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Have you ever wondered why the whistle of a traveling, distant locomotive predicts its approach several yards before anyone actually sees it? Or why an oncoming ambulance's screaming siren is heard momentarily several feet before the ambulance comes into full view, before it passes you, and why its siren is still heard faintly well after the ambulance is out of sight?What you are witnessing is a scientific phenomenon known as the Doppler Effect. What takes place is truly remarkable. In both of these instances, when the train or ambulance moves toward the sound waves in front of it, the sound waves are pulled closer together and have a higher frequency. In either instance, the listener positioned in front of the moving object hears a higher pitch. The ambulance and locomotive are progressively moving away from the sound waves behind them, causing the waves to be farther apart and to have a lower frequency. These fast-approaching modes of transportation distance themselves past the listener, who hears a lower pitch.
Which sound waves have a lower pitch?
- A. Those waves that are closer together
- B. Those waves that are farther apart
- C. Those waves that travel a long distance
- D. Those waves that travel a short distance
Correct Answer: B
Rationale: Sound waves that are farther apart have a lower pitch. The Doppler Effect explains that as objects emitting sound move away, the sound waves become more spaced out, resulting in a lower frequency and a lower pitch. Choice A is incorrect because waves that are closer together have a higher frequency and a higher pitch. Choices C and D are not directly related to determining the pitch of sound waves.
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Lub-dub! Lub-dub! Lub-dub! This sound is made by the rapid contracting and extending of the chamber doors on the inside of theheart. This ventricular contracting injects roughly 70 mL of blood into a vascular system with a given volume at differing pressure.Blood pressure refers to the pressure in the arterial system; and it is typically taken in the brachial artery of the arm because the pressure at different places along the circulatory route is different. Blood pressure is simply the force that the blood exerts in all directions within any given area and is the basis for the movement of blood from the heart, through the body, and back to the heart. This pressure is commonly expressed as a ratio of the systolic pressure over the diastolic pressure.The systolic pressure or “high peak†pressure takes place within the arterial system as ventricles contract and force blood into the arteries. The diastolic pressure or “low peak†pressure takes place within this arterial system just before the next ventricular contraction.An increase in blood pressure can occur if the arterial walls lose some of their elasticity with age or disease.
What is the meaning of the word 'elasticity' in the last paragraph?
- A. Something that is able to resist and be flexible
- B. Something that is like plastic
- C. Something that is dynamic and electrifying
- D. Something that is silly
Correct Answer: A
Rationale: 'Elasticity' refers to the ability of the arterial walls to resist and be flexible, which affects blood pressure. In the provided extract, it is mentioned that an increase in blood pressure can occur if the arterial walls lose some of their elasticity with age or disease. This demonstrates that elasticity refers to the property of being able to resist and be flexible, supporting choice A as the correct answer. The other choices, B, C, and D, do not accurately reflect the concept of elasticity in the context of arterial walls and blood pressure.
Water is needed to sustain practically all life functions on planet Earth. A single drop of this compound is composed of an oxygen atom that shares its electrons with each of the two hydrogen atoms. The cycle starts when precipitation, such as rain, snow, sleet, or hail, descends from the sky onto the ground. Water that is not absorbed immediately from the precipitation is known as runoff. The runoff flows across the land and collects in groundwater reservoirs, rivers, streams, and oceans.Evaporation takes place when liquid water changes into water vapor, which is a gas. Water vapor returns to the air from surface water and plants.Ultimately, condensation happens when this water vapor cools and changes back into droplets of liquid. In fact, the puffy, cotton clouds that we observe are formed by condensation. When the clouds become heavily laden with liquid droplets, precipitation ensues.
What was the author's primary purpose for writing this essay?
- A. To persuade the reader to conserve water
- B. To persuade the reader that runoff is not the best way to collect water
- C. To analyze different types of runoff
- D. To inform the reader about the stages of the water cycle
Correct Answer: D
Rationale: The correct answer is D. The author's primary purpose for writing the essay is to inform the reader about the stages of the water cycle. The essay discusses the various stages of the water cycle, including precipitation, runoff, evaporation, and condensation. Choices A, B, and C are incorrect because the essay focuses on explaining the water cycle stages rather than persuading the reader to conserve water, discussing the effectiveness of runoff, or analyzing different types of runoff.
