1. Photosynthesis and Cellular Respiration

2. Outline I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions

3. Photosynthesis Converts sun energy into chemical energy usable by cells Autotrophs: self-feeders, organisms can make their own food – Photoautotrophs: use sun energy (e.g. photosynthesis-makes glucose – Chemoautotrophs: use chemical energy (e.g. bacteria that use methane: CH 4 )

4. Photosynthesis Photosynthesis takes place in plant cell organelles called chloroplasts – Light absorbing pigment molecules (e.g. chlorophyll)

5. Overall Reaction 6CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6O 2 Carbohydrate made is glucose. Water is split as a source of electrons from H atoms releasing O 2 as a byproduct (used later?). Electrons increase potential energy when moved from water, so energy is required (from where?). Remember: atoms are made of protons (identity), neutrons (radioactivity) and electrons (energy).

6. Basic model of an atom

7. Light-dependent Reactions Overview: light energy is absorbed by chlorophyll, “exciting” electrons in H atoms and boosts them to higher energy levels (increased potential). These electrons then “fall back” to a lower energy state, releasing energy held in ATP

8. Light-dependent Reactions Electrons in chlorophyll must be replaced so cycle may continue-these come from water! Oxygen is “made” from left over oxygen atoms. Light reactions yield ATP and NADPH to fuel reactions of Calvin cycle (aka: “dark reactions”, do not need light)

9. Energy Shuttling Recall ATP: molecule with 3 phosphate groups bonded to it, when removing the third phosphate, lots of energy freed= superb molecule for shuttling energy around cells (ADP + P 3 ). Other energy shuttles: NADP + H

12. Calvin Cycle (“dark” reactions) ATP and NADPH made in light reactions fuel the dark reactions. Called carbon fixation: taking carbon from an atmospheric CO 2 and making glucose Simplified version of how carbon and energy enter the food chain

14. Harvesting Chemical Energy Now autotrophs (like plants) can “harvest” chemical energy to fuel their bodies. Heterotrophs must eat glucose for fuel. Heterotrophs: must take in energy from outside sources, cannot make their own (e.g. animals) When we take in glucose (or other carbs), proteins, and fats-these foods don’t come to us the way our cells can use them

15. Cellular Respiration Overview Transformation of chemical energy in food into chemical energy cells can use needs ATP. These reactions proceed the same way in plants and animals (cellular respiration). Overall Reaction: – C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O

16. C.R. Reactions Glycolysis – Reaction breaks 6-carbon glucose molecule into 2, 3-carbon molecules called pyruvate – Process is an ancient one-all organisms from simple bacteria to humans perform it the same way!! – Yields 2 ATP molecules for every one glucose molecule broken down – Yields 2 NADH per glucose molecule

18. Anaerobic Cellular Respiration Some organisms thrive in environments with little or no oxygen. – Marshes, bogs, gut of animals, sewage treatment ponds No oxygen used= ‘an’aerobic Results in no more ATP!! End products such as ethanol and CO 2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)

20. Aerobic Cellular Respiration Oxygen required=aerobic 2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria – 1. Kreb’s Cycle – 2. Electron Transport Chain

21. Kreb’s Cycle (aka citric acid cycle) Completes the breakdown of glucose – Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO 2 and H 2 O – Hydrogens and electrons are stripped and loaded onto NADH and other carriers. Production of only 2 more ATP but loads up with H + and electrons which move to the 3 rd stage

23. Electron Transport Chain Excited electrons from the Kreb’s cycle move to this chain-like series of molecules (“staircase”?). As electrons drop down “stairs” (less excited), energy released & stored in a total of 32 ATP! Oxygen waits at bottom of staircase, picks up electrons and H atoms and in doing so becomes water!

25. Energy Tally 34 ATP for aerobic vs. 2 ATP for anaerobic – Glycolysis 2 ATP – Kreb’s 2 ATP – Electron Transport32 ATP 36 ATP Anaerobic organisms can’t be too energetic but are important for global recycling of carbon!