events of telophase in animal cells are same as that of the plant cells except, in case of animal cell a cleavage or furrow appears in between the cytoplasm during the late telophase stage, instead of phragmoplast.

1. Cytokinesis in plant cells: The events which occur during cytokinesis in plant cells are as follows-[1] At the end of telophase, microtubules, microfilaments and endoplasmic reticular elements arrange along the equatorial plane to form phragmoplast. [2] Golgi vesicles align along the two sides of the phragmoplast and form the cell membrane of the two daughter cells. [3] In course of time, the phragmoplast forms a thin cell plate, which transforms into middle lamella, composed of calcium and magnesium pectate. [4] Cellulose, hemicellulose, callose etc. accumulate at two sides of the middle lamella to form the primary cell wall. With the formation of the primary cell wall, the cytoplasm of the mother cell separates completely to give rise to two daughter cells.
   
2. Cytokinesis in animal cells: The events which occur, during cytokinesis in animal cells are as follows-[1] At the start of telophase, the cell membrane moves inward along the equatorial line to form a constriction or furrow. Microfilaments accumulate below the cell membrane and their interaction pull it to develop the furrow. [2] With time, as the cell enters cytokinesis, the furrow grows deeper and finally separates the cytoplasm to form two identical daughter cells.
   

1. Chromosomal separation: [1] During prophase-I of meiosis-I, exchange of chromosomal materials occurs between homologous chromosomes. [2] In metaphase-I, the homologous chromosome pairs arrange along the equatorial plane. [3] In anaphase-I, homologous chromosome pairs separate and two separated sets of chromosomes move towards two opposite poles of the cell.
2. Reduction in chromosome number: In meiosis-I, each daughter nucleus gets half the pairs of homologous chromosomes. Therefore, chromosome number of daughter cell reduces to half of the somatic cell.
   
3. Crossing over: Exchange of portions between non-sister chromatids of homologous chromosomes occurs in meiosis-I. This is called crossing over. In this process, the chromosomes get new genetic combinations.

1. Separation of chromosomes: In anaphase of meiosis-II, centromere of each chromosome splits, sister chromatids get their share of centromeres and are transformed into daughter chromosomes. Two sets of daughter chromosomes move to two opposite poles of the cell and get into two daughter nuclei.
   
2. Equational division: Unlike mitosis, meiosis-II involves haploid set of chromosomes. However, equal division of chromosomes takes place in meiosis-II. As a result, chromosome number of the daughter cells of meiosis-1 and daughter cells of meiosis-II remains identical.

1. Crossing over: During prophase, homologous chromosomes arrange in parallel pairs, this event is called synapsis. The paired homologous chromosomes are known as bivalent. Later, each chromosome splits longitudinally into two sister chromatids. In this state, the bivalent appears with four chromatids, which is called tetrad. While coiling, the non-sister chromatids of a tetrad cross over each other at some points, which appear as chi (x). These points are called chiasmata. During crossing over, non-sister chromatids reciprocally exchange their segments, which results into new allelic combinations in the homologous chromosomes.
   
2. Reduction in chromosome number: In anaphase-I, homologous chromosome pairs separate and the two separated sets of chromosomes move towards two opposite poles of the cell. Finally, during telophase-I, each set of chromosomes gets into each of the daughter nuclei. By this process, diploid number of chromosomes of the mother cell becomes haploid in daughter cells.

1. Significance of crossing over: By means of crossing over, genetic recombination takes place, which creates variation. Crossing over confirms the linear arrangement of genes on a chromosome.
2. Significance of reduction in chromosome number: In meiosis, chromosome number reduces to give rise to haploid gametes. After fertilisation of two haploid gametes, diploid zygotes are formed. By this process, the chromosome number of a species remains constant.

1. Growth in size: Number of somatic cells in any organism increases by continuous mitotic division. By this process, the overall size of the organism increases. Unicellular zygote undergoes mitosis to develop into a multicellular organism.
2. Cell replacement and healing of wounds: The damaged and aged cells of the body are replaced by new cells through mitotic division of the healthy neighbouring cells. This process heals any wound of our body. For example, the epidermal cells of our body are depleted continuously by friction. These are replenished very quickly by the process of mitosis.
3. Regeneration: Certain animals have the ability to regenerate their lost body parts. Arms of starfish, appendages of prawns and crabs, tail of house-lizard etc. can be regenerated. Mitotic cell division makes it possible.
4. Reproduction: Several unicellular organisms undergo mitosis to perform asexual reproduction. Amoeba, Paramoecium, yeast etc. perform asexual reproduction by mitosis. The vegetative reproduction in plants like water hyacinth, sweet potato, Bryophyllum etc. occur by mitosis.
5. Equational division: The daughter cells produced by mitosis are genetically and morphologically identical to their mother cell. This process is essential to maintain integrity of cellular character of a tissue.

1. Keeping chromosome number of a species constant: During meiosis, chromosome number in daughter cells reduces to half of that of their mother cell. The haploid gametes, produced by this process, undergo fertilisation to produce a diploid zygote, which finally develops into a full-grown organism. By this process, chromosome number of parents remains identical to that of their offspring. If there had been no meiosis, the number of chromosomes in sexually reproducing organisms would have increased geometrically with generations.
2. Origin of genetic variation: During crossing over, exchange of segments of chromatids takes place between homologous chromosomes. By this process, recombination of genes occurs, which results into origin of new genetic variations.
3. Gamete formation: By meiosis, haploid gametes (sperms and eggs) are formed from diploid germ mother cells.
4. Maintenance of alternation of generation: By this cell division, a cyclic alternation occurs between diploid sporophytic generation and haploid gametophytic generation in several organisms. Thus, alternation of generation is maintained.

Short Answer Type Questions

Answer in a single word or sentence

Fill in the blanks

State true or false

TOPIC – 2

SUMMARY

• Reproduction is an important event for existence of living organisms.
• Reproduction is mainly of two types-asexual reproduction and sexual reproduction. Vegetative reproduction is a special type of asexual reproduction. Formation of new offsprings from somatic cell without fertilization is called asexual reproduction and formation of new offspring by fusion of gametes is called sexual reproduction. Formation of new individual directly from the segment of parent body is called vegetative reproduction.
• Asexual reproduction is mediated by single parent cell, whereas in sexual reproduction two parent cells need to participate. In sexual reproduction, due to meiotic division, variation occur in new offsprings, so the offsprings with new characteristics will be produced.
• Asexual reproduction may be of various types like fission [Amoeba] budding [Hydra, Yeast], fragmentation [Spirogyra), regeneration [Planaria] and sporulation [Moss, fern]
• In vegetative reproduction, a part of plant cell can produce new plantlets. It is of two types-natural and artificial. In natural process, shoot, root or leaf can give rise to new plantlets, whereas in artificial process cutting, grafting or micropropagation can mediate the generation of new plantlets.
• The alternation of a haploid and a diploid generation in the life cycle of an organism is called alternation of generations. It is most distinct in fern.

Long Answer Type Questions

1. Increasing population size: By means of reproduction, new individuals are born. As a result, the number of individuals in a population increases and the race of a species is maintained.
2. Maintaining flow of genes: By reproduction, the genes of a species flow from one generation to the next maintaining the hereditary characters.
3. Maintaining ecological balance: Natural or unnatural death of individuals reduce the population size of a species. By reproduction, this loss is replenished in the nature. This process keeps ratio of different species in an ecosystem constant and thus maintains the ecological balance.
4. Variation: By sexual reproduction, different genetic variations come into existence. These variations assist any species to adapt in its surroundings and finally help in the evolution of new species.

2. Briefly describe the different types of reproduction.

Ans. Types of reproduction

Two types of reproduction are seen in the living world. These are-[1] Asexual reproduction and [2] Sexual reproduction.

1. Asexual reproduction: The type of reproduction, in which formation of gametes and their fertilisation do not occur, instead, certain body cells or specialised cells, like spores, divide to form the progeny, is known as asexual reproduction. In this process, only one parent is required. All parental characters are inherited by the offspring. All the offsprings become genotypically and phenotypically ‘identical to their mother. Example-Bacteria, several protists like Amoeba, and some fungi like Mucor, Penicillium etc. perform asexual reproduction.
   
2. Sexual reproduction: The type of reproduction, that involves union of two different types of gametes to produce a zygote and development of a new progeny from it, is known as sexual reproduction. Most of the plants and animals perform sexual reproduction. This process requires a male and a female member of a same species or a single organism with two different types of gametangia to produce male and female gametes. In this process, union of male and female gametes takes place. As a result, the progeny gets the genotypic and phenotypic characters different from its parents. Sexual reproduction essentially requires meiotic cell division for gamete formation and for keeping the chromosome number of a species constant. Example-Sexual reproduction occurs in all higher animals and plants such as frog, man, birds, angiosperms etc.