The immune system is a network of cells, tissues, and organs that defends the body against attacks by foreign invaders. These invaders are primarily microbes—tiny organisms such as bacteria, parasites, and fungi—that can cause infections. Viruses also cause infections, but are too primitive to be classified as living organisms. The human body provides an ideal environment for many microbes. It is the immune system's job to keep the microbes out or destroy them.The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can secrete fluids and cells to wipe out nearly all of them. The secret to its success is an elaborate and dynamic communications network. Millions of cells, organized into sets and subsets, gather and transfer information in response to an infection. Once immune cells receive the alarm, they produce powerful chemicals that help to regulate their own growth and behavior, enlist other immune cells, and direct the new recruits to trouble spots.Although scientists have learned much about the immune system, they continue to puzzle over how the body destroys invading microbes, infected cells, and tumors without harming healthy tissues. New technologies for identifying individual immune cells are now allowing scientists to determine quickly which targets are triggering an immune response. Improvements in microscopy are permitting the first-ever observations of living B cells, T cells, and other cells as they interact within lymph nodes and other body tissues.In addition, scientists are rapidly unraveling the genetic blueprints that direct the human immune response, as well as those that dictate the biology of bacteria, viruses, and parasites. The combination of new technology with expanded genetic information will no doubt reveal even more about how the body protects itself from disease.
What is the meaning of the word 'enlist' as it is used in the second paragraph?
- A. call into service
- B. write down
- C. send away
- D. put across
Correct Answer: A
Rationale: In the context of the immune system, 'enlist' means to call into service. Immune cells recruit other cells to fight infection by producing chemicals that regulate their growth, behavior, and direct new recruits to trouble spots. This process is essential for the immune system's defense mechanism. The other choices are incorrect: 'write down' and 'put across' do not capture the action of mobilizing immune cells, and 'send away' is opposite in meaning to what is happening in the immune response.
Beep!…Beep!…Beep! is the audible rhythmic sound made as the strength of the heart muscle is measured. The signal cadence has a characteristic record that varies in every individual. This record is called an electrocardiogram, or ECG.In the body, an array of systemic neural responses constantly occur, emitting electric currents. The electric currents can be detected on the surface of the body, and if a person is hooked to an amplifier, these impulses are recorded by an electrocardiograph. Most of the information obtained is about the heart because the heart sends out electric currents in waves. This “wave of excitation†spreads through the heart wall and is accompanied by electric changes. The wave takes place in three distinct steps.Initially, the “wave of excitation†accompanied by an electric change lasts for approximately 1 to 2 seconds after the contraction of the cardiac muscle. The electric impulses are discharged rhythmically from the sinoatrial (SA) node, the pacemaker of the heart. This spread of excitation over the muscle of the atrium indicates that the atrium has contracted.Next, the peak of the ECG reading is due to the atrioventricular (AV) node, causing the ventricle to become excited.<p>Finally, the ventricles relax, and any changes in the wave indicate to trained medical staff any abnormalities within the heart.
What are the three steps of the 'wave of excitation'?
- A. The discharge from the SA node, the peak ECG, and the excitement of the ventricle.
- B. The excitement of the ventricle, the relaxing of the ventricle, and the systemic neural response.
- C. The contraction of the atrium, the relaxation of the atrium, and the contraction of the ventricle.
- D. The excitation of the atrium, the excitement of the ventricle, and the relaxing of the ventricle.
Correct Answer: D
Rationale: The correct steps of the 'wave of excitation' are the excitation of the atrium, excitement of the ventricle, and relaxation of the ventricle. In the described process, the 'wave of excitation' starts with the discharge from the SA node, leading to the excitation of the atrium. Next, the peak ECG corresponds to the excitement of the ventricle, not its relaxation. Finally, the wave concludes with the relaxation of the ventricle, not its contraction. Therefore, choices A, B, and C are incorrect as they do not accurately describe the sequential steps of the 'wave of excitation' as presented in the extract.
Have you ever wondered why the whistle of a traveling, distant locomotive predicts its approach several yards before anyone actually sees it? Or why an oncoming ambulance's screaming siren is heard momentarily several feet before the ambulance comes into full view, before it passes you, and why its siren is still heard faintly well after the ambulance is out of sight?What you are witnessing is a scientific phenomenon known as the Doppler Effect. What takes place is truly remarkable. In both of these instances, when the train or ambulance moves toward the sound waves in front of it, the sound waves are pulled closer together and have a higher frequency. In either instance, the listener positioned in front of the moving object hears a higher pitch. The ambulance and locomotive are progressively moving away from the sound waves behind them, causing the waves to be farther apart and to have a lower frequency. These fast-approaching modes of transportation distance themselves past the listener, who hears a lower pitch.
Which sound waves have a higher pitch?
- A. Those waves that are closer together
- B. Those waves that are farther apart
- C. Those waves that travel a long distance
- D. Those waves that travel a short distance
Correct Answer: A
Rationale: Sound waves that are closer together have a higher pitch. This is explained by the Doppler Effect, where as a source of sound moves closer to an observer, the waves are compressed, resulting in a higher frequency and a higher pitch. Conversely, when the source moves away, the waves are stretched, leading to a lower frequency and a lower pitch. Therefore, choice A is correct. Choices B, C, and D are incorrect as they do not accurately describe the relationship between sound wave frequency and pitch.