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Photosynthesis and Plants - What is photosynthesis? - How are plants suitable for photosynthesis? - Where, exactly, does it occur? - How, roughly, does it happen? - Why does it happen? chapters 20-22, 30.2-.4, and 4.1-4.3 in text What is photosynthesis? Photosynthesis involves the conversion of light energy into chemical energy. The primary storage of this chemical energy will be in 6 carbon sugars, usually glucose. → 6 H2O + 6 CO2 → C6H12O6 + 6 O2 So, we need water and carbon dioxide, an input of energy, (and to let out some oxygen): Then energy will be stored in the bonds of the glucose. - How are plants suitable for photosynthesis? - root to obtain water and minerals (and anchor plant) - stem for transport and support -buds where new growth can occur (meristems) - leaf to provide optimal situation for photosynthesis, including light exposure and gas exchange. Each has special tissues to enable these specific uses. (This is a dicotyledonous angiospermophyte) Root - epidermis covers the surfaces - root hairs shown here ↓ - Minerals enter root by active transport - Water follows by osmosis - Casparian strip: tight junctions between endodermis cells force all materials to pass through cytoplasmic membranes before entering xylem. It also keeps water in the xylem, building root pressure for water transport. Stem - phloem carries sugars from leaves to rest of plant. - cambium is main site of lateral (outward) growth. -Growth also builds bark. - Successive layers of 2o xylem are the “annular rings” or heartwood. - New length comes from apical meristem. - Capillary action is the second step in water transport. Plant circulation vs mammal circulation MAMMAL Arterial and venous systems In one continuous circuit. Powered by cardiac contraction. Circulatory system is closed. Flow is one way, ensured by valves in veins. Flow rate impacted by water volume, heart and vessel contraction, hormones…. Vessels have specialized tissue construction, distinct from other tissues. Provide for transport of water, essential nutrients, organics, ... and toxins. http://www.phschool.com/science/biology_place/biocoach/images/cardio2/BlVesStr.jpg http://ap-bio-patrick-steed.wikispaces.com/file/view/xylem__phloem.jpg/85280965/xylem__phloem.jpg PLANT Xylem and Phloem systems Two distinct pathways. Powered by transpiration or mass water flow. Xylem an open path, while phloem a closed circuit. Xylem is one way, while phloem can reverse. Flow rate dependant mostly on water volume http://www.inclinehs.org/smb/Sungirls/images/monocot%20leaf.JPG http://www.sbs.utexas.edu/bio406d/images/pics/poa/Arundo%20donax%20leaf5.jpg Leaf - Primary site of photosynthesis therefore, - primary site of gas exchange - Requires vascular tissue to bring nutrients to leaf, and carry products away. Monocotyledonous angiosperms ↑ (like wheat, corn,... tulips) have parallel veins. ←Dicotyledonous angiosperms (like sunflowers, ivy.... tulip poplars) have branched veins. Leaf (cont.) You should be able to identify the following: cuticle upper epidermis palisade mesophyll (mostly photosynthesis) spongy mesophyll (mostly gas exchange) vein, with xylem (carries water) phloem (carries sugars) lower epidermis stoma, (port for gas exchange, and for transpiration, the last step in water transport) bounded by guard cells http://kvhs.nbed.nb.ca/gallant/biology/leaf_structure.jpg Where, exactly, does photosynthesis occur? In chloroplasts within the mesophyllic leaf cells. intermembrane space inner membrane outer membrane granum stroma site of Calvin cycle, or light independent rxns. thylakoid site of lightdependent reactions lamella lumen What are the challenges of evolving from algae (aquatic protists) to plants on land? 1. Dehydration While living in water there is still the problem of water balance, but not like being surrounded by air. 2. Support Aquatic algae are supported by the water. 3. Nutrient acquisition/gas exchange These algae are surrounded by the nutrients they need, suspended in the water itself. 4. Nutrient dispersal Algae are generally small, or thin, and don’t have far to move materials internally. 5. Dispersal of reproductive structures Again, surrounded by water, reproductive cells are hydrated and washed away, but on land… These challenges were met in a step-wise progression, reflected in modern examples. Kingdom: Plantae - photosynthetic - cell walls -complex multicellularity -(In plants these are “divisions”, not “phyla”) bryophyta ↓ Vascular Roots Leaves Seeds Flowers No No No No No gymnosperms ↓ Yes Yes Yes No No ↑ pteridophytes Yes Yes Yes Yes No Yes Yes Yes Yes Yes ↑ angiosperms 6 H2O + 6 CO2 → C6H12O6 + 6 O2 We have brought water from the roots, via the xylem, through stems, to the leaves. Carbon dioxide is entering leaves through the stomata, and oxygen, when it is released, leaves leaves via stomata. Glucose, once made, will be actively transported into the phloem, and water will osmose after it to carry it where needed. Now all we need to do now is capture the sunlight… Adenosine TriPhosphate will be used as an intermediate in this solar-to-carbohydrate energy transfer. ATP will ultimately be re-charged from ADP when energy is released from the carbs in cellular respiration when the cell has business to do. NADPH2 is the other battery, ferrying energized