Short & Long Question Answers with Solution: Sexual Reproduction in Flowering Plants. - NEET PDF Download

Short Answer Type Questions

Q1: Explain the events which occur after the process of fertilization in plants.
Ans: Fertilization is a crucial process that occurs in all sexually reproducing organisms, including flowering plants. In flowering plants, fertilization typically follows pollination and germination. After fertilization takes place, the following events occur:

• The ovary transforms into the fruit.
• The ovules develop into seeds.
• Other structures such as the corolla, calyx, and remaining parts of the androecium and gynoecium deteriorate or drop off.

Q2: Why is emasculation done in the process of hybridization?
Ans: Emasculation is a technique used in artificial hybridization where the stamens of a flower are removed before pollination. This ensures that no unwanted or undesirable pollen from the flower itself falls on the stigma, allowing the flower to be pollinated exclusively with the desired pollen grains.

Q3: Cell division occurs in Angiospermic plants prior to the formation of microspores in sporogenous tissue.
Ans: Polyembryony is a phenomenon characterized by the existence of multiple embryos within a single seed. This can occur through various mechanisms, such as the splitting of the egg or cleavage within the embryo sac, endosperm, synergid, or antipodal divisions.
Among animals, insects, with bees being particularly significant, play a crucial role as pollinators in the process of fertilizing plants.

Q4: Why is it that the generative cell of 2-celled pollen divides in a pollen tube and not of 3-celled pollen?
Ans: The generative cell undergoes division to produce two male gametes. In the case of three-celled pollen, this division results in two gametes, and there are no additional divisions within the pollen tube. On the other hand, for two-celled pollen, the generative cell travels down the pollen tube and divides to yield two male gametes.

Q5: Why pollen grains can remain well preserved as fossils?
Ans: Pollen grains are effectively preserved as fossils due to the presence of sporopollenin in their exine. Sporopollenin is a chemical compound known for its resistance to high temperatures, powerful acids and bases, as well as strong enzymes. This robust composition makes pollen grains highly durable as fossils.

Q6: List any four distinguishing characteristics of the insect-pollinated flower.
Ans: The insect-pollinated flower has four distinguishing characteristics:

• The flowers are quite large.
• Flowers have colourful petals.
• The presence of perfume in flowers.
• They are rich in nectar.

Q7: The zygote divides only after the division of the primary endosperm cell. Give reasons in support of the statement.
Ans: The zygote needs nourishment to support its growth and division. This nourishment is supplied by the primary endosperm cell. Consequently, the zygote undergoes division only after the primary endosperm cell has completed its growth, food storage, and division.

Q8: How are the cells in an embryo sac organised?
Ans: The embryo sac is a seven-celled, eight-nucleated structure. At the micropylar end, there are three cells: two synergids and one egg cell. At the chalazal end, three cells are present, known as antipodals. In the center, there is a central cell with two polar nuclei.

Q9: Why are cleistogamous flowers invariably autogamous?
Ans: In a cleistogamous flower, the flower remains closed and when the anthers release pollen inside the unopened bud, the pollen grains fall onto the stigma of the same flower, making it a strictly autogamous or self-pollinating plant.

Q10: Is there any difference between apomixis and parthenocarpy? Explain the benefits of each.
Ans: Yes, parthenocarpy is distinct from apomixis. Parthenocarpy refers to the development of fruit without the fertilization of the female gamete. It is often utilized for cultivating seedless fruits like bananas and grapes for commercial purposes. On the other hand, apomixis is a process where seeds are formed without fertilization, but it occurs within the female reproductive structures of the plant. In apomixis, the megaspore mother cell does not undergo meiosis. This method is employed for producing hybrid varieties and generating virus-free plant strains for commercial use.

Q11: Distinguish microsporogenesis from megasporogenesis. What type of cell division takes place during these events? Name the structure that results from these two events.
Ans: Microsporogenesis is the creation of microspores from Pollen Mother Cells. Megasporogenesis is the formation of megaspores from MMCs. Meiotic division occurs during both processes, leading to the production of pollen grains and megaspores.

Q12: State any one advantage and disadvantage of pollen grains to humans.
Ans: Advantage: Pollen grains are nutrient-rich, and in Western countries, pollen tablets are consumed as dietary supplements.
Disadvantage: Pollen from various species can trigger severe allergies and respiratory issues, leading to chronic respiratory disorders.

