AP Biology : Understanding Bacteria

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Bacteria

Gram staining is a helpful technique for differentiating between different types of bacteria. What part of the bacterial envelope is exploited by the gram staining process?

Possible Answers:

The capsule

The plasma membrane

The peptidoglycan layer

The periplasmic space

Correct answer:

The peptidoglycan layer

Explanation:

The difference between gram-positive and gram-negative bacteria is the thickness of the peptidoglycan protein layer. Gram-positive bacteria have a thick peptidoglycan layer that retains the gram stain well, making it purple under a microscope. Gram-negative bacteria have a thinner peptidoglycan layer, and do not retain the stain as well as gram positive bacteria. This makes it pink when viewed under a microscope. 

Example Question #9 : Microorganisms And Viruses

Leukocytes are classified as either granulocytes or agranulocytes. Which of the following are granulocytes?

Possible Answers:

 Macrophages and lymphocytes

 T-cells and B-cells

 Basophils, eosinophils, and neutrophils

 Basophils

 Eosinophils and basophils

Correct answer:

 Basophils, eosinophils, and neutrophils

Explanation:

Leukocytes can be broken down into the following categories and cells types.

Example Question #1 : Understanding Bacteria

A cell placed in an environment in which there are more solutes outside the cell than inside the cell will __________ and is said to be in a __________  environment.

Possible Answers:

lyse . . . isotonic

swell . . . hypotonic

swell . . . hypertonic

shrivel . . . hypotonic

shrivel . . . hypertonic

Correct answer:

shrivel . . . hypertonic

Explanation:

We need to know the different between hypertonic, hypotonic, and isotonic. An environment is said to be hypertonic is there are more solute outside of the cell than inside. Since these solutes do not cross the cellular membrane very easily, but water can cross, water will travel out of the cell to balance the concentrations. This would cause the cell to shrink and shrivel.

The opposite is true for a hypotonic scenario, in which the cell will swell and maybe burst as water flows from the environment into the solute-filled cell. An isotonic environment is one in which solute concentrations are even, so there is no net movement of water into or out of the cell.

Example Question #1191 : Ap Biology

If a colony of round or oval-shaped bacteria are arranged in a random grape-like cluster, they must be:

Possible Answers:

Spirochetes

Staphylococci

Streptococci

There is no way to predict based on the information provided.

Streptobacilli

Correct answer:

Staphylococci

Explanation:

The two most common bacterial arrangements are Staph- and Strep-. Staph- is a non-symmetrical arrangement like a cluster of grapes. Strep- indicates a chain of bacteria.

The three most common bacterial shapes are listed below.

Coccus—round or oval

Bacillus—rectangular or rod-shaped

Spirilla (spirochete)—spiral

By breaking down names into arrangement and shape, students can predict or identify the appearance of an organism by its name. In the example Staph indicates arrangement in a chain. Coccus indicates round or oval in shape. Therefore, Staphylococci are round or oval-shaped organisms arranged in a cluster.

Example Question #12 : Microorganisms And Viruses

The aldehyde chemical family contains powerful microbial killing agents. Which bacterial structures do they effect?

Possible Answers:

Cytoplasm

Cell membranes

Cell walls

Ribosomes

Nucleic acids

Correct answer:

Nucleic acids

Explanation:

Aldehydes are powerful, toxic chemicals which work by denaturing DNA and RNA (nucleic acids).

Modern antibiotics are less toxic and work by disrupting cells' production of ribosomes. Common household cleaners, containing chlorine, work by oxidizing cell membranes. Older antibiotics, such as penicillin, work by dissolving cell walls. These modes of destruction are also known as mechanisms of cell death.

Example Question #5 : Understanding Bacteria

Which of the following would be considered a lethal means of controlling bacterial endospores?

Possible Answers:

None of these answers

Boiling

All of these answers

Freezing

Pasteurization

Correct answer:

None of these answers

Explanation:

Spores can survive most methods of control and are resistant to cold and heat. Pasteurization is a heating process that destroys some pathogenic microorganisms in foods and beverages, but does not kill spores. Boiling is not considered a reliable lethal control because the destruction of bacterial spores cannot be guaranteed. Cold temperature is a non-lethal means of microbial control that can slow multiplication or induce stasis, but cold is only effective while conditions are maintained.

Incineration is the use of extreme temperature to reduce matter to ash and is an effective means of sterilization.

Example Question #4 : Understanding Bacteria

Which of the following does not describe a detergent action against bacteria?

Possible Answers:

Removes lipids

Static control

Mechanical mode of action

Lethal control

Emulsification

Correct answer:

Lethal control

Explanation:

Detergents, or soaps, are non-lethal microbial controls. They emulsify lipids and oils, making it easier to wash them away. The action of washing away substances is strictly a mechanical mode of action. Detergents provide only static control, and have no killing power.

Example Question #2 : Understanding Bacteria

Which of the following can be found in prokaryotes, but never in viruses?

Possible Answers:

DNA

RNA

Ribosomes

Attachment proteins

Correct answer:

Ribosomes

Explanation:

Prokaryotes create their own proteins, which means that ribosomes are present in the cell. Viruses, however, rely on the ribosomes of the host cell in order to create proteins. This means that ribosomes are not present in viruses, but are present in prokaryotes.

DNA and RNA will both be found in prokaryotes. Some viruses will contain DNA, while others will contain RNA. Attachment proteins allow viruses to bind to cell membranes, but also can allow one cell to bind to another.

Example Question #4 : Understanding Bacteria

Bacterial ribosomes contain a __________ and __________ subunit. This forms a __________ ribosome.

Possible Answers:

40S . . . 60S . . . 80S

40S . . . 60S . . . 100S

30S . . . 50S . . . 70S

30S . . . 50S . . . 80S

Correct answer:

30S . . . 50S . . . 70S

Explanation:

Recall that bacterial ribosomes contain a 30S and a 50S subunit. The ribosome itself is a 70S ribosome, as the combination of the two subunits results in a smaller mass than the two separate units. Eukaryotic ribosomes contain a 40S and 60S subunit and form an 80S ribosome.

Example Question #5 : Understanding Bacteria

Which of the following statements is true regarding flagella?

Possible Answers:

Only bacterial flagella are made up of flagellin

Both bacterial and human flagella are made up of flagellin

Bacterial flagella are not used for mobility

Only human flagella are made up of flagellin

Correct answer:

Only bacterial flagella are made up of flagellin

Explanation:

Flagella are used for mobility by both prokaryotes (bacteria) and eukaryotes. In humans, you can find these structures in sperm cells, which are propelled by the motion of flagella. Similarly, bacterial cells move through the environment with the aid of flagella. The key difference between a bacterial and eukaryotic flagellum is its composition. Bacterial flagella are made up of a protein called flagellin, whereas eukaryotic flagella are made up of microtubules, formed from the protein tubulin.

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