WEEK 4.pdf

Biology of Farm Crops & Livestock Week 5  Pop Quiz! 1. Which of the following is not an 3. Rhizomes are sub-aerial example of a leaf shape: modifications. (True or a. Lanceolate False) b. Linear...

Biology of Farm Crops & Livestock Week 5  Pop Quiz! 1. Which of the following is not an 3. Rhizomes are sub-aerial example of a leaf shape: modifications. (True or a. Lanceolate False) b. Linear 4. Label the following: c. Rotate d. Ovate D 2. Which of the following is correct: a. Off-sets are examples of C aerial stem modifications b. Tubers are sub-aerial stem modifications c. Phyllocade are sub-aerial stem modifications B d. Rhizomes are examples of underground stem A modifications Leaf Functions  Photosynthesis – takes place in the mesophyll cells of the leaf  Transpiration – the loss of water from a plant through its leaves (helps to pull water up from the roots)  Gas exchange – taking in carbon dioxide and releasing oxygen (respiration)  Food storage: synthesis of secondary chemicals. Leaf Structure Palisade mesophyll – tightly packed cells that absorb light Spongy mesophyll – loosely packed cells with air spaces Stomata – pore-like openings for taking in CO2 and releasing O2 Guard cells – cells that open and close the stomata  Tissues of the Leaf (Epidermis) Cuticle  Waxy substance that covers the leaves & stems  Waterproof layer that keeps water in plants  Plant cuticles prevent the loss of water, regulate transpiration, and facilitate the transport of gases and solutes.  Acts as the first line of defense against environmental cues and biotic stresses triggered by a large array of pathogens and pests, such as fungi, bacteria, and insects  Tissues of the Leaf (Epidermis) Stomata (stoma – singular)  Openings in the epidermis mainly located on the underside of leaves  Exchange of gases. Tissues of the Leaf (Epidermis) Guard Cells  Two cells located on each side of stomata  Open and closes stomata  Guard cells actively pump potassium ions (K +) out of the guard cells and into surrounding cells. Tissues of the Leaf (Mesophyll Layer)  Palisade parenchyma  Primary site of photosynthesis  Spongy parenchyma  Contains air & chloroplasts  Site of photosynthesis and gas exchange Tissues of the Leaf  Vascular Bundles  Called veins  In spongy mesophyll  Phloem moves food from leaf to the rest of the plant  Xylem moves water & minerals up to leaves from roots Link: https://www.youtube.com/watch?v=pwymX2LxnQs Roots Functions Anchor the plant Absorb water & minerals Store food Propagate or reproduce some plants Embryonic root or radicle Tap root and Fibrous (Diffuse) Root Systems – Both arise from radicle Adventitious Roots: roots that arise from anything other than the radicle Adventitious Roots: roots that arise from anything other than the radicle  Roots: Function Roots anchor the plant in the substratum or soil. Roots absorb water and dissolved nutrients or solutes (nitrogen, phosphorous, magnesium, boron, etc.) needed for normal growth, development, photosynthesis, and reproduction. In some plants, roots have become adapted for specialized functions.  EXTERNAL ANATOMY Root cap Region of cell division Region of elongation Region of differentiation or maturation Root Cap thimble-shaped mass of parenchyma cells at the tip of each root protects the root from mechanical injury Dictyosomes or Golgi bodies release a mucilaginous lubricant (mucigel)  Region of Cell Division Apical meristem - cells divide once or twice per day. The transitional meristems arise from the tips of roots and shoots. These include: – the protoderm (which forms the epidermis) – the ground meristem (which forms the ground tissue) – the procambium (forms the primary phloem and xylem). Region of Elongation – cells become longer and wider Region of Maturation or Differentiation  Region of Maturation or Differentiation root hairs develop as protuberances from epidermal cells increase the surface area for the absorption of water cuticle exists on root but not on root hairs  Root modifications For storage of food These modified roots usually are swollen and assume different forms such as spindle shaped, e.g., radish; top shaped, e.g., beet, turnip; conelike, e.g., carrot; indefinite shape, e.g., sweet potatoes Dahlia, Portulaca are some other examples of plants with modified roots for food storage.  Root modifications Nodulated roots The roots of pea and other leguminous plants have numerous swollen nodules on fine branches of roots. These nodules are formed due to symbiotic association of Rhizobium (bacterium) that live inside the root cortical cells of the roots. They fix nitrogen. An active nodule is pink in color.  Root modifications For mechanical support Roots are modified to provide mechanical support as seen in banyan tree which has roots growing vertically/obliquely downwards (prop roots) sugarcane/maize in which roots arise from the nodes in cluster at the base of the stem (stilt roots) Black pepper in which nodes and internodes bear roots which help in climbing Buttress Roots  Root modifications For gaseous exchange Pneumatophores or breathing roots are found in plants growing in mangroves or swamps with saline water for exchange of gases. They are erect peg like structures with numerous pores through which air circulates e.g., Rhizophora mangrove Pneumatophores - black mangrow Cypress Knees  Symbiotic Roots Legumes (e.g., pea, beans, peanuts) form root nodules. Mutualism between a plant and bacterium which allows for the fixation of atmospheric nitrogen to form that the plant can utilized. The bacterium is reward with food and a place to live  Symbiotic Roots  Mycorrhizae or "fungus roots" where a symbiotic relationship forms between a plant and a fungus. In this partnership the fungus provides protection against some types of pathogens and increase the surface area for the absorption of essential nutrients (e.g. phosphorous) from the soil. The plant in return provides food for the fungus in the form of sugar and amino acids Photosynthetic Roots Parasitic roots - Dodder Further reading on Stem, Leaves and Roots  Read Chapter 5 (5.1, 5.2 and 5.3) in the text book ‘The Science of Plants  Review questions will be included in Test 1  https://open.lib.umn.edu/horticulture/ Root Structure External Parts of Roots  Root Hairs  Tiny one celled hair-like extensions of the epidermal cells located near the tips of roots.  Increase surface area.  Absorb water & minerals. Internal Parts of Roots Much like those of stems with phloem, cambium and xylem layers.  Phloem  Theouter layer.  Carries food down the plant.  Xylem  Theinner layer.  Carries water & minerals up to the stem. Root Structure & Growth  Root hairs – tiny projections from the epidermis that increases the surface area for absorption of water  Cortex – layer of ground tissue  Endodermis – layer of tissue that encloses the vascular tissue  Root cap – protects the root as it forces its way through the soil