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Plant Growth AP Biology 2007-2008 Growth in Animals Animals grow throughout the whole organism many regions & tissues at different rates versus… AP Biology Growth in Plants Specific regions of growth: meristems stem cells: perpetually embryonic tissue regenerate new cells apical shoot meristem growth in length primary growth apical root meristem growth in length primary growth lateral meristem growth in girth secondary growth AP Biology 2-year old stem AP Biology Apical meristems AP Biology shoot root Root structure & growth AP Biology protecting the meristem Shoot growth Apical bud & primary growth of shoot region of stem growth axillary buds “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium AP Biology Vascular tissue Primary xylem Growth in woody plants Primary phloem Woody plants grow in Epidermis height from tip Lateral meristems primary growth apical meristem Woody plants grow in diameter from sides secondary growth lateral meristems Primary phloem Secondary phloem Secondary Primary xylem xylem vascular cambium makes 2° phloem & 2° xylem cork cambium makes bark Annual AP Biology growth layers Bark Secondary growth Secondary growth growth in diameter thickens & strengthens older part of tree cork cambium makes bark growing ring around tree vascular cambium makes xylem & phloem growing ring around tree AP Biology Vascular cambium division… AP Biology Vascular cambium Why are early & late growth different? Phloem produced to the outside Xylem produced to the inside bark cork cambium phloem xylem vascular cambium AP Biology late early last year’s xylem cork cambium Woody stem How old is this tree? vascular cambium late early 3 2 1 xylem phloem AP Biology bark Tree trunk anatomy tree girdling What does girdling do to a tree? AP Biology Aaaargh! Murderer! Arborcide! Where will the carving be in 50 years? AP Biology Transport in plants H2O & minerals transport in xylem transpiration evaporation, adhesion & cohesion negative pressure Sugars transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure Gas exchange photosynthesis CO2 in; O2 out stomates AP Biology respiration O2 in; CO2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant? Ascent of xylem fluid Transpiration pull generated by leaf AP Biology Water & mineral absorption Water absorption from soil osmosis aquaporins Mineral absorption active transport proton pumps active transport of H+ aquaporin root hair AP Biology proton pumps H2O Water flow through root Porous cell wall water can flow through cell wall route & not enter cells plant needs to force water into cells Casparian strip AP Biology Controlling the route of water in root Endodermis cell layer surrounding vascular cylinder of root lined with impermeable Casparian strip forces fluid through selective cell membrane filtered & forced into xylem cells Aaaah… Structure–Function yet again! AP Biology Root anatomy dicot AP Biology monocot Mycorrhizae increase absorption Symbiotic relationship between fungi & plant AP Biology symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant Transport of sugars in phloem Loading of sucrose into phloem flow through cells via plasmodesmata proton pumps cotransport of sucrose into cells down proton gradient AP Biology Pressure flow in phloem Mass flow hypothesis “source to sink” flow direction of transport in phloem is dependent on plant’s needs phloem loading active transport of sucrose into phloem increased sucrose concentration decreases H2O potential water flows in from xylem cells increase in pressure due to increase in H2O causes flow AP Biology On a plant… What’s a source…What’s a sink? can flow 1m/hr