BIO 311D Lecture Notes - Lecture 30: Tuber, Water Potential, Phloem
Document Summary
Mycorrhizae = symbiotic association with fungi and roots. Fungi absorb and passes water and nutrients to the plant. Nitrogen fixations: symbiotic relationships with bacteria, rhizobia. According to cohesion-tension hypothesis, transpiration and water cohesion pull water from shoots to roots. Xylem sap is normally under negative pressure, or tension. The movement of xylem sap against gravity is maintained by the cohesion-tension mechanism. Bulk flow is driven by a water potential difference at opposite ends of xylem tissue. Sugars are transported from sources to sinks via phloem. The products of photosynthesis are transported through phloem by the process of translocation. It travels from a sugar source to a sugar sink. Phloem sap is an aqueous solution that is high in sucrose. A sugar source is an organ that is a net producer of sugar, such as mature leaves.
