Rajasthan Board RBSE Class 12 Biology Chapter 3 Pollination, Fertilization & Development of Endosperm and Embryo
RBSE Class 12 Biology Chapter 3 Multiple Choice Questions
Question 1.
In which of the following, cleistogamous pollination is found?
(a) Viola
(b) Papaya
(c) Jamun (BlackBerry)
(d) Cassia
Answer:
(a) Viola
Question 2.
Pollination in Anthocephalus occurs by –
(a) Bird
(b) Insect
(c) Bat
(d) Elephant
Answer:
(c) Bat
Question 3.
What develops after triple fusion?
(a) Embryo sac
(b) Embryo
(c) Endosperm
(d) Seed
Answer:
(c) Endosperm
Question 4.
Seed coats develop from –
(a) Integuments
(b) Nucellus
(c) Funicle
(d) Hilum
Answer:
(a) Integuments
Question 5.
Who discovered double fertilization?
(a) Robert Hooke
(b) Strasburger
(c) Nawaschin
(d) Leeuwenhoek
Answer:
(c) Nawaschin
RBSE Class 12 Biology Chapter 3 Very Short Answer Questions
Question 1.
What do you understand by “Heterostyly”?
Answer:
Heterostyly is an adaptation to prevent self-pollination and ensure cross-pollination. In this, the flowers are of two or three forms as regards to the length of stamens and styles so that the anthers and stigmas are at different levels. As a consequence pollen from a flower can not reach the stigma of the same flower.
Question 2.
Differentiate between homogamy and dichogamy.
Answer:
In some plants, stamens and carpels of a bisexual flower mature at the same time. This is known as homogamy. In such flowers, pollen grains of the flower can pollinate the stigma of the same flower whereas dichogamy is the condition where stamens and carpels of a bisexual flower mature at different times and hence self-pollination are eliminated. In short, homogamy promotes self-pollination and dichogamy promotes cross-pollination.
Question 3.
Define incompatibility?
Answer:
Failure of germination of pollen on the stigma of the same flower or on any flower of the same strain is called incompatibility or self sterility. It is on account of negative interaction between the pollen and pistol. The reason may be physiological or morphologically. It may be determined by pollen or the male gametophyte or by the sporophytic tissue. Thus cross-pollination becomes inevitable in such cases.
Question 4.
Name the scientist who first of all discovered fertilization in plants?
Answer:
The process of fertilization in plants was first discovered by Strasburger (1884).
Question 5.
Differentiate between epicotyl and hypocotyl.
Answer:
The portion of the axis of embryo lying below the base of cotyledons is called hypocotyl whereas the portion of the axis of embryo lying above the base of cotyledons is called epicotyl.
Question 6.
Differentiate between aril and caruncle.
Answer:
In some plants, an outgrowth looking like a third integument grows around the ovule and is called as aril. The juicy edible part in litchi on the seed surface is aril. Whereas a small corky outgrowth somewhat whitish in colour formed at the micropyle of the seed is known as caruncle.
(Example: Castor seed).
Question 7.
Name two hormones which induce parthenocarpy.
Answer:
Spraying auxins and gibberellins on the stigma can induce parthenocarpy in some plants.
Question 8.
What does plumule forms at the time of seed germination?
Answer:
Shoot system is formed by the plumule after germination of seeds.
Question 9.
From where does developing embryo gets nutrition?
Answer:
During development, the embryo derives nourishment from the endosperm.
Question 10.
Why pollen grains are conserved for a long time?
Answer:
The wall of the pollen grain has deposition of a complex compound known as sporopollenin. This substance is waterproof, resistant to microbial decay, and is very stiff. This hardshell ensures that the tender cell inside has a strong chance of survival.
Question 11.
Differentiate between albuminous and exalbuminous seeds.
