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Chptr 27 BI 111

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Tristan Long

Chapter 27 13-03-03 1:59 PM Photosynthetic autotroph: a photosynthetic organism that uses light as it’s energy source and carbon dioxide as its carbon source. Organ: two or more different tissues integrated into a structure that carries out a specific function. Tissue: a group of cells and intercellular substances with the same structure that function as a unit to carry out one or more specialized tasks. Totipotency: the ability to develop into any type of cells. Indeterminate Growth: growth that is not limited by the organism’s genetic program, so that the organism grows for as long as it lives; typical of many plants. Meristem: an undifferentiated permanently embryonic plant tissue that gives rise to new cells forming tissues and organs. Xylem: the plant vascular tissue that distributes water and nutrients. Phloem: the food conducting tissue of the vascular plant. Tracheid: a conducting cell of xylem, usually elongated and tapered. Vessel Members/Elements: any of the short cells joined end to end in tube-like columns in the xylem. Monocot: a plant belonging to the Monocotyledones, one of the two major classes of angiosperms; monocot embryos have a single seed leaf (cotyledon) and pollen grains with a single groove. Eudicot: a plant belonging to the Eudicotyledones, one of the two major classes of angiosperms; their embryo’s usually have two seed leaves (cotyledons), and their pollen grains have three grooves. Vascular cambium: a lateral meristem that produces secondary vascular tissues in plants. 27.1 Since plants are sessile (non-motile), they must obtain water and nutrients from the soil around them… nutrients and water are patchily distributed in the soil, (not even and gets used up by the plant) so the best solution for the plant is to INCREASE SURFACE AREA. • Both above and below ground.. not compact like animals, plants spread out in a dendritic form (tree-like/branched). o Large and spread out root and shoot system allows for greater access to water and nutrients in the soil, greater and more dominant access to sunlight, and stronger root systems keep plants in place. Plant cells: • Chloroplasts: function in photosynthesis; unique to plant cells. • Vacuole: may occupy majority of the volume in mature cells– important in cell elongation and maintenance of ridged tissues, also storage compartments • Primary Cell Wall: surrounds the plasma membrane and cell contents o Are the skeleton of the plant; serve as support o Made largely of microfibrils of cellulose, embedded into a matrix of other polysaccharides.  The combination of cellulose and other polysaccharides gives the cell wall strength and flexibility  Also contains proteins (add to strength).. not a solid barrier–> like a mesh or filter. • Plasmodesmata: cytoplasmic connections between adjacent cells o Allows solutes (ie. amino acids and sugars) to move from one cell to the next. • Middle lamella: the polysaccharide layer filling the space in between adjacent cells primary walls • Secondary wall: additional cellulose and other materials are deposited inside the primary wall to forma a strong secondary wall. o Often contain lignin–complex water insoluble polymer– which makes cell walls very strong, ridged and impermeable to water. Lignin pectin: Cellulose: Hemicellulose: Plants have a general growth pattern of indeterminate growth • Individual plant parts (leaves, flowers, fruits) exhibit determinate growth • Indeterminate growth gives plants a great deal of flexibility (plasticity) in their possible changes to an ever changing environment (changes in light, water and nutrient supply and temperature) • Allows plants to adapt: to a change in direction of light, to a depletion of water or nutrients in the soil. • Plants grow by two mechanisms: o 1. An increase in the number of cells by mitosis o 2. An increase in size of the individual cells Meristem Tissues: Meristems are responsible for growth in both girth and height Apical meristem: in all plants– clusters of self-perpetuating tissue at the tips of their buds, stems and roots. • Tissues that develop from apical meristems are called primary tissues–make up the primary plant body. • Called PRIMARY GROWTH o herbaceous plants (grass) only have primary growth. SECONDARY GROWTH: originate at cylinders of tissue called lateral meristems–increases the diameter of older roots and stems (secondary tissues) • Woody plants (trees and shrubs) have secondary tissues. Primary and secondary growth can occur simultaneously…. Apical Meristem: • Shoot apical meristem: dividing cells at all shoot tips are responsible for a shoot’s primary tissues and growth • Root apical meristem: dividing cells at root tips behind the root caps are responsible for a root’s primary tissues and growth. Lateral Meristem: • Vascular cambium: secondary growth around the middle vascular bundles • Cork cambium: secondary growth just inside the woody bark. Annuals: are herbaceous plants in which the life cycle is completed in one growing season • Minimal or no secondary growth (only apical meristems) Biennials: complete their life cycle in two growing seasons • Limited secondary growth • 1 season: roots stems and leaves form nd • 2 season: the plant flowers, forms seeds and dies Perennials: vegetative growth and reproduction continue year after year • Many have secondary tissues. monocot root system is branching and fibrous eudicot root system has a main taproot with smaller lateral roots. 