Lifesci 15 Midterm

Chapter 1 Short Answer:

In nationwide advertisements, the Dannon Company claimed that its Activia yogurt relieved irregularity and helped with “slow intestinal transit time.”

Dannon also claimed that its DanActive dairy drink helped prevent colds and flu.

These claims were based on no evidence.

How would you design an experiment to try to test these statements?

Two claims were made, requiring two double-blind experiments, because only one variable can be changed or tested at a time.

Experiment 1: Measure intestinal transit time (the time for consumed foods and other substances to travel through the digestive system) for two groups.

Group 1 (control group) does not receive Activia yogurt, but instead receives an inert yogurt substitute.

Group 2 (experimental group) receives Activia yogurt. Intestinal transit times are measured for both groups.

Neither the participants nor the administrators know which participants are consuming Activia and which are consuming the substitute. Data from group 2, the experimental group, are compared with data from group 1, the control group, to determine the effectiveness of Activia.

If the data show that intestinal transit time is shorter in the experimental group, the statement by the Dannon Company is supported.

Experiment 2: Determine whether DanActive dairy drink helps prevent colds and flu, again using two groups.

Group 1 (control group) does not receive DanActive dairy drink, but instead receives an inert dairy drink substitute.

Group 2 (experimental group) receives DanActive dairy drink.

The incidence of colds and flu is measured over a finite period of time, such as one year, for the two groups—the same period of time for both groups. Neither the participants nor the administrators know which participants are consuming the DanActive dairy drink and which are consuming the substitute. Data collected from the experimental group are compared with data from the control group.

If the incidence of colds and/or flu is lower in the experimental group, the statement made by the Dannon Company is supported.

Chapter 1 Short Answer:

Scientific thinking can be distinguished from alternative ways of acquiring knowledge in that it is empirical. What does empirical mean, and how does it relate specifically to the study of biology?

Empirical refers to knowledge gathered through observations and experiments that are rational, testable, and repeatable.

Because the study of biology is concerned with phenomena in the natural world, it is appropriate that it is an empirical science.

In contrast to this empirical approach, knowledge can also be gained through reason, reflection, and observation in the absence of experimentation.

Chapter 1 Short Answer:

An especially important feature of scientific thinking is that it is a self-correcting process. What does self-correcting mean in this context?

Predictions are made based on a formulated hypothesis and are tested with experiments.

If a hypothesis is not supported by the experimental results, it can be revised, new predictions made, and these predictions tested with new experiments. Experiments can be repeated many times by many different scientists, and the hypothesis can again be revised and tested if conflicting results arise.

In this way, the scientific method, done properly, is selfcorrecting.

Chapter 1 Short Answer:

Describe something that you could not study scientifically.

When a phenomenon can be measured, it can be tested through experimentation.

To be testable by the scientific method, all examples would need to comply with this requirement.

If a phenomenon cannot be measured, it cannot be tested using the scientific method; examples include determining the existence of God or the beauty of a Shakespearean sonnet.

Chapter 1 Short Answer:

A researcher hypothesizes that the more a person exercises, the less acne he or she will have. Write the null hypothesis for this experiment.

The null hypothesis would state that exercise does not affect the amount of acne a person develops.

Chapter 1 Short Answer:

What would be a reasonable prediction for the hypothesis “Eating fresh fruit reduces the likelihood that you will get sick”?

The prediction would be that a group of people who eat fresh fruit will have a lower rate of illness than another group of people who do not consume fresh fruit.

Chapter 1 Short Answer:

Describe the key features of a critical experiment.

Key features of a critical experiment:

Treatment: The condition that is changed for members of the experimental group. It is the variable (e.g., temperature, pressure, light) that is changed to test a hypothesis. Only the experimental group experiences this treatment; otherwise, comparison with the control group will not be possible and the hypothesis cannot be properly evaluated.

