Biology

Scientific studies show that gold is present in trace amounts throughout the human body, with the liver and bone marrow each containing about 25% of the total body gold, and skin and bone each about 20%. Among keratin-rich tissues, nails (including toenails) have been found to contain higher trace amounts of gold compared to skin, liver, or kidney. This is because gold can accumulate in keratinous tissues like nails. Although the amounts are extremely small, toenails have higher gold content relative to the other listed body parts, making option C (Toenails) the correct answer.

The human body has approximately 600 to 650 muscles, but the exact number varies depending on classification. None of the given options (632, 639, 642) are universally accepted as precise counts, so 'None of these' is the best choice.

The correct term for the framework made up of all the bones in the body is the 'skeleton'. It provides structure and support to the body.

Each human hand contains 27 bones: 8 carpal bones in the wrist, 5 metacarpal bones in the palm, and 14 phalanges in the fingers (3 in each finger and 2 in the thumb). This is confirmed by authoritative sources such as the National Institutes of Health and medical anatomy references. Therefore, the correct answer is 27 bones, which corresponds to option B.

Aldosterone is a hormone produced by the adrenal glands that regulates sodium and potassium levels in the blood by promoting sodium retention and potassium excretion in the kidneys. Cortisol primarily regulates metabolism and stress response, glycogens are storage forms of glucose, and pheromones are chemical signals for communication, not involved in electrolyte balance.

Proteins are polymers made up of amino acid monomers linked together by peptide bonds, forming polypeptides. Therefore, the correct answer is 'Polypeptide'.

The normal pH range of human blood is tightly regulated between 7.35 and 7.45, which is slightly alkaline. This range is essential for proper physiological functions. Options A, B, and D fall outside this normal range.

Reproduction is essential for the continuation and survival of species because it allows organisms to produce offspring and pass on their genetic material to the next generation. Without reproduction, a species would eventually become extinct.

Grebes have legs positioned far back on their bodies, which makes them excellent swimmers but awkward or unable to walk on land effectively. Hummingbirds, on the other hand, can walk or hop short distances. Therefore, the correct answer is Grebes.

The human skull is composed of 22 bones, including the cranial and facial bones. This is a well-established anatomical fact.