1. Myelin sheath is a fatty substance that insulates and protects the long extensions of some nerve cells. It is produced by:

A. Schwann cells
B. Astrocytes
C. Neurons
D. Oligodendrocytes

Correct answer: A

Rationale: The correct answer is A: Schwann cells. Schwann cells are a type of glial cell in the peripheral nervous system that produce the myelin sheath around axons. Myelin sheath is essential for the rapid conduction of nerve impulses and provides insulation and protection to nerve fibers. Astrocytes are glial cells that provide support and maintain homeostasis in the central nervous system, but they do not produce myelin. Neurons are the main functional units of the nervous system responsible for transmitting nerve impulses. Oligodendrocytes are another type of glial cell in the central nervous system that produce myelin sheath around axons in that region, not in the peripheral nervous system where Schwann cells are responsible for myelination.

2. Identify the reflexive pronoun in the sentence: "She prepared herself for the presentation."

A. herself
B. she
C. presentation
D. for

Correct answer: A

Rationale: "Herself" refers back to the subject "she," making it a reflexive pronoun.

3. What is the Doppler effect, and how does it explain the shift in frequency of sound waves perceived by an observer?

A. It only affects light waves, not sound waves.
B. It's the change in wave speed due to medium density.
C. It's the perceived change in frequency due to relative motion.
D. It's the bending of waves due to different mediums.

Correct answer: C

Rationale: The Doppler effect describes how the perceived frequency of a wave changes depending on the relative motion between the source and observer. For example, an approaching siren sounds higher pitched due to compressed wavefronts, while a receding siren sounds lower due to stretched wavefronts.

4. Delta waves, associated with deep sleep, exhibit what frequency range?

A. 0.5-4 Hz
B. 4-8 Hz
C. 8-13 Hz
D. 13-30 Hz

Correct answer: A

Rationale: Delta waves are slow brainwaves that are typically associated with deep sleep stages, such as stages 3 and 4 of non-REM sleep. These waves have a frequency range of 0.5-4 Hz, making option A the correct answer. During deep sleep, the brain slows down significantly, and delta waves are prominent on an electroencephalogram (EEG). The frequency range of 4-8 Hz corresponds to theta waves, which are more commonly observed during light sleep or drowsiness. Alpha waves fall within the 8-13 Hz range and are typically seen when an individual is awake but relaxed. Beta waves, ranging from 13-30 Hz, are associated with alertness and active thinking. Therefore, option A is the correct choice for delta waves, reflecting their slow frequency characteristic during deep sleep.

5. Which type of wave does not require a medium for propagation?

A. Transverse wave
B. Longitudinal wave
C. Mechanical wave
D. Electromagnetic wave

Correct answer: D

Rationale: Electromagnetic waves, like light and radio waves, can travel through a vacuum, unlike mechanical waves (sound, water waves) that require a medium to vibrate and transmit energy.