Correct Answer: C

Rationale: The correct answer is C: Lipids. Plasma membranes are primarily composed of lipids, specifically phospholipids, which form a lipid bilayer. While proteins are also an essential component of plasma membranes, they are not the primary constituent. Carbohydrates are present on the outer surface of the membrane but are not the main structural component. Nucleotides are the building blocks of nucleic acids like DNA and RNA and are not the main constituents of plasma membranes.

Correct Answer: B

Rationale: All humans have 23 pairs of chromosomes, totaling 46 chromosomes. Choice A is incorrect because humans do not have 24 pairs. Choice C is incorrect as humans have 23 pairs, not 22 pairs. Choice D is incorrect as humans have 23 pairs of chromosomes, not 20 pairs.

Correct Answer: A

Rationale: Correct! ATP (Adenosine Triphosphate) is the main molecule that stores and provides energy for cellular activities. ATP is known as the energy currency of the cell, where energy released from the breakdown of nutrients is stored in the high-energy phosphate bonds of ATP. Choices B, C, and D are incorrect because DNA carries genetic information, ADP is the precursor of ATP, and glycogen is a polysaccharide used for energy storage, not direct energy provision.

Correct Answer: B

Rationale: The Krebs Cycle is the correct answer. It is a series of reactions occurring in the mitochondria and is a crucial part of aerobic respiration. The Calvin Cycle is a part of photosynthesis, not respiration, making choice A incorrect. Photosynthesis (choice C) is the process by which plants, algae, and some bacteria convert light energy into chemical energy. Fermentation (choice D) is an anaerobic process that does not require oxygen and is not the primary energy-generating pathway during aerobic respiration, so it is incorrect.

Correct Answer: B

Rationale: The correct answer is B, eukaryotic. Animal cells are classified as eukaryotic cells because they contain membrane-bound organelles such as the nucleus, mitochondria, and endoplasmic reticulum. Choice A, prokaryotic, is incorrect as prokaryotic cells lack membrane-bound organelles. Choice C, Plant Cell, is incorrect as the question specifically asks about animal cells. Choice D, Bacterial Cell, is incorrect as bacteria are prokaryotic cells.