What happens to the potential energy of an object as it falls freely near the Earth's surface?

Correct Answer: A

Rationale: As an object falls freely near the Earth's surface, its potential energy decreases. This decrease occurs because the gravitational potential energy is being converted into kinetic energy as the object accelerates due to gravity. According to the law of conservation of energy, the total mechanical energy (the sum of potential and kinetic energy) remains constant in the absence of non-conservative forces like air resistance. Choice B ('Potential energy increases') is incorrect because the object's potential energy is being converted into kinetic energy, leading to a decrease. Choice C ('Potential energy remains constant') is incorrect as the conversion of potential energy to kinetic energy results in a decrease in potential energy. Choice D ('Potential energy becomes zero') is incorrect because potential energy is not reduced to zero but is transformed into kinetic energy as the object falls.

Correct Answer: A

Rationale: The critical angle is the minimum angle of incidence in a denser medium at which light undergoes total internal reflection instead of refraction. This phenomenon occurs when light travels from a denser medium to a less dense medium, and the angle of incidence is greater than the critical angle. Total internal reflection is a crucial concept in optics and is utilized in various applications such as fiber optics and prisms. Choice B, 'Continued refraction,' is incorrect as the critical angle specifically marks the point at which total internal reflection occurs, not continued refraction. Choice C, 'Specular reflection,' does not accurately describe the phenomenon associated with the critical angle. Choice D, 'Increased dispersion,' is unrelated to the concept of the critical angle and does not describe the behavior of light at this specific point.

Correct Answer: A

Rationale: The endoplasmic reticulum (ER) is a network of membranes within the cell that plays a crucial role in protein and lipid synthesis. It consists of two types: rough ER, which is studded with ribosomes and involved in protein synthesis, and smooth ER, which is involved in lipid synthesis and detoxification. The ER's main function is to synthesize proteins and lipids, not just package and transport them. While the ER is involved in transporting these synthesized proteins and lipids to other parts of the cell or outside the cell, its primary role is in their synthesis. Breaking down macromolecules is primarily the function of lysosomes, which are membrane-bound organelles containing enzymes for digestion. Storing genetic material is the function of the nucleus, which houses the cell's DNA. The ER is not involved in storing genetic material.

Correct Answer: B

Rationale: Convergent evolution refers to the process by which different species independently evolve similar traits or characteristics due to similar environmental pressures. In the case of bats and birds, both have evolved wings for flight despite not sharing a recent common ancestor with wings. Bats are mammals, while birds are avians, yet they both have wings adapted for flight, which is a classic example of convergent evolution. A) Humans and chimpanzees share a common ancestor and have not independently evolved similar traits. C) Dolphins and sharks are not closely related, and their similarities are due to adaptations to their aquatic environment rather than convergent evolution. D) Snakes and earthworms belong to different classes (reptiles and annelids, respectively) and do not share recent common ancestors, making their similarities not a result of convergent evolution.

Correct Answer: D

Rationale: Elasticity refers to a material's ability to resist deformation and return to its original shape after stress is applied. It is the property that resists a change in shape. Density is the mass per unit volume of a substance. Mass is the amount of matter in an object, while inertia is the tendency of an object to resist changes in its state of motion. Viscosity, not mentioned in the question, is the resistance of a fluid to flow, not shape change.

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: When ice melts, it undergoes a physical change, transitioning from a solid state to a liquid state. This change does not involve altering the chemical composition of the ice, making it a physical change rather than a chemical change, nuclear change, or radioactive decay. Choice A, 'Chemical change,' is incorrect because a chemical change involves a rearrangement of atoms resulting in new substances. Choice C, 'Nuclear change,' is incorrect as it refers to changes in the nucleus of an atom, not the phase transition of ice. Choice D, 'Radioactive decay,' is incorrect as it involves the spontaneous disintegration of an unstable atomic nucleus, which is not the process occurring when ice melts.

Correct Answer: B

Rationale: Sublimation is the process by which a solid directly transforms into a gas without passing through the liquid phase. This occurs when the atmospheric pressure is lower than the vapor pressure of the solid, causing it to transition to a gas state. Choice A, evaporation, is the process where a liquid changes into a gas, not a solid. Choice C, condensation, is the opposite process where gas changes into a liquid. Choice D, melting, is the process where a solid changes into a liquid, not a gas.

Correct Answer: B

Rationale: Autoimmune diseases occur when the immune system mistakenly targets and attacks healthy body tissues, leading to inflammation and damage. This results in conditions such as rheumatoid arthritis, lupus, and type 1 diabetes. Allergies, on the other hand, involve an exaggerated immune response to harmless substances like pollen or certain foods. Immunodeficiency refers to a weakened immune system, making individuals more susceptible to infections. Sepsis is a severe systemic response to an infection, leading to organ dysfunction and potentially life-threatening complications.