Life 103-Week 6 Notes
Life 103-Week 6 Notes Life 103
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This 8 page Class Notes was uploaded by Addy Carroll on Friday February 26, 2016. The Class Notes belongs to Life 103 at Colorado State University taught by Dr. Dale Lockwood and Dr. Tanya Dewey in Winter 2016. Since its upload, it has received 16 views. For similar materials see Biology of organisms-animals and plants in Biology at Colorado State University.
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Date Created: 02/26/16
Life 103 Notes *adapted from the lecture notes of Dr. Dale Lockwood* Plant Structure ctn. (see week 5 notes) • Plant Tissues (see textbook figure 35.8) -Three types of tissues ~Dermal ~Ground ~Vascular • Dermal Tissue System -Epidermis ~In non-woody plants -Cuticle ~Waxy coating ~Helps prevent water loss from the epidermis -Pericardium ~In woody plants ~Protective tissues ~Replaces the epidermis in older regions of stems and roots -Trichomes are outgrowths of the shoot epidermis and can help with insect defense • Vascular Tissue System -Carries out long-distance transport of materials between roots and shoots -Two vascular tissues -Xylem conveys water and dissolved minerals upward from roots into the shoots -Phloem transports organic nutrients from where they are made to where they are needed • Vascular Tissue -The vascular tissue of a stem or root is collectively called the stele -In angiosperms, the stele of the rot is a solid central vascular cylinder -The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem • Ground Tissue System -Tissues that are neither dermal nor vascular -Pith ~Ground tissue internal to the vascular tissue -Cortex ~Ground tissue external to the vascular tissue -Ground tissue includes cells specialized for storage, photosynthesis, and support Cellular Structure in Plants • Cells (see textbook figure 35.10) -Plants have a diversity of cells that perform a variety of functions ~Consider 5 general types -Parenchyma -Collenchyma -Sclerenchyma -Water conducting cells of the xylem -Sugar-conducting cells of the phloem • Ground Tissue -Composed of ~Parenchyma ~Collenchyma ~Sclerenchyma • Ground Tissue Cells -Mature parenchyma cells ~Have thin and flexible primary walls ~Large central vacuole ~Lack secondary walls ~Are the least specialized ~Perform the most metabolic functions -Store nutrients -Photosynthesize ~Retain the ability to divide and differentiate -Key for cloning -Collenchyma cells ~Grouped in strands and help support young parts of the plant shoot ~They have thicker and uneven cell walls ~They lack secondary walls ~These cells provide flexible support without restraining growth ~Example: strings in a celery stalk are bundles of collenchyma cells -Sclerenchyma cells ~Rigid because of thick secondary walls strengthened with lignin ~Dead at functional maturity ~Have very thick cell walls relative to the cell inside the walls ~Example: pears are grainy when bitten into due to bundles of sclerenchyma cells ~There are two types -Sclereids are short and irregular in shape and have thick lignified secondary walls ~Source of hardness in nutshells and seed coats -Fibers are long and slender and arranged in threads ~Source of linen (flax fibers) and rope (hemp fibers) -Linen is made from extracting fiber cells from the plant • Vascular Tissue Cells -Xylem cells ~Cells are dead at functionality because it’s not easy to move water through living cells because of the thick cytoplasm, while it’s easy to move water through dead, hollow cells ~Each cell has to be connected to allow water to move all the way through the plant ~Tracheids -Found in all vascular plants -Tubular, elongated and dead -Water transfers via pits in the tracheids ~Vessel Elements -Larger diameter and shorter -Aligned end-to-end to form vessels -End walls have perforation plates -Phloem Cells ~Sieve-tube elements -Alive at functional maturity ~Active transport is always required for sugar to get into a cell, which can only be performed by a living cell -They lack organelles, including nucleus -Allows sugars to flow more easily ~Sieve plates -The porous end walls that allow fluid to flow between cells along the sieve tube ~Companion cell -One for each sieve-tube element -Nucleus and ribosomes serve both cells ~Sends proteins etc. to sieve-tube elements to keep it alive and able to perform active transport while not having any organelles itself Cell growth • Growth -Indeterminate growth- growing throughout an organism’s life ~Example: roots and shoots -Determinate growth- some plant organs cease to grow at a certain size ~Example: leaves -Annuals complete their life cycle in a year or less -Biennials require two growing seasons and only bloom the second year -Perennials live for many years • Where growth occurs -Meristems ~Perpetually embryonic tissue ~Maintains