12th Bio Botany 

Chapter 1 Asexual and Sexual Reproduction in Plants

Book Back Questions and Answers

I. Choose the correct answer

1.Choose the correct statement from the following

a) Gametes are involved in asexual reproduction

b) Bacteria reproduce asexually by budding

c) Conidia formation is a method of sexual reproduction

d) Yeast reproduce by budding

Answer:

d) Yeast reproduce by budding

2.An eminent Indian embryologist is

a) S.R.Kashyap

b) P.Maheswari

c) M.S. Swaminathan

d) K.C.Mehta

Answer:

b) P.Maheswari

3.Identify the correctly matched pair

a) Tuber – Allium cepa

b) Sucker – Pistia

c) Rhizome – Musa

d) Stolon – Zingiber

Answer:

c) Rhizome – Musa

4.Pollen tube was discovered by

a) J.G.Kolreuter

b) G.B.Amici

c) E.Strasburger

d) E.Hanning

Answer:

b) G.B.Amici

5.Size of pollen grain in Myosotis

a) 10 micrometer

b) 20 micrometer

c) 200 micrometer

d) 2000 micrometer

Answer:

a) 10 micrometer

6.First cell of male gametophyte in angiosperm is

a) Microspore

b) megaspore

c) Nucleus

d) Primary Endosperm Nucleus

Answer:

a) Microspore

7.Match the following

I. External fertilization    -     i. pollen grain

II. Androecium         -           ii. anther wall

III. Male gametophyte    -            iii. algae

IV. Primary parietal layer    -        iv stamens

Answer:

a) I—iv; ll—i; III—ii; I’V—iii

b) 1—iii; J1—iv; III—i; V—ii

c) I—iii; I1—iv; III—ii, IV—i

d) I—iii; II—i; III—iv; IV—ii

Answer:

b) I—iii;II—iv;III—i;1 V—ii

8.Arrange the layers of anther wail from locus to periphery

a) Epidermis,middle layers, tapetum, endothecium

b) Tapetum, middle layers, epidermis, endothecium

c) Endothecium, epidermis, middle layers, tapetum

d)Tapetum, middle layers endothecium epidermis

Answer:

d) Tapetum, middle layers endothecium epidermis

9.Identify the incorrect pair

a) sporopollenin – exine of pollen grain

b) tapetum – nutritive tissue for developing microspores

c) Nucellus – nutritive tissue for developing embryo

d) obturator – directs the pollen tube into micropyle

Answer:

c) Nucellus – nutritive tissue for developing embryo

10.Assertion : Sporopollenin preserves pollen in fossil deposits.

Reason : Sporopollenin is resistant to physical and biological decomposition.

a) Assertion is true; reason is false

b) Assertion is false; reason is true

c) Both Assertion and reason are not true

d) Both Assertion and reason are true

Answer:

d) Both Assertion and reason are true

11.Choose the correct statement(s) about tenuinucellate ovule

a) Sporogenous cell is hypodermal

b) Ovules have fairly large nucellus

c) sporogenous cell is epidermal

d) ovules have single layer of nucellus tissue

Answer:

a) Sporogenous cell is hypodermal and d)ovules have single layer of nucellus tissue

12.Which of the following represent megagametophyte

a) Ovule

b)Embryo sac

c) Nucellus

d)Endosperm

Answer:

b) Embryo sac

13.In Haplopappus gracilis, number of chromosomes in cells of nucellus is 4. What will be the chromosome number in Primary endosperm cell?

a) 8

b) 12

c) 6

d) 2

Answer:

C) 6 (3n)

