Scientists have examined the genetic history of a large group of cheetahs and have found that
there was a significant decrease in the genetic diversity of the cheetah species about 10,000 years
ago. Scientists found that, even in unrelated groups of cheetahs, individual cheetahs had 99% of
the same alleles. By comparison, in a genetically diverse population, even closely related
individuals contain only 80% of the same alleles. Genetic diversity is important to the survival of a
species, and scientists worry that a disease that cheetahs are not resistant to could decimate the
population.
Major histocompatibility complex (MC) genes are used by the body to identify self from non-self
and direct the immune system to attack non-self particles. Invading bacteria and viruses do not
contain the same MHC genes and therefore are attacked by the immune system. Within a
population, a high diversity of MHC genes protects the population from attack by disease. In a
highly diverse population, it is likely that at least some individuals will contain an allele that
identifies a new disease as non-self and can direct the immune system to destroy it.
In 1985, research by Stephen O'Brien reported that skin grafts from cheetahs in a zoo in Oregon
were accepted by cheetahs in Africa. Skin grafts, like other organ donations, must be between
Individuals that have the same MHC factors. If any of the genetic factors are different, then the
immune system of the individual receiving the organ will identify the organ as non-self and the
body will attack the donated organ as if it were a foreign organism such as a virus or bacterium.
The conclusion from
O'Brien's research was that cheetah MHC genes are as alike as those of identical twins.
More recent research by Simone Sommer took a much more comprehensive approach to
examining the genes of a large sample of wild cheetahs. Sommer's research determined how
many alleles are present on two different types of MHC genes in approximately 150 cheetahs.
Sommer was able to show that the variation in some MHC genes was higher than previously
thought. The variation in MHC genes in cheetahs is still smaller than that for other big cat species
but appears to be sufficient to allow the populations to identify a wide variety of foreign particles.
Why is the conclusion about gene variation among cheetahs from Sommer's research more valid than the conclusion from O'Brien's research?
- A. Sommer's research was conducted more recently than O'Brien's
- B. Sommer's research used a different population of cheetahs than O'Brien's
- C. Sommer's conclusion is about disease response, while O'Brien's is about skin grafts.
- D. Sommer's conclusion is based on examining the genes, while O'Brien's conclusion is based on acceptance of a skin graft.
Correct Answer & Rationale
Correct Answer: D
Sommer's conclusion is more valid as it directly examines gene variation, providing a clearer understanding of genetic factors influencing traits. This direct analysis allows for more reliable insights into gene functionality. In contrast, O'Brien's research focuses on skin graft acceptance, which, while informative, does not provide the same depth of genetic examination. Option A is incorrect as recency does not inherently validate research findings. Option B is misleading; differing populations may affect findings but do not necessarily validate one conclusion over another. Option C misrepresents the focus of the studies; both are relevant but differ in application rather than validity.
Sommer's conclusion is more valid as it directly examines gene variation, providing a clearer understanding of genetic factors influencing traits. This direct analysis allows for more reliable insights into gene functionality. In contrast, O'Brien's research focuses on skin graft acceptance, which, while informative, does not provide the same depth of genetic examination. Option A is incorrect as recency does not inherently validate research findings. Option B is misleading; differing populations may affect findings but do not necessarily validate one conclusion over another. Option C misrepresents the focus of the studies; both are relevant but differ in application rather than validity.
Other Related Questions
Which statement describes one feature of the Rutherford-Bohr atom model that the Thomson model does not share?
- A. The Rutherford-Bohr model identifies different elements by the numbers of particles present.
- B. The Rutherford-Bohr model maintains the observed neutral charge of atoms.
- C. The Rutherford-Bohr model correctly describes the types of particles in the atom.
- D. The Rutherford-Bohr model restricts the positive charge of the atom to the nucleus.
Correct Answer & Rationale
Correct Answer: D
The Rutherford-Bohr model uniquely restricts the atom's positive charge to the nucleus, a significant advancement over the Thomson model, which depicts a diffuse positive charge throughout the atom. Option A is incorrect as both models can identify elements based on particle numbers, but the Rutherford-Bohr model adds more detail about electron arrangements. Option B is misleading; both models account for atomic neutrality, but the Rutherford-Bohr model provides a clearer structure. Option C is also inaccurate; while the Rutherford-Bohr model describes particles more accurately, it does not fundamentally change the types of particles present compared to Thomson's model.
The Rutherford-Bohr model uniquely restricts the atom's positive charge to the nucleus, a significant advancement over the Thomson model, which depicts a diffuse positive charge throughout the atom. Option A is incorrect as both models can identify elements based on particle numbers, but the Rutherford-Bohr model adds more detail about electron arrangements. Option B is misleading; both models account for atomic neutrality, but the Rutherford-Bohr model provides a clearer structure. Option C is also inaccurate; while the Rutherford-Bohr model describes particles more accurately, it does not fundamentally change the types of particles present compared to Thomson's model.
