An agronomist is investigating the effect that different types of soil have on the growth and yield of maize. Sweet corn (Zea mays) is planted in loamy soil of varying proportions of sand, silt, and clay. Growth is measured in inches after 15 days, again after 50 days and finally at 100 days. Dry mass of the yield is measured in grams at the same day intervals.

     Four experiments are conducted such that the average amount of sunlight per day is 15 hours at 75° F for the duration of each experiment. All plants where watered at exactly an inch of water per week. All plots where the sweet corn was grown were equally fertilized at about 25 pounds per 1,000 square feet.

     Weed growth and pest attack was mitigated by assiduous attentiveness and insecticide.

Experiment 1

     Sweet corn is planted in loamy soil of sand 33%, silt 33%, and clay 33% after soil was warmed to 50° F.

                                            Table 1

            Height (inches)                           Day                              Yield (g)

            7                                              15                                 0

            84                                             50                                 9

            94                                             100                               45

Experiment 2

     Sweet corn is planted in loamy soil of sand 40%, silt 40%, and clay 20% after soil was warmed to 50° F.

                                            Table 2

            Height (inches)                           Day                              Yield (g)

            8                                              15                                 0

            91                                             50                                 8

            101                                           100                               65

Experiment 3

     Sweet corn is planted in loamy soil of sand 40%, silt 20%, and clay 40% after soil was warmed to 50° F.

                                            Table 3

            Height (inches)                           Day                              Yield (g)

            7                                              15                                 0

            86                                             50                                 8

            96                                             100                               40

Experiment 4

     Sweet corn is planted in loamy soil of sand 20%, silt 40%, and clay 40% after soil was warmed to 50° F.

                                            Table 4

            Height (inches)                           Day                              Yield (g)

            9                                              15                                 0

            90                                             50                                 6

            98                                             100                               45

What conclusion can be made about the growth of sweet corn during the final 50 days?

Sleep plays a vital role in defining the daily activities of virtually all animals. During periods of sleep, the parasympathetic nervous system becomes active and induces a relaxed state in response to increased levels of the hormone melatonin. Despite its ubiquity in the animal kingdom, the purpose of sleep and its role in our daily lives has been disputed by scientists. Two scientists discuss their theories about the purpose of sleep.

Scientist 1

During periods of sleep, animals are able to conserve energy that they would otherwise be spending on unnecessary activity. If an animal’s primary food source is most abundant during daylight, it is a waste of precious energy to be moving about at night. For example, many herbivores, such as squirrels, are diurnal (asleep during the night) because their food source is available during the day, while many insectivores, such as bats, are nocturnal (asleep during the day) because their food source is available during the night. Food sources, as an animal’s most valuable resource, dictate their sleep cycles. Many animal traits observable today evolved as a result of the supply and demand of food in their natural habitat.

Scientist 2

During waking hours, it is true that the body utilizes large amounts of energy; however, the role of sleep is to restore biological products that were utilized during periods of wakefulness, rather than simply to avoid utilizing energy in the first place. Many types of biological molecules, such as hormones, are released throughout the body while an animal is active. Sleep serves as a period of inactivity during which the body can manufacture and store a supply of these molecules, for future use during the next period of activity; furthermore, sleep allows the body to repair cellular damage that has accumulated during waking hours. Experimental evidence shows that when animals are deprived of sleep, their immune system quickly weakens and death rates increase. Sleep is necessary for animals to prevent accumulation of damage and to regenerate crucial biomolecules for daily life.

Which of the following is likely true of melatonin?

Sleep plays a vital role in defining the daily activities of virtually all animals. During periods of sleep, the parasympathetic nervous system becomes active and induces a relaxed state in response to increased levels of the hormone melatonin. Despite its ubiquity in the animal kingdom, the purpose of sleep and its role in our daily lives has been disputed by scientists. Two scientists discuss their theories about the purpose of sleep.

