EXERCISE 5: THE ROOT PDF

EXERCISE 5: THE ROOT Main Functions of a Root: Anchorage: Roots firmly anchor the plant to the ground, preventing it from being uprooted by wind or water. Absorption: Roots absorb water and essential minerals from the soil, which are then transported to other parts of the plant....

EXERCISE 5: THE ROOT Main Functions of a Root: Anchorage: Roots firmly anchor the plant to the ground, preventing it from being uprooted by wind or water. Absorption: Roots absorb water and essential minerals from the soil, which are then transported to other parts of the plant. Storage: Some roots, such as carrots and beets, are modified for storing food (starch, sugars, etc.) for the plant. Support: In some plants, roots can provide additional support to the above-ground parts. General Characteristics of Roots: Lack of nodes and internodes: Roots do not have nodes (points where leaves or branches arise) or internodes (the spaces between nodes). Absence of chlorophyll: Roots typically do not contain chlorophyll and are not photosynthetic. Presence of root hairs: Root hairs are tiny, hair-like projections that increase the surface area for absorption of water and minerals. Growth direction: Roots generally grow downwards in response to gravity (geotropism). Branching: Roots often branch out to increase their surface area for absorption. SPECIMENS USED IN THE ACTIVITY: Monocots (Corn, Sweet Potato, Jicama) Other term for root epidermis is Rhizodermis which is the outermost layer of cells in the root. Corn (Zea mays): ○ Root type: Adventitious roots ○ Specialized function: Anchorage, nutrient and water absorption. Corn has a fibrous root system that spreads out horizontally near the soil surface.  Sweet Potato (Ipomoea batatas): ○ Root type: Adventitious roots ○ Specialized function: Storage of starch. Sweet potatoes have modified roots known as tubers that are specialized for storing nutrients, primarily starch. Jicama (Pachyrhizus erosus): ○ Root type: Adventitious roots ○ Specialized function: Storage of starch. Jicama also has a tuberous root that is adapted for storing starch. Dicots (Carrot, Radish, Avicennia marina, Rhizophora apiculata) Carrot (Daucus carota): ○ Root type: Taproot ○ Specialized function: Storage of beta-carotene. Carrots have a thick, primary root that is modified for storing beta-carotene, a precursor to vitamin A. Radish (Raphanus sativus): ○ Root type: Taproot ○ Specialized function: Storage of water and nutrients. Radishes have a fleshy taproot that is adapted for storing water and nutrients. Avicennia marina (Gray mangrove): ○ Root type: Adventitious roots (pneumatophores) ○ Specialized function: Respiration. Gray mangroves have aerial roots called pneumatophores that help them breathe in oxygen-poor soils.  Rhizophora apiculata (Red mangrove): ○ Root type: Adventitious roots (prop roots) ○ Specialized function: Support and anchorage. Red mangroves have prop roots that extend from the trunk and branches, providing stability and support in the soft, muddy sediments where mangroves grow. GUIDE QUESTIONS: WITH DISCUSSIONS 1. Which type of root system is more effective in preventing soil erosion? Which type of root system is more advantageous in drought conditions? Briefly explain your answer. Fibrous root systems are generally more effective in preventing soil erosion. These systems have a dense network of fine, branching roots that spread out horizontally near the soil surface. This creates a strong, interwoven structure that holds the soil in place, preventing it from being washed away by wind or water. Taproot systems are less effective in preventing soil erosion. They consist of a single, thick primary root that grows vertically downward. While taproots can provide anchorage, they do not have the same wide-reaching network as fibrous roots and are less able to bind the soil together. In drought conditions, taproot systems can be more advantageous. These systems can penetrate deeper into the soil, allowing plants to access water stored at greater depths. This can be particularly beneficial in arid or semi-arid environments where surface water is scarce. 2. What is the root cap? State its functions and describe how it is formed. The root cap is a protective layer of cells found at the very tip of the root. It functions to: Protect the root apex: The root cap acts as a cushion, protecting the delicate meristematic cells at the root tip from injury as the root grows through the soil. Sense gravity: The root cap contains specialized cells called columella cells that are sensitive to gravity. These cells help the root to grow downward in response to gravity, a process known as geotropism. Produce mucilage: The root cap secretes a slimy substance called mucigel that helps to reduce friction as the root grows through the soil. The root cap is formed from cells produced by the root apical meristem. These cells differentiate into specialized cell types that make up the various layers of the root cap. 3. Describe the cells in each region of the longitudinal section of the root.  A longitudinal section of a root reveals several distinct regions, each containing different types of cells: Root cap: As discussed above, the root cap is composed of specialized cells that protect the root tip and aid in geotropism. Zone of cell division (meristematic zone): This region contains actively dividing cells that give rise to all of the other cell types in the root. Zone of elongation: Cells in this region undergo rapid elongation, causing the root to grow in length. Zone of differentiation: Cells in this zone differentiate into specialized cell types, such as xylem, phloem, and endodermal cells. 4. What are root hairs? In which region can you find them and give their function. Root hairs are tiny, hair-like projections that extend from the epidermal cells of the root. They are typically found in the zone of maturation. Root hairs increase the surface area of the root, allowing for more efficient absorption of water and minerals from the soil. 5. Where can you find the quiescent center? Describe the cells found here and state its significance. The quiescent center is a small group of cells located in the center of the root apical meristem. These cells divide slowly or not at all, serving as a reservoir of undifferentiated cells that can be used to replace damaged or lost cells in the root. 6. What is the Casparian strip? Where can you find them and what is it made of? What is the significance of these cells? The Casparian strip is a band of suberin, a waxy substance, that forms a waterproof barrier around the endodermal cells of the root. It is located in the endodermis. The Casparian strip prevents water and minerals from moving between cells in the endodermis, forcing them to pass through the cytoplasm of the endodermal cells. This allows the plant to control the uptake of substances from the soil. 7. Give the function and the meristematic origin of the following tissues: epidermis, tissues in the cortex region, pericycle, endodermis, xylem, phloem, and pith. Epidermis: Function: Protection, absorption of water and minerals. Origin: Protoderm. Tissues in the cortex region: Function: Storage of food, support.  Origin: Ground meristem. Pericycle: Function: Formation of lateral roots, vascular cambium (in dicots). Origin: Procambium. Endodermis: Function: Control of water and mineral movement. Origin: Ground Meristem Xylem: Function: Transport of water and minerals from roots to shoots. Origin: Procambium. Phloem: Function: Transport of sugars and other organic compounds from leaves to other parts of the plant. Origin: Procambium. Pith: Function: Storage of food (if present). Origin: Ground meristem. 8. Define what stele is and differentiate the types of stele observed in this activity. The stele is the central vascular cylinder of a root. It is composed of the vascular tissues (xylem and phloem) and the surrounding pericycle. There are two main types of stele observed in this activity: SUNFLOWER - Protostele: A solid core of vascular tissue without a pith. CORN - Siphonostele: A hollow stele with a central pith. 9. What gives rise to lateral roots and briefly explain how they are formed Lateral roots are secondary roots that branch off from the primary root. They are formed from the pericycle. The pericycle cells divide and grow outward, eventually forming a new root that emerges from the side of the primary root.