4Structure of a plant determined by: 1. Genetics2. Environment – two time scales:a. Long-term: accumulation of adaptations that enhanced survival & reproduction (evolution by natural selection)b. Short-term: plasticity = wide range of phenotypes for each genotype. Allows plants to adjust to changing environment (ex. Shorter plant in dry year so that it can still reproduce)
5Muscle cellParenchyma cellCellsTissuesMuscle tissueDermal tissueOrgansHeartLeavesCirculatory systemSystemsShoot system
6Three organs: Roots, stems, leaves a. Collect water & minerals from soilb. Anchor plantc. Store food (carb’s from photosynthesis) to be used for flowering & fruitingd. Covered with root hairs – increased surface area for absorption
92. Stems/shoots a. Support, transport b. Some photosynthesis c. Two types of shoots* Vegetative – leaves only* Reproductive – produces flowersTwo parts of the stem:* Node – point of leaf attachment* Inter-node – stem segments between nodes
10Two types of budsApical dominance = the presence of an apical bud inhibits the growth of axillary buds.- remove or depress apical bud, axillary buds begin to grow.1. Terminal bud – contains a shoot apical meristem; shoot growth is concentrated here2. Axillary buds – in angle (axil) between leaf & branch, contain meristem with potential to become a vegetative shoot. Mostly dormant.
16Three main tissues: Dermal, Vascular, & Ground Fig 35.8
171. Dermal tissue or epidermis A. single layer of tightly packed cells covering the young parts of the plant.B. Functions in protectionC. Root hairs are specialized epidermal extensionsD. Secretes waxy cuticle of the leaf
182. Ground TissueA. Fills the space between dermal and vascular tissue systems.B. Diverse functions:photosynthesisstoragesupportpithIn eudicots:cortex
193. Vascular TissueA. function in transport between roots & shoots, and structural support of planta. Xylem: H2O & minerals transported up to shoot systemb. Phloem: Food transported to roots & non-photosynthetic parts such as the flowers
21The Plant Cell Same as animals, except: a. No lysozomes (digestive organelle)b. Cell walls: maintains shape, structural support, protects from damage. Made of cellulose, protein, & sometimes ligninc. Chloroplastsd. Vacuole – storage, waste breakdown, growth!e. Plasmodesmata – holes in cell wall, creates channels to connect cytoplasm of adjacent cells
225 Differentiated Plant Cell Categories 1. Parenchyma4. Water-conducting cells of the xylem3. Schlerenchyma5. Sugar-conducting cells of the phloem2. Collenchyma
231. ParenchymaA. Least specialized cell. Can differentiate into other cell typesB Primary cell walls only - thin and flexibleC. Lack secondary plant cell wallsD. Most metabolically active – lots of chloroplasts for PSN (PhotoSyNthesis)E. Starch, carbohydrate production & storage in stems
242. Collenchyma A. Primary walls are unevenly thickened B. Usually lack secondary walls.C. Usually grouped in strands to support young parts of plants without restraining growthD. Flexible, elongate with growing shoots
253. Schlerenchyma A. Function in mechanical support B. Have rigid and thick secondary walls strengthened with lignin.C. May be dead at functional maturity – ???D. Cell walls left behind as skeletonTwo types, both function in support:Fibers - long, slender, tapered cells occurring in bundles.Sclereids - short, irregularly-shaped. Ex. hard seed coats
335. Sugar-conducting cells of the phloem 2 types:A. Sieve-tube members:a. Chains of cells arranged end-to-endb. Alive at functional maturityc. Lack a nucleus, ribosomes, vacuoled. Cells separated by perforated sieve plates – allow sugar movementB. Companion cellsa. Load sugars into the sieve tube memberb. nucleus and ribosomes also serve the sieve-tube member.
36Development is the sum of all the changes that progressively elaborate the plant’s body.
37Three processes of development: 1. Growth = increase in mass, due to cell division & elongation2. Cellular differentiation = generation of different cell types3. Morphogenesis – creation of body form & organization.
381. GrowthA. Cell division in itself does not mean an increase in growth.B. Cell division yields no expansion of size.C. Cell elongation increases growth.
39Cell elongation 1. due to water uptake 2. Direction of expansion = perpendicular to alignment of cellulose microfibrils in cell wall3. Enzymes weaken cross-link between microfibrils, allowing cell to expand.
43Plant growth vs. Animal growth 1. Unlike animals, plants:A. Embryonic, developing, and mature organs exist together at the same time on one plant.B. Grow until they die, called indeterminate growth. Some determinate parts: leaves, flowers.
