Which of the following is a nitrogen-fixing bacterium in legume roots? MCQ with Answer and Explanation

Explanation:
Immunoglobulin G (IgG) is the most abundant antibody in human blood plasma, constituting about 75-80% of all antibodies. It is the only antibody that can cross the placenta, providing passive immunity to the fetus. IgG is crucial for long-term immunity, neutralizing toxins, viruses, and bacteria, and activating the complement system.

Explanation:
Leptin is a peptide hormone produced primarily by adipocytes (fat cells). Its concentration in the blood is proportional to the amount of body fat. Leptin acts as a satiety signal, crossing the blood-brain barrier to act on receptors in the hypothalamus. It suppresses appetite (anorexigenic effect) and increases energy expenditure, thereby regulating long-term food intake and body weight. It is often called the 'satiety hormone' or 'fat hormone'.

Explanation:
Rheumatoid arthritis is a chronic inflammatory autoimmune disease where the immune system mistakenly attacks the body's own healthy tissues, specifically the synovial membranes of joints. This leads to painful swelling, bone erosion, and joint deformity. Other examples of autoimmune diseases include Type 1 diabetes, multiple sclerosis, and systemic lupus erythematosus.