Transport in Plants 9-3

Q: How do plants take in carbon?

As CO₂ through their leaves.

Q: How do plants obtain most of their hydrogen and oxygen?

Through their roots as H₂O.

Q: Which nutrients do plants absorb through their roots?

Nitrogen, phosphorus, and sulfur.

Q: What happens first in plant transport?

Roots absorb water and minerals from soil.

Q: What is xylem sap?

Water and minerals transported upward from roots to shoots.

Q: What is transpiration?

Water loss through stomata that pulls xylem sap upward.

Q: What gases exchange through stomata?

CO₂ enters; O₂ exits.

Q: What triggers sugar production in leaves?

Adequate sunlight.

Q: What is phloem sap?

Sugars transported from leaves to the rest of the plant.

Q: What gas exchange occurs at roots?

Roots take in O₂ and release CO₂ into soil air spaces.

Q: What is the direction of water movement with respect to water potential?

Water moves from higher to lower water potential.

Q: Water potential of soil, root, leaf, atmosphere?

Soil −0.3 MPa → root −0.6 MPa → leaf −0.8 MPa → atmosphere ~−95 MPa.

Q: What is capillarity?

Upward movement of water in narrow tubes

Q: What three forces contribute to capillarity?

Surface tension, adhesion, and cohesion.

Q: What is the apoplastic route?

Movement through cell walls and extracellular spaces.

Q: What is the symplastic route?

Movement through the cytoplasm via plasmodesmata.

Q: What is the transmembrane route?

Repeated crossing of plasma membranes between cells.

Q: What is the endodermis?

A selective barrier controlling entry into the vascular cylinder (stele).

Q: What is the Casparian strip?

Waxy belt blocking apoplastic flow of water/minerals into the stele.

Q: What are plasmodesmata?

Cytoplasmic channels connecting plant cells, lined with membrane.

Q: What does xylem transport?

Water and inorganic minerals from roots to shoots.

Q: Two forces moving water in xylem?

Root pressure (positive), cohesion-tension (negative).

Q: What is the cohesion-tension theory?

Transpiration creates tension that pulls water upward from roots.

Q: Step 1 of transpiration pull?

Water diffuses down its potential gradient (atmosphere has lowest Ψ).

Q: Step 2 of transpiration pull?

Water evaporates from menisci at air-water interfaces.

Q: Step 3 of transpiration pull?

Evaporation pulls water from mesophyll cells and xylem.

Q: Step 4 of transpiration pull?

Cohesion transmits tension through continuous water column.

Q: Step 5 of transpiration pull?

Tension pulls water from root cortex into xylem.

Q: Step 6 of transpiration pull?

Tension pulls water from soil into roots.

Q: Step 1 of sugar translocation?

Sugar is actively loaded into phloem companion cells → sieve tubes.

Q: Step 2 of sugar translocation?

Water enters sieve tubes, increasing turgor pressure.

Q: What is turgor pressure?

Force of water pushing against a cell membrane.

Q: Step 3 of sugar translocation?

Sugar-rich sap moves by bulk flow toward lower pressure regions.

Q: What is bulk flow?

Movement of water and solutes together due to pressure gradients.

Q: Step 4 of sugar translocation?

Sugar unloads at sink; water moves back into xylem.

Q: What are the three lateral transport routes?

Apoplastic, symplastic, transmembrane.

Q: What is the main force pulling xylem sap upward?

Transpirational pull (cohesion-tension).

Q: What direction does xylem sap always move?

Unidirectional — from roots to shoots.

Q: How does phloem sap flow?

From source to sink via pressure potential gradients.

Q: Does phloem sap always move in one direction?

No — depends on source and sink locations.

Q: Where is the Casparian strip located?

Only in roots (in the endodermis).