The pollen tube enters the ovule through the: MCQ with Answer and Explanation

Explanation:
The pineal gland secretes melatonin in a daily rhythm, peaking at night, thus regulating the sleep-wake cycle and seasonal biological rhythms. The pituitary controls other glands, thyroid metabolism, adrenals stress response. Light signals from the retina influence pineal activity.

Explanation:
Xanthophylls, oxygenated carotenoids, are responsible for the yellow color of egg yolk, autumn leaves, and corn. Beta-carotene is orange, lycopene red.

Explanation:
Robert Brown, a Scottish botanist, discovered the nucleus in 1831 while studying orchid cells under a microscope. He named it 'nucleus'. Hooke discovered cells, Leeuwenhoek observed living cells, Schleiden proposed that all plants are made of cells. Brown's discovery was crucial for understanding cell structure and function.