BSC 2011 Study Guide - Comprehensive Midterm Guide: Flowering Plant, Fern, Axillary Bud

• School: University of Florida
• Department: Biology - Biological Sciences
• Course: BSC 2011
• Professor: Norman Douglas, Nicole Gerlach, Todd Palmer

Document Summary

Xylem flows upward: moves water from roots to leaves, in cross section, xylem is in the center of stem, composed of tracheids, functions in water conduction, acts as strengthening rod, holding the plant erect in terrestrial environment. Phloem flows downward: sugars from leaves to roots, can be reversed if necessary, sieve cells. Depend on companion cells to provide needs. Have perforated ends in the cell wall: in cross section, surrounds xylem, mostly sucrose in solution. Sink cells- net usage of sugar (use more than made) Sucrose moves out and water moves back to the xylem. Gradient of solute potential and pressure potential needed for movement of phloem sap (translocation) is maintained. Actively load sucrose into companion cells: flows through plasmodesmata. Enters sieve tube elements which reduces their solute potential: water enters from xylem osmosis, increases turgor pressure which pushes sieve tube contents towards the sink. Leaves: flow rate can be very high, movement of phloem sap requires living cells.