movement of water through root

Where is water taken up?

By the root hair cells

• crosses the cortex and enters the xylem in the centre of the root

• root hair cells take up mineral ions by active transport

• water potential decreases

• water is taken up by osmosis

Three routes through the cortex

1. apoplast pathway

2. symplast pathway

3. vacuolar pathway

Apoplast pathway

• travels through cell wall

• water can enter the cell wall and move due to the cohesive force of water

• water can move directly from cell wall to cell wall

• molecules stick together, forming a continuous stream towards xylem

Open structure of cellular wall = little resistance = fastest route

(diffusion not osmosis as water does not cross a membrane)

Symplast pathway

• moves through cytoplasm

• water moves by osmosis

• passes from cell to cell through pores in the cell wall called plasmodesmata

• each cell further away from roots has a lower water potential so this is why water is able to move by osmosis

Vacuolar pathway

• similar to symplast

• water passes through vacuole

• slowest as many membrane to cross

Three pathways of water through the root

What happens when the water reaches the endodermis during the apoplast pathway?

• apoplast pathway is blocked

• by a waterproof strip in the cell walls called the Capsarian Strip

• this is so water is forced to take the symplast pathway

• meaning it will have to pass through a selectively permeable membrane

• any toxins in the water will not pass through the membrane

• it is a protection mechanism

Adaptations of root hair cells

• microscopic size = penetrate between soil particles

• large SA : Vol ratio of hairs and there are thousands

• each hair has a thin walls = short distance for diffusion and osmosis

• conc of solute in cytoplasm maintains water potential gradients

How does the concentration of solute in cytoplasm maintain water potential gradients? (in root hair cells)

• soil water has low conc of dissolved mineral

• therefore high water potential

• cytoplasm in root hair cell - high conc of dissolved mineral

• therefore low water potential