Cell Process Photosynthesis CO 7 Cell Process Photosynthesis CO 7

Cell Process - Photosynthesis CO 7

- Occurs in the chloroplasts Photosynthesis is used to build carbohydrates (the main energy source of all life.) - Producers (like plants) use carbon dioxide and water to make carbohydrates; oxygen gas is released as waste - Occurs in the chloroplasts - 6CO2 + 6H2O  C6H12O6 + 6O2 Figure 7.1a

Chloroplast Structure Stroma is the space between the grana Grana are stacks of thylakoid membranes full of pigments Figure 7.1b

Figure 7.2 Figure 7.2

Photosynthetic Pigments – chemicals such as chlorophyll that absorb various portions of visible light energy for photosynthesis. (Anything green denotes chlorophyll and is photosynthetic. Chlorophyll is great at absorbing all colors except green. Green is reflected, which is why it looks green to our eyes.) 1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b. 2. Both chlorophylls absorb violet, blue, and red wavelengths best. 3.  Most green is reflected back; this is why leaves appear green.

Accessory pigments help absorb the light colors that chlorophyll can’t Accessory pigments help absorb the light colors that chlorophyll can’t. - Carotenoids are yellow-orange pigments which absorb violet, blue, and green regions. - Phycobilins are red-purple pigments - When chlorophyll breaks down and is reabsorbed in fall, it is pulled out of the leaves first. This allows the accessory pigments in leaves to show. Figure 7.3a

Absorption Spectrum - spectrophotometer measures the amount of light that passes through a sample of pigments (like crushed green leaves) Figure 7.3a

Action Spectrum - measures the rate of photosynthesis at different wavelengths of light; measured by the rate oxygen is produced

Figure 7.3b

In one sentence summarize what this graph says about wavelengths, color of light, absorption and photosynthesis.

Checkpoint 1. What is the relationship between the absorption spectrum and the action spectrum? 2. How can we measure the rate of photosynthesis? 3. How is the wavelength of light related to the rate of photosynthesis? 4. A radish plant is grown using lights of different colors. Explain the chart.

Photosynthetic Reaction 1. In 1930 C. B. van Niel showed that O2 given off by photosynthesis comes from water and not from CO2. 2. The net equation reads: Pg 119a

Two Sets of Reactions in Photosynthesis (general detail) 1 Two Sets of Reactions in Photosynthesis (general detail) 1. Light reactions only happen with light. They are the energy-capturing reactions that take place in the thylakoids. a. Water is split into oxygen, two H+, and two free e- b. The electrons and hydrogens are sent to the electron transport chain where they are used to make ATP and NADPH to power the Calvin Cycle c. Oxygen is released Pg 119b

2. Calvin Cycle Reactions (aka dark reactions) a. take place in the stroma in either light or dark. b. The NADPH and ATP from light rxns provide energy to combine 6CO2 molecules into a six carbon sugar carb. Figure 7.4

What you should know by now.. 1.  The equation for photosynthesis.  Write it! 2.  The structure of a chloroplast.  Sketch it! 3.  The two reactions of photosynthesis.

Same Photosynthesis Reactions (in more detail) - The Light Reactions occur in two systems: Photosystem I and Photosystem II. These photosystems create the cyclic and the non-cyclic electron transport chains to create energy molecules for stage 2. The ETC’s are able to create ATP (c and n-c) and NADPH (n-c only) through membrane compartments and gradients

Non-cyclic ETC – electrons are removed from the water using light energy at PSII; they are passed down a chain of enzymes (the ETC) where their energy is used to pull H+ molecules from the stroma (outside) into the thylakoid (inside) creating a concentration gradient; electrons are then re-charged at PSI and attached to an NADP+ to make NADPH and sent to power the Calvin cycle. - Summary- IN: Water and Light. OUT: equal amounts of ATP and NADPH. GEN DIRECTION: PSII  (energy used to pull in H+) PSI recharge  NADPH  Calvin Cycle Are you still confused?    Check out the videos on my website to see it in action.

Cyclic ETC – more ATP is needed for the Calvin Cycle than NADPH Cyclic ETC – more ATP is needed for the Calvin Cycle than NADPH. The Cy ETC just creates more ATP. Electrons are charged by PSI, then passed back down the ETC where their energy is used to pull more H+ into the thylakoid to maintain the concentration gradient. They are then returned to PSI, recharged, and used the same way all over again. IN: Electrons. OUT: ATP only. GEN DIRECTION: PSI  energy used to pull in H+  PSI  again! (cycles!) Are you still confused?    Check out the videos on my website to see it in action.

Why the concentration gradient Why the concentration gradient? The gradient created by the ETCs is used to drive… THE DAM METAPHOR!!! ATP Synthase – The H+ want out and away from that high concentration. The only way out is through ATP Synthase. As they move through ATP Synthase, the enzyme spins and generates power to recharge ATP. It’s remarkably like a hydroelectric power plant! Note, membranes and compartmentalization are HUGE here! It wouldn’t work without them! Are you still confused?    Check out the videos on my website to see it in action.

Now for the dark reactions… FORTUNATELY, AP Biology no longer requires the memorization of every step of the Calvin Cycle, but you should understand the beginning and the end and the purpose.   Summary Statements:    What is the purpose of the Calvin Cycle? To make sugar from carbon dioxide   Where does the cell get its energy to perform these reactions? From the ATP and NADPH charged in the light reactions What is the final product? Glucose (and ADP/NADP+ “dead batteries” to be sent back to light rxn)  Why is carbon dioxide necessary? The 6 carbons from 6CO2 molecules become the 6 carbons in one molecule of C6H12O6; process called carbon fixation Enzyme to know: Rubisco – used to bind the CO2 in carbon fixation; can bind to O2 accidentally if there’s too much around which leads to photorespiration (which is bad)

Photorespiration Problem caused when Rubisco bonds to O2 in the Calvin Cycle instead of CO2 (and you can’t make sugar without carbon); happens when too much O2 builds up in the leaf; a concern of hot weather plants who have to keep their stomata (holes to allow gas exchange) closed to prevent excess transpiration (water evaporation) Adaptations to Avoid… - CAM photosynthesis: temporal (timing) separation of photosynthesis reactions; close stomata during the day and just do light reactions, open at night to release O2 and bring in CO2 for calvin cycle; Note: store CO2 and preliminary sugar molecules as an acid overnight, use the acid during the day to make sugar when energy is available - C4 photosynthesis: spatial separation of photosynthesis reactions; convert CO2 into a carbon chemical (malate) and move it to cells in darker regions of the leaf for the Calvin cycle; the cells in the light do the light reactions while the cells in the dark do the Calvin Cycle

Factors the Affect Photosynthesis   1. Light Quality (color)- white is best, followed by blue; green is worst due to pigment absorption 2. Light Intensity (typically brighter = better) 3. Light Period (longer time in light = better) 4. Carbon Dioxide Availability – more is better 5. Water Availability – more is better Note: Rate of Photosynthesis can be measured by the amount of oxygen released OR the amount of CO2 absorbed. More O2 released or CO2 absorbed = more photosynthesis

Quick Practice

Quick Practice grana thylakoid stroma O2

Pg 129b Light & H2O CO2 ADP NADP ATP Pg 129b NADPH O2 glucose

AB = ATP AC = phospholipids AD = light (energy) A = photosystem II B = photosystem I C = H20 D = Electron Transport Chain E = ATP Synthase AB = ATP AC = phospholipids AD = light (energy)