Biology 203 1st Edition Lecture 17Outline of Last Lecture I. Limits to cell sizeII. Advantages to MulticellularityIII. What is necessary for multicellularity?IV. Organisms in-between unicellular and multicellularV. Complex cell differentiationOutline of Current Lecture I. Pros and cons of growing biggerII. Plant bodiesIII. Turgor pressureIV. Sclerenchyma cellsV. How do trees hold themselves up when they grow sideways?VI. Three tissue systemsVII. Bud primordia and axillary budsCurrent LectureI. Pros and cons of growing biggera. Pros:i. Greater reach for resource acquisitionii. Harder for consumers to kill youiii. Decreased surface area per unit volume iv. Good for holding temperaturev. Good for decreasing water lossb. Cons:i. Requires use of additional resourcesii. Bigger reward for consumersiii. Decreased surface area per unit volumeiv. Less exchange with the surrounding environmentII. Plant bodiesa. Leavesi. Most leaves have a petiole and a bladeii. Can be simple or compound in structureb. Stemsi. Composed of nodes and internodesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. If internodes do not elongate, plant has a basal growth form; elongation results in caulescent growth formiii. Branches are produced at the nodesc. Rootsi. Relatively simple branched structures; no nodes or internodesii. Root hairs are extensions of a single epidermal celliii. General term for plant hairs grown this way = trichomesd. Cellsi. Plant cells are surrounded by a rigid wall woven from cellulose strandsii. Adjacent cell walls are cemented together by middle lamellaiii. Plasma membrane and the cell’s contents are pushed up against cell walliv. Tunnels through walls allow for connection of plasma membranes of adjacent cells: plasmodesmataIII. Turgor pressurea. Non-woody plant parts are supported by turgor pressurei. Plant cells contain more solutes than the water surrounding themii. So water is always “trying” to flow into the celliii. Fills the cell until the pressure of the surrounding cell wall will not let any more iniv. Keeps cells “plump” (= turgid) v. This turgor pressure provides most of the support in non-woody plant partsb. Loss of turgor = wiltingi. If something happens so that individual cells are NOT surrounded by dilute water, water leaves the cells ii. Wilting is a loss of turgor; extreme wilting results in plasmolysis and deathof cellc. Turgor pressure + a thin cell wall is enough support for many plant partsi. Parenchyma is the name for plant tissues made of cells with just a primary cell wallii. Very common throughout living parts of plant bodiesd. A thin cell wall with thickened areas provides more supporti. Collenchyma cells have unevenly thickened primary wallsii. Support growing plant partsiii. Can grow along with whatever they are supporting iv. Common in non-woody stems and leaf petiolesIV. Sclerenchyma cellsa. Have a thick secondary cell wallb. Secondary wall forms INSIDE primary cell wall, but outside of plasma membranec. Development of secondary wall almost always kills the cell: dead at functional maturityd. Provides the support for woody plant partsi. Conducting cells of secondary xylem (more on that later) in softwoodsii. Conducting cells plus fiber cells in hardwoodsiii. Long, skinny cellsiv. Very thick secondary cell wallsv. Also found in mature non-woody structuresV. How do trees hold themselves up when they are growing sideways?a. Consider the whole plant’s body – how could roots help balance a tree?b. Consider wood density – how could growing stronger, denser wood in certain areas help hold a tree up?c. Woody gymnosperms produce compression wood on lower side which pushes tree upd. Woody Anthophyta produce tension wood on upper side which pulls tree upVI. Three tissue systemsa. Dermal tissue system: protection, mostly on outsideb. Vascular tissue system: transport of materials (xylem and phloem)c. Veins in leaves and other structuresd. Ground tissue system: everything else! Most living cells, basic physiologye. Present from the very beginning of a plant’s lifei. A seed contains a young sporophyte known as an embryoii. Embryos have stems, roots and leavesiii. Special seed leaves called cotyledonsiv. Also have partly-developed true leavesf. Primary growthi. Primary growth is the production of non-woody stems, roots and leavesii. Occurs from root and shoot apical meristems iii. A meristem is a plant growth point, where undifferentiated cells are producedg. Root apical meristemi. Located at the tip of a growing root, protected by root capii. Some of the cells produced in the root apical meristem replace root cap cells being sloughed offiii. The rest form the growing rootiv. Root hairs develop in slightly older regionh. Shoot apical meristem (SAM)i. SAM is protected by young leaves at shoot tip (apical or terminal bud)ii. SAM produces leaf and bud primordia iii. Will develop into leaves and axillary buds at the nodesiv. Spaces between leaf/bud primordia sets become the internodesVII. Bud primordia and axillary budsa. Bud primordia develop into axillary budsb. Each axillary bud contains a dormant meristem that is prevented from growing bychemicals secreted by shoot apical meristemc. When SAM gets far away enough or is removed, an axillary bud may start growing a lateral shoot = a new branchd. Axillary bud becomes the SAM for the new