14.Transmitting tissue is found in

a) Micropylar region of ovule

b) Pollen tube wall

c) Stylar region of gynoecium

d) Integument

Answer:

c) Stylar region of gynoecium

15.The scar left by funiculus in the seed is

a) tegmen

b) radicle

c) epicotyl

d) hilum

Answer:

d) hilum

16.A Plant called X possesses small flower with reduced perianth and versatile anther. The probable agent for pollination would be

a) water

b) air

c) butterflies

d) beetles

Answer:

b) air

17.Consider the following statement(s)

i) In Protandrous flowers pistil matures earlier

ii) In Protogynous flowers pistil matures earlier

iii) Herkogamy is noticed in unisexual flowers

iv) Distyly is present in Primula

a) i and ii are correct

b) ii and iv are correct

c) ii and iii are correct

d) i and iv are correct

Answer:

b) ii and iv are correct

18.Coelorhiza is found in

a) Paddy

b)Bean

c) Pea

d) Tridax

Answer:

a) Paddy

19.Parthenocarpic fruits lack

a) Endocarp

b) Epicarp

c) Mesocarp

d) seed

Answer:

d) seed

20.In the majority of plants, pollen is liberated at

a) 1 celled stage

b) 2 celled stage

c) 3 celled stage

d) 4 celled stage

Answer:

b) 2 celled stage

21.What is reproduction?

Answer:

Reproduction is the biological process of producing young ones of their own kind. It is a vital process for the existence of a species and it also brings suitable changes through variation in the offsprings for their survival on ear

22.Mention the contribution of Hofmeister towards Embryology.

Answer:

• He worked on flowering plant embryology.
• Discovered alternation of generation in plants.
• He described the structure of pollen tetrad.

23.List out two sub-aerial stem modifications with example.

Answer:

Subaerial stem modifications.

The stem is partly aerial and partly underground.

a) Runner. (Ex. oxalis, Centella Asiatica)

• It is running horizontally on the soil surface.
• Nodes have axillary buds, scale leaves, and adventitious roots.
• Runner arises from the axillary bud.
• Mother plant produces many runners in all directions.
• They break off and grow into individual plants.

b) Sucker. (Ex. Musa (banana), chrysanthemum)

• Grows horizontally for a distance under the soil. Then it emerges obliquely upwards.

c) Stolon (Ex. Strawberry, Vallisneria)

• Develop from underground stems.
• They grow horizontally outwards.

d) Offset (condensed runners)

• Unlike runners, they produce tilt of leaves above and duster of roots below Ex. Pistia, Eichhornia.

24.What is layering?

Answer:

• It is an artificial method of vegetative propagation.
• The stem of the parent plant is allowed to develop roots while still intact.
• The root develops. The rooted part is cut. It is planted to grow as a new plant.

Ex. Ixora, Jasminum.

25.What are clones?

Answer:

Individuals developed by asexual reproduction are morphologically and genetically identical. Such individuals are called clones.

26.A detached leaf of Bryophyllum produces new plants. How?

Answer:

• Bryophyllum undergoes vegetative reproduction in the leaf.
• The succulent leaf is notched in its margin.
• Adventitious buds develop at these notches. They are called epiphyllous buds.
• These buds develop a root system. When the leaf decays, they become independent plants.

27.Differentiate Grafting and Layering.

Answer:

Grafting:

• In grafting, two different plants (stock & scion) are used to develop new plants.
• The new plant will support to possess the characters of both the parents or new variation can be noticed.

Layering:

• In layering, only one plant is used to develop a new plant.
• Variation cannot be expected. The new individual is exactly similar to the parent plant.

28.“Tissue culture is the best method for propagating rare and endangered plant species” Discuss.

Answer:

Micropropagation.

The growth of plant tissue in special culture medium under suitable controlled conditions is known as “tissue culture”.

it is the regeneration of a whole plant from a single cell or tissue.

Advantages.

• Rare, Endangered plants are propagated.
• In a short duration, plants with desirable characteristics can be multiplied.
• Produce Genetically identical plants.
• Done in any season.
• Plants without viable seeds (or) difficult to germinate can be propagated.
• Meristem culture produces disease-free plants.
• Cells can be genetically modified or transformed.

29.Distinguish mound layering and air layering.