Placing solid ammonium nitrate, NH4NO3, in a container of water causes an endothermic reaction. The result is ammonium hydroxide, NH4OH, and nitric acid, HNO3. Which diagram shows the correct equation for the reaction?
- A. NH4OH + HNO3 → NH4NO3 + H2O + energy
- B. NH4NO3 + H2O + energy → NH4OH + HNO3
- C. NH4NO3 + H2O → NH4OH + HNO3 + energy
- D. NH4OH + HNO3 + energy → NH4NO3 + H2O
Correct Answer & Rationale
Correct Answer: B
The reaction involving solid ammonium nitrate and water is endothermic, meaning it absorbs energy. Option B accurately reflects this by showing ammonium nitrate and water reacting to form ammonium hydroxide and nitric acid while requiring energy input, consistent with the endothermic nature of the process. Option A incorrectly suggests that energy is released, which contradicts the reaction's endothermic characteristic. Option C also misrepresents the energy aspect, implying that energy is produced, which is not the case. Option D similarly indicates that energy is released, misaligning with the reaction's true nature.
The reaction involving solid ammonium nitrate and water is endothermic, meaning it absorbs energy. Option B accurately reflects this by showing ammonium nitrate and water reacting to form ammonium hydroxide and nitric acid while requiring energy input, consistent with the endothermic nature of the process. Option A incorrectly suggests that energy is released, which contradicts the reaction's endothermic characteristic. Option C also misrepresents the energy aspect, implying that energy is produced, which is not the case. Option D similarly indicates that energy is released, misaligning with the reaction's true nature.
Limestone and marble are often used in buildings. Both types of rock contain calcium carbonate, which is sensitive to chemical weathering by acids. A scientist conducted an experiment to test the effect of acid strength on calcium carbonate... Which change would reduce the possibility of error in the experiment?
- A. performing the experiment with a different acid in the solution
- B. performing multiple trials for each solution pH
- C. using more of the acidic solution
- D. using a solution with a pH below 3.00
Correct Answer & Rationale
Correct Answer: B
Performing multiple trials for each solution pH enhances the reliability of the experiment by allowing for the identification of consistent patterns and minimizing the impact of random errors. This approach provides a more accurate average result, leading to valid conclusions about the effect of acid strength on calcium carbonate. Option A introduces a variable that may not be relevant to the original question, potentially complicating the results. Option C does not address the variability inherent in a single trial, which could skew results. Option D restricts the experiment to a specific range of acidity, limiting the exploration of acid strength effects across a broader spectrum.
Performing multiple trials for each solution pH enhances the reliability of the experiment by allowing for the identification of consistent patterns and minimizing the impact of random errors. This approach provides a more accurate average result, leading to valid conclusions about the effect of acid strength on calcium carbonate. Option A introduces a variable that may not be relevant to the original question, potentially complicating the results. Option C does not address the variability inherent in a single trial, which could skew results. Option D restricts the experiment to a specific range of acidity, limiting the exploration of acid strength effects across a broader spectrum.
What natural process is required to connect the ice core data to the Tunguska Event?
- A. the cycling of carbon in forest fires
- B. the interaction of comets with the solar wind
- C. the movement of glaciers due to gravity
- D. the constant mixing of the atmosphere
Correct Answer & Rationale
Correct Answer: D
Connecting ice core data to the Tunguska Event necessitates understanding atmospheric dynamics, which is achieved through the constant mixing of the atmosphere. This mixing disperses particles and gases, allowing researchers to correlate ice core samples with historical events, including the Tunguska explosion. Option A, the cycling of carbon in forest fires, is unrelated to the atmospheric conditions or the specific data derived from ice cores. Option B, the interaction of comets with the solar wind, pertains to space phenomena rather than terrestrial atmospheric processes. Option C, the movement of glaciers due to gravity, describes glacial dynamics but does not address the atmospheric mixing needed to link ice core data to the event.
Connecting ice core data to the Tunguska Event necessitates understanding atmospheric dynamics, which is achieved through the constant mixing of the atmosphere. This mixing disperses particles and gases, allowing researchers to correlate ice core samples with historical events, including the Tunguska explosion. Option A, the cycling of carbon in forest fires, is unrelated to the atmospheric conditions or the specific data derived from ice cores. Option B, the interaction of comets with the solar wind, pertains to space phenomena rather than terrestrial atmospheric processes. Option C, the movement of glaciers due to gravity, describes glacial dynamics but does not address the atmospheric mixing needed to link ice core data to the event.