Understanding Photosynthesis and Cellular Respiration: Energy Conversions in Living Organisms

1. CELL ENERGETICS Photosynthesis and Cellular Respiration

2. Photosynthesis • All energy for Earth is from the sun. • Photoautotrophs- organisms that convert light energy to chemical energy. • This process is called photosynthesis and is summarized in the equation: light energy 6H2O + 6CO2 6O2+ C6H12O6

3. Photosynthesis • Occurs in chloroplasts of plant cells 2 sets of reactions • Light dependent reactions • occur in thylakoid- flattened membrane sac • use water and light energy • Produce Oxygen • Light independent reactions • occur in stroma • use carbon dioxide • produce Carbohydrates.

4. Light Dependent Reactions • Sunlight strikes chlorophyll molecules activating them • Photolysis- occurs when the energy of sunlight splits water molecules • Oxygen atoms are released as O2 • Hydrogen atoms are stripped of their electrons • The electrons pass to the electron carrier NADP+ forming NADPH and H+. • H+ forms a concentration gradient • The concentration gradient drives ATP Synthase to make ATP

5. Light Independent Reactions

6. Light Independent Reactions • CO2, ATP, and electrons carried by NADP+ are used to build sugar. • The molecule RuBP rearranges CO2 making the molecule PGA . • PGA is converted to PGAL, using ATP and the NADP+. • Some PGAL is made into glucose; some regenerates RuBP to continue the process.

7. Photosynthesis CO2 Water ADP + Pi + NADP+ RuBP PGAL Light Independent Reactions ATP + NADPH + H+ Light Dependent Reactions O2 Carbohydrates

8. Cellular Respiration • Both autotrophs and heterotrophs must convert glucose to ATP (the energy currency of the cell) first, then use it to drive any metabolic activity. • This process is cellular respiration and is summarized in the equation: C6H12O6 + 6O2 6H2O + 6CO2 + ATP • Aerobic organisms use cellular respiration • Aerobic = oxygen using

9. Cellular Respiration • Occurs in cytoplasm & mitochondria of eukaryote cells 3 sets of reactions • Glycolysisoccurs in cytoplasm • breaks down glucose to pyruvate • produces 2 molecules of ATP. • Kreb’s Cycle occurs in matrix of mitochondria • breaks down pyruvate • produces CO2 and 2 molecules of ATP. • Oxidative phosphorylation occurs in mitochondrial matrix • uses oxygen • produces 32 molecules of ATP.

10. Glycolysis • Glycolysis breaks down glucose (6-carbon sugar) into 2 molecules of pyruvate (3-carbon intermediate) • some hydrogen atoms are stripped of electrons, • electrons are passed to the carrier NAD+, forming NADHand H+ • Glycolysis uses 2 ATP to rearrange glucose • produces 4 ATP • net total of 2 ATP are made by glycolysis

11. Kreb’s Cycle • Pyruvate changes into Acetyl-Coenzyme A in the cytoplasm • Acetyl-CoA moves to the mitochondrial matrix, • In a series of reactions • carbon and oxygen molecules are pulled off to release CO2 • electrons are passed to NAD+and FAD • forms NADH and FADH2 and many H+ ions. • produces 2 molecules of ATP each time the cycle runs

13. Oxidative Phosphorylation • Only NADH and FADH2and H+ move into the mitochondrial membrane • Electrons from hydrogen pass through a series of enzymes and finally to oxygen (the electron acceptor) making O2 • As in light dependent reactions, H+ protons develop a steep concentration gradient, driving ATP synthase to produce ATP • 32 molecules of ATP are produced.

14. Electrons carried via NADH Electrons carried via NADH and FADH2 O2 OXIDATIVE PHOSPHORYLATION KREB’S CYCLE GLYCOLYSIS Glucose  Pyruvate ATPATP, CO2ATP, H2O Cellular Respiration

15. Fermentation • Aerobic cellular respiration occurs only when Oxygen is present. • Without oxygen, anaerobic respiration takes place. • Glycolysis occurs. • Fermentation- After glycolysis, pyruvate is converted to lactic acid or ethanol • Fermentation involves very few chemical reactions, • but only makes 2 molecules of ATP.