Experimental group: The group that receives the treatment, which is the variable being manipulated to test the hypothesis.

Control group: The group for which all variables, with the exception of the treatment, are the same as for the experimental group. This makes it possible to determine differences between the experimental group and the control group that result from the variable being tested.

Variables: Characteristics that can be changed, such as temperature, light, pressure, or quantity and type of food, and can potentially elicit a change. Blind experimental design: For studies involving human beings, a study design in which the placebo effect and bias can be minimized by preventing members of the experimental group from knowing whether they are part of the experimental (treatment) or control group. However, the experimenters know who is a member of the experimental group or the control group.

Double-blind experimental design: For studies involving human beings, a study design in which the placebo effect and bias can be minimized by preventing members of the experimental and control groups and the experimenters from knowing who is part of the experimental (treatment) and control groups.

Randomized: The random selection of participants to be in either the experimental or control group.

Chapter 1 Short Answer:

Many claims have been made concerning the health benefits of green tea. Suppose you read a claim that alleges drinking green tea causes weight loss. You are provided with the following information about the studies that led to this claim:

• People were weighed at the beginning of the study.

• People were asked to drink two cups of green tea every day for 6 weeks.

• People were weighed at the end of the study.

• People who drank green tea for 6 weeks lost some weight by the end of the study. It was concluded that green tea is helpful for weight loss.

This study obviously had some holes in its design. Assuming no information other than that provided here, list at least four things that could be done to improve the experimental design.

Include a control group that does not drink green tea and instead drinks water or some other inert drink.

(b) Conduct this as a double-blind experiment.

(c) Include a large number of people who would be representative of the population advised to drink green tea as a weight-loss method.

(d) Stipulate a certain amount of green tea of the same brand to be consumed by study participants. (

e) Ensure that only one variable, green tea consumption, differs between the experimental and control groups. In neither group should participants alter their consumption of food and beverages or change their total calories burned or consumed.

(f) Perform a statistical analysis of collected data to determine whether weight loss is significant.

Chapter 1 Short Answer:

Following an experimental conclusion, what is a likely next step? Why?

If the experimental conclusion does not support the hypothesis, the hypothesis can be revised and retested.

If the hypothesis is supported by the experimental conclusion, the experiment can be repeated by other scientists.

This will ensure that the process is selfcorrecting. (Also important is the reporting of findings in professional science publications.

Chapter 1 Short Answer:

Compare and contrast the terms theory and hypothesis.

Both theories and hypotheses are attempts to understand a natural phenomenon——and can be revised as new information arises from research and experimentation.

A hypothesis is an idea that has been proposed but not yet widely tested.

Whereas a theory has been widely tested by many different scientists, with repeated results to support it.

Chapter 1 Short Answer:

Describe what is meant by a randomized, controlled, double-blind study.

Chapter 1 Short Answer:

The American Dental Association (ADA) recommends cleaning between teeth with dental floss once a day to reduce the likelihood of suffering from a condition called gingivitis, the early stage of gum disease. In a recently published review of 12 published studies on the effects of flossing, however, researchers have questioned whether flossing has any value.

What is the ADA’s hypothesis? What are the associated predictions? Propose an experiment and analysis you would conduct and describe how it would test this assertion.

Chapter 1 Short Answer:

How are statistical analyses used to analyze data?

Statistics can help scientists determine whether differences between the control and experimental groups are a result of chance or are due to the experimental variable (treatment).

Chapter 1 Short Answer:

You notice that all of the male students who signed up for French tutoring have blue eyes.

What conclusions can you draw from this observation using scientific thinking?

No conclusion can be drawn.

The fact that the male students who signed up for French tutoring have blue eyes could be due to chance or to some biological differences.

Without a randomized, controlled, double-blind experiment, there is no way to determine whether these observations result from chance.

Chapter 1 Short Answer:

You have heard that people from Scandinavia usually have blond hair and fair skin. Your roommate is from Sweden and he has darker hair and more olive skin.

