Photosynthesis Chapter 7

PHOTOSYNTHETIC ORGANISMS 7.1

Photosynthetic Organisms Photosynthesis- converting solar energy into the chemical energy of a carbohydrate. −Produces copious amounts of oxygen gas as a by- product, which forms the ozone layer that protects us from UV rays. Makes life possible Autotrophs- produces own food. Heterotrophs- consumers, do not produce own food.

Flowering Plants Photosynthesis happens on the green parts of the plant. It needs CO2 and water. −Roots absorb water, goes up the stem to leaf. −CO2 enters the leaf through small openings called stomata. Both of these diffuse into the chloroplast.

1.Stroma- space 2.Thylakoid- disk −Thylakoid membranes contain the pigment chlorophyll which is the pigment that absorbs solar energy, making the plant green. 3.Granum- stack of disks Flowering Plants

THE PROCESS OF PHOTOSYNTHESIS 7.2

Photosynthesis Cells do not use solar energy directly for energy. It has to be converted to ATP. ATP (energy) is just like money, you spend it when needed. Ever saw a plant with bubbles on it under water?

Electrons needed to reduce (GAIN) CO2 are carried by the coenzyme, NADP+. Basically, it carries the electrons needed to portion of photosynthesis. NADP+ is a “Carrier” NADP+/ NADPH

Light Reactions −Take place on the thylakoids Calvin Cycle Reactions −Takes place in the stroma Two Sets of Reactions

Photosynthesis Overview Stage 1- energy is captured from sunlight Stage 2- light energy is converted to chemical energy (Temp. in ATP and NADPH) Stage 3- Energy in ATP and NADPH powers the formation of organic compounds using CO2. Light Reactions Dark Reaction

Light Reactions

Calvin Cycle Reactions

PLANTS CONVERT SOLAR ENERGY 7.3

Pigments and Photosystems energy Screened out by ozone Screened out by water vapor and CO2

Pigment molecules absorb wavelengths of light They absorb some wavelengths and reflect the others. Chlorophyll a and chlorophyll b absorb violet, blue, and red light −Reflect the green. −DOES NOT use the green wavelength Carotenoids absorb violet, blue, and green −Reflect orange, red, yellow −When do you think this is noticeable? Pigments and Photosystems

Spectrophotometer- measures the amount of light that passes through a sample Photosystem- pigment complex and electron acceptors within thylakoid membrane Pigments and Photosystems

2 photosystems ( Named when discovered, not when used) −PS II −PS I Electrons usually follow a noncyclic pathway starting with PS II This is where water is taken in to produce 2H+ and O2 *Remember the oxygen comes from the water. Electron Flow in Light Reactions

Electron receptor sends energized electrons down the electron transport chain (ETC) As they pass through, energy is captured and stored in the form of a hydrogen ion gradient. −Hydrogens flow through ATP synthase complexes, producing ATP Electron Flow in Light Reactions

When PS I absorbs energy electrons are captured by electron receptors and passed to NADP+ molecules which then becomes reduced to NADPH. ATP and NADPH are not made in equal amounts. More ATP is made Electron Flow in Light Reactions

PS II- pigment complex and electron receptor molecules, releases O2 ETC- Pq (plastoquinone) and cytochrome complexes carry electrons from PS II to PS I PS I- pigment complex and electron acceptor molecules. Adjacent to NADP reductase (NADP+  NADPH) ATP synthase- channel and a protruding ATP synthase. Enzyme that joins ADP + P  ATP Organization of Thylakoid Membrane

Each time water is oxidized (loss) 2H+ is released in the thylakoid. As electrons move along, electrons give up energy which is used to pump H+ into the thylakoid. Now, thylakoid has more H+ than stroma creating concentration gradient. As H+ flow out of the thylakoid through ATP synthase making energy for ATP production. ATP Production

PLANTS FIX CARBON DIOXIDE 7.4

The Calvin Cycle uses high energy molecules for carbon dioxide fixation. −Humans cannot extract CO2 from the atmosphere and make sugars. Can occur in the dark Calvin Cycle has three steps: The Calvin Cycle

CO2 attaches to RuBP (ribulose 1, 5-biphosphate), a 5-C molecule CO2 + RuBP (5-C molecule)  6-C molecule 3-C (3PG) Enzyme that speeds this is RuBP carboxylase 1) CO2 Fixation

3PG  G3P in 2 steps 1.3PG BPG 2.BPG G3P G3P has been reduced, has more electrons larger for storage and for making larger organic molecules such as glucose 2) Reduction of CO2 ATP NADPH

Notice in Calvin Cycle that the reaction is X3 because it takes 5 G3P to make 3 RuBP 5G3P 3RuBP 3ATP 3ADP + P 3) Regeneration of RuBP

OTHER TYPES OF PHOTOSYNTHESIS 7.5

This type is the type we have been studying. RuBP carboxylase to fix CO2 to RuBP in MESOPHYLL CELLS When it gets hot, the stomata on the leaves close which leads to decrease in CO2 and an increase in O2 because it cannot get out. SO, RuBP carboxylase combines O2 with RuBP instead of CO2  1 3PG and eventual release of CO2. This is called photorespiration. C3 Photosynthesis

PLANTS adapted. Bundle sheath cells as well as mesophyll cells have chloroplasts in C4 plants. Fix CO2 to PEP using PEPcarboxylase or PEPCase. PEP + CO2 Oxaloacetate 1.CO2 taken up in mesophyll cells 2.Reduced form of oxaloacetate pumped into bundle sheath cells. ONLY here does CO2 enter the Calvin Cycle C4 Photosynthesis PEPCase

Moderate weather- C3 plants have the advantage Hot and dry weather- C4 plants have the advantage Early Summer- Kentucky bluegrass and creeping bent grass Midsummer- Crabgrass Plants and Weather

CAM happens in water containing plants ( flowering succulent) These plants live in warm, dry regions Ex: Pineapple, Jade Plant CAM Photosynthesis

C4- partitioning in space: CO2 fixation- mesophyll cells Calvin Cycle- bundle sheath cells CAM- partitioning by use of time Night- PEPcase to fix CO2 forming C4 molecules Day- C4 molecules release CO2 to Calvin Cycle when we have energy from light reactions CAM Photosynthesis

Primary Advantage- conservation of water Open stomata at night to let CO2 in Close them during the day −Conserves water but no CO2 uptake This allows these plants to live under stressful conditions CAM Photosynthesis

C4 plants adapted to high light intensities, increase in temp, and limited rainfall. C3 plants are better than C4 plants in colder climates. CAM plants can live in extremely arid environments. −Becoming more widespread Adaptation to their environment