BIO203 Midterm 2 Review PDF

BIO203 MIDTERM II REVIEW TEST DATE: Chapters Studied: Week 5: The Evolutionary History and Diversity of Land Plants Week 6: Plant Water Relations I/Photosynthesis II (C4 and CAM) Week 7: Plant Water Relations II. Acquiring Water and Nutrition by Roots Week 8: Nitrogen Assimilation and S...

BIO203 MIDTERM II REVIEW TEST DATE: Chapters Studied: Week 5: The Evolutionary History and Diversity of Land Plants Week 6: Plant Water Relations I/Photosynthesis II (C4 and CAM) Week 7: Plant Water Relations II. Acquiring Water and Nutrition by Roots Week 8: Nitrogen Assimilation and Secondary Metabolites Week 9: Hormones in Growth and Development LECTURE 5 – The Evolutionary History and Diversity of Land Plants Overview of Plant Evolution Plants are important to the Earth’s ecosystems as it provides O2 and plays a part in terrestrial food chains Land plants (embryophytes) originated from green algae (a.k.a. charophytes) The transition from water to land is one of the most important evolutionary steps that shaped life on earth Origins of Land Plants (embryophytes) Ancestors: Green Algae (Charophytes) Key Milestones: ○ CAMBRIAN: ○ ORDOVICIAN: first embryophyte (land plant) ○ SILURIAN: vascular plants with xylem and phloem emerging ○ DEVONIAN: the development of seed plants (early gymnosperms and trees) ○ CARBONIFEROUS: Very high O2 levels, so the plants underwent lots of evolution of cuticles, stomates, vasculature, lignin roots, vascular cambium, Bark, seeds, dominance of forests and coal formation ○ PERMIAN: Dry (arid) conditions, diversification of gymnosperms (naked seeds) ○ TRIASSIC: Gymnosperms became more dominant (recovery of ecosystems after Permian mass extinction) ○ JURASSIC: Gymnosperms dominating, angiosperms merge towards the end ○ CRETACEOUS: rise of angiosperms (flowering) ○ NEOGENE/PALEOGENE: no new major groups, total numbers of Plant Species Grow, Angiosperms biggest contributors, C4 metabolism arises in multiple families The Transition to Land Challenges: drying out, structural support in a non-buoyant medium, obtaining nutrients, reproduction without water to transport gametes (reproductive cells for plants) ADAPTATIONS: ○ Gametangia: protect gametes from desiccation ○ Stomata: minimizes water loss ○ Cuticle: prevents water loss Alternation of Generations: the life cycle alternates between the multicellular gametophyte (haploid) and sporophyte (diploid) stages 4 Groups of Plants Bryophyte ○ non-vascular (ex. liverworts, mosses, and hornworts) ○ Reproduction: depends on water, using flagellated sperm that swims to eggs (dominant gametophyte stage) ○ Small: the lack of conducting cells limits the size of the plants, generally keeping them under 5 inches high ○ Major adaptations to life on land: waxy cuticles and root-like structures Vascular: ○ Tracheophytes developed during the Silurian period ○ Earliest vascular plants had no roots, leaves, fruits or flowers ○ Vascular tissue allows plants to grow larger and transport water and nutrients more efficiently ○ 2 groups: Non-Seeded Vascular Plants: free sporing (lycophytes and ferns) Have a dominant sporophyte 2n generation Reproduction is still dependent on water for sperm movement using spores Ferns were dominant in the carboniferous period (coal formation) Ferns were certainly the first vascular plants that evolved on Earth (mid-Silurian), still abundantly present today Pteridophytes: spore-forming plants – clubmosses, ferns 3 major adaptions: true roots, vascular tissue, lignin Seeded Vascular Plants: non-flowering (gymnosperms and angiosperms) Gymnosperms: ○ Characteristics: naked seeds (not enclosed in fruits) Adapted to drier environments Wind pollination common in gymnosperms  ○ Key Adaptations: pollens and seeds Angiosperms (flowering plants): ○ Innovations: Flowers: specialized reproductive structures that attract pollinators, increasing reproductive success Fruits: structures that enclose seeds and aid in dispersal Double fertilization: one sperm fertilizes the egg, and the other sperm forms the endosperm and provides nutrition