Life 103- week 6
Life 103- week 6 LIFE 103
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This 4 page Class Notes was uploaded by Alexis Darling 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 7 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
Tissue organization of leaves: Epidermis spotted with stomata pores, mostly on the undersides of leaves (because the spongy mesophyll is the lower layer), for the exchange of carbon dioxide and oxygen gas and the evaporation of water which works to pull water up from the roots. Guard cells (2) on both sides of each stomata contract or relax to open and close the pores; may close completely at night because no photosynthesis occurring, may open more on humid days, etc. Mesophyll=the ground tissue of a leaf (between the upper and lower epidermis, around the vascular tissue), responsible for nearly all photosynthesis (therefore many chloroplasts), consists of 2 types in eudicots: ● Palisade mesophyll upper layer, tightly packed ● Spongy mesophyll lower layer, loosely arranged with many gaps/pathways for air to pass through and circulate carbon dioxide and oxygen Veins form skeleton structure for leaf with vascular bundles, includes bundle sheath around veins. Remember this vascular tissue in the leaf is continuous with that of the stem. Secondary Growth: Increases diameter of stems and roots, produced by lateral meristems ● Vascular cambium as this ring of cells (one cell thick) divides, it adds layers of secondary xylem (wood) on the inside of it and secondary phloem (part of the bark) outside of it ● Cork cambium the ring of cells further outside of secondary phloem which produces cork cells forms tough, thick periderm to replace epidermis *Bark=secondary phloem + cork cambium + periderm ● Heartwood the center, older layers of secondary xylem, dead and dried out; no longer usable for transport of materials but highly lignified for structural support ● Sapwood outer layers, newer secondary xylem useful for transport, softer than heartwood *Wood=layers of secondary xylem Early wood is produced in spring and its xylem cells typically have a large diameter Late wood is produced in late summer, early fall and its cells have smaller diameter but thicker cell walls. ★ Overall point Primary and secondary growth continue at the same time, but primary occurs only at the tips of shoots and roots and secondary growth occurs only in the stems and roots grown previous years. Development: A) Growth irreversible size increase B) Morphogenesis cells organize into tissues which organize into organs which determine the shape of the body C) Cell differentiation process by which cells, despite having the same genes, develop unique characteristics of different cell types; controlled by gene expression through the functioning of transcription factors Resource Acquisition and Transport Pathways: ● Apoplast flows outside of the plasma membrane through cell walls, extracellular spaces, interior of vessel elements, or tracheids ● Symplast flows through cytosol of all the living cells by plasmodesmata (the membrane lined holes between cells which connect them) Routes (using these pathways): ● Apoplastic route through the apoplast; mainly in cell walls and between cells (ie. extracellular spaces) ○ Must cross plasma membrane when it reaches the Casparian strip before entering the xylem ● Symplastic route through cytosol ○ Must cross plasma membrane of root hair in order to begin this route ● Transmembrane route through cell walls, across membranes, and through cytosol ○ Crosses many plasma membranes as it passes through cells in its path ~Water Potential: measure which takes into account both pressure and solute concentration ➔ More dissolved solutes lowers water potential ➔ More pressure raises water potential Water flows from high to low water potential! Therefore this determines the direction of water flow. *Bulk flow= fluid movement due to pressure differences The path: 1. Most water and mineral absorption through root hairs 2. Water and mineral solution travels through cortex via one or a combination of the above mentioned routes 3. When it reaches the endodermis the layer of cells surrounding the vascular cylinder, therefore the innermost portion of the cortex it will run into the casparian strip if it has not already entered the cytoplasm of a previous cell, and all of the solution that will enter the vascular tissue must pass through a plasma membrane here. ★ Casparian strip waxy belt before the vascular cylinder which ensures that all water and minerals must pass through a selectively permeable membrane before entering vascular tissue (blocks toxins and unneeded materials). No solution that had previously been traveling through the apoplastic route (not entering cells) will be able to enter the xylem if it cannot pass a membrane, because this strip blocks it. 4. Once in the vascular tissue, the water uses cohesive properties to pull more water up as some evaporates from the leaves above. (this is called transpirational pul) Other process which works with the pull is root pressure, which acts as a pushing force from the xylem sap. Strongest process in water movement: Transpiration as water evaporates from leaves, the transpired water is replaced by water which is coming up from the roots, which pulls by cohesion the water molecules below it and creates this tension up reaching all the way to the roots. Rate of transpiration controlled by guard cells of stomata: ● When stomata must be open (for gas exchange during photosynthesis), guard cells transport K+ions through plasma membrane and vacuolar membrane into their vacuoles so that water flows in by osmosis (more ion solute lowers water potential). High water pressure makes guard cells turgid, pushing against each other and increasing diameter of the stoma. ● When stomata must be closed (to minimize water loss during night/times of little photosynthesis), the opposite K + pumping occurs so that guard cells have little turgor pressure, become flaccid, and close in on each other, decreasing diameter. Summary: Transpirational pulls is the negative pressure from evaporation through stomata, which works with positive root pressure for bulk flow of xylem sap against gravity. The key aspect through the xylem is cohesion tension of polar water molecules pulling each other. Sugar Transport ❖ Translocation the term for the movement of products of photosynthesis (mostly sucrose) through phloem ❖ Phloem sap the solution of sugars dissolved in water ❖ Sugar source organ that has a net production of sugar (it also uses some but it gives more than it uses) ➢ Usually leaves ❖ Sugar sink organ that has a net consumption of sugar (whether through growth processes or storage) ➢ Usually tuber or bulb ➢ *Role reversal: Leaves can be the sugar sink in the spring, as they require a lot of sugar to grow and do not yet produce as much as they use. That makes the storage root the sugar source as it pumps out sugar and gives it for the leaves to use. But during the summer, the leaves produce a lot of sugars through photosynthesis and movement of sugar is directed down to roots for storage (making leaves the sugar source and the tuber or bulb the sink). ➢ Sugar must be pumped by active transport into sieve tube elements. ➢ First sugar is loaded in, then water follows by osmosis, creates solution, and increases pressure so that it moves to the low pressure area of the sugar sink; movement of phloem= pressure flow because of this positive pressure. ➢ Once in sink, sugar is moved out of sieve tubes and into tissues, once again by active transport: ➢ Movement of sugars across membranes accomplished by proton pumping moving lots of + + + H ions out then cotransporting the sugar in with an H ion (because H ions will be trying to get in to reestablish equilibrium, so the cotransporter pumps bring in sugar with them).
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