5.6. Transport in plants and animals

Question 1

What is capillary action?

Answer 1

movement of water from higher to lower water potential by attaching from one cell wall (cellulose fibres) to another – more efficient, no gradient or aquaporins needed – from the soil until it nearly reached the xylem

Question 2

What is the difference in water movement into the xylem when a plant is transpiring and when it is not transpiring?

Answer 2

1) When a plant is transpiring, xylem vessels are filled by sap under tension (that have a very low WP). This tension draws water into xylem vessels even though solute concentration is low.
2) When a plant is not transpiring (WP is not as low), root pressure is used. Water molecules cannot pass the barrier to capillarity outside of the xylem so endodermal cells pump mineral ions into the xylem, making the sap hypertonic (decreasing WP) so water molecules move inside by osmosis. This causes the pressure in xylem to rise and push sap up against the gravity (continues to climb due to capillary action due to adhesion to cellulose fibres and cohesion)

Question 3

When is root pressure used as a mechanism to move water?

Answer 3

a) At high atmospheric humidity
b) At night
c) In deciduous trees during winter

Question 4

Xylem adaptations for water transport:

Answer 4

1. Thick wall and lignification (providing structural support and strength to the plant) – walls are impregnated with a polymer called lignin (prevents the vessels from collapsing when pressure is low)
2. Lack of wall and cell components – end walls between adjacent cells are removed during xylem development (long continuous tubes)
3. Pores for entry and exit of water (wall is impermeable to water but it can move through pores)

Question 5

Phloem adaptations for translocation of carbon compounds

Answer 5

1. Phloem sap dissolves compounds (it flows due to a concentration gradient between sources and sink)
2. Cell walls not broken down completely as in xylem to withstand higher pressures
3. Thin, non-lignified cell wall
4. Companion cell (helps with loading, provide ATP for active transport) and plasmodesmata (cytoplasmic connection, sucrose-rich sap flows to adjacent sieve tube from the cell)
5. Sieve plate with pores through which phloem sap can flow in either direction but not in both directions simultaneously

Question 6

How are marine mammals are adapted for swimming (locomotion in viscous water)

Answer 6

1. Streamlining – animals shaped to minimize drag and resistance to motion by:
   - Shaped to be widest near the front and narrowest at the rear
   - Flippers, flukes and dorsal fin
   - Smooth body surface due to even blubber distribution and absence of hind limbs
   - Skin is hairless (friction reduced)
2. Adaptations for locomotion
   - Flippers (steering)
   - Tail flukes (increase thrust)
   - Dorsal fin (stability)
   - Blubber (buoyancy)
3. Adaptations for periodic breathing between dives
   - Airways can be closed during dives using nostrils or blowhole
   - Airways are reinforced with rings of cartilage pr smooth muscle to ensure ventilation can restart quickly after a dive