Correct Answer: B

Rationale: Chromosomes are made up of DNA and associated proteins. These proteins help package and organize the DNA within the cell, playing a crucial role in gene regulation and cell division. While RNA is involved in various cellular processes, it is not a primary component of chromosomes. Lipids are not a fundamental component of chromosomes, which primarily consist of DNA and proteins.

Correct Answer: B

Rationale: The lysosome is the correct cellular organelle used for digestion to recycle materials. Lysosomes contain enzymes that break down waste materials, cellular debris, and ingested substances. This process helps in recycling nutrients and maintaining cellular homeostasis. The Golgi apparatus is involved in processing and packaging proteins, the centrioles play a role in cell division, and the mitochondria are responsible for energy production. However, none of these organelles are primarily used for digestion and recycling of materials within the cell.

Correct Answer: B

Rationale: The correct answer is B: Swallowing, peristalsis, segmentation. Food moves through the digestive tract by first being swallowed, then undergoing peristalsis (wave-like movements that propel food along the digestive tract), and finally undergoing segmentation (mixing movements in the intestines). Chewing and digestion occur in the mouth and stomach, respectively, while absorption and excretion happen later in the digestive process. Choice A is incorrect as absorption is a later stage in the process. Choice C is incorrect because defecation is the elimination of waste, not the movement of food. Choice D is incorrect as excretion is the elimination of waste products, not the movement of ingested food through the digestive tract.

Correct Answer: A

Rationale: The correct answer is A: Complement system. The complement system is a vital component of the immune system responsible for destroying pathogens through various mechanisms like promoting inflammation, enhancing phagocytosis, and directly lysing pathogens. Fibrinogen is crucial for blood clotting, the major histocompatibility complex is involved in immune responses, and platelets aid in blood clotting and wound healing. However, none of these directly destroy pathogens as the complement system does.

Correct Answer: B

Rationale: The correct answer is B. The first heart sound, known as the 'lub' sound, is produced by the closure of the tricuspid and mitral valves, which are the atrioventricular valves. This sound marks the beginning of systole in the cardiac cycle. Choice A, the closing of the aortic and pulmonary valves, is incorrect as these valves produce the second heart sound ('dub'). Choice C, the opening of the aortic and pulmonary valves, is incorrect because the first heart sound occurs during ventricular contraction (systole). Choice D, the opening of the tricuspid and mitral valves, is incorrect as the 'lub' sound is associated with the closure, not the opening, of these valves.