Cells & Size
Which sequence lists objects from smallest to largest?
A. Human skin cell → bacterial cell → molecule
B. Bacterial cell → molecule → human skin cell
C. Molecule → bacterial cell → human skin cell
D. Bacterial cell → human skin cell → molecule
C. Molecule → bacterial cell → human skin cell.
Which statement is true of all living things?
A. They are made of one cell only.
B. They are made of cells.
C. They can be seen without a microscope.
D. They live only inside other organisms.
B. They are made of cells.
MODEL: Stage 1: many helpful bacteria, very little C. difficile. After antibiotics, Stage 2: fewer helpful bacteria. Several days later, Stage 3: few helpful bacteria, much C. difficile. After fecal transplant, Stage 4: many helpful bacteria, very little C. difficile.
Suppose the patient had not received a fecal transplant after Stage 3. What would most likely happen next?
A. Helpful bacteria would quickly return to their original numbers without treatment.
B. C. difficile would likely continue to outnumber helpful bacteria.
C. All bacteria would disappear from the gut.
D. The digestive system would stop functioning immediately.
B. C. difficile would likely continue to outnumber helpful bacteria.
DATA: Group A: no antibiotics; high helpful bacteria; no C. difficile infection. Group B: antibiotics only; low helpful bacteria; infection. Group C: antibiotics + fecal transplant; high helpful bacteria; no infection.
Which conclusion is best supported by the results?
A. Antibiotics permanently remove all bacteria.
B. Restoring helpful bacteria can reduce the likelihood of infection.
C. Harmful bacteria improve digestion.
D. Every microbiome contains identical bacteria.
B. Restoring helpful bacteria can reduce the likelihood of infection.
MODELS: Model A shows many helpful bacteria using food and space, and few C. difficile bacteria. Model B shows fewer helpful bacteria, more available food and space, and more C. difficile bacteria.
Which explanation is best supported by the models?
A. After antibiotics, remaining bacteria become larger and reproduce more quickly.
B. When antibiotics reduce helpful bacteria, more food and space become available for C. difficile to grow.
C. After antibiotics, the digestive system produces new helpful bacteria immediately.
D. After antibiotics, all bacteria stop competing for food and space.
B. Fewer helpful bacteria leave more food and space available for C. difficile.
A student says, “Cells and molecules are about the same size because neither can usually be seen without a microscope.” Which statement best evaluates the claim?
A. Correct: cells and molecules are the same size.
B. Incorrect: molecules are much smaller than cells.
C. Incorrect: molecules are larger than cells.
D. Correct: molecules are made of cells.
B. Molecules are much smaller than cells.
A scientist observes bacteria dividing into two new bacteria over time. What does this observation provide evidence for?
A. Bacteria are made of rocks.
B. Bacteria are living organisms.
C. Bacteria are larger than human cells.
D. Bacteria are molecules.
B. Bacteria are living organisms; division is reproduction.
MODEL: Stage 1: many helpful bacteria, very little C. difficile. After antibiotics, Stage 2: fewer helpful bacteria. Several days later, Stage 3: few helpful bacteria, much C. difficile. After fecal transplant, Stage 4: many helpful bacteria, very little C. difficile.
Which pattern best supports the idea that helpful bacteria help prevent C. difficile infections?
A. Helpful bacteria decrease after antibiotics.
B. C. difficile increases after antibiotics.
C. As helpful bacteria increase after the fecal transplant, C. difficile decreases.
D. The microbiome contains many kinds of bacteria.
C. Helpful bacteria increase after the transplant while C. difficile decreases.
DATA: Group A: no antibiotics; high helpful bacteria; no C. difficile infection. Group B: antibiotics only; low helpful bacteria; infection. Group C: antibiotics + fecal transplant; high helpful bacteria; no infection.
Why did scientists include Group B?
A. To make all groups identical.
B. To increase the amount of data.
C. To compare mice that received antibiotics with mice that also received a fecal transplant.
D. To prove the hypothesis was correct.
C. Group B allows comparison of antibiotics alone with antibiotics plus a fecal transplant.
Claim: “Fecal transplants help restore the normal functioning of the digestive system.” Which explanation best supports this claim?
A. They restore many helpful bacteria, allowing competition with C. difficile for food and space and helping normal digestive function.
B. They cause all bacteria to grow at the same rate.
C. They replace digestive-system cells with infection-resistant cells.
D. They remove harmful bacteria without affecting helpful bacteria already there.
A. Fecal transplants restore helpful bacteria that compete with C. difficile for food and space.
DATA: Group A: no antibiotics; high helpful bacteria; no C. difficile infection. Group B: antibiotics only; low helpful bacteria; infection. Group C: antibiotics + fecal transplant; high helpful bacteria; no infection.
Scientists observed bacteria under a microscope before and after treatment. Why was a microscope needed?
A. Bacteria are made of cells too small to see with the unaided eye.
B. Bacteria are made of molecules only.
C. Bacteria are larger than mouse cells.
D. Bacteria are not living organisms.
A. Bacterial cells are too small to see with the unaided eye.
Scientists describe the digestive system and microbiome as interacting systems. Which statement best explains this idea?
A. The digestive system provides food and space for bacteria, and bacteria help keep it healthy.
B. The digestive system changes bacteria into human cells.
C. Bacteria digest the digestive system.
D. Human cells and bacteria are the same type of cell.
A. The digestive system provides food and space; bacteria help keep it healthy.
MODEL: Stage 1: many helpful bacteria, very little C. difficile. After antibiotics, Stage 2: fewer helpful bacteria. Several days later, Stage 3: few helpful bacteria, much C. difficile. After fecal transplant, Stage 4: many helpful bacteria, very little C. difficile.
Claim: “A healthy microbiome helps prevent C. difficile infections.” Which observation provides the strongest evidence?
A. All stages show bacteria inside the large intestine, although numbers change.
B. Stage 2 shows fewer helpful bacteria before severe infection.
C. Stages 1 and 4 have many helpful bacteria and very little C. difficile; Stage 3 has few helpful bacteria and much more C. difficile.
D. Different colored circles allow the groups to be compared.
C. Stages 1 and 4 have many helpful bacteria and little C. difficile; Stage 3 shows the reverse.
DATA (helpful bacteria / C. difficile): Healthy: high / very low. After antibiotics: low / low. One week later: very low / high. After fecal transplant: high / very low.
Which claim is best supported by the data?
A. Antibiotics increase helpful bacteria.
B. Helpful bacteria help limit the growth of C. difficile.
C. C. difficile causes helpful bacteria to reproduce.
D. Helpful bacteria turn into harmful bacteria.
B. Helpful bacteria help limit the growth of C. difficile.
MODELS: Model A shows many helpful bacteria using food and space, and few C. difficile bacteria. Model B shows fewer helpful bacteria, more available food and space, and more C. difficile bacteria.
Claim: “A healthy microbiome helps protect the digestive system from C. difficile infections.” Which observation provides the strongest evidence?
A. Both models include helpful bacteria and C. difficile for comparison.
B. Both models show bacteria in the large intestine, but numbers change over time.
C. Both show food throughout the large intestine used by different bacteria.
D. Model A shows many helpful bacteria using food and space; Model B shows more C. difficile when helpful bacteria are fewer.
D. Many helpful bacteria use food and space in Model A; C. difficile is more abundant with fewer helpful bacteria in Model B.