1. Which of the following observations best supports the hypothesis that a large object collided with Earth in a period of time associated with a mass extinction?
(A) A species found only in Australia resembles a species found only in North America.
(B) An analysis of radiation reaching Earth from outer space suggests that water might have existed on distant planets.
(C) A fossil of an extinct species of mammal is found to have morphological characteristics that are similar to those of a living nocturnal mammal.
(D) Iridium, which is common in meteorites but rare on Earth, is found in sedimentary rock that contains the last appearance of many species in the fossil record.
2. Which of the following observations best represents a mutualistic relationship?
(A) Some bacteria and fungi obtain their nutrients by enzymatically digesting larger organisms.
(B) Chloroplasts in green algae provide sugars for use in cellular metabolism.
(C) Hermit crabs utilize empty sea snail shells to protect themselves from predators.
(D) Flowers produce nectar that bees gather to make honey, and in the process the bees pollinate the flowers.
3. A blue-flowered African violet of unknown ancestry self-pollinated and produced 50 seeds. These seeds germinate and grow into flowering plants. Of these plants, 36 produce blue flowers and 14 produce pink flowers. What is the best explanation for the pink-flowered offspring?
(A) Blue flowers are incompletely dominant to pink flowers.
(B) Pink flower color is a trait recessive to blue flower color.
(C) Pink flower color is the result of somatic mutations in the flower color gene.
(D) A previous generation of the blue-flowered parent must have included 50 percent pinkflowered plants.
4. While there is only one species of Galapagos Island tortoise, there are several subspecies. Larger islands with more wet highlands have lush vegetation near the ground. Tortoises there tend to have high-domed shells and shorter necks, which restrict upward head movement. They also have shorter limbs. They are the heaviest and largest of the subspecies. Smaller, drier islands are inhabited by tortoises with longer necks and limbs and with shells that are elevated above the neck, which allow them to browse taller vegetation. Based on the information given, which of the following is a plausible explanation for the ancestry of the tortoise subspecies?
(A) The subspecies share a recent common ancestor whose neck length, shell shape, and leg length were intermediate between the two subspecies.
(B) The tortoises with shorter legs and necks were most easily preyed on as young animals by the rats that were introduced, so they survived only on a few islands.
(C) Random mutations coupled with the inheritance of acquired characteristics resulted in distinct subspecies.
(D) Individuals with different adaptations in shell shape and leg length best exploited the food resources and left more surviving offspring on each island.
1. In bacterial communities, where resources are often limited, survival requires the ability to sense, respond to, and cooperate or compete with neighboring organisms. In communities containing Burkholderia thailandensis bacteria, these abilities rely in part on contact-dependent communication with neighboring cells. This communication involves a signaling protein, protein S, that gets transported to the surface of the cell. When in direct physical contact with another bacterial cell, protein S is cleaved and internalized by the recipient cell, where it can act as a nuclease. There are different forms of protein S (e.g., Sl, S2, S3) and different forms of an internal protein, protein R (e.g., Rl, R2, R3). Recipient cells are protected from the nuclease activity of protein S if they produce the appropriate form of protein R.
In an investigation, B. thailandensis strains were genetically engineered to produce different combinations of proteins Sand R. The cells were placed in a nutrient-deficient medium (T=0 hours) and cultured for 4 hours (T=4 hours). The density of live cells in the culture was recorded at the two time points, T=0 hours and T=4 hours. The data are shown in Table 1.
(a) Construct an appropriately labeled graph that represents the density of live cells in each culture of the three genetically altered B. thailandensis strains at both time points.
(b) Explain the effect of expressing only S 1 on the cells in culture 1. Describe the effect of expressing combinations of protein S and protein Ron the survival of the cells in culture 2 AND culture 3.
(c) In naturally occurring solid surface environments, such as soil, bacteria use this same signaling pathway to initiate formation of biofilms, which are densely populated aggregates of bacteria. In the center of the biofilm, cells are more likely to interact only with cells of the same bacterial strain. At the edges of the biofilm, cells are more likely to encounter cells of a different bacterial strain or species. Identify the most likely type of ecological relationships among cells in the center of the biofilm AND cells at the edges of the biofilm. Provide reasoning to support a researcher's claim that the bacteria cannot form biofilms at a low population density.