Ch. 9 Photosythesis and Cellular Respiration Honors Biology I Loulousis

Leaves Optimized for absorbing light and carrying out photosynthesis. Consist of: BLADE – thin, flattened section that absorbs sunlight PETIOLE – thin stalk that attaches the blade to the stem Covered by epidermis and cuticle Creates water-proof barrier

Leaf Functions PHOTOSYNTHESIS Occurs in the Mesophyll (specialized ground tissue) STOMATA – pores in the underside of a leaf that allows for the diffusion of O2 and CO2. GUARD CELLS – control the opening and closing of stomata

Leaf Functions TRANSPIRATION The loss of water from a plant through its leaves. Replaced by water drawn into the leaf

Leaf Functions GAS EXCHANGE Take in CO2 and release O2. Keep stomata open just enough to allow photosynthesis to take place Can’t leave them open too long… can lead to water loss by transpiration

What type of organisms utilize photosynthesis What type of organisms utilize photosynthesis? Plants, some bacteria, and algae (protista) Photoautotrophs- autotrophs that depend on photosynthesis for both energy and carbon compounds NOT chemoautotrophs- live in areas where it is too extreme – get energy by oxidizing inorganic substances such as iron or sulfur

Where does photosynthesis take place? Leaves : the photosynthetic organs of the plant Mesophyll: main photosynthetic tissue a. Palisade cells: full of chloroplasts b. Spongy cells: fewer chloroplasts and many air spaces

Photosynthesis – An Overview Living things get energy from food Food is broken down and energy is stored as ATP Heterotrophs have to consume other organisms for energy Autotrophs are able to make their own food – Sugar (C6H12O6)/ glucose

How do Autotrophs Make Their Own Food? Through photosynthesis – the process of using energy from the sun to convert Water and Carbon Dioxide into Oxygen and Sugar. Equation: 6H2O + 6CO2 6O2 + C6H12O6

An organism’s metabolism is part of Earth’s carbon cycle

Carbohydrates Sugars are a type of organic molecule called carbohydrates Carbohydrates are: used for short term energy storage Made up of basic units called monosaccharides More complex sugars are disaccharides & polysaccharides Plants make glucose through photosynthesis, also have an important polysaccharide called cellulose that makes up their cell walls

Cellular Energy Cells use a form of chemical energy called Adenosine Triphosphate (ATP) Cells store & use ATP to fuel necessary metabolic reactions Such as maintaining internal chemical conditions (homeostasis) 10 MILLION molecules of ATP are consumed & regenerated per second per cell! Cells store & use ATP to fuel necessary functions biosynthesis reactions, remove wastes, take in nutrients, maintain internal chemical conditions (homeostasis) & also for locomotion!

Adenosine Triphosphate (ATP) Nucleotide 3 Energy Rich Phosphate Bonds Sugar

ATP-Energy Currency Holt Slide 13 ATP (adenosine triphosphate) -nucleotide with two extra energy-storing phosphate groups Energy is released when the bonds that hold the phosphate groups together are broken The removal of a phosphate group from ATP produces adenosine diphosphate -ADP: H2O + ATP  ADP + P + energy

ATP Synthase An enzyme that catalyzes the synthesis of ATP Recycles ADP by bonding a third phosphate group to the molecule to create ATP Energy is stored when a phosphate is added to ADP to become ATP Is a carrier protein for hydrogen ions (H+) Flow of H+ ions through ATP synthase powers the production of ATP

ATP – ADP Cycle:

Light and Pigment Plants also need light and chlorophyll to undergo photosynthesis. Plants absorb the sun’s light with chlorophyll. There is chlorophyll a and chlorophyll b. Sunlight is a mixture of colors (ROYGBIV)

Light and Pigment cont. The color we see with our eyes is the result of colors being reflected and absorbed. A red flower appears red because all of the colors from the spectrum are being absorbed, EXCEPT red. Red is the color being reflected. Both chlorophylls absorb the red and blue spectrums easily. They DO NOT ABSORB green light, they reflect green light. (See the previous color spectrum chart)

