Refined Midterm Notes PDF

Lecture 2 Plant evolution/Evolution of Photosynthesis Began 3.5 billion years ago Strarted by Cyanobacteria (Blue Green Algae) Had the ability to synthesise food/energy from Light Evidence of life on earth -Stromatolites: Layered sediment formations that are created by photosynthetic o...

Lecture 2 Plant evolution/Evolution of Photosynthesis Began 3.5 billion years ago Strarted by Cyanobacteria (Blue Green Algae) Had the ability to synthesise food/energy from Light Evidence of life on earth -Stromatolites: Layered sediment formations that are created by photosynthetic organisms -Formed by Cyanobacteria Where Plants started on earth Aquatic environment: Land plants evolved from aquatic blue green algae Intertidal Zones and estuary environments: Where plant began to come up to land Were non vascular limiting them to wet or damp environments (Mosses, Liverworts) Pressures plants faced on land Obtaining resources staying upright Fluctuation of heat and cold Aquatic Environment temps are moderate C02 for photosynthesis dissolved in water and easier to access Important Features of Plants Cell Wall made of cellulose: Provides structural support and rigidity Chloroplasts: Small organelles needed for Vacuole: Large organelles containing water, Sugars and salt to provide turgor pressure for support 1. What helped plants evolve on land Vascular tissue: 410 mya Xylem: Tissue that transport water Phloem: Tissue transport photosynthate (sugars), and hormones 2. Plants with true Roots Has Vascular tissue Provided absorption of water and dissolved nutrients Anchored Plant to ground Club mosses -Vascular: have evolved to land as they have vascular tissue to evolve to live on land -Moss: Non vascular: haven't evolved to land as they dont have vascular tissue Early Forest makeup Large Vascular plants such as ferns, horse tails, club mosses Evolution continued: - Early plants had phoo synthetic stems -Some plant lineages evolved megaphylls: Larger leaves with multiple veins containing vascular tissue Plant evo in chrono order 1. Common green algae 2. Embryo Protection: Liverworts 3. Apical Growth: Mosses and horn warts 4. Vascular tissue: club mosses 5. MegaPhylls: Ferns Terrestrial forests 6. Seeds 7. Flowering plants Lecture 3: Trees Seeds Importance of Seeds Diets on seed and fruits Nutriton for mammals, birds insects Plants before Seeds dispersed through spores: club mosses, mosses, liverworts, and ferns are made of spores Disadvantages: Spores are small, short lived, lack protection, and needs to disperse by winter or damp enviro Evolution of Seeds Can dispersese to wider range of environments Protect and nourish embryo Can persist in dormant state Regenerate after disturbance Angiosperm seed Structure Enclosed within a fruit Reproduces through flowering Dispersed via fruits: Animals, wind, water Have a Diploid Embryo: Presence of two complete sets of chromosomes Have endosperm triploid nutritive tissue called endosperm Maturity of Angiosperm growth one or two ways 1. Dicots- Stores resources in two cotyledons that are called seed leaves All Angiosperm trees are Dicots Are Hard woods and have broad , flat leaves  2. Monocots: Stores resources in endosperm Grains, corn palm trees, are monocots Gymnosperm Seed Structure Naked Seeds: Not enclosed in fruit Reproductive Structure: Cones Seed dispersal: Mostly wind, sometimes animals Seed nutrition: Female gametophyte tissue Seed Dormancy - Many seeds are dormant when they mature and are dispersed and can't grow even if conditions are favourable -Seeds with embryo dormancy require chilling exposure to low temps to break dormancy -After Dormancy: Seed need to adequate heat and moisture to germinate Lecture 4: How trees Grow Tall 1. Vascular tissue 2. Photosynthesis: does not help them grow tall Development of Vascular System 1. Xylem: A sturdy organic polymer providing support and ability to move water from the roots to leaves 2. Phloem: Allowed plants to distribute the products of photosynthesis (sugars) to different part of the plant 3. Cell division of stem cells happen in shoot apical meristem at the tip of shoots adding to height of the main stem or make branches longer Roots importance to tree growth Anchor plants in cell Mycorrhizal relationship :with fungi to get more water Trade sugar for water with funghi Bacteria: Frankia bacteria from nodules remove nitrogen from air and trees How Trees get bigger Dividing cells at the top Growth in height occurs in Primary Growth: Produced in shoot apical meristem and root apircal meristem Shoot Apical meristem and primary roots Contain Primary Xylem for water transport and Phloem for transports for sugars and hormones Xylem: Transports water and nutrients up and Phloem transports others up or down Seedling and trees growing Taller: Secondary growth  Vascular Cambium: The inner soft bark, provides Cells in vascular cambium divide to form secondary xylem (=wood) cells to the inside and Wood: Transports water up tree Secondary Phloem: transports food and other substances