XII BIOLOGY
CH-1 Reproduction in Lower and Higher PLANTs EXERCISE
Q. 1. Multiple choice questions :
(1) Insect pollinated flowers usually possess
(a) sticky pollen with rough
surface
•
(b) large quantities of pollens
•
(c) dry pollens with smooth surface
•
(d) light coloured pollens
(2) In ovule,
meiosis occurs in …………….
•
(a) Integument
•
(b) Nucellus
•(c)Megaspore
•
(d) Megaspore mother cell
(3) The ploidy level
is not the same in………..
(a) Integuments and nucellus
(b) Root tip and shoot tip
(d) Megaspore mother cell
(d) Antipodals and synergids
(4) Which of the
following types require pollination but result is genetically similar to
autogamy?
•
(a) Geitonogamy
•
(b) Xenogamy
•
(c) Apogamy
•
(d) Cleistogamy
(5) If
diploid chromosome number in a • flowering
plant is 12, then which one of the following will have 6 chromosomes?
•
(a) Endosperm
•
(b) Leaf cells
•
(c) Cotyledons
•
(d) Synergids
(6) In angiosperms;
endosperm is formed by/ due to ……..
•
(a) free nuclear divisions of megaspore
•
(b) polar nuclei
•
(c) polar nuclei and male gamete
•
(d) synergids and male gametes.
(7) Point
out the odd one ……….
•
(a) Nucellus
•
(b) Embryo sac
•
(c) Micropyle
• (d) Pollen grain
Q. 2. Very short answer questions.
(1) Name The part of gynoecium that determines the compatible nature of pollen grain.
Ans. Stigmatic surface.
(2) How many haploid cells are present in a mature embryo sac?Ans.6 cells, 2 synergtds, 1 egg cell, 3 antipodals.
(3) Even though each pollen grain has 2 male gametes why at least 20 pollen grains are required to fertilize 20 ovules in a particular carpel?
Ans. Yes, Angiosperms have a double fertilization in which both the male gametes are utilized, one for fusion with egg cell to form zygote and other for fusion with secondary nucleus to form endosperm.
(4) DefineMegasporogenesis .
ans-It is the process of formation of haploid megaspores from diploid megasporemother cell.
(5) What is hydrophily?
Ans. Transfer of pollen grains in pollination process through agency of water is known as hydrophily.
(6 )Name The layer which supplies nourishment to the developing pollen grains. Ans. Tapetum .
(7)Define Parthenocarpy:- ans- in which fruit is developed without the process of fertilization is called parthenocarpy.
(8) Are pollination and fertilization necessary in apomixis?
Ans. No, need of pollination and fertilization. Apomixis is formation of embryos without formation of gametes .
(9) The part of pistil which develops into fruit and seed.
Ans. Ovary develops into fruit and ovules into seed.
(10) What is the function of filform apparatus?
Ans. Filiform apparatus guides the pollen tube towards egg cell.
Q.3.
Short Answer Questions.
(1) How polyembryony can be commercially
exploited?
Ans.(i ) Polyembryony is the development of more than one embryo inside the seed.
(ii) When polyembryonic seed germinate we get multiple seedlings from it.
(iii) This condition increases the chances of survival of new plants.
(iv) Nucellar embryos are genetically identical to parent plants hence we get uniform plants.
(v) In the horticulture we can utilize these as rootstock for grafting.
(vi) So they have significant role in fruit breeding programmes e.g. Citrus, Mango.
(2) Pollination and seeds formation are
very crucial for the fruit formation,
Justify the statement.
Ans.( I) After fertilization, ovary is transformed into fruit, where ovary wall becomes fruit wall, i.e pericarp.
(2) Mature ovules are transformed into seeds after fertilization.
(3) In Fertilization a male gametes unites with female gamete to form zygote which develops into embryo.
( 4) In pollination process pollen grains carrying non-motile male gamete are transferred on stigma.
(5) The Seeds have embryo which germinate into new plant.
6) So,The goal of reproduction to create offspring for next generation is achieved. Hence the crucial events for fruit formation .
(3) Incompatibility is a natural barrier
in the fusion of gametes. How will you explain this statement?
Ans.(i ) Self incompatibility is a genetic mechanism that prevents germination of pollen on stigma of same flower. This favours for cross pollination. E.g. Tobacco.
(ii) In pollen-pistil interaction, when pollen grain is deposited on stigma, pistil has the ability to recognize and allow germination of right type of pollen.
(iii) Special type of proteins present on stigmatic surface determine compatibility or incompatibility.
(iv) The physiological mechanism operates to ensure successful germination of compatible pollen.
(v) Compatible pollen absorbs water and nutrients from stigmatic surface that are absent in pollen and pollen tube emerges which grows through style.
(4)Describe three devices by which cross pollination is encouraged in Angiosperms by avoiding self-pollination?
Ans- Following are the outbreeding devices.
(1) Unisexuality: The plants bear either male or female flowers. Due to unisexual nature, self-pollination is avoided. Plants are either dtoectous, e.g. Papaya or monoecious, e.g. maize.
(2) Heteromorphy: In same plants different types of flowers are produced. In these flowers, stigmas and anthers are situated at different levels. There is heterostyly and heteroanthy. This prevents self-pollination e.g. Primrose.
(3) Herkogamy : In bisexual flowers we may come across mechanical device to prevent self-pollination. Natural physical barrier avoids contact of pollens with stigma. E.g. Calotropis where pollinia are situated below the stigma.
Q.4. Long A nswer Questions.
(1) Describe the process of double fertilization.
Ans.Double fertilization :
(I) The two male gametes produced by the male gametophyte in angiosperms, one unites with the female gamete and the other unites with the secondary nucleus
(2) Here, both the male gametes take part in fertilization and fertilization occurs twice, it is called double fertilization..
(3) During double fertilization, the pollen tube on reaching the ovule enters the embryo sac through micropyle and bursts in one of the synergtds.
(4) Owing to this, the two male gametes contained in the pollen tube, are set free.
(5) Out of the two male gametes, one unites with the egg and the other unites with the secondary nucleus of the embryo sac, forming a triploid or triple fusion nucleus, called the primary endosperm nucleus.
(6) The process involving the fusion of one of the male gametes with the egg nucleus, resulting in the formation of a diploid zygote is called syngamy.
(7) The reproductive process in which nonmotile male nuclei are carried to the egg cell through a pollen tube is called siphonogamy.
(8) After fertilization, zygote develops into an embryo. These changes take place in the ovule leading to the development of a seed.
(2) Explain the stages involved in the maturation of microspore into male gametophyte.
Ans-
- 1) Microspore is first cell of male gametophyte.
- 2) The protoplast of pollen grain divides mitotically to form two cells a small thin walled generative cell and a large naked vegetative or tube cell.
- (3) The generative cell is thin cytoplasm and a nucleus.It separates and floats in the cytoplasm of vegetative cell.
- (4) The vegetative is thick cytoplasm, irregular shaped nucleus and the reserved food.
- (5) In majority of the angiosperms, the pollen grains are liberated at two-celled stage after the dehiscence of the anther.
- (6) The generative cell of the pollen grain divides by mitosis to form two male nonmotile gametes.