Answer:

Mound Layering:

In mound layering, a lower flexible branch with leaves is bent to the ground and a part of the stem is buried in the soil and the tip of the branch is exposed above the soil. After the roots emerge from the buried stem, a cut is made in the parent plant so that the buried plant grows into a new plant.

30.Explain the conventional methods adopted in the vegetative propagation of higher plants.

Answer:

Conventional methods of vegetative propagation.

a) Cutting (Ex. Hibiscus)

• Plant parts like stem, leaf are cut from the parent plant.
• Cut part is placed in suitable medium,
• It produces root and grows into a new plant.

b) Grafting (Ex. Citrus, Mango)

• Two different plants are joined.
• They grow as one plant.
• Plant in soil is called stock.
• Plant used for grafting is the scion.

It is of 5 types.

i) Bud grafting – scion is placed in the incision of stock.

ii) Approach grafting – Cut surfaces of stock scion are tied together.

iii) Crown Grafting – Wedge-shaped scion is inserted into the cleft of stock.

iv) Tongue grafting – Stock and scion are cut obliquely scion is fit into stock and bound with tape.

v) Wedge grafting – Twig of the scion is inserted into slot in the stock.

c) Layering

• Stem of parent plant is allowed to develop roots while still intact. The root develops. The rooted part is cut and planted to grow as a new plant.

I) Mound Layering

• Flexible branch is buried in soil.
• Roots emerge from buried stem. It grows into a new plant.

ii) Air Layering

• Nodal region is girdled.
• Hormones are applied.
• Rooting is promoted.
• This area is covered by moist soil.
• Roots emerge in 2-4 months.
• Roots branches are removed from parent. They are grown separately.

31.Highlight the milestones from the history of plant embryology.

Answer:

• 1682 – Nehemiah Grew mentioned stamens as the male organ of a flower.
• 1694 – R.J. Camerarius described the structure of a flower, anther, pollen, and ovule
• 1761 – J.G. Kolreuter gave a detailed account of the importance of insects in pollination.
• 1824 – G.B. Amici discovered the pollen tube.
• 1848 – Hofmeister described the structure of pollen tetrad.
• 1870 – Hanstein described the development of embryos in Capsella and Alisma.
• 1878 – E. Strasburger reported polyembryony.
• 1884 – E. Strasburger discovered the process of Syngamy.
• 1899 – S.G. Nawaschin and L. Guignard independently discovered Double fertilization.
• 1904- E. Hanning initiated embryo culture.
• 1950 – D.A. Johansen proposed classification for embryo development.
• 1964 – S. Guha and S.C. Maheswari raised haploids from Datura pollen grains
• 1991 – E.S. Coen and E.M. Meyerowitz proposed the ABC model to describe the genetics of initiation and development of floral parts
• 2015 – K.V. Krishnamurthy summarized the molecular aspects of pre and post-fertilization reproductive development in flowering plants.

32.Discuss the importance of Modern methods in reproduction of plants.

Answer:

The genetic ability of a plant cell to produce the entire plant under suitable condition is said to be totipotency.

• This characteristic feature of a cell is utilized in horticulture, forestry and industries to propagate plants.
• The mature phloem parenchyma cells removed from the carrot were placed in a suitable medium under controlled conditions.
• It stimulate to start dividing again to produce a new carrot plant.

Importance of modern methods of reproduction in plants.

• Rapid Multiplication of desired plants in short duration.
• Genetically identical plants are produced.
• Tissue culture can be done at any season
• Plants without viable seeds (or) difficult to germinate can be propagated.
• Rare, Endangered plants are propagated.
• Meristem culture produces disease-free plants.
• Cells are genetically modified or transformed.

33.What is Cantharophily?

Answer:

• It is the cross-pollination of flowers by beetles. They feed on pollen or juicy tissues of their flower.
• The plants using this mode of pollination
• Er. Nymphaea species of plants – Rhinoceros beetle.
• Giant Water lily – Scarab beetle
• Illicium plant – Diptera files.

34.List any two strategy adopted by bisexual flowers to prevent self-pollination.

