Questions 87-89 Four test tubes are required for this...

Questions $87-89$ Four test tubes are required for this experiment. All the tubes contain pond water and the pH indicator bromothymol blue, which turns yellow when acidic and blue in the neutral or basic range. Carbon dioxide is bubbled into all four test tubes, causing the solutions to turn yellow. Sprigs of the plant elodea are placed into test tubes I and III. Test tubes I and II are kept in the light; test tubes III and IV are kept in the dark. After 24 hours, all tubes are examined and the observations are recorded in the table below. $$\begin{array}{|c|c|c|}\hline \text { Test Tube } & {\text { Color at Time Zero }} & {\text { Color After } 24 \text { Hours }} \\ \hline \mathrm{I} & {\text { Yellow }} & {\text { Blue }} \\ \hline \text { II } & {\text { Yellow }} & {\text { Yellow }} \\ \hline\text { III } & {\text { Yellow }} & {\text { Yellow }} \\ \hline \text { IV } & {\text { Yellow }} & {\text { Yellow }} \\ \hline\end{array}$$ After 24 hours, tube I turned blue because the (A) plant excreted a by-product of cellular respiration, which has pH of 10 (B) plant excreted carbon dioxide as a result of carrying out cellular respiration (C) plant excreted oxygen as a result of carrying out cellular respiration (D) plant excreted oxygen as a result of carrying out photosynthesis (E) plant absorbed carbon dioxide to use in photosynthesis

Questions $87-89$ Four test tubes are required for this experiment. All the tubes contain pond water and the pH indicator bromothymol blue, which turns yellow when acidic and blue in the neutral or basic range. Carbon dioxide is bubbled into all four test tubes, causing the solutions to turn yellow. Sprigs of the plant elodea are placed into test tubes I and III. Test tubes I and II are kept in the light; test tubes III and IV are kept in the dark. After 24 hours, all tubes are examined and the observations are recorded in the table below.
$$\begin{array}{|c|c|c|}\hline \text { Test Tube } & {\text { Color at Time Zero }} & {\text { Color After } 24 \text { Hours }} \\ \hline \mathrm{I} & {\text { Yellow }} & {\text { Blue }} \\ \hline \text { II } & {\text { Yellow }} & {\text { Yellow }} \\ \hline\text { III } & {\text { Yellow }} & {\text { Yellow }} \\ \hline \text { IV } & {\text { Yellow }} & {\text { Yellow }} \\ \hline\end{array}$$
After 24 hours, tube I turned blue because the
(A) plant excreted a by-product of cellular respiration, which has pH of 10
(B) plant excreted carbon dioxide as a result of carrying out cellular respiration
(C) plant excreted oxygen as a result of carrying out cellular respiration
(D) plant excreted oxygen as a result of carrying out photosynthesis
(E) plant absorbed carbon dioxide to use in photosynthesis

Key Concepts

Carbon Dioxide Equilibrium

When carbon dioxide dissolves in water, it forms carbonic acid, which lowers the pH of the solution. Removing CO2 from the aqueous system through photosynthesis shifts this equilibrium, reducing the acid concentration and increasing the pH.

pH Indicators

pH indicators are substances that change color based on the pH of the solution. In this context, bromothymol blue is used, which appears yellow in acidic conditions and turns blue as the solution becomes more basic due to the reduction of carbonic acid when CO2 is absorbed.

Photosynthesis

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen. In aquatic environments, this process results in the uptake of carbon dioxide from the surrounding water, which can change the pH of the solution.

Light Dependence of Photosynthesis

Light dependence is a critical aspect of photosynthesis; plants require light to drive the reaction that consumes carbon dioxide. This dependency explains why a system in the light shows a different pH change compared to one kept in the dark.

Transcript

00:01 All right.

00:05 Question 90.

00:07 So the question that the students asked is how well ph influences enzyme activity.

00:22 So, enzyme activity basically means how well can an enzyme work at certain conditions? maybe it works better at certain temperatures or maybe better at certain ph levels.

00:35 And that is what the students are testing.

00:38 And specifically they're testing the enzyme that is named catalase.

00:46 And catalase basically helps a reaction go through to completion.

00:52 Let's start it with hydrogen peroxide.

01:00 And this is just water with an extra oxygen molecule.

01:05 And catalase can basically take this enzyme, put it through a reaction, into two molecules and an oxygen molecule and that's what happens when the enzyme is able to work on hydrogen peroxide test tubes 6 through 10 had water put in them they didn't have catalase so all the others 1 through 5 they all had catalase the enzyme we're looking at but 6 through 10 had water and this was added simply because they needed a control just to see that none of the test tubes were tampered with or there was no outside influence.

01:57 Just to know for sure that, yes, catalase was the only thing acting on the hydrogen peroxide.

02:02 So these are all control, and it's actually good that there were no bubbles in it.

02:15 So this is actually good.

02:20 Now, why is that good? well, bubbling was actually oxygen molecules.

02:25 So if you see an oxygen molecule, that means this reaction went through.

02:30 That means the catalase enzyme took this hydrogen peroxide, made it into oxygen that was in the form of air bubbles.

02:41 So air bubbles are good.

02:42 Air bubbles mean the reaction was carried through successfully...