Sexual Reproduction in Flowering Plants (Advanced Level / Expected MCQs)

Correct Answer: (d)
A typical flower is composed of four whorls: sepals, petals, stamens, and carpels. A bract is a modified leaf that may be associated with a flower or inflorescence, but it is technically not part of the flower itself.

Correct Answer: (a)
Plants detect changes in day/night length (photoperiodism) using photoreceptors. Phytochromes primarily detect red and far-red light, while cryptochromes detect blue light. Chlorophyll is used for energy conversion, not primary signaling for photoperiod.

Correct Answer: (a)
Angiosperms undergo double fertilization. While one sperm fuses with the egg, the second sperm fuses with the two polar nuclei in the central cell of the embryo sac to form the triploid endosperm.

Correct Answer: (a)
Asexual reproduction is favored in stable and predictable environments. Tropical rainforests provide such conditions because they have a constant temperature, high and regular rainfall, and very little seasonal variation. This environmental stability allows organisms to survive and reproduce successfully without the need for genetic variation. In contrast, temperate grasslands experience strong seasonal changes, the arctic tundra has extremely cold and harsh conditions, and deciduous forests show marked seasonal variation, all of which favor sexual reproduction rather than asexual reproduction.

Correct Answer: (a)
Primary meristems (protoderm, ground meristem, and procambium) are derived directly from the apical meristem. The cork cambium is a lateral (secondary) meristem responsible for secondary growth.

Correct Answer: (c)
Short-day plants require a long, uninterrupted dark period to flower. By providing a brief flash of light during the night (a 'night break'), you prevent the short-day plant from flowering and actually trigger flowering in a long-day plant.

Correct Answer: (c)
The WOODEN LEG mutation results in a failure of phloem differentiation. Without functional phloem, the plant is incapable of transporting the products of photosynthesis (photosynthate) to its roots and other sinks.

Correct Answer: (b)
α-amylase is responsible for breaking down the starch in the endosperm into sugars. If this enzyme is absent, the developing embryo has no fuel source and will starve before it can establish itself.

Correct Answer: (a)
Senescence is the final stage of biological development in which the plant or its organs (like leaves) undergo a programmed process of aging and eventual death.

Correct Answer: (a)
Morphogenesis refers to the biological process that causes an organism to develop its shape. In plants, it specifically describes the development of the growth form through orchestrated cell division and expansion.

Correct Answer: (c)
STM is required for shoot development at the apical end, while MP is required for root development at the basal end. Reversing their functional domains would flip the identity of the poles, reversing the root-shoot axis.

Correct Answer: (c)
Gibberellic acid (GA) is synthesized by the embryo and moves to the aleurone layer, where it triggers the production of α-amylase and other enzymes to hydrolyze stored starch.

Correct Answer: (d)
The globular stage is a critical phase where the plant's polarity is established, defining the root-shoot axis that determines the subsequent growth pattern of the seedling.

Correct Answer: (b)
By introducing S genes (self-incompatibility genes), the plants would naturally reject their own pollen, making the manual removal of staminate flowers (detasseling) unnecessary and making the process more efficient.

Correct Answer: (a)
In the ABC model of flower development, stamens are produced by the combination of B and C genes. If B-type genes are expressed in the innermost whorl (normally just C, which makes carpels), it would result in stamens being formed instead of carpels.

Correct Answer: (b)
In gametophytic SI, the compatibility of the pollen is determined by its own haploid genotype. Since the pollen of an S₂S₅ plant is either S₂ or S₅, the S₂ pollen will be compatible with an S₁S₅ carpel, while the S₅ pollen will not. Thus, 50% (half) is successful.

Correct Answer: (c)
If the loss of the gene causes the suspensor cells to turn into a second embryo, the normal role of that protein must be to suppress embryonic identity in the suspensor cells, thereby inhibiting embryonic development in that specific tissue.

Correct Answer: (c)
The zygote divides asymmetrically to form a smaller apical cell and a larger basal cell. The apical cell gives rise to the embryo, while the larger basal cell divides to form the suspensor.

Correct Answer: (b)
A protoplast is defined as a plant, bacterial, or fungal cell that has had its cell wall completely removed by mechanical or enzymatic means.

Correct Answer: (c)
Vernalization is the acquisition of a plant's ability to flower in the spring by exposure to the prolonged cold of winter. This ensure that reproductive development occurs at an appropriate time.

Correct Answer: (c)
In monocots like maize, the emerging shoot (plumule) is encased in a protective sheath called the coleoptile, which pushes through the soil.

Correct Answer: (c)
Perennials are plants that live for more than two years. This group includes both woody plants (like trees) and many herbaceous plants (where top growth dies back but roots survive).

Correct Answer: (d)
Birds have highly developed color vision, particularly in the red portion of the spectrum, and a poor sense of smell. Consequently, bird-pollinated flowers are often red and lack the strong scents found in bee-pollinated flowers.

Correct Answer: (c)
The stamen is the male reproductive organ of the flower and is comprised of an anther (pollen-bearing part) and a stalk known as the filament. Style and stigma are parts of the carpel.

Correct Answer: (d)
In the life cycle of an angiosperm, the megaspore mother cell located within the ovule undergoes meiosis to produce four haploid megaspores (though usually only one survives).

Correct Answer: (b)
In animals, meiosis directly produces gametes. In plants, meiosis produces haploid spores; these spores grow into a haploid gametophyte, which then produces gametes through mitosis.