Answer:

1) Dichogamy

Anthers and stigmas mature at different times.

• Protandry – Stamens mature earlier.
• Protogyny – Stigmas mature earlier.

2) Herkogamy

• Self pollination is impossible by the arrangement of stamens and stigmas.
• Ex: In Hibiscus, stigmas project above the stamens.
• In some plants, when the pollen grain of a flower reaches the stigma of the same.
• It is unable to germinate or prevented to germinate on its own stigma.
• It is a genetic mechanism.
• Example: Abutilon, passiflora.

35.What is the endothelium?

Answer:

In the Asteraceae species, the inner layer of the integument gets specialized for nourishing the embryosac and this is called the integumentary tapetum or endothelium.

36.“The endosperm of angiosperm is different from gymnosperm”. Do you agree? Justify your answer.

Answer:

Endosperm of Angiosperms

• Triploid Endosperm
• Endosperm is formed by triple fusion.
• Endosperm surrounds the embryo.

Endosperm of Gymnosperm

• Haploid endosperm.
• The endosperm is formed before fertilisation.
• Gymnosperms (Ex; pine) produce embryos. It provides nutrition as starch. with many cotyledons. Primary Endosperm is used as food.

37.Define the term Diplospory.

Answer:

Diplospory is a condition where a diploid embryosac is formed from megaspore mother cells without a regular meiotic division.

E.g: Eupatorium.

38.What is polyembryony? How can it be commercially exploited?

Answer:

Polyembryony

• The occurrence of more than one embryo in a seed is called poly embroyony.

Practical Applications.

• Seedlings from nucellar tissue of citrus are better clones for orchards.
• Embryos from polyembryonic are virus-free.

39.Why does the zygote divide only after the division of the Primary endosperm cell?

Answer:

The primary endosperm nuclear (PEN) divides prior to zygotic division and form endosperm. Endosperm acts as a nutritive tissue and nourishes the developing embryo.

40.What is Mellitophily?

Answer:

Pollination by honeybee is called mellitophily (Latin word mellitus= honey or sweet), Among the insects the bees are the main flower visitors and dominant pollinators.

41.“Endothecium is associated with dehiscence of anther” Justify the statement.

Answer:

The inner tangential wall develops bands (sometimes radial walls also) of cellulose (sometimes also slightly lignified). The cells are hygroscopic. The cells along the junction of the two sporangia of an anther lobe lack these thickenings. This region is called stomium. This region along with the hygroscopic nature of endothecium helps in the dehiscence of anther at maturity.

42.List out the functions of tapetum. Tapetum is the innermost layers of anther wall.

Answer:

• Supplies nutrition to developing microspores.
• Contributes sporopollenin through ubisch bodies. They play role in pollen wall formation.
• Pollenkitt material is contributed by tapetal cells. It is layer transferred to pollen surface.
• Exine proteins for rejection reaction are derived from tapetal cells.

43.Write a short note on Pollen kitt.

Answer:

Pollenkitt is contributed by the tapetum and coloured yellow or orange and is chiefly made of carotenoids or flavonoids. It is an oily layer forming a thick viscous coating over pollen surface. It attracts insects and protects damage from UV radiation.

44.Distinguish tenuinucellate and crassinucellate ovules.

Answer:

Tenuinucellate ovule

• The sporogenous cell is hypodermal
• It has single layer of nuclear tissue.
• It has very small nucellus

Crassinucellate ovule

• These ovules have sub-hypodermal sporogenous cell
• They have large nucellus.
• Many layers of cells are seen.

45.‘Pollination in Gymnosperms is different from Angiosperms’ – Give reasons.

Answer:

In gymnosperms, the ovules are exposed and the pollens are deposited directly on it. Hence the pollution is direct in a gymnosperm. Whereas in angiosperms it is said to be indirect, as the pollens are deposited on stigma or the pistil.

46.Write a short note on Heterostyly.

