Photosynthesis

reduction reaction light, water and chlorophyll –> ATP + NADPH + O2 light energy converted to chemical energy in the form of ATP (NADPH is the reducing power to cause reduction) 6H2O + 6CO2 –> C6H12O6 + 6O2 H2O –> H+ + e + O occurs in membrane of thylakoid
 * LR light reaction (light dependent)**

epidermis: transparent, no chlorophyll, light can pass through guard cells embedded within epidermis mesophyll (inside cells): two layers of cells –> all have chloroplasts, chlorophyll, can absorb light top layer (rectangular cells): palisade mesophyll. compact, longer axis of palisade mesophyll at right angle to upper epidermis so that more cells are exposed to sunlight. everyone of them has chlorophyll bottom layer (circular cells): spongy mesophyll

thylakoid so many membranes increase surface area to volume ratio chloroplasts have their own nuclei electrons get excited, shoot out of chlorophyll leaves have water coming in from the xylem, carbon dioxide from the stoma

chloroplasts made up of many membranes outer membrane, inner membrane, thylakoid, granum (stack of thylakoids) membrane of thylakoid made up of phospholipids proteins: photosystem 1 (PS1): first discovered. P700: best wavelength of light absorbed in reaction centre photosystem 2 (PS2): discovered later. P680. Lumen: centre of thylakoid space enzymes split water molecule membrane not permeable to hydrogen, hydrogen ions remain in lumen while oxygen is liberated electron becomes from oxidised state to reduced state (a lot of energy at this stage) hydrogen ions concentrated, moves out of lumen through carrier proteins, hence producing ATP NADPH and ATP (in stoma) are the end products, which go on to power the dark reactions

Hydrogen bond soil water diffuse by osmosis, enters root hairs to enter the xylem in the roots, part of the vascular bundle, travels up stem into leaves high pressure of water entering stem, xylem (vessel) is like a drinking straw, suction is evaporation through the vessel, transpiration pull, continuous column of water, water also joined to the wall of the vessel (forces) cohesion + adhesion (water molecule to wall) –> capillary action for transport because of two factors: continuous column (cut the stem under water so as not to break the column of water to maintain strong suction of water) aphids suck plant sap

Autotrophic Nutrition – plant cells structure and adaptation Autotrophs able to synthesise own food – producers heterotrophs: unable to synthesise own food, get energy from autotrophs – herbivore, omnivore, carnivore stomata: - makes sugar too, increase osmotic concentration so water can pass through - takes in air, carbon dioxide used for photosynthesis - water leaves the cell as water potential is higher inside - they are on the underside of the leaves to avoid direct sunlight - guard cells have chloroplasts, can make food, so osmotic concentration/pressure increases and water potential decreases –> water moves into guard cells from epidermal cells which have higher water potential (they do not contain chlorophyll) –> guard cells become turgid; cell wall on the outer side is thinner so stretches more –> hence the guard cells open - only open when photosynthesising Main pigment: chlorophyll: a, b. absorb blue and red, reflect green carotenoids: carotene, xanthophyll. absorb blue and green, reflect mostly yellow phycocyanin: absorb green and yellow, reflect yellow, orange or red chlorophyll b, carotene and xanthophyll are accessory pigments; chlorophyll a is the main pigment light comes in a packet: photon – light shines on pigment, vibrates, energy passed on, excite electrons, until energy accumulated in reaction centre, have enough energy to leave orbit, so electron shoots off from reaction centre and is caught by electron transport chain electron transport chain (ETC): plastoquinons, b6f complex, ferridoxine, plastocyanin electron from PS2 moves to PS1. as the electron is transported along the ETC, ATP is synthesised. PS2 –> PS1 –> ATP. the lack of 1 electron in PS2 is replaced by the H+ ions from the water sucked up by the plant, H+ ions goes into the lumen. electron shoots out at both PS2 and PS1 PS2 –e–> PS1 –e–> NADPH ATP ATP therefore, product of light reaction is ATP and NADPH The light reaction involves two sets of pigments: PS2 and PS1. PS2 is responsible for synthesis of ATP and for the photolysis of water into H+ + e + O2-; PS1 synthesises compound NADPH, the reducing power to reduce carbon dioxide to form ATP
 * Plant Pigments**

