Chapter 10 Biology Sixth Edition Raven/Johnson (c) The McGraw-Hill Companies, Inc.

Photosynthesis converts solar energy into the chemical energy of a carbohydrate : Solar energy + 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 Electrons from H 2 O are energized by the sun. The oxygen given off comes from water – 18 O experiments. Illustrate that two sets of reactions are happening

A.Light Reactions (Capturing solar energy) 1.Cyclic phosphorylation (some bacteria) a)Produces ATP 2.Non-cyclic electron transfer (Photosystem I & II) a)Splits water to harvest electrons b)Produces ATP c)Produces NADPH B. Dark Reactions (Calvin Cycle – CO 2  glucose) 1. Carbon fixation 2. CO 2 Reduction 3. RuBP regeneration

Cyclic Phosphorylation (Bacteria)

It takes just the right amount of energy to push an electron to the next energy level. Chlorophyll reflects green light; carotenoids reflect orange and red light

Solar energy + 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 Light-Dependant Reactions of Photosynthesis produce O 2, ATP, and NADPH – not glucose. ADP + P  ATP NADP + H  NADPH

Dark reactions -NADPH and ATP  are used to reduce CO 2 to carbohydrate. -This occurs in the stroma of a chloroplast by a series of reactions called the Calvin cycle.

CO 2 H 2 O Calvin CycleElectron Pathways Solar Energy RuBP PGAL ATP O 2 Glucose Aerobic Cellular Respiration in Mitochondria makes new ATP Light Independent ReactionsLight Dependant Reactions Photosynthesis in Chloroplast NADPH

Photosynthetic organisms carry on both photosynthesis and cellular respiration and rely on solar energy. Solar Energy + CO 2 + H 2 0  C 6 H 12 O 6 + O 2 C 6 H 12 O 6 + O 2  CO 2 + H chemical energy(ATP) Non-photosynthetic organisms only carry on cellular respiration and must rely on an external source of energy. C 6 H 12 O 6 + O 2  CO 2 + H chemical energy(ATP)

Solar Energy O 2 and Glucose CO 2 Plant Cell Animal Cell Mitochondria (Respiration) Chloroplast (Photosynthesis)

Rubisco is the enzyme that carboxylates RuBP with CO 2. However, in the presence of high O 2, it will oxidize RuBp and release a CO 2. This represents a loss of CO 2 that was already ‘fixed’ – this is called photorespiration. Because Carbon is fixed as a 3 carbon molecule, this is called C3 photosynthesis.

In C 4 plants, bundle sheath cells also contain chloroplasts, and mesophyll cells are arranged concentrically around bundle sheath cells. C4 plants are typical of warm climates, so they keep their stomata closed during the day to prevent water loss.

C4 plants close their stomata during the day to prevent water loss. Oxygen is produced in the Mesophyll cells, so it does not accumulate in the bundle sheath cells when the stomata are closed. High concentration of CO 2 in the bundle-sheath cell

Partition by spacePartition by time Reduces photorespiration

The End.