44Three types of life cycles: 1. Annual – complete life cycle (germination through fruiting) in one year or less. Examples: grasses, crops, wildflowers2. Biennial – complete life cycle in two years (first year = vegetative, second year = reproductive). Some need a cold winter period to initiate flowering from vegetative state. Ex. carrots3. Perennial – live year after year, do not die after reproduction. Examples: trees, shrubs, some grasses. Causes of death = fire, disease
46Meristems1. region of the plant with continuous cell division (i.e. perpetually embryonic tissue)2. Two types of meristems:A. Apical meristem – located at the root and shoot tips, responsible for growth in length (called primary growth)B. Lateral meristems – extend lengthwise along the axis of the stem & roots. Responsible for growth in girth in older parts of the plant (called secondary growth). Exist only in perennials
48Primary Growth of Roots 1. Occurs at root tip (Root Apical Meristem)2. Root cap – layer of cells that protect the RAM as it pushes through the soil
493 zones moving upward from RAM: 1. Zone of cell division – contains the RAM2. Zone of cell elongation – cells elongate, thereby pushing the root tip through the soil3. Zone of maturation – cells differentiate and become functionally mature (i.e. become part of one of the 3 tissue systems)
51Arrangement of Primary Tissues in Roots 1. Epidermis – water, minerals absorbed through root hairs2. Stele – central cylinder of vascular tissue (monocots have slightly different arrangement).A. Pericycle = outermost layer of stele. Lateral roots arise from this in order to remain continuous with vascular system.3. Ground tissue – mostly parenchyma cells of the cortex – area between the stele & epidermis; stores food & takes up minerals.A. Endodermis – single cell layer between cortex & stele. Selective barrier for uptake of soil solution contents into vascular system.
53epidermisxylemphloemcortexpithendodermispericycleFig Cross section of a monocot root
54Primary Growth of Shoots 1. Leaves arise on sides of the SAM2. Axillary buds arise from areas of meristematic cells left behind at the bases of the leaf primordia.3. Bud = cluster of leaf primordia created by meristem. No internodes4. Lateral branches arise from axillary buds
59Tissue arrangement of leaves 1. Ex. of how structure reflects function – designed for maximum photosynthetic efficiency2. 3 parts:A. Upper & lower epidermis – tightly interlocked cells, secrete waxy cuticle. Contains stomata flanked by guard cellsB. Vascular tissue – leaf veins, branch throughout mesophyll
60C. Mesophyll – ground tissue between upper & lower epidermis a. 2 kinds of parenchyma cells:i. Palisade – columnar, at top of leafii. Spongy – smaller, below palisade, gas-filled spaces between cells
62Secondary Growth 1. Shoots & roots of perennials only, not in leaves 2. Occurs in oldest parts of plant3. Two lateral meristems:A. Vascular cambium – produces secondary xylem (= wood) & phloemB. Cork cambium – replaces the epidermis with cork: tough, thick cover for stems, roots.
63Secondary growth of stems 1. Vascular cambium – layer of cells between primary xylem & primary phloem. Puts on successive layers of secondary phloem to outside & secondary xylem to inside =====> stem widensA. Dormant in winter, leaves scar when activity resumes ==>annual ring2. Wood = accumulation of secondary xylem. Dead at maturity, contains lignin
64Cork cambium 1. Located in the cortex 2. Produces cork cells to replace epidermis3. Periderm = cork + cork cambium4. Lenticels = cracks in the periderm that allow gas exchange for living cells in the interior5. “bark” = all cells external to the vascular cambium (secondary phloem & periderm)6. Cork continually sloughs off7. Growing secondary phloem becomes new cork cambium (thus no build up of secondary phloem)
69Secondary growth in roots 1. Vascular cambium forms within stele, produces secondary xylem & phloem2. Cortex & epidermis shed3. Cork cambium arises from pericycle & produces the periderm4. Periderm – impermeable to water!Thus only young roots absorb from soil, old roots function = anchor & transport
70Three processes of development: 1. Growth2. Cellular differentiation3. Morphogenesis
71Cellular Differentiation 1. transformation of genetically identical cells into cells with diverse biochemical and structural features. How?A. Selective transcription of appropriate genesB. How? Ch.39
72The Flow of Information TranscriptionReplicationTranslationModificationRNAPolypeptideFunctional ProteinDNAEnergyAmino AcidsAdditional Materials
731. Regulation at transcriptional level 2. Regulation at translational level3. Regulation at post translational level4. Hormonal controls5. Regulation at substrate level6. Regulation by environmental signals: light, gravity,…..
74Morphogenesis1. The coordinated arrangement of cells into tissues & organs2. Pattern formation – development of specific structures in specific places (e.g. Flowers born on the terminus of branches as opposed to leaf axils.3. Depends on:A. Positional information – chemical signals from surrounding cells indicate the cell’s position on plantB. Polarity of the plant, asymmetrical cell divisionsC. Both affect the transcription of homeotic genes
751. Meristem identity genes – cause a vegetative shoot to become a floral shoot 2. Positional information (derived from chemical messengers) selectively turn on or off organ–identity genes.3. Organ–identity genes - code for transcriptions factors that regulate expression of genes controlling the development of specific organs.
76Fig 35.31By “turning off” organ identity genes, we can give a rose more petals
77The fleeting moments captured in engrains of the mind.