Biology Unit 2 Module 2

Topics: Cell wall, Photosynthesis, Plant physiology Pages: 2 (581 words) Published: April 1, 2011
Biology Unit 2 Module 2

1.1: Explain the uptake of ions by active transport in roots; * Emphasize the role of the endodermis.

Most plants secure the water and minerals they need from their roots. The path taken is: soil -> roots -> stems -> leaves The minerals (e.g., K+, Ca2+) travel dissolved in the water (often accompanied by various organic molecules supplied by root cells).Less than 1% of the water reaching the leaves is used in photosynthesis and plant growth. Most of it is lost in transpiration. However, transpiration does serve two useful functions:

* It provides the force for lifting the water up the stems. * It cools the leaves.
Water and minerals enter the root by separate paths which eventually converge in the stele.

Soil water enters the root through its epidermis. It appears that water then travels in both * The cytoplasm of root cells — called the symplast — that is, it crosses the plasma membrane and then passes from cell to cell through plasmodesmata. * In the nonliving parts of the root — called the apoplast — that is, in the spaces between the cells and in the cells walls themselves. This water has not crossed a plasma membrane.

Apoplast Pathway
Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant.

Structurally, the apoplast is formed by the continuum of cell walls of adjacent cells as well as the extracellular spaces, forming a tissue level compartment comparable to the symplast. The apoplastic route facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport.

The apoplast is important for all the plant's interaction with its environment. The main carbon source (carbon dioxide) needs to be solubilized in the apoplast before it is taken up by chloroplasts and consumed...
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