Invasive species lack the natural competitors in a given area to properly regulate population growth and development. Myriophyllum spicatum is a Eurasian milfoil. It was first used in the United States as an aesthetic for aquatic fish tanks. Later, it was accidentally introduced into local ponds and lakes where it became a dominant invasive species and has began to choke out native and naturally occurring plant life. To make matters worse, phosphorus-rich fertilizers and cleaners have contaminated many freshwater biomes due to runoff and pollution. As a result, many standing freshwater pools contain heavy amounts of phosphorus. These species readily utilize the phosphorus and have become nearly unmanageable. Two ecologists express their views on how to control the invasive population.

Ecologist 1

     The best way to control the problem is to limit the nutrients in the biome. If the nutrients are controlled then the plants will be unable to grow and flourish. After several generations, the nutrients will be depleted and the plant species will become more manageable or disappear altogether.

Ecologist 2

     The best way to control the vegetation would be to physically cut and remove it from the biome. Seasonal cuttings would minimize the population and decrease reproductive success. Furthermore, any nutrients contained in the decomposing plant litter would be removed with the waste. Therefore, after several sweeps the plants would be removed altogether.

The ecologists decide to study the lake together. They choose to study three other local lakes with the same issues in order to get a representative sample. They notice a small stream running adjacent to the lakes. Should the researchers sample the stream as well?

     Invasive species lack the natural competitors in a given area to properly regulate population growth and development. Myriophyllum spicatum is a Eurasian milfoil. It was first used in the United States as an aesthetic for aquatic fish tanks. Later, it was accidentally introduced into local ponds and lakes where it became a dominant invasive species and has began to choke out native and naturally occurring plant life. To make matters worse, phosphorus-rich fertilizers and cleaners have contaminated many freshwater biomes due to runoff and pollution. As a result, many standing freshwater pools contain heavy amounts of phosphorus. These species readily utilize the phosphorus and have become nearly unmanageable. Two ecologists express their views on how to control the invasive population.

Ecologist 1

     The best way to control the problem is to limit the nutrients in the biome. If the nutrients are controlled then the plants will be unable to grow and flourish. After several generations, the nutrients will be depleted and the plant species will become more manageable or disappear altogether.

Ecologist 2

     The best way to control the vegetation would be to physically cut and remove it from the biome. Seasonal cuttings would minimize the population and decrease reproductive success. Furthermore, any nutrients contained in the decomposing plant litter would be removed with the waste. Therefore, after several sweeps the plants would be removed altogether.

A field researcher suggests using copper sulfate as a herbicide to introduce to the lake and kill off the invasive species completely. Which ecologist would agree with this idea?

     Osmoregulation is a necessary function to maintain homeostasis in organisms. Fish gills form the boundary between fish body fluid and environmental conditions. The regulation of water transport across barrier epithelial membranes in gills is assisted by membrane composition and affected by solute concentration on either side of the membrane. Fish body fluids are isotonic and have compositions of about 300 milliosmoles of solutes per liter. Freshwater environments are hypotonic and typically have compositions of about 1 milliosmole of solutes per liter. Saltwater environments are hypertonic and typically have a composition of about 1,000 milliosmoles of solutes per liter. Based on observed osmoregulation across varying concentration gradients, it is expected that gills exposed to isotonic solutions maintain steady water weight, while those exposed to hypotonic solutions increase in water weight, and those exposed to hypertonic solutions decreased in water weight.

Study 1

     Gills dissected from a fish were exposed to different ambient environments of salinity including an isotonic control solution (301.5 milliosmoles), a hypotonic solution (1.5 milliosmoles), and a hypertonic solution (601.5 milliosmoles). Percent water weight change between treatments was observed and calculated.

Which of the treatment groups could be considered as an analog for a saltwater environment?

