Correct Answer: B

Rationale: The correct answer is B: Humoral. Humoral immunity involves B-cells secreting antibodies to fight pathogens. In this type of immunity, antibodies circulate in the blood and other body fluids to neutralize pathogens and prevent infections. Cell-mediated immunity, on the other hand, involves the activation of T-cells to directly attack infected or abnormal cells, not the secretion of antibodies. Innate immunity refers to the nonspecific defense mechanisms the body has in place from birth, such as physical barriers and inflammatory responses. Phagocytic immunity is not a recognized type of immunity; phagocytosis is a mechanism used by cells like macrophages to engulf and digest pathogens, but it is not a specific form of immunity like humoral or cell-mediated immunity.

Correct Answer: D

Rationale: The correct answer is D, 'Researching previous studies for background.' Before formulating a hypothesis, it is essential to review existing literature, studies, and information related to the topic to understand the context and identify gaps in knowledge. This step helps researchers build on existing knowledge and formulate a clear hypothesis based on the information gathered. Choices A, B, and C are incorrect because they come after the step of researching previous studies and developing a hypothesis. Collecting and organizing data, conducting an experiment, and communicating results typically follow the hypothesis generation step in the scientific method.

Correct Answer: C

Rationale: The mitochondrion is a membrane-bound organelle, while cytosol is the fluid part of the cytoplasm. This differentiation highlights that the mitochondrion has its own membrane structure separating it from the cytoplasm, whereas cytosol is not membrane-bound and represents the liquid portion of the cytoplasm. Choice A is incorrect because cytosol is not a membrane-bound organelle, and the mitochondrion is also not described accurately. Choice B is incorrect as cytosol is indeed part of the cytoplasm. Choice D is incorrect because both the mitochondrion and cytosol are part of the cytoplasm, but the mitochondrion is a membrane-bound organelle unlike cytosol.

Correct Answer: B

Rationale: The spleen is located in the abdomen, specifically in the upper left part of the abdomen, under the ribcage and above the stomach. It is an important organ in the lymphatic system responsible for filtering blood, storing blood cells, and fighting infection. It is not located in the chest, pelvis, or head and neck regions. Therefore, the correct answer is 'B: Abdomen.' Choices 'A: Chest,' 'C: Pelvis,' and 'D: Head and neck' are incorrect as the spleen is not situated in these anatomical areas.

Correct Answer: B

Rationale: Thyroxine, also known as T4, is the hormone produced by the thyroid gland to regulate metabolism. It is essential for controlling the body's metabolic rate, heart and digestive function, muscle control, brain development, and bone maintenance. Adrenaline is produced by the adrenal glands, not the thyroid gland. Cortisol is produced by the adrenal cortex, not the thyroid gland. Insulin is produced by the pancreas, not the thyroid gland. Therefore, the correct answer is Thyroxine (B).