Answer:

• Heterostyly is a mechanism to promote cross-pollination.
• Different forms of flowers with different lengths of stamen and style.
• Pollination takes place between organs of same length.

a) Distyly. (Ex. Primula)

• Thrum-eyed flowers have short styles. Anthers of pin have short stamen.
• Anthers of thrum-eyed flowers and stigma of the pin are of the same height (both are long). This helps in effective pollination.

b) Tristyly (Ex. Lythrum)

• 3 kinds of flowers are there, with respect to the length of style and stamens. Flower of one type can’t pollinate their own type. They pollinate the other 2 types.

47.Enumerate the characteristic features of Entomophilous flowers.

Answer:

The characteristic features of entomophilous flowers are as follows:

• Flowers are generally large or if small they are aggregated in dense inflorescence. Example: Asteraceae flowers.
• Flowers are brightly coloured. The adjacent parts of the flowers may also be brightly coloured to attract insects. For example in Poinsettia and Bougainvillea, the bracts become coloured.
• Flowers are scented and produce nectar.
• Flowers in which there is no secretion of nectar, the pollen is either consumed as food or used in building up of its hive by the honeybees. Pollen and nectar are floral rewards for visitors.
• Flowers pollinated by flies and beetles produce foul odour to attract pollinators.
• In some flowers, juicy cells are present which are pierced and the contents are sucked by the insects.

48.Discuss the steps involved in Microsporogenesis. Microsporogenesis.

Answer:

Formation of haploid microspores from diploid microspore mother cell by meiosis.

• The primary sporogeneous cells undergo mitosis to form sporogenous tissue. ‘
• Sporogenous tissue functions as microspore mother cells.
• Microspore mother cell divides meiotically to form a tetrad (4 haploid microspores)
• Microspores get separated. They remain free in the anther locule. They develop into pollen grains.
• Microspores are held together by pollinium. Filament (or thread) like part form pollinium is called retinaculum. Through retinaculum pollinia are attached to clip like corpusculum. This structure is called Translator (Y shapled).

49.With a suitable diagram explain the structure of an ovule.

Structure of ovule (Megasporangium)

Answer:

• Ovule of ovule (Megasporangium)
• It has a stalk and a body.
• stalk (funiculus) is at the base of ovule. It attaches ovule to the placenta.
• Hilum is the junction (point of attachment) between ovule and funicle.
• In an inverted ovule, the funicle is fused to the body of ovule. Thus a ridge called raphe is formed.
• Body of ovule has central mass of reserve food called nucellus.
• Nucellus is covered by 2 layers, called integuments.
• Integument covers the nucellus completely except at the top. This forms a pore called micropyle.
• Ovule with single integument is called unitegmic.
• At the base of body, nucellus, integument and funicle meet. This is called chalaza.
• Sac like structure in nucellus towards micropylar end is called embryosac (or) female gametophyte. It is formed from functional megaspore of nucellus.
• The nutritive inner intergument layer is called integumentary tapetum or endothelium.
• Tenuinucellate type ovule has hypodermal sporogenous cell. It has single layer of nucellar tissue.
• Crassinucellate type, ovule has subhypodermal sporogenous cell.
• Group of cells between chalaza and embryosac is called hypostase.
• Thick walled cells above micropyle are called epistase.

50.Give a concise account on steps involved in the fertilization of an angiosperm plant.

Answer:

Steps in the fertilization of Angiosperms

1. Germination of pollen to form pollen tube in the stigma.

• Pollens fall on receptive stigma.
• Compatible pollen germinates to form a tube.
• This is helped by stigmatic fluid in wet stigma and pellicle in dry stigma.
• Compatibility is decided by recognition, rejection protein reaction, between pollen and stigma surface.
• Pollen undergoes hydration. Pollen wall proteins cire released.
• The entire content moves into pollen tube.
• Growth is at the cytoplasmic contents at the tip.
• The remaining part of pollen tube is occupied by a vacuole.
• It is cut off from tip by callose plug.
• The hemispherical, transparent pollen tip of pollen tube is called ‘cap block.
• The “cape block” disappears and the growth of the pollen tube stops.

