Ch 29: Resource Acquisition - Nutrition and Transport in Vascular Plants

Question 1

Explain why plants need nutrients

Answer 1

Nutrients are essential elements that plants use for growth, development and reproduction. Plants need a balanced source of nutrients to support growth.

Question 2

Define bulk flow

Answer 2

Bulk flow isthe movement of a mass of fluid that is due to the presence of a pressure gradient

Question 3

Describe the movement of water in the xylem (what is the driving force, how does it work, and which way do things move) (Cohesion-water hypothesis)

Answer 3

• Negative pressure (tension) created by evaporation of water from the leaves (transpiration) provides the pulling force
• Hydrogen bonds between water molecules (cohesion) transmits this tension throughout the xylem

Question 4

Describe the movement of materials in the phloem (what is the driving force, how does it work, and which way do things move)

Answer 4

• Bulk flow through the phloem is due to positive pressure
  
  • Turgor pressure in the phloem is high because water is drawn in by osmosis as sugars are added to the phloem
  • Pressure difference between source and sinks drives the movement of phloem sap
  • Turgor pressure in sink phloem is low because water flows out by osmosis as sugars exit the phloem and are utilized by sink cells

Question 5

NOTES

Answer 5

• In plant cells, the membrane potential (the voltage across the membrane) is established mainly through the pumping of H+by proton pumps rather than the pumping of Na+by sodium-potassium pumps as in animal cells. Also, H+is most often cotransported in plants, whereas Na+is typically cotransported in animals.
• As long as most stomata remain open, transpiration is greatest on a day that is sunny, warm, dry, and windy because these environmental factors increase evaporation.
• Human-made fertilizers usually supply mainly nitrogen, phosphorus, and potassium.
• Stomata open during the day in response to blue light triggering the uptake of K+by guard cells.