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The tissue responsible for producing spores is diploid. The endothecium, the second layer of the anther wall, provides protection and aids in the splitting of the anther to release pollen. The tough outer covering of pollen grains is termed the exine, while the tapetum supports the nourishment of developing pollen. Tapetal cells are rich in cytoplasm and often exhibit multiple nuclei (polyploidy).

1. Cleistogamous flowers keep their reproductive structures enclosed. The anthers and stigma are positioned close to one another, ensuring complete self-pollination without any possibility of cross-pollination. This is an effective adaptation for self-pollination, as seen in plants like Viola mirabilis and Oxalis autosella.
2. A single Megaspore Mother Cell (MMC) forms near the micropylar end of the nucellus, characterized by dense cytoplasm and a distinct nucleus. This MMC undergoes meiosis to produce four haploid megaspores, a process referred to as megasporogenesis.
3. Pollination involves various agents. For instance, wind facilitates pollination in maize and mulberry, water aids pollination in Vallisneria, and bees are used commercially for pollinating cucumber plants.
4. Pollen grains are typically round and possess a distinct two-layered wall. The durable outer layer, called the exine, is composed of sporopollenin, a highly resistant organic compound that can endure extreme temperatures, strong acids, and alkalis.

Correct answer: Pollen grains are typically round and possess a distinct two-layered wall. The durable outer layer, called the exine, is composed of sporopollenin, a highly resistant organic compound that can endure extreme temperatures, strong acids, and alkalis.

Solution

The correct statement matches the structure of pollen grains: they have a two-layered wall, and the outer exine is made of sporopollenin. Sporopollenin is extremely resistant to heat, acids, and alkalis, which is why this option is correct.

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