Explain: Powering Cellular Activities

1. Explain: Powering Cellular Activities Update TOC Create Section Header Include Key Idea (p 318) Include Linking Question

2. Powering Cellular Activitiesaka Cellular Respiration • You should be able to define: • cellular respiration (aerobic & anaerobic) • Krebs cycle • glycolysis • electron transport system • You should be able to answer: • What are the 3 stages of cellular respiration? • What happens in each of the 3 stages? • What is the balanced equation for cellular respiration? • In what organelle does cellular respiration take place? • What are NADP & ATP needed for? • How are photosynthesis and respiration related?

3. Reading & Questions Page 340: How Cells Convert Food Into Energy Read & take notes in your notebook Page 344: Stop & Think Questions #1-5 in your notebook

4. Reading Notes How Cells Convert Food Into Energy Cellular Respiration occurs in ALL cells (plant/animal/etc.) ALL THE TIME! Definition: Cellular Respiration is the process by which cells break down fuels ( mainly glucose) to free up the energy required for cellular functions. Aerobic respiration: uses oxygen Anaerobic respiration: does not use oxygen.

5. Aerobic Respiration has 3 stages: • glycolysis • Krebs cycle • Electron Transport System • Each stage is a series of reactions catalyzed by enzymes • Final result is ATP, which each cell needs to do its ‘job’. • The equation for respiration is: • C6H12O6 + 6 O2 6 CO2 + 6 H2O + heat

6. Glycolysis • Starch (and/or sucrose) is broken down into glucose [a 6-carbon molecule] before Glycolysis begins • Glycolysis happens in the cytoplasm. • Glycolysis means “splitting of sugar”

7. Glucose breaks down into two molecules of 3-carbon pyruvate • Some initial energy (ATP) is required to split the glucose molecule in half. • Hydrogen ions and electrons from the glucose are transferred to a molecule of NAD+, creating NADH. • NADH is a hydrogen carrier and energy source (Does it remind you of a molecule we saw in photosynthesis?) • A small amount of ATP is also created • Most of the energy of the original glucose molecule remains in the pyruvates

8. Krebs or No Krebs? • If oxygen is present, the Krebs cycle begins. • Krebs cycle occurs in the mitochondria (or in the cytosol of bacteria) (they don’t have mitochondria!) • breaks the pyruvates into CO2 and releases it as a gas. • More ATP and NADH are produced • Two passes through the Krebs cycle are necessary (2 pyruvates). • Sometimes called the Citric Acid Cycle • If no oxygen is present, the cell uses other pathways – called fermentation - to break down the pyruvates into lactic acid, ethyl alcohol, acetic acid and other compounds. No ATP is produced beyond the 2 ATP created in glycolysis. • Fermentation by bacteria and yeast are important to the production of yogurt, vinegar, wine, and other good things.

9. Electron Transport System (ETS) • A series of electron carrier proteins in the inner membrane of the mitochondria • The ETS uses the NADH molecules that were created during the previous stages. • NADH broken into protons (H+) and electrons (a NAD+. Molecule is left) • As electrons transfer from one protein to another in the ETS, they continually release energy.

10. This energy is used to pump protons (H+) across the mitochondria (active transport). • This creates a concentration gradient • protons diffuse back into the mitochondria, passing through an enzyme complex which creates ATP • MOST ATP is formed here, as long as oxygen was present! (up to 36 ATP) • When oxygen is present: At the end of ETS, electrons and protons join with Oxygen to form water. (without Oxygen, this step can’t happen!)

11. Energy Yield of Respiration • Aerobic respiration has a much higher energy yield than anaerobic respiration. • Aerobic respiration – net 36 ATP (mostly from ETS) • Anaerobic respiration – net 2 ATP (from glycolysis) • Anaerobic respiration is sufficient for many single-celled organisms. • Anaerobic respiration helps cells temporarily function when oxygen levels are low • Anaerobic respiration does not produce sufficient energy for multicellular organisms.

12. Reading Notes From Mz. R… • ATP: The Fuel of Cells • The cells of ALL living organisms use ATP as fuel to complete their basic cell functions. • Cellular respiration takes place constantly. • Examples of cellular work: actively transport ions and molecules across membranes, trigger muscle contraction, send nerve impulses, clean up waste, biosynthesis of complex molecules (such as amino acids and starch).

13. Reading Notes From Mz. R… • Respiration During Exercise • Cells need the energy from ATP at all times, even while at ‘rest’. • During exercise, we need more glucose and oxygen to create the ATP more quickly. • Cells respond by increasing respiration rate. • Increased respiration rate means greater CO2 production. • When CO2 levels rise, our breathing rate increases to rid excess CO2 and bring in more O2. • O2 starved muscles switch to anaerobic respiration which produces lactic acid which splits into lactate and hydrogen ions. The increase in H+ means ‘more acid’ [lower pH] which ‘burns’ our muscles! • Aerobic respiration produces 19 times more ATP than anaerobic! • During aerobic respiration, muscle cells produce more mitochondria. • A more fit person has more mitochondria than someone who exercises less often. • Exercise also helps deliver more oxygen to the muscles. • So, a conditioned person can convert more energy from glucose into useable energy. They will have greater stamina… the ability to continue exercising.

14. Reading Notes From Mz. R… • Aerobic vs. Anaerobic • Aerobic respiration yields MUCH MORE energy than anaerobic respiration. • Small energy yields are OK for small organisms (single-celled little dudes). • Anaerobic respiration helps cells survive periods when oxygen levels are low.