transport in roots xylem

what are the 2 different pathways water can take

the symplast and the apoplast

what is the Caspian strip and what is it made out of

Its found in the endodermis which is a layer of the cells right next to the xylem a band of waterproof suberin runs around the cell walls

How are root hair cells adapted for osmosis

1. they have a large surface area meaning more water can move in by osmosis.

2. There is a short pathway of only cell wall and cell membrane to get into the cell this increases the rate of osmosis

3. Finally the root hair cells use another mechanism to increase the rate of osmosis they move ions into the plant cells by active transport this lowers the water potential ( conc of water) meaning that water moves into the cells

Describe the symplast pathway

In the symplast pathway water moves by osmosis from the soil to the cell. The water moves through the cytoplasm by diffusion. The water travels through the plasmodesmata of one cell to the cytoplasm of an adjacent cell . The symplast is driven by the water potential gradient between the root hair cells and the xylem. Water continuously moves into the root hair cells from the soil by osmosis meaning it has a higher water potential than the xylem. This meaning water moves into the xylem by osmosis.

why is the symplast pathway relatively slow

This is because the pathway for water in the cytoplasm is obstructed by the organelles. Therefore more resistant than the apoplast pathway

Describe the apoplast pathway

Here the water doesnt get into the cytoplasm instead moves within the cell walls and the spaces between cells. The celulose cell wall have a relativly open structure meaning water can easily move between fibres. eventually the water reach the endodermis a layer of cells around the cortex which contains the casparian strip. This is water proof so water now has to use symplast pathway.

why does water keep being drawn to the apoplast membrane

As water forms hydrogen bonds with each other meaning that it sticks together by cohesion dragging more water with it to the xylem

explain what is meant by root pressure

The endodermis cells use active transport to pump mineral ion into the xylem lowering the water potential of the xylem this triggers water to move into the xylem vessels by osmosis. This is called root pressure

what would happen to the root pressure is there were lower levels of photosynthesis

There would then be less glucose to break down so less respiration. To get root pressure active transport is needed to pump ions into the xylem. Active transport isn’t passive and requires energy. so root pressure would be lower and eventually stop