Reproduction in lower and higher plants. Exercise

 Reproduction in lower and higher plants.           

                                      Exercise

Q. 2 Very short answer type questions :

1. Name the part of gynoecium that determines the compatible nature of pollen grain.

ANS : stigma

2. How many haploid cells are present in a mature embryo sac ?

ANS : An unfertilized embryo sac of angiosperm is composed of 7 cells i.e., 7-celled and

8-nuclei. Among 8-nuclei, 6 are enclosed by cell walls and are organized into cells, which

are haploid in number - 3 antipodal, 2 synergids and 1 egg cell and a large central cell

with 2 pollen nuclei.

3. Even though each pollen grain has 2 male gametes, why atleast 20 pollen grains are

required to fertilize 20 ovules in a particular carpel?

ANS : because only one male gamete is involved in syngamy or the fusion of male

gamete with the egg cell.

4. Define megasporogenesis ?

ANS : Formation of megaspores from megaspore mother cell called megasporogenesis. It

occurs inside the nucellus of ovule of angiosperm. The process begins very early then

nucellus is not completely surrounded by the integuments.

5. What is hydrophily ?

ANS : Hydrophily is the term given to pollination occurred by water. Some plants

distribute their pollen to the surface of water and some plants distribute pollens

beneath the surface of water.

6. Name the layer which supplies nourishment to the developing pollen grains. 

ANS: Tapetum is the innermost layer of the microsporangium. It provides nourishment to the developing pollen grains.

7. Define parthenocarpy.

ANS: Parthenocarpy is the development of fruit without the formation of seeds due to lack of 

pollination, fertilization and embryo development. The condition can be artificially induced by the application of hormones. Such fruits are seedless. Example: Grapes, Banana, Oranges.

8. Are pollination and fertilization necessary in apomixis ? 

ANS: Apomixis or Agamospermy involves formation of embryos and seeds by asexual methods without involving meiotic gametogenesis and sexual fusion of gametes. Pollination and fertilization are not necessary in apomixis.

9. Name the parts of pistil which develop into fruits and seeds.

ANS: A pistil has three parts , i.e., stigma (receives pollen), which grows down through style to ovary. Ovary contains ovules, which contain an egg. The ovary develops into the fruit and ovule develops into a seeds.

10. What is the function of filiform apparatus ?

ANS : The function of filiform apparatus is to guide entry of pollen tube and release of sperm cells.

Q. 3 Short Answer Questions : 

1. How polyembryony can be commercially exploited ?

ANS : 

• It offers consequent result of multiple seedlings in an emergency.

• However, it exploited disease of free plants which acquired by specific methods.

• It makes to improve the probability of survival under different conditions.

• It might keep using on hybrid seeds to increase crops on the year.

2. Pollination and seeds formation are very crucial for the fruit formation. Justify the 

statement.

ANS : 

• TRANSFERENCE OF POLLEN GRAIN FROM THE ANTHER TO THE STIGMA IS POLLINATION. 

• THEN A POLLEN TUBE IS FORMED THROUGH WHICH THE 2 MALE GAMETES PASS.

• THEN ONLY FERTILISATION OCCURS...THE FERTILISED OVULE DEVELOPS INTO SEED.OVARY 

INTO FRUIT.

• SO WE CAN CLEARLY SAY THAT POLLINATION AND SEED FORMATION ARE VERY 

IMPORTANT FOR FRUIT FORMATION.WITHOUT THESE PROCESSES FRUITS are NOT 

FORMED.

3. Incompatibility is a natural barrier in the fusion of gametes. How will you 

explain this statement? 

ANS : 

• Gametic incompatibility is a natural prezygotic reproductive isolation mechanism.

• Prezygotic isolation mechanisms are defined as the mechanisms which prevent the 

formation of zygote between incompatible organisms.

• In gametic incompatibility, if the sperm and ova are from different species then they 

do not recognize each other and hence do not fuse to form the zygote.

• Hence, incompatibility act as a natural barrier for fusion of gametes to prevent 

reproduction between individuals of different species.

