Please enable JavaScript.
Coggle requires JavaScript to display documents.
Plants, - Coggle Diagram
Plants
-
Structure
-
-
Leaf
-
External structure:
apicle bud
leaf scar
lenticles
lateral bud
internode
node
petiole
leaf blade
Midrib
vein
scale scars
Internal structure:
cuticle
upper epidermis
palisade layer
mesophyll
air a pace
lower epidermis
stoma
guard cell
-
Transport
Water is absorbed through the roots hairs by osmosis . Root hairs are an extension of the epidermis and have many adaptions for effective absorption of water:
- thin walls
- not covered by a waxy cuticle
- very numerous (increases surface area)
Root pressure-the build up water in the xylem tissue in the roots of a plant, which causes water to be pushed up the stem.
This does not fully explain the transport of water to great heights in very tall plants .
The cohension tension model :
- This was developed by two Irish scientists Dixon and Joly in 1895
- Water evaporates from the xylem into the airs spaces of the leaf. As transpiration pulls each water molecule out of the xylem, the next water molecule is pulled up the xylem with it because of the high cohesion between water molecules
- The water molecules form a column that is very hard to break because of cohension between water molecules and adhesion of water molecules to the xylem walls
- The tension in the xylem due to transpiration pulls the water to great heights
Control of transpiration in leaves :
- presence of a waxy cuticle
- stomata located on the underside of leaves- less evaporation because the underside is cooler
- guard cells open and close stomata when necessary
Gas exchange takes place in:
- lenticels in stems
- stomata in leaves
Stomatal opening and closing :
- when water enters guard cells by osmosis they become turgid which increases the size of the gap in the stoma
- when they lose water by osmosis they shrink back to their normal size which closes the gap
- a high concentration of CO2 causes the stomata to close
- a low concentration of CO2 causes the stomata to open
-
-
-
-