up or down Wood Specifications Cells that have strong secondary cell walls In Conifers Sequoia : most wood cells are called tracheids: The water conducting and mechanical supporting cells in gymosperms Mostly Dead tracheid cells oriented vertically, Late wood trachieds have thick cell walls for transport, early woods conduct water Angiosperm cells - Large diameter cells called vessel elements stack up on eachother into vessels capable of high rates of water flow Defining Bark Inner Bark: is Secondary Phloem: Consists of living cells that store and transports materials both down to the roots and up the stem Outer bark: produced by one or more meristems called cork cambiums Lecture 6: Leaves and Photosynthesis Photosynthesis: a trait inherited from a green algae ancestor Can Occur in any tissue that has chloroplasts (leaves, Green Stems) Two sets of reactions: Both reactions occur in chloroplasts Chloroplast Structure Complex organelles with a double membrane Evolved from relationship between Eukaryote and Cyanobacteria Chloroplasts contain chlorophyll, a green pigment Primary function of leaves is to conduct photosynthesis 2 reactions of photosynthesis 1. Light reactions (H20-O2) Involves chlorophyll: a pigment that absorbs light energy (red and blue light) Light energy and water Creates energy molecules and oxygen Light reactions take place in thylakoids Water transported from Xylem from roots to leaves Mesophyll Cells in Leaves  Photosynthesis occurs in palisade mesophyll of leaves Pallisade mesophyll have largest concentration of chloroplasts Release of Oxygen O2 exits leaf via stromata 2. Dark reactions (Co2-Glucose) Involves enzyme rubisco, the most abundant protein on earth Requires carbon dioxide Creates glucose: Occur in the stroma Creates carbohydrates Requires energy from light reactions High amounts of carbon are needed for dark reactions Higher Carbon dioxide result in increase of growth unless theres a limiting factor (nitrogen) Stomata Pores in leaves that plants open or close, depending on conditions Found mostly underside of leaves Temperature effect Photosynthetic rate can occur over a wide range of temperatures Ever green trees like douglas fir can photosynthesize in the winter when temps are a little above 0 degrees Tropical species have higher minimum and optimum temps than alpine or boreal species Damage due to excess light Leaves can become sunburned Sun leaves and shade leaves Sun leaf: thicker than shade leaves and can have more palisade Lecture 7: How water is transported Large amounts of water are recycled through evapotranspiration Evaporation: Water evaporation Transpiration: Water vaour loss through stomata and lenticles Function of Water in Plants Required for photosynthesis Solvent for movement of materials  Maintenance of turgidity Temp regulation- Evaporations of water loss leaves Turgor Pressure: Low turgor pressure makes plant wilt Loss of water: 5% through lenticels 3% through leaf cuticle 92% through stomata: Due to photo synthesis Stromata water loss and usage in Plants Controlled to regulate water loss Closing stromata helps prevent or delay wilting Angiosperm Trees Scientific name of Phylum: Antophyta Common name: Hardwoods, broadleaves Number of Species: -70,000: Maples, beeches, poplars, cherries, oaks Leaves: Broad and flat Gymnosperm trees Scientific Name of phylum: Ginkgophyta, ConiferoPhyta (Softwoods) Examples of species: Gingko biloba (only species) and Pines Spruces, douglas fir, larch, cedar, cypress (over 600 species) Leaves shape: Needle or scaled Seeds: naked seeds Water Potential Is expressed as units of pressure Negative water potential means water is under tension, a positive water potential means water is under tension, a positive water potential means water is under pressure Water moves from higher to lower potential (from lower tension to high tension) Potential in Trees Water travels from roots up to canopy by negative series of water potential Water columns under tension are pulled up through dead cells in wood by transpiration Columns move up through narrow trachieds in conifers (earlywood) and through wider vessels in angio sperms Process requires cohesion (from roots to leaves) to remain unbroken Water moves up sapwood only outer ring of wood) because the middle (heartwood) cells are dead  Left: Early wood tracheids trachieds in conifers Right: Vessels in Angiosperms Osmosis: Water moves into roots through osmosis Movement up Xylem from roots Water need to move up from roots in secondary Xylem (wood) If water potential in xylem= potential in roots, no water mvmt If water potential is greater than water potential in roots: water will mover up into trachied/ vessels Mvmt to leaves Water needs to move from secondary xylem into veins and then the cells of leaves Lecture 8: Colour change in leaves Autumn leaf falling Deciduous trees cannot survive freezing temperatures Soil water is unavailable when it is cold loosing the canopy reduces evaporative stress Temps of freezing result in ice crystals damaging leaf