CHAPTER 3 Test Your Knowledge
Driving Question 1
What structural features are shared by all cells, and what are the key differences between prokaryotic and eukaryotic cells?
By answering the questions below and studying Infographics 3.2, 3.3, and 3.4, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
What does the cell theory state?
The cell theory states that all living organisms are made of cells, and that all cells arise from existing cells.
Which of the following statements best explains why bacteria are considered living organisms?
a. They can cause disease.
b. They are made up of biological macromolecules.
c. They move around.
d. They are made of cells.
e. They contain organelles.
d
What are the two main types of cells found in organisms?
prokaryotic and eukaryotic
Which of the following is not associated with human cells?
a. cell membrane
b. ribosomes
c. DNA
d. cell wall
e. All of the above are associated with human cells.
d
Bacteria have _______ cells, defined by the ______.
a. prokaryotic; presence of a cell wall
b. eukaryotic; presence of organelles
c. eukaryotic; absence of a cell wall
d. prokaryotic; absence of organelles
e. eukaryotic; absence of organelles
d
Which of the following is associated with eukaryotic cells but not with prokaryotic cells?
a. cell membrane
b. cell wall
c. DNA
d. ribosome
e. nucleus
e
USE IT
According to the cell theory, all living organisms are made of cells. More specifically, what do all living organisms have in common? For example, do all living organisms carry genetic instructions? Do their cells all have a nucleus? What other features do they have in common?
Because all living organisms are made of cells, they all have a cell membrane surrounding cytoplasm. They all carry genetic instructions, in the form of DNA, that they can pass on to their cellular descendants during cellular reproduction. They all have ribosomes, and they all are built from the four classes of organic molecules: proteins, carbohydrates, lipids, and nucleic acids.
You find a single-cell organism with a cell wall in the soil of a forest—can this organism be an animal? Why or why not? Which of the following facts would convince you that the organism is a bacterium and not a plant?
a. The cell wall is made of cellulose.
b. The DNA is contained in a nucleus.
c. The cell wall is made of peptidoglycan.
d. a and b
e. b and c
This organism cannot be an animal because animal cells do not have cell walls. Choice c is convincing evidence that the organism is a bacterium and not a plant.
Driving Question 2
How do solutes and water cross membranes, and what determines the direction of movement of solutes and water in different situations?
By answering the questions below and studying Infographics 3.5 and 3.7, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
The two major components of cell membranes are _______ and ______.
a. phospholipids; DNA
b. DNA; proteins
c. peptidoglycan; phospholipids
d. peptidoglycan; proteins
e. phospholipids; proteins
e
If a solute is moving through a phospholipid bilayer from an area of higher concentration to an area of lower concentration without the assistance of a protein, the manner of transport must be
a. active transport.
b. facilitated diffusion.
c. simple diffusion.
d. any of the above, depending on the solute.
e. Solutes cannot cross phospholipid bilayers.
c
Consider the movement of molecules across the cell membrane.
a. What do simple diffusion and facilitated diffusion have in common?
b. What do active transport and facilitated diffusion have in common?
a: They both involve the movement of a solute across a membrane from an area of higher solute concentration to an area of lower solute concentration, without the input of any additional energy. b: They both require a transport protein in order to carry a solute across a membrane.
Water is moving across a membrane from solution A into solution B. What can you infer?
a. Solution A must be pure water.
b. Solution A must have a lower solute concentration than Solution B.
c. Solution A must have a higher solute concentration than Solution B.
d. Solution A and Solution B must have the same concentration of solutes.
e. Solution B must be pure water.
b
USE IT
Why does facilitated diffusion require membrane transport proteins while simple diffusion does not?
Facilitated diffusion requires membrane transport proteins because the solutes that move by facilitated diffusion are too large or too charged (or both) to cross a membrane by simple diffusion. The transport proteins “facilitate” the movement of these solutes across a membrane.
Sugars are large, hydrophilic molecules that are important energy sources for cells. How can they enter cells from an environment with a very high concentration of sugar?
a. by simple diffusion
b. by osmosis
c. by facilitated diffusion
d. by active transport
e. by using ribosomes
c
Many foods—for example, bacon and salt cod—are preserved with high concentrations of salt. How can high concentrations of salt inhibit the growth of bacteria? (Think about the high solute concentration of the salty food relative to the solute concentration in the bacterial cells. What will happen to the bacterial cells under these conditions?)
In a high-salt environment, water will leave the bacterial cells by osmosis (from the lower-solute-concentration bacterial cells to the higher-solute/high-salt environment in the food). This will cause the cytoplasm of the bacteria to shrivel within the cell wall, thus preventing their growth. This is true for most, but not all, bacteria—some bacteria have mechanisms that enable them to tolerate a high-salt environment.