Does this disprove the idea that Scandinavians are fair and blond? Why or why not?

This does not disprove the hypothesis that Scandinavians are usually fair-skinned and blonde.

There is a greater likelihood of people from this region being fair-skinned and blonde, but there will always be some people with genetic variation that includes darker skin and/or hair. This could result from variation within the population or migration of individuals into the area.

Chapter 1 Short Answer:

Describe the five major unifying themes in biology.

The study of life is unified by five themes. (

a) Evolution: Populations have the capacity to change over time. As a consequence of organisms’ ability to reproduce and of evolutionary change—the change in genetic characteristics of a population over time—populations may become better adapted to their environments. This accounts for the diversity of organisms and the unity among them.

(b) Structure and function: Across all levels of organization, the physical features of organisms are closely related to function.

(c) Information flow, exchange, and storage: Genetic information—instructions for biochemical, physical, and behavioral traits—is carried in all organisms and passed to their offspring. Its expression influences the organisms’ growth and functioning.

(d) Pathways and transformations of energy and matter: Within organisms, pathways of chemical reactions use energy to transform matter and enable growth, movement, reproduction, and other processes.

(e) Systems: Life is organized on many interconnected levels within individual organisms, including atoms, cells, tissues, and organs. And in the larger world, organisms themselves are organized into many levels: populations, communities, and ecosystems within the biosphere.

Chapter 1 Multiple Choice:

Science is…

B) Both a body of knowledge and an intellectual activity encompassing observation, description, experimentation, and explanation of natural phenomena.

Chapter 1 Multiple Choice:

Superstitions are…

D) irrational beliefs that actions not logically related to a course of events influence its outcome.

Chapter 1 Multiple Choice:

Empirical results…

C) Are based on observation

Chapter 1 Multiple Choice:

Which of the following statements is correct?

A) A hypothesis that does not generate a testable prediction is not useful.

Chapter 1 Multiple Choice:

The placebo effect…

A) Is the frequently observed phenomenon that people tend to respond favorably to any treatment

Chapter 1 Multiple Choice:

In controlled experiments…

A) One variable is manipulated while others are held constant.

Chapter 1 Multiple Choice:

If a researcher uses the same experimental setup as in another study, but with different research participants, the process is considered…

D) Replication

Chapter 1 Multiple Choice:

An independent variable…

A) Can cause a change in a dependent variable.

Chapter 1 Multiple Choice:

Statistical methods make it possible to…

B) Determine how likely it is that certain results have occurred by chance.

Chapter 1 Multiple Choice:

Anecdotal evidence…

E) Can seem to reveal links between two phenomena, but the links may not actually exist.

Chapter 1 Multiple Choice:

Which of the following issues would be least helped by application of scientific thinking?

D) Formulating public policy on euthanasia

Chapter 10 Short Answer:

Describe one benefit of conducting research on evolution in a population of short-lived species such as fruit flies.

Fruit flies reach maturity in about two weeks, so a scientist can study many generations during an experiment on starvation resistance. With an organism having a late age of maturity, it would require many years to complete a study such as the starvation resistance experiments.

Chapter 10 Short Answer:

Describe three commonly held Western beliefs about the natural world that were overturned in the 18th and 19th centuries.

It was commonly thought that

(a) as in the biblical account, the earth was only about 6,000 years old;

(b) the earth had not changed very much over time, with the exception of the occasional earthquake, flood, or volcanic eruption; and

(c) all species, including humans, were created at the same time, and species never change or die out.

Chapter 10 Short Answer:

How did Darwin’s time traveling around the world help him develop his ideas on evolution?

Darwin found many fossils that were very similar to species still living in the same area.

He also noticed that finches on the Galápagos Islands, which he assumed were all of the same species, had different physical characteristics on different islands.

Biologists at the Zoological Society in London later found that there were 13 different finch species.

