Most water molecules take a one way trip up the xylem

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Unformatted text preview: irculatory systems. It’s important, though, to remember that there is no systematic circulation involved. Most water molecules take a one-way trip up the xylem vessels. Those that move into phloem by osmosis may be circulated, but this is a by-product of the main process, which moves sap in one direction or another in the phloem. Sap is moved from source to sink, and does not circulate. • Students are familiar with the idea that sugars are made in the leaves and stored in the roots. They sometimes forget, though, that the stored sugars must be moved to cells that need them. They may also not realize that sugars are stored in other parts of the plant besides the roots. Reading notes: • List and describe the four steps of mineral acquisition that occur in the roots. • Refer to figure 24-18, and explain the role of the Casparian strip. • Describe how fungi and bacteria help plants absorb nutrients. • Read the “Earth Watch” section, and summarize how plants help regulate water distribution on land. • Define “cohesion” and “tension.” Explain how cohesion and...
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