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Questions and Answers of Biology

What is a keystone species? Paine (1966, 1969) experimented with two sea stars that act as keystone species in their intertidal communities along the west coast of North America and in New Zealand.
Explain how the experiments of Lubchenco (1978) showed that feeding preferences, population density, and competitive relations among food species all potentially contribute to the influences of
When Power (1990) excluded predaceous fish from her river sites, the density of herbivorous insect larvae (chironomids) decreased. Use the food web described by Power to explain this response.
Some paleontologists have proposed that overhunting caused the extinction of many large North American mammals at the end of the Pleistocene about 11,000 and 10,000 years ago. The hunters implicated
Population, community, and ecosystem ecologists study structure and process. However, they focus on different natural characteristics. Contrast the important structures and processes in a forest from
M. Huston (1994b) pointed out that the well-documented pattern of increasing annual primary production from the poles to the equator is strongly influenced by the longer growing season at low
Compare the pictures of trophic structure that emerged from our discussions of food webs in chapter 17 with those in chapter 18. What are the strengths of each perspective? What are their limitations?
Suppose you are studying a community of small mammals that live on the boundary between a riverside forest and a semidesert grassland. One of your concerns is to discover the relative contributions
Most of the energy that flows through a forest ecosystem flows through detritus-based food chains, and the detritus consists mainly of dead plant tissues (e.g., leaves and wood). In contrast, most of
In chapter 17, we examined the influences of keystone species on the structure of communities. In chapter 18, we reviewed trophic cascades. Discuss the similarities and differences between these two
Of all the naturally occurring elements in the biosphere, why have the cycles of carbon, nitrogen, and phosphorus been so intensively studied by ecologists?
If rates of decomposition are higher in ecosystems with higher nutrient availability, how should nutrient enrichment affect rates of decomposition? Because of its effects on fungal diversity, could
Review figure 18.2, in which Rosenzweig (1968) plotted the relationship between actual evapotranspiration and net primary production. How do you think that decomposition rates change across the same
Melillo, Aber, and Muratore (1982) suggested that soil fertility may influence the rate of decomposition in terrestrial ecosystems. Design an experiment to test this hypothesis. If you test for the
Likens and Bormann (1995) found that vegetation substantially influences the rate of nutrient loss from small stream catchments in the northern hardwood forest ecosystem. How do vegetative biomass
McNaughton, Ruess, and Seagle (1988) proposed that grazing by large mammals increases the rate of nitrogen cycling on the savannas of East Africa. Explain how passing through a large mammal could
Kauffman and his colleagues (1993) estimated that burning the tropical forest at their study site resulted in the loss of approximately 21 kg per hectare of phosphorus. This quantity is about 11% to
As we saw in figure 20.5, Johnston and Odum (1956) documented substantial change in the richness of bird species in a successional sequence going from the earliest stages in which the plant community
Succession seems to lead to predictable changes in community and ecosystem structure. Predict the characteristics of a frequently disturbed community/ecosystem versus a largely undisturbed
The successional studies in Sycamore Creek produced patterns of variation in diversity that differed significantly from those observed during primary succession at Glacier Bay (see fig. 20.2), old
In most studies of forest succession such as that of Reiners and colleagues (1971) and Oosting (1942), researchers study succession by comparing sites of various ages. This approach is called a
The rapid succession shown by the Sycamore Creek ecosystem is impressive. How might natural selection influence the life cycles of the organisms living in Sycamore Creek? Imagine a creek that floods
When Mount St. Helens in Washington erupted in 1980, it created a gradient in disturbance. In the pumice plains near the eruption, the devastation was almost total. The extent of disturbance was much
Ecological succession has been compared to the development of an organism and the climax community to a kind of superorganism. F. E. Clements (1916, 1936) was the best-known proponent of this idea,
How does landscape ecology differ from ecosystem and community ecology? What questions might an ecosystem ecologist ask about a forest? What questions might a community ecologist ask about the same
The green areas represent forest fragments surrounded by agriculture. Landscapes 1 and 2 contain the same total forest area. Which landscape, 1 or 2, will contain more forest interior species?