Answer:
In albuminous seeds, the endosperm tissue persists in the mature seed and is used up at the time of germination. In these seeds, the embryo is minute, whereas in exalbuminous seeds the endosperm is used up during embryo development and the mature seed does not contain endosperm. In such seeds, the embryo is bulky and food is stored in cotyledons of the seed.
Question 12.
Name the types of endosperm formed in angiosperms.
Answer:
In angiosperms, three types of endosperm are formed.
These are:
- Nuclear endosperm
- Cellular endosperm
- Global endosperm
Question 13.
Name the Scientist and the plant in which double fertilization was first observed.
Answer:
Double fertilization was first studied by Nawaschin in 1898 and it was first worked out in Fritillaria SPS.
Question 14.
Write peculiarities of pollen formed in wind-pollinated flowers.
Answer:
Wind pollinated flowers produce pollen in large amount and the pollen is small, dry, light and smooth so that they can be blown by the wind to a great distance.
Question 15.
Write the ploidy (n or 2n or 3n) nature of polar nuclei, primary endosperm nucleus, definitive nucleus synergids and nucellus.
Answer:
- Polar nuclei (n)
- Primary endosperm nucleus (3n)
- Definitive nucleus (2n)
- Synergids (n)
- Nucellus (2n)
Question 16.
Diferentiate between pericarp and perisperm.
Answer:
After pollination and fertilization, the ovules develop into seed and the ovary is transformed into fruit. The wall of ovary forms the fruit wall and it is called pericarp whereas perisperm is the remains of nucellus in the form of a thin and papery membrane in the seed in some cases.
(Example: Black pepper).
RBSE Class 12 Biology Chapter 3 Short Answer Questions
Question 1.
Describe two adaptations for cross-pollination in plants.
Answer:
Adaptation for cross-pollination is unisexuality and dichogamy. In unisexual flowers, stamens and carpels are borne in different flowers either on the same plant or in flowers borne on separate plants ensuring cross-pollination. In dichogamy, stamens and carpels in a flower do not mature at the same time and hence self-pollination is eliminated. When pollen grains are transferred to the stigma of the flower on the different plant it is called Cross-pollination or Allogamy.
Two adaptations for cross-pollination:
- Xenogamy: Pollen grains of a flower is transferred to the stigma of a different flower on a different plant of same species.
- Hybridism: Pollen grains of a flower is transferred to the stigma of a flower of a plant of different species.
Question 2.
What is meant by self sterility?
Answer:
Self sterility is also known as incompatibility. Failure of germination of pollen on the stigma of the same flower or on any flower of the same strain is called incompatibility or self sterility. It is on account of negative interaction between the pollen and pistol. The reason may be physiological or morphological. It may be determined by pollen or the male gametophyte or by the sporophytic tissue. Thus cross-pollination becomes inevitable in such cases.
Question 3.
What is double fertilization?
Answer:
This is a unique feature of angiosperms. Here one of the two male gametes fertilizes the egg to form zygote or oospore. This act is called fertilization. This is necessarily followed by the fusion of the second male gamete with the product of a fusion of the two polar nuclei, i.e. with the secondary nucleus. This act of fusion of the second male gamete with the secondary nucleus to form the primary endosperm nucleus is called triple fusion and the whole process is referred to as double fertilization.
Question 4.
What is the importance of triple fusion?
Answer:
The result of the triple fusion is the formation of a triploid nucleus called a primary endosperm nucleus. This nucleus by repeated mitotic divisions gives rise to the formation of the endosperm. This endosperm provides nourishment to the developing embryo. It is a unique event in the entire living world where a triploid tissue nourishes a diploid tissue, and also that the nourishing tissue has genome both of maternal as well as paternal parents.
Question 5.
What is the role of the suspensor in embryo?
Answer:
The suspensor pushes the developing embryo in the food-laden endosperm and thus ensures proper development of an embryo. The extreme micropylar cell of suspensor becomes enlarged and also functions as haustorium. The lowermost cell of suspensor, in contact with the developing embryo, is called hypophysis and gives rise to the tip of radicle.
