Transcript File
13B-3 Roots Not always underground Anchor the plant Absorb water and minerals Some do food storage Root systems Taproot system Primary root continues to grow as the main root Has secondary branching roots Ex. Carrot Root systems Fibrous Many Not root system secondary roots one main root Found in monocots. Growth Primary growth (in length) takes place in the meristematic region near tip of root Does mitosis Root cap- dead cells, push through soil, protects the root (see diagram) Growth Elongation region Above meristematic region, cells elongate (provides length) Cells begin to differentiate and become various root tissues Maturation region- most differentiation takes place Tissues of root Primary tissues formed during primary growth Epidermis with root hairs (extensions of epidermis) increase surface area Cortex- inside of epidermis, stores minerals Endodermis One cell layer thick, inside cortex All incoming substances must pass through it to enter rest of plant (endodermis controls what can enter) Tissues of root Vascular cylinder- center of young root Vascular cambium- makes additional xylem and phloem (secondary growth) Pericycle- will produce secondary root & growth in diameter 13 B-4 stems Woody or herbaceous Woody (tree trunk) Herbaceous – green, live for one year, rely on turgor pressure 13 B-4 stems Function of stems 1. manufacture, support and display leaves 2. conduct materials to and from leaves 13 B-4 (Draw them to remember) Branching patterns 1. Excurrent = apical dominance (grows tall first and suppress wide then grow wide later) Ex. pine tree 2. Deliquescent = apical dominance only when young (then lateral buds more active & main stem branches repeatedly) Ex. Mango tree 3. Columnar = unbranched stem with crown of leaves Ex. Coconut tree Apical meristem: cells become leaves, stem tissues, & flowers Apical bud: at end of twig Lateral buds: on sides Dormant buds: survive through winter Bud scales: protect tiny leaves, fall off & leave bud scale scars Nodes: place on stem where leaves produced Lenticels: openings for gas exchange Leaf scars: where petiole (or leaf) was attached Growth of Woody Stems Cork cambium: makes cork to protect stem (under epidermis) Pith: inside xylem, largest area of young stem, stores/conducts materials, is central material Vascular rays: from central pith horizontally outward, conduct water Growth of Woody Stems Wood: secondary xylem, made by vascular cambium during growing season Springwood: lighter color Annual ring Summerwood: darker Sapwood: functional Heartwood: dead xylem filled with chemicals, hard Bark: tissues from vascular cambium outward, protective covering on tree Inner bark: phloem & cortex Outer bark: cork expands & cracks, textured Lenticels: opening for oxygen Girdling: strip off a section of bark all the way around tree will die because phloem is disrupted Sugars can’t go down to roots, water can still go up but roots eventually die Herbaceous Dicot & Monocot Stems Stem cortex is photosynthetic, retains epidermis Vascular tissues not in concentric circles but found as fibrovascular bundles (usually at edges of stem) In some (bamboo) pith disappears hollow stem