Biology - Plant Transport

Adaptations of Root Hairs for Absorption

• thin walls

• not covered by a cuticle

• very numerous, large surface area

Xylem

transports water from the roots to all parts of the plant

Transport of Water in a Plant

caused by:

• root pressure

• transpiration

Transpiration

the loss (by evaporation) of water vapour from the leaves and other aerial parts of a plant

Control of Transpiration in Leaves

• waterproof cuticle covering the top and bottom of leaves

• stomata being on the lower surface of a leaf

• closing of the stomata at night, and during the day when transpiration rates are high

Active Transport

uses energy in the from of ATP

Stomata

function is gas exchange:

• carbon dioxide diffuses inwards in daylight

• oxygen and water vapour diffuse outwards during daylight

Air Spaces

increase the surface area for gas exchange inside a leaf

Lenticels

opening in the stems of plants for gas exchange

Guard Cells

change shape to open and close the stomata

• swell when full of water to open the stomata

• shrink to close the stomata when water is lost

Carbon Dioxide

• high levels (at night) cause the stomata to close

• low levels (by day) cause the stomata to open

Dixon and Joly

scientists who proposed the cohesion-tension model in plants

Adhesion

occurs when different molecules stick together

Cohesion

the sticking of similar molecules to each other

Cohesion Tension Model

• root pressure pushes water into xylem

• cohesion (water molecules stick together) → due to hydrogen bonding

• adhesion (water molecules stick to sides of xylem)

• transpiration - water evaporates

• water pulled upwards