Although more than three-quarters of the atmosphere is nitrogen, atmospheric nitrogen cannot be used directly by plants and animals. Instead, certain bacteria and blue-green algae take nitrogen from the air and, through a process called nitrogen fixation, turn it into compounds that plants can use. Nitrogen-fixing bacteria are found in the roots of some plants such as peas and beans. When these plants are present, the nitrate content of the soil is increased. Nitrates are absorbed by plants, which are eaten by consumers. Eventually the nitrogen returns to the soil in excrement and when organisms die. What is the role of nitrogen-fixing bacteria in the nitrogen cycle?

A student is examining a cell using a microscope. She is able to identify the cell membrane, cytoplasm, a small vacuole, and the nucleus, but she does not see a cell wall or any chloroplasts. She concludes that the cell is a eukaryotic cell.

Which of the following is evidence that her conclusion is correct?

In addition to the cell wall, the water stored in a plant cell’s vacuole helps give the plant firmness and shape. When a plant is not taking in enough water from the soil through its roots, it uses up its stored water and its vacuoles shrink. When the vacuoles shrink, the plant wilts.

Which of the following is a conclusion based on the paragraph above rather than a given fact?

Some animals have been genetically engineered to grow larger. Plants have been engineered to resist diseases or insects. Some fruits have been engineered to ripen more slowly. Genetic engineering of domesticated plants and animals is controversial. According to some people, these foods pose a risk because their effects on consumers and the environment are unknown. Others claim that genetically engineered foods are safe.

Which of the following statements is an opinion about genetic engineering rather than a fact?

The more similar the DNA of two species, the more closely related they are. Scientists have used modern DNA analysis to trace the evolutionary relationships among Darwin’s 13 species of finches. DNA analysis revealed that the finch species all had very similar DNA. Thus, Darwin was correct when he proposed that they had evolved from a common ancestor.

Which of the following best explains why DNA analysis provides better evidence to support the hypothesis that Darwin’s finches evolved from a common ancestor than the scientific methods that Darwin used?

How are the alveoli in the lungs and the villi in the small intestine similar?

Which human body system interacts with each cell of the body?

In the 17th century, English physician William Harvey concluded that blood in the veins flows toward the heart. Which of the following facts helps support Harvey’s conclusion?

What does the theory of plate tectonics explain?

Which of the following provides evidence that the present-day continents were once one large continent that broke apart?

Which of the following is implied by the fact that seafloor spreading at the Mid-Atlantic Ridge is causing the Atlantic Ocean to widen by about 5 centimeters a year?

Which of the following proverbs best expresses the views of a conservationist?

The overall demand for water in developed nations is rising. But it is not rising as quickly as people had predicted it would. In fact, the rate of water consumption per person per year in developed nations has actually dropped. This means that even though the population has increased and industrial output has grown, the rate at which people withdraw water from reservoirs, rivers, and aquifers has slowed. Which of the following is a likely reason for the drop in per person consumption of water in developed countries?

Soil erosion occurs when soil is worn away by the natural action of wind, water, and ice or by deforestation and poor farming practices. If soil erosion continues for a long time, it can lead to the formation of deserts. Some scientists estimate that the world lost about 20 per cent of its farm topsoil between 1950 and 1990. Contour plowing, planting trees to serve as windbreaks, and other techniques can all reduce soil erosion. Which of the following statements is supported by the information above?

Which of the following help even out the unbalanced heating of Earth as a whole?

Hurricanes are violent storms with high winds and rain that form over the ocean. They cover an area 300 to 600 miles across and move relatively slowly—between 5 and 15 miles per hour. Meteorologists can now predict their paths with a great deal of accuracy. Which of the following technologies best accounts for accurate hurricane tracking?

The daily cycle of night and day is caused by

A year is the length of time it takes for a planet to complete one entire orbit around the sun. If each of the planets revolved around the sun at exactly the same speed, which of the planets would have the longest year?

The tilt of Earth’s rotational axis toward or away from the sun causes:

The Big Bang theory provides the leading model for the formation of the

The death of a supergiant star can result in a

Which of the following temperature scales does NOT have negative numbers?

A solid, liquid, and gas can exist at the same time at the:

Consider the following information:
Bob pushes against a rock of mass 50 kg for 20 minutes exerting an average force of 100 N but the rock never budges. He really wants to move the rock so he asks his wife Barbara to come out and help. She pushes on the rock with another 100 N and eventually the rock starts to move. As the couple keeps pushing, it becomes easier and easier to move.
At the end of the driveway is a ledge and the couple push the rock off the ledge. The rock falls for 3 seconds and eventually crashes into the riverbed below.