indeterminate growth ~Functionally similar to animal stem cells -Apical Meristems ~Located at the tips of roots and shoots and at the axillary buds of shoots -Primary growth occurs when apical meristems elongate shoots and roots (see textbook figures 35.13, 35.14, and 35.15 for root growth) (see textbook figures 35.16 and 35.17 for stem growth) -Secondary growth (see textbook figure 35.11 for types of growth) (see textbook figure 35.19 for stem growth) ~Lateral meristems add thickness to woody plants, which is required for structural support -Two lateral meristems ~Vascular cambium -Adds layers of vascular tissue called secondary xylem (wood) and secondary phloem ~Cork cambium -Replaces the epidermis with periderm, which is thicker and tougher • Secondary Growth (see textbook figure 35.22 for tree trunk anatomy) -The vascular cambium is a cylinder of meristematic cells one cell layer thick ~”Rings” go all the way up the tree trunk, hence, cylinders -It develops from undifferentiated parenchyma cells -Secondary xylem accumulates as wood, and consists of tracheids, vessel elements (only in angiosperms), and fibers -Early wood, formed in the spring, has thin cell walls to maximize water delivery -Late wood, formed in late summer, has thick-walled cells and contributes more to stem support -In temperate regions, the vascular cambium of perennials is dormant through the winter ~Stops growing cells ~New growth is fragile and the thin-walled cells could burst due to cold -Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age -Dendrochronology is the analysis of tree ring growth patterns, and can be used to study past climate change ~If the rings are closer together, that indicates that it was colder, and if they are farther apart, that indicates that it was warmer -As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals ~Used for structural support -The outer layers, known as sapwood, still transport materials through the xylem ~In other words, only the more recent secondary growth is still functioning as xylem -Older secondary phloem sloughs off and does not accumulate Plant Anatomy • Morphogenesis in plants, as in other multicellular organisms, is often controlled by homeotic genes -Morphogenesis=a change in the structure in plants -Homeotic gene=influences where an organ is located on an organism • Gene Expression and Control of Cellular Differentiation -In cellular differentiation, ~Cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome -Homeotic genes -Positional Information ~Where a cell is positioned determines what they will grow into • Location and a Cell’s Developmental Fate -Positional information underlies all the processes of development: growth, morphogenesis, and differentiation -Cells are not dedicated early to forming specific tissues and organs -The cell’s final position determines what kind of cell it will become • Shifts in Development: Phase Changes -Plants pass through developmental phases, called phase changes, developing from a juvenile phase to an adult phase ~Juvenile phase=not sexually mature ~Adult phase=sexually mature -Phase changes occur within the shoot apical meristem ~In other words, plants grow from the top -The most obvious morphological changes typically occur in leaf size and shape • Phase Changes -Juvenile plants are not competent (not sexually mature) to flower -Some woody plants accumulate secondary compounds in juvenile phase -Regulation is controlled by plant hormones, similar to how hormones control development in mammals ~Giberellic Acid plays an important role • Genetic Control of Flowering -Flower formation involves a phase change from vegetative growth to reproductive growth -It is triggered by a combination of environmental cues and internal signals -Transition from vegetative growth to flowering is associated with the switching on of floral meristem identity genes -In some plants, this requires vernalization ~Vernalization is when a plant has to first go through a cold period to alter gene expression and then hit a warm period ~As the world gets warmer, vernalization may happen prematurely, but pollinators aren’t on the same schedule, so many flowers go unfertilized and there is less reproductive success -Plant biologists have identified several organ identity genes (plant homeotic genes) that regulate the development of floral pattern ~MADs box genes -A mutation in a plant organ identity gene can cause abnormal floral development • Analogous genes exist in animals (see textbook figure 35.31 for plant example) -Mutations in Hox genes result in misplaced structures • Flower Development (see textbook figures 35.34 and 35.35) -Researchers have identified three classes of floral organ identity genes -The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs -An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes Water and Sugar (see textbook