Charles Darwin proposed the theory of natural selection based on observations during his voyage on: MCQ with Answer and Explanation

Explanation:
Xylem is the vascular tissue responsible for the unidirectional upward transport of water and dissolved minerals from the roots to the aerial parts of the plant. Phloem is the vascular tissue responsible for the translocation of organic nutrients (primarily sucrose) from sources to sinks, which can be bidirectional (up or down depending on the plant's needs). Cambium (vascular and cork) is a lateral meristem responsible for secondary growth, which is the increase in the girth or thickness of stems and roots. All statements are correct.

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.

Explanation:
Meristem culture, a type of tissue culture, involves excising the virus-free apical meristem (shoot tip) and growing it on a nutrient medium to produce a whole plant free of viruses. This is because meristematic cells lack vascular connections through which viruses spread. Cloning produces identical copies, hybridization crosses varieties, mutagenesis uses mutagens.