All of these species closely resembled a single species of finch on the nearest mainland, in Ecuador.

Chapter 10 Short Answer:

What is evolution?

Evolution is a genetic change in a population over time.

A change in allele frequency in the population occurs as a result of natural selection, mutations, genetic drift, and/or migration

Chapter 10 Short Answer:

What does it mean when fixation for an allele occurs in a population?

Fixation for an allele occurs as a result of genetic drift, when an allele frequency becomes 100% in a population.

As a result, there is no genetic variation for that gene. This can be detrimental because the population may be less able to adapt to environmental change.

Chapter 10 Short Answer:

Do recessive alleles tend to decrease in frequency in a population? Why or why not?

The frequency of a recessive allele does not change in a population as long as the allele does not affect reproductive success.

If a recessive allele does affect reproductive success, its frequency will change.

Recessive alleles that adversely affect reproduction will decrease in frequency, and those that improve reproductive success will increase in frequency.

Chapter 10 Short Answer:

Describe three important components to an organism’s evolutionary fitness.

Fitness is a measure of the reproductive success of individuals.

(a) An organism’s fitness depends on the environment in which it lives. The organism may be more fit in one environment, but less fit in another environment.

(b) Fitness is relative to that of other organisms in the same environment. The fitness of one individual is measured against that of other individuals with specific genotypes and phenotypes.

(c) The relative fitness of an individual is measured against that of other individuals of the same species in the same population. Those individuals that reproduce more frequently than others are more fit, irrespective of the age at which they die.

Chapter 10 Short Answer:

How does the increasing frequency of antibiotic-resistant strains of bacteria represent an example of evolution in progress?

The use of an antibiotic creates environmental pressure, and bacteria with one or more alleles imparting resistance to that antibiotic are more likely to reproduce than those that do not possess such alleles. Over time, bacteria with antibiotic-resistance alleles become more frequent in the population. Should another antibiotic be introduced, other alleles present in the population that impart resistance to that antibiotic will become more frequent over time.

Chapter 10 Short Answer:

In The Origin of Species, Charles Darwin wrote: “We may look with some confidence to a secure future of great length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.”

Give three reasons why he was wrong.

Natural selection requires time—sometimes more time than is allowed by the rate at which changes are occurring in the environment. The world’s environments are constantly changing and require continual evolutionary change if organisms are to maintain fitness. No single perfect organism for all environments will ever evolve. (b) Because mutations occur regardless of the needs of the organism, new mutations (i.e., new alleles) may not be those required for the organism to adapt to changes in its environment. (c) More than one allele may be suitable for selection in an environment, so there is no single optimal adaptation.

Chapter 10 Short Answer:

How does modern medicine alter the selective pressures on birth weight in humans?

Most babies weigh between 7 and 8 pounds at birth, as a result of stabilizing selection.

Modern medicine has enabled very-lowweight, premature babies to survive, and very large babies to be delivered through cesarean births.

This has prevented selection against extremes in the size of babies born, and greater numbers of babies of extreme size (small or large) may become more prevalent in the future.

Chapter 10 Short Answer:

Giving an example of each, compare and contrast homologous and analogous structures.

Analogous structures have similar functions and developed as a result of convergent evolution, forming from different starting materials in unrelated species. For example, the wings of insects, birds, and bats are all used for flying, but developed independently in each group of animals.

Homologous structures develop in related species in which the same structures are modified to perform different functions. An example is the modification of the bones making up the forelimbs of mammals. All mammals have a common ancestor, but the bones of the forelimbs have been modified for different functions, such as flying, swimming, and walking.

Chapter 10 Short Answer:

When evolutionary biologists speak of a “molecular clock, ” what do they mean?

A molecular clock is a way for biologists to determine how long two different species have been evolving separately.

The longer the two species have been evolving separately, the greater are the differences in their genetic sequences.

For example, humans and chimpanzees share many genes, whereas fruit flies and humans share much fewer genes.

