Question

1.) During Phloem transport, which of the following occur at, or close to the SINK? Select all that apply

a. Sugars move out of sieve tubes by active transport.

b. Sugars move into sieve tubes by active transport.

c. Water moves from the xylem into the sieve tubes

d. Water moves from phloem into the xylem.

e. Solution in sieve tubes becomes hypertonic

f. Solution in sieve tubes becomes hypotonic.

g. Tugor pressure decreases

h. Tugor pressure increases

Answer 1

Phloem:

Phloem transports sugars produced from leaves to the other parts of the plants.

Phloem tissue is made of sieve tubes, companion cells, phloem fibers and parenchyma cells.

• Transportation in phloem is due to osmotic pressure gradient.
• Sieve pores in the sieve tubes are interconnected. The mass flow is achieved by the pressure gradient – tugor pressure.
• Sieve tubes are separated by plasma membrane of surrounding cells, higher solute concentration creates tugor pressure and water enter into the sieve tube through osmosis.
• Due to the increase and decrease of the tugor pressure between the sieve cells and companion cells the transportation takes place from one to another.
• The pressure is created by the accumulation of sugars from the leaves and it is released at its sinks. Sinks are parts which need energy root, fruit etc.

Close to the sink following takes place

a) Sugars move out of sieve tubes by active transport

Sugars through diffusion move out of sieve tube and enter into the sink

d) Water moves from the phloem into xylem

    After diffusion water which is left enters into the xylem tissue

f) Solution in sieve tube becomes hypotonic

    As the solutes move from the sieve tube into the sink, the sieve tube becomes hypotonic and the sink becomes hypertonic.

g) tugor pressure decreases.

   Tugor pressure decreases because the materials get transported into the sink and the pressure decreases.