Scientist 1

During periods of sleep, animals are able to conserve energy that they would otherwise be spending on unnecessary activity. If an animal’s primary food source is most abundant during daylight, it is a waste of precious energy to be moving about at night. For example, many herbivores, such as squirrels, are diurnal (asleep during the night) because their food source is available during the day, while many insectivores, such as bats, are nocturnal (asleep during the day) because their food source is available during the night. Food sources, as an animal’s most valuable resource, dictate their sleep cycles. Many animal traits observable today evolved as a result of the supply and demand of food in their natural habitat.

Scientist 2

During waking hours, it is true that the body utilizes large amounts of energy; however, the role of sleep is to restore biological products that were utilized during periods of wakefulness, rather than simply to avoid utilizing energy in the first place. Many types of biological molecules, such as hormones, are released throughout the body while an animal is active. Sleep serves as a period of inactivity during which the body can manufacture and store a supply of these molecules, for future use during the next period of activity; furthermore, sleep allows the body to repair cellular damage that has accumulated during waking hours. Experimental evidence shows that when animals are deprived of sleep, their immune system quickly weakens and death rates increase. Sleep is necessary for animals to prevent accumulation of damage and to regenerate crucial biomolecules for daily life.

Adenosine is a damaging by-product of the brain that is produced during waking hours. If Scientist 2’s theory is correct, which of the following is likely true?

Sleep plays a vital role in defining the daily activities of virtually all animals. During periods of sleep, the parasympathetic nervous system becomes active and induces a relaxed state in response to increased levels of the hormone melatonin. Despite its ubiquity in the animal kingdom, the purpose of sleep and its role in our daily lives has been disputed by scientists. Two scientists discuss their theories about the purpose of sleep.

Scientist 1

During periods of sleep, animals are able to conserve energy that they would otherwise be spending on unnecessary activity. If an animal’s primary food source is most abundant during daylight, it is a waste of precious energy to be moving about at night. For example, many herbivores, such as squirrels, are diurnal (asleep during the night) because their food source is available during the day, while many insectivores, such as bats, are nocturnal (asleep during the day) because their food source is available during the night. Food sources, as an animal’s most valuable resource, dictate their sleep cycles. Many animal traits observable today evolved as a result of the supply and demand of food in their natural habitat.

Scientist 2

During waking hours, it is true that the body utilizes large amounts of energy; however, the role of sleep is to restore biological products that were utilized during periods of wakefulness, rather than simply to avoid utilizing energy in the first place. Many types of biological molecules, such as hormones, are released throughout the body while an animal is active. Sleep serves as a period of inactivity during which the body can manufacture and store a supply of these molecules, for future use during the next period of activity; furthermore, sleep allows the body to repair cellular damage that has accumulated during waking hours. Experimental evidence shows that when animals are deprived of sleep, their immune system quickly weakens and death rates increase. Sleep is necessary for animals to prevent accumulation of damage and to regenerate crucial biomolecules for daily life.

Studies have shown that students who sleep well the night before an exam receive better marks. Why might this be, according to the hypotheses of both scientists?

A scientific experiment is conducted to test if calcium can affect gene regulation. Scientists hypothesize that high levels of calcium would interact with the proteins Cs3 and Gfy, which would increase the transcription of genes F4597 and BC392. The experiment procedure is summarized below.

1. Isolate the genes F4597 and BC392.
2. Create a vector within yeast cells containing the two genes
3. Culture yeast cells
4. Grow yeast cells in different growth mediums—one medium lacking calcium (plate A), and one medium with supplemented calcium (plate B)

According to the experiment, what data results would support the hypothesis? 

In the 1980’s, an epidemic of bovine spongiform encephalopathy, or mad cow disease, swept through cattle herds in the United Kingdom.   Scientists and veterinarians were troubled and had a difficult time managing the disease because it spread from one animal to another, and behaved differently than other diseases in the past. 

When infectious material from affected animals was treated with high levels of radiation, for example, the material remained infectious.  All known bacteria or viruses that carry disease would have been killed by such a treatment.  Additionally, some animals developed the disease without first being exposed to sick animals. Perhaps most frustratingly, among those animals that are exposed before becoming sick, it can take many years after exposure for illness to appear.

There quickly emerged two distinct explanations for the disease. 