3. Describe the five processes of asexual reproduction with one suitable example for each.

Ans. Processes of asexual reproduction

The following types of asexual reproduction can be seen in organisms-

1. Fission: In most of the unicellular organisms two or more offspring are produced through mitosis or amitosis. This process is called fission. Some example are given below.
   [A] Amoeba
   (i) Binary fission: In favourable condition, the nucleus of Amoeba undergoes amitotic division and gives of two nuclei. Its cytoplasm divides longitudinally creating a furrow and forms two offsprings.
   (ii) Multiple fission: In unfavourable condition, pseudopodia of Amoeba are destroyed and the body gets encapsulated by cyst wall. Inside the cyst numerous small spores are formed through multiple fission of nucleus and cytoplasm. This type of multiple fission is called sporulation. When the condition becomes favourable, spores come out rupturing the cyst wall and give rise to new Amoeba offsprings.
   [B] Plasmodium: In case of Plasmodium multiple fission takes place in two stages-Schizont and sporont. In the stomach of female Anopheles mosquito, numerous Plasmodium offsprings are born by the multiple fission called schizogony and sporogony is schizont and sporont stage respectively. The Plasmodium offsprings born through schizogony and sporogony are called merozoit and sporozoit respectively.
2. Budding: Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or bud of the parent body due to cell division at one particular site. Some example of budding are given below.
   [A] Yeast: Due to unequal division of yeast parent cell, small outgrowth or bud is formed which contains parent’s nucleus. Later on the bud separates from the parental body and develops into new yeast. In special case, the bud of yeast divides many times in torula stage through torulation process and forms mycelium.
   [B] Hydra: In case of Hydra, bud is formed outside the parent body (exogenous bud). After formation of oral aperture, tentacles etc. when the offspring matures, it gets detached from the parent body.
3. Fragmentation: The type of asexual reproduction where parent body is fragmented into two or more pieces and each fragment turns into new offspring, is called fragmentation. Example- The filamentous body of Spirogyra, an alga gets fragmented due to water current or external damage. Each fragment undergoes mitotic cell division and gives rise to new offspring.
4. Regeneration: The type of asexual reproduction where a mere body part of parent organism creates a new offspring, is called regeneration. It is also called morphallaxis. Example-If any body part of Planaria, a flat worm gets detached, it forms a new offspring. This process also can be seen in Hydra.
5. Sporulation: Sporulation is a type of asexual reproduction in which unicellular spores are produced in moss, fern and fungi, they are dispersed and give birth to new offsprings. Examples of sporulation are given below.
   [A] Fungi: In fungi, spores with different structure and with or without motility can be seen. These spores germinate in favourable condition and new fungi are born. Different types of spores are-motile zoospores, non-motile aplanospores, thick walled chlamydospores, oidia and conidia formed from fragments of filaments, sporangiospore formed in sporangium.
   [B] Moss and fern: Spores are formed from the sporophytic tissue of sporophytic plant body of moss. In sporangium of sporophytic plant body of fern, spores with similar or different shapes are formed.

4. Describe the mechanism of fission in Plasmodium with diagram.

Ans. Mechanism of fission in Plasmodium

Plasmodium is a unicellular parasitic protist. It causes malaria in human beings. It goes through a number of multiple division to complete its life cycle. In human liver cells, this type of division is called schizogony. The stage of Plasmodium undergoing schizogony is known as schizont. A schizont undergoes several successive karyokinesis to produce many nuclei in it. Then each nucleus undergoes cytokinesis and liberates as a tiny daughter cells, called merozoites. By this multiple fission, several hundreds of merozoites are formed, which again attack neighbouring liver cells and propagate in the same manner. Inside mosquito gut, the oocyst or sporont phase undergoes similar type of multiple fission to produce sporozoites. This type of division is called sporogony.

5. Briefly describe the asexual reproduction of bryophyta, pteridophyta and fungi through spore formation.

Ans. Bryophytes

Bryophytes have two phases in their life cycle-the sporophytic (2n) and gametophytic (n) phase. The diploid sporophyte produces spores through meiosis in the specialized structure called sporangium. All the spores are look alike i.e. homosporous. The sporangia are located in the capsule part of sporophyte. The spores (n) are aplanospores, endogenous and when fall on suitable substratum produce new gametophyte.

Pteridophyta

In pteridophytes spores (n) are formed by sporophytes (2n) in specialized sporangium. The spores may be homosporous or heterosporous. Homosporous spores are alike and produce a bisexual gametophyte. Heterospores are of two types with microspore producing male gametophytes and megaspore producing female gametophyte. Spores are endogenous and haploid in nature as they are produced through meiosis from spore mother cell.

Fungi

The spores in fungi may be endogenous in origin when produced in sporangia or may be exogenous origin like conidia producing by cutting the tip of fungi. In fungi the endogenous spores are formed inside sporangia through mitosis. The hyphal tip swells forming the sporangia. The nuclei undergoes free nuclear division. Each nuclei with cytoplasm and membrane becomes a spore. The spores on suitable substratum germinate to produce new hypha.

6. What is meant by vegetative propagation? Briefly describe the processes of natural vegetative propagation.

Part Question, ‘The adventitious leaf bud plays significant role in natural vegetative propagation of plant’ Evaluate the validity of the statement with a proper example. 

Ans. Vegetative propagation

The asexual reproduction, in which any portion of the vegetative body of certain plants separates out from the mother’s body and finally grows into a new individual by mitotic cell division, is known as vegetative propagation.

Processes of natural vegetative propagation

Vegetative propagation occurs by the growth of different parts of plants naturally, which are mentioned below.

1. By leaves: Certain plants like Bryophyllum, Bigonia etc. develop buds along the edges of their leaves. These are called leaf buds. These buds grow adventitious roots from their base. When such a leaf detaches from the plant body and comes in contact with the soil, each of the buds grows into an individual daughter plant.
2. By roots: Roots of sweet potato, pointed gourd etc. grow adventitious buds. These are called root buds. When detached from the root, these buds grow into new daughter plants.
3. By stem: Vegetative propagation by stem occurs by two different types of modified stems[1] Underground modified stems-Tuber of potato, bulb of onion, rhizome of ginger, turmeric etc. are underground stems, modified for storage of food. These organs have buds, which may grow into daughter plants. [2] Sub-aerial modified stems-Nodes of sub-aerial modified stems of Mentha, Marsilea, Oxalis, Centella, water hyacinth, Chrysanthemum etc. plants adventitious roots. When detached from the mother plant, the rooted branches grow as daughter plant.

7. Mention the advantages and disadvantages of vegetative propagation.

Ans. Advantages of vegetative propagation

[1] Identical character-bearing plants can be produced by vegetative propagation. [2] By this process, several daughter plants may be produced from a single mother plant within a brief period of time. [3] Vegetative propagation can be practiced in any season throughout a year. [4] Desired characters of the mother plant remain intact in the daughter plants.

Disadvantages of vegetative propagation

[1] Daughter plants from vegetative propagation do not have any newer character. [2] The daughter plants formed by this type of reproduction do not show any variation. Therefore, these plants cannot adapt themselves to changed environment. [3] Vegetative propagation does not provide any chance for evolution of a new species. Hence, there is a chance of extinction.

8. How is layering technique used for artificial vegetative propagation of certain plants? How is the “gootee” prepared for artificial vegetative propagation in certain plants? 

Ans. Use of layering technique for artificial vegetative propagation

In layering technique, a comparatively young and tender twig is bend, such that the nodal of it touches the soil. Now, the portion of the branch, touching the ground, is covered with a of moistened soil and then a brick or stone is placed on it. The layered portion is watered regularlyAfter few weeks, adventitious roots develop from that portion of the stem under the soil. The branch is then chopped off from the mother plant and the twig with roots is planted elsewhere to grow further as a progeny. Layering is applicable to plants like lemon, jasmine, wood-apple etc.

Preparation of “gootee” for artificial vegetative propagation

In this artificial vegetative propagation technique, a strong and stiff twig of a shrub or tree is selected to prepare a gootee. First, few inches of the bark is peeled off with a knife. Now this portion is covered with a muddy mixture of organic manure and soil. Then the soil layer is wrapped with moistened rag or coir. An additional layer of polythene sheet may be wrapped to prevent quick drying. After few weeks, adventitious roots grow there and appear on the surface of the gootee. Now, the twig is chopped off and used for plantation. Gootee is applicable in plants like mango, guava, litchi etc.

9. Briefly describe the methods of cutting and grafting for artificial vegetative propagation.

Ans. Methods of artificial vegetative propagation

Artificial vegetative propagation of plants is done in different ways, which are mentioned below.

1. Cutting: In this process, 20-30 cm long twigs of certain plants are cut up from the mother plant. These are then planted in moistened soil. Within a week or so, adventitious roots develop from the nodes and the twig grows as an individual plant. Cutting is successfully practiced upon rose, china rose, drumstick plants etc.
   