Question 6.
What changes occur during the transformation of the ovule into a seed?
Answer:
After a successful act of fertilization and double fertilization, each ovule is transformed into the seed.
The parts of ovule undergo morphological changes as follows:
- Funicle – Stalk of seed
- Micropyle – Gets sealed
- Nucellus – Degenerates in most cases.
- Integuments – Seed coat, (outer integument-Testa and inner integument-Tegmen).
- Fertilized egg – Embryo
- Primary endosperm nucleus – Endosperm (Present in albuminous seeds and not in exalbuminous seeds).
- Antipodals and synergids – Degenerate.
Question 7.
In how many ways, pollen tube may enter into ovule?
Answer:
The pollen tube may enter the ovule by three different paths as follows:
- The most common method of entry of pollen tube into ovule is through the micropyle and this method is called polygamy.
- In some cases, the pollen tube enters the ovule through the chalazal end and this is called chalazogamy.
- In a few cases, the pollen tube enters the ovule by penetrating through integuments and this type of entry is called misogamy.
RBSE Class 12 Biology Chapter 3 Essay Type Questions
Question 1.
How many types of pollination is found? Explain adaptations in flower for cross-pollination in brief.
Answer:
Transfer of pollen from the anther to the stigma of the flower is called pollination.
It can be of two types:
- Self-pollination
- Cross-pollination
In cross-pollination, pollen grains are transferred by some agency from the flower to the stigma of the flower on a different plant of the same species or a different species. To eliminate self-pollination and to promote cross-pollination, flowers develop following adaptations:
- Self sterility or incompatibility
- Unisexuality or Decline
- Dichogamy
- Herkogamy
- Heterostyly
Following contrivances or adaptations always promote cross-pollination:
1. Self sterility or Incompatibility:
In this condition, the pollen grains of the same flower cannot fertilize their own ovules even though there are favourable conditions and so they do not germinate on the stigma of the same flower.
Example: Passiflora, Malva, Potato, Vitis, Petunia etc.
2. Unisexuality or Dicliny:
In unisexual flowers, stamens and carpels are found in different flowers.
Unisexuality can be of two types:
- Monoecious: When male and female flowers are borne on the same plant.
Example: Maize, Cucurbita, Castor. - Dioecious Plants: When male and female flowers are borne on different plants.
Example: Carica papaya, Cannabis sativa.
3. Dichogamy: In many hermaphrodite or bisexual flowers stamens and carpels of a flower do not mature at the same time.
Dichogamy is of two types:
- Protandry: The anthers of a flower mature earlier than carpels.
Example: Jasminum, Foeniculum, Tagetus, Sunflower. - Protogyny: The carpels of a flower, mature earlier than stamens.
Example: Ficus bengalensis Polyalhia, Anona, Michelia, Rose.
4. Herkogamy: In some homogeneous flowers there are some adaptations due to which self-pollination cannot occur. These adaptations are as follows: In caryophyllaceous flowers, the stigma projects beyond the stamens so that pollen does not fall on it, conversely, in Gloriosa, they dehisce at a distance so that stigma is out of reach to its own pollen.
5. Heterostyly: The flowers may be of two or more types with regard to the length of the style and length of stamens and hence pollen from a flower cannot bring about effective pollination in flowers of its own type.
Example: Oxalis, Lythrum, Primula.
Question 2.
Write a brief account of fertilization in angiospermous plants. Explain major events, basically the changes in ovule after fertilization.
Answer:
Out of two male gametes released from the pollen tube, one fuses with the egg cell. This act is called fertilization. In angiosperms, this is necessarily followed by fusion of the second male gamete with the product of a fusion of two polar nuclei i.e. with the secondary nucleus. This is called triple fusion and thus both the male gametes participate in the act of fertilization. This is called double fertilization and is a unique feature of angiosperms. After a successful act of fertilization and double fertilization, each ovule is transformed into the seed.
