Correct Answer: A

Rationale: Nuclear fission is the process where a heavy nucleus, like uranium-235, captures a neutron, leading to its division into two lighter nuclei. This process releases a substantial amount of energy in the form of heat and gamma rays. It is utilized in nuclear power plants and atomic bombs due to its capacity to produce significant energy. Choices B, C, and D describe different nuclear processes: fusion of two nuclei to form a heavier element, emission of alpha particles from a lighter element through radioactive decay, and absorption of an electron by the nucleus with the release of a gamma ray, respectively. These processes are distinct from nuclear fission and do not involve the splitting of heavy nuclei into lighter ones.

Correct Answer: B

Rationale: The balanced chemical equation for the combustion of methane is: CH4 + 2O2 -> CO2 + 2H2O. This equation shows that 1 mole of methane produces 2 moles of water. Therefore, when 0.5 moles of methane react, they will produce 1 mole of water. The ratio of water to methane is 2:1, meaning that for every mole of methane that reacts, it produces 2 moles of water. Since only 0.5 moles of methane are reacting, the amount of water produced will be half of what would be produced if 1 mole of methane reacted, resulting in 1 mole of water being produced. Choice A is incorrect because it does not consider the stoichiometry of the reaction. Choices C and D are incorrect as they do not align with the balanced chemical equation and the stoichiometric ratios involved in the reaction.

Correct Answer: D

Rationale: Vacuoles in plant cells primarily function as storage organelles. They store water, enzymes, pigments, and waste products, helping to maintain turgor pressure within the cell. This turgor pressure provides structural support for the plant cell. While vacuoles can also participate in transporting substances within the cell, their main role is storage. The synthesis of proteins and lipids is mainly handled by other organelles such as the endoplasmic reticulum and Golgi apparatus. Choice A is incorrect because while vacuoles indirectly contribute to structural support by maintaining turgor pressure, their primary function is storage. Choice B is incorrect as vacuoles are not primarily responsible for transporting substances in and out of the cell. Choice C is incorrect as vacuoles do not synthesize proteins and lipids; this function is carried out by other organelles.

Correct Answer: C

Rationale: A) Population refers to a group of individuals of the same species living in a specific area. B) Community refers to all the populations of different species living and interacting in a particular area. C) Biome is a large geographic area characterized by similar climate, plants, and animals. Biomes are defined by factors such as temperature, precipitation, and vegetation types. D) Ecosystem refers to a community of living organisms interacting with each other and their physical environment. An ecosystem can be part of a biome.

Correct Answer: D

Rationale: Keystone species play a crucial role in maintaining the balance and structure of an ecosystem due to their significant influence. If a keystone species is removed, it disrupts the delicate food web dynamics and can trigger cascading effects throughout the ecosystem. The disruption in predator-prey relationships can lead to population declines and even extinctions of other species. Options A, B, and C are incorrect because the removal of a keystone species would not decrease competition among other species, cause a slight increase in primary productivity, or have a minimal impact on the overall ecosystem structure. Instead, it would have a profound impact, disrupting the food web and causing cascading effects on other populations.