2. Grafting: Grafting is the process of artificial vegetative propagation by which younger branches or buds of a superior variety of plants are affixed with an older and healthy stem of same species to grow better varieties of plants in short time. It is of two types-scion grafting and bud grafting.
   
   [A] Scion grafting: In scion grafting, stem of two different varieties of plants are attached together. Of these two, the stem of the older one is chopped off leaving a portion of it above the ground. This rooted portion is called the stock. A younger stem branch with superior features is affixed with the stock, which is called the scion. The end of the scion is cut with a sharp knife to StockGrafting give it a shape of wedge. The top or side of the stock is also cut to allow the scion to fit there perfectly. This region is wrapped with moist rag or coir. After some days, the scion joins to the stock and grows further.
   [B] Bud grafting: In this process, axillary bud from a superior variety of plant is sliced off. Now a T shaped slit is made on the bark of a healthy quick-growing plant of the same species. The bud is then fitted in the slit and is tied with string. Finally the bud joins to the stem and grows as a branch with superior features. Grafting is applicable for plants like mango, guava, litchi etc.

10. Classify sexual reproduction based on the nature of gametes. Name the different types of asexual reproduction with example.

Ans. Types of sexual reproduction

Based on the nature of gametes, sexual reproduction can be classified into three types. These are-

1. Anisogamy: It occurs by the union of two morphologically non-identical gametes.
2. Isogamy: It occurs by the union of two morphologically and physiologically identical gametes.
3. Oogamy: This type of sexual reproduction occurs by the union of a smaller motile and a larger non-motile gamete.

Types of asexual reproduction

In the living world, different types of asexual reproduction are seen. These are-[1] Fission (Amoeba, Plasmodium), [2] Budding (Yeast, Hydra), [3] Fragmentation (Spirogyra), [4] Sporulation (Moss, fern, fungi), [5] Regeneration (Planaria).

11. Mention the advantages and disadvantages of sexual reproduction.

Ans. Advantages of sexual reproduction

[1] By sexual reproduction, genetic characters of the parents are inherited by the offsprings and this event is carried forward in the following generations as well. [2] In sexual reproduction, recombination of genes takes place, which results into formation of new genetic variations. [3] New genetic variations, which develop among the progeny, help them to adapt efficiently with the changing environment. [4] Due to better adaptability, progeny of sexual reproduction come out as winner in the struggle for existence. They get the favour of natural selection and finally take part in evolution of new species.

Disadvantages of sexual reproduction

[1] Sexual reproduction is a slow process. Therefore, it takes longer time to produce offspring.

[2] Availability of two different types of gametes is essential, which may not always be available.

[3] Success rate of fertilisation depends upon large number of male gametes, which may not always be available.

12. Mention the advantages and disadvantages of asexual reproduction. 

Ans. Advantages of asexual reproduction

[1] Asexual reproduction involves only one parental member, so it is an easier process. [2] By this process, numerous offsprings are produced at a time. [3] This process needs very little energy. [4] This is a very simple process and takes very short time to complete. [5] The parental features are retained within the progeny without any change. [6] All progeny grow in close vicinity to its mother. Therefore, the progeny adapt easily to the known environment.

Disadvantages of asexual reproduction

[1] Meiosis does not occur in asexual reproduction. Therefore, recombination of genes does not occur. [2] Variations do not occur in the offsprings of asexual reproduction. [3] The chance of adaptability of these offsprings is very low. Therefore, there is possibility of their extinction.

13. What is meant by alternation of generations? Mention the importance of meiosis in alternation generations?

Ans. Alternation of generations

The cyclic alternation between haploid gametophytic and diploid sporophytic generations in the life cycle of any sexually reproducing organism is called alternation of generation. Example-In plants like moss, fern etc. and protists like Paramoecium, Monocystis etc. distinct alternation of generation is seen.

Importance of meiosis in alternation of generations

During alternation of generation, cyclic rotation continues between haploid (n) and diploid (2n) generations. Diploid spore mother cells divide by meiosis to give rise to haploid spores. These spores germinate to grow as haploid (n) gametophytes. The gametophytes carry separate gametangia to produce haploid male and female gametes. These gametes fertilise to form diploid zygotes to initiate the sporophytic generation. That is why meiosis is important for alternation of generations.

Short Answer Type Questions

1. Mention two characteristic features of sexual reproduction.

Ans. Two characteristic features of sexual reproduction are as follows-[1] In sexual reproduction, two different gametes, i.e., male and female gametes, unite to form the offspring. [2] The progenies are born with variations, which in long run, help in the formation of new and evolved species.

2. How is a definitive nucleus formed during sexual reproduction of angiospermic plants?

Ans. Within the embryo sac of ovule of flowers in angiospermic plants, two haploid (n) polar nuclei unite together. As a result, diploid (2n) definitive nucleus is formed.

Polar nucleus (n) + Polar nucleus (n) = Definitive nucleus (2n)

3. What is syngamy?

Ans. Syngamy is a the complete and permanent union of two different gametes, i.e., male and female gametes, outside the gametangia. Syngamy is found in all sexually reproducing organisms.

4. What is oogamy?

Ans. Oogamy is a type of sexual reproduction, where a small and motile male gamete fertilises a large and non-motile female gamete. This is noticed among some algae like Oedogonium, Chara etc. and in all higher plants and animals.

5. What is isogamy?

Ans. Isogamy is a type of sexual reproduction where two morphologically and physiologically identical gametes unite to form a zygote. Isogamy occurs in certain lower organisms like Chlamydomonas, Monocystis etc.

6. What is anisogamy?

Ans. Anisogamy is a type of sexual reproduction where two morphologically different gametes unite to form the zygote. This type of sexual reproduction is seen in certain species of Chlamydomonas.

7. What is meant by asexual reproduction?

Ans. The type of reproduction, in which formation of male and female gametes and their fertilisation do not occur. Instead, certain body cells or specialised cells like spores divide to form the progeny. This is known as asexual reproduction.

Example-Fungi, like yeast and certain lower animals perform asexual reproduction.

8. What is meant by asexual reproduction by fission?

Ans. For propagation, most unicellular organisms undergo two or multiple number of cell divisions to form two or more offsprings, either through mitosis or amitosis. This type of asexual reproduction is called fission. Example-Amoeba and Plasmodium perform asexual reproduction by binary and multiple fissions respectively.

9. What is budding?

Ans. In certain lower organisms, a small portion of the vegetative body swells out as an outgrowth and finally it gets detached from the mother body and grows as a new progeny. This of asexual type reproduction is called budding. ExampleBudding is commonly seen in yeast and Hydra.

10. What is meant by sporulation?

Ans. In certain lower plants, numerous, typically thick-walled cells or spores are produced in sporangia. On attaining maturity, these spores are liberated from the mother plant and fall on ground and finally germinate to form the new progeny. This type of asexual reproduction is own as sporulation. Example-Sporulation occurs in fungi, moss, fern etc.

11. What is binary fission?

Ans. Binary fission is a type of asexual reproduction found in some prokaryotes and some unicellular eukaryotes in which the parent cell divide amitotically into two daughter cell. e.g. Amoeba.

12. What are the different type of fission found in Amoeba.

Ans. Amoeba is an unicellular eukaryote which reproduce asexually by two methods binary fission and multiple fission. Amoeba produce two daughter cells from a parent cells at a time by binary fission and numerous daughter cells by free nuclear division through multiple fission.

13. What are zoospores?

Ans. Certain asexual spores are capable of locomotion with the help of cilia or flagella. These spores are called zoospores. Example-Spores of Volvox, Chlamydomonas etc. are zoospores.

14. What is meant by zygospore?

Ans. In certain lower organisms, two different a diploid cell by gametes unite to form conjugation, which develops a thick protective cell wall to form a typical spore. This type of spore is known as zygospore. Example-Spirogyra, Oedogonium have zygospores.

15. What is propagule?

Ans. The plant part from which a new plant is formed during reproduction is called propagule. Bud is a propagule of asexual reproduction and seed is a propagule of sexual reproduction.

16. What are the processes of asexual reproduction in spirogyra and planaria?

Ans. Spirogyra mediate their reproduction by fragmentation, whereas planaria make it by regeneration.

17. What is gametophyte and sporophyte?

Ans. The plant gamete which is produced from spore and produce gamete is called gametophyte. The plant which is produced from zygote and produce spore is called sporophyte.

18. What is meant by artificial vegetative propagation? 

Ans. In the practice of agriculture and horticulture, vegetative propagation of different plants is done under human manipulation. This is known as artificial vegetative propagation.

19. What is stolon?

Ans. The internodes of certain herbs grow to form arches which remain above the ground. However, their nodes remain affixed with the soil by adventitious roots. This type of sub-aerial modified stem is known as stolon, which is seen in plants like Mentha, strawberry etc.

20. Give examples of few plants, which naturally perform vegetative propagation.

Ans. Many plants naturally perform vegetative propagation. These include sweet potato, potato, pointed gourd, onion, water hyacinth, Bryophyllum etc.

