http://www.fugu-sg.org/~elia/cambodia/templesfacesweb/pages/A3_Embracing_Roots.htm Structure Reflects Function
Structure of a plant determined by: 1. Genetics 2. 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)
Cells Tissues Organs Systems Muscle cell Muscle tissue Heart Circulatory system Parenchyma cell Dermal tissue Leaves Shoot system
Three organs: Roots, stems, leaves 1. Roots a. Collect water & minerals from soil b. Anchor plant c. Store food (carb’s from photosynthesis) to be used for flowering & fruiting d. Covered with root hairs – increased surface area for absorption
2. Stems/shoots a. Support, transport b. Some photosynthesis c. Two types of shoots * Vegetative – leaves only * Reproductive – produces flowers Two parts of the stem: * Node – point of leaf attachment * Inter-node – stem segments between nodes
Apical dominance = the presence of an apical bud inhibits the growth of axillary buds. - remove or depress apical bud, axillary buds begin to grow. Two types of buds 1. Terminal bud – contains a shoot apical meristem; shoot growth is concentrated here 2. Axillary buds – in angle (axil) between leaf & branch, contain meristem with potential to become a vegetative shoot. Mostly dormant.
Fig 35.8 Three main tissues: Dermal, Vascular, & Ground
1. Dermal tissue or epidermis A. single layer of tightly packed cells covering the young parts of the plant. B. Functions in protection C. Root hairs are specialized epidermal extensions D. Secretes waxy cuticle of the leaf
pith cortex In eudicots: 2. Ground Tissue A. Fills the space between dermal and vascular tissue systems. B. Diverse functions: –photosynthesis –storage –support
3. Vascular Tissue A. function in transport between roots & shoots, and structural support of plant a. Xylem: H 2 O & minerals transported up to shoot system b. Phloem: Food transported to roots & non- photosynthetic parts such as the flowers
The 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 lignin c. Chloroplasts d. Vacuole – storage, waste breakdown, growth! e. Plasmodesmata – holes in cell wall, creates channels to connect cytoplasm of adjacent cells
5 Differentiated Plant Cell Categories 1. Parenchyma 2. Collenchyma 3. Schlerenchyma 4. Water-conducting cells of the xylem 5. Sugar-conducting cells of the phloem
1. Parenchyma A. Least specialized cell. Can differentiate into other cell types B Primary cell walls only - thin and flexible C. Lack secondary plant cell walls D. Most metabolically active – lots of chloroplasts for PSN (PhotoSyNthesis) E. Starch, carbohydrate production & storage in stems
2. 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 growth D. Flexible, elongate with growing shoots
3. 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 skeleton Two types, both function in support: Fibers - long, slender, tapered cells occurring in bundles. Sclereids - short, irregularly-shaped. Ex. hard seed coats
4. Water conducting cells of the xylem: A. 2 types: tracheids & vessel elements
Tracheids a. are long, thin tapered cells having lignin-hardened secondary walls with pits. b. Dead at maturity c. Water flows from cell to cell (laterally) through pits in cell wall d. Support function
Vessel Elements a. are wider, shorter b. Arranged end-to-end to form tubes c. End walls are perforated for free flow of water d. More efficient as water conductors than tracheids
5. Sugar-conducting cells of the phloem 2 types: A. Sieve-tube members: a. Chains of cells arranged end-to-end b. Alive at functional maturity c. Lack a nucleus, ribosomes, vacuole d. Cells separated by perforated sieve plates – allow sugar movement B. Companion cells a. Load sugars into the sieve tube member b. nucleus and ribosomes also serve the sieve- tube member.
http://www.cneccc.edu.hk/subjects/bio/album/Chapter20/PLANT_GROWTH.html Growth & Development
Development is the sum of all the changes that progressively elaborate the plant’s body.
Three processes of development: 1. Growth = increase in mass, due to cell division & elongation 2. Cellular differentiation = generation of different cell types 3. Morphogenesis – creation of body form & organization.
