Blog

Regulation of gene expression occurs first at the DNA structural level, but it is even more tightly regulated at the transcription level. ______ are proteins that block the action of activators, either by blocking their access to the control elements, or binding the control element directly.

The deep ocean floor communities contain very little life. In constant darkness, the water at these depths hovers around 2°C. Sparsely distributed in this environment are hydrothermal vent ecosystems. Superheated water streams out of the vents at temperatures approaching 400°C. These waters are rich in inorganic materials, including carbon dioxide and hydrogen sulfide. Hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater than found on the surrounding seafloor. Scientists have studied these vents to determine the energy source for these communities and the identity of the primary producers in the perpetual darkness of the ocean floor. As expected, they found a total absence of photosynthetic organisms at all vents, identifying mats of bacteria as the producers of the carbon compounds that are used by the rest of the community for growth, repair, and as an energy source. Which of the following describes how the vent bacteria harvest energy to produce organic compounds for use by the vent community?

Spirogyra (a green alga), a moss, a spruce tree, and an apple tree. Table 1 compares several characteristics in the organisms (+ indicates the trait is present, − indicates the trait is absent). Table 1. Comparison of several characteristics in four photosynthetic eukaryotic organisms Green Alga Moss Spruce Tree Apple Tree Cell wall composed of cellulose + + + + Vascular tissue – – + + Roots – – + + Seeds enclosed in fruit – – – + Flagellated sperm cells – + – – Which of the following rows of data listed in table 1 best supports the possibility of a common ancestor for the organisms listed there?

Researchers investigated the habitat preferences of two species of garter snakes, Thamnophis sirtalis and Thamnophis atratus. To create a choice chamber, the researchers built a meshed enclosure and positioned one end of the enclosure at the edge of a small pond. Zone I of the enclosure was located in the water, whereas zone IV of the enclosure was located 2–3 meters away from the water, as represented in the figure below. Snakes inside the enclosure were able to move freely between zones. From left to right, the zones are labeled 4 through 1. The side length of each square is 1 meter. A large semicircular shaded region, labeled “Pond,” completely covers square 1 and a very small part of square 2. The “Pond” region also extends beyond square 1 to the outside of the enclosure. In a series of experiments, the researchers introduced a single snake into zone IV of the enclosure at 7:00 A.M. The researchers recorded the location of the snake at six time points throughout the day. In a related experiment, the researchers introduced two snakes, one of each species, into the enclosure at the same time and observed the location of each of the two snakes at the same six time points as before. The researchers repeated both the one-snake and two-snake experiments using different individual snakes of each species. The results are presented in the table. The title of the table is ZONES MOST FREQUENTLY OCCUPIED BY GARTER SNAKES IN A MESHED ENCLOSURE. The top row contains the column labels, from left to right: column one, Time of Day; column two, Zone Most Frequently Occupied by T. atratus; column three, Zone Most Frequently Occupied by T. sirtalis; column four, Zone Most Frequently Occupied by T. Based on the data in the table, which of the following best predicts the results of a study in which natural populations of T. atratus and T. sirtalis are observed together in an environment that includes a freshwater pond?

Mechanical isolation is a reproductive barrier that refers to

Which of the following is not an explanation for why genetic diversity isn’t eliminated in the presence of strong selective pressures?

A scientist used the amino acid sequence of cytochrome c in different species to consider evolutionary relationships. The data below summarize the number of differences in the amino acid sequences of cytochrome c found in selected species. Differences in the amino acid sequences of cytochrome c found in selected species Species Compared Number of Differences Humans – Chimpanzees 0 Humans – Rhesus monkeys 1 Humans – Horses or donkeys 7 Humans – Cows or pigs or sheep 7 Humans – Rabbits 7 Mammals – Birds and reptiles 10-15 Mammals – Fish 18-20 Animals – Plants 45-48 Interpretation of the data supports which of the following statements?

The figure below represents a food web in a particular ecosystem. Each letter represents a species. The arrows indicate the direction of energy flow. A is arranged at the bottom of the food web with decomposers on the right. The other letters are arranged from the far left above A, starting with E, then D up and to the right, then at the top of the web above A is C, with B to the right and lower than C, but above decomposer. The letter A has an arrow pointing up to D, an arrow pointing up to C and an arrow pointing to decomposer on the right. C has an arrow to decomposer. D has an arrow pointing left to E, an arrow pointing right to C, an arrow pointing right to B and an arrow pointing to decomposer. E has an arrow pointing to decomposer. C has an arrow pointing to decomposer. B has an arrow pointing to C and an arrow pointing to decomposer. A photosynthetic organism would be represented by which species?

A moth’s color is controlled by two alleles, G and g, at a single locus. G (gray) is dominant to g (white). A large population of moths was studied, and the frequency of the G allele in the population over time was documented, as shown in the figure below. In 1980 a random sample of 2,000 pupae was collected and moths were allowed to emerge. Each figure shows an image of a stickleback fish with a genetic structure below it. The left figure is labeled Figure 1. Marine stickleback. A long Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. The right figure is labeled Figure 2. Freshwater stickleback. A short Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. The Hindlimb enhancer is crossed out with an X, and it is labeled Disabled Due to Mutation. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. Assuming that the population was in Hardy-Weinberg equilibrium for the G locus, what percentage of moths in the natural population was white in 1962?

In an experiment, three different animals were exposed to a series of environmental temperatures and their body temperatures were assessed at multiple temperature points between 10 and 40 degrees Celsius. Ten different individuals of each type of animal were included in the study to produce an average body temperature profile for each type of animal. Figure 1 shows the data collected. The horizontal axis is labeled Temperature, in degrees Celsius, and no numbers are indicated along it. The rightward direction along the horizontal axis is indicated as increasing in temperature with an arrowhead at the right end. The vertical axis is labeled Body Temperature, in degrees Celsius, and the numbers 5 through 45, in increments of 5, are indicated. The three lines are described as follows. Each line begins at the same value along the horizontal axis near the vertical axis, and ends at the same value further to the right along the horizontal axis. Note that all values are approximate. The upper line, labeled Gerbil, begins at body temperature 39 degrees Celsius. The line moves gradually downwards and to the right, ending at body temperature 37 degrees Celsius. The line under the Gerbil line, labeled Armadillo, begins at body temperature 34 degrees Celsius. The line moves very gradually upwards and to the right, ending at body temperature 35 degrees Celsius and never crosses the Gerbil line. The remaining line, labeled Snake, begins at body temperature 15 degrees Celsius. The line moves upwards and to the right, ending at body temperature 40 degrees Celsius and crosses the Gerbil and Armadillo lines further to the right along the horizontal axis. Figure 1. Effect of environmental temperature on body temperature of selected animals Which of the following statements is most consistent with the data in Figure 1?