Assertion & Reason Test: Sexual Reproduction in Flowering Plants - NEET MCQ

Primary sporogenous cell gives rise to microspore mother cells or pollen mother cells (PMCs). They are sporophytic in nature i.e., diploid. These cells undergo meiosis (reduction division) which gives rise to 4 microspores or pollens and this formation of microspores or pollens is called microsporogenesis. Microspores represent the beginning of the gametophytic phase and they are haploid in nature.
Topic in NCERT: Microsporogenesis
Line in NCERT:
"Each one is a potential pollen or microspore mother  cell. As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. The microspores, as they are formed, are arranged in a cluster of four cells–the microspore tetrad." 

Fertilization occurs when one of the sperm cells fuses with the egg inside of an ovule. After fertilization occurs, each ovule develops into a seed. Each seed contains a tiny, undeveloped plant called an embryo. The ovary surrounding the ovules develops into a fruit that contains one or more seeds

Topic in NCERT: POST-FERTILISATION: STRUCTURES AND EVENTS

Line in NCERT: "As ovules mature into seeds, the ovary develops into a fruit, i.e., the transformation of ovules into seeds and ovary into fruit proceeds simultaneously."

Internal copulatory organs are absent in plants and thus the aid of an external agency is required for the transfer of pollen grains from the anther to the stigma.

Topic in NCERT: Pollination

Line in NCERT: "Transfer of pollen grains (shed from the anther) to the stigma of a pistil is termed pollination. Flowering plants have evolved an amazing array of adaptations to achieve pollination. They make use of external agents to achieve pollination."

The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion.
Pollen grains are well preserved as fossils because their outer wall exine is made up of a highly resistant organic material called sporopollenin.
Sporopollenin is able to withstand high temperatures and strong acids and alkali. It cannot be degraded by any enzyme known so far.
Therefore, both assertion and reason are true and reason is the correct explanation of assertion.

Topic in NCERT: Pollen Grains

Line in NCERT: "Pollen grains are well-preserved as fossils because of the presence of sporopollenin."

The majority of angiosperms bear chasmogamous flowers, which means the flowers expose their mature anthers and stigma to the pollinating agents. There is another group of plants which set seeds without exposing their sex organs. Such flowers are called cleistogamous and the phenomenon is cleistogamy.

Topic in NCERT: SEXUAL REPRODUCTION IN FLOWERING PLANTS

Line in NCERT: "Chasmogamous flowers require pollinating agents."

Cleistogamous flowers are bisexual flowers which do not open at all. Therefore they never expose the anthers and stigma.
Cleistogamous flowers produce assured seed-set even in the absence of pollinators. This is because the anther and stigma lie close to each other. When pollen is released, it comes in contact with the stigma resulting in pollination. Hence, pollinators are not required for pollination in cleistogamous flowers.
Topic in NCERT: Cleistogamous flowers
Line in NCERT: "Cleistogamous flowers produce assured seed-set even in the absence of pollinators."

A typical microsporangium consists of two parts, outer wall and central homogeneous sporogenous tissue. Microsporangial wall has four types of layers– epidermis, endothecium, 1–3 middle layers and tapetum. The outer three wall layers perform the function of protection in the young anther and mechanism of dehiscence in the ripe anther.

Topic in NCERT: Structure of microsporangium

Line in NCERT: "A typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers - the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen."

Perisperm is a nutritive tissue of a seed derived from the nucellus and deposited externally to the embryo sac. It is diploid.

Topic in NCERT: Seed

Line in NCERT: "Occasionally, in some seeds such as black pepper and beet, remnants of nucellus are also persistent. This residual, persistent nucellus is the perisperm."

Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
Explanation: Insects do visit flowers to gather honey (nectar), which is a source of food for them, so the assertion is true. The reason is also true, as the attraction of flowers can help prevent insects from damaging other parts of the plant. However, the reason is not the correct explanation of the assertion, as insects visit flowers primarily for the nectar, and the prevention of damage to other parts of the plant is a secondary benefit.
Topic in NCERT: Pollination
Line in NCERT: "To sustain animal visits, the flowers have to provide rewards to the animals. Nectar and pollen grains are the usual floral rewards."

Assertion is true, but the reason is wrong because tapetum plays an important role in nourishing pollen mother cells (PMCs) or microspores.

Topic in NCERT: Tapetum

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