MINI CASE
Marc, a first-year college student, starts out on a backpacking trip in southern New Mexico. It is September, so the daytime temperatures are quite high, and the desert air is very dry. He has a portable water filter to treat river and stream water that he finds on his planned route through the Gila wilderness. On the second day of his weeklong trip his water filter breaks. He is afraid of contracting giardiasis (a protozoal disease spread through water contaminated by animal feces) so he drinks only the small amount of water that he can boil on his camp stove at night. By the fifth night he is feeling weak and thirsty, and starts to hike out. He makes it to a local highway and collapses. A passing motorist calls 911 for an ambulance.
a. Given that Marc has sweat a lot, and that sweat causes the loss of more water than solutes, what has happened to the solute concentration of his blood as a result of his dehydration?
b. From the solute concentration of his blood, what is likely to be happening to his body cells that are in contact with his blood and related fluids (e.g., lymph and cerebral spinal fluid)?
c. The paramedics have available three saline solutions. One is a “normal” isotonic saline—0.9% NaCl. One is a hypertonic saline (3% NaCl). The last is a “half normal” saline (0.45% NaCl). Which one would you use to treat Marc? Why?
a: Marc has lost more water than solutes, so his blood now has a higher solute concentration than normal. b: Because his blood has a higher than normal solute concentration, cells in contact with the blood are likely to be losing water (by osmosis) and beginning to shrivel. c: Marc needs to have his blood volume restored, as well as his current concentration of solutes diluted (back to a normal concentration). This means that the “half normal” saline is probably the best bet. It will add volume, but because it has a lower than normal solute concentration, when it is added to his concentrated blood, it will cause the solute concentration to return to normal.
Driving Question 3
How do antibiotics target bacteria, and in what situations is antibiotic therapy indicated?
By answering the questions below and studying Infographics 3.1, 3.5 (bottom), and 3.6, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Penicillin interferes with the synthesis of ___________.
a. bacterial cell membranes
b. peptidoglycan
c. the nuclear envelope
d. membrane proteins
e. ribosomes
b
Would phospholipids of the cell membrane be a good target for an antibiotic? Explain your answer.
Phospholipids of the cell membrane would not be a good target for an antibiotic because human as well as bacterial cells have phospholipids in their cell membranes, and thus the proposed antibiotic would harm both bacterial and human cells.
USE IT
If a bacterial infection were treated with two different antibiotics, one that stopped bacterial reproduction and one (penicillin, for example) that inhibited the production of new peptidoglycan, would this use of penicillin or similar drug be effective? Explain your answer.
No. The use of the second antibiotic would not be effective in this situation. If the first antibiotic has stopped the bacteria from reproducing, then they are not synthesizing new cell wall material (peptidoglycan), and thus the second antibiotic would have no additional effect.
If bacterial cells were placed in a nutrient-containing solution (one that supports their growth) that had the same solute concentration as the cytoplasm, and which also contained penicillin, would the cells burst? Explain your answer. What if the same experiment were repeated with lysozyme? What if the two experiments were repeated in solutions that have lower solute concentrations than the cytoplasm, and did not contain growth-supporting nutrients?
In the case of bacteria growing in a solution with the same solute concentration as their cytoplasm, they would not burst, even though their newly made cell walls would be weak because of the exposure to penicillin. This is because there is no net flow of water into or out of the cells. In the second case (growing in the presence of lysozyme, which disrupts intact peptidoglycan), again, because the environment has a solute concentration that is the same as that of the cells, there is no net movement of water into or out of the cells. If the two experiments were repeated with solutions with lower solute concentrations than the cells, we would expect water to flow from the solution into the cells. Bacteria need a strong cell wall in order to survive the influx of water without bursting, but in this case, there are no growth-supporting nutrients, so the cells are not actually growing. If the cells are not growing, they are not synthesizing peptidoglycan, so penicillin will have no effect (it weakens peptidoglycan as it is being made). However, as lysozyme can digest intact peptidoglycan, the cell wall will be destroyed, and the cells will burst as the water flows in by osmosis.
Fungi are eukaryotic organisms. Scientists have found it more challenging to develop treatments for fungal infections (e.g., yeast infections, athlete’s foot, and certain nail infections) than for bacterial infections. Why is this so?
As both fungi and humans are eukaryotic organisms, they share many characteristics. This makes it hard to find a target that is present in fungi and not in humans. Many fungal structures are also present in human cells, so interfering with those structures will inhibiting growth of (or kill) the fungus, but will also inhibit (or kill) the human cells.
INTERPRETING DATA
Bacteria can be characterized as sensitive, intermediately resistant, or fully resistant to different antibiotics. If a strain of bacteria is sensitive to an antibiotic, we can prescribe that antibiotic to treat an infection caused by that strain and have confidence that it will work. If the strain is fully resistant to an antibiotic, that antibiotic cannot treat that infection. In cases of intermediate resistance, it is better to try and find an antibiotic to which the strain is sensitive, as the infection may not respond to antibiotics to which it has intermediate resistance.
