3.8 Transport In Plants - Phloem Flashcards
Phloem Properties
- Transports water and food
Movement in two ways - Composed of sieve element cells which connect to form a tube
- Connecting sieve cells share a highly perforated sieve plate
- Supported by companion cells that help with loading/unloading
- Movement of sap is mediated by hydrostatic pressure from xylem
What is Phloem?
Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to the rest of the plant
Sieve Elements Properties
Limited cytoplasm, few mitochondria/other organelles, no nucleus
What is Phloem?
Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to th
What is Phloem?
Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to th
How are sieve Elements connected to the companion cell
By a pore called the plasmodesmata
Source
The production of the compounds to be transported (Leaves)
Sink
Rapidly growing tissues and organs; storage; non-photosynthetic regions (Fruit, Flowers, Roots)
Active Loading at the Source
- Glucose produced from photosynthesis is converted into sucrose for transport
- Sucrose actively transported (ATP) from leaf mesophyll into Phloem
- Increases concentration of sucrose inside phloem
- Called phloem loading
Sucrose
- disaccharide (more energy efficient than glucose)
- more stable/less reactive than glucose (easier transport)
Translocation Process
- Increase in sucrose concentration causes water to move into phloem from xylem by osmosis
- Influx of water increases the hydrostatic pressure inside phloem, causing contents to move to a lower pressure area (Sink)
Translocation Definition
Movement of sucrose from one location to another in the plant
Unloading at the Sink
- Sucrose moves via facilitated diffusion into cells
- Sucrose can be used in metabolism or stored
- Water moves back into xylem via osmosis as concentration decreases
- Pressure at sink always lower than at source
Phloem Function
Transport of carbohydrates and amino acids in both directions (to leaves and to roots)
Aphids
Insects used to measure phloem transport
Phloem Structure
- Sieve elements are elongated and narrow to form sieve tubes
- Sieve plates connect the elements
- Sieve tubes are associated with a companion cell that assists with loading of nutrients and transport
Stylets
Sucking mouthpart of aphids
- Stylets pierce phloem tubes and suck out sucrose-rich sap
Explain Aphid experiment
- Scientists attach aphids to different locations on the stem, euthanize them, then remove body, leaving style embedded in phloem
- Expose plants to radioactive carbon, that gets incorporated in sucrose transport
- Concentration of sucrose made from radioactive carbon can be measured at different locations
- Rate of tranlocation estimated based on this
Radioactive Carbon
C-14