figure 36.2) • Evolutionary Notes -The algal ancestors of land plants absorbed water, minerals, and CO 2 directly from the surrounding water ~These plants always had access to everything they needed, but couldn’t grow too big -The evolution of xylem and phloem in land plants made possible the long- distance transport of water, minerals, and products of photosynthesis ~Plants gain ability to maximize access to light, increase dispersal distance, and occupy new habitats ~Have the ability to grow bigger because of vascular tissue -This comes at a cost involving the loss of H2O • Light -Light absorption is affected by the leaf area index, the ratio of total upper leaf surface of a plant divided by the surface area of land on which it grows (see textbook figure 36.4) ~How much of the surface area of the ground the plant is growing on is covered by leaves ~Look at the plant from above and see how much of the ground can be seen inside the diameter of where the plant is growing ~Example: If you see no ground and just leaves, the index is 1 -Self-pruning ~When photosynthesis is reduced below basal respiration ~When the leaf doesn’t make enough sugars to survive without help from the rest of the plant, the plant gets rid of it ~Example: A tree cuts off lower branches as it grows and gets taller and just keeps the topmost ones with the best access to light -Leaf orientation affects light absorption • Leaf Orientation -Orientation affects sun angle ~Influences photosynthetic rate ~Influences water loss ~With more direct sunlight, the leaf gets hot and there is more evaporation/water loss, so the plant requires more uptake of water -Some plants control leaf orientation ~Many plants must strike a balance between minimizing water loss while maximizing light energy gained for photosynthesis ~Heliotropic- moving in relation to the sun -Diaheliotropism-following the sun -Paraheliotropism-avoiding the sun ~This is a water stress adaptation and often occurs to plants in an environment with limited access to water • From Roots to Shoots -Transport begins with the absorption of resources by plant cells -Selective permeability is the control of movement of substances into and out of cells ~Plants only want certain things from the soil because other things could harm them, so they have to be able to control what goes in and out of their cells -Diffusion ~Passive movement of particles across a membrane ~No energy is required for facilitating movement ~Moving from an area of high density and low density in an effort to reach equilibrium ~A type of diffusion is facilitated diffusion; it doesn’t require energy because its not going against a gradient, but it can’t get through the membrane without a transport protein -Active transport ~Pumping of solutes across a membrane ~Generally requires transport proteins embedded in the cell membrane ~Works against a gradient and against diffusion ~Sometimes the particles won’t fit through the membrane by themselves • Active transport (see textbook figure 36.6) -Proton pump ~Most important transport protein for active transport ~Create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work ~They contribute to a voltage known as a membrane potential -Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes -Cotransport ~A transport protein couples the diffusion of one solute to the active transport of another ~The “coat-tail” effect of cotransport is also responsible for the uptake of the sugar sucrose by plant cells • Diffusion of Water -Plants must uptake water to offset the loss of water ~Plants lose water out their leaves during photosynthesis because they open their stomata to uptake CO ,2simultaneously causing water loss -Osmosis ~Movement of water across a semi-permeable membrane down a water potential gradient ~Determines the net uptake or water loss by a cell and is affected by solute concentration and pressure -Water potential is a measurement that combines the effects of solute concentration and pressure ~Water potential determines the direction of movement of water across a membrane ~Water flows from regions of higher water potential to regions of lower water potential ~Water always wants to flow to a more negative region to reach equilibrium -Water potential is abbreviated as Ψ and measured in units of pressure called megapascals (MPa) - Ψ=0MPa for pure water at sea level and room temperature -The solute potential (Ψ )sof a solution is proportional to the number of dissolved molecules -Solute potential is also called osmotic potential -Pressure potential (Ψ ) Ps the physical pressure on a solution -Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast - Ψ= Ψ + Ψ P S ~water potential=pressure potential+solute potential -Plasmolysis-the cell membrane pulls away from the cell wall (see textbook figure 36.7a)
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