jimtrue.com : school : BSC2011L : Lab 04: Kingdom Plantae - Part 1 - Plant Tissues & Non-Vascular Plants

Posted by Jim True on September 28, 2004 2:24 PM. Last Updated October 22, 2006 9:23 PM

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Lab 04: Kingdom Plantae - Part 1 - Plant Tissues & Non-Vascular Plants

Plant Tissues & Organs

• Plants have fewer tissues and organs (roots, stems & leaves) than animals
• Simple Tissues - Formed by 1 cell type.
1. Parenchyma - simplest, most widespread type, found throughout body of plant..
• Thin primary cell wall. Two different types of cell wall; all contain Primary cell wall, rather thin, made of cellulose, can expand and contract.
• Cell is alive at maturity.
• Occurs throughout plant.
• Functions in support (pith & cortex), storage (starch & water), phtosynthesis ("chlorenchyma").
2. Collenchyma - Thick primary cell walls ("squared off appearance")
• Cell is alive at maturity, mainly along outside of stems, provide support against gravity.
3. Sclerenchyma ("scler" - hard) - Primary & Secondary Cell wall; hollow box; cell is dead at maturity, found along vascular bundles and "veins" also in some fruit tissues and around seeds. Support & Protection.
• Two types:
1. Fibers - Cells are filamentous - form long strands, e.g. Woven from flax sclerenchyma fibers to form linen
2. Sclereids (aka stone cells) - Small clusters in tissues (e.g. Pear 'grit") or fused to form 'pits' (e.g. Cherry, Peach).
• Complex Tissues - Several cell types:
1. Xylem ("wood") - formed by special tubular cells. two different types:
1. Tracheids (primitive vascular plants); lie side by side
2. Vessel elements (advanced vascular plants);
• Carry water upwards & outwards; like pipes running through the plant.
• Support for xylem comes from parenchyma & schlerenchyma
2. Phloem ("bark") Formed by Companion cells - provide functional support for the sieve tube cells; and, sieve tube elements - carry food and nutrients from psyn sites. Support for phloem comes from phloem parenchyma and phloem sclerenchyma.
   • Xylem & Phloem found together known as Vascular bundles ("veins"); plants do not possess a circulatory system. Xylem ONE-WAY flow of water. Phloem is ONE-WAY flow of nutrients. Presence of Vascular bundles DEFINE Vascular plants.

Organs

• Three main organ systems - Leaves, Stems & roots
• Leaves main site of psyn; typically have in construction in cross-section:
• cuticle, upper surface - waxy secreted layer for water-proofing (to prevent loss of water); (99% of water absorbed at the roots);
• Upper/Lower epidermis - modified parenchyma - no chloroplasts; clear, allow light to enter.
• Openings in lower epidermis (stomata/stoma) - openings for gas exchange) Oxygen out, CO2 in, water vapor in; guard cells on either side of the stoma (only epidermal cells with chlorplasts), kidney bean shape; in Turgor, open; low water; closed.
• Palisades layer - chlorenchyma - psyn.
• Beneath, spongy mesophyll - chlorenchyma - psyn & gas exhange (main function).
• Cacti - stems are the main psyn site in cacti; not the leaves.
• Stems - 2 types:
  1. Herbaceous (always soft & green) - support + PSYN.
  2. Woody - become quite hardened - function is support, protection.
• Herbaceous plants primary xylem & phloem is all that is ever found. Woody plants gives rise to secondary x + p.
• Vascular cambium - gives rise to secondary x + p; x always deposited to intertior of v.c., p always deposited to the exterior.
• Cork cambium - produces outer layer of dead, waterproof cells ('cork') - a/k/a bark. constantly being sloughed off. Secondary phloem is trapped between cork & vascular cambium. Every year a tree grows, it accumulates another layer of secondary xylem (wood). Girdling a tree (cutting into the section of the bark (the phloem) will cut-off the food supply).
• Root - Two functions: water and miineral transport; anchoring the plant in the soil. No pith parenchyma (all cortical); central cylinder - single large vascular bundle. Outer surface of roots, epidermal cells form elongate structures called root hairs - extensions of single epidermal cells on surface of roots. Increase supply of food/water and gas exchange. Responsible for ALL the water uptake.

Differentiation