What are the small, finger-like projections in the small intestines called?

Correct Answer: D

Rationale: The correct answer is D: Villi. Villi are small, finger-like projections in the small intestine that increase the surface area for absorption, aiding in the absorption of nutrients. Cilia (Choice A) are tiny hair-like structures found in various parts of the body but are not present in the small intestine. Rugae (Choice B) are folds in the mucosa of the stomach that allow for its expansion during digestion. The trachea (Choice C) is part of the respiratory system, responsible for carrying air to and from the lungs, and is not related to the small intestine.

Correct Answer: C

Rationale: The correct answer is C: GABA (gamma-aminobutyric acid). GABA acts as an inhibitory neurotransmitter that reduces neuronal activity, thus preventing overexcitation. Acetylcholine (choice A) is involved in muscle control and cognitive function, but it is not primarily responsible for slowing down neuronal activity. Dopamine (choice B) plays a role in reward-motivated behavior and motor control, rather than inhibiting neuronal firing. Serotonin (choice D) is involved in mood regulation, sleep, and appetite but does not primarily slow down neuronal activity to prevent overexcitation.

Correct Answer: A

Rationale: The endoplasmic reticulum is the correct answer. It is the cytoplasmic organelle that contains fluid-filled tubules responsible for carrying and transporting substances within the cell. The endoplasmic reticulum plays a crucial role in protein synthesis, lipid metabolism, and detoxification processes. The Golgi apparatus, although important in modifying, sorting, and packaging proteins for secretion or for use within the cell, does not primarily contain fluid-filled tubules for carrying and transporting substances. Mitochondria are responsible for generating ATP through cellular respiration, not for carrying and transporting substances. The nucleus contains the cell's genetic material and is involved in regulating cellular activities but does not contain fluid-filled tubules for transportation.

Correct Answer: A

Rationale: The correct answer is A: Protein synthesis. Ribosomes are the cellular organelles responsible for protein synthesis. They read the messenger RNA (mRNA) and translate the genetic information into specific proteins. This process is essential for building and maintaining the structures and functions of the cell. Choice B, DNA replication, is incorrect because ribosomes are not involved in replicating DNA; that process occurs in the nucleus. Choice C, cell division, is incorrect as ribosomes are not directly involved in cell division but rather in protein synthesis. Choice D, lipid synthesis, is also incorrect as ribosomes are not responsible for synthesizing lipids, which primarily occurs in the endoplasmic reticulum and other organelles.

Correct Answer: B

Rationale: Mitochondria are the powerhouse of the cell and are responsible for producing ATP through cellular respiration. ATP, or adenosine triphosphate, is the energy currency of the cell that is essential for various cellular processes. The Golgi apparatus is involved in modifying, sorting, and packaging proteins for secretion. The nucleus is responsible for housing the cell's genetic material and controlling cell activities. Ribosomes are involved in protein synthesis. However, the actual production of ATP occurs in the mitochondria through processes like the citric acid cycle and oxidative phosphorylation.