Roots213S - Roots - 1 As we have discussed and observed in...

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Roots - 1 As we have discussed and observed in the laboratory, plants have two general systems that grow along an axis. The above ground portion of most plants comprises the shoot system (with leaves and stems); root systems constitute the below ground portion of most plants. Because they are unseen, many people don't think about the root systems of plants, unless the roots have grown so much that one's sidewalks get cracked and lifted, or one's septic system needs cleaning because roots have invaded the drain tiles. In this section we will discuss the structure and function of roots. You will recognize the tissues we have previously discussed and see how they are organized in roots, and how tissues are specialized for optimal root functions. Root Functions Anchor Absorb (and conduct) H 2 0 and minerals Store food reserve materials Produce certain hormones (the gibberellins and cytokinins) in the root meristem that are translocated through the plant to control growth and development Produce some secondary metabolites that are translocated upward Most root systems are fairly shallow (2 - 3 feet), deep enough to anchor the plant, but still growing in soil that contains nutrients that cycle through the ecosystem. Most of the smaller roots active in water and nutrient uptake are found very close to the soil surface. This is one reason why some trees are fragile when planted in traffic areas and lawns. Pressure can damage roots. Roots of some plants access deep water sources; roots have been measured at depths of almost 175 feet in some desert areas. Roots can easily spread in width many times the distance of a tree’s crown. Roots of herbaceous plants have proportionately wide and deep root systems, too. For most plants there is a balance between the root area and shoot area. Shoots must have adequate surface area for photosynthesis for the entire plant and roots must have adequate surface area to provide water and nutrients to the entire plant. If roots are damaged, shoot growth can be affected. Poor shoot growth limits the available fuel needed for root growth. Fortunately, plants are able to replace damaged roots with new root growth pretty rapidly in most cases, just as new leaves and shoots are readily produced. A common problem with houseplants is “root rot”, in which roots do not obtain enough oxygen and suffocate (generally caused by water-logged soils). Once the roots die, the shoot system also dies.
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Roots - 2 There are two major root systems (plus adventitious roots) that differ in the structure and number of roots. When a seed germinates, the primary root, or radicle as it is called in the embryo, emerges from the seed coat. That primary root may develop into a taproot or die and be replaced by a system of fibrous roots. In addition, adventitious roots arise from stem or leaf cuttings. Root
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Roots213S - Roots - 1 As we have discussed and observed in...

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