Scientist 1:

Mad cow disease is unlike any disease we have handled before.  It is increasingly clear that the best explanation for the disease’s dynamics involve proteins, called the protein-only hypothesis.   These protein molecules are likely causative of the disease, and they lack any DNA or RNA.  It is damage to these DNA or RNA molecules that kills bacteria or viruses when exposed to high levels of radiation.  The most important observations that made scientists consider a unique, protein-only model for this disease involved its resistance to radiation.  Remarkably, this would be the first example of an infectious agent copying itself without DNA or RNA to mediate the process.

Moreover, some animals develop the disease spontaneously, without physically being infected by another animal. This suggests that internal disorder among protein molecules is a potential route to developing disease, and may be accelerated by exposure to other sick animals.

In fact, this is consistent with the proposed mechanism. It is likely that proteins fold incorrectly, and then influence proteins around them to take on this errant conformation.  Some proteins may fold incorrectly by chance, which explains spontaneous disease development.  It also explains the long course of disease, as it takes many years for enough proteins to fold incorrectly and result in observable disease.

Scientist 2:

The suggestion that mad cow disease is caused exclusively by protein, in the absence of DNA or RNA, is such a dramatic departure from accepted biological processes that it warrants careful scrutiny. Additionally, other more conventional explanations should be thoroughly investigated before coming to such a conclusion.

Some scientists have shown that very small particles resembling viruses are visible in infectious material under powerful microscopes.  Additionally, these viruses are consistent in size and shape with known, highly radiation-resistant viruses called polyomaviruses.  It takes much higher-than-typical doses of radiation to cause enough DNA damage to inactivate these viruses.

The observation that mad cow disease occurs spontaneously in some animals is also explained by the viral explanation. Many viruses exist in animals and humans for years, undetected and no causing any observable disease. Sickness or stress can make these viruses reactivate, offering the illusion of spontaneous illness.  All of these observations are consistent with the viral hypothesis.

Which of the following would be most consistent with both views presented in the passage?

Understanding the biological features of different bacteria that allow them to grow in unwelcoming environments is necessary to treat and prevent human disease. Modern scientific laboratories, such as those in major hospitals, take blood, urine, and mucus samples from patients and culture them for bacterial growth. During the culturing process, laboratory technicians stain the growing bacteria for a component of their cell wall, the structure that provides shape and rigidity to the bacterium, through a process called Gram staining. Bacteria are typically classified as Gram Positive or Gram Negative, a distinction that is important in selecting the most effective antibiotic for treatment. Gram Positive bacteria appear purple under a microscope, while Gram Negative bacteria appear red. However, some bacteria do not Gram Stain and cannot be seen under a microscope when prepared this way.

Technicians also grow the bacteria on various types of plates containing special growth nutrients to determine which bacteria are causing a specific illness. If a bacterium is able to grow on a selective plate, meaning a plate that contains additional nutrients required for a specific bacterium to grow if it is present in the culture, doctors are able to determine the exact cause of a patient’s illness and prescribe targeted antibiotics to eliminate the infection. Bacteria that commonly cause human illness, their growth requirements, and their appearance on specific growth media are presented below in Table 1.

                                                           Table 1 

Scientists can take the bacteria cultured on the plate and further analyze their enzymes. Three enzymes—urease, catalase, and beta-lactamase—are important for bacterial survival against the human immune system. Urease is responsible for producing urea, a basic molecule that can counteract the bactericidal (bacteria-killing) activity of stomach acid. Catalase, on the other hand, helps bacteria neutralize toxic substances released from human immune cells, allowing them to survive oxidative stress in high-oxygen areas. Finally, beta-lactamase allows Gram Positive bacteria to break down antibiotics called penicillins. While this ability to break down penicillin and its related antibiotic ampicillin was not initially present, bacteria, especially E. coli, have adapted by developing the new enzyme beta-lactamase that opens the ring responsible for penicillin’s bactericidal activity, rending the antibiotic ineffective. This and other examples of antibiotic resistance are becoming more common and are making treatment of serious human diseases very challenging.

