Correct Answer: C

Rationale: The correct answer is C: Double helix. The shape of the DNA molecule is a double helix, a structure first described by James Watson and Francis Crick in 1953. This shape consists of two strands twisted around each other in a spiral. The double helix structure allows DNA to be compactly stored within the cell nucleus and provides stability to the molecule. Options (A) Linear, (B) Circular, and (D) Straight chain are incorrect as they do not accurately represent the shape of the DNA molecule. DNA is not linear but rather forms a twisted double helix; it is not circular like a ring but has a spiral structure, and it is not a straight chain but a twisted ladder-like structure.

Correct Answer: C

Rationale: The involuntary reflex arc that withdraws your hand from a hot object involves both the central nervous system (CNS) and the peripheral nervous system (PNS). When your hand touches a hot object, sensory neurons in the PNS detect the heat and send signals to the spinal cord in the CNS. The spinal cord processes this information and sends a signal back through motor neurons in the PNS to move your hand away from the hot object. This coordinated response requires the collaboration of both the CNS and PNS to protect the body from harm. Choice A is incorrect because the reflex arc involves more than just the central nervous system. Choice B is incorrect because the reflex arc involves more than just the peripheral nervous system. Choice D is incorrect because the reflex arc also involves motor neurons, not just sensory neurons.

Correct Answer: B

Rationale: Smooth muscle is responsible for causing the hair follicles to stand on end when you get a goosebump. This type of muscle tissue is found in the skin attached to hair follicles and contracts in response to stimuli such as cold or fear, causing the hair to stand up. Skeletal muscle is responsible for voluntary movements, and cardiac muscle is found in the heart and is not directly involved in causing goosebumps. Therefore, choices A, C, and D are incorrect as they do not represent the specific type of muscle tissue responsible for this physiological response.

Correct Answer: A

Rationale: The correct answer is A: Insulin. Type 1 diabetes is characterized by the body's inability to produce insulin, the hormone responsible for regulating blood sugar levels. Insulin deficiency in type 1 diabetes leads to high blood sugar levels as the body cannot effectively utilize glucose for energy. Glucagon (Choice B) is a hormone that works opposite to insulin, raising blood sugar levels. Estrogen (Choice C) and testosterone (Choice D) are not directly involved in blood sugar control or the pathophysiology of type 1 diabetes.

Correct Answer: D

Rationale: The van't Hoff factor (i) represents the number of particles a solute dissociates into in solution. For a compound that dissociates completely in water, i would be more than 1 because it breaks apart into more particles than the original compound. This is due to complete dissociation leading to an increase in the number of particles in solution, resulting in i being greater than 1. Choice A is incorrect as a compound that dissociates completely will not have an i value of 0. Choice B is incorrect because when a compound dissociates completely, the van't Hoff factor is not less than 1. Choice C is incorrect as a compound that dissociates completely will not have an i value of 1, but rather more than 1 due to the increased number of particles in solution.