Capillary Action

There is a great importance of a transport system in plants. It helps to ensure efficient and uninterrupted movement of substances from one part of the plant to another.

In the plants there are two types of conducting vessels. They are the xylem, which conducts water, and mineral salts from the roots to the stem and leaves and the phloem, which transports sucrose and amino acids from the leaves to all parts of the plant.

Water is absorbed by the roots of the plant.

The root hair cells protect the outside of the plant and have specialised features to favour water absorption. There are two paths that water moves through.

First is the Symplast pathway that consist of the living cytoplasm of the cells in the root (10%). Water is absorbed into the root hair cells by osmosis, since the cells have a lower water potential that the water in the soil. Water then diffuses from the epidermis through the root to the xylem down a water potential gradient. The cytoplasm of all the cells in the root are connected by plasmodesmata through holes in the cell walls, so there are no further membranes to cross until the water reaches the xylem, and so no further osmosis.

Secondly, the Apoplast pathway consists of the cell walls between cells (90%). The cell walls are quite thick and very open, so water can easily diffuse through cell walls without having to cross any cell membranes by osmosis. However the apoplast pathway stops at the endodermis because of the waterproof casparian strip, which seals the cell walls. At this point water has to cross the cell membrane by osmosis and enter the symplast. This allows the plant to have some control over the uptake of water into the xylem.

Water moves up the xylem by two modes of transport. They are transpiration pull and capillary action.

In the narrow tubes such as the xylem vessel, two processes occur. When water molecules are attracted to each other due to electrical attractions, this attraction is called cohesion. When water molecules are attracted to other substances, like soil or the xylem wall, it is called adhesion.

Acknowledgements:

http://www.biologymad.com/master.html

http://www.biologymad.com/planttransport/planttransport.htm