The production of ATP AND NADPH the light reaction of photosynthesis Figure 7.9 Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE

ATP and NADPH power sugar synthesis in the Calvin cycle The Calvin cycle occurs in the chloroplast’s stroma – This is where carbon fixation takes place and sugar is manufactured INPUT Figure 7.10A OUTPUT: CALVIN CYCLE

Figure 7.10B Details of the Calvin cycle INPUT: Step Carbon fixation. In a reaction catalyzed by rubisco, 3 molecules of CO 2 are fixed. 1 1 Step Energy consumption 2 3P P P6 6 2 ATP 6 ADP +P 6 NADPH 6 NADP + 6P G3P Step Release of one molecule of G3P. 3 CALVIN CYCLE 3 OUTPUT: 1P Glucose and other compounds G3P Step Regeneration of RuBP. 4 G3P 4 3 ADP 3ATP 3 CO 2 5P RuBP3-PGA

Step 1 carbon Fixation CO 2 is incorporated (fixed) into a five-carbon sugar named ribulose bisphosphate (RuBP). The enzyme that does this is RuBP carboxylase or rubisco. – The most abundant protein protein on Earth. The product is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate (3PGA).

Step 2 Energy consumption ATP and NADPH 2 (from the light reaction) are used to convert 3-phosphoglycerate (3GPA) to glyceraldehyde 3-phosphate (G3P) – three-carbon carbohydrate precursor to glucose and other sugars.

Step 3 Output of G3P output is one molecule of glyceraldehyde 3- phosphate For every three molecules of CO 2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate Used to make Glucose

Step 4 Regeneration of RuBP ATP is used to regenerate RuBP from G3P

Energy cost of Calvin Cycle For each G3P synthesized, the cycle spends: 9 ATP 6 NADPH2. Both are made in the light reaction

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Review: Photosynthesis uses light energy to make food molecules A summary of the chemical processes of photo- synthesis Figure 7.11 Light Chloroplast Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons LIGHT REACTIONSCALVIN CYCLE Cellular respiration Cellulose Starch Other organic compounds

Many plants make more sugar than they need –The excess is stored in roots, tubers, and fruits –These are a major source of food for heterotrophs

C 4 and CAM plants have special adaptations that save water Most plants are C 3 plants, which take CO 2 directly from the air and use it in the Calvin cycle – In these types of plants, stomata on the leaf surface close when the weather is hot – This causes a drop in CO 2 and an increase in O 2 in the leaf – Photorespiration may then occur No sugar or ATP

Photorespiration in a C 3 plant CALVIN CYCLE 2-C compound Figure 7.12A

Some plants have special adaptations that enable them to save water CALVIN CYCLE 4-C compound Figure 7.12B –Special cells in C 4 plants—corn and sugarcane—incorporate CO 2 into a four-carbon molecule –This molecule can then donate CO 2 to the Calvin cycle 3-C sugar

The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism CALVIN CYCLE 4-C compound Figure 7.12C –They open their stomata at night and make a four-carbon compound –It is used as a CO 2 source by the same cell during the day 3-C sugar Night Day

Due to the increased burning of fossil fuels, atmospheric CO 2 is increasing – CO 2 warms Earth’s surface by trapping heat in the atmosphere – This is called the greenhouse effect PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE

Figure 7.13A & B Sunlight ATMOSPHERE Radiant heat trapped by CO 2 and other gases

Because photosynthesis removes CO 2 from the atmosphere, it moderates the greenhouse effect –Unfortunately, deforestation may cause a decline in global photosynthesis

Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer His research focuses on how certain pollutants (greenhouse gases) damage that layer Figure 7.14A

Figure 7.13A & B Sunlight ATMOSPHERE Radiant heat trapped by CO 2 and other gases

Because photosynthesis removes CO 2 from the atmosphere, it moderates the greenhouse effect –Unfortunately, deforestation may cause a decline in global photosynthesis

7.14 Talking About Science: Mario Molina talks about Earth’s protective ozone layer Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer His research focuses on how certain pollutants (greenhouse gases) damage that layer Figure 7.14A

The O 2 in the atmosphere results from photosynthesis –Solar radiation converts O 2 high in the atmosphere to ozone (O 3 ) –Ozone shields organisms on the Earth’s surface from the damaging effects of UV radiation

Industrial chemicals called CFCs have hastened ozone breakdown, causing dangerous thinning of the ozone layer Figure 7.14B Sunlight Southern tip of South America International restrictions on these chemicals are allowing recovery Antarctica