21 What is meant by stock and scion? 1

Ans. In grafting, stems of two different varieties of plants are attached together. Of these two, the stem of the older plant is chopped off leaving a portion of it above the ground. This rooted portion is called the stock and the younger stem branch with superior features which is affixed with the stock, is called the scion.

22. Why grafting is not possible in paddy or maize plant.

Ans. During grafting stem of two different varieties of plant are attached together at the cambium region. So, for the grafting process, cambium play a major role. But paddy and maize, are monocot in nature and they do not contain cambium. So due to lack of cambium, grafting is not possible in these plants.

23. Which type of root is seen in sweet potato and what is its function?

Ans. Fleshy tuberous adventitious roots are seen in sweet potato. The function of roots of sweet potato is to store food. It also helps in vegetative propagation.

24. What is micropropagation?

Ans. The process by which tissues, cells, protoplasts or organs are collected from plants and cultured in laboratories within proper nutritive medium to produce progeny plants, is known as micropropagation. By means of micropropagation large number of identical progeny plants, can be produced within a short period.

25. What is totipotency?

Ans. The inherent ability of any cell to divide and develop into a full-grown plant under proper environmental condition outside the living body, is known as totipotency. Due to this unique ability, small segments of plant tissue can be

26. Mention two distinctive features of micropropagation. 

Ans. Two distinctive features of micropropagation are as follows-[1] Micropropagation is a tissue culture technique by which several clones of plants can be produced vegetatively. [2] By this process, the number of desired varieties of plants can be increased within a short time.

27. Mention the disadvantages of micropropagation.

Ans. The disadvantages of micropropagation- [1] In micropropagation, no genetic variations are developed. Therefore, the plants produced in this process have lesser adaptability. [2] Due to lack of variation, micropropagation reduces the chance of evolution.

28. What is meant by tissue culture?

Ans. The biotechnological process in which tissues, collected from different organisms are cultured in laboratory within proper nutritive culture medium, under suitable sterile environment, is known as tissue culture. This process can form sprouts within laboratories from small plant tissues.

29. Which plant hormones are mixed with special tissue culture medium and why?

Ans. Auxin and cytokinin are the hormones which are mixed in special tissue culture medium. These two hormones regulate the growth of the cultured tissues. Therefore, these two growth regulators are used in tissue culture medium.

30. What are explants?

Ans. The small plant parts, tissues, or cells, which are collected from plant bodies for culturing in laboratories, are called explants. The meristematic tissue-rich portions of plants, like apical buds, root tips, tubers are mostly collected as explants.

31. What is callus?

Ans. While growing in sterile culture media, mitosis starts in explants. After some time, a cluster of undifferentiated cells are produced from the cells of explants. This cluster of cells is known as callus. The cells of callus are totipotent in nature, which may divide to form a full-grown plant.

32. What is meant by caulogenesis?

Ans. Development of stem from a callus, within a tissue culture medium, is called caulogenesis. This is a tissue differentiation process, which is initiated by higher concentration of auxin and cytokinin in the culture medium.

33. What is meant by rhizogenesis?

Ans. Development of root from a callus, within a tissue culture medium, is called rhizogenesis. This is a tissue differentiation process, which is initiated by lower concentration of auxin and cytokinin in the culture medium.

34. What is meant by histogenesis? 

Ans. Development of xylem and phloem tissues by the differentiation of a callus within a tissue culture medium is called histogenesis. This is a tissue differentiation process, which is regulated by auxin and cytokinin in the culture medium.

35. What is alternation of generations?

Ans. The alternation of a haploid (n) and a diploid (2n) generation in the life cycle of an organism showing sexual reproduction is called alternation of generations. e.g. Fern.

36. Mention the importance of alternation of generations.

Ans. The cyclic rotation of haploid and diploid generations helps in keeping the chromosome number constant. Alternation of generations also helps in maintaining genetic identity of any organism for generations.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. Which of the following organisms performs reproduction by fission?

A. Plasmodium

B. Hydra

C. Fern

D. Planaria

Ans. A

2. Which of the following organisms performs reproduction by budding?

A. Amoeba

B. Plasmodium

C. Hydra

D. Planaria

Ans. C

3. Amoeba performs-

A. Fission

B. Budding

C. Fragmentation

D. Sporulation

Ans. A

4.  Yeasts reproduce by-

A. Fragmentation

B. Sporulation

C. Regeneration

D. Budding

Ans. D

5. Which of the following organisms does not perform reproduction by spore formation?

A. Moss

B. Planaria

C. Fern

D. Fungi

Ans. B

6. Fragmentation is seen in-

A. Hydra

B. Yeast

C. Plasmodium

D. Spirogyra

Ans. D

7. Which of the following organisms performs reproduction by regeneration?

A. Hydra

B. Spirogyra

C. Planaria

D. Amoeba

Ans. C

8. Adventitious bud formation occurs in leaves of which of the following plants?

A. Sweet potato

B. Potato

C. Water hyacinth

D. Bryophyllum

Ans. D

9. Which of the following organisms performs reproduction by sporulation?

A. Fungi

B. Planaria

C. Hydra

D. Amoeba

Ans. A

10. An example of juicy root is-

A. Water hyacinth

B. Sweet potato

C. Potato

D. Bryophyllum

Ans. B

11. Which of the following organisms shows both asexual as well as sexual reproduction?

A. Hydra

B. Amoeba

C. Paramoecium

D. Horse

Ans. C

12. Grafting is a technique of-

A. Sexual reproduction

B. Asexual reproduction

C. Vegetative propagation

D. Parthenogenesis

Ans. C

13. Reproduction in plants by cutting method is a type of-

A. Artificial vegetative propagation

B. Asexual reproduction

C. Sexual reproduction

D. Natural vegetative propagation

Ans. A

14. The reproductive stage, produced by conjugation of similar gametes, is called-

A. Zygote

B. Zygospore

C. Azygospore

D. Oospore

Ans. B

15. Which of the following performs reproduction by conjugation?

A. Spirogyra

B. Mucor

C. Moss

D. Fern

Ans. A

16. Fern performs reproduction by-

A. Budding

B. Fragmentation

C. Spore formation

D. Regeneration

Ans. C

17. Fertilised ovum is known as-

A. Spermatozoon

B. Zygote

C. Zygospore

D. Spore

Ans. B

18. An unfertilised egg, taking part in parthenogenesis, is known as-

A. Zygote

B. Zygospore

C. Azygospore

D. Oospore

Ans. C

19. The process of ovum formation is called-

A. Spermatogenesis

B. Oogenesis

C. Parthenogenesis

D. Gametogenesis

Ans. B

20. The process of sperm formation is known as-

A. Spermatogenesis

B. Oogenesis

C. Parthenogenesis

D. Gametogenesis

Ans. A

21. Union of two identical gametes is called-

A. Isogamy

B. Anisogamy

C. Oogamy

D. Syngamy

Ans. A

22. The process of reproduction, in which offsprings are formed by division of body cells without union of gametes, is called-

A. Sexual reproduction

B. Vegetative propagation

C. Asexual reproduction

D. Parthenogenesis

Ans. C

23. In which of the following organisms sexual dimorphism is seen?

A. Cockroach

B. Earthworm

C. Amoeba

D. Plasmodium

Ans. A

Answer in a single word or sentence

1. What is the process of formation of similar or dissimilar character-bearing offsprings from parent organism called?

Ans. Reproduction

2. What is the main cause of reproduction?

Ans. To maintain the race of a species

3. What is the unit of sexual reproduction?

Ans. Gamete

4. In which organ the spores for asexual reproduction of a plant are produced?

Ans. Sporangium

5. What is produced after the union of sperm and ovum, during sexual reproduction?

Ans. A zygote is produced.

6. Name a dioecious or unisexual plant.

Ans. Papaya plant

7. Name a bisexual but monoecious plant.

Ans. Mango plant

8. Name a bisexual flower.

Ans. China rose (Hibiscus sp.)

9. Name a unisexual flower.

Ans. Flower of pumpkin is a unisexual flower.

10. Which is the unit of asexual reproduction of a plant?

Ans. Spore is the unit of asexual reproduction of a plant.

11. Which type of reproduction is performed by Amoeba?

Ans. Amoeba performs asexual reproduction.

12. Name a plant, which shows alternation of generation in its life cycle.

Ans. Selaginella (a fern)

13. Name an animal, which shows alternation of generations in its life cycle.

Ans. Obelia (a cnidarian)

14. Name animal, which performs reproduction by conjugation. 

Ans. Paramoecium (a protist)

15. Name an animal, which can reproduce by parthenogenesis.

Ans. Honey bee

16. Name an oviparous animal.

Ans. Bird

17. Name a viviparous animal.

Ans. Human

18. Name the event of union of male and female gametes in sexual reproduction.

Ans. Fertilisation

19. Name two hormones used for micropropagation.

Ans. Auxin and cytokinin

20. In which type of reproduction new genetic features may appear in the offspring?

Ans. In sexual reproduction, new genetic features may appear in the offspring.