cells Senescence in deciduous plants Senescence is the co-ordinated and controlled loss of function and deterioration of leaves Process is from a critical photoperiod but can be affected by enviro conditions such as drought or early freeze Example: Vancouver has photo period of -16 hours light/8 hours dark in late june and - 9 hours light/15 hours dark in late Dec Night length, not day length that trees detect to begin senescence Senescence of leaves in Autumn Nutrients are broken down and absorbed (nitrogen, proteins, fats, chlorophyll) Recover more than half the nitrogen before leaves fall Nutrients are moved to the inner bark (secondary phloem) to store Loss of chlorophyll pigments Chlorophyll (green) is constantly replaced during active growth breaks down in bright light Carotenoid pigments Yellow and orange carotenoids are present in leaves by hidden chlorophyll Become visible as chlorophyll declines (western larch, Aspen) Anthocyanin in leaves (Purple leaves) Acts as a sun block to prevent photo oxidative damage to other pigments Produced on exposed portions of canopy Colour is more intense of the weather is sunny during leaf senesence (japanese maple, Black tupelo, Red maple) Preexistent anthocyanin pigments Some species purple leaves already known as “copper coloured” Purples foliage turn red as chlorophyll fades Rhodaxanthin pigments in Conifers Western red cedar and pine can poth accumulate a pigment call rhodax in leaves over winter Abscission Zone Occurs at the base of the petiole Layers forming in the zone 1. Separation (abscission) layer 2. Protective layer Leaf Abscission Occurs between the separation and protective layers 1. middle lamella between cells 2. Cells in separation layer expand 3. zone becomes weekend and unstable 4. Leaves fall while freezing temps, wind or gravity break abscisison zone Trees that dont fall Red Alder: because they have marescence Branch Abscission Bald cypress: undergo cladoptosis=whole branch abscisission , Dawn Redwood: Branch abscission Evergreen species Dont drop leaves all at once Leaves live for more than one growing seaso (douglas fir Some can live for as long as 7 years  Western red cedar undergoes cladaptosis Urban trees -Light can delay senescence by interfering with natural photoperiod Lecture 9: Bud Dormancy Deteminate versus indeterminate growth Determinate: when the number of leaves and internodes developing in the current season are predetermined buds formed from the previous growing season All Leaves on branches on the main stem that will develop in the spring of 2025 were initiated in buds in the summer and fall of 2024 All leaves are Preformed Terminal buds will form when the preformed shoots expand in late spring or early summer 2025 as part of shoot devo, not night length Woody plant: Trees that are “determinate” have finite growth (genetically predetermined) and stop primary growth early Indeterminate: when leaves are being produced through the current growing season All seedlings are indeterminate: in first year of growth (because there are no buds within seeds) Trees that are indeterminate have non finite growth (enviro determined) and stop growing much later Western red cedar: indeterminate species: have no buds Many species form Terminal and lateral buds containing part (indetemrinate species or all (determinate species) of the growth for the following years Neo Formed Vs Formed leaves Neoformed: initiated the same year they develop and mature (Juvenile Aspen) Preformed: leaves developing from leaf primordia within bud are pre formed leaves Active growth in Woody Plants During growing season, shoot apical meristem of tree produces new leaves and internodes, increasing the main stem or branch length Active meristems: begin to grow in temperate enviros such as spring and summer (active growing season What is a bud? A structure containing embryonic shoot protected by bud scales Vegetative buds have leaf and internode primordia as well as shoot apical meristem (=a new shoot leader or branch)  In most cases, buds are formed in one year and contain some (indeterminate species) or all (determinate of the growth the following year) Lateral buds and terminal buds Lateral buds formin some or all leaf axils throughout the growing season Terminal buds form when development is complete (determinate species) or when triggered by photo period (indeterminate species ) Most species have terminal bud at end of each branch and leader that results in growth in height or length the following year Some species abscise the tip of shoots and a lateral bud at the tip called the pseudoterminal will take over growing the next year Cues for bud set In species that are Determinate, bud set occurs early in growing season (late spring) Buds creates all growth for the following season Cue is developmental Ie. Spruce buds Cue for terminal bud formation in indeterminate growth, bud set occurs in the the growing season ( july-september) Creates only some of the growth (pre formed leaves) for the following season Cue is environment ie : maple