12.5 - Transport in Vascular Plants

Question 1

Passive vs Active Transport

Answer 1

Passive - uses concentration gradient & doesn’t require energy

Active - needs energy (ATP) as it goes against the concentration gradient

Question 2

Water Transport (Transport in Xylem)

1. Ground to roots

Answer 2

Water moves into the roots by osmosis (diffusion of water molecules across a selectively permeable membrane)

Nutrients move by active transport.

Water diffuses into epidermis, then cortex, then endodermis.

Endodermis regulates water flow through the roots. Endodermal cells are surrounded by the Casparian strip, wax-like and prevents water from diffusing back into cortex

Question 3

Water Transport (Transport in Xylem)

2. Roots to stem

Answer 3

Xylem sap moves up stem due to:

1. Root pressure (from osmosis force aka nutrients & water moving into roots)
2. Capillary action (attraction between water molecules allowing them to move together)

Question 4

Water Transport (Transport in Xylem)

3. Stem to leaves

Answer 4

Transpiration (evaporation of water through the stomata) from leaves pulls the xylem sap upward & is the main driving force of transport in xylem

Question 5

Sugar Transport (Transport in Phloem)

Source and Sink?

1. Source to Phloem

Answer 5

Sugar move from source (cells with high concentration of sugars) to sink (cells with low concentration of sugars)

• Sugars actively transported
• Water moves into phloem through osmosis (passive)

Question 6

Sugar Transport (Transport in Phloem)

2. During transport in phloem

Answer 6

Translocation - long-distance transport of substances through phloem. Caused by differences in pressure in phloem & sink cells

Question 7

Sugar Transport (Transport in Phloem)

3. Phloem to sink

Answer 7

Sugars diffuse from phloem (passive)

Water returns to xylem by osmosis (passive)