4. Describe three devices by which cross pollination is encouraged in 

Angiosperms by avoiding self pollination.

ANS : 

Three outbreeding devices that flowering plants have developed:

• Receptivity of stigma and release of the pollen grain is not synchronized, i.e., stigma 

becomes receptive much before pollens are released or after they are released to avoid 

self-pollination.

• Self-incompatibility: A genetic method to prevent pollens from fertilizing ovules of the 

same flower by inhibiting their germination on stigma or pistil.

• Production of unisexual flowers: So that the male and female parts will be present on 

different plants i.e., dioecious or on different flowers in the same plant (monoecious).

• This prevents both autogamy and geitonogamy.

Q. 4 Long Answer Questions : 

1. Describe the process of double fertilization ?

ANS : 

DEFINITION :- 

“Double fertilization is a complex process which involves the fusion of one female 

gametophyte with two male gametes”

EXPLANATION : 

• Angiosperms are flower-bearing plants and are the most diverse group of terrestrial plants. The flowers form the reproductive part of angiosperms with separate male and female reproductive organs. 

• Each contains gametes – sperm and egg cells respectively. Pollination helps the pollen grains to reach stigma via style. The two sperm cells enter the ovule-synergid cell. This proceeds to fertilization.

• In angiosperms, fertilization results in two structures, namely, zygote and endosperm, hence named, double fertilization.

• Double fertilization is a complex process where out of two sperm cells, one fuses with the egg cell and the other fuses with two polar nuclei which result in a diploid (2n) zygote and a triploid (3n) primary endosperm nucleus (PEN) respectively. Since endosperm is a product of the fusion of  three haploid nuclei, it is called triple fusion.

• Eventually, the primary endosperm nucleus develops into the primary endosperm cell (PEC) and then into the endosperm.The zygote becomes an embryo after numerous cell divisions.

2. Explain the stages involved in the maturation of microspore into male
gametophyte ?

ANSWER :-

• The nucleus of each microspore mother cell undergoes meiosis or reduction division

and gives rise to four haploid nuclei. This process is called microsporogenesis.

• The four nuclei are arranged tetrahedrally and soon get enclosed with cell walls. These

are now called microspores or pollen grains.

• These microspores fiurther divide once by mitosis to form two-celled microspore.

differentiates into pollen grain.

• Each microspore The pollen grains soon dry up and become powdery while the

tapetum gets absorbed.

• The partition walls between the sporangia get destroyed and the microspores are

liberated by the dehiscence of the anther.

3. Explain the development of dicot embryo.

ANSWER :-

• The oospore divides transversely forming two cells, a terminal cell and basal cell. The cell 

towards the micropylar end of the embryo sac is the suspensor cell (i.e., basal cell) and the 

other one makes to the embryo.

• cell (i.e., terminal cell). The terminal cell by subsequent divisions gives rise to the embryo 

while the basal cell contributes the formation of suspensor.

• The terminal cell divides by a vertical division forming a 4-celled 1-shaped embryo. In 

certain plants the basal cell also forms the hypocotyl (i.e., the root end of the embryo) in 

addition of suspensor.

• The terminal cells of the four-celled pro-embryo divide vertically at right angle to the first vertical wall forming four cells. Now each of the four cells divides transversely forming the octant stage (8-celled) of the embryo.

• The four cells next to the suspensor are termed the hypo-basal or posterior octants while 

the remaining four cells make the epibasal or anterior octants.

• The epibasal octants give rise to plumule and the cotyledons, whereas the hybobasal

octants give rise to the hypocotyl with the exception of its tip.

• Now all the eight cells of the octant divide periclinally forming outer and inner cells. The 

outer cells divide further by anticlinal division forming a peripheral layer of epidermal cells, 

the dermatogen.

 

4. Draw a labelled diagram of the L.S. of anatropous ovule and list the components of embryo sac 

and mention their fate after fertilization ?

ANSWER :

LIST OF COMPONENTS :

• The egg cell forms the 

zygote.

• Antipodals degenerate.

• Central nuclei forms 

primary endosperm 

nucleus​

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