Q13: Explain the term polyembryony. How is it exploited commercially?
Ans: Polyembryony is the term used when multiple embryos are present within a single seed. This phenomenon is observed in certain citrus fruits and mango varieties. Polyembryony has considerable importance in the fields of plant breeding and horticulture. These embryos contribute to the development of healthy, virus-free plantlets. Hybrid plant varieties derived from this process have become widely cultivated due to their high productivity.

Q14: What exactly is triple fusion? Where does it happen?
Ans: The fusion process involving the nucleus of a pollen grain's vegetative cell and the two polar nuclei of the female gametophyte's central cell, resulting in the primary endosperm formation, is referred to as vegetative fusion or triple fusion. This fusion event occurs within the central cell of the egg apparatus.

Q15: What relationship exists between a species of moth and Yucca plant?
Ans: A mutual relationship exists between moths and Yucca plants. The moth deposits its eggs inside the ovary's locule, effectively pollinating the plant's flowers in the process. As the seeds begin to develop, the moth larvae also develop from these eggs.

Long Answer Type Questions

Q1: What are the functions of a flower?
Ans: The flowers are the reproductive organs of plants and are mainly involved in the reproduction process.
The essential functions of flowers are mentioned below:

• Enhancing the plant's aesthetic appeal.
• Housing the gametophytes.
• Facilitating the development of seeded fruits.
• Enabling the fusion of male and female gametes.
• Providing a location for the plant's reproductive organs.
• Offering nectar as a food source for specific birds and insects.
• Shielding the plant's reproductive organs.
• Allowing for the production of diaspores without fertilization.
• Promoting the union of sperm and eggs within the same or different flowers.
• Aiding in pollination by attracting insects and other animals, which help transfer pollen grains.

Q2: Follow the growth of microsporocytes into mature pollen grains.
Ans: In the early stages of anther development, the microsporangium consists of closely packed, uniform cells that make up the sporogenous tissues.
Each of these sporogenous tissue cells eventually transforms into a pollen mother cell (PMC) and gives rise to microspore tetrads or pollen grains. However, some cells lose this potential and instead differentiate into pollen or microspore mother cells (MMC). Each microspore mother cell (MMC) undergoes meiosis, resulting in the formation of a cluster of four haploid cells referred to as a microspore tetrad. As the anther matures, the microspores separate from the tetrad and develop into individual pollen grains. During this process, mitosis occurs in the microspore nuclei, leading to the formation of larger vegetative cells and smaller generative cells. These cells are surrounded by a double-layered wall, with the outer layer (exine) composed of sporopollenin. The inner layer (intine) is made up of cellulose and pectin. Pollen grains are typically released in a two-celled stage.

Q3: “Incompatibility is the natural barrier in fusion of gamete”. Justify this statement.
Ans: Pollen grains from one plant species are unable to germinate on the stigma of unrelated plant species due to their incompatibility. This phenomenon is referred to as pollen-pistil incompatibility. In some angiospermic plants, pollen grains may germinate on the stigma of unrelated species, but the male gametes produced in the pollen tube are unable to fertilize the egg, resulting in gametic incompatibility.
Self-incompatibility can be achieved through various mechanisms:

• Pollen-Stigma Interaction: In this process, pollen grains fail to germinate on the stigma due to incompatibility.
• Pollen Tube-Style Interaction: In this process, pollen grains are able to germinate on the stigma, and the pollen tube penetrates the stigmatic surface. However, due to incompatibility, the growth of the pollen tube within the stigma and style is inhibited.
• Pollen-Ovule Interaction: In this scenario, the pollen tube successfully pierces and grows within the style, but its growth is inhibited at the micropyle of the ovule.

Q4: Explain the structure of the pollen.
Ans: Pollen grains are tiny structures that transport the male reproductive cells of a plant. They have a double-walled structure, consisting of a thin inner wall called the endospore, made of cellulose, and a thick outer wall called the exospore, made of sporopollenin.
The primary function of the exospore is to protect the male genetic material during its journey from the anther to the stigma. Additionally, the surface of the pollen grains contains waxes and proteins that serve to repel moisture and facilitate interactions with the stigma.

