Question

1. at the end of the 24 hr incubation, why was the color of the btb solution in tube 7 different from the color of the btb solution in tube 8? in the absence of light, the elodea in tube 7 could not undergo:

a. photosynthesis, so it consumed less co₂ than did the elodea in tube 8
b. photosynthesis, so it consumed more co₂ than did the elodea in tube 8
c. cellular respiration, so it consumed less co₂ than did the elodea in tube 8
d. cellular respiration, so it consumed more co₂ than did the elodea in tube 8
support with evidence:

1. at the end of the 24 hr incubation, the student removed the snail from tube 6 and added 10 drops of a new solution, causing the color of the btb solution in the tube to change to blue. was the new solution more likely acidic or basic?

a. acidic, because the ph of the btb solution increased when the new solution was added
b. acidic, because the ph of the btb solution decreased when the new solution was added
c. basic, because the ph of the btb solution increased when the new solution was added
d. basic, because the ph of the btb solution decreased when the new solution was added
support with evidence:

1. the student had hypothesized that in the absence of photosynthesis and cellular respiration, light would break down the btb in the solution during the 24 hr incubation, causing the solution to become yellow. are the results of the experiment consistent with this hypothesis?

a. yes; the solution in tube 2 was yellow at the end of the 24 hr incubation.
b. yes; the solution in tube 5 was yellow at the end of the 24 hr incubation.
c. no; the solution in tube 2 was green at the end of the 24 hr incubation.
d. no; the solution in tube 5 was green at the end of the 24 hr incubation.
support with evidence:

1. suppose that an additional tube, tube 9, had been included in the experiment and that tube 9 contained a small fish, but no elodea or snail, and received the light treatment. at the end of the 24 hr incubation, would the color of the bromothymol blue solution in tube 9 more likely have been yellow or blue?

a. yellow, because the fish would have undergone photosynthesis, consuming co₂
b. yellow, because the fish would have undergone cellular respiration, producing co₂
c. blue, because the fish would have undergone photosynthesis, consuming co₂
d. blue, because the fish would have undergone cellular respiration, producing co₂
support with evidence:

Explanation:

• Question 2: Photosynthesis requires light. In the absence of light (Tube 7), elodea cannot perform photosynthesis. Photosynthesis consumes \(CO_2\). Since Tube 7 has less \(CO_2\) consumption (due to no photosynthesis) compared to Tube 8 (which has light and can perform photosynthesis), the BTB color differs.
• Question 3: BTB (bromothymol blue) is a pH - indicator. It turns blue in basic solutions. If adding the new solution made the BTB blue, the pH increased (became more basic).
• Question 4: If the hypothesis was that light breaks down BTB (in the absence of photosynthesis and respiration) causing yellow color. But if there are tubes (like Tube 2 which might be a control without the processes that affect \(CO_2\) in a non - light - breaking - BTB way) that are green (not yellow), the hypothesis is not supported.
• Question 5: Fish cannot perform photosynthesis. They perform cellular respiration which produces \(CO_2\). An increase in \(CO_2\) (from cellular respiration) makes the solution more acidic. BTB turns yellow in acidic solutions.

Answer:

• Question 2: A. Photosynthesis, so it consumed less \(CO_2\) than did the elodea in Tube 8
• Question 3: C. Basic, because the pH of the BTB solution increased when the new solution was added
• Question 4: C. No; the solution in Tube 2 was green at the end of the 24 hr incubation
• Question 5: a. Yellow, because the fish would have undergone cellular respiration, producing \(CO_2\)