21. By which process does Spirogyra perform sexual reproduction?

Ans. Spirogyra performs sexual reproduction by conjugation.

22. Which type of offsprings are produced in asexual reproduction?

Ans. The offspring produced in asexual reproduction, become genetically identical to its parents, i.e., no genetic variation occurs.

23. How does the body fragment of a Planaria grow into a fully formed one?

Ans. By regeneration.

24. How do you denote the union of a male and a female gamete of identical shape and size?

Ans. Isogamy.

25. What is heterogamy?

Ans. Heterogamy is the union of two gametes with non-identical size and shape.

26. How do you refer to the union of two gametes, produced in the body of the same animal?

Ans. The union of two gametes, produced in the body of the same organism, is called self-fertilisation.

27. How do you refer to the union of two gametes, produced in two different animals?

Ans. The union of two gametes, produced in two different animals, is called cross-fertilisation.

28. Name the type of fertilisation that occurs in open environment, outside the animal body.

Ans. External fertilisation

29. Which phase of life cycle starts in an organism with the formation of haploid spores?

Ans. Gametophytic generation starts with the formation of haploid spores, in the life cycle of an organism.

30. Name an organism, which performs asexual reproduction by multiple fission.

Ans. Plasmodium

31. Name the process of fertilisation of male and female gametes in sexual reproduction of higher organisms.

Ans. The process of fertilisation of male and female gametes in sexual reproduction of higher organisms is known as oogamy.

32. Upon which type of cell division does sexual reproduction depend directly?

Ans. Meiotic cell division

33. Which type of cell division occurs during gametogenesis of sexually reproducing higher organisms?

Ans. In higher organisms meiotic cell division occurs during gametogenesis.

34. Which type of cell division occurs during sporogenesis of ferns and mosses?

Ans. Meiotic cell division

35. Which type of cell division occurs during spore formation in Mucor and Penicillium?

Ans. Mitosis

36. Which type of reproduction helps in creating variations among offsprings?

Ans. Sexual reproduction

37. Name one organism that can reproduce through motile spore.

Ans. Chlamydomonas

38. Name one organism that can reproduce through non motile spore.

Ans. Mucor

39. Name a fungi reproduce through conidia.

Ans. Penicillium

40. Give one example of a fleshy not, helping in vegetative reproduction.

Ans. Sweet potato

41. Which plant vegetatively reproduce through stolon?

Ans. Mentha

42. Which plant reproduce through leaf?

Ans. Bryophyllum

43. Who discoered micropropagation?

Ans. Frederick Campion Steward

44. Micropropagation is based on which property of a cell?

Ans. Totipotency

45. What is plantlet?

Ans. The small plants produced through micropropagation are called plantlet.

46. Name one organism reproduce through Congugation.

Ans. Paramoecium

47. What is torula stage?

Ans. The bud of yeast looks like the animal Torula hence this stage is called torula stage.

48. What is syngamy?

Ans. Syngamy is the fusion of two different gametes.

49. What is rhizogenesis?

Ans. Rhizogenesis is the production of root in callus culture.

50. Name one animal showing, vegetative, asexual and sexual reproduction.

Ans. Hydra sp.

Fill in the blanks

1. A progeny comes from ……….. generation.

Ans. Parental

2. The individual of new generation that originates from the parental generation is known as ………

Ans. Offspring

3. The number of a population ……….. by reproduction.

Ans. Increases

4. In sexual reproduction, …….. originate in a population.

Ans. Variations

5. In asexual reproduction, only ………. parent is required. 

Ans. One

6. Union of male and female gametes is known as ………..

Ans. Fertilisation

7. Based on the nature of gametes, sexual reproduction can be classified into ……… types.

Ans. Three

8. The sexual reproduction, in which the sizes of male and female gametes are unequal, is called ……..

Ans. Anisogamy

9. The sexual reproduction, in which the sizes of male and female gametes are identical, is called ……..

Ans. Isogamy

10. The sexual reproduction, in which the male gametes are small and motile, whereas the female gamete is large and non-motile, is called ……….

Ans. Oogamy

11. Daughter cells of Plasmodium, produced by schizogony, are called ……….

Ans. Merozoites

12. Daughter cells of Plasmodium, produced by sporogony, are called ……….

Ans. Sporozoites

13. Planaria can perform asexual reproduction by ……….. of its body fragments.

Ans. Regeneration

14. Numerous ………… are produced from the sporogenous tissue of moss.

Ans. Spores

15. Bryophyllum performs vegetative propagation by the ………. on its leaf margins.

Ans. Buds

16. …………. is a type of tissue culture technique.

Ans. Micropropagation

17. Spore-producing plants are known as ………… plants.

Ans. Sporophytic

18. The ……….. used in the grafting process, carries the superior characters of a plant.

Ans. Scion

19. The diploid cell produced by ferilization is ………..

Ans. Zygote

20. Spore is formed within ……….

Ans. Sporangium

TOPIC – 3

SEXUAL REPRODUCTION IN FLOWERING PLANTS

SUMMARY

• A flower is the main reproductive part for sexual reproduction in flowering plants. A typical flower has four whorls of which the calyx is protective in nature and corolla helps in pollination by attracting pollinating agents. Therefore, these are called as accessory whorls, as they don’t take part reproduction directly. Androecium contains stamen which produces pollen. The gynoecium is consisted of carpels. Female gamete is produced within the ovary of carpel.
• The transfer of pollen from anther of stamen to stigma of carpel is called pollination. When pollen of one plant is transferred to the stigma of a flower located in the same plant, then it is called as self pollination. Self pollination within same flower is called autogamy and between two flowers of a same plant is called geitonogamy. When pollens are deposited on the stigma located in a different plants of same or different species, then it is called as cross pollination. Cross pollination is also known as xenogamy or allogamy.
• Both self and cross pollination have advantages and disadvantages.
• Cross pollination needs vectors like air (rice) water (Hydrilla), insect (mango), bird (silk cotton), etc.
• Offspring produced through cross pollination are with greater genetic variation than the offspring of self pollination.
• The male gamete from pollen and female gamete in ovule fuses together to form diploid zygote. This fusion of gametes is called fertilisation. The zygote forms embryo. The ovule along with embryo become seed and the ovary along with seed is transformed into fruit.
• On getting favourable conditions seed germinates to produce a new baby plant at the end of dormancy.

Long Answer Type Questions

1. Describe the structure of a typical flower.

Ans. Structure of a typical flower

A typical flower has all four floral parts (calyx, corolla, androecium and gynoecium) arranged in concentric rings on the flat, thick disc-like thalamus (e.g.-Hibiscus). The different floral parts of a typical flower are described below.

1. Calyx: The calyx is the first or outermost whorl of the flower, which is green, cup-shaped and composed of mostly five leafy segments, called sepals. In certain plants, at the base of calyx, there are some narrow leaf-like projections, which constitute the epicalyx (e.g.-Hibiscus).
2. Corolla: It is the second whorl, located towards the inner side of calyx. Petals are white in colour with sweet smell or of any bright colour other than green. It is composed of leafy units called petals.
3. Androecium: It is the third whorl, present at the inner side of the corolla. It is composed of three to many units, known as stamens. Each stamen has two parts, a fine, elongated, slender, cylindrical filament and a small, sac-like anther on it. Within the anther the pollens are produced.
4. Gynoecium: It is the fourth and central floral part of a typical flower. It may be composed of one or more units called carpels or pistils. Each carpel has three components-ovary, style and stigma. The ovary is the swollen base of a carpel. The filamentous portion emerging from it is called style, which ends in a swollen, knob-like structure called the stigma.

2. Why is flower called a modified shoot? Distinguish between accessory and essential whorls. 

Ans. Flower is a modified shoot

A flower is called a modified shoot due to following features-[1] Like leaf buds, floral buds also grow from the axil or tip of stem. [2] The floral parts are arranged on the thalamus like the arrangement of leaves on the stem. [3] Like stem, thalamus also has nodes and internodes. [4] Sepals and petals have similar venations like leaves.

Distinguishing features between accessory and essential whorls

Features	Accessory whorls	Essential whorls
1. Components	Calyx and corolla	Androecium and gynoecium
2. Production of gametes	Play no role in production of gametes	Produce male and female gametes in the form of pollen and egg cell
3. Function	Protection of essential floral parts and help in pollination	Gamete formation, fertilisation, fruit and seed formation

3. Mention the important features of self pollination.

Ans. Important features of self pollination

[1] Self pollination occurs in monoecious plant. [2] The stamens and carpels of self-pollinating flowers mature at same time. [3] This pollination occurs within the same flower (autogamy) or between separate flowers of the same plant (geitonogamy). [4] It generally occurs in bisexual flowers. [5] Loss of pollens in self pollination is almost neglible. [6] Plants produced from self pollination do not have newer characters. [7] Offspring produced through self pollination show little or no genetic variations with their parents. On the contrary, qualitative degradation is evident in successive generations. [8] Pollinating agents are usually not required in this pollination.

