Plants II Plant organs

Plant organs Root system – roots Shoot system – stem and leaves Vegetative organs – (allow to live and grow): roots, leaves, stem Reproduction: flowers, seeds and fruits

Roots Underground, usually equal to shoot system in size Anchors and gives support Absorbs water and minerals Penetrates soil as it grows Root hairs increase surface area Produce hormones

stems Main axis of plant Support leaves so that leaves are exposed to as much light as possible Node – where leaf is attached Internode – space between nodes Vascular tissue used in transport Can store nutrients and water and conduct photosynthesis

leaves Photosynthesis Size, shape and texture vary and is used in identification Blade – wide portion of leaf Petiole – stalk, attaches blade to stem Axillary bud – where branch or flower may originate

Monocot vs Eudicot fig 25.3 Compare seed leaf, root, stem, leaf and flower Monocot – 1 seed leaf, xylem and phloem in a ring, vascular bundles scattered, leaf veins parallel, flower parts in 3’s and multiples of 3 Eudicot – 2 seed leaves, phloem between arms of xylem, vascular bundles in ring, leaf veins in net pattern, flower parts in 4’s, 5’s Eudicots make up larger group and include most familiar flowering plants Monocots include grasses and most of food sources, like rice, wheat and corn

Plant tissues Meristematic tissue = embryonic Apical meristem – located on tip of stem and roots, growth produces 3 types of meristem Protoderm epidermis Ground meristem  ground tissue Procambium  vascular tissue Woody (non herbaceous), non woody (herbaceous – perennial, dies back in winter)

Epidermal tissue Forms outer protective covering of plant Walls of epidermal cells exposed to air are covered with a waxy cuticle Roots – form root hairs Stems and leaves – trichomes – hairs that protect form too much sun and moisture reserve Leaves – guard cells, stomata Periderm – old woody plants, replaces epidermis Cork cells – protection Cork cambium – new cork cells made from Lenticels – areas of overproduction of cork cells, gas exchange

Ground tissue Bulk of a plant 3 types: Parenchyma cells – most abundant, found in all organs of plant, least specialized Collenchyma – thick primary walls, flexible support to immature regions, celery strand Sclerenchyma – thick secondary walls that contain lignin (make walls tough), support mature region of plant

Vascular tissue Xylem – water and minerals, roots to leaves Phloem – sucrose and organic molecules (hormones) form leaves to roots Complex tissues – contain 2 or more kinds of cells Both extend from roots to leaves Roots- located in vascular cylinder, stem – vascular bundles, leave – leaf veins

Xylem figure 25.6 2 types of conducting cells, hollow and non-living Tracheids – tapered ends, contain pits where secondary wall does not form Vessel elements – larger, perforation plates Parenchyma cells that store substances

Phloem – fig 25.7 Sieve tube members – continuous sieve tube – no nucleus Companion cells – have nucleus Connected to sieve tube member by plasmodesmata

Root organization Root cap – apical meristem, replaced often Zones Cell division – primary meristem, mitosis Elongation – cells lengthen and specialize Maturation – root hairs, fully differentiated

Eudicot root tissue Epidermis – single outer layer, root hairs Cortex – thin walled parenchyma, food storage Endodermis – boundary between cortex and vascular tissue Casparian strip – prevents water and mineral ions between cell walls Vascular tissue – xylem and phloem Pericycle – first layer of cells Monocots similar, differ in arrangement of xylem and phloem in a ring, ground tissue is pith

Root diversity Taproot – grows straight down, fleshy, stores food, carrot, beet Fibrous root system – in monocots – seen in grasses, strong anchorage Adventitious roots – develop from shoot system instead of root system, seen in corn, can come above soil line Root nodules – beans, peas…, nitrogen fixation Mycorrhizae – plant roots and funugs

Stem organization Terminal bud – shoot tip protected by bud scales Leaf and bundle scars – location of leaves that have dropped Axillary buds – give rise to branches or flowers Bud scale scar – indicates age of stem, one for each year of growth Primary meristem  primary tissues Protoderm  epidermis Ground meristem  pith (ground tissue) Procambium  cortex (vascular tissue)

Herbaceous stems Non woody, die off in winter, perennial Only primary growth Eudicot, vascular bundle in rings, cortex separate from pith Monocot – vascular bindles scattered, no well defined cortex or pith

Woody Stems Primary (length) and secondary (girth of trunks) tissues Secondary tissues form from lateral meristem: vascular cambium and cork cambium Vascular cambium produces new xylem and phloem each year 3 distinct areas: bark, wood and pith

Bark and Wood Contains periderm Wood is secondary xylem, girth when stem becomes woody, replaces epidermis Cork, cork cambium and phloem Removing bark and be fatal to tree Wood is secondary xylem, girth Vascular cambium is dormant in winter Annual ring – sapwood, inner rings - heartwood

Stem diversity Stolons – aboveground horizontal stems, reproduce where nodes touch ground, runners, strawberries Rhizomes – underground, horizontal stems, some contain tubers (food storage) like potatoes Corm – bulbous underground stems, gladiolus

Leaf organization Consist of blade and petiole Veins are netted in eudicots, parallel in monocot

Cross section leaf Trichomes – protective hairs Cuticle – prevent desiccation but prevent gas exchange Stomata on underside Mesophyll tissue Palisade spongy

Leaf diversity Simple Compound Arrangement Pinnately compound Palmately compound Arrangement Alternate Opposite Whorled Leaves based on adaptation to environment