According to a physicist, work is defined as the force applied to an object multiplied by the distance the object moves during the time the force is applied. Using this definition, how much work did Bob do before Barbara helped him?

When propane interacts with oxygen, a chemical reaction occurs, creating carbon dioxide and water. The balanced chemical equation for this reaction is shown below.
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

Based on the information above, which of the following is true?

According to the diagram, the function of the _______ is to supply energy to the cell.

Chromosomes come in pairs and contain genes, which code for inherited traits. If a gene is always expressed when present, it is called dominant and is represented by a capital letter. A dominant gene will be expressed whether an individual is pure and has two copies of the dominant gene or is hybrid and contains one dominant copy and one copy of another gene. In the case of hybrids, the dominant gene hides the expression of the recessive gene. A recessive gene is expressed only when it is pure, and it is represented by a lowercase letter.
In pea plants, the gene for round pea shape is dominant and the gene for wrinkled pea shape is recessive. A plant that produces wrinkled peas must be pure for the wrinkled gene, meaning it must contain two copies of the wrinkled gene. A plant that produces round peas can either be pure for the round gene or be hybrid and have one gene for round shape and one gene for wrinkled shape.
Punnett Squares are charts used to predict the odds of specific gene combinations in offspring. Below is a Punnett Square of a cross between a pea plant purebred for wrinkled peas and a pea plant that produces round peas.

Which of the following describes the offspring of this cross?

Based on the information in the chart above, which of the following animals are vertebrates?

Consider the following passage:
Energy exists in many forms around us. The development of modern civilization has been accomplished because scientists and engineers had learned the mechanism of converting one form of energy into another to do useful work. The transformation of energy from coal into steam and then into mechanical energy in engines that do heavy work enabled the Industrial Revolution. There are different forms of energy around us, such as mechanical energy (potential energy and kinetic energy), chemical energy, electrical energy, radiant energy, nuclear energy, and thermal energy. All of these forms of energy are related and can be transformed or changed into the other forms to do useful work.
Hydroelectric dams make use of the differences in water levels to generate electricity. Which of the following shows the energy conversion in a dam?

Consider the following passage:
Energy exists in many forms around us. The development of modern civilization has been accomplished because scientists and engineers had learned the mechanism of converting one form of energy into another to do useful work. The transformation of energy from coal into steam and then into mechanical energy in engines that do heavy work enabled the Industrial Revolution. There are different forms of energy around us, such as mechanical energy (potential energy and kinetic energy), chemical energy, electrical energy, radiant energy, nuclear energy, and thermal energy. All of these forms of energy are related and can be transformed or changed into the other forms to do useful work.
Which of the following shows the energy conversions that are required to illuminate a battery-operated table lamp?

Consider the following passage:

Kinetic energy is the energy of motion. An object that has motion has kinetic energy. The amount of kinetic energy that an object in motion possesses depends on its mass (m) and speed (v). The following equation represents the kinetic energy (K_E ) of an object:

Kinetic energy (K_E) = ½mv²

where m = mass in kg of object; v = speed of object.

Kinetic energy is a scalar quantity; it does not have a direction. The kinetic energy of an object is completely described by its magnitude alone. The unit of measurement for kinetic energy is the joule.

What is the kinetic energy, in joules, of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s?

Consider the following passage:

Kinetic energy is the energy of motion. An object that has motion has kinetic energy. The amount of kinetic energy that an object in motion possesses depends on its mass (m) and speed (v). The following equation represents the kinetic energy (K_E ) of an object:

Kinetic energy (K_E) = ½mv²

where m = mass in kg of object; v = speed of object.

Kinetic energy is a scalar quantity; it does not have a direction. The kinetic energy of an object is completely described by its magnitude alone. The unit of measurement for kinetic energy is the joule.

Which form of energy does a flowing river possess?

Consider the following passage:

Kinetic energy is the energy of motion. An object that has motion has kinetic energy. The amount of kinetic energy that an object in motion possesses depends on its mass (m) and speed (v). The following equation represents the kinetic energy (K_E ) of an object:

Kinetic energy (K_E) = ½mv²

where m = mass in kg of object; v = speed of object.

Kinetic energy is a scalar quantity; it does not have a direction. The kinetic energy of an object is completely described by its magnitude alone. The unit of measurement for kinetic energy is the joule.