2. Growth of pollen tube in the style.

• Hollow style glandular canal cells secrete mucilaginous substance. These secretions are nutrition for growing pollen tube. They control compatibility of style and pollen tube.
• In solid style the pollen tube grows through the intercellular space of transmitting tissue. Semisolid style is intermediate between solid and open type.

3. Entry of the pollen tube into the ovule.

• Propgamy – Pollen tube enters through the micropyle.
• Chalazogamy – Pollen tube enters through chalaza.
• Monogamy – Pollen tube enters through integument.

4. Entry of pollen tube into the embryo sac.

• Pollen tube enters embryosac at the micropylar end. It is guided by an obturator.
• Pollen tube enters into one of the synergids.

5. Double fertilization and Triple fusion.

• In Angiosperms, both the male gametes are involved in fertilization, it is called double fertilisation.
• One of the male gametes fuses with the egg nucleus (syngamy). Thus zygote is formed.
• The second gamete migrates to central cell. It fuses with polar nuclei (or) secondary nucleus. Thus primary Endosperm nucleus is formed. This involves the fusion of 3 nuclei so it is called Triple fusion.

51.What is endosperm. Explain the types. (OR) Write the three fusion of Antisper- mous plant fertilization.

The zygote divides into an endosperm.

The primary Endosperm Nucleus is the regulatory structure. It nourishes the developing embryo.

These types of endosperms are based on the mode of development.

a) Nuclear Endosperm. (Ex.Arachis)

• Primary Endosperm Nucleus undergoes mitosis.
• No cell wall formation.
• A free nuclear condition exists

b) Cellular Endosperm (Ex. Helianthus)

• Primary Endosperm Nucleus divides into 2 nuclei.
• It is followed by wall formation.

c) Helobial Endosperm. (Ex. Vallisneria)

• Primary Endosperm Nucleus moves towards the base of the embryo sac. It divides into 2 nuclei.
• Cell wall is formed. It divides large micropylar chamber into form the small chalazal chamber.
• Nucleus of micropylar chamber divides. The Chalazal chamber nucleus does not divide.

52.Differentiate the structure of Dicot and Monocot seed.

Answer:

Structure of Dicot seed

• Two cotyledons
• Two seeds may be seen
• The seed coat has outer coat testa and inner tegmen.
• In pea the cotyledons store the food. In castor the endosperm, stores reserve food.
• Coleoptile (sheath of plumule) coleorhiza (sheath of radicle) are absent.

Structure of Monocot seed :

• Only one cotyledon
• Paddy is one-seeded.
• Seed is enclosed by husk. The brown membranous seed coat closely adheres to grair
• Scutellum supplies embryo with food from endosperm through epithelium
• Coleoptile and coleorhiza are seen.

53.Give a detailed account of parthenocarpy. Add a note on its significance.

Answer:

In some plants, fruit-like structures may develop from the ovary without the act of fertilization. Such fruits are called parthenocarpic fruits. Invariably they will not have true seeds. Many commercial fruits are made seedless.

Examples: Banana, Grapes, and Papaya. Nitsch in 1963 classified the parthenocarpy into the following types:

1. Genetic Parthenocarpy: Parthenocarpy arises due to hybridization or mutation.
2. Examples: Citrus, Cucurbita.
3. Environmental Parthenocarpy: Environmental conditions like frost, fog, low temperature, high temperature etc., induce Parthenocarpy. For example, low temperature for 3-19 hours induces parthenocarpy in Pear. Chemically
4. induced Parthenocarpy: Application of growth-promoting substances like Auxins and Gibberellins induces parthenocarpy.
5. Significance: The seedless fruits have great significance in horticulture.
6. Seedless fruits have great commercial importance.
7. Seedless fruits are useful for the preparation of jams, jellies, sauces, fruit drinks, etc.
8. A high proportion of edible parts is available in parthenocarpic fruits due to the absence of seeds.