Water Transportation | Plant Physiology - Biology IB23

Water Transportation

Water and minerals flow in only one direction from the roots along the stem to exit the leaves. This transportation is possible through xylem vessels.

Xylem

Made of dead cells with no cell walls in-between to form a tube for water and minerals to flow through. Their walls are composed of lignin to withstand pressure.

• Can be found inside of roots.

• Can be found in the vascular bundles of the stem.

• Can be found on the upper part of the vascular bundles.

Humidity

Lowers transpiration due to the causation of less of a concentration gradient between the leaf and air which will lead to less evaporation.

Wind

Increases transpiration, the wind moves humidity away from the leaf which causes a greater concentration gradient between the water within the leaf and the air.

Temperature

Increases transpiration because molecules will move faster due to the thermal energy so evaporation will process faster.

Darkness

Decreases transpiration because the stoma will close off.

Mass Flow

Water moves up the stem and partly happens due to root pressure which is caused by cells in the roots that actively pump in H+ ions to create a more hypertonic concentration than the soil.

Adhesion

Polar water molecules will stick to polar surfaces such as xylem and cellulose walls to help move them upward.

Cohesion

Water molecules will stick together with intermolecular hydrogen bonds and will pull other water molecules to stick together as it evaporates from the leaves.

Transpiration Stream

A passive water movement which makes water transportation possible.

Evaporation

Occurs as a result of water diffusion from an area of high water concentration within the leaf to a low concentration in the air.

Stomata

Water evaporates from the underside of the leaf through their holes, they’re holes for gas exchange for photosynthesis where water is lost during this exchange. They’re controlled by guard cells which can close off the holes to conserve water at night or when there’s a shortage through abscisic acid.

Halophytes

Salt Water Plants

• Cellular Sequestration —> Salt is stored within the vacuoles.

• Tissue Partitioning —> Abscission of leaves containing salt.

• Salt Excretion —> Salt is actively removed from the plant.

• Root Level Exclusion —> Roots avoid salt uptake.

Xerophytes

Desert Plants

• Reduced Leaves —> Lower evaporation surface area.

• Less Stomata —> Less transpiration.

• Thick, Waxy Cuticles —> Reduced water loss.

• Stomata w/ Hair —> Traps vapor reducing evaporation.

• CAM Physiology —> Stomata only opens at night.

• Long Roots —> Reach further for water.