Correct Answer: C

Rationale: Platelets, also known as thrombocytes, play a crucial role in blood clotting. When there is an injury, platelets adhere to the site and release substances that form a clot, preventing excessive bleeding. This function is vital for maintaining hemostasis and preventing blood loss. Choice A is incorrect because red blood cells, not platelets, are responsible for transporting oxygen. Choice B is incorrect as white blood cells are primarily responsible for fighting infections. Choice D is incorrect as nutrients are mainly transported by plasma and red blood cells, not platelets.

Correct Answer: B

Rationale: The correct answer is B: Energy production. Mitochondria are known as the powerhouses of the cell because they generate adenosine triphosphate (ATP) through the process of cellular respiration. ATP is a molecule that stores and releases energy, providing the cell with the necessary energy for various activities and functions. Choices A, C, and D are incorrect. Protein synthesis primarily occurs in the ribosomes, breaking down waste is mainly carried out by lysosomes, and cell division is orchestrated by the nucleus and other organelles like the centrioles.

Correct Answer: B

Rationale: The correct answer is B: 'To transport oxygen.' Hemoglobin in red blood cells plays a crucial role in transporting oxygen. It binds to oxygen in the lungs and carries it to the body's tissues and organs for cellular respiration. Choices A, C, and D are incorrect because hemoglobin's primary function is to bind and transport oxygen, not to fight infections, carry carbon dioxide, or store oxygen.

Correct Answer: D

Rationale: The correct answer is D: Producing enzymes. The liver is involved in metabolism by producing enzymes that are essential for regulating various metabolic processes in the body. While the liver does store glucose, secrete bile, and detoxify harmful substances, its primary role in metabolism is producing enzymes that facilitate biochemical reactions necessary for energy production, nutrient breakdown, and waste elimination. Choices A, B, and C are incorrect because although the liver performs these functions, they are not directly related to its primary role in metabolism, which is producing enzymes.

Correct Answer: B

Rationale: Digestion begins in the mouth. Mechanical digestion through chewing and chemical digestion through saliva initiate the breakdown of food. Enzymes in saliva start breaking down carbohydrates, marking the beginning of the digestive process. The stomach primarily functions in further breaking down food and mixing it with gastric juices. The small intestine is where most of the digestion and absorption of nutrients occur. The esophagus is a muscular tube that helps move food from the mouth to the stomach, but digestion does not begin there.