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Answer:
C. NAD⁺
Step-by-step explanation:
NADH is oxidized to NAD⁺ in Complex I of the Electron Transport Chain.
NADH ⟶ NAD⁺ + H⁺ + 2e⁻
The electrons continue through the Electron Transport Chain, and the NAD⁺ is used in three places during the Krebs Cycle.
(a) Isocitrate to oxalosuccinate
Isocitrate + NAD⁺ ⟶ oxalosuccinate + NADH + H⁺
(b) α-Ketoglutarate to succinyl-CoA
α-ketoglutarate + NAD+ + CoA → succinyl CoA + CO₂ + NADH
(c) Malate to oxaloacetate
Malate + NAD⁺ ⟶ oxaloacetate + NADH + H⁺
The NADH produced by these three reactions can then be used by Complex I in the Electron Transport Chain.
ATP provides CHEMICAL ENERGY to drive chemical reactions for the cell.
Explanation:
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For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/weathering/
Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering.
Once a rock has been broken down, a process called erosion transports the bits of rock and mineral away. No rock on Earth is hard enough to resist the forces of weathering and erosion. Together, these processes carved landmarks such as the Grand Canyon, in the U.S. state of Arizona. This massive canyon is 446 kilometers (277 miles) long, as much as 29 kilometers (18 miles) wide, and 1,600 meters (1 mile) deep.
Weathering and erosion constantly change the rocky landscape of Earth. Weathering wears away exposed surfaces over time. The length of exposure often contributes to how vulnerable a rock is to weathering. Rocks, such as lavas, that are quickly buried beneath other rocks are less vulnerable to weathering and erosion than rocks that are exposed to agents such as wind and water.
For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain.
