Homework Assignment 8: Photosynthesis In the space below show what happened duri
ID: 300840 • Letter: H
Question
Homework Assignment 8: Photosynthesis
In the space below show what happened during this experiment. With a drawing and phrases of explanation. Show where the new mass in the plant came from. Also show the specific types of energy conversions.
In photosynthetic organisms, the photosystems and ATP synthase are only able to make ATP when the light is shining. This is why these reactions have historically been called the light dependent reactions. However, scientists have found that if they extract thylakoids from plant cells and subject them to the experimental protocol described below, they can get them to produce ATP in the dark.
Experimental protocol:
The fluid in a thylakoid is usually at a pH of 7. In the experiment the thylakoids were made acidic by soaking them in a solution with a pH of 4. Then the thylakoids were placed in a solution with a pH of 8 and kept in the dark at which ATP began to be produced. How are these thylakoids producing ATP without light?
To answer this question, you will need to know that pH is a measure of H+ concentration in a solution. The chart below shows the H+ concentration that is associated with each of the pH values shown:
pH
H+ concentration
4
1 X 10-4 moles H+/L H2O
7
1 X 10-7 moles H+/L H2O
8
1 X 10-8 moles H+/L H2O
pH
H+ concentration
4
1 X 10-4 moles H+/L H2O
7
1 X 10-7 moles H+/L H2O
8
1 X 10-8 moles H+/L H2O
Explanation / Answer
At low pH, H+ ion concentration is very high so H+ ions transport inside the thylakoid membrane. After thylakoids were placed in a solution with a pH of 8 it has low H+ ion concentration in the medium. So H+ ions present in thylakoid membrane try to come outside to maintain the equilibrium. It comes outside from thylakoid membrane to stroma only through ATP synthease. When H+ ions passes through ATP synthease ATP will be synthesis so no light is required now to synthesis the ATP.
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