Biology

The adult human body typically has 206 bones. This is a well-established fact in human anatomy, making option C the correct answer.

The femur is the longest bone in the human body, located in the thigh. It is longer than the ulna, tibia, and humerus, making option C the correct answer.

Kidney stones are primarily composed of calcium oxalate, which is the most common constituent of these stones formed in the human kidney. Other options like sodium acetate, magnesium sulphate, and calcium alone are not typical components of kidney stones.

The pancreas secretes insulin, a hormone that regulates blood sugar levels. It does not secrete Vitamin A or bile juice, which are produced by other organs.

Vitamin K is synthesized by intestinal bacteria in the human gut, making option D the correct answer. Vitamins B1, B12, and E are not primarily produced by intestinal bacteria.

During a total solar eclipse, sunlight is blocked, reducing light availability for photosynthesis, causing the rate of photosynthesis to decrease.

Muscle fatigue occurs due to the accumulation of lactic acid in muscles during intense exercise when oxygen supply is limited, causing a burning sensation and reduced muscle performance.

The heart beats approximately 100,000 times per day. Each heartbeat causes the four heart valves (mitral, tricuspid, aortic, and pulmonary) to open and close once. Therefore, the total number of valve openings and closings per day is about 100,000 beats × 4 valves = 400,000 valve movements. However, the question asks approximately how many times each day do our heart valves open and close normally, and the options given are much lower. Since each valve opens and closes about 100,000 times per day (once per heartbeat), the closest approximate answer for a single valve is 100,000 times (option B). The original question's option C (150,000) is not the closest to the actual figure. Thus, the correct answer should be B (100,000).

Insulin was discovered by Sir Frederick Grant Banting and Charles Herbert Best in 1921. Among the options, Banting is the most commonly credited primary discoverer, making option C correct.

The AIDS virus, known as HIV, is a retrovirus that contains single-stranded RNA as its genetic material, which it uses to replicate inside host cells.

In eye donation, the cornea is the part of the donor's eye that is typically utilized for transplantation to restore vision in recipients with corneal blindness. Other parts like the iris, lens, and retina are generally not used in standard eye donation procedures.

Kidney stones are primarily composed of calcium oxalate, which is the most common constituent of these stones formed in the human kidney.

The AIDS virus, known as HIV, is a single-stranded RNA virus. It belongs to the retrovirus family, which uses RNA as its genetic material.

The human heart beats about 100,000 times per day. Each heartbeat causes the four heart valves (mitral, tricuspid, aortic, and pulmonary) to open and close once. Since there are four valves, the total number of valve openings and closings per day is approximately 400,000. The closest option to this is 200,000 (option D), which is a reasonable approximation given the options provided, although the actual total is higher. The question likely refers to the total number of times all valves open and close combined, not just a single valve.

Insulin was discovered by Sir Frederick Grant Banting and Charles Herbert Best in 1921. Banting is often credited as the primary discoverer, which is why option C is correct. Leonard Thompson was the first patient to receive insulin treatment, and Macleod was a supervisor and co-recipient of the Nobel Prize.

During a total solar eclipse, sunlight is blocked, reducing light intensity drastically. Since photosynthesis depends on light, its rate decreases during the eclipse.

In eye donation, the cornea is the part of the donor's eye that is commonly utilized for transplantation to restore vision in recipients with corneal blindness. Other parts like the iris, lens, and retina are generally not used in standard eye donation procedures.

The pancreas secretes insulin, a hormone that regulates blood sugar levels. It does not secrete Vitamin A or bile juice, which are produced by other organs.

Vitamin K is synthesized by intestinal bacteria in the human gut, making option D correct. Vitamins B1, B12, and E are not synthesized by gut bacteria.

The iris contains the pigment that determines the color of a person's eyes. The amount and type of pigment in the iris control eye color, making option B correct.

Acclimatization refers to the gradual physiological adjustment of an organism to changes in its environment, such as temperature or altitude, over time. This distinguishes it from terms like selection or quarantine, which have different meanings.

Melanin is the pigment produced by cells in the skin called melanocytes, and it is responsible for the color of human skin. The other options do not influence skin color.

Periodontics is a branch of dentistry that focuses on the structures supporting the teeth, such as gums and bones, making option D the correct answer.

Smoking introduces carbon monoxide into the bloodstream, which binds to hemoglobin in red blood cells more effectively than oxygen, thereby reducing their oxygen-carrying capacity. This impairs oxygen delivery to tissues.

Alzheimer’s disease primarily affects the brain by causing degeneration of nerve cells (neurons), leading to memory loss and cognitive decline. Other cell types like kidney, liver, or spleen cells are not involved in this disease.