Plant Structure and Growth Ch 35 Plant Tissues

Plant Structure and Growth Ch. 35

Plant Tissues l Plants have three types of tissue: l l l Dermal Tissue Vascular Tissue Ground Tissue l Each tissue has a different function

l Dermal Tissue l l l Covers the plant, acts as protection Made of endodermis, epidermis, guard cells, root hairs, and cuticle. Vascular Tissue l l Transports water and nutrients throughout the plant Made of xylem and phloem l Xylem: Carries water and minerals and is made of two type of cells:

l Tracheids: long, skinny cells that overlap and are tapered at the ends. l Water goes from one cell to the next through areas with no secondary wall called pits l The secondary walls of the tracheids are hardened with lignin, making tracheids useful for support as well as transport l Vessel Elements: Usually wider, shorter, thinner walls and less tapered than tracheids l Linked together end to end, while water flows from cell to cell through perforated end walls l Water can also move laterally to neighbor cells through pits

l Phloem: Carries sugars from the leaves to the rest of the plant using active transport. Consists of: l Sieve tube members: end walls contain sieve plates that allow the flow of fluid from one cell to the next. l Unlike xylem, phloem cells are alive at maturity even though they don’t have nuclei, ribosomes, or vacuoles. l Every sieve tube member has at least one companion cell which has a full set of cell organelles, so it can nurture the sieve tube member

l Ground Tissue l l l Most common type of tissue in a plant. Main function is support Ground tissue consists of three types of cells: l Parenchyma l Look like traditional plant cells l Primary cell wall is thin and flexible l No secondary wall l One large vacuole l Carries out most metabolic functions l When turgid with water give support and shape to plant l Ability to divide and differentiate into other cell types when a plant has been injured

l Collenchyma l Unevenly thickened primary cell walls l No secondary cell walls l Mature collenchymal cells are alive l Function is to support the growing stem l Sclerenchyma l Very thick primary & secondary cell walls that are fortified with lignin l Function is to support the plant l Two forms: l Fibers: long, thing, fibrous, occur in bundles l Sclerids: short, irregular shape

Plant Organs l Plants have three basic organs: l Roots l Stems l Leaves l Roots l Absorbs nutrients from soil l Anchors the plant l Stores Food

l Root surfaces are covered by epidermis which is modified for absorption l Root hairs: Skinny extensions from the epidermal cells that extend out and increase surface area l Cortex: parenchymal cells that contain plastids for storage of starch and other materials l Stele: Vascular cylinder of the root made of xylem and phloem covered by a layer of pericycle which gives rise to lateral roots l Endoderm: Tightly packed layer of cells surrounding the stele. Selects what minerals enter the stele and the body of the plant

l Types of roots: l Taproot: single, large root that gives rise to lateral roots called branch roots l Taproot is the primary root in many dicots and some go deep in soil for water l Fibrous Root System: Common in monocots and hold plant firmly in place l Adventitious Roots: Rise above ground and help support the plant

l Stems l Vascular tissue called vascular bundles run through stems l Vascular bundles have xylem facing outward and phloem facing inward, with meristem tissue between the two. l l l Monocots have vascular bundles scattered throughout the stem Dicots have vascular bundles formed in a ring on the edge of the stem Ground tissue of the stem is made of parenchymal tissues modified for storage called cortex and pith

l Leaves l Designed to maximize sugar production and limit water loss l Epidermis is covered with waxy material called cutin to minimize water loss l Guard cells: control opening of stomates l Inner section of leaves are made of palisade and spongy mesophyll cells used for photosynthesis l Vascular bundles (also called veins) located in the mesophyll carry water and nutrients from the soil to the leaves l Vascular bundles can also carry sugar from leaves to other parts of the plant

Plant Growth l Meristems: embryonic tissue that continually divides, creating new cells l Plant growth is based on meristems l Primary Growth: Elongation of the plant down into soil and up into the air l Apical Meristems are responsible for primary growth and are located at tips of roots and in buds of shoots l Secondary Growth: Increase in girth l Lateral Meristems are responsible for secondary growth

l Growth in length is concentrated at the root’s tip l There are three zones: l Zone of Cell Division l Meristem cells that are actively dividing l Produce new cells that extend down into soil l Zone of Elongation l Cells elongate l Push root cap down into soil l Zone of Maturation l Cells undergo specialization l Root Cap: Protects root tip by secreting substance that helps digest earth so the root tip can grow into soil