Q5: What are the post-fertilization changes that occur in a flowering plant?
Ans: (i) Development of Endosperm: Endosperm development precedes embryo development. The most common method of endosperm development is the nuclear type, where the triploid endosperm (PEN) undergoes multiple rounds of mitotic divisions without cytokinesis. Cell walls form from the periphery, and the endosperm serves as a storage site for food materials.
(ii) Development of Embryo: Initially, the zygote undergoes mitotic division to form a pro-embryo. Subsequent development leads to the formation of a globular embryo, which then takes on a heart-shaped structure and eventually matures into a horseshoe-shaped embryo with one or more cotyledons. In a dicot embryo, the part of the embryonal axis near the attachment level becomes the epicotyl, which later becomes the plumule. The portion of the embryonal axis below the attachment level is the hypocotyl and eventually gives rise to the radicle.

Q6: What are the characteristics of wind, water and insect-pollinated flowers?
Ans: Characteristics of wind-pollinated flowers:

• Lack of bright colors.
• Absence of distinct odors or nectar.
• Small size and no petals.
• Exposed stigma and stamens, facilitating exposure to air currents.
• Smooth and lightweight pollen that can be easily carried by the wind in large quantities.
• Feathery stigma designed to capture wind-borne pollen.

Characteristics of water-pollinated flowers:

• Small, inconspicuous male flowers.
• Release of numerous pollen grains into the water.
• Pollen grains remain buoyant on the water's surface until captured by female flowers.
• Presence of large, feathery stigmas on female flowers to trap water-borne pollen.

Characteristics of insect-pollinated flowers:

• Large size with bright-colored petals to attract insects.
• Production of nectar and a pleasant fragrance to lure insects.
• Sticky pollen grains that readily adhere to an insect's body.

Q7: Explain the development of embryo in a dicotyledonous plant with neatly labeled diagrams.
Ans: The embryo's development begins at the micropylar end, where the zygote is situated. However, the zygote's development initiates only after a sufficient amount of endosperm is produced to provide nourishment to the embryo. The zygote undergoes successive mitotic divisions, leading to various developmental stages such as the pro-embryo, globular stage, heart-shaped stage, and ultimately, the fully mature embryo.

Q8: How is it that the embryo sacs of some apomictic species look normal but contain diploid cells?
Ans: Apomixis results in offspring that are genetically identical to the parent plant. In flowering plants, apomixis serves as a means of asexual reproduction through the formation of seeds. In certain plant species, the diploid egg cell does not undergo meiosis, leading to the development of an embryo without fertilization. In specific citrus species, the nucellar cells that encircle the embryo sac divide and generate an embryo. This process occurs within the megaspore mother cell, which undergoes only mitosis, producing diploid cells within the embryo sac.

Q9: Explain the formation of an embryo sac with diagrams.
Ans: 

• The process begins with the enlargement of the functional megaspore.
• Next, the nucleus within the megaspore undergoes mitotic division, resulting in the formation of two nuclei, which migrate to opposite poles.
• At each pole, these nuclei undergo two additional rounds of mitotic division, resulting in a total of four nuclei at each pole, or eight nuclei in total.
• Two nuclei from each pole move towards the center to create the polar nuclei.
• The remaining nuclei, three at each pole, become enveloped by a small amount of cytoplasm to form cells.
• As a result, the female gametophyte, or embryo sac, consists of seven cells and eight nuclei.

Q10: Describe the structure of the embryo sac of a mature angiosperm. Explain the role of synergids in it.
Ans: 

• In the eight-nucleate stage, the cell walls are organized to form the female gametophyte or embryo sac.
• Six of the eight nuclei are enclosed by cell walls.
• The egg apparatus includes two synergids and one egg cell.
• At the chalazal end, three cells known as antipodals are present.
• The central cell results from the fusion of two polar nuclei.
• Upon maturity, the angiosperm embryo sac consists of 8 nuclei and 7 cells.
• A single megaspore gives rise to the embryo sac, making it a monosporic embryo sac.

Role of Synergids

• The synergids play a crucial role in angiosperm reproduction. During fertilization, a pollen tube grows into one of the synergids. The tube stops growing, ruptures, and releases two sperm cells.