Transport in plants (2)

Transport of water and mineral ions

Transport of water and mineral ions

Froom root upwards

1. soil

2. root hair

3. cortex

4. endodermis

5. xylem (in root to stem to leaves)

6. mesophyll cells (in leaves)

7. stomata

8. atmosphere

Movement of water from soil to root hair

1. root hairs are permeable to water

2. mineral ions are taken up by facilitated diffusion and active transport

3. they are long thin extensions of epidermal cells

4. able to reach into spaces between soil particles

5. has very large surface area for increased area of absorption

Water travels down the ____

water potential gradient

Movement of water from soil to root hair in terms of water potential

1. soil has a higher water potential than the root hairs cytoplasm (so water can move from high to low water potential)

2. soil has a higher water potential because the cytoplasm has more concentration of ions

3. therefore water diffuses down the water potential gradient via osmosis through the partially permeable cell surface membrane

   into the vacuole & cytoplasm of root hair

Movement of water from root hair to cortex

1. root hairs have a higher water potential than cortex

2. water moves down the water potential gradient via osmosis (root hair → cortex)

three possible pathways for water to travel from the root hair to the cortex

1. Apoplastic pathway: (cell wall)

   water travels between the cellulose fibers → there is adhesion of water to cellulose

2. Symplastic pathway: cell membrane, travels cell-to-cell via plasmodesmata

3. Vacuolar pathway

Movement of water from the root hair to the cortex to the endodermis

1. the endodermis has a Casparian strip = suberized cell wall (Casparian strip is made up of suberin which is impermeable to water)

2. in endodermal cell apoplast pathway is blocked because of the casparian strip

3. the only way for water to travel is through the endodermis is by symplast pathway

4. water and ions must pass through endodermal cells so that transport of mineral ions can be controlled

Movement of water from endodermis to xylem

1. water continues to move down the water potential gradient

2. from the endodermis to the xylem you have to cross the pericycle (layer of cells just below the endodermis)

3. water gets into xylem vessels through the pits in the cell wall

Movement of water in xylem vessels from roots to leaves

1. roots have a higher water potential than leaves

2. water moves down the water potential gradient travelling up xylem from roots to leaves

Movement of water from xylem in leaves to atmosphere

1. xylem vessel in leaves

2. water moves through the pits

3. arriving at the palisade/spongy mesophyll cells via apoplastic or symplastic pathway

4. water gathers onto the surface of spongy mesophyll cell walls

5. evaporates into air spaces

6. diffusion of water vapour from stomata into atmosphere

Transpiration

is the loss of water from leaves (side effect is the cooling of plant)

Two ways for transpiration to occur

1. via the stomata

   → diffusion of water vapour from air space to atmosphere, occurs only when stomata is open for gas exchange

2. via the cuticle, only a small amount of water is lost