Test: Conflicting Viewpoints in Biology - ACT MCQ

In the 17th century, scientists were just beginning to understand the circulatory system of the heart. The two following viewpoints are the two most popular theories of the day.

Scientist I The heart pumps blood through arteries and veins but the two systems are separate. They are similar, just as the senses of smell and taste are when observing food, but ultimately they are two separate systems which perform separate functions. Hot blood flows from the heart, through the arteries, and to the organs which consume the blood much as a human would consume nourishment to survive. Venous blood originates in the liver and follows the veins to the organs where it is similarly consumed.

Scientist II The arteries and veins are two parts of one system. Blood flows from the heart, around the body, and back into the heart through the veins like two sets of one way streets. The idea of two systems, each pumping blood to the organs is unreasonable. If the heart can pump 6 oz of blood per minute, then the liver would have to produce 540 pounds of blood per day. A simple measurement of a human’s weight shows how unlikely that solution is. The single circulatory system is far superior as it explains the function of the heart, the arteries, and the veins clearly.

Q. Why does Scientist I compare the arteries and veins to smell and taste?

Genes are hereditary units that are responsible for the phenotypes of an organism. Genes are the directions for the body. Genetic change exists when genes are altered from their previous form. Genes are made up of DNA, or deoxyribonucleic acid. DNA is made up of four bases- adenine, guanine, cytosine, and thymine. Genetic change can result from a variety of factors. Both scientists mentioned below agree on this basic information about genes. However, the scientists do not agree on the primary driving force behind genetic change.

Scientist 1

A mutation is a permanent change in the sequence of the DNA of a gene. There are several types of mutations—point mutations, silent mutations, frame mutations, and nonsense mutations. Mutations are very important because proteins are synthesized by reading the DNA sequence. If the DNA sequence is changed, the proteins transcribed from the DNA will be different proteins. Mutations directly and substantially change the genes by changing the sequence of the four bases. Therefore, mutations are the main factor when looking at genetic change.

Scientist 2 

Sexual reproduction is the biggest contributor to genetic change. New combinations of genes are created with every random union of a sperm and egg. During division of the sex cells, or meiosis, crossing over can occur. Crossing over describes the situation when the genes from one parent’s chromosome are traded with genes from the other parent’s chromosome. This results in new combinations of genes. Lastly, a phenomenon called independent assortment results from sexual reproduction. Independent assortment is the random assortment of chromosomes during reproduction. Therefore, by its random nature, sexual reproduction is the largest contributor to genetic change.

What information would weaken the viewpoint of Scientist 1?

Genes are hereditary units that are responsible for the phenotypes of an organism. Genes are the directions for the body. Genetic change exists when genes are altered from their previous form. Genes are made up of DNA, or deoxyribonucleic acid. DNA is made up of four bases- adenine, guanine, cytosine, and thymine. Genetic change can result from a variety of factors. Both scientists mentioned below agree on this basic information about genes. However, the scientists do not agree on the primary driving force behind genetic change.

Scientist 1

A mutation is a permanent change in the sequence of the DNA of a gene. There are several types of mutations—point mutations, silent mutations, frame mutations, and nonsense mutations. Mutations are very important because proteins are synthesized by reading the DNA sequence. If the DNA sequence is changed, the proteins transcribed from the DNA will be different proteins. Mutations directly and substantially change the genes by changing the sequence of the four bases. Therefore, mutations are the main factor when looking at genetic change.

Scientist 2 

Sexual reproduction is the biggest contributor to genetic change. New combinations of genes are created with every random union of a sperm and egg. During division of the sex cells, or meiosis, crossing over can occur. Crossing over describes the situation when the genes from one parent’s chromosome are traded with genes from the other parent’s chromosome. This results in new combinations of genes. Lastly, a phenomenon called independent assortment results from sexual reproduction. Independent assortment is the random assortment of chromosomes during reproduction. Therefore, by its random nature, sexual reproduction is the largest contributor to genetic change.

Q. The viewpoints of Scientist 1 and Scientist 2 both support what theory? 

Eukaryotic cells, cells that contain membrane-bound organelles and generally reside within multicellular organisms, contain DNA, or deoxyribonucleic acid, which is organized into chromosomes. DNA is a double-stranded nucleic acid that forms a double helix. The bases found within a DNA molecule are adenine (A), thymine (T), guanine (G), and cytosine (C). DNA is organized into functional units, called genes, that encode the basic traits and characteristics of living organisms. DNA can be replicated within the nucleus prior to cell division to ensure each daughter cell receives an identical copy of DNA. The central dogma of molecular biology states that DNA is transcribed to RNA which is then translated into protein. RNA, or ribonucleic acid, is a nucleic acid found in all cells that serves a messenger to carry the genetic code from DNA to produce a functional molecule, the protein. RNA is a single-stranded nucleic acid and consists of the bases adenine (A), uracil (U), guanine (G), and cytosine (C). RNA is translated into amino acids on the ribosome to produce a polypeptide chain, or a protein. There are two general hypotheses for the original evolutionary molecule. The “RNA world” hypothesis states that the original genetic molecule is RNA, and RNA was able to be translated into protein and reverse transcribed to produce DNA. Alternatively, the “DNA, RNA, and Protein World” suggests that DNA was the original genetic molecule and was responsible for subsequent production of RNA and protein.