4. Mention important features of cross pollination.

Ans. Important features of cross pollination

[1] Cross pollination occurs mostly in unisexual flowers. [2] The male and female floral parts of cross pollinating bisexual flowers mature different times. [3] Due to structural barriers, self pollination is hindered in some bisexual flowers and as a result cross pollination occurs. [4] Pollinating agents are essential for cross pollination. [5] The hybrids produced through cross pollination, show different higher genetic variations as compared to their parents.

5. Mention the advantages and disadvantages of self and cross pollination.

Ans. Advantages and disadvantages of self and cross pollination

6. Describe the structure of an ovule with a diagram of its longitudinal section.

Similar question, Draw a labelled diagram of the longitudinal section of an ovule of flowering plant.

Ans. Structure of ovule

Longitudinal section of an ovule reveals the structural detail of the same.

1. Funiculus: The small stalk-like structure, that attaches the ovule on placenta, is called funiculus.
2. Chalaza: The base of the ovule from which the integuments develop is called chalaza.
3. Hilum: The point of attachment of funiculus with chalaza is known as hilum.
4. Integument: Single or double layered coating of the ovule is called integument.
5. Nucellus: The thin nutritive tissue layer below the integuments, that surrounds the embryo sac, is called nucellus.
6. Micropyle: The minute opening, just opposite to chalaza of the ovule, which is not covered by the integuments, is called micropyle.
7. Embryo sac: The thin membrane-bound, large sac-like cell, inside the nucellus is known as embryo sac. It carries eight haploid (n) nuclei in the beginning of its formation. Out of these eight nuclei, three, present near micropyle, constitute the egg apparatus. One of these form the ovum or egg cell and two others form synergids. Three other nuclei arranged in a cluster near the chalaza are known as antipodal cells. Remaining two nuclei unite near the centre of the embryo sac to form a diploid definitive nucleus (2n).

7. Describe the method of fertilisation and development of a new plant in angiosperms with diagram.

Similar question, Draw the labelled diagram of the fertilisation process in angiospermic plant.

Part question, State what happens in following three phases of sexual reproduction of flowering plants-[i] Production of gamete or reproductive cell. [ii] Fertilisation and [iii] Formation of embryo and new plant. 

Ans. Fertilisation in angiosperms and development of new plant

The method of fertilisation in angiosperms and development of a new plant includes a number of steps, which are described below.

1. Pollen formation: Numerous haploid pollen grains (n) are formed inside anthers by meiotic division of diploid (2n) pollen mother cells. The haploid nucleus of pollen divides mitotically to produce two haploid nucleus, viz.-tube nucleus and generative nucleus.
2. Production of egg cell: Ovary of a flower contains one to many ovules. Each ovule has a haploid (n) nucleus.
   This nucleus undergoes three consecutive mitotic divisions to form eight nuclei, four of which stay at each pole of the ovule. Three of these nuclei stay at chalazal pole in a cluster. These are called antipodal cells (n) and one polar nucleus (n) move to the centre of the ovule. At the opposite pole, three nuclei remain near the micropylar pole and one polar nucleus moves towards the centre. Of these three, one nucleus becomes more conspicuous, which forms the egg cell or ovum (n) and remaining two stay near the pole as the synergids (n). At the centre, the two polar nuclei unite to form a diploid definitive nucleus (2n).
   
3. Pollination: In this phase, pollens from same or separate flower of the same or another plant of same species are transferred to the stigma. After successful pollination, pollen grain germinates to produce pollen tube which grows through the style towards the ovary. Meanwhile, two haploid male gametes ar formed within the pollen from generative nucleus.
4. Fertilisation and zygote formation: As soon pollen tube enters into the style, two male gametes move towards the tip of it. The pollen tube then enters into the ovule by any of the three paths, viz.-through micropyle (porogamy), through chalaza (chalazogamy) or through integuments (mesogamy). After piercing the membrane of the embryo sac, the tip of the pollen tube dissolves to release the two male gametes inside it. Here, one male gamete fertilises the egg cell (n) to form a diploid (2n) zygote. The other male gamete fertilises the diploid definitive nucleus (2n) to form a triploid endosperm nucleus (3n). In case of sexual reproduction in angiospermic plants, fertilisation occurs two times. Therefore, this type of phenomenon is known as double fertilisation.
5. Embryo formation: The zygote undergoes continuous mitosis division to form a multicellular embryo.
6. Formation of fruit and seed: The ovule with embryo transforms into seed and the ovary matures as fruit.
7. Germination of seed and formation of new plant: In presence of favourable temperature, light, oxygen, water, hormones and enzymes, the seed germinates. The radicle gives rise to the root system and the plumule grows to form the shoot.

Short Answer Type Questions

1. What is a flower?

Ans. A flower is a highly condensed, specially modified shoot of plants, with limited growth. It is customised to protect the reproductive whorls (androecium and gynoecium) within it and thus, help in sexual reproduction.

2. Mention the important features of a flower.

Ans. The important features of a flower are as follows-[1] Flower is the specially modified shoot of a plant. [2] Flower grows from apical or axillary bud. [3] A flower has four whorls-calyx, corolla, androecium and gynoecium.

3. What is meant by an typical flower?

Ans. An typical flower is that flower, which has all the four floral parts, i.e. calyx, corolla, androecium and gynoecium, arranged in a proper concentric circles on a thalamus. Example-Hibiscus, lily, rose, etc.

4. What are the functions performed by a typical flower?

Ans. Different functions of a typical flower are[1] Sexual reproduction in flowering plant is performed by a flower. [2] After fertilisation, flower is transformed into a fruit which contains seed for formation of new generation.

5. What is pedicel? Mention its function. 

Ans. Pedicel: The slender, cylindrical, stalk-like structure, that holds the thalamus of a flower on a branch of the stem, is called pedicel.

Function: Pedicel connects the flower with the stem of a plant.

6. What is meant by pedicellate and sessile flower?

Ans. Pedicellate flower: The flower, which is held on a branch with the help of a pedicel, is called a pedicellate flower. Example-Hibiscus, rose, etc. Sessile flower: The flower, which does not possess pedicel and directly attaches with stem, is called sessile or non-pedicellate flower. Example-Tube rose

7. What is thalamus? Mention its function.

Ans. Thalamus: The convex or flat or concave, compact and thick disc-like structure, present on the top of the pedicel, is called thalamus. It has nodes and internodes.

Function: Upon thalamus the floral parts remain arranged in whorls or in spiral fashion. Thus the thalamus holds these floral parts.

8. What is meant by complete flower?

Ans. A flower carrying all four floral parts or whorls, i.e. calyx, corolla, androecium and gynoecium, is called a complete flower. Example-Clitoria, Hibiscus, mustard flower, etc.

9. What is meant by incomplete flower?

Ans. A flower, lacking any one or more of the four floral parts or whorls, i.e. calyx, corolla, androecium and gynoecium, is known as incomplete flower. Example Flowers of pumpkin, gourd, etc.

10. What is meant by unisexual flower?

Ans. A flower, which has any one of the two reproductive floral parts, i.e. androecium and gynoecium, is known as unisexual flower. The flower having androecium only is called a male flower or staminate flower. On the other hand, the flower that carries the gynoecium only, is known as female or pistillate flower. Example-Flowers of pumpkin.

11. What is meant by bisexual flower?

Ans. A flower, having both the reproductive whorls, i.e., androecium and gynoecium, is called bisexual flowers. Example-Flowers of Hibiscus, Datura, etc.

12. What is meant by neuter or sterile flower?

Ans. Sterile flower (Arum) A flower, lacking both androecium and gynoecium, is called neuter or sterile flower.

Example-Ray florets of sunflower, some flowers of arum, etc.

13. Differentiate between complete and incomplete flower.

Ans. Differences between complete and incomplete flowers are

Features	Complete flower	Incomplete flower
1. Number of Whorl	All the four different whorls are present	One or more than one type of whorl is absent
2. Nature of Flower	Bisexual	Unisexual, bisexual or neuter
Example	Hibiscus, datura	Pumkin, tuberose

14. What is meant by regular flower?

Ans. The flowers, which have every single unit of a whorl like petals, sepals, etc. with identical size and shape, are called regular flowers. Example-Flower of Hibiscus, datura, etc.

15. What is meant by irregular flower?

Ans. A flower in which one or more members of single or several floral whorls differ in size and shape from other members, is called irregular flower. Example Flowers of sweet pea, Clitoria, etc.

16. What is meant by asymmetric flower? Give an example. 

Ans. Asymmetric flower: A flower, which is indivisible into two equal halves at any of the planes through the axis, is called asymmetric flower.

Example: Orchid flower is the example of asymmetric flower.

