Cells obtain energy through two main processes: photosynthesis and respiration. Photosynthesis uses sunlight to convert carbon dioxide and water into glucose and oxygen in chloroplasts. Respiration breaks down glucose in mitochondria to release energy, usually using oxygen but sometimes without oxygen through fermentation. The energy is stored in ATP molecules as energy is released from breaking phosphate bonds. Cells then use this stored energy to power their functions and processes.

1. Energy in a Cell

13. Sunlight NADP + ADP NADPH CO 2 H 2 O O 2 CHLOROPLAST Calvin cycle ATP Glucose Photosystem I & II

22. MITOCHONDRION CO 2 H 2 O O 2 ATP NADH Heat Electron Transport System ATP NAD + citric acid cycle Pyruvate Glucose ATP

23. Sunlight Photo- System I Photo- system II NADP + ADP NADPH ATP Calvin CO 2 H 2 O O 2 ATP ATP NAD + NADH Electron Transport System Cycle Krebs Heat CHLOROPLAST MITOCHONDRION Glucose Pyruvate Cycle ATP Glycolysis

24. Sunlight Photo- System I Photo- system II NADP + ADP NADPH ATP Cycle Calvin CO 2 H 2 O O 2 ATP ATP NAD + NADH Electron Transport System Cycle Krebs Heat CHLOROPLAST MITOCHONDRION Glucose ATP Pyruvate Glycolysis