27.2 Tissue System Name of Tissue Types of Cells in Tissue Function Tissues Ground Tissue Parenchyma Parenchyma cells Photosynthesis, respiration, storage, secretion Colenchyma Colenchyma cells Flexible strength for growing plant parts Sclerenchyma Fibres or Rigid support, sclereids deterring herbivores Vascular Tissue Xylem Conducting cells Transport water (tracheids, vessel and dissolved members), minerals parenchyma cells and sclerenchyma cells Phloem Conducting cells Sugar transport (sieve tube members), parenchyma cells and sclerenchyma cells Dermal Tissue Epidermis Undifferentiated Control of gas cells, guard cells,exchange, water other specialized loss and cells protection Periderm Cork, cork Protection. cambium, phelloderm Xylem: Conducts water and dissolved minerals absorbed from the soil upward from a plant’s roots to the shoot. Was a key adaptation for plants to make the transfer to land. Contains two types of conducting cells: tracheids and vessel members. • Both develop thick, lignified secondary walls and die at maturity… the now empty cell walls (cytoplasm not longer exists after death) serve as pipelines for water and minerals • Tracheids: are elongated with tapered, overlapping ends… keep plants from collapsing in dry conditions o Water moves from cell to cell in pits… water seeps laterally from tracheid to tracheid. • Vessel members: shorter and wider cells joined end to end in a tube-like colomn o Several centimeters long… in vines and trees they may be meters long o Adaptation that increases water flow: as vessel members mature, enzymes breakdown portions of their end walls, producing perforations.. holes in the ends o Water moves more efficiently through vessels than tracheids due to their greater diameter and perforated ends. Problem is air bubbles– potentially lethal to a plant • Air bubbles can get stuck in vessels, and prevent water flow… killing the plant • But the air bubbles in tracheids stay where they are and to not affect the water flow o Even though tracheids may be slower at transporting water, their pits are impermeable to air bubbles. Phloem: Transports solutes (sugars made in photosynthesis and other organic molecules) throughout the plant body. Sieve Tube Members: main conducting cells, connected end to end • Their end walls are called sieve plates– are studded with pores • Fibres and sclereids (often in the phloem as well) strengthen stems. • As the cells mature they loose the nucleus and most organelles, but continue to live • Companion cells are connected to the mature sieve cells by plasmodesmata (companion cells retain their nuclei) o Assist the sieve cells with the uptake and unloading of sugars o Help regulate the metabolism of mature sieve cells. 27.3 There are four key functions of stems: 1. Stems provide mechanical support, generally along a vertical axis, for body parts involved in growth, photosynthesis, and reproduction. These parts include meristematic tissues, leaves and flowers. 2. Stems house the vascular tissues (xylem and phloem), which transport products of photosynthesis, water and dissolved minerals, hormones and other substances throughout the plant. 3. Stems are often modified to store water and food 4. Buds and specific stem regions contain meristematic tissue that gives rise to new cells of the shoot. The Modular Organization of a Stem A plant stem develops in a pattern that divides the stem into modules, each consisting of a node and internode • Node is a place on the stem where one or more leaves are attached; the region between the two nodes is the internode. New primary growth occurs in buds– a terminal bud at the apex of the main shoot, and axillary buds which produce branches (lateral shoots) at the point where leaves meet the stem. Meristematic tissue in buds give rise to leaves, flowers or both. • We usually think that flowering plants grow from the base of their stems, but shoot grow actually occurs from the apical meristem (the tip of the plant, not the base) In eudicots, most of the growth occurs just below the apical meristem, as internode cells divide and elongate–internode cells nearest the apex are the most active Meristems in grass
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