Lecture Slides on How Plants Work | BIO 152, Study notes of Biology

Download Lecture Slides on How Plants Work | BIO 152 and more Study notes Biology in PDF only on Docsity! HOW PLANTS WORK Life: Transformation of “other” into “self” Plants: Transformation of non-life (abiotic) into living self (biotic) Question: How does a typical multicellular terrestrial (land dwelling) plant today accomplish this? Our approach – think like a plant! Look at a plant as a machine (or factory) for making more plant. Machine requires 1. materials (to make more plant) 2. energy (to do the work) (3. information - how to do it ?) Photosynthesis important for both of these needs Light energy + H2O + CO2 => Carbohydrate + O2 Carbohydrates (variations on CH2O) 1. materials e.g. cellulose 2. energy e.g. sugar How are these resources SUPPLIED by the environment? SUN: Light AIR: CO2, O2 (also N2, H2O, but not major direct source to plants) SOIL: 1. Other elements come mainly from decaying organic matter 2. Originally, most of these elements (except Nitrogen) derive from mineral rock (earth’s crust). Nitrogen enters the system from (N2 gas) via nitrogen fixation by bacteria (including cyanobacteria) 3. Water (from precip and ground flow) in soil spaces. Many elements are dissolved in soil water solution as ions (charged molecules), a main source for plants How do plants obtain these resources? Light: converted to chemical energy in the chloroplasts concentrated in leaves CO2: adjustable holes in the leaves called STOMATES expose the wet inside of the leaf to the air, allowing CO2 to diffuse into the internal leaf surfaces to be used by chloroplasts Water: taken up by the roots, which grow in a network in the soil spaces Mineral nutrients: elements in the soil water or on soil particles are selectively taken up by ACTIVE TRANSPORT across the root membrane (requires energy). (also important symbioses) How are the resources distributed throughout the plant? A system of pipes, the VASCULAR SYSTEM connect the leaves, stems and roots allowing 1. Water and nutrients to move up from the roots 2. Carbohydrates from photosynthesis to move from the leaves to the root and other demand sites. PLANT STRUCTURE We will look at plant structure in two ways Tissues Parts (organs) All tissues are found in all parts All tissues are made of CELLS, and cell wall development is a key feature distinguishing tissues in plants. PLANT CELLS - Plant cells are eukaryotic (nucleus, organelles, membranes etc.) and have external wall NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Microfilaments Intermediate filaments Microtubules CYTO- SKELETON Chloroplast Plasmodesmata Wall of adjacent cell Cell wall Plasma membrane Peroxisome Mitochondrion Golgi apparatus 6.9 6.28 Cell Wall – distinctive feature of plant cell Wall surrounds the cell and plasma membrane and is produced by it. Functions: 1. supports and protects cell 2. contributes to absorption, transport, and secretion 3. structural unit of whole plant (support) 39.8 Other molecules in wall – affect properties Hemicellulose, pectin, cutin, suberin, waxes Lignin – increases wall rigidity Important in wood Reduces hydration of cellulose 35.29 (6th only) 29.2 Wall is constructed by the plasma membrane Rosette Wall Layers Wall is deposited by the cell, and can have several layers All cells have 1. Middle lamella (between cells) 2. Primary cell wall Many cells deposit additional layers 3. Secondary wall 7.28 6.31/6.30 Thin areas in wall maintaining cytoplasmic connections between cells – PLASMODESMATA 3. Secondary Cell Walls When growth is complete, cell may deposit additional layers INSIDE the primary wall. Cell often dies after making the second wall. These cells important for - structural support - water conduction Wood – mainly highly lignified secondary walls. Several layers, alternating orientation of fibrils – like laminated plywood. Plant development – “morphogenesis” Mitosis ensures all cells have all genes. Differentiation requires that different cells express different genes depending on where they are in the plant. This is a very active area of research. Read more about this in your text: pp757-760 (pp730-733 7th) 35.30/35.27 One gene did this! CELLS AND TISSUES To build a multicellular plant, cells must not only multiply, they must differentiate to produce the different plant structures (leaf, stem, root etc.) Main tissues – found throughout plant (all “parts”) 1. Ground tissues (“simple” – single cell type) parenchyma (most common) collenchyma sclerenchyma 2. Vascular tissues (“complex” – multiple cell types) xylem phloem 3. Dermal tissues epidermis periderm 35.8 1. Ground tissues – key distinction is cell wall development Parenchyma - thin primary wall - alive a maturity - progenitor of other tissues (meristems) - diverse functions – regeneration, recovery from damage, photosynthesis, storage, secretion 35.10/35.9 Collenchyma - alive at maturity - thickened (flexible) primary wall - elongated, often in strands (e.g., celery) - support in stems and petioles 35.10/35.9 2. Vascular Tissues – Xylem and Phloem Xylem - main water conducting tissue - also mineral conduction, food storage, support - with phloem, form plant-wide conduction system – the “plumbing” - both primary and secondary in origin - “complex” tissue – contains other cell types – parenchyma cells for storage and translocation Tracheary elements – main conducting units (single or multicellular) - elongated open conduits, closed ends - dead at maturity - pits throughout cell walls - water flows up through and between elements (via pit-pairs) 35.10/35.9 Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids Pits Tracheids and vessels (colorized SEM) Vessel Tracheids 100 µm Phloem - main sugar (photosynthate) conducting tissue - alive at maturity - both primary and secondary in origin Sieve elements – main conducting units, single or multicellular (parallel to tracheary elements) - “sieve” refers to dense pore region between cells (analogous to pit pairs) - protoplasm along walls, lack nuclei or vacuoles - specialized Associated Cells – nucleated cells that regulate inputs and outputs - “Companion Cells” Complex tissue - includes storage cells and support fibers Epidermis contains many specialized cells 1. Guard Cells – create stomatal opening, regulate CO2 intake and transpiration 2. Trichomes – variable outgrowths, including leaf hairs, root hairs, glandular hairs, stinging hairs - nutrient uptake - temperature regulation - protection - excretion (salts) Very hairy pod (10 trichomes/ mm2) Slightly hairy pod (2 trichomes/ mm2) Bald pod (no trichomes) Very hairy pod: 10% damage Slightly hairy pod: 25% damage Bald pod: 40% damage EXPERIMENT RESULTS Fig 35.9 summarizes a simple experiment investigating trichome function using soybeans and bean leaf beetles Periderm - replaces epidermis in secondary growth of stems and roots - mostly cork cells – non-living and heavily suberized (suberin) We will see this again when we look at secondary growth 35.22/35.20