electrons. far red↑ - Visible light is one part of the electromagnetic spectrum. - The strongest absorption is in blue-violet (400-500nm) and near red (650-700). - The middle of the spectrum – green – is NOT absorbed: It is reflected. Hence, plants appear green. http://www.uic.edu/classes/bios/bios100/lecturesf04am/absorption-spectrum.jpg The absorption spectrum of selected plant pigments: - How, actually, does it happen? - The chloroplast is the site of photosynthesis in eukaryotes. - Two chief parts: “photo-” light-dependent reactions in thylakoid membranes, “-synthesis” light-independent reactions (aka Calvin cycle) in stroma. - note ATP/ADP and NADPH/NADP+ bridging the two - note two photosystems (II comes before I) for light energy capture. - note electron transport chain http://www.55a.net/firas/ar_photo/11/photosynthesis-overview.gif -Light absorbed by chlorophyll a in photosystem II: -An e- is energized, and handed off to the electron transport chain. - Water split, providing e- to replace them, with O2 off as waste. -ETC pumps protons into the thylakoid lumen. -Light absorbed by chlorophyll a in photosystem I -e- are re-energized, and handed off to NADP+, which is reduced to NADPH - The proton motive force powers ATP synthase, in photophosphorylation. http://cache.eb.com/eb/image?id=72207&rendTypeId=35 1. Light-dependent reactions - Carbon fixation: - CO2 is attached to a 5C molecule (H comes from light-dependent reactions.) 2. Light-independent reactions - The intermediate falls into two 3C units which are reduced by ATP and NADPH. - every third time around a 3C molecule is spun off, which may become glucose and other molecules. - Another ATP is invested to replace the original 5C molecule. * “probably the most abundant protein on Earth” How can we know if photosynthesis is taking place? 6 CO2 + 6 H2O → C6H12O6 + 6 O2 ------------------------------------------------------------------- Directly: 1. Measure the CO2 consumed. 2. Measure the O2 generated. Indirectly 3. Determine the net increase in biomass. 4. Measure the reduction of NADP+ by providing a colorimetric substitute for NADP+...(?) What do you think would influence the rate of photosynthesis? What would be the effect…, and why? light? (intensity, duration)? temperature? pH? CO2 levels? .... www.climateaudit.org/?p=884 http://www.marietta.edu/~spilatrs/biol103/photolab/rspCrve.gif generalhorticulture.tamu.edu/.../light.html Variations on a theme…. Oxygen actually binds to Rubisco more readily than does CO2, so in low CO2 (like stomata closed to conserve water) O2 is taken into the Calvin cycle, and CO2 is released: Called photorespiration, but generates no ATP. Ouch. Dry environments cause problems for photosynthesis: Two specialized alternative photosynthetic adaptations that you will want to know… C4 pathway: In arid climates is helps to be able to just crack the windows: In order to increase the carbon locally available to the Rubisco carbon is first fixed, more aggressively (to PEP by PEP carboxylase), resulting in a 4-C molecule. This is carried to bundle sheath cells around the leaf vein, (which is where the Calvin cycle occurs in these plants) and C is handed off into the Calvin cycle. ← Most commonly seen in corn, sugar cane and other grasses. www.steve.gb.com/science/photorespiration.html CAM pathway: Another route is to simply close the windows during the day: By attaching the CO2 to some other organic molecule at night, and then releasing it to Rubisco in the presence of light, while the stomata are closed: In both C4 and CAM carbon is first fixed by some other molecule: - is C4 this is separated from Calvin by space (structural). - in CAM they are separated by time. Found in pineapples ↑ and cacti. How do water, carbon, and nitrogen enter a plant? Trace energy’s path from sun to glucose. Write the balanced equation for photosynthesis, and describe where each component comes from and/or goes to. What are the structure and function of the major plant parts. How do you predict amount of light, wavelength of light, amount of CO2, or temperature change would influence rate of photosynthesis? Benchmark SC.912.L.14.7 Relate the structure of each of the major plant organs and tissues to physiological processes. Benchmark SC.912.L.14.36 Describe the factors affecting blood flow through the cardiovascular system. Enduring Understandings Organism development facilitates efficient metabolic processes. (?) Essential Questions How have the structures and functions of plants enabled them to survive? Photosynthesis capillary action lumen 6 H2O + 6 CO2 → C6H12O6 + 6 O2 gas exchange ATP root vascular tissue ADP stem monocot absorption spectrum bud dicot pigment meristem cuticle eukaryote leaf upper epidermis light-dependent reactions epidermis palisade mesophyll light-independent reactions root hair spongy mesophyll Calvin cycle active transport vein chlorophyll a osmosis lower epidermis photosystem II: Casparian strip stoma electron transport chain endodermis guard cell photosystem I xylem chloroplast NADPH phloem outer membrane ATP synthase cambium stroma photophosphorylation bark granum carbon fixation C4 pathway heartwood thylakoid CAM pathway stomata guard cell chemical reaction reactants products conservation of mass photosynthesis chlorophyll chloroplast grana stroma thylakoid membrane glucose