1. A scientific theory is:

A. A personal belief or hunch about how something works.
B. A well-substantiated explanation based on evidence and repeated testing.
C. A single experiment's findings not yet confirmed by others.
D. A fixed and unchanging dogma beyond questioning.

Correct answer: B

Rationale: Theories in science are constantly evolving and open to revision as new data emerges, unlike personal beliefs or fixed dogmas.

2. What effect does doubling the net force applied to an object have on its acceleration, assuming mass remains constant?

A. Acceleration doubles
B. Acceleration is halved
C. Acceleration remains the same
D. Acceleration quadruples

Correct answer: a

Rationale: According to Newton's second law (F = ma), if mass remains constant and force doubles, acceleration also doubles.

3. Which element has the same number of protons and neutrons?

A. Carbon (C)
B. Oxygen (O)
C. Lithium (Li)
D. Helium (He)

Correct answer: D

Rationale: Helium (He) - He-4 has 2 protons and 2 neutrons, while the other options have differing numbers.

4. What is the name of the sheath of connective tissue that surrounds a skeletal muscle?

A. Epimysium
B. Perimysium
C. Endomysium
D. Myofibril

Correct answer: A

Rationale: The correct answer is A: Epimysium. The epimysium is the outermost layer of connective tissue that surrounds a skeletal muscle. It provides protection and support to the muscle fibers within, as well as helps in transmitting forces generated by the muscle. Perimysium (B) is the connective tissue that surrounds bundles of muscle fibers called fascicles, while endomysium (C) is the connective tissue that surrounds individual muscle fibers. Myofibril (D) is a structure within muscle fibers that contains the contractile units responsible for muscle contraction. Therefore, in this context, the sheath of connective tissue surrounding a skeletal muscle is specifically referred to as the epimysium.

5. The feedback loop is a crucial concept in endocrine regulation. In a negative feedback loop, high levels of a hormone can:

A. Further stimulate the release of the same hormone
B. Inhibit the release of the hormone or its production
C. Have no effect on the hormone's regulation
D. Increase the need for another hormone entirely

Correct answer: B

Rationale: In a negative feedback loop, high levels of a hormone signal the body to stop producing more of that hormone in order to maintain homeostasis. This is a self-regulating mechanism to prevent excessive levels of the hormone. Option B is correct because in this scenario, the high levels of the hormone will inhibit its further release or production. This feedback loop helps ensure that hormone levels stay within a narrow range, preventing overstimulation or imbalance in the endocrine system. Options A, C, and D are incorrect as they do not align with the concept of negative feedback regulation in endocrine systems.

6. Which state of matter has both definite volume and definite shape?

A. Solid
B. Liquid
C. Gas
D. Plasma

Correct answer: a

Rationale: Solids have both definite volume and definite shape. The particles in solids are closely packed, maintaining their positions, resulting in a fixed shape and volume.