Sexual Reproduction In Flowering Plants

Answer (c) Anemophily

In most of the plants the pollen tube enters the ovule through the micropyle and the phenomenon is called as porogamy. Entry through chalaza is chalazogamy and through integuments or funiculus is mesogamy.

Answer (d) Secondary nucleus

The maintenance of genetic stability or purelines is helpful to retain the parental characters in the progeny and is an advantage of self pollination.

In some species of Family Asteraceae, egg or other cells associated with egg like antipodals, synergids, etc., develop into embryo without fertilisation. This type of asexual reproduction is called apomixis.

During embryo development in an angiosperm, oospore is transversely divided into a basal cell and apical (embryonal) cell. Basal cell further divides transversely to form a row of cells called suspensor.

The fusion of one male gamete with egg and that of another male gamete with secondary nucleus is called double fertilisation. All angiosperms are characterised by double fertilisation. It was discovered by S.G. Nawaschin (1898) in Lillium and Fritillaria plants.

When the second male gamete fuses with the diploid secondary nucleus to form the triploid primary endosperm nucleus (PEN). This is called triple fusion. Since each of the polar nuclei is sister nucleus of the egg and it is called second fertilisation

Answer (c) The upper branch of bifurcated connective bears sterile anther lobe and lower branch bearsfertile anther lobe

Step 1: Understanding gamete development in angiosperms.
In angiosperms, the microspore mother cell undergoes meiosis to form four haploid microspores, and then each microspore undergoes one round of mitosis to form the pollen grain, which is the male gamete.
Step 2: Analyzing the options.
(A) two and two: Incorrect, two rounds of meiosis occur, but only one round of mitosis happens.
(B) two and one: Correct, meiosis happens in two stages, and one round of mitosis occurs for the microspore.
(C) one and two: Incorrect, meiosis is two stages, and only one mitotic division occurs.
(D) one and three: Incorrect, there is no third division in the process of gametogenesis.
Step 3: Conclusion.
The correct answer is (B) two and one, as meiosis occurs in two stages, followed by one mitotic division.

Step 1: Understanding the terms.
- Sunflower exhibits protandry, meaning the male parts mature first, followed by the female parts.
- Castor has unisexual flowers, where male and female flowers are present on separate plants.
- Michellia exhibits self-incompatibility, meaning it cannot self-pollinate.
- Orchid displays protogyny, where the female parts mature first.
Step 2: Analyzing the options.
(A) a - iii: Correct, sunflower exhibits protandry.
(B) b - iv: Correct, castor has unisexual flowers.
(C) c - ii: Correct, Michellia shows self-incompatibility.
(D) d - i: Correct, orchids show protogyny.
Step 3: Conclusion.
The correct answer is (A) a - iii, b - iv, c - ii, d - i.

The embryo sac in plants is formed within the ovule and typically consists of 7 cells. These cells include: 1. One egg cell, 2. Two synergids, 3. Three antipodal cells, 4. One central cell with two polar nuclei. This structure is found in most flowering plants, and the number of cells in the embryo sac is typically seven.

An example of chiropterophily is pollination by bats.

Chiropterophily refers to the process of pollination that occurs with the help of bats. This is a specific type of pollination that is less common than pollination by insects or birds, but it is crucial for certain plants, especially in tropical and desert regions.

How chiropterophily works:

• Attraction to flowers: Bats are attracted to flowers that are typically large, have strong, sweet fragrances, and bloom at night. These flowers often have a pale color, which is easier for bats to see in low light.
• Flower characteristics: Flowers that are adapted for bat pollination are often large and sturdy, with copious amounts of nectar to attract the bats. These flowers are usually positioned on plants that can withstand the weight and activity of a bat feeding on them.
• Pollination process: As bats feed on the nectar of these flowers, they brush against the plant's reproductive structures, transferring pollen from one flower to another, thus pollinating the plant.

Examples of plants pollinated by bats:

• Agave: The plant that produces tequila is pollinated by bats, particularly the lesser long-nosed bat.
• Durian: The durian fruit, known for its strong odor, is pollinated by fruit bats in Southeast Asia.
• Cacti: Some species of cacti, especially in desert regions, rely on bats for pollination.

Chiropterophily is an important ecological interaction in areas where bats are abundant, helping ensure the reproductive success of certain plant species.

The correct answer is: Germ pores of pollen grains are useful for helping in the formation of the pollen tube and the release of male gametes during fertilization.

Explanation of germ pores:

• Germ pores: These are specialized openings in the outer layer (the exine) of the pollen grain. They are typically present at specific locations on the pollen grain and are important for the development of the pollen tube.
• Pollen tube formation: When a pollen grain lands on the stigma of a flower, the germ pores provide a point of entry for the growth of the pollen tube. The tube grows through the style toward the ovary, carrying the male gametes (sperm cells) with it.
• Release of male gametes: As the pollen tube reaches the ovule, the male gametes (sperm cells) are released from the tube into the ovule, where fertilization occurs, resulting in the formation of a zygote.

Importance of germ pores in fertilization:

• The germ pores allow the pollen tube to emerge from the pollen grain and grow toward the ovule, ensuring that the male gametes can be transported to the female gametes for fertilization.
• Without the presence of germ pores, the pollen grain would not be able to successfully form a pollen tube, hindering the fertilization process.

Thus, germ pores play a crucial role in the reproductive process of plants by facilitating the formation of the pollen tube and ensuring the release of male gametes, which is essential for fertilization and the development of seeds.