how exchange of gases ocuur in (a) young roots (b) old roots (c)old and young stem
Asked by sakshi | 21st Apr, 2012, 10:07: AM
a) In young roots, gases can diffuse readily across the membranes of root hairs and other epidermal cells, which present an enormous surface area for gas exchange as well as for nutrient procurement.
b) In older roots, the epidermis and cortex is often replaced by bark; lenticels are present in such roots to allow the exchange of gases in the interior tissues.
(For all roots, however, the soil in which they grow must be well aerated to provide sufficient oxygen for the cells of the root.)
c) Young stems have stomata through which gases are exchanged, but older stems have impermeable bark on their surface, so gas exchange generally takes place through numerous lenticels. Lenticels are groups of loosely arranged cells with many spaces between them through which gases move to reach the interior tissues. Since most of the cells in the inner layers of large stems are dead, there is little need for oxygen in the intercellular spaces to penetrate deep into the stem.
Answered by | 23rd Apr, 2012, 11:31: AM
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