     Osmoregulation is a necessary function to maintain homeostasis in organisms. Fish gills form the boundary between fish body fluid and environmental conditions. The regulation of water transport across barrier epithelial membranes in gills is assisted by membrane composition and affected by solute concentration on either side of the membrane. Fish body fluids are isotonic and have compositions of about 300 milliosmoles of solutes per liter. Freshwater environments are hypotonic and typically have compositions of about 1 milliosmole of solutes per liter. Saltwater environments are hypertonic and typically have a composition of about 1,000 milliosmoles of solutes per liter. Based on observed osmoregulation across varying concentration gradients, it is expected that gills exposed to isotonic solutions maintain steady water weight, while those exposed to hypotonic solutions increase in water weight, and those exposed to hypertonic solutions decreased in water weight.

Study 1

     Gills dissected from a fish were exposed to different ambient environments of salinity including an isotonic control solution (301.5 milliosmoles), a hypotonic solution (1.5 milliosmoles), and a hypertonic solution (601.5 milliosmoles). Percent water weight change between treatments was observed and calculated.

Which of the treatment groups could be considered as an analog for a freshwater environment?

Carbonic anhydrase is an enzyme that is used by the human body to interconvert carbon dioxide (a gaseous compound) and bicarbonate (a compound composed of hydrogen, carbon, and oxygen), using water as a reactant. The human body needs to convert carbon dioxide to bicarbonate in the tissues to transport it in the blood to the lungs, as carbon dioxide is relatively insoluble. In the lungs, bicarbonate is converted back to carbon dioxide to be exhaled. In humans, there are two different carbonic anhydrase isomers, one that works in the lungs (isomer A) and one that works in the tissues (isomer B). Mutations in the chromosomes can prevent carbonic anhydrase from converting carbon dioxide to bicarbonate. In the following four experiments, the chromosomes of none, one, or both of the isomers were mutated per experiment.

Experiment 1

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Bicarbonate was measured in the tissues but carbon dioxide was not measured in the lungs.

Experiment 2

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be abnormally high in the tissues and no bicarbonate was measured in the lungs.

Experiment 3

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be slightly low in the tissues and bicarbonate levels were abnormally high in the lungs.

Experiment 4

Radiation was not used, A probe was placed into the tissues and lungs of a model animal and found normal carbon dioxide and bicarbonate levels.

Mutating the chromosomes of the animal cells is most likely useful in this passage because it __________.

Carbonic anhydrase is an enzyme that is used by the human body to interconvert carbon dioxide (a gaseous compound) and bicarbonate (a compound composed of hydrogen, carbon, and oxygen), using water as a reactant. The human body needs to convert carbon dioxide to bicarbonate in the tissues to transport it in the blood to the lungs, as carbon dioxide is relatively insoluble. In the lungs, bicarbonate is converted back to carbon dioxide to be exhaled. In humans, there are two different carbonic anhydrase isomers, one that works in the lungs (isomer A) and one that works in the tissues (isomer B). Mutations in the chromosomes can prevent carbonic anhydrase from converting carbon dioxide to bicarbonate. In the following four experiments, the chromosomes of none, one, or both of the isomers were mutated per experiment.

Experiment 1

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Bicarbonate was measured in the tissues but carbon dioxide was not measured in the lungs.

Experiment 2

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be abnormally high in the tissues and no bicarbonate was measured in the lungs.

Experiment 3

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be slightly low in the tissues and bicarbonate levels were abnormally high in the lungs.

Experiment 4

Radiation was not used, A probe was placed into the tissues and lungs of a model animal and found normal carbon dioxide and bicarbonate levels.

Which of the experiments most likely served as the control experiment?

Many motile organisms exhibit “fight or flight” responses in order to survive and reproduce. Aggressive posturing and combative behavior are important for the reproductive success and the formation of pack hierarchies of some species. Submissive actions and retreats permit other species the ability to evade capture or danger and enhance survival capabilities. Scientists have debated about the mechanics and moderation of these behaviors within organisms. Two studies regarding this behavior were performed.

