Pre-Fertilization Events in Flowering Plants MCQ - Practice Questions with Answers

• All the events of sexual reproduction that take place before the fusion of gametes are included in this category. 
• Two main pre-fertilization events are:
  • gametogenesis (formation of gametes) 
  • gamete transfer

Gametogenesis:

• The process of formation of male and female gametes is called gametogenesis.
• Gametes are haploid cells.
• Organisms such as monerans, fungi, algae, and bryophytes have a haploid parental body. 
• Such types of organisms produce gametes by mitotic division. 
• If the parent body is diploid gametes are formed by meiosis.
• When male and female gametes are similar in appearance and it is not possible to differentiate them into male and female gametes, they are called homogametic or isogametes. 
• If the male and female gametes are morphologically dissimilar they are called heterogametes. 
• Among heterogametes, the male reproductive unit is called antherozoid or sperm and the female reproductive unit is known as egg or ovum.
• Plants belonging to the pteridophyte, gymnosperms, angiosperms and most of the animals including human beings have a diploid parental body. 
• In such organisms, specialized cells are present, which take part in the production of gametes. 
• These cells are called meiocytes.
• On the basis of the stage at which the meiosis occurs, the meiosis can be of following types:
  • Zygotic meiosis: Meiosis occurs in the zygote.
  • Sporic meiosis: Meiosis occurs in sporangia to produce haploid spores that produce gametophytes.
  • Gametic meiosis: Meiosis occurs in the diploid germinal cells.
     

• Gamete transfer must occur in order to facilitate the fusion.
• In some algae and fungi, both male and female gametes are motile. 
• In the majority of organisms, male gametes are motile while the female gametes are stationary. 
• After gamete formation, male and female gametes should come in the physical association, so that they can be fused with each other.
• In algae, bryophytes, and pteridophytes, for the transfer of male gametes water acts as the medium. 
• During this transfer, a large number of gametes fail to reach the female gametes. 
• To fulfill this loss, the number of male gametes produced is several thousand times the number of female gametes.
• In seed plants, pollen grains are the carriers of male gametes and ovule have the egg.
• Pollen grains are produced in anthers, therefore, they have to be transferred to the stigma before it can lead to fertilization.
• In bisexual, self-fertilizing plants, e.g., peas, transfer of pollen grains to the stigma is relatively easy as anthers and stigma are located close to each other; pollen grains soon after they are shed, come in contact with the stigma.
• But in cross-pollinating plants (including dioecious plants), a specialized event called pollination facilitates the transfer of pollen grains to the stigma. 
• Pollen grains germinate on the stigma and the pollen tubes carrying the male gametes reach the ovule and discharge male gametes near the egg. 
• In dioecious animals, since male and female gametes are formed in different individuals, the organism must evolve a special mechanism for gamete transfer. 
• Successful transfer and coming together of gametes is essential for the most critical event in sexual reproduction, the fertilization.