Topic 3---B- More Exchange and transport systems - 7. Transport in plants (phloem)

Question 1

What does the phloem transport?

Answer 1

dissolved substances around the plant to where they are needed

Question 2

Structure of the phloem

Answer 2

• sieve tube element form the tube for transporting solutes
• there is a companion cell for each sieve tube element which carry out living functions for sieve cells
• sieve plate

Question 3

What is translocation?

Answer 3

its the movement of solutes (amino acids and sugars like sucrose) to where they’re needed in the plant

Question 4

What does translocation move solutes from and to?

Answer 4

from source to sinks

Question 5

What is the source?

Answer 5

where the assimilates are produced so there is a High concentration there

Question 6

What is the sink?

Answer 6

its where assimilates are used up so there at a lower concentration there

Question 8

mass flow hypothesis

Answer 8

1. Sucrose is actively transported from source into sieve tube element (phloem) via companion cells
2. High concentration of sucrose in phloem at source creates a lower water potential
3. Water moves by osmosis from xylem to phloem down a water potential Gradient as its higher in the xylem
4. This creates a High hydrostatic pressure in the phloem at the source end
5. At the sink end solutes are removed from the phloem to be used up which increases the water potential inside the sieve tubes so water also leaves the tubes by osmosis lowering the pressure inside the sieve tines
6. Sucrose solution moves down pressure Gradient from source to sink

Question 9

Mass flow evidence

Answer 9

• if a ring of bark which includes the phloem is removed from a woody stem a bulge forms above the ring
• the fluid from the bulge has a higher concentration of sugars than the fluid from below the ring as sugars can’t move past the area where the bark has been removed