Question

 

Part III: More Results

Bill and Fernando continued testing. Bill told Fernando about the water collection, the hailstorm, and the neighbor’s garden. Fernando thought about this, and wondered aloud, “You said the neighbor’s garden was put in late. I wonder if they might have sprayed an herbicide to kill the weeds before planting. If they did, this might explain why your grandparents’ garden is dying, particularly the plants on one side.” So they set out testing for herbicides in the dead plants and came up with the second most commonly used: atrazine.

1. How does the atrazine act to kill plants?
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2. Predict how this would affect both parts of photosynthesis. Be as detailed as possible, and include in your answer both of the main steps in photosynthesis.
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Part IV: The Reveal

The new neighbors were deeply apologetic and offered to share whatever fruits and vegetables they were able to grow. His grandparents took it well and we're lucky enough not to rely on the garden for food. However, it did get Bill thinking about how important photosynthesis is, not only to humans but to all life on earth.

1. In a paragraph or two, describe the importance of photosynthesis to life on earth.
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2. Bill also started thinking about the damage herbicides can cause if not used properly. In a paragraph or two, describe one to two of the dangers of atrazine in particular. Remember to cite your sources using APA Style.
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Answer 1

Question

Part III

1. Atrazine is a herbicide that inhibit the process of photosynthesis in the plants and therefore lead to the growth of the plant. Atrazine work by inhibiting one of the protein involve in the electron transport that take place during light reaction of the photosynthesis. Atrazine inhibit the process of photosynthesis by binding to the QB(plastoquinone) protein. This lead to the inhibition of process of electron flow from plastoquinone A to QB. This inhibition of electron flow lead to inhibition of light reaction of photosynthesis that lead to the death of the plant.

Figure: Inhibition of electron flow in PSII

2. Atrazine binds by inhibiting the electron flow from one protein to another in the photosystem II that are present in the thylakoid membrane of the chloroplast. The PSII get active during the light reaction of the photosynthesis. The inhibition of electron flow result in decreased synthesis of ATP and NADPH that are the product of light reaction. These two products : ATP and NADPH are the reactants of the Calvin cycle (dark cycle) and require to fix carbon dioxide into glucose. Therefore, products of light reaction are the substrate of dark reaction , so if light reaction is inhibited it lead to the inhibition of dark cycle of photosynthesis too.

Part IV

I. The photosynthesis is one of the most important process in the Earth. This process is able to convert solar energy into chemical energy using carbon dioxide and the water. This process is perform only by plants and some algae and known as autotrophic. It means they can prepare their food. Other organism like animals are dependent on plants for their food.

The photosynthesis is the primary source of energy in the Earth. Also, the photosynthesis is the only process that realease oxygen in the atmosphere which are used by animals and plants for performing the process of cellular respiration.

II. Atrazine is used as herbicides but it have severe side effects because it kill the normal plant also. Atrazine kill the plants by inhibiting the process of photosynthesis and specifically inhibiting the light reaction of the photosynthesis.

The light reaction inhibition further lead to non formation of ATP and NADPH that are substrate of the dark reaction of photosynthesis. Therefore, dark cycle get inhibited too and in this way photosynthesis is inhibited and lead to the death of the plant.