for the embryo ○ Monocots VS Dicots: Monocots: one cotyledon Dicots: two cotyledons The Evolution of Seed Plants: The Earliest seed plants emerged in the late Devonian Seeds represent significant evolutionary advancement: ○ Protection: from harsh conditions ○ Dormancy: seeds can wait for favourable conditions to germinate ○ Dispersal: seeds are spread to new environments Dominated terrestrial ecosystems during the Mesozoic era (Triassic, Jurassic, cretaceous; age of dinosaurs) LECTURE 6 – Plant Water Relations I IMPORTANCE OF WATER Cells contain mostly water (80% to 95%) which hydrates cells and participates in photolysis and hydrolysis (biochemical reactions) Medium for transportation of solutes Maintains plant shape Supports cell expansion and growth Transpiration: more than 99% of the water that enters a well-watered plant through the roots is generally transpired directly Water is for cooling and temperature regulation Case study/example: ○ If a plant has less than the full amount of water in its cells, the leaves start to wilt ○ Water loss by transpiration also regulates the temperature Ex. grass stays cool on a hot day  How? – grass plants have narrow leaves (little leaf surface), thick cuticles and sunken stomata Sunken Stomata: found below the leaves surface, usually found in arid environments, like cacti and conifers, minimizes water loss (reduces the gradient of water vapour concentration between inside of leaf and external environment, protection from air currents because of location, temperature moderation at opening) WATER RELATIONS Water Potential ○ Water Potential(𝛹): a measure of the potential energy of water in a system that affects the direction of water movement – water moves from high to low ○ Measured in megapascals (MPa) or bars Healthy hydrated cells = 0.05 to -0.2 MPa Compared to: seawater (-2.5 MPa), 1M of sucrose (-2.7 MPa), 1M of NaCl (-4.4 MPa), water-stressed plants (-1 MPa to -1.5 MPa) ○ Formula: 𝛹 = 𝛹p + 𝛹s (+ 𝛹g) ○ Factors that affect water potential = Osmotic Potential (solute potential) 𝛹s or 𝛹𝛑: solute concentration Pure water has a water potential of 0, sugar/solute decrease 𝛹s, becoming more negative 𝛹s = 𝛹pure water (0) - 𝛹water with solute Pressure Potential 𝛹p : the physical pressure exerted on the water (ex. Turgor pressure) Typically positive in cells under turgor pressure (0.1-1MPa) ○ Positive because water gains energy under pressure Negative in xylem during transpiration: -1 to -2 mPa or lower in tall trees ○ Negative because water is being pulled up the xylem + 𝛹p: mechanical support and drives expansion - 𝛹p: in xylem supporting water transport over long distances (esp. in tall plants) Gravitational Potential 𝛹g: effect of gravity on water movement Not relevant for short plants but significant for trees and tall plants (to reach the top leaves) ○ The Osmometer: a device used to measure the osmotic potential or osmolarity of a solution and determines the concentration of the solute particles that affect the movement of water through a selectively permeable membrane  ^ movement of water from lower solute concentration (higher water potential) to higher solute concentration (lower water potential) across semipermeable membrane ○ The Cell as an Osmometer When the osmotic potential in the vacuole is more negative than the surrounding solution – the water flows in As water enters the cell, the pressure potential builds up and applies the pressure on the cell wall When 𝛹𝛑 = 𝛹p – Dynamic Equilibrium ○ When water availability drops: Turgor pressure ↓ Water potential ↓ Plant begins to wilt when 𝛹cell = 𝛹pi outside cell (because the pressure potential:0) Selective Membrane Permeability ○ Osmosis – the movement of water across cell membrane according to concentrations of dissolved substances inside and outside cell ○ Plant cells have TWO selectively permeable membranes: Plasma membrane (cell membrane) – regulates movement of dissolved substances into cytoplasm and external environment Active transport (using energy)/Passive Transport (diffusion) for essential ions/moleucles – Potassium, calcium, sucrose Vacuolar membrane (tonoplast) – reculates movement of dissolved substances between the vacuole and cytoplasm – in and out of vacuole Turgor Pressure regulation – controls the movement of water and ions to maintain pressure Ion storage: the vacuole stores ions (K, Cl, Na) and regulates ion balance within  Removes harmful substances ○ How does this work? The water passes freely through the membrane through: The water channels (aquaporins) which aid in faster movement ○ Aquaporins: specialized protein channels in membranes that facilitate the rapid movement of water molecules – regulates the water flow without requiring energy The salts pass through ion channels Other solutes also moved selectively though channel and transporters Different concentrations differ inside and outside the cells and the organelles Inside a plant: ○ Root: water uptake ○ Xylem: water transport ○ Stomata: water loss CELL ELONGATION AND GROWTH The movement of water in the cell: ○ The maintenance of Turgor Pressure: pressure exerted by the cell’s contents against the cell wall that keeps the cell firm and contributes to the structural support ○ 1. Absorbing water through Osmosis/Vacuole The cell must absorb water from the surrounding cells or tissues through the process of osmosis and the vacuole is like the sponge taking in the water and swelling, increasing the turgor pressure Osmosis is driven by the movement of water into the cell due to a higher concentration of solutes/ions in the vacuole compared to the outside environment More ions in> outside – strong osmotic gradient brings water in ○ 2. Expanding the Cell Wall Turgor pressure increases and the vacuole presses against the cell wall = tension Auxin induces the loosening of the cell wall and allows it to expand in response to the internal pressure Wall-loosening enzymes (expansins) make the cell wall more stretchy and pliable as the vacuole absorbs more water Vacuole stores water with ions like potassium, chloride, nitrate and other ions = high osmotic potential, so water comes in – maintaining a steady water balance ○ Regulates turgor pressure ○ Ion storage and release for osmotic adjustment  Calculation of Water Content ○ Most cells contain 90+% water (fresh cut wood contains over 65% water ○ FORMULA: FW-DW FW(fresh weight) = water + cell wall + cell contents DW (dry weight) = cell wall + cell contents WATER LOSS (Transpiration) Water loss occurs through transpiration (process of water evaporation from plant surfaces like leaves) Purpose of transpiration: cooling plant, maintaining water flow, enabling uptake of minerals 3 main types of transpiration (CLS) ○ Cuticular transpiration: water lost through the cuticle (waxy outer layer of plant’s epidermis) Role of Cuticle: serves as protective barrier, lowering water loss, while allowing for gas exchange through stomata he cuticle helps to prevent excessive water loss but is not impermeable so small amounts of water can evaporate especially when very hot Factors affecting Cuticular transpiration: Humidity – high humidity = lower gradient for water loss Temperature – high temps can increase water evaporation = more water loss Cuticle Thickness – thick cuticles reduce water loss (for dry conditions – xerophytes, thin cuticles lose more water) ○ Lenticular transpiration: water lost through the lenticels (small pores on the stems, roots, other tissues) – prominent on woody stems/involved in gas exchange Role of lenticels: Allow for exchange of gases (O2/CO2) between internal tissues and environment Contribute to water vapour loss (minor pathway though) Not significant but still contributes to overall water loss in woody plants and trees Factors affecting Lenticular Transpiration Size and number of lenticels (the bigger the more SA for water vapor loss) Environment condition: influencyed by temperature, humidity, wind speed – alters the rate of evaporation  ○ Stomatal Transpiration: water evaporates form the leaf surface through small openings called stomata – MAIN FORM (most plants lose 90% of water through this way) The