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Ch 10-Roots and Plant Nutrition Roots play a variety of roles in plants -roots anchor plants and absorb water and minerals -some roots are useful as human food -roots are important sites of hormone production -the roots of some plants help support stems -human use of roots Roots anchor plants and absorb water and minerals When seeds germinate, the first plant organ to emerge is the root. As the plant develops, the primary root is replaced by a more extensive, branched root system. Some roots are useful as human food http://www.foodofy.com/wpcontent/uploads/2015/06/sweetpotato-2.jpg http://www.gardeningclan.com/12-radish-varietykitchen-garden.html https://www.morningagclips.com/swee t-potatoes-are-healthy-and-tasty/ http://www.turniprecipes.co.uk/types-of-turnip/ Roots play a variety of roles in plants Roots are important sites of hormone production The roots of some plants help support stems Buttress roots These roots aid tropical plants growing in thin soils. Aerial roots Rope-like roots from tree branches which anchor in the soil. Prop roots in corn Human uses of roots Spruce roots are used by Native Americans in the construction of traditional birch bark canoes. Thirty-five percent of the world’s sugar comes from the roots of sugar beets (Beta vulgaris). In pre-modern Europe, human-shaped roots of the mandrake plant, Mandragora officinarum, were thought to indicate special powers, and extracts used as a pain reliever and anesthetic. Plants produce specialized roots Pneumatophores The pneumatophores grow upward Into the air and absorb oxygen through lenticels. Contractile roots Common in dandelions. Epiphytic plants that grow nonparasitically on other plants have specialized roots. Ex: The “flower pot plant” Dischidia rafflesiana There are two major types of root system: 1) Fibrous root system Annual grasses generally have fibrous root systems. 2) Tap root system. Carrots and radishes have tap roots. Adventitious roots develop from the shoot system. Adventitious roots in tomato Prop roots in corn Root structure -External root structure The branch roots and main root axis are covered with an epidermis. Branch roots or lateral roots The branch roots decrease in age from the soil surface to the root tip. (youngest branches at the root tip) (youngest branches at the root tip) Numerous root hairs At the root tip is the root apical meristem, RAM This is the region of meristematic cells which divide rapidly and increase the number of cells in the main portion of the root. Root cap The root cap protects the RAM The cells in the root cap are generated by the RAM Mucigel The tips of the root are embedded in mucigel. Mucigel is a gluey polysaccharide produced by the Golgi of the root tip epidermal cells. Internal view of the roots The last few millimeters of a root tip consists of 4 major zones: 1)Root cap 2)The root meristem, a zone of cell division 3) The elongation zone 4) The zone of maturation Root apical meristem gives rise to 3 precursor tissues: During tissue specialization, procambium gives rise to the mature vascular tissues. Protoderm develops into the epidermis of young roots Ground meristem produces tissue known as the cortex Monocot Root Eudicot Root endodermis pericycle pith cortex cortex phloem xylem Cortex -air spaces provide oxygen to diffuse through roots Vascular cylinder Endodermis – cells of the innermost cortex layer that forma waterproof barrier between the cortex and vascular cylinder Water and minerals that have entered roots via cell walls cannot cross the endodermis to the vascular tissue (xylem and phloem). Casparian strip Endodermal cell walls of dicots have a strip of water repellent material, suberin, that forms the Casparian strip on the top, bottom,and side walls. Walls facing inward and outward do not. Water from the cortex can move through the cell walls without suberin. Dissolved minerals can enter the cytoplasm of endodermal cells if their cell membranes contain the appropriate transporter protein. The primary vascular system includes: -a surrounding cylinder of tissue known as the pericycle The pericycle produces branch roots. Branch roots start to form while embedded in the root tissue. The branch roots push through the cortex to the surface. In plants with woody roots, cell division in the pericycle contributes to the formation of vascular cambium to generate secondary xylem and phloem. Epidermal Root Hairs Root hairs may reach 1.3 cm, but most root hairs are only about 10 um in diameter. Epidermal Root Hairs As root hairs develop,their cell membranes become embedded with proteins that selectively transport materials from the environment into the root hair cytoplasm. ATP is hydrolyzed to drive the uptake process through an electrochemical gradient. As the protons move back into the cell through the transporter protein, a mineral ion is carried with it. Root xylem obtains minerals and water in 2 different ways: Symplastic transport- Apoplastic transport- Study outline for Chapter 10-Roots and Plant Nutrition List the 4 major roles of roots in the plant. Name some examples of roots that are useful for human food. Define the following terms and label the figures below. -buttress roots -aerial roots -prop roots -pneumatophores -contractile roots roots that support stems specialized roots Explain how the following root examples are used by humans. -spruce roots -sugar beets (Beta vulgaris) -mandrake (Mandragora officinarium) Draw and label the two major types of root systems. Give an example for each type of root system. Define the following terms of root external structure and label the figure below. -branch roots/lateral roots -epidermis -root hairs -root apical meristem (RAM) -root cap -mucigel Study outline for Chapter 10-Roots and Plant Nutrition The root apical meristem (RAM) gives rise to 3 precursor tissues in the root. Fill in precursor tissues and tissue systems. Precursor tissues Tissue systems in root What are the main differences between a eudicot root and a monocot root? Label the figure below with following terms and give the function of each term. -epidermis -cortex -endodermis -pericycle -xylem -phloem Label the figure below with the following terms: root hair, epidermis, cortex, endodermis, Casparian strip, pericycle, xylem, phloem, plasmodesmata, air space, apoplastic route, symplastic route and transport protein. Explain the difference between symplastic transport and apoplastic transport of minerals and water in the root.