A. Cell division in itself does not mean an increase in growth. C. Cell elongation increases growth. B. Cell division yields no expansion of size. 1. Growth
Cell elongation 1. due to water uptake 2. Direction of expansion = perpendicular to alignment of cellulose microfibrils in cell wall 3. Enzymes weaken cross-link between microfibrils, allowing cell to expand.
Plant 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.
Three types of life cycles: 1. Annual – complete life cycle (germination through fruiting) in one year or less. Examples: grasses, crops, wildflowers 2. 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. carrots 3. Perennial – live year after year, do not die after reproduction. Examples: trees, shrubs, some grasses. Causes of death = fire, disease
Meristems 1. 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
Primary 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
3 zones moving upward from RAM: 1. Zone of cell division – contains the RAM 2. Zone of cell elongation – cells elongate, thereby pushing the root tip through the soil 3. Zone of maturation – cells differentiate and become functionally mature (i.e. become part of one of the 3 tissue systems)
Arrangement of Primary Tissues in Roots 1. Epidermis – water, minerals absorbed through root hairs 2. 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.
epidermis xylem phloem cortex pith endodermis pericycle Fig 35.13 Cross section of a monocot root
Primary Growth of Shoots 1. Leaves arise on sides of the SAM 2. 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 internodes 4. Lateral branches arise from axillary buds
Primary tissue arrangement of stems 1. Eudicots: A. Epidermis B. Vascular bundles arranged in ring a. Ground tissue = pith & cortex b. xylem faces pith, phloem faces cortex 2. Monocots: vascular bundles scattered throughout ground tissue
Tissue arrangement of leaves 1. Ex. of how structure reflects function – designed for maximum photosynthetic efficiency 2. 3 parts: A. Upper & lower epidermis – tightly interlocked cells, secrete waxy cuticle. Contains stomata flanked by guard cells B. Vascular tissue – leaf veins, branch throughout mesophyll
C. Mesophyll – ground tissue between upper & lower epidermis a. 2 kinds of parenchyma cells: i. Palisade – columnar, at top of leaf ii. Spongy – smaller, below palisade, gas-filled spaces between cells
Secondary Growth 1. Shoots & roots of perennials only, not in leaves 2. Occurs in oldest parts of plant 3. Two lateral meristems: A. Vascular cambium – produces secondary xylem (= wood) & phloem B. Cork cambium – replaces the epidermis with cork: tough, thick cover for stems, roots.
Secondary 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 widens A. Dormant in winter, leaves scar when activity resumes ==>annual ring 2. Wood = accumulation of secondary xylem. Dead at maturity, contains lignin
Cork cambium 1. Located in the cortex 2. Produces cork cells to replace epidermis 3. Periderm = cork + cork cambium 4. Lenticels = cracks in the periderm that allow gas exchange for living cells in the interior 5. “bark” = all cells external to the vascular cambium (secondary phloem & periderm) 6. Cork continually sloughs off 7. Growing secondary phloem becomes new cork cambium (thus no build up of secondary phloem)
Secondary growth in roots 1. Vascular cambium forms within stele, produces secondary xylem & phloem 2. Cortex & epidermis shed 3. Cork cambium arises from pericycle & produces the periderm 4. Periderm – impermeable to water! Thus only young roots absorb from soil, old roots function = anchor & transport
Three processes of development: 1. Growth 2. Cellular differentiation 3. Morphogenesis
Cellular Differentiation 1. transformation of genetically identical cells into cells with diverse biochemical and structural features. How? A. Selective transcription of appropriate genes B. How? Ch.39
The Flow of Information Transcription Replication Translation Modification RNA Polypeptide Functional Protein DNA Energy Amino Acids Additional Materials Energy
1. Regulation at transcriptional level 2. Regulation at translational level 3. Regulation at post translational level 4. Hormonal controls 5. Regulation at substrate level 6. Regulation by environmental signals: light, gravity,…..
Morphogenesis 1. The coordinated arrangement of cells into tissues & organs 2. 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 plant B. Polarity of the plant, asymmetrical cell divisions C. Both affect the transcription of homeotic genes
1. 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.
Fig 35.31 By “turning off” organ identity genes, we can give a rose more petals
The fleeting moments captured in engrains of the mind.