Study 1

Researchers decided to study crayfish, a type of freshwater arthropod, in an aquarium. They placed two crayfish opposing one another in an enclosed space. The crayfish were divided by an opaque screen that inhibited their ability to notice one another. The screen was lifted and the crayfish were permitted to interact with one another. The scientists observed their interactions and noted the crayfish's submissive and aggressive behaviors. The scientists noticed that more dominant and aggressive behaviors correlated with larger sized individuals. Their observations indicate that large size and aggression are traits actively selected for within the crayfish population and are necessary for survivorship and reproductive success.

Study 2

Researchers in this study suggest that aggressive behaviors are linked to chemical messengers. They attempted to alter the crayfish’s lateral giant escape reaction through chemical manipulation. They injected crayfish with serotonin, an aggression stimulant, and octopamine, a natural facilitator of the flight response. They monitored and recorded the crayfish’s response to aggressive stimuli (see Figure 1). The researchers concluded that the crayfish escape response is significantly different in the chemical trials in comparison to the control trial that observed the injection of an inert saline solution into the arthropods.

Figure 1

Why was the control trial completed in Study 2?

Bacterial resistance is a common issue encountered in various infections. Scientists have attributed this phenomenon to the overuse of anti-bacterial sanitizers and prescription antibiotics. Two groups of researchers performed studies to test bacterial resistance.

Study 1

Researchers in this study state that bacterial resistance is the result of bacterial plasmid translocation. Bacteria carry their genes on circular rings of bacterial DNA and on small, physically separate molecules known as plasmids. Plasmids are unique because they are replicons that are capable of replication autonomously within a suitable host. Researchers radioactively marked plasmids in bacterial specimens and noted that they could be easily transmitted from one bacterium to another via horizontal gene transfer. They then observed that the genes transferred from the plasmid could be incorporated into the bacteria’s genetic makeup. These genetic alterations enhanced survivorship within the environment and promoted resistance to antibiotics. They concluded that plasmids carry genes important for survival and facilitate bacterial resistance to antibiotics.

Study 2

Researchers in this study state that resistance is the result of the misuse of antibiotics. Researchers administered various antibiotics to a culture of E. coli and studied their effects over time (Figure 1). They concluded that bacterial resistance is the result of natural selection. In other words, the strongest bacteria survive antibiotics and reproduce, which produces anitbiotic-resistant offspring bacteria. 

Figure 1

What happened to the control culture over the 15-day trial in Figure 1?

Bacterial resistance is a common issue encountered in various infections. Scientists have attributed this phenomenon to the overuse of anti-bacterial sanitizers and prescription antibiotics. Two groups of researchers performed studies to test bacterial resistance.

Study 1

Researchers in this study state that bacterial resistance is the result of bacterial plasmid translocation. Bacteria carry their genes on circular rings of bacterial DNA and on small, physically separate molecules known as plasmids. Plasmids are unique because they are replicons that are capable of replication autonomously within a suitable host. Researchers radioactively marked plasmids in bacterial specimens and noted that they could be easily transmitted from one bacterium to another via horizontal gene transfer. They then observed that the genes transferred from the plasmid could be incorporated into the bacteria’s genetic makeup. These genetic alterations enhanced survivorship within the environment and promoted resistance to antibiotics. They concluded that plasmids carry genes important for survival and facilitate bacterial resistance to antibiotics.

Study 2

Researchers in this study state that resistance is the result of the misuse of antibiotics. Researchers administered various antibiotics to a culture of E. coli and studied their effects over time (Figure 1). They concluded that bacterial resistance is the result of natural selection. In other words, the strongest bacteria survive antibiotics and reproduce, which produces anitbiotic-resistant offspring bacteria. 

Figure 1

What was the independent variable in Study 2?

A group of scientists wanted to test the effects of Nitra-Grow, a chemical additive that can be given to plants to help them grow. 3 test groups of plants were given all the same time of sunlight, the same type of soil, and the same amount of water. Plant A was given no extra chemicals. Plant B was given 5g of Nitra-Grow. Plant C was given 5g of Ammonia to see if Nitra-Grow worked any better than a basic nitrogen-based household product. The plants are then measured on 5 consecutive days to find their average height (in cm).

What is the dependent variable?