Chapter 10 Multiple Choice:

Selecting for increased starvation resistance in fruit flies…

C) Can produce populations in which the average time to death from starvation is 160 hours.

Chapter 10 Multiple Choice:

Which of the following statements about mutations is incorrect?

E) All of these statements are correct.

Chapter 10 Multiple Choice:

In a fish population in a shallow stream, the genotypic frequencies of yellowish-brown fish and greenish-brown fish changed significantly after a flash flood randomly swept away fish from the stream.

This change in genotypic frequency was most likely attributable to…

A) Gene flow

Chapter 10 Multiple Choice:

When a small group of individuals colonizes a new habitat, an evolutionary event is likely to occur, because…

E) Small founding populations are rarely genetically representative of the initial population.

Chapter 10 Multiple Choice:

“Survival of the fittest” may be a misleading phrase to describe the process of evolution by natural selection because…

B) Survival matters less to natural selection than does reproductive success.

Chapter 10 Multiple Choice:

Adaptations shaped by natural selection:

C) May be out of date, having been shaped in the past under conditions that differed from those in the present.

Chapter 2 Multiple Choice:

In a population in which a trait is exposed to stabilizing selection:

D) The average value for the trait stays approximately the same, and the variation for the trait decreases.

Chapter 10 Multiple Choice:

Maze-running behavior in rats…

B) Is a heritable trait.

Chapter 10 Multiple Choice:

What can be concluded from comparing differences in molecular biology among different species?

D) Genetic similarities and differences demonstrate species relatedness.

Chapter 10 Multiple Choice:

Evolution…

C) Is responsible for the increased occurrence of antibiotic-resistant bacteria

Chapter 9 Short Answer

Why do offspring resemble their parents?

Offspring usually resemble their biological parents because they receive genes from their parents.

Genes code for traits that determine physical characteristics that parents and offspring may share.

Chapter 9 Short Answer

What was Mendel hoping to understand from his research on pea plants? How did he design his experiment to accomplish his goals?

Gregor Mendel wanted to understand how traits are passed from one generation to the next. For his research, he chose easily observable traits that he could categorize and count, in organisms (pea plants) that he could manipulate experimentally to understand their patterns of inheritance.

Chapter 9 Short Answer

Why does a sperm or egg have only one copy of a gene?

The cells of diploid organisms, with the exception of gametes, have two copies (alleles) of each gene, one allele on each of a pair of homologous chromosomes. For offspring to inherit the same (diploid) number of chromosomes and genes, they must receive only one copy in each parent’s gamete. The two gametes combine to form a diploid zygote.

Chapter 9 Short Answer

Compare and contrast the terms phenotype and genotype

Phenotype describes the expression of alleles as physical, physiological, or behavioral characteristics. Genotype describes the alleles an organism has inherited, which determine the phenotypes expressed.

Chapter 9 Short Answer

In what situation is a test-cross helpful in determining an individual’s genotype?

If an individual exhibits a dominant trait but has an unknown genotype, a test-cross can reveal the genotype (whether homozygous or heterozygous).

The individual is crossed with an individual that is homozygous recessive for the trait. If all the offspring express the dominant trait, the unknown genotype is homozygous dominant.

If half the offspring exhibit the recessive trait and half exhibit the dominant trait, the individual with the unknown genotype must be heterozygous for that trait

Chapter 9 Short Answer

What does it mean to be the carrier of a trait?

A “carrier” is an individual who carries one copy of a recessive allele, which is not expressed in the phenotype.

There is no outward evidence that the individual is carrying the recessive allele

Chapter 9 Short Answer

Describe the phenotype of an individual heterozygous for an allele with incomplete dominance.

In incomplete dominance, an individual that is heterozygous for a trait expresses a phenotype intermediate between the phenotypes associated with the two alleles

An example is the snapdragon flower.

