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Nutrients213-page4 - 2 for cell respiration there are...

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Plant Nutrients and Soils - 4 How Do Plants Obtain Mineral Nutrients? Plants obtain their nutrient needs from air and substrate (generally soil). John Baptist van Helmont demonstrated in the 17 th century that increase in plant growth weight is primarily from water. He grew his famous willow tree for five years and weighed the soil and the plant at the beginning and at the end of five years. The soil lost just 0.06kg while the willow gained 76.8 kg. Van Helmont concluded that plants grew mostly from water. A century later, Stephen Hales established that air (CO 2 ) also provided materials for plant growth. Obtaining Gases from the Atmosphere The gases needed for plant growth, CO 2 (needed for photosynthesis) and O 2 , (needed by all living cells) are atmospheric gases. As we have discussed, CO 2 diffuses into the plant through open stomata. Excess oxygen produced in photosynthesis will diffuse out of the plant through stomata as well. Other Gas Exchange Mechanisms Since all living cells of plants also require O
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Unformatted text preview: 2 for cell respiration, there are mechanisms in plants for gas exchange besides stomata. Oxygen produced during photosynthesis does not diffuse to all parts of the plant. Substances will diffuse along the easiest route and gradient, and much oxygen is lost through stomata. However, plants have a number of ways to get oxygen to cells. Oxygen Routes • Primary growth stems have stomata in the stem epidermis. • Secondary growth stems have lenticels in the cork (bark) • Roots obtain oxygen by diffusion through the root epidermis, which is not cutinized. Oxygen competes with water for essential soil spaces, and water saturated soils may cause the roots to suffocate from lack of oxygen. • Submerged aquatic plants must obtain both CO 2 and O 2 from gases dissolved in water, and growth rates are generally lower, since amounts of O 2 and CO 2 are less in water than in the atmosphere....
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