Consider statements about scientists: 1. Charles Darwin proposed the theory of evolution. 2. Gregor Mendel proposed the laws of inheritance. 3. Robert Hooke discovered the cell nucleus. Which are correct? MCQ with Answer and Explanation

Explanation:
Pellagra, characterized by dermatitis, diarrhea, and dementia (3 Ds), is caused by a deficiency of niacin (vitamin B₃) or its precursor tryptophan. It is common in populations with corn-based diets lacking tryptophan. Beriberi is due to B₁ deficiency, cheilosis to B₂, peripheral neuropathy to B₆. Niacin is a component of coenzymes NAD and NADP.

Explanation:
RNAi is a cellular defense mechanism in eukaryotes that silences specific mRNA. To create nematode-resistant tobacco, scientists used Agrobacterium as a vector to introduce nematode-specific genes into the host plant. The plant then produced both sense and anti-sense RNA for these genes. The double-stranded RNA (dsRNA) formed triggered the RNAi pathway, degrading the nematide's mRNA when it tried to express those essential genes inside the plant roots, killing the nematode.

Explanation:
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, sealing breaks in the DNA backbone. It is essential for joining Okazaki fragments on the lagging strand during replication and in DNA repair. Polymerase adds nucleotides, helicase unwinds, primase synthesizes RNA primer.