Life 103 Week 6
Life 103 Week 6 LIFE 103
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This 4 page Class Notes was uploaded by Caroline Hurlbut on Friday February 26, 2016. The Class Notes belongs to LIFE 103 at Colorado State University taught by Jennifer L Neuwald; Tanya Anne Dewey in Fall 2016. Since its upload, it has received 13 views. For similar materials see Biology of Organisms-Animals and Plants in Biology at Colorado State University.
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Date Created: 02/26/16
Plant Structure, Growth, & Development • destruction of habitat is causing extinction of many plant species • tropical forests estimated to be eliminated in 200 years —loss of forests reduces absorption of atmospheric CO2 • at current rate, 50% of animal species will become extinct in the next 100-200 years • 3 basic plant organs (leaves, stem, roots) are organized into a root system and a shoot system —roots rely on sugar produced by shoot system —shoots rely water and minerals absorbed by the root system • root function —anchor plant —absorb water and minerals —store carbs —radicle: embryonic root—>primary root—>taproot, which anchors the plant deeply into the ground —lateral roots: branch off taproot, improve anchorage and water absorption —root hairs: grow off lateral roots, very high surface area to access water and nutrients • types of root systems —taproot: one main root develops from radicle —ﬁbrous: radicle dies and is replaced by network of ﬁne adventitious roots • root adaptations —prop roots: anchor top heavy plants —storage roots: foods like radishes are expanded carb storage bulbs for the plant • stem - plant organ consisting of an alternating system of nodes, where leaves come out, and internodes, the segments between nodes —apical bud: growing shoot tip—>elongation of a young shoot —axillary bud: structure that has potential to form large branch, thorn, or ﬂower —many plants have modiﬁed stems A. rhizomes: horizontal shoots that grow just below the surface B. stolons: move above ground and allow for asexual reproduction of plants C. tuber: large stem full of storage material that can grow new plant (ex. potato plant) leaves are the main photosynthetic organ of most vascular plants • —intercept light, exchange gases, dissipate heat, defense —generally consist of ﬂattened blade and stalk called a petiole (axillary bud) • leaf adaptations —spines: provide protection (ex. cactus) —tendrils: grow around support structures —storage leaves: layers of leaves used to store sugars (ex. onion) • tissue systems —dermal —vascular —ground • dermal tissue - outer protective layer —epidermis: outer layer of cells (ex. root hairs) —cuticle: waxy coating over epidermis • vascular tissue - long distance transport of materials between root and shoot —xylem: conducts water and minerals —phloem: transports sugars • water conducting cells of xylem —tracheids: connect cells for water distribution —vessel elements: align to form micropipes called vessels for water transport —these cells are dead at maturity • sugar conducting cells of phloem —sieve tube elements: alive at maturity —sieve plates: porous end walls that allow ﬂuid to ﬂow between sieve tube elements —each sieve tube element has a companion cell, whose nucleus and ribosomes serve both cells • ground tissue - tissues that are not dermal or vascular —pith: ground tissue internal to vascular tissue —cortex: ground tissue external to vascular tissue —include cells specialized for storage, photosynthesis, support, and transport • 3 basic cell types —parenchyma A. least specialized B. perform most metabolic functions C. store sugars —collenchyma A. grouped in strands B. provide ﬂexible support —sclerenchyma A. rigid due to thick secondary cell walls (contain lignin) B. dead at maturity (associated with xylem) C. only exist in parts of plant that have stopped growing different meristems generate new cells for primary and secondary growth • —meristems are perpetually embryonic and allow for indeterminate growth —apical and lateral types —the root cap protects the meristem • indeterminate growth - a plant can continue to grow throughout its life • determinate growth - some plant organs stop growing at a certain size • in woody plants, primary and secondary growth occur simultaneously but in different locations apical meristems allow for growth in length—>primary growth • • lateral meristems allow for growth in thickness—>secondary growth —vascular cambium: adds layers of secondary xylem/phloem —cork cambium: produces cork cells that replace epidermis with thicker and tougher periderm —bark is composed of the periderm and secondary phloem • growth occurs just behind the root tip in 3 zones —zone of cell division —zone of elongation —zone of differentiation • most plant growth is done by elongation —they elongate by ﬁlling a large central vacuole with water • endodermis - innermost layer of cortex —regulates passage of substances from soil to vascular cylinder • lateral roots arise from the pericycle, the outermost cell layer in vascular cylinder • a shoot apical meristem is a dome shaped mass of dividing cells at the shoot tip —leaves develop from leaf primordia along sides of apical meristem —the closer an axillary bud is to the active apical bud, the more inhibited it is • tissue organization of stems —vascular tissue in eudicots arranged in a ring —vascular tissue in monocots scattered in ground tissue • tissue organization of leaves —stomata: epidermal pores ﬂanked by regulatory guard cells, allow for gas exchange and evaporative loss of water —mesophyll: ground tissue in a leaf located between upper and lower epidermis A. palisade mesophyll in upper leaf B. spongy mesophyll in lower leaf —veins: vascular bundles surrounded by bundle sheath and function as the skeleton • anatomy of a tree trunk —trees have heartwood (older dead inner layers of secondary xylem) and sapwood (younger living outer layers of secondary xylem) • developmental plasticity describes the effect of environment of development • factors of development —growth —morphogenesis: development of body form and organization —cell differentiation Resource Acquisition & Transport 2 major pathways through plants • —apoplast —symplast • apoplast - consists of everything external to plasma membrane • symplast - consists of cytosol of all living cells in the plant as well as plasmodesmata • 3 transport routes for water and solutes —apoplastic route: through cell walls —symplastic route: through cytosol —transmembrane route: across cell walls • water potential - measurement that combines the effects of solute and concentration and pressure and determines the direction of the movement of water —water ﬂows from areas with high water potential to low water potential —measured in megapascals (MPa) —addition of solutes lowers water potential —negative pressure is the mechanism by which water moves against gravity from the roots to the leaves of plants • efﬁcient long distance transport of ﬂuid requires bulk ﬂow, the movement of ﬂuid driven by pressure (not osmosis) —water and dissolved substances move together through tracheas and vessel elements of xylem and sieve-tube elements of phloem • most water and mineral absorption occurs near root tips where root hairs are located soil solution enters roots and is transported through cortex of root to vascular • cylinder, which contains xylem vessels • endodermis is last checkpoint for passage of minerals from cortex to vascular tissue —waxy Casparian strip composed of suberin in endodermal wall blocks ﬂow of water and solutes from cortex to vascular cylinder via apoplastic route —water and minerals must cross plasma membrane to enter vascular cylinder • supply of water through vascular tissue requires 2 complementary processes —*transpirational pull: evaporation of water from leaves, cohesion of water molecules by hydrogen bonding —root pressure: push of xylem sap transported by bulk ﬂow water is pulled from shoots to roots by transpiration and water cohesion according to • cohesion-tension hypothesis • rate of transpiration regulated by stomata —guard cells control diameter of stoma by changing shape —balance water conservation with gas exchange —changes in turgor pressure open and close stomata —transport of K+ ions across membranes causes turgor changes of guard cells • sugar is moved through phloem sap by translocation from sources to sinks —sugar source: organ that is a net producer of sugar, such as mature leaves —sugar sink: organ that is a net consumer or storer of sugar (ex. tubers, bulbs) • phloem sap moved by bulk ﬂow driven by positive pressure called pressure ﬂow • sugars must enter sieve-tube elements via active transport and cotransport