Correct Answer: B

Rationale: Enzymes lower the activation energy needed for a reaction to occur, not raise it. By lowering the activation energy, enzymes facilitate reactions, making them occur more easily and rapidly. Choice A is correct as enzymes indeed catalyze reactions. Choice C is correct as enzymes have specific active sites where substrates bind. Choice D is correct as enzymes are commonly proteins, although some RNA molecules also exhibit catalytic properties.

Correct Answer: D

Rationale: The head of a phospholipid is hydrophilic (water-loving) and is located on the outer side of the lipid bilayer, interacting with water molecules. This arrangement positions the hydrophobic tails inward, away from water. Therefore, the correct answer is D. Choice A is incorrect because the head is hydrophilic, not hydrophobic. Choice B is incorrect as the head is on the outer side, not the inner side of the layer.

Correct Answer: B

Rationale: The Krebs cycle, also known as the citric acid cycle, involves a series of redox reactions that occur in the mitochondria. The cycle begins with the oxidation of acetyl CoA, which is derived from the breakdown of sugars produced during glycolysis. These sugars are broken down further in the Krebs cycle to produce ATP and reduce electron carriers such as NADH and FADH2. The cycle does not involve proteins produced during glycolysis. Protons are not passed along a gradient to produce ATP directly in the Krebs cycle; rather, they are used in the electron transport chain to generate ATP. The Krebs cycle is not known as the glycolic acid cycle; glycolysis is the metabolic pathway that produces pyruvate from glucose.

Correct Answer: A

Rationale: The mixture of gases surrounding a planet is referred to as its atmosphere. The atmosphere plays a crucial role in supporting life on Earth by providing oxygen, regulating carbon dioxide levels, and shielding the planet from harmful radiation. While the stratosphere, troposphere, and other layers are part of the atmosphere, the term 'atmosphere' encompasses the entire gaseous envelope surrounding a planet. The stratosphere, troposphere, mesosphere, thermosphere, and exosphere are specific layers within the atmosphere, each with distinct characteristics and functions.

Correct Answer: B

Rationale: 1 liter has 1000 milliliters. To convert from milliliters to liters, the decimal point moves three places to the left. So, the bottle has 12000 mL of solution, which is a lot more than the required 12 mL. Therefore, the scientist has more than what they need. Choice A is incorrect as the bottle has more than the required amount. Choice C is incorrect as the bottle contains significantly more solution than needed. Choice D is incorrect as the scientist does have more than enough solution.