Chapter 36: plant form and Function -2

Negative pressure

• caused by water evaporating from the leaves and leaving negative space that pulls up molecules

• EX: sucking up water through a straw, vacuum cleaner, syringe pulling in liquid

Positive pressure

• materials being pushed to where they are needed or stored

• pushing plunger down to increase pressure and push liquid out, squeezing a plastic water bottle and water exploding

osmosis

diffusion of free water across a semi-permiable membrane

water potential

they physical property that predicts the direction of water flow across a membrane

Solute potential

• directionally proportional to its molarity

• as solute concentration increases, solute potential becomes more negative and water potential is reduced

pressure potenial

• the physical pressure on a solution

• can be positive or negative

• water in cells is usually positive pressure

Turgor pressure

the exerted force of water on the cell walls of a plant

• high turgor pressure makes the plant erect

pressure is lower outside the cell then inside…

water moves outside of the cell and plants wilts (flaccid cells)

Higher outside of the plant cell

water moves into the cells, resulting in an erect plant

Transpiration

main driver of water movement in xylem and creates negative pressure in the plant

regulation of transpiration

• plants covered by a waxy on the outer surface prevents water loss

• opening and closing of the stomata

stomata

surrounded by gaurd cells for protection of water movement

Cohesion-tension theory

• evaporation from the mesophyl causes negative pressure at the top of the plant

• causes water to move upwards formt he roots in the xylem

• water from the root is pulled up by tension

• at night, stomata close and transperation stops so water is held in place

• transpiration is a passive process, it doesnt need ATP

Sap through phloem

• Phloem sap travels through perforations called sieve tubed plats

• neighboring companion cells carry out metabolic functions and provide them with energy

• lateral sieve areas connect the sieve tube elements to the companion cells