Correct Answer: A

Rationale: The correct answer is pinocytosis. Pinocytosis is a process where cells in the small intestine absorb nutrients by engulfing them. This process is different from phagocytosis, which involves engulfing large particles, and excretion, which is the removal of waste products. Electrochemical diffusion is not directly involved in the absorption of food in the small intestine.

Correct Answer: A

Rationale: Ketones are produced when the body uses fat for energy due to the depletion of carbohydrate stores. When carbohydrate stores are depleted, the body turns to fat as its primary source of energy, leading to the production of ketones. Excess protein consumption does not directly lead to ketone production. Similarly, the depletion of protein stores or fat stores is not directly related to the production of ketones.

Correct Answer: C

Rationale: The correct answer is C: water. Water is the main component of blood plasma, interstitial fluid, and intracellular fluid. It plays a crucial role in various bodily functions, including transporting nutrients, regulating body temperature, and maintaining cell structure. Choices A, B, and D are incorrect because while potassium, sodium, and calcium are essential electrolytes found in the body, they are not the main constituents of these fluids as water is.

Correct Answer: A

Rationale: The correct answer is the amino group. Amino groups are functional groups found in amino acids, which are the building blocks of proteins. These groups contain nitrogen and are essential for the structure and function of proteins. The carboxyl group (choice B) contains carbon, oxygen, and hydrogen, while the peptide bond (choice C) is a covalent bond formed between amino acids in a protein chain. The side chain (choice D) refers to the unique chemical structure attached to the central carbon of an amino acid and varies among different amino acids, but it does not specifically contain nitrogen.

Correct Answer: A

Rationale: The correct answer is A: Smelling or seeing food. When an individual smells or sees food, it can trigger the body to start producing digestive secretions in anticipation of food consumption. This physiological response helps prepare the digestive system for the incoming meal. Choices B, C, and D are incorrect because grocery shopping, fasting, and exercise do not directly stimulate digestive secretions in the same way that the sight or smell of food does.