Correct Answer: B

Rationale: A decomposition reaction involves a single compound breaking down into two or more simpler substances. In option B, CaCO3 breaks down into CaO and CO2, making it an example of a decomposition reaction. Options A, C, and D involve different types of chemical reactions such as synthesis, combination, and combustion, respectively. Option A represents a synthesis reaction, where two elements combine to form a compound. Option C demonstrates a combination reaction, where two elements combine to form a compound. Option D is an example of a synthesis reaction, where two reactants combine to form a single compound. It is important to recognize the specific characteristics of each type of chemical reaction to identify the correct example of decomposition reaction, where a compound breaks down into simpler products.

Correct Answer: C

Rationale: Phagocytes are a type of white blood cell that is crucial in the initial attack on pathogens. These cells have the ability to engulf and digest foreign particles such as bacteria and viruses, thereby preventing infections. Red blood cells primarily function in oxygen transport, platelets are vital for blood clotting, and lymphocytes are involved in the immune response. However, phagocytes are specifically designed to provide the initial defense against pathogens by directly attacking and eliminating them.

Correct Answer: D

Rationale: The correct answer is D, 'All of the above.' Saltatory conduction is faster than normal nerve conduction, occurs from one node of Ranvier to the next, and is exclusive to myelinated neurons. This form of conduction allows for the rapid transmission of nerve impulses by the action potential jumping between the nodes of Ranvier in myelinated neurons, enhancing the efficiency of signal propagation along the axon. Choice A is correct as saltatory conduction is indeed faster than normal conduction. Choice B is accurate as it describes the mechanism of conduction 'jumping' from one node of Ranvier to the next. Choice C is correct because saltatory conduction occurs specifically in myelinated neurons where the myelin sheath insulates the axon except at the nodes of Ranvier, facilitating faster transmission of nerve impulses.

Correct Answer: B

Rationale: Gravitational potential energy is directly proportional to the height or distance from the ground. As the object is raised higher, its gravitational potential energy increases. While the mass of the object influences gravitational potential energy, the distance from the ground has a more significant impact on it. The gravitational force does not directly affect the gravitational potential energy; it is the force that causes the potential energy to change with height. The shape of the object also does not determine gravitational potential energy, as it is primarily determined by the object's position in a gravitational field.

Correct Answer: C

Rationale: The correct answer is C: Testes. The testes are responsible for producing testosterone, the hormone that plays a crucial role in male secondary sexual characteristics such as facial hair, deepening of the voice, and muscle development. The adrenal glands primarily produce cortisol and aldosterone, not testosterone. The pituitary gland regulates hormone production in various glands, including the testes, but it does not directly produce testosterone. The pancreas is responsible for producing insulin and glucagon to regulate blood sugar levels, not testosterone.