Assertion (A): Fermentation produces less ATP than aerobic respiration. Reason (R): Fermentation involves only glycolysis and does not use the Krebs cycle or electron transport chain. MCQ with Answer and Explanation

Explanation:
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.

Explanation:
Glucagon, from the pancreatic alpha cells, raises blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver. Cortisol and growth hormone also raise blood glucose but glucagon is the primary direct antagonist of insulin. Thyroxine increases metabolic rate. The balance between insulin (hypoglycemic) and glucagon (hyperglycemic) maintains glucose homeostasis.

Explanation:
Robert Koch, a German physician and microbiologist, formulated Koch's postulates in the late 19th century. These four criteria are designed to establish a causal relationship between a specific microbe and a specific disease. The postulates require that the microbe must be found in all cases of the disease, isolated and grown in pure culture, cause the disease when inoculated into a healthy susceptible host, and be re-isolated from the experimentally infected host.