How do the positions of patches in a landscape affect the movement of individuals among habitat patches and among portions of a metapopulation? Again, consider the hypothetical landscapes shown in
Analyses such as Milne's comparison (1993) of bald eagles and barnacles demonstrate that organisms of different sizes interact with the environment at very different spatial scales. With this in mind
How do the activities of animals affect landscape heterogeneity? You might use either beaver or human activity as your model. What parallels can you think of between the influence of animal activity
We discussed how Diamond (1969) documented immigrations and extinctions on the California Channel Islands by comparing his censuses of the birds of the islands with the birds recorded over 50 years
Diamond's estimates (1969) of numbers of species immigrating and numbers that became extinct (six versus five) were virtually identical. Is this near equality in numbers of extinction and immigration
Suppose you are about to study the bird communities on the islands shown above, which are identical in area but lie at different distances from the mainland. According to the equilibrium model of
Now, suppose you are going to study the bird communities on the islands shown below, which lie equal distances from the mainland but differ in area. According to the equilibrium model of island
Explain how speciation and extinction rates might be affected by the area of continents. What evidence is there to support your explanation? What does the influence of area on rates of extinction and
Ricklefs (1987) pointed out that many large-scale contrasts in species richness and composition cannot be explained by local processes such as competition and predation. Ricklefs proposed that
Ecologists are now challenged to study global ecology. The apparent role played by humans in changing the global environment makes it imperative that we understand the workings of the earth as a
What evidence is there that variation in atmospheric CO2 concentration is linked to variation in global temperatures? In recent years, the governments of most countries of the world have been working
Geologists, atmospheric scientists, and oceanographers have been conducting global-scale studies for some time. What role will information from these disciplines play in the study of global ecology?
What changes in sea surface temperatures and atmospheric pressures over the Pacific Ocean accompany El Niño? What physical changes accompany La Niña? How do El Niño and La Niña affect
Review evidence that the El Niño Southern Oscillation significantly influences populations around the globe. Much of our discussion in chapter 23 focused on the effects of the El Niño Southern
In chapter 23, we briefly discussed how humans have more than doubled the quantity of fixed nitrogen cycling through the biosphere. In chapter 15, we reviewed studies by Nancy Johnson (1993) on the
As we saw in chapters 18 and 19, nitrogen availability seems to control the rates of several ecosystem processes. How should nitrogen enrichment affect rates of primary production and decomposition
Skole and Tucker (1993) documented the rate and extent of recent deforestation in the Amazon Basin in Brazil. This is a prominent example of the land cover changes that likely threaten biological
Review the long-term atmospheric CO2 record as revealed by studies of air trapped in ice cores. What is the evidence that burning of fossil fuels is responsible for recent increases in atmospheric
Pick any example of a genetic technology and describe how it has directly affected your life.
What is a DNA sequence?
Explain the relationships between the following pairs of genetic terms: A. Gene and trait B. Gene and chromosome C. Allele and gene D. DNA sequence and amino acid sequence
What are the primary interests of researchers working in the following fields of genetics? A. Transmission genetics B. Molecular genetics C. Population genetics
At the molecular level, what is a gene? Where are genes located?
Briefly explain how gene expression occurs at the molecular level.
A human gene called the β-globin gene encodes a polypeptide that functions as a subunit of the protein known as hemoglobin. Hemoglobin is found within red blood cells; it carries oxygen. In human
What is meant by the term "genetic variation"? Give two examples of genetic variation not discussed in Chapter 1. What causes genetic variation at the molecular level?
Your textbook describes how the trait of phenylketonuria (PKU) is greatly influenced by the environment. Pick a trait in your favorite plant and explain how genetics and the environment may play
Your textbook describes how the trait of phenylketonuria (PKU) is greatly influenced by the environment. Pick a trait in your favorite plant and explain how genetics and the environment may play
What is meant by the term "diploid"? Which cells of the human body are diploid, and which cells are not?
Many organisms are studied by geneticists. Of the following species, do you think it would be more likely for them to be studied by a transmission geneticist, a molecular geneticist, or a population
Why did Mendel's work refute the idea of blending inheritance?
A cross is made between a pea plant that has constricted pods (a recessive trait; smooth is dominant) and is heterozygous for seed color (yellow is dominant to green) and a plant that is heterozygous
Describe the significance of nonparentals with regard to the law of independent assortment. In other words, explain how the appearance of nonparentals refutes a linkage hypothesis.
For the following pedigrees, describe what you think is the most likely inheritance pattern (dominant versus recessive). Explain your reasoning. Filled (black) symbols indicate affected
Ectrodactyly, also known as "lobster claw syndrome," is a recessive disorder in humans. If a phenotypically unaffected couple produces an affected offspring, what are the following probabilities? A.
Identical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate sperm and separate egg cells. If two
In cocker spaniels, solid coat color is dominant over spotted coat color. If two heterozygous dogs were crossed to each other, what would be the probability of the following combinations of
A cross was made between a white male dog and two different black females. The first female gave birth to eight black pups, and the second female gave birth to four white and three black pups. What
In humans, the allele for brown eye color (B) is dominant to blue eye color (b). If two heterozygous parents produce children, what are the following probabilities? A. The first two children have
A true-breeding tall plant was crossed to a dwarf plant. Tallness is a dominant trait. The F1 individuals were allowed to self-fertilize. What are the following probabilities for the F2
For pea plants with the following genotypes, list the possible gametes that the plant can make: A. TT Yy Rr B. Tt YY rr C. Tt Yy Rr D. tt Yy rr
In people with maple syrup urine disease, the body is unable to metabolize the amino acids leucine, isoleucine, and valine. One of the symptoms is that the urine smells like maple syrup. An
A true-breeding pea plant with round and green seeds was crossed to a true-breeding plant with wrinkled and yellow seeds. Round and yellow seeds are the dominant traits. The F1 plants were allowed to
What are the expected phenotypic ratios from the following cross: Tt Rryy Aa x Tt rr YY Aa, where T = tall, t = dwarf, R = round, r = wrinkled, Y = yellow, y = green, A = axial, a = terminal; T, j R,
When an abnormal organism has three copies of a chromosome I and therefore contains three copies of the genes on that chromosome (instead of the normal number of two copies), the alleles for each
Honeybees are unusual in that male bees (drones) have only one copy of each gene, but female bees have two copies of their genes. That is because drones develop from eggs that have not been
Describe the difference between genotype and phenotype. Give three examples. Is it possible for two individuals to have the same phenotype but different genotypes?
