9.2: Phloem
Mission 1: Plant Highways, Exit 2: Phloem
Mission Objectives: You should be able to...
1. Analyze data from experiments measuring phloem transport rates using aphid stylets and radioactively-labeled carbon dioxide.
2. Identification of xylem and phloem in microscope images of stem and root.
3. Describe and explain the structure-function relationship of phloem sieve tubes.
Phloem tissue is found throughout plants, including stems, roots & leaves. Phloem are composed of sieve tubes, which are themselves composed of columns of specialized cells. Individual sieve tube cells are separated by perforated walls called sieve plates.
Phloem transports organic compounds throughout the plant. The transport of organic solutes in a plant is called translocation. Phloem links parts of the plant that need a supply of sugars and other solutes such as amino acids to other parts that have a surplus. See Table 1 on page 413. Sources are areas where sugars and amino acids are loaded into the phloem and sinks are areas where the sugars and amino acids are unloaded and used.
Image courtesy of Bioninja.
Mission Objectives: You should be able to...
1. Analyze data from experiments measuring phloem transport rates using aphid stylets and radioactively-labeled carbon dioxide.
2. Identification of xylem and phloem in microscope images of stem and root.
3. Describe and explain the structure-function relationship of phloem sieve tubes.
Phloem tissue is found throughout plants, including stems, roots & leaves. Phloem are composed of sieve tubes, which are themselves composed of columns of specialized cells. Individual sieve tube cells are separated by perforated walls called sieve plates.
Phloem transports organic compounds throughout the plant. The transport of organic solutes in a plant is called translocation. Phloem links parts of the plant that need a supply of sugars and other solutes such as amino acids to other parts that have a surplus. See Table 1 on page 413. Sources are areas where sugars and amino acids are loaded into the phloem and sinks are areas where the sugars and amino acids are unloaded and used.
Image courtesy of Bioninja.
Active transport is used to load organic compounds into phloem sieve tubes at the source. Sucrose is the most prevalent solute in tree sap. It is not as readily available for plant tissues to metabolize directly in respiration and therefore makes a good transport form of carbohydrate as it will not be metabolized during transport.
Phloem transport using aphid stylets. Aphids are insects that feed on the sap extracted from phloem. Their feeding tubes are called stylets. Pages 417-420 discuss aphid stylet experiments. Read and work your way through the DBQs.
Below is some sample data from Bioninja.
Below is some sample data from Bioninja.
Go here to compare and contrast phloem and xylem tissue. The below image comes from passmyexams.co.uk.
