B4-Transport in Plants

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  • Created by: Lauren
  • Created on: 13-03-13 18:25

Vascular bundles

The xylem and phloem form a continuous system of tubes from roots to leaves, called vascular bundles.

-Xylem transports water and soluble mineral salts from the roots to the leaves (transpiration)

-Phloem allows the movement of food substances (sugars) around the plant (translocation), up and down stems to growing tissues an storage tissues.

Xylem vessels are made from dead plant cells. They have a hollow lumen. The cellulose cell walls are thickened with a waterproof substance. Phloem cells are long columns of living cells.

Root hairs have an enormous surface area for absorbing water and so increase the plant's ability to take up water 

Transpiration

Transpiration is the diffusion and evaporation of water from inside a leaf. It causes water to be moved up xylem vessels and provides plants with water for cooling, photosynthesis and support and brings minerals to the plant. 

The transpiration stream is powered by the evaporation of water from the leaf:

1. Water evaporates from the internal leaf cells through the stomata

2. Water passes by osmosis from the xylem vessels to leaf cells, which pull the thread of water in that vessel upwards by a very small amount. 

3. Water enters the xylem from root tissues, to replace water which has moved upwards.

4.Water enters root hair cells by osmosis to replace water which has entered the xylem. 

The rate of transpiration can be affected by:

-light: more light increases the rate of photosynthesis and transpiration

-air movement (wind): as the movement of the…

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