17. What is meant by monoecious plant?

Ans. The plant, which carries separate male and female flowers on the same plant body, is called a monoecious plant. Example-Pumpkin, gourd, etc.

18. What is meant by dioecious plant?

Ans. The plant, which carries male and female flowers on separate plant bodies, is called a dioecious plant. Example-Papaya, palm, etc.

19. What is meant by calyx?

Ans. The green coloured outermost whorl of a flower, that protects all other floral parts within a bud, is called calyx. The leafy units of a calyx are called sepals.

20. What are sepals?

Ans. The green leafy units, which unite to compose a calyx, are known as sepals. Generally, three to five sepals form a calyx. Sepals of a flower are either free from each other or united together. The sepals protect the other parts of a flower while those are inside the flower bud.

21. Mention two functions of calyx.

Ans. Two functions of calyx are-[1] While in bud, the calyx protects all other floral parts from bright light, heat, rain and insect attacks. [2] Calyx has mesophyll tissue which helps in photosynthesis.

22. What is epicalyx?

Ans. In some flowers (e.g.-Hibiscus), an additional whorl of smaller leafy projections occurs at the junction of calyx and thalamus. This whorl of floral part is called epicalyx. In some floral buds, the epicalyces provide additional protection to the other floral parts along with the calyces.

23. What is meant by corolla?

Ans. The most conspicuous and second whorl of a flower, which is white or of any colour other than green is known as corolla. Corolla is meant for attracting insects for pollination and protecting the reproductive parts from external injury. The leafy units of corolla are known as petals.

24. Mention the functions of corolla?

Ans. The functions of corolla aree-[1] It protects the androeciun and gynoecium from external injury while in bud and even after blooming. [2] It attracts insects for helping in pollination by sweet smell and bright colour.

25. Why are calyx and corolla treated as ‘accessory floral parts’ of a flower?

Ans. The calyx and corolla do not take part in reproduction process directly. Instead, they protect androecium and gynoecium within the bud and the petals attract insects to help in pollination. Therefore, calyx and corolla are treated as ‘accessory floral parts.

26. What is meant by a naked flower?

Ans. The flower which does not have any of the two accessory floral parts, i.e., calyx and corolla, so as to leave the essential reproductive parts (androecium and gynoecium) exposed, is called a naked flower. Example-Poinsettia pulcherrima.

27. What is meant by androecium? Mention its function.

Ans. Androecium: The essential third whorl of a flower, located towards the inner side of the corolla and composed of three to many stamens, is known as androecium.

Function: Androecium is meant for the production of pollens, the male reproductive units of a flower.

28. What is meant by gynoecium? Mention its function.

Ans. Gynoecium: The essential fourth whorl of a flower, composed of one or more carpels, located at the centre of the floral axis, is known as gynoecium.

Function: Gynoecium produces the egg cell and acts as the centre for production of fruit and seed.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

1. Flower is a modified –

A. Root

B. Leaf

C. Inflorescence

D. Shoot

Ans. D

2. The shoot with limited growth, which is modified for reproduction and meant for production of fruits and seeds, is-

A. Root

B. Flower

C. Leaf

D. Branch

Ans. B

3. The floral parts remain arranged on a flat thick base, which is known as-

A. Sepal

B. Thalamus

C. Petiole

D. Ovary

Ans. B

4. Number of floral parts in a complete flower is-

A. Three

B. Four

C. Five

D. Six

Ans. B

5. The flower, which has sepals, petals, androecium and gynoecium arranged on the thalamus, is called-

A. Regular flower

B. Complete flower

C. Inflorescence

D. Incomplete flower

Ans. B

6. The accessory floral parts of a flower are-

A. Calyx and gynoecium

B. Androecium and gynoecium

C. Corolla and calyx

D. Corolla and androecium

Ans. C

7. A flower having both androecium and gynoecium is called-

A. Unisexual flower

B. Bisexual flower

C. Actinomorphic flower

D. Irregular flower

Ans. B

8. Which of following is not a bisexual flower? 

A. Datura

B. Tube rose

C. Bok (Sesbania) flower

D. Bottle gourd flower

Ans. D

9. The flower, in which either androecium or gynoecium is absent, is called-

A. Bisexual flower

B. Regular flower

C. Irregular flower

D. Unisexual flower

Ans. D

10. Androecium and gynoecium directly take part in reproduction, therefore, these two floral parts are called-

A. Helping whorls

B. Accessory whorls

C. Essential whorls

D. Unnecessary whorls

Ans. C

11. The outermost floral part is-

A. Calyx

B. Thalamus

C. Corolla

D. Androecium

Ans. A

12. Number of sepals in Hibiscus flower is-

A. 3

B. 4

C. 5

D. 6

Ans. C

13. Number of sepals in a Datura flower is-

A. Three

B. Four

C. Five

D. Six

Ans. C

14. Epicalyx is present in-

A. Bok (Sesbania) flower

B. Hibiscus

C. Sweet pea flower

D. Datura

Ans. B

15. Example of an irregular flower is-

A. Pea flower

B. Pumpkin

C. Datura

D. Hibiscus

Ans. A

16. A complete, regular, polypetalous flower is-

A. Datura

B. Bok (Sesbania)

C. Hibiscus

D. Pumpkin

Ans. C

17. A regular, unisexual flower is-

A. Hibiscus

B. Datura

C. Pumpkin

D. Pea flower

Ans. C

18. Which of the following flowers is an example of a regular, complete, gamopetalous flower?

A. Sweet pea flower

B. Datura flower

C. Aparajita (Clitoria) flower

D. Bok (Sesbania) flower

Ans. B

19. Calyx and corolla unite to form a combined structure in some flowers. This structure is called-

A. Thalamus

B. Perianth

C. Naked flower

D. Bract

Ans. B

20. A flower without calyx and corolla is called-

A. Unisexual flower

B. Bisexual flower

C. Naked flower

D. True flower

Ans. C

21. Each unit of perianth is called-

A. Tepal

B. Petal

C. Sepal

D. Calyx

Ans. A

22. Perianth is present in the flowers of-

A. Tube rose

B. Datura

C. Sunflower

D. Hibiscus

Ans. A

23. Plants of same species, carrying male flowers on one plant and female flowers on another, is called-

A. Zygomorphic

B. Monoecious

C. Bisexual

D. Dioecious

Ans. D

24. A plant bearing male, female and bisexual flower all together, is called-

A. Monoecious

B. Dioecious

C. Polygamous

D. Monogamous

Ans. A

25. The discoverer of sex in plants is-

A. Camerarius

B. Nawaschin

C. Linneaus

D. Sanger

Ans. A

26. Which of the following is not a component of androecium?

A. Anther

B. Filament

C. Ovule

D. Pollen

Ans. C

27. In which part of the flower, pollens are produced?

A. Stigma

B. Filament

C. Ovary

D. Anther

Ans. D

28. Waxy coating is seen on the surface of pollens in-

A. Anemophilous flowers

B. Hydrophilous flowers

C. Entomophilous flowers

D. Ornithophilous flowers

Ans. B

29. Which of the following is not a component of gynoecium?

A. Stigma

B. Style

C. Pollen

D. Ovule

Ans. C

30. Number of stigma in Hibiscus flower is-

A. 2

B. 3

C. 5

D. Numerous

Ans. C

31. Embryo sac in flowering plants is formed by-

A. Embryo

B. Megaspore

C. Zygote

D. Nucellus

Ans. B

Answer in a single word or sentence

1. What are the other names of sexual reproduction?

Ans. Amphimixis and syngenesis

2. What is the name of the process of gamete formation?

Ans. Gametogenesis

3. What does a zygote form by mitotic cell division?

Ans. An embryo

4. How do you denote the arrangement of flowers on a plant?

Ans. Inflorescence

5. What is main function of a flower?

Ans. Main function of a flower is to carry out sexual reproduction of the plant.

6. Which portion of a shoot grows as a flower?

Ans. Floral bud

7. How do you denote the axis of a flowering plant, which carries a cluster of flowers?

Ans. Peduncle

8. Absence of which floral part reduces the attractiveness of a flower for the insects?

Ans. Petals

9. How do you designate the small stal-like structure that holds a flower on a branch?

Ans. Pedicel

10. Name the floral parts, which remain arranged on the thalamus.

Ans. The floral parts, which remain arranged on the thalamus are- -[1] Calyx, [2] Corolla, [3] Androecium and [4] Gynoecium.

11. Name the units of a calyx.

Ans. Sepals

12. What do you call each unit of corolla of a flower?

Ans. Petal

13. Name the long tubular part of gynoecium, that is connected to the ovary and holds the stigma.

Ans. Style

14. From where are the male gametes of a flower produced?

Ans. Pollen grains

15. What is first cell of male gametophyte?

Ans. Pollen grain

16. What are the different cells present in pollen grain during pollination?

Ans. One generative nucleus and one tube nucleus

17. Give example of a flower, which has a tubelike calyx.

Ans. Datura sp.

