Test: Sexual Reproduction in Flowering Plants - 1 - NEET MCQ

Assertion (A) is true because apomixis is an asexual process that results in seed formation without fertilization.
Reason (R) is false because apomictic plants do produce seeds despite the lack of fertilization.
So option (A) is True but (R) is False is correct .
Topic in NCERT: APOMIXIS AND POLYEMBRYONY
Line in NCERT: "Thus, apomixis is a form of asexual reproduction that mimics sexual reproduction."

(A) To determine the correctness of the statements regarding the given diagram:
- Statement I: The pollen tube enters a synergid under guidance from A, which is correct.
- Statement II: Male gametes are discharged into a synergid, which is correct
Statement I is correct, Statement II is correct SO OPTION (A)
Topic in NCERT: DOUBLE FERTILISATION
Line in NCERT: "the pollen tube releases the two male gametes into the cytoplasm of the synergid."

PEN (primary endosperm nucleus) divides into two nuclei and subsequent division of nucleus produce large number of nucleus without cell wall formation. These types of endosperm are called free nuclear type of endosperm.
Topic in NCERT: Endosperm
Line in NCERT: In the most common type of endosperm development, the PEN undergoes successive nuclear divisions to give rise to free nuclei. This stage of endosperm development is called free-nuclear endosperm.

Double fertilisation involves fusion of one male gamete with egg during Syngamy and fusion of two polar nuclei with other male gametes. So, total 5 nuclei are involved in double fertilisation.

Topic in NCERT: DOUBLE FERTILISATION

Line in NCERT: "Since two types of fusions, syngamy and triple fusion take place in an embryo sac the phenomenon is termed double fertilisation, an event unique to flowering plants."

Anther is bilobed structure at the tips of stamen. Each lobe consists of two theca. Each theca change into microsporangium. Anther forms four sided structure having four microsporangia in which pollen grains are formed.

Topic in NCERT: Anther Structure and Function

Line in NCERT: "The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe."

Ovule/s are located inside the ovary. The point of attachment of the ovule to the ovary is called the funicle. Funicle extends to hilum as stalk.

Topic in NCERT: The Megasporangium (Ovule)

Line in NCERT: "The ovule is a small structure attached to the placenta by means of a stalk called funicle."

In an artificial hybridization program with dioecious plants:
- Bagging of the female flower: Relevant to prevent unwanted pollen contamination.
- Dusting of pollen on the stigma: Essential for pollination to occur.
- Emasculation: Not relevant because dioecious plants have separate sexes; emasculation is for monoecious plants.
- Collection of pollen: Necessary for controlled pollination process.
Therefore, in this context, the step that would not be relevant is C: Emasculation.
Topic in NCERT: Artificial Hybridization Techniques
Line in NCERT: "Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen."

(C)

Pollen grains lose viability within 30 minutes of their release in some members of:

• In some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release, and in some members of Rosaceae, Leguminoseae and Solanaceae, they maintain viability for months.

Topic in NCERT: Pollen Viability and Storage

Line in NCERT: "In some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release."

About 60% of angiosperms, pollen grains are shed at two celled stage. The larger cell is called vegetative cell and the smaller one is called generative cell. Each generative cell produces two male gametes.

Topic in NCERT: Pollen Grain Development

Line in NCERT: "In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled stage."

The seedless fruit develops without fertilisation by using some plant hormones. The fruit so formed are called parthenocarpic.

Topic in NCERT: PARTHENOCARPY

Line in NCERT: "Such fruits are called parthenocarpic fruits."

The innermost wall layer is the tapetum. It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.

Topic in NCERT: Tapetum

Line in NCERT: "Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus."

• True Fruit: A true fruit is one that develops only from the ovary. 
• Example: Mango, Coconut, Zizyphus etc.
• False Fruit or Pseudocarp: In some fruits, it is not the ovary that forms the fruit. In fact, some other parts of the flower, like the thalamus, inflorescence, calyx are modified to become a part of the fruit. These types of fruit are called false fruits. 
  Example: Apple, Strawberry etc.

Topic in NCERT: FRUIT DEVELOPMENT AND CLASSIFICATION
Line in NCERT: However, in a few species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit formation. 
Such fruits are called false fruits

Placenta is located inside the ovarian cavity. It help in transport of nutrient to megasporangium or ovule. Ovule is attached to placenta by means of stalk called funicle.

Topic in NCERT: The Pistil, Megasporangium (ovule) and Embryo sac

Line in NCERT: "The placenta is located inside the ovarian cavity."

Maize grain is monocotyledonous, having a single cotyledon. This cotyledon is also called scutellum.

Topic in NCERT: Embryo

Line in NCERT: "In the grass family the cotyledon is called scutellum that is situated towards one side (lateral) of the embryonal axis."

Topic in NCERT: Structure of microsporangium
Line in NCERT: "Four wall layers, the epidermis, endothecium, middle layers and the tapetum surround the microsporangium."

Angiospermic embryo sac is 8-nucleate but 7-celled at maturity. This includes 3- celled egg Synergids, 3 antipodal cells and 2 polar nuclei.

Topic in NCERT: Female gametophyte formation

Line in NCERT: "Thus, a typical angiosperm embryo sac, at maturity, though 8-nucleate is 7-celled."

• Nucellus: The tissue within the ovule where megagametogenesis occurs.

• Megaspore mother cell (Megaspore mother cell): The diploid cell in the nucellus that undergoes meiosis to form a megaspore tetrad.

• Megaspore tetrad: The four haploid megaspores resulting from meiosis of the megaspore mother cell.

• Megaspore: Typically, three of the four megaspores degenerate, leaving one functional megaspore.

• Female gametophyte: The functional megaspore undergoes mitotic divisions to form the female gametophyte (embryo sac).

Thus, the correct sequence is: Nucellus → Megaspore mother cell → Megaspore tetrad → Megaspore → Female gametophyte.

Lotus is an aquatic plant but the flower of lotus is outside and above the water surface. So, it cannot be pollinated by water. It is generally pollinated by insects.

• Endospermic: Castor seeds contain endosperm, which is the tissue that provides nourishment to the developing embryo.

• Albuminous: The endosperm in castor seeds remains in the mature seed and is not consumed during seed development, so it is termed albuminous.

Topic in NCERT: Seed

Line in NCERT: "Albuminous seeds retain a part of endosperm as it is not completely used up during embryo development (e.g., wheat, maize, barley, castor)."

(a) Tetrasporangiate: Correct. A typical anther has four pollen sacs or microsporangia.
(b) Tetragonal: Correct - The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe.
(c) Trilobed: No, anthers are typically bilobed, not trilobed
(d) Surrounded by four wall layers: Correct. The anther is surrounded by four distinct wall layers: the epidermis, endothecium, middle layer, and tapetum.
Topic in NCERT: Anther Structure and Function
Line in NCERT: "A typical anther is bilobed, dithecous and tetrasporangiate. Four wall layers, the epidermis, endothecium, middle layers and the tapetum surround the microsporangium."