Mario sets up an experiment to determine the source of the oxygen gas produced by photosynthesis. To determine this, he uses an isotope of oxygen called O-18. He labels the O-18 oxygen so he can follow its path through photosynthesis. Plant A is given carbon dioxide that contains the O-18 isotope. Plant B is given water that contains the O-18 isotope. When he examines the oxygen from both plants, only plant B produced O-18 oxygen. This indicates that the source of oxygen is water. The photosynthesis involves the transfer of electrons between the photosystem I and II. The water gets split into oxygen, hydrogen ions and electrons in the photosystem I. The electrons move to the photosystem II where the carbon fixation into sugars takes place. The plant A will have O-18 isotope in its synthesised sugar molecule, which gets stored inside it.
The substances that protect against oxidative stress and the resultant tissue damage at the cellular level is, option B. Antioxidants. Oxidation can cause imbalance in the body. Antioxidants are used to counteract the damage produced by free radicals. Good natural sources of antioxidants include fruits and vegetables.
The correct answer of the given question above would be NUTRIENT-POOR SOIL. The characteristic about the Tundra biome listed below that does not contribute to a reduction of carbon dioxide on earth is the nutrient-poor soil. Other choices for this question include permafrost, carbon dioxide sink and <span>plants and their trapped carbon dioxide are frozen in the earth. </span>
A) Cell wall (animal cells don't have these structures)