Why Leaves Change Color? A color palette needs pigments, and there are 3 types: 1. Chlorophyll 2. Carotenoids 3. Anthocyanins

Stop & Think 1. Why are light & chlorophyll needed for photosynthesis? 2. Why are plants green? 3. How well would a plant grow under pure yellow light? 4. Write the equation for photosynthesis. Identify reactants and products. 5. Use the graph below to figure… In which regions of the spectrum will chlorophyll a absorb the most light? In which regions of the spectrum will chlorophyll b absorb the most light? Chlorophyll b Chlorophyll a

What are Chloroplasts? Organelles that house photosynthetic material and enzymes necessary for photosynthesis Stroma – large central compartment, where Calvin cycle takes place Thylakoids – flattened sacs within stroma that contain chlorophyll Grana – stacks of thylakoids Thylakoid space – within thylakoid, where light reactions take place

Chloroplast Structure

What is the first reaction of photosynthesis? Light dependent reactions- occurs in thylakoid membrane pigments release electrons as light hits photolysis- water is split and electrons replace pigment electrons electrons move down electron transport system producing ATP NADP+ pick up electrons and H+, holds energy NADPH and ATP carried to Calvin Cycle

What are photosystems? pigment complex that serves as antennae to gather solar energy in the form of photons energy is passed from one pigment to the next until it reaches chlorophyll a electrons escape as they become excited picked up by nearby electron carrier

Light Dependent Reactions There are two Electron Transport Chains (ETC) Chlorophyll in Photosystem II (PSII) absorbs photons Energy is passed along the (ETC) The electrons lost to the chain from PSII are replaced by electrons from the splitting of water (photolysis) Produces 4 electrons, 2 H+, O2 is released through stomata High concentration of H+ in thylakoid, so move out to stroma by attaching to electrons, creating ATP in ATP synthase (from the ADP hanging around) ATP move on to Calvin Cycle by a electron carrier molecule

Light Dependent Reactions cont. Photosystem I receives photons from sunlight Electrons are excited and move down the ETC Electrons from PSII replace the lost electrons from PSI The electrons are used by NADP reductase to change NADP+ to NADPH NADPH is transported (carrier molecule) to the Calvin Cycle.

Calvin Cycle Aka the dark cycle or light independent reaction The products from the light reaction , ATP and NADPH, fuel cycle After energy released from ATP and NADPH, the now ADP and NADP+ go back to the light reaction to be used again The product of the Calvin Cycle is glucose

Calvin Cycle Steps 1. Carbon Dioxide (CO2) enters leaf through stomata from atmosphere 2. Combines with a 5-carbon molecule called RuBP in process called carbon fixation RuBP stands for ribulose biphosphate 3. Catalyzed by rubisco, RuBP becomes a temporary unstable 6-carbon molecule 4. The 6-carbon molecule quickly splits in half and forms two 3-carbon molecules called PGA

Calvin Cycle steps 5. The energy from ATP and NADPH is used to convert PGA into PGAL 6. Three turns of cycle, each picking up CO2, makes six molecules of PGAL 7. Five PGAL go to make more RuBP 8. 1 molecule of PGAL is used to make larger compounds such as starch, glucose (simple sugars), or cellulose for plant cell walls

H2O Light NADP+ ADP + P i Light Reactions Chloroplast

H2O Light NADP+ ADP + P i Light Reactions ATP NADPH Chloroplast O2

i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH H2O CO2 Light NADP+ ADP + P i Calvin Cycle Light Reactions ATP NADPH Chloroplast O2

i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH H2O CO2 Light NADP+ ADP + P i Calvin Cycle Light Reactions ATP http://www.neok12.com/php/watch.php?v=zX707369565d560e73435445&t=Photosynthesis NADPH Chloroplast [CH2O] (sugar) O2

Grand Totals During the Light Reactions: Enters = H2O Leaves = O2 During the Calvin Cycle: Enters = CO2 Leaves = C6H12O6 _____________________________ Total Equation: 6CO2 + 6H20 6O2 + C6H12O6

Stop & Think 1. Summarize the light dependent reactions. 2. Summarize the events of the Calvin Cycle. 3. What is the function of NADP+? 4. Why must the light reactions take place before the Calvin Cycle can occur?

