Correct Answer: B

Rationale: The main function of the skeletal system is to provide structural support for the body, protect internal organs, facilitate movement, and produce blood cells in the bone marrow. Choice A, 'To regulate blood pressure,' is incorrect as blood pressure regulation is primarily controlled by the circulatory and endocrine systems. Choice C, 'To produce hormones,' is incorrect as hormone production is mainly carried out by the endocrine system. Choice D, 'To fight infection,' is incorrect as the immune system is responsible for fighting infections, not the skeletal system.

Correct Answer: B

Rationale: Adrenaline, also known as epinephrine, is produced by the adrenal glands in response to stress. It helps prepare the body for the 'fight or flight' response by increasing heart rate, dilating airways, and mobilizing energy sources. Choice A, Insulin, is incorrect as it is produced by the pancreas and regulates blood sugar levels. Choice C, Glucagon, is also produced by the pancreas and functions to increase blood glucose levels. Choice D, Thyroxine, is produced by the thyroid gland and regulates metabolism, not specifically in response to stress.

Correct Answer: A

Rationale: The correct answer is A: B cells, a type of white blood cell, are responsible for producing antibodies in response to pathogens. Antibodies play a crucial role in identifying and neutralizing foreign substances like bacteria and viruses in the body, aiding in the immune response and protecting against infections. This function is essential for maintaining a healthy immune system. White blood cells, including B cells, are produced in the bone marrow before entering the bloodstream. Platelets, not white blood cells, are a specialized class of blood cells that function to clot blood and stop bleeding. While white blood cells provide immunity, not all of them are active throughout life as some have specific lifespans and functions.

Correct Answer: B

Rationale: The testes play a crucial role in male reproduction by producing sperm and testosterone. Sperm production is essential for fertility, while testosterone is responsible for the development of secondary sexual characteristics. The epididymis functions to store and mature sperm, allowing them to become motile. The prostate gland, not listed among the choices, secretes fluid that nourishes and protects sperm. The urethra serves the purpose of conducting both urine and semen out of the body, enabling the excretion of waste and reproductive fluids.

Correct Answer: A

Rationale: The correct answer is A: Nucleotide. Nucleotides are indeed the monomers that make up nucleic acids like DNA and RNA. They consist of a sugar molecule, a phosphate group, and a nitrogenous base. Amino acids are the monomers of proteins, not nucleic acids. While the phosphate group is a component of nucleotides, it is not the sole monomer. Ribosome is a cellular organelle involved in protein synthesis and is not a monomer for nucleic acids.