Light independent reactions (DR) carbon dioxide + NADPH –> sugar takes place in the stroma (semi-liquid substance) RuBP: Ribulose Biphosphate: molecule that will take in carbon dioxide, made up of 5 carbon joined in a row 5 carbon + 1 carbon from CO2 –> 6C –> split into two: 3C (triose phosphate: glycerate). at this stage, take in ATP and NADPH. ATP –> ADP (–> AMP); NADPH <–> NADP+ + H+. One 3C will need 2ATP and 1NADPH to form 3C glyceraldehyde –> product: glucose –> entry of ATP and ADP –> remainder goes back to RuBP: CYCLE 1 of the 3C forms glucose while the other 5 goes back to RuBP
 * The Calvin's Cycle**

convert solar energy to chemical energy second step is independent, solar energy already captured, needs carbon dioxide for carbon fixation, using the chemical energy from ATP
 * Big picture:**

starch: storage substance – insoluble, immobile, inert destarching: plant kept in darkness for few days 1) put leaf in water – kills the enzymes to stop reaction 2) put leaf in ethanol to decolourise leaf so that colour change can be observed –> ethanol dissolves the lipids in the cell membrane so chlorophyll leaks out
 * **Structure** || **Function** ||
 * Leaf: thin, flat || Maximises surface area to volume ratio for photosynthesis; gases can pass easily, have excess to upper mesophyll layer ||
 * Waxy cuticle || Prevents water loss through transpiration; focuses sunlight like a convex lens ||
 * Epidermis: transparent (no chlorophyll) & thin || Allows sunlight to reach mesophyll tissue for photosynthesis; protects internal tissues from mechanical damage ||
 * Palisade mesophyll:thin-walled cells with cylindrical shape, packed with chlorophyll, orientated vertically and compactly along upper epidermis || Maximises number of cells that are exposed to sunlight for maximum photosynthesis ||
 * Spongy mesophyll: round-shaped cells are arranged in loose and open arrangement (large intercellular air space), contain fewer chloroplasts, found nearer lower epidermis || Allows carbon dioxide to diffuse; interchange of gases; nearer to stoma ||
 * Stomata: on the underside of leaf, pair of bean-shaped guard cells which contain chloroplasts, outer wall is thin while inner wall is thin, size regulated by guard cells || Prevents excess water loss through transpiration; photosynthesises to open guard cells; outer wall stretches more when cell is turgid to allow opening of stomata ||
 * Leaf vein system-vascular bundle: xylem cells situated towards upper epidermis while phloem cells situated towards lower epidermis || Transports water to mesophyll tissue for photosynthesis as well as transports glucose/sucrose away to other parts of the plant (as too much glucose will overly increase the osmotic concentration of the cells); provides support which keeps the leaf up ||
 * Chloroplast: many membranes || Increases surface area to volume ratio ||

Carbon dioxide Light Temperature: with every 10 degree Celsius increase in temperature, photosynthesis rate doubles - enzymes: water molecules bind to enzymes to split - on hot day, water molecules move more actively –> more binding to enzymes –> higher rate of photosynthesis - but too much heat denatures enzymes (lose critical shape) –> water molecules can no longer bind –> cannot photosynthesise –> shrivel up and die
 * Factors affecting photosynthesis** **[[image:http://c1.wikicdn.com/i/editor/insert_table.gif width="1"]]

Enzymes are involved in photosynthesis – as light intensity increases, rate of photosynthesis increases until it reaches saturation point (rate cannot increase beyond this point): limiting factor –> graph like enzymes graph Changes in limiting factors affect the saturation point

What is the relationship between CO2 release and uptake? use the products from processes of respiration and carbon dioxide, but if photosynthesising at high rate, need to take in more CO2 from environment for enough input plants take more and more CO2 until light saturation point is reached (maximum rate of photosynthesis)

plants get nitrates from insects they eat to make amino acids (proteins: C,H,O,N), and nitrate, sulfate, phosphate from the soil

creepers need to find a host, prop to climb. when they are young, they grow away from sunlight to find a trunk, and grow horizontally. After touching tree, they grow vertically and develop leaves. At the canopy, the leaves turn from broad and wide to young plants have tiny roots, less chlorophyll, thinner cells, thinner wax layer, fine xylem tubes, tend to lose a lot of water –> hair on leaf surface to trap moisture –> surface is humid –> prevent excess water loss. different shapes of leaves: palmate, lobed. what factors cause unfolding of leaves? water: hydraulic pressure (pressure travelling from one place to another). undergrowth plant: grow in shade

1. move in direction of light 2. positioning of leaves – grow in mosaic way so they don't overlap, grow in gaps: crown shying 3. some leaves have red undersides to reflect light, upperside very dark green with lots of chloroplasts, spine-like things to increase surface ares 4. whitish small patches act as lenses to focus light to chloroplasts **
 * strategies to absorb maximum sunlight**