, . CONCEPTUAL Life Science Cells and Tissues [ln1rodUClOIy note: This is • roJl unitin1M course 15Jteach it. The pIJ15 ell lIIimaJ dssucs couJd be caily ilKlOqlOJ'llled inIo the inuodudion to SCClion 011 the human lIIilllll. Not 10 CISY to do with tbe p1llllS because die only real emphasis on pllln1S 1hlIt 1bac is will be wi1h tbe enersY 8IId photosynthesis Wlil So, lun cnterin& it heR. We 1liiy WII'IIIO 1hink IbouI die pboIosyntbcsis IOIlIC II1CR end come up wi1h somdhin& tike the BJCCI!. pllll~ makes food for us, or IJ'CCII pllll15 IIId photos)'nlhcsis. . .~ AI, III expedient, Jh."e typed in all ofthe notes that I use with my studcn1s. In _ lecture book I usc, there Ire drawinp for IICIriy nery tissue. 1bcsc hIVe been oml1lcd bere. I till always dnIw diem later ifwe decide to 10 tblllOUtf. FHO 3/J1104) PYRAMID OF BIOLOGICAL STRUcnJRE Organism OrganSystems . Organs Tissues Cells Figure CT-1. The ~yramid ofbiological structure. Living things exhibit stnlcture and organization. The basic unit ofstructure and function is the cell. CeJls are organized into units containing similar cells. These are called tissues. Different types oftissues are found in an organ. For example, an organ . such as the stomach has epithelium, muscle and nerve tissue in it Organs are organized into structmal· units called organ systems. The stomach is part ofthe digestive system. The digestive system also contains other organs. Therefore, a living creature, such as a human, is an organism containing various organ systems with their component organs, made oftissues ofwhich the basic units are the cells. PLANT TISSUES I. Meristematic tissues Meristematic tissues have embryonic, undifferentiated cells. Undifferentiated is a tenn used to mean that the cells have not changed into other cells yet•. CT-1C1-2 When embryonic cells change into other cells they undergo a process called differentiation. Differentiation is the process ofbecoming different. In meristematic tissue, the ceJls have the ability to divide using mitosis but they have not chBnged into othertissuetypesyet. Theyeventuallywillbecomecellsofothertypes. Flowering plants such as trees have meristems located in three places: the shoot tip, the root tip and the cambium layerbetweenthe barkofthetreeandthewood. A. Shoot tip Thereisameristemattheendofeachbranchofatree. Itisprotectedbya bud. The ceJlsin the shoot tip meristem (also known as,the' apical meristein) prod~ce embryonic cells thatwill eventually developinto the stems, branches and leaves ofthe tree. The bud has one year's worth ofgrowth inside. In the spring when the trees deploy their leaves, the bud begins to grow and the leaves develop and deploy quickly. During the summer, the tree makes another set ofleafbuds for next year so that next spring, it is ready to deploy its leaves a~ the appropriate time. B. Root tip There is a meristem at the tip of each root. The meristem enables the I'QOt to grow deeper into the soil. It also produces the other root tissues. The root tip meristem is protected by a root cap so that friction with the soil does not wear it down. After the cells ofthe root tip divide, they begin to elongate. This produces a zone of elongation in theroot. Thisproductionofnewcellsandelongationprocesspermitsthe root to penetrate deeper into the soil. . C. Cambium The cambium is found between the xylem and phloem layers of woody stems. It producesnewxylemandphloemcells. Thisactivityincreasesthediameterofthe ~. Since cambium is active only dming the growing season, the xylem tissue forms in rings. Atree generally produces one ring ofxylem per year. Therefore you can detennine the age ofthe tree by counting the rings. The appearance ofrings is produced by placing this spring's new, large-diameter cells immediately adjacent to last summer's old, small-diameter cells. D. Pennanent tissues A. Surface tissues 1. . Epidermis. . CT-3 The epidermis contains living cells and is found on the surfacesofyoung stems and leaves. The lower epidennis ofleaves contains specialized occlusive cells known as guard cells that SlDTOund openings in the leaves called stomates. "Stomate" is derived from Latin and means hole. The guard censregulatethesizeoftheholes in the leaves and pennit exchange of gases (CO2. 02) and water vapor with the air. The epidermis generally has a waxy outersurfacetopreventlossofwaterbytheplant exceptwhenthe . stomates are open. 2. Periderm The periderm contains non-living cells that have thick secondary walls. The walls are waterproofed and made impenneable with a material called suberin. Periderm is a tissue thatreplacestheepidermisonolderstemsoftheplant. Thesuberin-containingsecondary walls ofthe peridenn prevent loss ofwaterby the plant B. Fundamental tissues 1. ParenChyma Parenchyma contains living cens that are capable ofceD division. It is the least specialized ofthe plant tissues. These cells have thin primary waIls. Parenchyma is \ISed as a filler tissue in such plant structures as com stalks. 2. Collencl1yma Thecellsofcollenchymaareusuallyalive. Theyhavesecondarywallmaterial that is deposited in the comers giving them a characteristic appearance under the .microscope. This type oftissue is.found in c~ types ofstems. Itservesasasupport tissue. 3. Sclerenchyma a. Fibers Thefibersofsclerenchymaaredead. Thesecellshaveverythicksecondarywalls and very small lumens. A lumen is a cylindrical space surrounded by a cylindrical structure. The space inside a garden hose is a Imnen. "Lumen" means light-sort oflike the light at the end ofthetwmel. The very thick waIls offiber cells give them much strength. This type oftissue serves as a structural support tissue in stems. It is often associated with vascular bw1C:Ues.CT-4 b. Sclereids The cells ofsclereidsare'also dead. Like the fibers, they have very thick secondarywallswithverytinylumens. Sclereidsarespherical. Theyarepart of such. plant stJUctures as peach pits. 4; Endodennis Theendodermisisalayeroflivingcellsfoundintheroot. It has awaterproofing layer known ~ the Casparian strip containing lignin and suberin, two impermeable materials. The Casparian strip prev~ts materials from leaking .from the outer tissues of the root into the center where the vascular tissue is located. The plant uses the endodermis to regulate what materials enter the plant and are transported up to the stem and leaves. C. Vascular tissues 1. Xylem Xylem ~lls are dead. Xylem is a transport tissue that conducts water and minerals upward in the