Plant Organs: Roots PDF

Bio 17 Botany BS Bio I-A Benguet State University MODULE/ CHAPTER 5 **Plant Organs: ROOTS** MOTIVATION It is expected by now that the preparatory knowledge on plant cells and tissues are embedded in your understanding. You will need those understanding for the upcoming chapters. We would shift n...

Bio 17 Botany BS Bio I-A Benguet State University MODULE/ CHAPTER 5 **Plant Organs: ROOTS** MOTIVATION It is expected by now that the preparatory knowledge on plant cells and tissues are embedded in your understanding. You will need those understanding for the upcoming chapters. We would shift now our focus from predominantly microscopic to somewhat macroscopic study of plants. We would deal now with plant organs, studying its structure and functions. In this chapter, we will deal with the plant ROOT. But before we go down to business, let's have some laughs (if you would care to understand it first)! Question: Why do hackers grow their plants with hydroponics? Answer: To get root access. Question: How can you tell an unidentified plant in your garden is a weed? Answer: Try to pull it out. If it comes out easily, it\'s not a weed. Hope, you enjoyed this but we have to go now to the topic at hand. Again, I present to you the PLANT ROOTS! LESSON PROPER **Overview of the Plant Body** The typical plant body is organized into two major systems, namely: 1\. **Shoot system --** includes all the aerial organs naemly the stem, leaves, flowers, fruits and seeds \- Environment: bright dry air \- Develop from the hypocotyl and epicotyl of a germinating seed 2\. **Root system** -- the underground or subterranean organs of the plants \- Environment: dark moist soil \- Develop from the radicle **CHAPTER V. The Plant ROOTS** **ROOTS** ⮚ The underground organs of the plant ⮚ It is non-green, it has no cuticle in the epidermis ⮚ Growth: downward (towards the gravity) ⮚ Main Functions: 1\. Anchorage -- keeps the plant in one place Bio 17 Botany BS Bio I-A Benguet State University 2\. Absorption of water and minerals from the soil 3\. Storage **Kinds of Root** according to **Origin** **1. Primary roots** ⮚ Main roots which develops directly from the radicle **2. Lateral Roots** ⮚ Roots arising from the primary roots ⮚ Named as secondary, tertiary **3. Adventitious roots** ⮚ Roots arising from other plant organs than the radicle **Kinds of Root Systems** 1\. **Tap root system** -- the root system that have primary root (tap root) which gives off lateral roots. ⚫ They provide very strong anchorage as they are able to reach very deep into the soil ⚫ The common root system in dicots. **2. Fibrous root system** ⚫ Has no main or tap root, instead it consist of a cluster of slender fiber-like roots (the same sizes) ⚫ The roots are generally shallow and spread horizontally ⚫ This is the common root system of monocot plants, particularly grasses **Anatomy of THE ROOT** If we will dissect the root tip of a plant **longitudinally**, we will observe the following parts: 1. [**Root Cap**--] a thimble-like structure that contains a polysaccharide slime called the MUCIGEL that acts as lubricants \- The functions of the root cap are: Protection Lubrication Downward growth of the roots toward the gravity (we call this phenomenon gravitotropism) 2\. **[Region of meristematic cells/ Apical]** [**Meristem** --] small region of actively dividing cells called the root apical meristem. This where we usually observed cell undergoing the different stages of mitosis. 3 types of meristematic cells are observed here: a\. Protoderm -- the outermost primary meristem which give rise to dermal tissue system Bio 17 Botany BS Bio I-A Benguet State University b\. Ground meristem -- the middle primary meristem which give rise to ground tissues (cortex) c. Procambium -- the innermost primary meristem which give rise to vascular tissues (stele) 3. [**Region of cell elongation** --] lies next to the meristematic region, cells elongate and enlarge to make the root grow in length. 4\. [**Region of cell differentiation**--] lies next to the region of elongation. The cells mature and differentiate into various tissues. \- this is indicated by presence of root hairs On the other hand, if we will dissect the root in the region of cell maturation at **cross-section**, we will observe the following parts: 1\. **Epidermis** -- the single, outermost layer covering the roots  \- contain root hairs, which greatly increases the surface area of the roots for greater absorption \- has no cuticle 2\. **Cortex** -- composed mainly of parenchyma cells (primarily for storage) \* **Endodermis** -- innermost layer of the cortex; cells here fit snuggly \- contains a band-like region around the cell called the [Casparian Strip] = suberin \- its function is to regulate the movement of the waters and minerals into the inner layer 3\. **Stele** -- consist of the cells inside the endodermis a\) Pericycle -- single layer of cell between the epidermis and vascular tissues, these cells retain their meristematic potentials and give rise to lateral roots b\) Vascular Tissues -- contains: i\. Xylem -- water and mineral conduction ii\. Phloem -- food conduction \* **Pith** -- centermost portion of the stele in Monocot plants \- this is generally composed of parenchyma tissues \* In dicot plants, roots have **vascular cambium** interspersed with xylem and phloem in the stele. The vascular cambium give rise to secondary tissues like secondary xylem and secondary phloem. Arrangement of the vascular tissues in the stele For Monocot Plants: the arrangement is called **Siphonostele** -- the xylem and phloem are located around the pith Bio 17 Botany BS Bio I-A Benguet State University For Dicot Plants: the arrangement is called **Protostele** -- xylem form a solid mass at the center with arms and phloem fits b/n these arms. The vascular cambium is located in between xylem and phloem.  Siphonostele ----------------------- -------------- Protostele Difference between monocot and dicot root **Structures/ Characters Monocot Root Dicot Root** ---------------------------------------------------- -------------------- ------------------------------------ Stele (central cylinder arrangement) Radial or circular Star-shaped or arm-like projection Cortex width Narrower Wider Cambium Absent Present Pith Present (Large) Absent Bio 17 Botany BS Bio I-A Benguet State University **Modified/ Specialized Roots** -- has specialized function  1\. AERATING ROOTS - roots arising from the ground, especially above water \- contains breathing cells called pneumatophores 2\. CONTRACTILE ROOTS - contraction or shortening of some roots to help pull down and anchor the plant more firmly into the soil. 3\. SUPPORTIVE ROOTS/ ADVENTITIOUS ROOTS - roots which function as a stem TYPES:  A. Brace Roots -- arise from the stem e.g. corn B. Prop Roots -- arise from the branches C. Buttress Roots -- trunk-like extensions growing from upper portion of large roots 4\. REPRODUCTIVE ROOTS - roots which perform seed function, for propagation of the plants 5\. PHOTOSYNTHETIC ROOTS -- roots that have chlorophyll, thus green in color and can perform  photosynthesis 6\. STORAGE ROOTS -- enlarged or swollen roots that contains stored food such as starch 7\. MYCORRHIZAL ROOTS - forms a symbiotic relationship with fungus for enhance uptake of water and minerals  8\. NODULATED ROOTS - symbiosis with beneficial bacteria called rhizobium