5) Transport in Plants (Water + Sugar)

Capillary action

Water rises in small tubes due to adhesion to tube walls and cohesion between water molecules.

Limit of capillary action

Approximately 1 meter.

Root osmotic push

Water moves through a semipermeable membrane from low solute to high solute due to active ion pumping into root hair cells.

Limit of root osmotic push

Approximately 3 meters.

Transpiration (transpirational pull)

Mechanism explaining how water evaporates from leaf xylem endings due to heat, creating a pull on the water column.

Limit of transpiration pull

Maximum pull is approximately 130 meters.

Total-transport synthesis

Cohesion and adhesion work together in water transport; water loss from leaves draws water up from roots.

Cohesion in water transport

Cohesion holds the string of water molecules together.

Adhesion in water transport

Adhesion helps slightly in the upward movement of water.

Apoplastic transport

Transport of water through cell walls, which is faster and encounters less resistance.

Symplastic transport

Transport of water through cells and plasmodesmata.

Endodermis

Control layer regulating what enters the xylem via its Casparian strip.

Casparian strip

Structure in the endodermis that blocks apoplastic flow, forcing a selective symplastic route.

Photosynthesis-transpiration compromise

Stomata need to open for CO₂ intake, but over 90% of water is lost through transpiration.

Guard cells

Cells that regulate the opening and closing of stomata, using osmosis via active management of K⁺ concentration.

ATP-driven pump in guard cells

Pump that regulates potassium ions to control guard cell turgor and stomatal opening.

Source in sugar transport

Tissues that produce or release sugars, including seed endosperm and photosynthetic leaves.

Sink in sugar transport

Tissues that require sugars for energy and biosynthesis, such as developing roots and flowers.

Pressure-flow model

Model explaining sugar transport in phloem driven by a pressure gradient from high to low sugar concentrations.

Energy requirement in pressure-flow model

Energy is needed to set up the pressure gradient but not during the pathway movement of sugars.

Sieve elements

Components of phloem involved in transporting sugars.

Companion cell

Cell that aids in loading sugars into sieve elements using ATP-driven pumps.

Osmotic flow in phloem

Water follows osmotically to help move sugars through the phloem.

Bulk flow of sugars

Movement of sugars through phloem once the pressure-flow gradient is established.

Water transport through xylem

Process by which water is absorbed from roots and transported upwards in plants.

Sugar transport through phloem

Process by which sugars produced in photosynthetic tissues are distributed throughout the plant.

Role of stomata

Structural openings on leaves which manage gas exchange and water loss.

Mechanism of transpiration pull

Evaporation of water from leaf surfaces creates a continuous pull facilitating upward water movement.

Functional significance of endodermis

Regulates water and nutrient uptake into the xylem, enhancing plant efficiency.

Relationship between temperature and transpiration

Higher temperatures increase transpiration rates due to enhanced evaporation.

Role of ions in root osmotic push

Active ion pumping creates osmotic pressure that facilitates water movement into roots.