1. The microscopic units responsible for muscle contraction are called

A. Neurons
B. Myofibrils
C. Tendons
D. Sarcomeres

Correct answer: D

Rationale: The correct answer is D: Sarcomeres. Sarcomeres are the fundamental contractile units of skeletal muscle. They are composed of overlapping actin and myosin filaments that slide past each other during muscle contraction, resulting in muscle shortening. Neurons (A) are nerve cells that transmit signals to and from the brain. Myofibrils (B) are thread-like structures within muscle fibers that contain sarcomeres. Tendons (C) are fibrous connective tissues that attach muscles to bones, but they are not directly involved in muscle contraction like sarcomeres are.

2. Which of the following numbers is the greatest common factor (GCF) of 12 and 18?

A. 2
B. 3
C. 6
D. 9

Correct answer: C

Rationale: The GCF is the largest number that is a factor of both 12 and 18. We can factor each number to find common factors: 12 = 2 x 2 x 3 and 18 = 2 x 3 x 3. The greatest common factor that appears in both factorizations is 6 (2 x 3).

3. Which property of a substance refers to its ability to be hammered or pressed into thin sheets without breaking?

A. Malleability
B. Ductility
C. Viscosity
D. Conductivity

Correct answer: a

Rationale: Malleability is the property that describes a substance's ability to be hammered or pressed into thin sheets without breaking.

4. Which vitamin is essential for calcium absorption and bone health?

A. Vitamin A
B. Vitamin C
C. Vitamin D
D. Vitamin E

Correct answer: C

Rationale: The correct answer is Vitamin D. Vitamin D plays a crucial role in calcium absorption in the intestines, which is essential for maintaining strong and healthy bones. It helps regulate calcium and phosphorus levels in the body, promoting bone mineralization and growth. Vitamin A is important for vision and immune function, not specifically for bone health. Vitamin C is essential for collagen synthesis but not directly involved in calcium absorption. Vitamin E is an antioxidant that protects cells from damage but does not have a direct role in bone health. Therefore, Vitamin D is the correct choice for supporting calcium absorption and bone health.

5. The innate immune system provides:

A. Nonspecific, immediate defense against pathogens
B. Specific, long-term immune response through memory cells
C. Both (a) and (b)
D. Neither (a) nor (b)

Correct answer: A

Rationale: The correct answer is A: 'Nonspecific, immediate defense against pathogens.' The innate immune system is the body's first line of defense against pathogens and provides a rapid, nonspecific response. It includes physical barriers like the skin, chemical barriers like stomach acid, and cellular responses like inflammation. This system does not involve memory cells or provide long-term immunity, which are characteristics of the adaptive immune system. Therefore, option A accurately describes the function of the innate immune system as a quick and nonspecific defense mechanism.

6. A rocket blasts off from Earth. What is the main force propelling the rocket upwards?

A. Gravitational force
B. Air resistance
C. Thrust from the rocket engine
D. Normal force from the launchpad

Correct answer: C

Rationale: Thrust from the rocket engine. This force is produced by the action-reaction principle and pushes the rocket upwards against the exhaust gases.