Movement of water through roots

Anyone one doing AQA AS biology should explain what happens this topic please. I don't understand it. Thanks.

Anyone one doing AQA AS biology should explain what happens this topic please. I don't understand it. Thanks.

Vacuolar pathway

The what now? I know the other two but I've never heard of that one.

Water is absorbed from the soil through the root hairs, which increase the surface area, thereby speeding up water intake.

After the water has been absorbed the water has to get through the cortex, which includes the endodermis, before it can get to the xylem.

*Just remember the soil generally has a higher water potential than the cells of the plant, hence osmosis occurs.

Okay, the symplastic pathway is the pathway where water goes through the "living" parts of the cells (the cytoplasm)
The cytoplasm of neighbouring cells connect through plasmodesmata, which are just smalls gaps in the cell wall.

The Apoplastic pathway goes through the cell wall "dead parts", and it is faster as water simply diffuses through.
However, this pathway is eventually blocked by a waterproof barrier (The Casparian Strip) Now the water has to take the symplastic pathway. The barrier forces the ions to go through the endodermis cell, and the ions are pumped through by active transport. Because of the high ion conc. a water potential gradient is established.

Cohesion and Tension are important as well:

Water evaporates from the leaves at the "top" of the xylem; this creates tension (suction) so more water goes into the leaf. H2O molecules are cohesive (stick together - sorry to be patronising) so the whole column of H2O goes into the xylem.

Do you want to know about Transpiration as well?

Yes i don't understand transpiration that well as well.
Thanks you very much for your help.

No worries.

Transpiration is just the evaporation of water from a plan't surface.

Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf. The stomata open and water moves out (high to low conc.)

Four main factors affect Transpiration:

1) Light

- more light = faster transpiration rate, as the stomata open when they receive light.

2) Humidity

- Lower humidity results in increased transpiration as the air around the plant is dry, to conc. gradient will be higher.

3) Temperature

- higher temp = faster Transpiration rate as watermer H2O molecules have more energy, therefore they evaporate faster. Increases the conc. gradient between inside/outside of leaf so water diffuses out faster.

4) Wind - the windier it is, the faster the transpiration rate. Lots of air movement blows away water molecules from around the stomata, therefore, again, increasing the conc. gradient.

Nothing conceptually difficult.

*Everything is to do with concentration gradient

Anyone one doing AQA AS biology should explain what happens this topic please. I don't understand it. Thanks.

root vacuoles have a low water potential because of dissolved sugars and minerals. there is a higher water potential in the soil solution, water diffuses by osmosis along the water potential gradient from the soil into the root hair cell. The majority of water moves via the apoplastic pathway. By the apoplast water diffuses(not osmosis because not through membranes) along cell walls to the endodermis where it encounters the waterproof casparian strip so it enters the symplast by osmosis. Through the symplastic pathway water diffuses through the cytoplasm of adjacent cells connected by plasmodesmata, through the parenchyma cells of the cortex to the endodermis where it enters the xylem vessels

Thank you

Can anybody explain Cohesion and Tension to me please? We just finished the spec last lesson and this part was really rushed. I really do not understand it.

Water moves up the xylem by mass flow by the cohesion-tension mechanism. Water evaporates from the spongy mesophyll into the air spaces of the leaf and out through the stomata by transpiration, this process is driven by the sun. The loss of water from the leaf lowers the water potential so water moves from higher water potential in the xylem into the leaf. Water molecules stick together(cohere) due to hydrogen bonding forming a continuous column of water which adheres to the xylem putting it under tension. So when water diffuses into the leaf by osmosis form the xylem this sucks up more water

Wow thanks, rep for you

Anyone one doing AQA AS biology should explain what happens this topic please. I don't understand it. Thanks.

Water is absorbed from the soil through the root hairs, which increase the surface area, thereby speeding up water intake.

After the water has been absorbed the water has to get through the cortex, which includes the endodermis, before it can get to the xylem.

*Just remember the soil generally has a higher water potential than the cells of the plant, hence osmosis occurs.

Okay, the symplastic pathway is the pathway where water goes through the "living" parts of the cells (the cytoplasm)
The cytoplasm of neighbouring cells connect through plasmodesmata, which are just smalls gaps in the cell wall.

The Apoplastic pathway goes through the cell wall "dead parts", and it is faster as water simply diffuses through.
However, this pathway is eventually blocked by a waterproof barrier (The Casparian Strip) Now the water has to take the symplastic pathway. The barrier forces the ions to go through the endodermis cell, and the ions are pumped through by active transport. Because of the high ion conc. a water potential gradient is established.

Cohesion and Tension are important as well:

Water evaporates from the leaves at the "top" of the xylem; this creates tension (suction) so more water goes into the leaf. H2O molecules are cohesive (stick together - sorry to be patronising) so the whole column of H2O goes into the xylem.

Do you want to know about Transpiration a