18. How do you denote each unit of the gynoecium?

Ans. Carpel

19. Give examples of two monoecious plants.

Ans. Gourd and pumpkin plants

20. Give examples of two dioecious plants.

Ans. Papaya and palm trees

21. Name the parts of a carpel.

Ans. Stigma, style and ovary

22. Which two parts of a flower mature to form fruit and seed?

Ans. Ovary and ovule of a flower respectively mature to form fruit and seed.

23. How many thalami are present in a flower?

Ans. A flower has only one thalamus (Singular form of thalami).

24. Name the event of union of male and female gametes?

Ans. Fertilisation

25. Which type of cell division, does a pollen mother cell undergo to form pollens?

Ans. Meiotic cell division

26. Which famous scientist first observed the event of pollination in date palm tree?

Ans. Greek botanist Theophrastus

27. Which scientist coined the term ‘double fertilisation’?

Ans. Russian botanist S G Nawaschin (1898)

28. Which are the reproductive parts of a flower?

Ans. Stamens and carpels

29. State the location of ovule in a carpel.

Ans. Ovule is located inside the ovary of a carpel.

30. Mention the chromosome number of definitive nucleus.

Ans. Diploid (2n) number of chromosomes

31. What is the chromosome number of endosperm nucleus?

Ans. Triploid (3n) number of chromosomes

32. Write down the common name and scientific name of an anemophilous flower.

Ans. Common name of an anemophilous flower is paddy and its scientific name is Oryza sativa.

33. What is zoophily?

Ans. Zoophily is a type of cross pollination which is facilitated by different animals (e.g.-bat, snail, insects, birds, etc.) is called zoophily.

34. Write down the scientific name of a hydrophilous flower.

Ans. Hydrilla verticillata

35. Write down the common name and scientific name of an entomophilous flower.

Ans. Common name of an entomophilous flower is mango flower and its scientific name is Mangifera indica.

36. Write down the common name and scientific name of an ornithophilous flower.

Ans. Common name of an ornithophilous flower is silk cotton and its scientific name is Bombax cieba.

37. What does the definitive nucleus create after fertilisation?

Ans. After fertilisation, definitive nucleus (2n) produces an endosperm nucleus (3n), which later divides to create endosperm of the developing seed.

38. What does a pollen nucleus produce after its division?

Ans. The pollen nucleus divides to produce one generative nucleus and one tube nucleus.

39. How many stamens are there in the flower of Hydrilla?

Ans. 30-40 stamens

40. Name two flowers, which bloom at night and which do not have bright colours?

Ans. Flowers of Polianthes tuberosa and Cestrum nocturnum bloom at night and do not have bright colours.

41. Name the unit of androecium that is composed of a filament and an anther.

Ans. Stamen

42. Name the first cell of male gametophyte.

Ans. Pollen

43. Name the thicker outer coating of pollen grain.

Ans. Exine

44. Name the delicate inner coating of a pollen grain.

Ans. Intine

45. What will happen to a bisexual flower if all of its stamens are removed?

Ans. If all stamens of a bisexual flower are removed, the flower will survive as a unisexual female flower.

46. What does funiculus of the ovule transform into after fertilisation?

Ans. Funiculus is transformed into seed-stalk after fertilisation of ovule.

47. What will happen to Hibiscus flower if all is petals are cut off just after its blooming?

Ans. If the petals of a Hibiscus are cut off just after its blooming, entomophily will be obstructed.

48. Why is the stigma of paddy flower long and feathery?

Ans. The stigma of paddy flower is long and feathery to catch the air-borne pollens.

49. Why do the pollens of entomophilous flowers Ihave spiny and sticky outer surface?

Ans. Pollens of entomophilous flowers have spiny and sticky outer surface to adhere to the body parts of visiting insects.

Fill in the blanks

1. Flower is the ……….. organ of a plant.

Ans. Reproductive

2. Sepals and petals are the ………. parts of a flower.

Ans. Accessory

3. Flowers grow from apical or ……….. buds.

Ans. Axillary

4. In angiosperms, certain portions of the ……….. is modified into flower.

Ans. Shoot

5. The leaf-like segments of a calyx are called ……….

Ans. Sepals

6. The thin cylindrical portion of a stamen is known as ……….

Ans. Filament

7. The capsular portion at the top of a filament is known as ……….

Ans. Anther

8. Pollen divides to form ………. gametes.

Ans. Male

9. The third floral part of a complete flower is called ……….

Ans. Androecium

10. The calyx of Datura flower appears like a ……….

Ans. Bell

11. The tubular portion that remains in between stigma and ………. is known as style.

Ans. Ovary

12. Pollens settle on ……….. of a flower during pollination.

Ans. Stigma

13. The androecium of Datura flower is composed of ……….. stamens.

Ans. Five

14. Sweet pea flower has ……….. stamens in its androecium. 

Ans. Ten

15. The slightly swollen head-like portion of the style of a gynoecium is called ……….

Ans. Stigma

16. Pollination within the same flower is called ………..

Ans. Homogamy

State true or false

1. The accessory floral parts of a flower are sepals and petals.

Ans. True

2. Each part of a corolla is called petal.

Ans. True

3. Pollens are haploid in nature.

Ans. True

4. The future plant remains protected within a seed.

Ans. True

5. The seed coat and fruit coat of maize are inseparable.

Ans. True

6. An ovary may carry one to many ovules.

Ans. True

7. Pollinating agent is not required for cross pollination.

Ans. False

8. Pollinating agents are essential for self pollination.

Ans. False

9. Paddy is an hydrophilous plant.

Ans. False

10. Hydrilla is a anemophilous plant.

Ans. False

11. Mango flower shows entomophily.

Ans. True

12. Silk cotton plant shows ornithophily.

Ans. True

13. Anthers contain pollens.

Ans. True

14. Blastula develops from morula.

Ans. True

15. Zygote is haploid in nature.

Ans. False

1. Phase of cell division: In this phase, cells divide mitotically to increase in number in a living body. Cells of apical and lateral meristem divide to make a plant body grow in length and width. In animals, a unicellular zygote divides repeatedly and undergoes through the different stages, like-morula, blastuta, gastrula of a multicellular embryo to give rise to a fully grown animal body.
2. Phase of cell enlargement: In this phase, the newly divided cells absorb water and synthesise different cellular components to increase the protoplasmic volume. By this process, the cells become larger and the tissues formed by these cells grow in volume irreversibly. In some tissues, secretory materials accumulate in the intercellular spaces to increase the volume of that region, as we can see in bones and cartilages.
   
3. Phase of cell differentiation: In this phase, the fully grown daughter cells slowly modify and gain certain specialised features. These typical cells then form different tissues and tissue systems to perform specific functions. Finally, these tissue systems form different organs and organ systems of a living body.

According to WHO human development includes five different stages which are described below.

1. Newborn or neonatal phase: This phase of development lasts for the first one month after the birth of a baby. During this phase, the baby remains asleep most of the time and show very high rate of metabolism. In this phase, a baby can detect light, direction of sound, primary colours and above all, can recognise mother’s face. Body weight may reduce during the first few days but soon it resumes. For newborn babies, laughing and crying are the main signs of communication.
2. Childhood: This phase of life starts from second month and continues upto ten years. During this period, physical, mental and emotional development occurs at faster rate. Motor activities increases and limbs grow quicker than other parts of the body. Power to memorise, ability of reading, writing, drawing and problem solving improve gradually. A child can express fear, anger and excitement but finer emotions are not expressed perfectly.
3. Adolescence: This is the intermediate phase between childhood and adulthood. The span between the age of 10 to 19 years (according to WHO) is treated as adolescence. The age of adolescence is not fixed for all. It varies with gender, environment, nutrition, geographical location, etc. During this phase, several hormones come into action to regulate the growth and functioning of sexual organs. An adolescent boy and girl go through significant changes in physical, mental, emotional and social aspects. From this phase of life, sexual attraction towards opposite gender emerges. Mature gamete formation starts during this phase. Concentration, thinking skill, analytical ability and intelligence grow very fast in adolescent individuals. At this age, they dare to take risks. Therefore, adolescence is treated as the ‘period of turmoil.
4. Adulthood or matured stage: The age between 19 to 60 years is denoted as adult age. This phase is characterised by maturity, self-confidence, practical, purposeful and self-directed attitude. In this period, physical growth reduces quickly and ultimately stops. At this age, sense of responsibility towards family and society grows significantly. An adult person gains experiences of life and mostly follows moral values.
5. Old age: The age beyond 60 years is treated as old age. In this age, cellular activities gradually slow down. Visual and auditory abilities get weakened. Old age is characterised by thinning and greying of hairs. Skin gets heavily wrinkled and muscles become weak. Bones gradually degenerate and joints lose their movability which are the consequences of different bone diseases like osteoporosis and osteoarthritis. People at old age lose memory and become mentally fatigued.

Very Short Answer Type Questions

Multiple Choice Questions & Answers [MCQ]

State true or false