BIO1L - Morphology of Stem.pptx

UNIT 3 MORPHOLOGY OF STEM Importance of Stem 1. Support 2.Growth 3.Conduction Stem stems develop from the plumule of the germinating seed. an ascending growing organ of the plant Plumule is the part of the seed embryo that develops into the shoot of the pla...

UNIT 3 MORPHOLOGY OF STEM Importance of Stem 1. Support 2.Growth 3.Conduction Stem stems develop from the plumule of the germinating seed. an ascending growing organ of the plant Plumule is the part of the seed embryo that develops into the shoot of the plant.  External Structure of the Stem  External Structure of the Stem 1.Terminal Bud: Located at the tip of the stem, the terminal bud contains developing leaves or flowers. responsible for the plant’s vertical growth 2.Axillary Bud: found at the junction of the leaf and stem (in the axil). These are dormant buds which can potentially develop into future lateral branches, flowers, or leaves 3. Node: a point on the stem where leaves or buds emerge. It is crucial for leaf attachment and branching 4. Internode: the section of the plant stem between two nodes (where leaves attach). The length of the internode affects the overall height of the plant​ 5. Lenticel: Small, porous openings in the bark of woody stems that allow for gas exchange between the plant and the atmosphere. 6. Leaf Scar: a mark left on the stem after a leaf falls off. It helps identify where leaves were once attached. Leaf Scar 7. Bundle Scar: these are Bundle small marks inside the leaf Scar scar, indicating the vascular bundles. Bundle Scar INTERNAL STRUCTURE OF STEM Arrangement of vascular bundles in monocot and dicot stems differs significantly: In monocot stems, the vascular bundles are scattered In dicots, the vascular bundles are arranged in a throughout the entire stem. Found in periphery area ring near the periphery of the stem, leaving the and at central parts of the stem. center with no vascular bundles in the middle. Gabi (Taro) Monocot or Dicot? Gabi (Taro) is a Monocot Vascular Bundle Consist of vascular tissues; Xylem and Phloem which are responsible for water and food transport. Cambium: in the vascular bundle refers to a layer of actively dividing cells found between the xylem and phloem. Produces new cells of xylem and phloem and responsible for secondary growth of stem. The cambium produces new xylem and phloem cells: the growth direction is xylem toward the center, phloem toward the outside. Epidermis The outermost layer of the stem. It protects the plant from damage and water loss. It also have a waxy coating called the cuticle (prevent water loss). Pith the central part of the stem made up of soft, spongy parenchyma cells. It stores nutrients, water and food.  Collenchyma cells Found under the epidermis and provides flexibility. Sclerenchyma cells provide structural support and forming tough fibers that strengthen the stem. Cortex - layer of cells located between Parenchyma cells the epidermis and the vascular bundle. It most common plant cell/tissue is made up of parenchyma cells, type, found throughout the collenchyma and sclerenchyma cells, stem. For photosynthesis and depending on the plant. storage. Does stem of Plant has Endodermis? Yes or No Stems don’t have an endodermis because the stem don’t absorb water and nutrients directly from the soil like the root does. The endodermis is primarily found in roots and acts as a protective barrier that controls movement of water and nutrients into the vascular system. Which in stem, this role is handled by the vascular bundle (controls transport of water and nutrients) and the epidermis (serve as protective barrier), so an endodermis isn’t needed.  How to Determine Age of a Tree? Just count the annual rings! One ring = One year