Ch. 6 & 7 Photosynthesis & Cellular Respiration
6.1 Energy Reactions
The Cycle of Energy Sun CO 2 H 2 O Photosynthesis (energy stored) Cellular Respiration (energy released) O 2 Glucose
Obtaining Energy Autotrophs Make their own nutrients (producers) Most photosynthetic: use energy of light to make glucose Few chemosynthetic: use inorganic compounds to make glucose Heterotrophs Cannot make own food Get energy from food they eat (consumers)
Overview of Photosynthesis In sunlight, plants change carbon dioxide & water into carbohydrates & oxygen. light 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Carbon + Water Glucose + Oxygen Dioxide
4 Requirements for Photosynthesis 1. Sunlight - Radiant energy of light excites electrons of chlorophyll to begin photosynthesis 2. Chloroplast: - Internal Structure: grana: stacks of flattened discs thylakoid: individual membranous disc stroma: space & material around grana
Chloroplast Structure
3. Pigments: Colored substances that absorb light Chlorophylls are green pigments: - 1 pigment: chlorophyll-a - accessory pigments: (absorb what a can t): chlorophyll-b & carotenoids 4. Energy-storing compounds: ATP & NADP + Temporarily store E until glucose formed
2 ways energy is stored 1. Electron Carrier: Electrons are passed to an electron carrier NADP+ NADP+ is converted to NADPH (reduction) Later, NADPH will transfer this energy to glucose recycling NADP+ (oxidation)
2. Use of ATP: ATP is Adenosine TriPhosphate: Adenosine: 1 nitrogenous base (adenine) + 5 carbon sugar (ribose) Triphosphate: 3 phosphate groups Green plants make ATP during photosynthesis All life uses ATP to power cell functions
Phosphate groups are added to store energy: AMP ADP ATP Phosphate groups are removed to release energy: ATP ADP AMP
6.2 Photosynthesis
2 Stages of Photosynthesis 1. Light Dependent Reactions: requires light - Light E changed to chemical E & temporarily stored in ATP & NADPH - occurs in photosystem: clusters of pigment molecules in the thylakoid
ATP forms by chemiosmosis: water is split, oxygen is a by-product 2 H 2 O 4 e - + 4 H + + O 2 Build up of H +, powers formation of ATP
2. Light Independent Reactions aka Calvin Cycle Does not require light (can occur in dark or ( light Glucose formed using CO 2 & E stored in ATP & NADPH Occurs in stroma Carbon fixation occurs: inorganic CO 2 fixed & becomes organic
In summary.
Alternative Pathways Plants in hot, dry climates close stomata to prevent water loss As a result: O 2 and CO 2 - this inhibits carbon fixation Alternate pathways allow carbon fixation to still occur:
1. C4 pathway: plants form 4-C molecules instead of typical 3-C molecules (saves time/energy) 2. CAM pathway: stomata open @ night, closed during heat of day C4
Ch. 7 Cellular Respiration
7.1 Glycolysis
Cellular Respiration Overview Glucose is broken down; its energy RELEASED ATP is produced & powers ALL cell functions Occurs in autotrophs & heterotrophs (ALL LIFE!) Can be Aerobic (requires O 2 ) Can be Anaerobic (does not require O 2 )
Stages of Cellular Respiration 1. Glycolysis: ( needed Anaerobic (no O 2 Occurs in cytoplasm of cells ( compound Glucose 2 Pyruvic Acid (3-C NADH (e- carrier) & ATP produced Enzymes catalyze reactions
After Glycolysis: If O 2 present: Pyruvic acid enters aerobic respiration If O 2 is not present: Pyruvic acid enters anaerobic Fermentation
2. Aerobic Respiration O 2 required Prokaryotes: occurs in cytoplasm Eukaryotes: occurs in mitochondria (! lot Pyruvic Acid ATP (a Energy stored in NADH used Produces ~ 20 x more ATP than glycolysis
Structure of Mitochondria
7.2 Aerobic Respiration
Steps of Aerobic Respiration 1. Krebs Cycle 2. Electron Transport
1. The Krebs Cycle Discovered by Hans Krebs Occurs in mitochondrial matrix Goal: temporarily store energy (attach e- to carriers) NAD+ NADH FAD+ FADH 2 CO 2 produced (by-product)
2. Electron Transport e- from NADH & FADH 2 : passed along electron transport chain Occurs along mitochondrial cristae At end of chain: 4 e- + 4 H+ + O 2 2 H 2 O Build up of H+, powers formation of ATP ( Chemiosmosis )
Total Energy from Glucose: Glycolysis: 2 ATP Krebs Cycle: 2 ATP ETC: 34 ATP Total: 38 ATP from Cellular Respiration - only 39% of the energy in glucose
7.3 Fermentation
Fermentation Follows glycolysis if no O 2 : Anaerobic Occurs in cytoplasm Recycles NAD+ from NADH keeps glycolysis going Does NOT form ATP but each time glycolysis occurs 2 ATP formed
2 Types of Fermentation 1. Lactic Acid Fermentation 2. Alcoholic Fermentation
Lactic Acid Fermentation Pyruvic acid lactic acid NADH NAD+ Keeps glycolysis going (2 ATP) Makes cultured dairy products: sour cream, yogurt, buttermilk, cheese Occurs in muscles too
Lactic Acid & Exercise Occurs in muscles during heavy exercise O 2 used up faster than it gets to cells Lactic acid builds up in muscles - burns Muscles fatigue, cramp When exercise stops: O 2, lactic acid removed by liver
Alcoholic Fermentation ( fungus ) Occurs in yeast Important for making beer, wine & bread Pyruvic acid CO 2 & alcohol CO 2 forms bubbles in champagne CO 2 allows bread to rise In bread, alcohol evaporates during baking (darn!)