Stomata: the size of the stomatal opening is controlled by guard cells on the leaf epidermis, which open and close the pore Water is lose by evaporation from the substomatal space to the atmosphere VIA stomata The vapour pressure difference (vpd) between the substomatal space and the surrounding atmosphere determines the rate of evaporation As water evaporates from the substomatal atmosphere, water is drawn from the surrounding leaf cells as the change in matric potential (𝛹m) makes 𝛹𝛑 of the walls more negative than the 𝛹𝛑 of the vacuoles THE STOMATA ○ The stomata are surrounded by guard cells, which regulate their opening and closing through the changes in turgor pressure The mechanism relies on the movement of water and ions ○ The opening During daylight (or when conditions favour photosynthesis, the stomata open to allow for gas exchange (CO2 intake for photosynthesis and O2 release) ○ Mechanism: Ion Uptake: The light activates proton pumps in the guard cell membranes, which pump H+ ions out of the cells – creating a negative charge inside Potassium Ions (K+) and Chloride Ions (Cl-) enter guard cells through specific ion channels Osmotic Gradient: The increased ion concentration inside the guard cells lowers the water potential The water enters the guard cells through osmosis from the surrounding cells Turgor pressure The influx of water causes guard cells to swell, and because of their unevenly thickened cell walls (thicker on the inner side), they bow outward, creating a pore (stoma) in the center ○ The closing When the conditions are unfavourable (at night, drought, etc.), the stomata closes to reduce water loss Ion Efflux  ○ Proton pumps deactivate so the potassium and chloride ions exit the guard cells Water loss ○ The exit of ions increases the water potential in guard cells so the water moves out into the surrounding cells Loss of Turgor Pressure ○ The guard cells lose turgor, become flaccid (flabby), and the stomatal pore closes ○ Factors that affect stomata activity Openin: Light stimulates opening in many species Lowering of CO2 due to photosynthesis Overheating (cool) Closing: Water loss increases ABA (absicisic acid), which promotes K+ efflux from guard cells ○ Root to shoot signalling (ex. ABA) may precede any water stress in the shoot ○ Factors that affect stomatal transpiration Air movement Temperature Increase in temp, increases the vpd inside and outside Evaporation cools the leaf Pollutants SO2 can cause stomata to remain open Small dust particles can block stomatal apertures EVAPOTRANSPIRATION ○ Combined process of water loss from the Earth’s surface to the atmosphere through evaporation and transpiration ○ In the leaf, there is vapor pressure difference between the inside of the leaf and the surrounding atmosphere ○ Water loss is achieved through Stomata PHOTOSYNTHESIS II The Calvin Cycle 3 steps: Carbon Fixation, Reduction, Regeneration Carbon Fixation ○ Purpose: capturing atmospheric COs, and attaching it to a 5-carbon molecule RuBP (ribulose-1,5-biphosphate)  ○ Key Enzyme: Rubisco (Ribulose-1,5-biphosphate carboxylase/ocygenase) ○ Process: 3 molecules of CO2 combine with 3 molecules of RuBP (a 5-carbon compound) This reaction forms 6 molecules of a 3-carbon compound called 3-PGA (3-phosphoglycerate) Reduction ○ Purpose: convert 3-PGA into G3P using energy from ATP and NADPH ○ Process: Each 3-PGA is phosphorylated by ATP, forming 1,3-biphosphoglycerate into G3P (glyceraldehyde-3-phosphate) Out of the 6 molecules of G3P formed, 1 molecule exits the cycle to contribute to glucose synthesis, while the ramining 5 proceed to the next stage Regeneration ○ Purpose: Recycle G3P to regenerate RuBP, enabling the cycl eto continue ○ Process: The 5 remaining G3P molecules are reorganized into 3 molecules of RuBP (a 5-carbon compound) using energy from ATP This regeneration ensures the cycle can fix more CO2 Net Output of the calvin cycle ○ For 3 CO2 molecules Consumes: 9 ATP, 6 NADPH Produces: 1 G3P molecule – used to form glucose and carbohydrates SO: for every 3 CO2 molecules, the cycle produces 1 G3P