The parts of ovule undergo morphological changes as follows:
- Funicle – Stalk of seed
- Micropyle – Gets sealed
- Nucellus – Degenerates in most cases.
- Integuments – Seed coat, (outer integument-Testa and inner integument-Tegmen).
- Fertilized egg – Embryo
- Primary endosperm nucleus – Endosperm (Present in albuminous seeds and not in exalbuminous seeds).
- Antipodals and synergids – Degenerate.
Question 3.
With the help of well-labelled diagrams, Explain different types of endosperm development in
angiosperms.
Answer:
Three types of endosperms are formed in angiosperms. These are:
- Nuclear type
- Cellular type
- Global type
1. Nuclear endosperm:
The primary endosperm nucleus divides repeatedly without wall formation. All the divisions are mitotic. Many nuclei are formed by free nuclear division. Nuclei arrange towards the periphery of the embryo sac and a large vacuole is formed in the centre. After sometime wall formation starts and it becomes cellular. 56% of families of angiosperms have this kind of endosperm. Coconut water is an example of the nuclear endosperm. There is liquid filled in endosperm in which many nuclei float. This is called liquid endosperm.
2. Cellular endosperm: The primary endosperm nucleus divides mitotically. The first and most of the subsequent nuclear divisions are accompanied by wall formation so that the embryosac becomes divided into several chambers. This type of endosperm formation is common in gamopetalous.
Example: Villarsia, Adoxa.
3. Global endosperm: It is intermediate between nuclear and cellular type. The first division of endosperm mother nucleus is followed by wall formation forming two unequal cells, (a very large micropylar and small chalazal). Micropylar cell divides by free nuclear divisions later followed by wall formation. In the chalazal cell, 1 or 2 divisions may take place and it functions as small haustorial cell.
Example: Order Helobiales of monocot plants.
Question 4.
Describe embryo development in angiosperms with the help of a well-labelled diagram.
Answer:
The embryo development in Capsella bursa pattern is considered as typical of dicotyledons. A line diagram shows the pattern of division.
Question 5.
Write a short note on:
- Incompatibility
- Development of seed
- Development of fruit
- Alternation of generation
Answer:
1. Incompatibility:
Failure of germination of pollen on the stigma of same plant or failure of fusion between the functional male gamete with the mature and functional egg is called as incompatibility or self sterility. This may be physiological or morphological and is considered as an adaptation to eliminate self-pollination and promote cross-pollination
2. Development of seed:
After successful fertilization, the ovule is transformed into seed by several morphological and physiological changes. After a successful act of fertilization and double fertilization, each ovule is transformed into the seed.
The parts of ovule undergo morphological changes as follows:
- Funicle – Stalk of seed
- Micropyle – Gets sealed
- Nucellus – Degenerates in most cases.
- Integuments – Seed coat, (outer integument-Testa and inner integument-Tegmen).
- Fertilized egg – Embryo
- Primary endosperm nucleus – Endosperm (Present in albuminous seeds and not in exalbuminous seeds).
- Antipodals and synergids – Degenerate.
3. Development of fruit:
The stimulus of pollination and fertilization induces several changes in the ovary and it is transformed into fruit. The ovary wall forms the fruit wall called pericarp and it encloses the seeds formed by the transformation of ovules.
4. Alternation of generation:
In all sexually reproducing plants, there are two phases or generations in the life cycle. These two generations are haploid gametophytic (n) and diploid sporophytic (2n) phase and the two occur alternately. “This is called alternation of a generation”.
In angiosperms, the prominent phase is diploid sporophyte, differentiated into root, stem and leaves. It gives rise to haploid phase by meiotic division of microspore mother cells and megaspore mother cells. The gametophytic phase produces male gametes and egg cell which by syngamy bring the diploid phase into existence. Here the gametophytic phase is short-lived and is completely dependent on the diploid sporophytic phase.
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