Photosynthesis and Respiration Chapter 5

Key Terms Photosynthesis- the process where plants convert light energy (sun) into chemical energy (glucose, starch) Respiration- the process where chemical energy (glucose) is broken down into ATP (adenosine triphosphate) Autotroph- organisms that can make their own organic compounds Heterotroph- organisms that must eat other organic compounds

Transfer of energy to ATP This is similar to burning gasoline to get the energy from it. Our mitochondria will “burn” sugar and turn it into ATP. Our cells will then use the ATP to do work. ATP is a nucleotide that has the ability to store energy in its bonds ATP will be broken down into ADP + P and then recycled back into ATP when we eat.

PHOTOSYNTHESIS Happens in three stages- 1. energy is captured from the sun 2. Light energy is converted into ATP and NADPH 3. ATP, NADPH, and CO2 are used to make organic compounds such as glucose, sucrose and starch

Photosynthesis

Overall Equation 6CO2 + 6H2O + light  C6H12O6 + 6O2

Stage 1 Light Absorption Light is found as wavelengths of electromagnetic spectrum- ROYGBV Pigments- light-absorbing substances Chlorphyll- absorbs all but green Carotenoids- absorb all but orange The colors we see are the wavelengths that are being reflected by a pigment

Light absorption

Oxygen production Sunlight is absorbed by thylakoids- disk-shaped structures that contain chlorophyll This energy “excites” electrons which cause the breakdown of water molecules Water is split into 3 parts 2 H+ ions Oxygen molecules 2 electrons The electrons replace those lost by energy absorption Oxygen is waste The 2 H+ ions will be used later

Electron Transport Chain I The electrons that have been freed from H2O are absorbed by molecules called PHOTOSYSTEM II They accumulate and leave and are absorbed by an ELECTRON ACCEPTOR They travel through an ELECTRON TRANSPORT CHAIN where they slowly release energy to ATP synthase ATP synthase uses the energy to produce ATP

ELECTRON TRANSPORT CHAIN II The “spent” electrons arrive at PHOTOSYSTEM I and are “excited” again by light energy The electron accumulate again and are accepted by a second ELECTRON ACCEPTOR The electron travel down a second ELECTRON TRANSPORT CHAIN where they provide the energy to join NADP+ and the 2H+ ions that were released earlier

SO FAR At this point we have USED We have also MADE Light energy H2O We have also MADE Oxygen as waste Since this part of photosynthesis must have light in order to work it is called LIGHT DEPENDENT PHASE

CALVIN CYCLE Also called the “LIGHT-INDEPENDENT” phase “carbon-dioxide” fixation- transferring CO2 into organic compounds. ATP and NADPH that were made earlier will be used during this phase

Calvin Cycle steps 3 CO2 join with RuBP (ribulose biphosphate) This forms 3 6-Carbon molecules that immediately split to form 6 3-carbon molecules called PGA PGA uses the energy from 6 ATP and 6 NADPH to be converted into 6 PGAL 5 PGA use 3 ATP and are converted back to RuBP. The 1 remaining PGAL is used to make organic compounds Since only 3 of the 6 CO2 are used, the Calvin Cycle must go through twice The result is a 6 carbon organic molecule - glucose

Factors that affect photosynthesis There reaches a point where so much sunlight is absorbed that photosynthesis cannot happen any faster. Think of a car that reaches it’s top speed. Water loss happens too fast

Cellular Respiration Key Terms Aerobic- with oxygen present Anaerobic- without oxygen present Glycolysis- splitting of sugar NADH- FADH2 Kreb’s Cycle- Fermentation

Aerobic Respiration

Stages of Respiration Glycolysis- splitting of sugar that happens in the cytoplasm Aerobic Respiration- Kreb’s Cycle Electron Transport Chain Anaerobic Respiration Either Alcoholic Fermentation or Lactic Acid Fermentation

Glycolysis Occurs in cytoplasm 1 glucose is split into 2 Pyruvate molecules This uses 2 ATP but produces 4 ATP and 2 NADH The net gain from glycolysis is 2 ATP

KREB’S CYCLE If O2 is present then the pyruvate will enter the mitochondria and proceed through a series of events This immediately makes 1 NADH molecule and pyruvate is converted into Acetyl Co-enzyme A (ACoA) At the end of the cycle three molecules are made for every ACoA 1 ATP 3 NADH 1 FADH2 Since 2 pyruvate are made during glycolysis Kreb’s Cycle must happen twice.

Electron Transport Chain NADH and FADH2 will lose electrons and H+ ions and will be converted into ATP This is similar to ATP production in photosynthesis For every NADH= 3 ATP For every FADH2= 1 ATP

ATP Production 2 NADH from glycolysis = 6 ATP 2NADH from ACoA = 6 ATP 6 NADH from Kreb’s cycle= 18 ATP 2 FADH2 from Kreb’s cycle= 4 ATP 2 ATP from Kreb’s cycle Electron Transport will yield up to 34 ATP + 2 ATP from Kreb’s + 2 ATP from Glycolysis = 38 ATP

ATP PRODUCTION

Anaerobic respiration Still begins with glycolysis If oxygen is ABSENT then the pyruvate made will not enter Kreb’s cycle to recycle NAD+ Instead the pyruvate enters one of two fermentation processes Lactic acid fermentation Alcoholic fermentation

Lactic acid fermentation Pyruvate will be converted into an ion of LACTIC ACID If muscles operate without oxygen then lactic acid will build up in the muscles causing soreness

Alcoholic fermentation Pyruvate may enter alcoholic fermentation in other organisms Pyruvate will be converted into alcohol and CO2 Organisms such as bacteria and fungi such as yeasts perform this type of fermentation. We use these actions to produce wine, beer, sourdough, breads, and ethanol In both types of fermantation- no further ATP is made after glycolysis

Efficiency of ATP production The total amount of ATP made from glycolysis is 2 Both types of fermentation will yield no further ATP Aerobic respiration will yield up to another 36 ATP Aerobic respiration is obviously the more efficient process

What does all this mean? The food that we eat is broken down (digested) into simple molecules- carbohydrates, lipids, proteins. These are absorbed by our cells and respiration starts. So all that food we eat will be used to recharge ADP + P into ATP ATP is the rechargable batteries that our cell use to do work. When the batteries run low we eat to do respiration to recharge them. If we do not use all the energy then it will be stored in cells called fat cells.