1. Which of the following structures is responsible for preventing the backflow of blood from the left ventricle into the left atrium?

A. Aortic valve
B. Pulmonary valve
C. Tricuspid valve
D. Mitral valve

Correct answer: D

Rationale: The correct answer is D, the mitral valve. The mitral valve, also known as the bicuspid valve, is located between the left atrium and the left ventricle. Its main function is to prevent the backflow of blood from the left ventricle into the left atrium during ventricular contraction. The aortic valve (A) is responsible for preventing the backflow of blood from the aorta into the left ventricle, the pulmonary valve (B) prevents backflow from the pulmonary artery into the right ventricle, and the tricuspid valve (C) prevents backflow from the right ventricle into the right atrium. Therefore, the mitral valve is specifically responsible for preventing backflow in the left side of the heart, making it the correct answer in this case.

2. Which sentence uses parentheses correctly?

A. The suspect was seen driving a red car (a witness reported).
B. The movie (released in 2022) received critical acclaim.
C. The restaurant offers a variety of dishes (including vegetarian options).
D. All participants (must register by Friday) will receive a free gift.

Correct answer: B

Rationale: Parentheses are used for non-essential information that clarifies or adds detail. Option (a) is unnecessary and disrupts the flow of the sentence.

3. Which digestive enzyme is primarily responsible for breaking down proteins?

A. Pepsin
B. Lipase
C. Amylase
D. Maltase

Correct answer: A

Rationale: The correct answer is A: Pepsin. Pepsin is primarily responsible for breaking down proteins in the stomach. It is an enzyme produced by the gastric chief cells in the stomach lining and works in a highly acidic environment to break down proteins into smaller peptide fragments. Lipase, on the other hand, is responsible for breaking down fats, amylase for breaking down carbohydrates, and maltase for breaking down maltose (a type of sugar). Therefore, pepsin is the correct enzyme involved in the digestion of proteins.

4. What is the general formula for an alcohol?

A. CnH2n
B. CnH2n+2
C. CnH2n-1
D. CnH2nO

Correct answer: D

Rationale: The general formula for an alcohol is $C_nH_{2n}O$, indicating the presence of a hydroxyl group (-OH).

5. Which cartilage type allows for smooth movement at joints and absorbs shock?

A. Hyaline cartilage
B. Fibrocartilage
C. Elastic cartilage
D. None of the above

Correct answer: A

Rationale: The correct answer is A: Hyaline cartilage. Hyaline cartilage is the most abundant type of cartilage in the body and is found in the joints, providing a smooth surface for movement. It also acts as a shock absorber, cushioning the joints during activities. Fibrocartilage is found in intervertebral discs and provides strength and support, but it is not as effective at absorbing shock as hyaline cartilage. Elastic cartilage is found in the external ear and epiglottis, providing flexibility and maintaining shape, but it does not have the same shock-absorbing properties as hyaline cartilage. Therefore, hyaline cartilage is the best choice for a cartilage type that allows for smooth movement at joints and absorbs shock.

6. What is the term for the distance between the center of a lens or curved mirror and its focal point?

A. Aperture
B. Focal length
C. Refractive index
D. Lens thickness

Correct answer:

Rationale: The focal length of a lens or curved mirror is the distance between its center and the focal point, where parallel light rays converge or appear to diverge from.