1. Photosynthesis and Cellular Respiration

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

3. Photosynthesis
Method of converting sun energy into chemical energy usable by cells
Autotrophs: self feeders, organisms capable of making their own food
Photoautotrophs: use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from light
Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

4. Photosynthesis
Photosynthesis takes place in specialized structures inside plant cells called chloroplasts
Light absorbing pigment molecules e.g. chlorophyll

5. Overall Reaction 6CO2 + 12 H2O + light energy → C6H12O6 + 6O2+ 6H2O
Carbohydrate made is glucose
Water appears on both sides because 12 H2O molecules are required and 6 new H2O molecules are made
Water is split as a source of electrons from hydrogen atoms releasing O2 as a byproduct
Electrons increase potential energy when moved from water to sugar therefore energy is required

6. Light-dependent Reactions
Overview: light energy is absorbed by chlorophyll molecules-this light energy excites electrons and boosts them to higher energy levels. They are trapped by electron acceptor molecules that are poised at the start of a neighboring transport system. The electrons “fall” to a lower energy state, releasing energy that is harnessed to make ATP

7. Energy Shuttling
Recall ATP: cellular energy-nucleotide based molecule with 3 phosphate groups bonded to it, when removing the third phosphate group, lots of energy liberated= superb molecule for shuttling energy around within cells.
Other energy shuttles-coenzymes (nucleotide based molecules): move electrons and protons around within the cell
NADP+, NADPH NAD+, NADP FAD, FADH2

8. Light-dependent Reactions
Photosystem: light capturing unit, contains chlorophyll, the light capturing pigment
Electron transport system: sequence of electron carrier molecules that shuttle electrons, energy released to make ATP
Electrons in chlorophyll must be replaced so that cycle may continue-these electrons come from water molecules, Oxygen is liberated from the light reactions
Light reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

11. Calvin Cycle (light independent or “dark” reactions)
ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.
Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)
Simplified version of how carbon and energy enter the food chain

13. Harvesting Chemical Energy
So we see how energy enters food chains (via autotrophs) we can look at how organisms use that energy to fuel their bodies.
Plants and animals both use products of photosynthesis (glucose) for metabolic 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

14. Cellular Respiration Overview
Transformation of chemical energy in food into chemical energy cells can use: ATP
These reactions proceed the same way in plants and animals. Process is called cellular respiration
Overall Reaction:
C6H12O6 + 6O2 → 6CO2 + 6H2O

15. Cellular Respiration Overview
Breakdown of glucose begins in the cytoplasm: the liquid matrix inside the cell
At this point life diverges into two forms and two pathways
Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration

16. C.R. Reactions Glycolysis
Series of reactions which break the 6-carbon glucose molecule down into two 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, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis.
End products such as ethanol and CO2 (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 Completes the breakdown of glucose
Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2O
Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2
Production of only 2 more ATP but loads up the coenzymes with H+ and electrons which move to the 3rd stage

23. Electron Transport Chain
Electron carriers loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase).
As electrons drop down stairs, energy released to form a total of 32 ATP
Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water

25. Energy Tally 36 ATP for aerobic vs. 2 ATP for anaerobic
Glycolysis ATP
Kreb’s ATP
Electron Transport 32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but are important for global recycling of carbon