Question

microbial growth - effects of ph

what is your prediction for this experiment?
a. an organism will grow at the same rate but only across a narrow range of ph levels.
b. an organism will grow equally well at all levels between ph 3 and ph 11.
c. an organism will have varied growth at different ph values with fastest growth at an optimum ph.

what is your strategy?
a. inoculate a ph 3 broth and look for growth, then transfer the culture to a ph 5 broth, to a ph 7 broth, to a ph 9 broth, and finally a ph 11 broth.
b. inoculate a ph 7 broth to verify growth at a neutral ph, then transfer the culture to a ph 3 broth and a ph 5 broth to check for acidophiles. if no growth, transfer from the ph 7 tube to a ph 9 broth and a ph 11 broth to check for alkaliphiles.
c. inoculate ph 3, ph 5, ph 7, ph 9 and ph 11 broths with the same organism and determine the growth in each.

Explanation:

Analyze the prediction question

The first question asks: "What is your prediction for this experiment?"

• Option A states that an organism will grow at the same rate but only across a narrow range of pH levels, which is biologically incorrect because growth rates vary across a pH range.
• Option B states that an organism will grow equally well at all levels between pH 3 and pH 11, which is incorrect because microbes have specific pH optima and ranges.
• Option C states that an organism will have varied growth at different pH values with fastest growth at an optimum pH, which correctly describes microbial growth characteristics.

Analyze the strategy question

The second question asks: "What is your strategy?"

• Option A describes a sequential transfer strategy starting from pH 3, which is inefficient and introduces confounding variables.
• Option B describes a conditional transfer strategy starting from pH 7, which is also sequential and inefficient.
• Option C describes inoculating pH 3, pH 5, pH 7, pH 9, and pH 11 broths with the same organism simultaneously and determining the growth in each, which is the correct parallel experimental design to determine pH range and optimum.

Answer:

Question 1

• A. An organism will grow at the same rate but only across a narrow range of pH levels.
• B. An organism will grow equally well at all levels between pH 3 and pH 11.
• C. An organism will have varied growth at different pH values with fastest growth at an optimum pH. (Correct answer)

Question 2

• A. Inoculate a pH 3 broth and look for growth, then transfer the culture to a pH 5 broth, to a pH 7 broth, to a pH 9 broth, and finally a pH 11 broth.
• B. Inoculate a pH 7 broth to verify growth at a neutral pH, then transfer the culture to a pH 3 broth and a pH 5 broth to check for acidophiles. If no growth, transfer from the pH 7 tube to a pH 9 broth and a pH 11 broth to check for alkaliphiles.
• C. Inoculate pH 3, pH 5, pH 7, pH 9 and pH 11 broths with the same organism and determine the growth in each. (Correct answer)