A pea plant that is dwarf with green, wrinkled seeds was crossed t' a true-breeding plant that is tall with yellow, round seeds. The F1 generation was allowed to self-fertilize. What types of
A true-breeding plant with round and green seeds was crossed to true-breeding plant with wrinkled and yellow seeds. The F1 plants were allowed to self-fertilize. What is the probability of obtaining
Wooly hair is a rare dominant trait found in people of Scandinavian descent in which the hair resembles the wool of a sheep. A male with wooly hair, who has a mother with straight hair, moves to an
Huntington disease is a rare dominant trait that causes neuro-degeneration later in life. A man in his thirties, who already has three children, discovers that his mother has Huntington disease
A woman with achondroplasia (a dominant form of dwarfism) and a phenotypically unaffected man have seven children, all of whom have achondroplasia. What is the probability of producing such a family
Describe three advantages of using pea plants as an experimental organism.
In fruit flies, curved wings are recessive to straight wings, and ebony body is recessive to gray body. A cross was made between true-breeding flies with curved wings and gray bodies to flies with
A recessive allele in mice results in an abnormally long neck. Sometimes, during early embryonic development, the abnormal neck causes the embryo to die. An experimenter began with a population of
The data in Figure 2.5 show the results of the F2, generation for seven of Mendel's crosses. Conduct a chi square analysis to determine if these data are consistent with the law of segregation.
Let's suppose you conducted an experiment involving genetic crosses and calculated a chi square value of 1.005. There were four categories of offspring (i.e., the degrees of freedom equaled 3).
A tall pea plant with axial flowers was crossed to a dwarf plant with terminal flowers. Tall plants and axial flowers are dominant traits. The following offspring were obtained: 27 tall, axial
A cross was made between two strains of plants that are agriculturally important. One strain was disease-resistant but herbicide-sensitive; the other strain was disease-sensitive but
A cross was made between a plant that has blue flowers and purchased seeds to a plant with white flowers and green seeds. The following data were obtained: F1 generation: All offspring have blue
For all seven characters described in the data of Figure 2.5, Mendel allowed the F, plants to self-fertilize. He found that when F2 plants with recessive traits were crossed to each other, they
From the point of view of crosses and data collection, what are the experimental differences between a single-factor and a two-factor cross?
As in many animals, albino coat color is a recessive trait in guinea pigs. Researchers removed the ovaries from an albino female guinea pig and then transplanted ovaries from a true-breeding black
The fungus Melampsora lini causes a disease known as flax rust. Different strains of M. lini cause varying degrees of the rust disease. Conversely, different strains of flax are resistant or
For Mendel's data shown in Figure 2.8, conduct a chi square analysis to determine if the data agree with Mendel's law of independent assortment.
Consider this cross in pea plants: Tt Rr yy Aa X Tt rr Yy Aa, where T = tall, t = dwarf, R = round, r = wrinkled, Y = yellow, y = green, A = axial, a = terminal. What is the expected phenotypic
A cross was made between two pea plants, TtAa and Ttaa, where T = tall, t - dwarf, A = axial, and a = terminal. What is the probability that the first three offspring will be tall with axial flowers
If a diploid cell contains six chromosomes (i.e., three per set), how many possible random arrangements of homologs could occur during metaphase of meiosis I?
A cell has four pairs of chromosomes. Assuming that crossing over does not occur, what is the probability that a gamete will contain all of the paternal chromosomes? If n equals the number of
With regard to question C13, how would the phenomenon of crossing over affect the results? In other words, would the probability of a gamete inheriting only paternal chromosomes be higher or lower?
Eukaryotic cells must sort their chromosomes during mitosis so each daughter cell receives the correct number of chromosomes. Why don't bacteria need to sort their chromosomes?
Why is it necessary for the chromosomes to condense during mitosis and meiosis? What do you think might happen if the chromosomes were not condensed?
Nine-banded armadillos almost always give birth to four offspring that are genetically identical quadruplets. Explain how you think this happens.
A diploid species has four chromosomes per set for a total of eight chromosomes in its somatic cells. Draw the cell as it would look in late prophase of meiosis II and prophase of mitosis. Discuss

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