buds Night length is measured by a compound called Phytochrome ○ -Phytochrome has two states -far red phytochrome and red phytochrome Bud Dormancy -After bud is formed they become dormant- they cannot grow even if conditions are favourable -Buds require exposure to chilling meaning temps below 5 degrees in order to break dormancy -after adequate chilling, buds will be ready to grow when temps are warmer Lecture 10:Surviving winter Determinate growth All Leaves on branches on the main stem that will develop in the spring of 2025 were initiated in buds in the summer and fall of 2024 All leaves are Preformed Leaves are preformed Terminal buds will form when preformed shoots expand in late spring or early summer 2025 as part of shoot devo not night length Indeterminate growth if species forms buds, only some leaves for 2025 will be initiated in summer in summer and fall 2024 will be pre formed leaves Added neo formed leaves will devo in 2025 If species has no buds, then all leaves will be neoformed Terminal buds will form in summer or 2025 in response to night length Anatomy of buds (Vegetative Bud) A shoot apical meristem Leaf primordia (immature pre formed leaf for next year) on an immature shoot (lateral branch or leader) that will develop next spring Strategies used for surviving winter in boreal forests Annual plants: complete their lifecycle within a year from germination to reproduction, over winter as seed (wheat, corn, watermelon, Seablush) Herbaceous perennial plants: live for multiple years, but the above ground portions senescence (dies back) each year and nutrients are transported below ground where freezing cant occur. (sprout in spring: Common camas) Woody perennials: (trees and shrubs) have to be able to survive freezing temps. Living cells in wood bark, and buds, and leaves in evergreen species must acclimate in fall (garry oak) Tropical Trees species Most are indeterminate and many are evergreen Decidous tropical tree species can be found in climates with predictable wet and dry season Tropical Species: do not to develop cold hardiness as temps fluctuate very little seasonally but they are sensitive to chilling Cold Hardiness in temperate plants Has evolved in temperate and boreal woody plants so they can with stand temps below 0 Trees Species (White spruce can tolerate the most, douglas fir, arbutus) Develops along with bud dormancy Cold Hardiness is induced by photo period Long nights trigger first phase of cold hardiness Cold acclimation begins after bud set Buds will accumulate sugars and become fully dormant Late autumn After cold hardiness starts to develop in response to night length, it accelerates in response to lower temps and mild frosts Seasonal changes in cold hardiness LT (lethal temperature) at which 50 % of tissue is damaged (Jan-Feb) Ways to prevent ice crystals inside cells 1. Extraorgan freezing: Form ice in buds outside of leaf and shoot primordia ( ice layer draws more water out of cells 2. Deep supercooling: ice crystal formation is initiated by nucleating agents including bacteria, dust and pollen Works well in many plants to prevent cold and freeze damage by stopping ice from forming even when temps or -40 Increase solute concentration in cell isolating cells from ice nucleating agents Produces anti freeze chemical 3. Extracellular freezing Ice forms-between plant cells (outside cell walls) Formation of ice is controlled to prevent tissue damage Common strategy for boreal and high elevation species Best protective mechanism for plants in very cold regions (Coastal douglas fir) Snowfall Adaptations: Flexible branches to shed snow (white pine) Spruce have narrow crowns/short branches to avoid big snow loads Loss of Hardiness in spring Dormancy ends when it receives enough chilling (temps below 1 to 5) After buds are no longer dormant, exposure to warm temps In spring they have lost their hardiness and frost tolerance Lecture 11: Spring arrives Phenology: study of the timing of bio events Records of tree Phonology- especially time of leafing out and of flowering in spring or important to understand the bio effects of climate change Enivro triggers for bud break Chilling with heat sum Resumption of growth in spring dormancy ends when buds receive enough chilling (temps between 1-5 degrees) buds become quiescent Quiescent: exposure to warm temps for long time to result in bud break Heat sum requirement bud quiescence is ended through accumulation of heat (heat and chilling are integrated) A warm winter with less chilling requires more heat sum A colder winter with more chilling requires less heat sume Optimal time for tree leaf to grow out Wait until the risk of freezing has passed needs to leaf out early to be competitive Decidious would grow out earlier Concerns about pheneology with warm climates if temps are to warm, the chilling requirement may not be met and tree will break bud to late If chilling requirement is met in early winter, warm spells may initiate growth of quiescent bud and if followed by freezing could lead to injury