3.8 Transport In Plants - Phloem

Question 1

Phloem Properties

Answer 1

• 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

Question 2

What is Phloem?

Answer 2

Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to the rest of the plant

Question 2

Sieve Elements Properties

Answer 2

Limited cytoplasm, few mitochondria/other organelles, no nucleus

Question 3

What is Phloem?

Answer 3

Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to th

Question 3

What is Phloem?

Answer 3

Vascular tissue that transports the carbohydrates produced in photosynthesis, as well as amino acids, to th

Question 4

How are sieve Elements connected to the companion cell

Answer 4

By a pore called the plasmodesmata

Question 5

Source

Answer 5

The production of the compounds to be transported (Leaves)

Question 6

Sink

Answer 6

Rapidly growing tissues and organs; storage; non-photosynthetic regions (Fruit, Flowers, Roots)

Question 7

Active Loading at the Source

Answer 7

• 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

Question 8

Sucrose

Answer 8

• disaccharide (more energy efficient than glucose)
• more stable/less reactive than glucose (easier transport)

Question 9

Translocation Process

Answer 9

• 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)

Question 10

Translocation Definition

Answer 10

Movement of sucrose from one location to another in the plant

Question 11

Unloading at the Sink

Answer 11

• 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

Question 12

Phloem Function

Answer 12

Transport of carbohydrates and amino acids in both directions (to leaves and to roots)

Question 13

Aphids

Answer 13

Insects used to measure phloem transport

Question 13

Phloem Structure

Answer 13

• 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

Question 14

Stylets

Answer 14

Sucking mouthpart of aphids
- Stylets pierce phloem tubes and suck out sucrose-rich sap

Question 15

Explain Aphid experiment

Answer 15

• 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

Question 16

Radioactive Carbon

Answer 16

C-14