The table shows the concentrations of antibiotics that determine how a bacterial species will respond to those antibiotics. A sensitive strain will be killed by the concentration of antibiotic shown in the “sensitive” column. A strain with intermediate resistance will only be affected by concentrations in the range indicated in the “intermediate” column. And a fully resistant strain requires concentrations shown in the “fully resistant” column.
The best option in this case is vancomycin. The strain appears to be resistant to all of the other antibiotics.
A hospital patient has a Staphylococcus aureus infection. As part of laboratory testing, the S. aureus from the patient was grown in different concentrations of various antibiotics. For oxacillin, the lowest concentration that inhibited the growth of the strain was 8 µg/ml; for vancomycin, 4 µg/ml; for erythromycin, 16 µg/ml; for tetracycline, 32 µg/ml; and for levofloxacin, 8 µg/ml. Which antibiotic should be used to treat the infection in this patient?
BRING IT HOME
Many patients attempt to pressure their physician to prescribe antibiotics for colds. Is this a good idea? Why or why not?
Antibiotics are not effective against colds because colds are caused by viruses. Antibiotics are not effective against viruses. Thus, using an antibiotic to treat a cold will not treat the cold and may increase the chance of antibiotic-resistant bacterial infections in the future.
Driving Question 4
What are some key eukaryotic organelles and their functions?
By answering the questions below and studying Infographic 3.8 and Up Close: Eukaryotic Organelles, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Briefly describe the structure and function of each of the following eukaryotic organelles:
a. mitochondrion
b. nucleus
c. endoplasmic reticulum
d. chloroplast
a: Mitochondria are rod-shaped organelles. They are surrounded by a double membrane (they have both an inner and outer membrane). They are important in the reactions that extract energy from food and convert it to an immediately usable form. b: The nucleus is a large organelle that stores the genetic instructions (DNA). The nucleus has a double membrane (the nuclear envelope) that has pores that permit the movement of molecules into and out of the nucleus. c: The endoplasmic reticulum is an extensive network of membrane tubes. The endoplasmic reticulum is connected to the nucleus and has a variety of critical functions in the cell, including protein synthesis, lipid synthesis, and drug detoxification. d: Chloroplasts are organelles found in plant cells. They are enclosed by a double membrane and appear green because of the pigments involved in photosynthesis. Photosynthesis is the process by which energy from sunlight and carbon dioxide from the air are used to synthesize sugars.
Which of the following is not a cytoskeletal fiber in eukaryotic cells?
a. macrotubules
b. intermediate filaments
c. microfilaments
d. microtubules
e. All of the above are cytoskeletal fibers.
a
Insulin is a protein hormone secreted by certain pancreatic cells into the bloodstream. Which of the following organelles are involved in the synthesis and secretion of insulin?
a. rough ER
b. Golgi apparatus
c. ribosomes
d. all of the above
e. a and c
d
USE IT
Some inherited syndromes, for example Tay-Sachs disease and MERF (myoclonic epilepsy with ragged red fibers), interfere with the function of specific organelles. MERF disrupts mitochondrial function. From what you know about mitochondria, why do you think the muscles and the nervous system are the predominant tissues affected in MERF? (Think about the activity of these tissues compared to, say, skin.)
Muscle and nervous tissue are both very active and require large amounts of energy. They rely on mitochondria to provide energy to power their activities. Thus, a condition (such as MERRF) that interferes with mitochondrial function will limit the amount of energy they can provide to cells, and active cells (such as muscle and nervous tissue cells) will not be able to carry out their normal functions. Less active cells will not be affected as dramatically because their energy demands are so much lower.
Which organelle would cause the most damage to cytoskeletal fibers in the cytoplasm if its contents were to leak into the cytoplasm?
a. smooth ER
b. nucleus
c. lysosome
d. Golgi apparatus
e. rough ER
c
Cystic fibrosis is an inherited condition that affects the lungs and digestive tract (see Chapter 11). In many people with cystic fibrosis, a membrane channel protein is found in the rough endoplasmic reticulum instead of the cell membrane. How could a cell membrane protein end up in the rough endoplasmic reticulum? (Hint: Look at the box about the cooperation of the nucleus, endoplasmic reticulum, and Golgi apparatus in Up Close: Eukaryotic Organelles.)
As the relevant protein is a membrane channel protein, it must pass through the rough endoplasmic reticulum and the Golgi apparatus. If this delivery system is impaired, the protein could be trapped in the rough endoplasmic reticulum and never reach the cell membrane and so be unable to fulfill its function; the result is symptoms of cystic fibrosis