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Saturday, 2 October 2021

APOMIXIS AND POLYEMBRYONY l Sexual Reproduction in Flowering Plants - NCERT Based

 

APOMIXIS AND POLYEMBRYONY

 

·         Although seeds, in general are the products of fertilisation, a few flowering plants have evolved a special mechanism, to produce seeds without fertilisation, called apomixis.

 

such as some species of

-- Asteraceae

-- grasses

 

·          Thus, apomixis is a form of asexual reproduction that mimics sexual reproduction.

 

·         There are several ways of development of apomictic seeds.

 

      In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation.

 

·         More often, as in many Citrus and Mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred as polyembryony.

 

·         IMPORTANCE OF APOMICTIC SEEDS:

 

      Hybrid varieties of several of our food and vegetable crops are being extensively cultivated.

      Cultivation of hybrids has tremendously increased productivity.

      One of the problems of hybrids is that hybrid seeds have to be produced every year.

       If the seeds collected from hybrids are sown, the plants in the progeny will segregate and do not maintain hybrid characters.

      Production of hybrid seeds is costly and hence the cost of hybrid seeds become too expensive for the farmers.

       If these hybrids are made into apomicts,

--  there is no segregation of characters in the hybrid progeny.

--  Then the farmers can keep on using the hybrid seeds to raise new crop year after year

--  Farmer does not have to buy hybrid seeds every year.

 

·          Because of the importance of apomixis in hybrid seed industry, active research is going on in many laboratories around the world to understand the genetics of apomixis and to transfer apomictic genes into hybrid varieties.

 

 

 

 

 

MCQs - Sexual Reproduction in Flowering Plants l NEET l Biology l ABHYAS l NTA

 MCQs - Sexual Reproduction in Flowering Plants

1.        Which statement is not correct?

a.       The gynoecium represents the female reproductive part of the flower.

b.       The gynoecium may consist of a single pistil (monocarpellary) or more than one pistil (multicarpellary).

c.       When there are more than one, the pistils may be fused together (apocarpous) or may be free (syncarpous)

d.       The placenta is located inside the ovarian cavity

    2. Find correct statement

a.       Megasporangia are called ovules and arise from placenta

b.       Megasporangia are present inside the anther

c.       There are four mega sporangia in each anther

d.       Megasporangia are present in the embryosac

   3. The number of ovules in the ovary of Orchids and Paddy are respectively

a.       many and one

b.       many and two

c.       one and five

d.       one and many

  4. Ovule is attached  to the placenta by means of stalk called

a.       Hilum

b.       Funicle

c.       Raphe

d.       Micropyle

 5. The body of the ovule fuses with funicle in the region called

a.       Hilum

b.       Funicle

c.       Raphe

d.       Micropyle

6. Integuments encircle the ovule except at the tip where a small opening is organized. This opening is called the

a.       Raphe

b.       Chalaza

c.       Micropyle

d.       Hilum

7. Find the incorrect statement

a.        Enclosed within the integuments is a mass of cells called the nucellus

b.       Cells of the nucellus have no reserve food materials

c.       Located in the nucellus is the embryo sac or female gametophyte

d.       Embryo sac is also called female gametophyte

8. In Angiosperms an ovule generally has

a.       Two embyo sacs

b.       Many embryo sacs

c.       Single embryo sac

d.       No embyo sac

9. Ovule is  formed from a

a.       megaspore through reduction division

b.       microspore through reduction division

c.       megaspore through equational division

d.       microspore through equational division

10. Ovules generally differentiate

a.       a single megaspore mother cell (MMC) in the micropylar region of the nucellus

b.       four megaspore mother cells (MMC) in the micropylar region of the nucellus

c.       a single megaspore mother cell (MMC) in the chalazal region of the nucellus

d.       four megaspore mother cells (MMC) in the chalazal region of the nucellus

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