A novice technician reverses the two materials needed to complete a Gram stain. Which of the following effects will this likely have on a patient’s treatment?

Population dynamics can be described as the intricate relationships and mechanics of a given ecological community. Ecology attempts to study the interactions between organisms and between organisms and their environments. Populations of organisms may be impacted by abiotic (nonliving) and biotic (living) factors within their environment. These factors may or may not depend on population densities. Density-independent factors such as weather patterns can affect a population of any size. Conversely, density-dependent factors such as predation have differing effects on populations based on the number of individuals present.

Utilizing this information, consider the following scenario.

An island contains several wolf and moose populations. Ecologists studied these populations through several generations and made observations on each population's size and relative fitness. In the initial years of the investigation, wolf populations declined due to a disease known as canine parvovirus. Due to decreased predatory pressures, the moose population rose to higher numbers than seen in previous years. Several years later, environmental temperatures rose dramatically in the area. Increased environmental temperatures resulted in reduced fitness and health within the island's moose population. Individuals were exposed to rising tick populations that caused blood loss and spread disease. Likewise, increased temperatures induced weight loss in the moose population; moose cannot perspire and must cool themselves by resting in the shade, and this detracts from their ability to forage and gain weight and insulation for the colder winter months. The weakened moose population became susceptible to increased predation by wolves, which resulted in an increase in the wolf population. (See Figures 1, 2, and 3.)

Which of the following choices describe the living factors present in a species' environment?

Population dynamics can be described as the intricate relationships and mechanics of a given ecological community. Ecology attempts to study the interactions between organisms and between organisms and their environments. Populations of organisms may be impacted by abiotic (nonliving) and biotic (living) factors within their environment. These factors may or may not depend on population densities. Density-independent factors such as weather patterns can affect a population of any size. Conversely, density-dependent factors such as predation have differing effects on populations based on the number of individuals present.

Utilizing this information, consider the following scenario.

An island contains several wolf and moose populations. Ecologists studied these populations through several generations and made observations on each population's size and relative fitness. In the initial years of the investigation, wolf populations declined due to a disease known as canine parvovirus. Due to decreased predatory pressures, the moose population rose to higher numbers than seen in previous years. Several years later, environmental temperatures rose dramatically in the area. Increased environmental temperatures resulted in reduced fitness and health within the island's moose population. Individuals were exposed to rising tick populations that caused blood loss and spread disease. Likewise, increased temperatures induced weight loss in the moose population; moose cannot perspire and must cool themselves by resting in the shade, and this detracts from their ability to forage and gain weight and insulation for the colder winter months. The weakened moose population became susceptible to increased predation by wolves, which resulted in an increase in the wolf population. (See Figures 1, 2, and 3.)

Which of the following choices can be defined as the complex inner workings of a given ecological community?

Population dynamics can be described as the intricate relationships and mechanics of a given ecological community. Ecology attempts to study the interactions between organisms and between organisms and their environments. Populations of organisms may be impacted by abiotic (nonliving) and biotic (living) factors within their environment. These factors may or may not depend on population densities. Density-independent factors such as weather patterns can affect a population of any size. Conversely, density-dependent factors such as predation have differing effects on populations based on the number of individuals present.

Utilizing this information, consider the following scenario.

An island contains several wolf and moose populations. Ecologists studied these populations through several generations and made observations on each population's size and relative fitness. In the initial years of the investigation, wolf populations declined due to a disease known as canine parvovirus. Due to decreased predatory pressures, the moose population rose to higher numbers than seen in previous years. Several years later, environmental temperatures rose dramatically in the area. Increased environmental temperatures resulted in reduced fitness and health within the island's moose population. Individuals were exposed to rising tick populations that caused blood loss and spread disease. Likewise, increased temperatures induced weight loss in the moose population; moose cannot perspire and must cool themselves by resting in the shade, and this detracts from their ability to forage and gain weight and insulation for the colder winter months. The weakened moose population became susceptible to increased predation by wolves, which resulted in an increase in the wolf population. (See Figures 1, 2, and 3.)

Was the factor that reduced the wolf population caused by a biotic or abiotic component of the environment?