The pigment that absorbs light in photosystem I is primarily: MCQ with Answer and Explanation

Explanation:
Kala-azar, also known as visceral leishmaniasis, is caused by the protozoan parasite Leishmania donovani. It is transmitted by the bite of the infected female sandfly (Phlebotomus). The disease affects internal organs, particularly the liver, spleen, and bone marrow, causing prolonged fever, weight loss, and enlargement of the liver and spleen. Trypanosoma brucei causes sleeping sickness, and Plasmodium causes malaria.

Explanation:
Rhizobium is a symbiotic bacterium found in legume root nodules that fixes atmospheric nitrogen into ammonia. Yeast (Saccharomyces cerevisiae) undergoes anaerobic respiration, producing CO2 that leavens bread dough. The vast majority of bacteria are harmless or beneficial (e.g., gut flora, decomposers); only a small fraction are pathogenic to humans. Thus, statements 1 and 2 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.