Q. A new organism is identified and the only nucleic acid contained within its cells is RNA. Which hypothesis would be supported by such a finding?

Before modern technologies and experiments allowed scientists to understand different organisms' mechanisms of reproduction, numerous theories existed about how populations came to exist. Two scientists from the 1800s describe their theories. Here are their arguments.

Scientist I

Just like some plants come from seeds and others are capable of vegetative (asexual) reproduction, some animal organisms come from non-sexual reproduction as well. Maggots, for example, appear on rotting carcasses. It is clearly illogical to suggest that the dead animal created or gave birth to the maggots, as it is no longer alive and is therefore incapable of sexual reproduction. The only rational conclusion for the appearance of maggots is a spontaneous generation. This is similar to how, if one were to leave a bowl of broth in the open air for a week, it would turn cloudy from bacteria appearing in the liquid.

Scientist II

Animate objects cannot arise from inanimate objects. Even when plants perform asexual reproduction, daughter plants are still coming from parent plants. There is no other example in nature of a living organism spontaneously coming into being. It is true that we observe maggots on rotting carcasses, but that does not necessarily mean that the maggots came from the rotting carcass. Similarly, bacteria growing in broth do not necessarily come directly from the broth. If a living organism appears, then it must have come from another animate object, even if we did not witness it. It is more likely that these invisible organisms have come in through the air and we simply do not see them until they have had a chance to replicate in these locations.

Which of the following is a valid summary of Scientist II's argument against Scientist I?

Before modern technologies and experiments allowed scientists to understand different organisms' mechanisms of reproduction, numerous theories existed about how populations came to exist. Two scientists from the 1800s describe their theories. Here are their arguments.

Scientist I

Just like some plants come from seeds and others are capable of vegetative (asexual) reproduction, some animal organisms come from non-sexual reproduction as well. Maggots, for example, appear on rotting carcasses. It is clearly illogical to suggest that the dead animal created or gave birth to the maggots, as it is no longer alive and is therefore incapable of sexual reproduction. The only rational conclusion for the appearance of maggots is a spontaneous generation. This is similar to how, if one were to leave a bowl of broth in the open air for a week, it would turn cloudy from bacteria appearing in the liquid.

Scientist II

Animate objects cannot arise from inanimate objects. Even when plants perform asexual reproduction, daughter plants are still coming from parent plants. There is no other example in nature of a living organism spontaneously coming into being. It is true that we observe maggots on rotting carcasses, but that does not necessarily mean that the maggots came from the rotting carcass. Similarly, bacteria growing in broth do not necessarily come directly from the broth. If a living organism appears, then it must have come from another animate object, even if we did not witness it. It is more likely that these invisible organisms have come in through the air and we simply do not see them until they have had a chance to replicate in these locations.

An experiment is performed in which a bowl of broth containing bacteria is boiled and then left in the open air. After a day, the broth is observed to be cloudy. How might Scientist I explain this result?

Before modern technologies and experiments allowed scientists to understand different organisms' mechanisms of reproduction, numerous theories existed about how populations came to exist. Two scientists from the 1800s describe their theories. Here are their arguments.

Scientist I

Just like some plants come from seeds and others are capable of vegetative (asexual) reproduction, some animal organisms come from non-sexual reproduction as well. Maggots, for example, appear on rotting carcasses. It is clearly illogical to suggest that the dead animal created or gave birth to the maggots, as it is no longer alive and is therefore incapable of sexual reproduction. The only rational conclusion for the appearance of maggots is a spontaneous generation. This is similar to how, if one were to leave a bowl of broth in the open air for a week, it would turn cloudy from bacteria appearing in the liquid.

Scientist II

Animate objects cannot arise from inanimate objects. Even when plants perform asexual reproduction, daughter plants are still coming from parent plants. There is no other example in nature of a living organism spontaneously coming into being. It is true that we observe maggots on rotting carcasses, but that does not necessarily mean that the maggots came from the rotting carcass. Similarly, bacteria growing in broth do not necessarily come directly from the broth. If a living organism appears, then it must have come from another animate object, even if we did not witness it. It is more likely that these invisible organisms have come in through the air and we simply do not see them until they have had a chance to replicate in these locations.

Q. An experiment is performed in which a rotting carcass is vacuum sealed. After several weeks, no maggots are observed. The rotting carcass is removed from the vacuum seal, and several days later maggots are observed. Which theory does this best support?