ANNOUNCEMENTS Donovan office hours this week in Biological Sciences building Wed 12 20 1 10 in room 526 Fri 2 30 3 20 room 412 Learning survey 2 closes today 11 55 pm Case Study 1 session s occur this week HW assigned 2 7 is due at beginning of class on Wed 2 12 Exam 1 Pick up your exams from the BLC picture ID required If you think that your answer deserves more points based on the answer key please write a written hardcopy regrade request that carefully argues your evidence facts and logic reasoning for why more points are requested Please submit your request along with your exam to Dr Donovan no later than the beginning of class on Mon Feb 17 IF UGA closes due to weather this week Lectures and exam 2 will be shifted The missed case studies will be made up one week later same day and time TODAY Primary and Secondary Growth Clicker For plants meristems allow plants to grow or extend in A length C neither length not width B width D both length and width Dicot Plant example subset of angiosperms Primary growth from apical meristems produces short lived expendable organs with lots of SA for resource acquisition leaves and roots with hairs and other structures o Axillary bud meristem dormant apical meristem o Root tips root apical meristems o Shoot tips shoot apical meristem and young leaves Herbaceous plants ONLY have primary growth Secondary growth from lateral meristems produce width growth increasing circumference in true woody plants gymnosperms and angiosperm dicots o Vascular cambium cork cambium lateral meristems Apical meristems increasing length of plant parts reaching growth Assigned reading Essence of Plantness New leaves and stem produced by growth at shoot apical meristem Apical meristems on top of developing vascular strand surrounded by leaf primordia baby leaves where mitotic division have occurred As apical meristems grow out in length the leaves will grow out to full size leaves If most of the mitotic divisions occur at the apical meristem then what dominates as leaves expand grow to full size A turgor drives cell elongation of flexible cell walls B leaf apical meristem produces new cells that elongate C Lateral meristem in leaf drives width growth D meiosis produces cells with larger volume Leaf doesn t have apical meristem so B is incorrect No lateral meristem this occurs on stems to make it wider so C is incorrect Meiosis doesn t happen in any apical meristems so D is incorrect Elongate cells through turgor pressure because cell walls are flexible so A is CORRECT o Sets up water potential gradient to bring water in to expand walls o Signal to lock down cell wall connections to make cell walls rigid once elongated completely o No turgor no growth Cells doing mitosis are right behind apical meristems Root apical meristem Zone of cell division right around apical meristem Root cap Protective layer of cells over apical meristem o First parts are living but some are dead that are just protective Zone of elongation o In between cell division and differentiation Zone of differentiation o root hairs forming o no longer moving any more o movement would rip off root hairs Lateral meristems Lateral branching roots arise from de differentiated parenchyma near xylem Root hairs don t grow into multicellular lateral roots these are entirely different structure Root hairs epidermal cells Lateral meristems new apical meristem that grows out can produce new root hairs Study question Why do new roots arise near vascular tissue Clicker primary growth from apical meristems produces cells with A primary cell walls C both B secondary cell walls D neither Primary cell walls have to be able to expand Secondary cell walls produce all other cell types o Primary growth produces all tissue types vascular epidermal ground Primary secondary growth very different from primary secondary cell walls o Cell walls what cell type is it o Growth what type of meristem is it Secondary growth Lateral meristems add girth or thickness Stems and roots Woody plants only 2 lateral meristems Vascular cambium up stem but not out to leaves and out to roots Secondary growth produced from lateral meristems Secondary lateral meristems Vascular cambium Cork cambium Secondary tissues Function secondary xylem wood more transport tissue Secondary phloem part of bark Cork or periderm part of bark Protection This year s growth reaching Primary and secondary growth occurring at the same time just different section of plant Where is the vascular cambium and the tissues it produces Xylem is on inside of dicot Vascular cambium forms between primary xylem and phloem Where the newest tissue produced by this cambium occur in 2 nd year stem Where is vascular cambium moved to for next year How does vascular cambium form Secondary vascular tissue Cambium continually displace outward o Cambial initial stem cell divides to form 2 cambial initials or 1 cambial initial and 1 secondary xylem cell or 1 cambial initial and secondary phloem cell More xylem than phloem produced o secondary xylem cells tracheids vessel elements fibers o Secondary phloem cells sieve0tube elements companion cells parenchyma fibers In temperate regions Spring wood xylem relatively large diameter thinner walls Clicker Which wood was most recently produced A1 B2 C3 D4 Wood xylem 1 secondary phloem 2 secondary xylem 3 primary phloem 4 primary xylem When tree is cut down vascular cambium is right under bark All phloem has been pushed off There is still phloem in a living tree Sapwood xylem Secondary xylem layers active in water transport Active in water transport Heartwood xylem Older secondary xylem layers No longer active in water transport Darker due to resins Dendrochronology study of tree ring growth pattern More secondary tissue produced in warm years and less in cool years Graph showing ring width for a series of cores taken from preserved Mongolian conifers Can be used to reconstruct climate date archeological sites determine age of oldest living trees Wood is xylem dead sclerenchyma tissue Secondary dermal tissue Where is the cork cambium and what tissues does it produce