Phloem and translocation

Question 1

what is translocation

Answer 1

the transport of organic molecules from source to skin in the phloem by mass transport

Question 2

what is the function of a companion cell

Answer 2

has organelles that perform metabolic functions that maintain sieve tube

Question 3

what occurs in the source of a plant

Answer 3

where the products of photosynthesis are produced e.g. leaf

Question 4

what is the roll of a transfer cell

Answer 4

specialised parenchyma that actively transports the products of photosynthesis to sieve tube

Question 5

what is the sink of a plant

Answer 5

where sugars are being used

Question 6

what are the adaptations of a transfer cell

Answer 6

• many infoldings of the cell wall and membrane
  increases surface area
• numerous plasmodesmata
  links cytoplasm with adjacent cells
• lots of mitochondria
  provide energy for the loading of solutes into the sieve tubes (for active transport)

Question 7

what is the process of translocation

Answer 7

1. sucrose is produced in the source by photosynthesis in the in leaf cells
2. transfer cells actively pump sucrose into phloem sieve tubes against a concentration gradient using ATP from respiration
3. high sucrose concentration in the sieve tube at the source
4. this draws water into the sieve tube by osmosis from adjacent xylem vessels which increases the hydrostatic pressure at the loading end of the sieve tube
5. fluid in the sieve tube flows from high to low hydrostatic pressure by mass transport
6. sucrose is actively unloaded using ATP into the sinks
7. water moves back into the xylem by osmosis which decreases hydrostatic pressure