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Why does dipping an apple slice in lemon juice prevent it from browning through an enzymatic reaction?

  • A. Lemon juice has a pH that inactivates the enzymes.
  • B. Lemon juice has enzymes that reverse the browning.
  • C. Lemon juice functions to dilute the brown material.
  • D. Lemon juice functions to bleach the brown material.
Correct Answer: A

Rationale: The correct answer is A: Lemon juice has a pH that inactivates the enzymes. Enzymatic browning in apples is caused by the enzyme polyphenol oxidase. When an apple is sliced, the enzyme comes into contact with oxygen in the air, leading to the browning process. Lemon juice contains citric acid, which lowers the pH of the apple's surface, creating an acidic environment that inactivates the polyphenol oxidase enzyme, thus preventing the browning reaction. This acidic environment denatures the enzyme, rendering it unable to catalyze the browning reaction. Therefore, by dipping the apple slice in lemon juice, the enzymatic activity that causes browning is effectively inhibited, maintaining the apple's color and freshness.

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In a plant in which fuzzy leaves (F) are dominant over smooth leaves (f), which of the following crosses will reproduce only offspring with smooth leaves?

  • A. FF by ff
  • B. ff by ff
  • C. Ff by Ff
  • D. FF by FF
Correct Answer: B

Rationale: The correct answer is B: 'ff by ff.' When a plant with fuzzy leaves (Ff) is crossed with another plant with smooth leaves (ff), all the offspring will inherit one smooth leaf allele from the smooth-leaved parent, resulting in only smooth leaves. The genotype of the offspring will be ff, leading to the expression of smooth leaves. This cross ensures that both alleles for leaf texture are the recessive smooth allele (f), resulting in all offspring having smooth leaves.

Which of the following molecules are found in substantial quantities in both the cell membrane and DNA?

  • A. Phosphate groups
  • B. Steroids
  • C. Lipids
  • D. Nitrogenous bases
Correct Answer: A

Rationale: Phosphate groups are essential components of the DNA backbone and are also present in phospholipids, which are fundamental structural components of cell membranes. They play vital roles in maintaining the integrity and function of both DNA and cell membranes by contributing to the structure and stability of these crucial cellular components. Steroids are not typically found in substantial quantities in DNA or cell membranes. While lipids are present in cell membranes, they are not specific to DNA. Nitrogenous bases, on the other hand, are specific components of DNA but are not major components of the cell membrane.

Which of the following statements best describes the function of a buffer?

  • A. It permanently binds hydrogen ions.
  • B. It causes the pH of a solution to become neutral.
  • C. It decreases the pH of the solution.
  • D. It enables resistance to a change in pH.
Correct Answer: D

Rationale: The correct answer is D: 'It enables resistance to a change in pH.' Buffers function by resisting changes in pH when small amounts of acid or base are added to a solution, thereby maintaining a stable pH. Option A is incorrect because buffers do not permanently bind hydrogen ions; they can release or absorb them as needed to maintain pH. Option B is incorrect because buffers do not necessarily cause a solution's pH to become neutral; they stabilize the pH at a specific value. Option C is incorrect; buffers can increase or decrease pH depending on the conditions to maintain stability. Therefore, the best description of a buffer's function is its ability to resist changes in pH.

What is the function of the myelin sheath for a nerve cell?

  • A. Sensory perception
  • B. Insulation
  • C. Nutrition
  • D. Regeneration
Correct Answer: B

Rationale: The myelin sheath functions as an insulator for nerve cells, enabling the rapid transmission of electrical impulses along the nerve fiber. This insulation is essential for maintaining the speed and efficiency of nerve signal conduction. Sensory perception involves detecting sensory stimuli, nutrition involves the supply of nutrients, and regeneration is the process of regrowth or repair, which are distinct functions from what the myelin sheath provides.

Which of the following triangular areas of the human body is described as the perineum?

  • A. The area between the nipples on the chest and the belly button.
  • B. The area on the back between the neck and the two shoulder blades.
  • C. The area that contains the orifices of the urinary, digestive, and reproductive systems.
  • D. The area between the edges of the eyes and the chin.
Correct Answer: C

Rationale: The perineum is the specific triangular region in the pelvic area that houses the openings of the urinary, digestive, and reproductive systems. It is essential for supporting these vital bodily functions. The other options describe different anatomical areas that are not related to the perineum. Understanding the location and function of the perineum is crucial for healthcare professionals to provide accurate assessments and care to patients.

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