If the speed of an object is doubled, then its kinetic energy is

Heat is the transfer of thermal energy from one substance to another or within a substance. Thermal energy includes both potential and kinetic energy of the particles that make up the substance. A warmer substance becomes cooler and a cooler substance becomes warmer when heat flows from one to the other. This flow of heat is always from the substance with a higher temperature to the substance with a lower temperature.
Which of the following statements is correct?

Temperature is a measure of the average kinetic energy of the particles that make up a substance. Because it is not possible to measure the kinetic energy of individual particles of a substance and take the average, a thermometer is used to measure temperature. The following diagram shows the comparison between the various scales commonly used to measure temperature.
Scientists worldwide use the Celsius scale. It is based on the properties of water, and the unit for it is degrees Celsius, written as °. On the Celsius scale, water freezes at 0° and boils at 100°. Kelvin is the SI unit of temperature, written as K. Absolute zero, 0 K, which is equivalent to −273°, is the lowest temperature possible for any substance. The Fahrenheit scale is commonly used in the United States for weather reports and to measure temperatures indoors. The unit is degrees Fahrenheit, written as °F. To convert between Fahrenheit and Celsius scales, any temperature y°F is converted to the temperature x° with the following equation:

\(y^oF = \frac{9}{5} x^oC + 32\)

At what temperature on the Fahrenheit scale does water boil?

Employees at GetWell research labs are analyzing mechanical waves, which require a medium to pass through, and electromagnetic waves, which travel through space. Jose Gonzalez IV is studying electromagnetic waves and their potential, real-world health and medical applications. He records the lengths of the various waves, noting that radio waves are the longest, while Gamma rays are the shortest. When calculating the frequency of the wave, or the number of wavelengths that occur in a distinct amount of time, Jose notes that there is an inverse relationship between the frequency of a wave and its period, which is the time it takes for a single wave to occur.

Wave type	Wave length size	Application
Radio Waves	Grater than 30cm	Aircraft Naviagtion, TV, AM/FM Radio
Infrared Waves	30cm - 1mm	Microwave Ovens, Mobile Phones
Visible Light	1mm - 700nm	Remote Controls, Toasters, Night Vision
X-Rays	700nm - 400nm	Physical Therapy, Light Bulbs, Photography
Ultraviolet Light	400nm - 60 nm	Sanitation, Air Purification, Forgery Detection
X-Rays	60nm - \(1 \times 10^{4}\)nm	Medical Examination, Cancer Treatment
Gamma Rays	0.1 nm - \(1 \times 10^{5}\) nm	Cancer Treatment, Food Irradiation

Based on the information provided, which types of waves have potential medical applications? Choose all that apply.

Consider the following information:

Waves are disturbances that propagate energy through a medium. Propagation of the energy depends on interactions between the particles that make up the medium. Particles move as the waves travel, but there is no net motion of particles. Thus, mechanical waves require matter through which to propagate. These waves are of the following types:

• Longitudinal waves: Movement of the particles is parallel to the direction the wave travels; that is, the direction of displacement is the same as the direction of propagation. Sound waves are longitudinal waves.

• Transverse waves: Movement of the particles is perpendicular to the direction the wave travels; that is, the direction of displacement is perpendicular to the direction of propagation. Movement of a wave through a stretched rope or a trampoline is an example of this type of wave.

Wavelength (λ) is the distance between identical points in the adjacent waves such as from crest to crest or trough to trough. It is measured in meters.

Frequency (f) describes the number of waves that passes a fixed place in a given amount of time. It is measured in hertz or cycles/s.

A period (T) is the time needed for one complete cycle of vibration to pass through a given point. Frequency (f) and period (T) have a reciprocal relationship that can be expressed mathematically as:

T = total time / number of cycles

→ T = 1 / frequency = 1 / f

The wave equation states the mathematical relationship between the speed (v) of a wave and its wavelength (λ) and frequency (f):

Speed = wavelength x frequency

→ v = λ x f

Or:

V = f / T since λ = 1 / f

The amplitude (A) of a wave refers to the maximum amount of displacement of a particle of the medium from its rest position

A swing completes a back-and-forth cycle every 2 seconds. What is the frequency of the swing?

The diagram of global wind patterns suggests that weather systems between 30°N and 60°N generally move in which direction?

Based on the diagram, how do the prevailing winds in the Northern Hemisphere compare to the prevailing winds in the Southern Hemisphere?