Which of the following pairs is a symbiotic nitrogen fixer in leguminous plants?
A. Azotobacter - Wheat
B. Anabaena - Azolla
C. Frankia - Casuarina
D. Rhizobium - Soybean
Answer: Option D
Solution (By JKExamLibrary)
Rhizobium species form root nodules in leguminous plants like soybean, pea, and bean, where they fix atmospheric nitrogen symbiotically. Azotobacter is free-living, Anabaena associates with Azolla (a fern), Frankia with non-leguminous plants like Casuarina and Alnus. This symbiosis reduces the need for nitrogen fertilizers in agriculture.
Consider statements about diseases: 1. Cholera is caused by a bacterium. 2. AIDS is caused by a retrovirus. 3. Dengue is transmitted by Culex mosquito. Which are correct?
Explanation:
Cholera is a severe diarrheal disease caused by the bacterium Vibrio cholerae. AIDS is caused by the Human Immunodeficiency Virus (HIV), which is a retrovirus. Dengue fever is transmitted by the bite of an infected female Aedes aegypti mosquito, not Culex (which transmits filariasis and Japanese encephalitis). Thus, statements 1 and 2 are correct.
Explanation:
Australopithecus (e.g., 'Lucy') is considered one of the earliest direct ancestors or a very close relative of the genus Homo. They were bipedal hominins who lived in Africa about 4 to 2 million years ago. Dryopithecus and Ramapithecus are earlier ape-like ancestors. Homo neanderthalensis was a close relative but is generally considered a separate species that went extinct, though some interbreeding occurred.
Explanation:
Filariasis, commonly known as elephantiasis due to the severe swelling of limbs and genitals, is caused by filarial worms like Wuchereria bancrofti and Wuchereria malayi. These thread-like nematodes are transmitted by the bite of infected Culex mosquitoes. The adult worms lodge in the lymphatic vessels, causing chronic inflammation and blockage.
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