What is the difference between active and passive immunity?

Correct Answer: B

Rationale: Active immunity involves the body's own immune response, where the individual's immune system produces antibodies in response to exposure to a pathogen or vaccine. This type of immunity is long-lasting because the immune system 'remembers' the pathogen and can mount a rapid response upon re-exposure. In contrast, passive immunity provides immediate protection through the transfer of pre-formed antibodies from another source, such as through maternal antibodies crossing the placenta or receiving antibodies through an injection. Passive immunity is short-lived because the transferred antibodies eventually degrade and are not produced by the recipient's immune system. Choice A is incorrect because active immunity is generally long-lasting, as it involves the production of antibodies by the individual's immune system. Choice C is incorrect as both active and passive immunity can work against various pathogens, not limited to bacteria or viruses. Choice D is incorrect as passive immunity does not require repeated vaccinations but provides temporary protection through the transfer of antibodies from an external source.

Correct Answer: B

Rationale: A) This statement is true. Fungi can exist in both unicellular (yeast) and multicellular (molds and mushrooms) forms. B) This statement is false. While some fungi can be parasitic and cause diseases in humans, not all fungi exhibit this behavior. Many fungi are beneficial and play essential roles in ecosystems. C) This statement is true. Fungi are crucial for decomposition and nutrient cycling in ecosystems. They break down organic matter and recycle nutrients back into the environment. D) This statement is true. Some fungi, like mushrooms, are used in food production and are consumed by humans.

Correct Answer: C

Rationale: In most ecosystems, the primary source of energy is sunlight. This energy is captured by plants and other photosynthetic organisms through the process of photosynthesis. These organisms convert light energy into chemical energy stored in the bonds of organic molecules, such as glucose. This stored chemical energy is then passed on to other organisms in the ecosystem through the food chain, making sunlight the fundamental source of energy for most ecosystems. Thermal energy from the Earth's core (option B) is not a primary source of energy for ecosystems, as it is not readily accessible to most organisms. Kinetic energy from wind and water (option D) can play a role in some ecosystems, but it is not the primary source of energy. Chemical energy stored in bonds (option A) is a form of energy that is ultimately derived from the sun through photosynthesis, making it a product of the primary energy source rather than the primary source itself.

Correct Answer: A

Rationale: A) Desertification is the correct term for the gradual loss of topsoil due to wind or water erosion. It refers to the process by which fertile land becomes desert, usually due to factors like drought, deforestation, or inappropriate agriculture practices. This process can lead to the degradation of land and contribute to the expansion of deserts. B) Leaching is the process in which minerals are washed out of the soil by water moving downwards through it. This is different from the loss of topsoil due to erosion. C) Salinization occurs when salt accumulates in the soil, typically as a result of irrigation in arid regions. While salinization affects soil quality, it is not specifically related to the gradual loss of topsoil due to erosion. D) Acidification refers to the decrease in soil pH, often caused by factors like acid rain or the use of acidic fertilizers. This process is distinct from the gradual loss of topsoil due to erosion.

Correct Answer: A

Rationale: When sodium hydroxide (NaOH) reacts with hydrochloric acid (HCl), a neutralization reaction occurs. The products of this reaction are water (H2O) and a salt, which is sodium chloride (NaCl). The chemical equation for this reaction is: NaOH + HCl -> NaCl + H2O. Choice B is incorrect because chlorine gas and sodium oxide are not the products of this reaction. Choice C is incorrect as sodium metal and water are not the products formed in this neutralization reaction. Choice D is incorrect because a reaction does occur between NaOH and HCl, resulting in the formation of NaCl and H2O. Therefore, the correct answer is A: Hydrogen gas and sodium chloride (NaCl).