Rates of Photosynthesis (limiting factors) Four things affect rate of Photosynthesis 1. Light intensity 2. temperature 3. CO2 concentration 4. Oxygen concentration

Rates of Photosynthesis (limiting factor) Four things affect rate of P.S. Light intensity increases rate of p.s. up to light saturation point as temperature increases, p.s. rate increases to point, then decreases concentration of CO2 increases rate of p.s. as oxygen increases, p.s. rate decreases

Light Intensity As light intensity increases, rate increases until the saturation point, leveling off, then decreasing slightly Why level off? Light reactions are saturated with light electrons and are proceeding as fast as possible Photoinhibition: chlorophyll takes on energy faster than it can transfer e- to ETS. O2 reacts with e- and H2O to make OH- and H2O2 (hydrogen peroxide) Products cause damage to chloroplast Decline in rate

Temperature As the temperature increases, rate increases until a point, then decreases If temperature gets too high, enzymes involved (Rubisco), which is a protein, become denatured

Concentration of Carbon dioxide As CO2 increased, rate increases to a maximum until it reaches the saturation point. After that, there is no effect on photosynthesis What would the graph for this look like?

Oxygen Concentration Increasing the level of oxygen, decreases the rate of photosynthesis in C3 Plants. As a result the plants undergo photorespiration.

Photorespiration Enzyme rubisco is needed to incorporate CO2 into the Calvin Cycle. Rubisco can bind to CO2 or O2 If there is a higher concentration of oxygen than carbon dioxide, oxygen interferes with Carbon Fixation. The enzyme rubisco will bind with oxygen and combines with RuBP which produces only 1 PGA molecule and glycolate. PGA will eventually be used to form simple sugar RuBP releases CO2 which resembles cellular respiration Overall rate of photosynthesis slows

Inefficient C3 Pathway Under conditions such as hot dry days, which cause water stress in plants Plants close their stomata to conserve water Photosynthesis in the chloroplasts rapidly uses up the CO2 remaining in the leaf Also, oxygen produced during photosynthesis accumulates in the chloroplasts Thus, the conditions are perfect for photorespiration

Special Heat Adaptations Two groups of plants have evolved adaptations that reduce photorespiration : C4 & CAM Plants C4 Plants: a. 2 systems of CO2 fixation occur in different parts of leaves b. CO2 is 1st incorporated into a 4C acid in the mesophyll cells (no Rubisco is there) c. 4C acid is transported to the bundle sheath where Calvin cycle resumes Examples: sugar cane, corn, crabgrass

What is the advantage of C4 plants? Can reduce amount photorespiration because CO2 is delivered to bundle sheath cells that have chloroplasts No air space to allow rubisco to come in contact with oxygen

What is the advantage of partitioning space in a C4 plant? 1. Avoid photorespiration and can keep stomates open longer 2. CO2 is converted to oxaloacetate and delivered to bundle sheath cells which reduces O2 being fixed Disadvatage 1. water is lost as stomates are opened

Special Heat Adaptations CAM Plants: a. Opens stomates at night b. Incorporates CO2 into a 4C acid (malate) which is stored in vacuole for use later c. Not very efficient d. Found in snake plants, jade, and cactus e. Slow growers

What is the advantage of partitioning in time? CAM Plants What is the advantage of partitioning in time? Can keep stomates open longer because CO2 is stored as malate in vacuoles during the evening and used by Calvin cycle during the day once ATP and NADPH get made Stomates closed during day, reduces water loss by plant