AP Biology: Chapter 9 SI, Chapter 10-10.4 #1-2, Chapter 10 SI

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Chapter 9 SI: In the 1940s some physicians prescribed low doses of a drug called dinitrophenol (DNP) to help patients lose weight. This unsafe method was abandoned after a few patients died. DNP uncouples the chemiosmotic machinery by making the lipid bilayer of the inner mitochondrial membrane leaky to H+. Explain how this causes weight loss.

In chemiosmosis the electrons from NADH are passed along an electron transport chain. As the electrons are passed along, their energy is used to pump protons across the inner mitochondrial membrane. This is a gradient of protons; the protons can come back across the membrane through an enzyme called ATP synthase “energy production.” If the membrane was leaky, which means many of the hydrogens are leaking back across, energy cannot be made properly therefore halting the production of energy. No energy = no calories = losing weight.

Chapter 10 – 10.4 #1-2

  1. Explain why photorespiration lowers photosynthetic output for plants

Photorespiration is a consequence of the high oxygen content of the air, which leads to a competing oxidation reaction at the same site as fixation, resulting in loss of carbon and energy from the plant. With this is mind, oxygen will rise inside the plant and when it becomes too high the enzyme “rubisco” will fix oxygen in replace of carbon dioxide to RuBP. This scenario will not create G3P and the oxygen and RuBP will start to weary. Lacking G3P lowers photosynthetic output for plants.

  1. How would you expect the relative abundance of C3 versus C4 and CAM species to change in a geographic region whose climate becomes much hotter and drier?

C4 and CAM species would take over C3 species. C3 is notoriously poor in high light intensities and high temperatures because when C3 plants close their stomata(to prevent dehydration) they go into photorespiration where their photosynthetic output is reduced. This is terrible for the plant and may cause it to die. In this case we need something where the stomata are open at night and close during the day to survive this arid climate. C4 plants go though carbon fixation, where an enzyme called PEP carboxylase attaches only carbon dioxide to organic acid. In CAM species (similar to C4 species), carbon fixation and the use of PEP carboxylase occur at night. In CAM species the stomata opens at night and closes during the day. C3 plants make go through photosynthesis faster but it can not adapt to hot and arid climates unlike C4 and CAM species.

Chapter 10 SI: The diagram below represents the experiments with isolated chloroplasts. The chloroplast were first made acidic by soaking them in a solution at ph 4. After the thylakoid space reached ph 4, the chloroplasts were transferred to a basic solution at ph 8. The chloroplasts then made ATP in the dark.

In this experiment the chloroplast went from an acidic solution at ph 4 to a basic solution at ph 8. The reason the chloroplasts made ATP in the dark was that it had a great concentration of hydrogen ions (because the ph is low). In other words, you would expect a greater concentration of hydrogen ions when the chloroplasts immerses in ph 4.

These ions would also be expected to flow back across the membrane to drive an ATP synthase. No light equals no photo system two activity, which equals no pumping of hydrogen ion. The low pH is substituting for the lack of a photo system two proton pumping mechanism.


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