Correct Answer: A

Rationale: When plants do not receive enough water, their photosynthetic rate drops because water is a raw material required for the light reactions in photosynthesis. In the light reactions, water is split to provide electrons, which are then utilized to produce energy carriers used in converting carbon dioxide into glucose during the Calvin cycle. Therefore, without sufficient water, the light reactions cannot proceed effectively, ultimately leading to a decrease in photosynthetic rate. Choice B is incorrect because carbon dioxide is a separate raw material needed for the Calvin cycle, not the light reactions. Choice C is incorrect as water provides electrons, not carbon atoms, for photosynthesis. Choice D is incorrect because fermentation is not directly related to photosynthesis; oxygen is produced during photosynthesis, not fermentation.

Correct Answer: A

Rationale: DNA is stored in the nucleus of a cell. The nucleus houses the cell's genetic material, including the DNA, which contains the instructions for building and operating the cell. The nucleus controls the activities of the cell and is essential for proper cell function and reproduction. Ribosomes are responsible for protein synthesis, not DNA storage. The endoplasmic reticulum is involved in protein and lipid synthesis, storage, and transport but does not store DNA. Mitochondria are known as the powerhouse of the cell, producing energy in the form of ATP, but they do not store DNA.

Correct Answer: C

Rationale: Metabolism is the sum of all chemical reactions that occur within an organism to maintain life. It involves all the processes that break down molecules to release energy (catabolism) and build new molecules to support growth and maintenance (anabolism). Respiration refers specifically to the process of generating energy from the breakdown of glucose molecules. Synthesis is the creation of complex molecules from simpler ones. Therefore, metabolism is the most comprehensive term that encompasses all these processes within an organism.

Correct Answer: A

Rationale: To convert centimeters to millimeters, you need to multiply by 10 since 1 centimeter is equal to 10 millimeters. Therefore, 8 cm x 10 mm/cm = 80 mm. The pencil measures 8 cm, which is equivalent to 80 mm when converted. Choice A is correct as it correctly converts 8 cm to mm by multiplying it by 10. Choices B, C, and D are incorrect because they do not apply the correct conversion factor.

Correct Answer: A

Rationale: The correct answer is A. The function of a cell membrane is to control the substances entering and leaving the cell. The cell membrane is selectively permeable, allowing it to regulate the movement of ions and molecules in and out of the cell to maintain internal balance and proper function. Choice B is incorrect because while the cell membrane does provide some structural support, its primary function is not to maintain the cell's shape. Choice C is incorrect because the cell membrane controls both the substances entering and leaving the cell, not just those entering. Choice D is incorrect as the primary function of the cell membrane is not to support the cell's structures but to regulate the movement of substances.