What are the two main divisions of the skeletal system?

Correct Answer: B

Rationale: The skeletal system is divided into two main divisions: the axial skeleton and the appendicular skeleton. The axial skeleton comprises the skull, vertebral column, and rib cage, providing structural support and protection for vital organs. On the other hand, the appendicular skeleton includes the bones of the upper and lower limbs, shoulder girdle, and pelvic girdle, facilitating movement and flexibility. The divisions are based on the location and function of the bones within the skeletal system, making choices A, C, and D incorrect as they do not represent the primary divisions of the skeletal system.

Correct Answer: B

Rationale: The main organ responsible for regulating sleep is the hypothalamus. The hypothalamus plays a crucial role in controlling the body's circadian rhythm, which is the internal clock that regulates the sleep-wake cycle. It receives input from the eyes about light and darkness, aiding in determining when it's time to sleep or wake up. Additionally, the hypothalamus regulates the production of melatonin by the pineal gland, a hormone that helps control sleep patterns. While the thalamus relays sensory information to the brain, the pituitary gland is primarily responsible for hormone production and release, and the pineal gland produces melatonin under the control of the hypothalamus. Therefore, the hypothalamus is the correct choice as the main organ involved in sleep regulation.

Correct Answer: A

Rationale: Mass is a measure of the amount of matter in an object and remains constant regardless of changes in gravity. This is because mass is an intrinsic property of an object and does not depend on the gravitational field it is in. Weight, on the other hand, is the force of gravity acting on an object's mass and can vary depending on the strength of gravity. Volume is the amount of space an object occupies, which can change depending on the environment. Density is the mass of an object per unit volume, which can also change with variations in gravity. Therefore, the correct answer is Mass as it remains the same regardless of gravitational changes.

Correct Answer: C

Rationale: The primary function of hair on the human body is protection. Hair acts as a barrier to protect the skin from external factors such as sunlight, dust, and other environmental elements. While hair can also provide some insulation by trapping heat near the body and contribute to sensory perception by detecting touch or movements, its main role is to safeguard the skin from potential harm, making protection the most essential function. Vitamin D synthesis is primarily related to the skin's exposure to sunlight and is not a direct function of hair.

Correct Answer: B

Rationale: Vaccines work by introducing weakened or inactive versions of pathogens to trigger an immune response in the body. This exposure helps the immune system recognize and remember the pathogen, enabling a faster and more effective response upon future exposure. Vaccines do not directly kill pathogens but prepare the immune system for a potential encounter, enhancing protection. They also do not stimulate the immediate production of specific antibodies as the immune response takes time to develop upon vaccination. Choice A is incorrect because vaccines do not kill pathogens directly; they prime the immune system to recognize and respond to them. Choice C is incorrect because while vaccines lead to the production of specific antibodies, it is not immediate, as it takes time for the immune response to develop and produce these antibodies.

Correct Answer: A

Rationale: Refraction is the phenomenon that occurs when a wave encounters a change in medium, causing a change in its speed and direction. This change in speed and direction is due to the wave bending as it passes from one medium to another with a different density. It is essential to understand refraction as it plays a crucial role in various phenomena, such as the bending of light in lenses, the formation of rainbows, and the way seismic waves travel through the Earth's layers. Reflection, while also a wave phenomenon, involves the bouncing back of a wave when it encounters a boundary. Diffraction refers to the bending of waves around obstacles or through openings, and interference involves the combination of two or more waves to form a new wave pattern.

Correct Answer: C

Rationale: The main target organ for insulin is muscles. Insulin plays a crucial role in regulating glucose metabolism by promoting the uptake of glucose into muscle cells. This glucose can then be utilized for energy production or stored for later use. Therefore, muscles are the primary site where insulin exerts its effects on glucose uptake and utilization. The liver primarily responds to insulin by regulating glucose storage and release, but the main target for insulin-mediated glucose uptake is muscles. Kidneys are not a target organ for insulin action in glucose metabolism. The brain does not heavily rely on insulin for glucose uptake as it primarily uses glucose independently of insulin for energy production.

Correct Answer: A

Rationale: Molality (m) is the unit used to express concentration as a mass of solute per unit volume of solution. It is calculated by dividing the mass of solute in grams by the mass of the solvent in kilograms. Molality is preferred over molarity when there are large temperature variations as it is temperature-independent, making it a more accurate measure of concentration. Molarity (B) is the unit used to express concentration as moles of solute per liter of solution, weight percent (C) is the mass of solute per 100 parts of the total mass of the solution, and parts per million (D) is used to express very small concentrations where 1 ppm is equivalent to 1 mg of solute per liter of solution.

Correct Answer: C

Rationale: The cerebellum is the part of the brain that plays a crucial role in the regulation of balance, coordination, and posture. It receives information from the sensory systems, the spinal cord, and other parts of the brain to coordinate voluntary movements. While the thalamus is involved in relaying sensory and motor signals to the cerebral cortex, the cerebrum is responsible for higher brain functions such as thought and action. The hypothalamus is involved in various bodily functions including the regulation of body temperature, hunger, and thirst, but it is not primarily responsible for balance, coordination, and posture. Therefore, the correct answer is the cerebellum.