If a true-breeding red-flowered plant is crossed with a true- breeding white-flowered plant, all their offspring have pink flowers —intermediate between red and white

Chapter 9 Short Answer

Describe why being heterozygous for the sickle-cell allele can confer resistance to malaria.

An individual who is heterozygous for the sickle-cell allele has resistance to malaria because the parasite that causes malaria does not survive well in sickled cells, the red blood cells with the defective hemoglobin.

Chapter 9 Short Answer

Why are sex-linked recessive traits more commonly observed in males than in females?

Both the X and Y chromosomes are sex chromosomes. There are many more genes on the much larger X chromosome, with no corresponding alleles on the Y chromosome. If a recessive allele on the X chromosome is inherited by a male (XY), that allele will always be expressed.

Chapter 9 Short Answer

How does the case of PKU support the notion that our phenotype is a product of our genotype in combination with the effect of our environment?

An individual with PKU inherits a defective allele for an enzyme needed to convert phenylalanine to tyrosine; in such an individual, phenylalanine builds up in cells, eventually increasing to toxic levels. If the person modifies his or her diet—that is, modifies the environment—to largely exclude phenylalanine, this amino acid will not increase to toxic levels in the body.

Chapter 9 Short Answer

What is Mendel’s second law? Why doesn’t it apply for all traits?

Mendel’s second law states that allele pairs separate independently during the formation of gametes

However, this is not true for traits determined by alleles located on the same chromosome, especially if they are close together.

When a chromosome is inherited, groups of alleles, especially those found close together, are inherited together

Chapter 9 Short Answer

The more closely two genes are located on a chromosome, the less likely it is that alleles for those genes will be inherited independently. Why?

During meiosis, only one of the two copies of each chromosome ends up in a gamete. That copy is from either your mother or your father.

All of the alleles on the chromosome from one parent get passed on as a group to the child at fertilization. The alleles for those genes remain together unless, during meiosis, recombination occurs, exchanging one or more alleles with the other chromosome in the pair so that they now become linked with the alleles on that chromosome.

The closer two genes are on a chromosome, the less likely it is that a recombination event will occur between them, splitting up the maternal and paternal alleles.

Chapter 9 Multiple Choice:

Most genes come in alternative forms called…

A) Alleles

Chapter 9 Multiple Choice:

All of the following are accurate descriptions of why pea plants were well suited for Mendel’s breeding experiments except…

E) Pea plants have a particularly long generation time.

Chapter 9 Multiple Choice:

The law of segregation states that…

D) The two alleles for a given trait segregate into different gametes.

Chapter 9 Multiple Choice:

In pea plants, purple flower color is dominant to white flower color. If two pea plants that are true-breeding for purple flowers are crossed, in the offspring…

A) All of the flowers will be purple

Chapter 9 Multiple Choice:

A test-cross….

D) Choices a, b, and c are correct.

Chapter 9 Multiple Choice:

All of the offspring of a black hen and a white rooster are gray. The simplest explanation for this pattern of inheritance is…

C) Incomplete dominance

Chapter 9 Multiple Choice:

A woman with type B blood and a man with type A blood could have children with which of the following phenotypes?

E) A, B, AB, or O

Chapter 9 Multiple Choice:

A rare X-linked dominant condition in humans, congenital generalized hypertrichosis (CGH), is marked by excessive hair growth all over a person’s body. Which of the following statements about this condition is incorrect?

D) Every son of a woman with CGH will have this disorder.

Chapter 9 Multiple Choice:

Individuals carrying two nonfunctioning alleles for the gene producing the enzyme that converts phenylalanine into tyrosine…

B) May or may not develop PKU symptoms, because diet also plays a role in determining their phenotype.

Chapter 9 Multiple Choice:

Thousands (or even tens of thousands) of different traits make up an individual. For this reason…

A) In a species with 23 different chromosomes, some traits must be coded for by genes on the same chromosome.