BIOLOGY: Today and Tomorrow, 4e starr evers starr Chapter 5 Capturing and Releasing Energy

5.1 A Burning Concern  Photosynthesizers remove CO 2 from the atmosphere and lock its carbon atoms in organic compounds  When organisms break down organic compounds for energy, carbon atoms (CO 2 ) reenter the atmosphere  When humans began burning forests to clear land, and fossil fuels (coal, petroleum, natural gas) for energy, we put the atmospheric carbon cycle out of balance

Products of fossil fuel combustion

Producers and Consumers  Autotroph  Organism that makes its own food using carbon from inorganic sources (CO 2 ) and energy from the environment  Heterotroph  Organism that obtains energy and carbon from organic compounds assembled by other organisms  Photosynthesis  Metabolic pathway by which photoautotrophs capture light energy and use it to make sugars from CO 2 and water

5.2 Capturing Rainbows  Energy radiating from the sun travels through space in waves and is organized in packets called photons  Humans perceive different wavelengths of visible light as different colors  Wavelength  Distance between the crests of two successive waves

Wavelength and the Electromagnetic Spectrum shortest wavelengths (highest energy) range of most radiation reaching Earth’s surface longest wavelengths (lowest energy) visible light gamma rays x-rays ultraviolet radiation near-infrared radiation infrared radiation microwavesradio waves 400 nm500 nm600 nm700 nm

Capturing Rainbows  Photosynthetic species use pigments to harvest light energy for photosynthesis  Pigment  An organic molecule that can absorb light at specific wavelengths  Chlorophyll a  Main photosynthetic pigment in plants

Photosynthetic Pigments

5.3 Storing Energy in Sugar  Photosynthesis converts light energy into energy of chemical bonds, which power reactions and can be stored for later use 6CO 2 + 6H 2 O → (light energy) → C 6 H 12 O 6 + 6O 2

The Chloroplast  Chloroplast  Organelle of photosynthesis in plants and some protists  Thylakoid membrane  Chloroplast’s highly folded inner membrane system  Forms a continuous compartment in the stroma  Stroma  Semifluid matrix between the thylakoid membrane and the two outer membranes of a chloroplast

two outer membranes of chloroplast stroma part of thylakoid membrane system: thylakoid compartment, cutaway view The site of photosynthesis

Two Stages of Photosynthesis  Light-dependent reactions (“photo”)  Convert light energy to chemical energy of ATP and NADPH, releasing oxygen  Occur at the thylakoid membrane in plant chloroplasts  Light-independent reactions (“synthesis”)  ATP and NADPH drive synthesis of glucose and other carbohydrates from water and CO 2  Occurs in the stroma

Two Stages of Photosynthesis ADP NADP + H 2 O energy O2O2 A) Light-dependent reactions NADPH ATP NADPH CO 2 B) Light-independent reactions (Calvin–Benson cycle) NADP + glucose ATPADP

5.4 The Light-Dependent Reactions  Chlorophylls and other pigments in the thylakoid membrane absorb light energy and pass it to photosystems, which then release electrons  Energized electrons leave photosystems and enter electron transfer chains in the membrane; hydrogen ion gradients drive ATP formation  Oxygen is released; electrons end up in NADPH

Steps in Light-Dependent Reactions 1. Light energy ejects electrons from a photosystem 2. Photosystem pulls replacement electrons from water, releasing O 2 3. Electrons enter an electron transfer chain (ETC) in the thylakoid membrane 4. Electron energy is used to form a hydrogen-ion gradient across the thylakoid membrane

Steps in Light-Dependent Reactions 5. Another photosystem receives electrons from the ETC 6. Electrons move through a second ETC; NADPH is formed 7. Hydrogen ions flow across the thylakoid membrane through ATP synthase 8. ATP forms in the stroma

Electron Transfer Phosphorylation  Electron transfer phosphorylation  Metabolic pathway in which electron flow through electron transfer chains sets up a hydrogen ion gradient that drives ATP formation

Light-Dependent Reactions light energy electron transfer chain ATP synthase photosystem ADP, phosphate thylakoid compartment H2OH2O stroma O2O

5.5 The Light-Independent Reactions  Calvin–Benson cycle  Light-independent reactions of photosynthesis  Cyclic carbon-fixing pathway that forms sugars from CO 2  Driven by energy of ATP and electrons from NADPH  Carbon fixation  Process by which carbon from an inorganic source such as CO 2 gets incorporated into an organic molecule  In most plants, the enzyme rubisco fixes carbon by attaching CO 2 to RuBP

chloroplast stroma CO 2 PGARuBP Calvin– Benso n Cycle glucose Light-Independent Reactions

Adaptations to Hot and Dry Climates  Adaptations such as a waterproof cuticle allow plants to live where water is scarce  Stomata  Gaps that open between guard cells on plant surfaces  Allow gas exchange through the cuticle  C3 plants  Use only the Calvin-Benson cycle to fix carbon  Conserve water by closing stomata on dry days; oxygen builds up and interferes with sugar production

Stomata A) Tiny pores called stomata are visible in this close-up of a leaf. Stomata close to conserve water on hot, dry days, and this causes oxygen to accumulate inside the plant’s tissues. The buildup makes sugar production inefficient in C3 plants.

