Chapter 30.5

1. Chapter 30.5 How Do Organic Compounds Move Through Plants? AP Biology Spring 2011

2. Conducting Tubes in Phloem • Phloem: living vascular tissue with organized arrays of conducting tubes, fibers, and parenchyma cells

3. Conducting Tubes in Phloem • Sieve tube cells: alive at maturity and are interconnected side by side and end to end from the roots to the leaves • Companion cells: located next to sieve tubes and function to actively transport the products of photosynthesis into the sieve tubes

4. Conducting Tubes in Phloem • Carbohydrates are mainly stored as insoluble starch molecules that must be converted to more soluble carbohydrates • Such as sucrose before being transported throughout the plant

5. Translocation • Translocation: transport of sucrose and other compounds through phloem • Movement of molecules through phloem is from sources to sinks • Source: mostly leaves • Sink: flowers and fruits

6. Translocation • Observations of plant-sucking insects demonstrates that the sugary fluid in the phloem is under high pressure

7. Translocation • Pressure flow theory: translocation depends on pressure gradients • Solutes are loaded by active transport into the phloem from a source (ex. Leaves) • Water enters by osmosis due to increase in solutes • Pressure builds in sieve tubes pushing the sucrose-laden fluid out of the source, into the stems, and on the sink (ex. Fruit)