Double Fertilisation

Step 1: Understanding double fertilization. Double fertilization is a unique process in angiosperms where two fertilization events occur simultaneously.

Step 2: The two events in double fertilization. 1. One sperm cell fuses with the egg cell to form the zygote, which develops into the embryo. 2. The other sperm cell fuses with the two polar nuclei in the central cell to form a triploid structure that develops into the endosperm.

Step 3: Explanation of other options.

- (B): Incorrect because the endosperm is formed from the polar nuclei, not the egg cell.

- (C): Incorrect because the seed formation involves the zygote and maternal tissues, not directly from the sperm cell.

- (D): Incorrect because the polar nuclei form the endosperm, not the zygote.

Thus, the correct sequence of events is described in (A).

Step 1: Analyze the assertion. The statement "Insects are important pollinators for many flowering plants" is correct because many plants rely on insects to transfer pollen, which is essential for reproduction and seed formation.

Step 2: Analyze the reasoning. The reasoning explains that insects visit flowers for nectar or pollen. During this process, they facilitate the transfer of pollen between flowers, enabling cross-pollination. This reasoning directly supports the assertion.

Step 3: Verify the connection between the assertion and reasoning. The reasoning not only explains the assertion but also provides the biological basis for the statement. Hence, both the assertion and reasoning are correct, and the reasoning correctly explains the assertion.

Step 1: Characteristics of bird-pollinated flowers.
Bird-pollinated flowers (ornithophilous flowers) exhibit the following traits: Bright colors (e.g., red, orange, yellow) to attract birds. Long, tubular shapes that allow birds to access nectar. No strong fragrance since birds rely on sight, not smell.

Step 2: Explanation of options.
Option (A): Correct. Long, tubular, and brightly colored flowers are adapted for bird pollination

Option (B): Incorrect. Strongly fragrant flowers are more likely to attract insects, not birds.

Option (C): Incorrect. Flowers that open at night and emit strong scents are adapted for moth pollination.

Option (D): Incorrect. Small and inconspicuous flowers rely on wind or water pollination, not birds.

The correct Option is : 3

Step 1: Understanding outbreeding devices.
Outbreeding devices in plants promote cross-pollination and genetic diversity by preventing self-pollination. They ensure that pollen from one flower fertilizes the ovule of another flower, typically from a different plant.

Step 2: Xenogamy as an outbreeding device.
Xenogamy refers to cross-pollination between flowers of different plants. This process promotes genetic recombination and variation, which are crucial for adaptation and survival in changing environments.

Step 3: Explanation of other options.
Option (A): Cleistogamy. Incorrect. Cleistogamy involves self-pollination within closed flowers, which reduces genetic diversity.

Option (B): Autogamy. Incorrect. Autogamy is self-pollination within the same flower, which does not promote outbreeding.

Option (D): Geitonogamy. Incorrect. Geitonogamy involves pollination between flowers of the same plant, which does not promote true genetic recombination.

Step 4: Conclusion.
Among the given options, only xenogamy represents an outbreeding device, as it involves cross-pollination between different plants.