Adaptations to Hot and Dry Climates  Alternative light-independent reactions minimize binding of oxygen to rubisco in some types of plants  C4 plants  Plants that minimize photorespiration by fixing carbon twice, in two cell types  CAM plants  C4 plants that conserve water by fixing carbon twice, at different times of day

C4 Plants B) Crabgrass “weeds” overgrowing a lawn. Crabgrasses, which are C4 plants, thrive in hot, dry summers, when they easily outcompete Kentucky bluegrass and other fine-leaved C3 grasses commonly planted in residential lawns.

CAM Plants C) The jade plant, Crassula argentea, and other CAM plants survive in hot deserts by opening stomata to fix carbon only at night. They run the Calvin–Benson cycle during the day, when stomata are closed.

5.6 Photosynthesis and Aerobic Respiration: A Global Connection  Ancient organisms extracted energy and carbon from molecules such as methane and hydrogen sulfide in Earth’s early atmosphere  Earth’s atmosphere was permanently altered by the evolution of photosynthesis, when oxygen accumulated in the ocean and the atmosphere

Then and Now

Oxygen and the Atmosphere  Oxygen reacts with metals such as enzyme cofactors – free radicals form and damage biological molecules, so they are dangerous to life  Anaerobic  Occurring in the absence of oxygen  Aerobic  Involving or occurring in the presence of oxygen

Aerobic Respiration  Aerobic respiration  Aerobic pathway that breaks down sugars to produce ATP  Requires oxygen  Produces carbon dioxide and water

Aerobic Respiration  Glycolysis (stage 1)  Reactions in which glucose or another sugar is broken down into 2 pyruvates, netting 2 ATP  Coenzymes (2 NADH) pick up electrons  Krebs cycle (stage 2)  Along with acetyl CoA formation, breaks down pyruvate to CO 2, netting 2 ATP and reduced coenzymes (8 NADH and 2 FADH 2 )

Oxidation of glucose to CO 2

Aerobic Respiration  Electron transfer phosphorylation (stage 3)  NADH and FADH 2 deliver electrons to the inner mitochondrial membrane  Electron flow through chains pumps H + from inner to outer compartment, forming a gradient  O 2 accepts electrons and H +, forming H 2 O  H + flows back into inner compartment through ATP synthase, forming ATP from ADP and P i

glucose Cytoplasm 2 2 NAD + Glycolysis 4 (2 net) 2 NADH 2 pyruvate 2 NADH Mitochondrion 2 NADH 2 CO 2 2 acetyl–CoA 4 CO 2 6 NADH 2 FADH 2 Krebs Cycle 2 32 Electron Transfer Phosphorylation oxygen H2OH2O Overview of Aerobic Respiration

Final Stage of Aerobic Respiration electron transfer chain ADP, phosphate 2H 2 O outer membrane O2O2 inner membrane cytoplasm

Summary: Aerobic Respiration C 6 H 12 O 6 (glucose) + 6O 2 (oxygen) + 36 ADP → 6CO 2 (carbon dioxide) + 6H 2 O (water) + 36 ATP

3D ANIMATION: Cellular Respiration

3D ANIMATION: Photosynthesis Bio Experience 3D

5.7 Fermentation  Fermentation  Anaerobic pathway that harvests energy from carbohydrates  Alcoholic fermentation  Lactate fermentation  In fermentation, ATP is formed by glycolysis only  Net yield of 2 ATP per glucose molecule  Coenzyme NAD + is regenerated, which allows glycolysis to continue  Fermentation pathways finish in the cytoplasm

Alcoholic Fermentation  Anaerobic pathway that converts pyruvate to ethanol and produces ATP  Examples: baking, wine and beer production

+ carbon dioxide pyruvate acetaldehydeethanol NADHNAD + A) The last stages of alcoholic fermentation produce CO 2, ethanol, and NAD +. Alcoholic Fermentation

B) One product of alcoholic fermentation in Saccharomyces cells (ethanol) makes beer alcoholic; another (CO2) makes it bubbly. Holes in bread are pockets where CO2 released by fermenting Saccharomyces cells accumulated in the dough. The micrograph shows budding Saccharomyces cells.

Lactate Fermentation  Lactate fermentation  Anaerobic pathway that converts pyruvate to lactate and produces ATP  Examples: cheese, pickles  Lactate production in muscles  Skeletal muscles have two types of fibers: slow-twitch (aerobic) and fast-twitch (anaerobic)  Fast-twitch fibers have few mitochondria and rely on lactate fermentation for quick energy  Good for quick, strenuous activity such as sprinting or weight-lifting

Lactate Fermentation A) The last stage of lactate fermentation produces lactate and NAD +.

Lactate Fermentation B) Lactate fermentation occurs in white muscle fibers, visible in this cross-section of human thigh muscle. The red fibers, which make ATP by aerobic respiration, sustain endurance activities.

Lactate Production in Muscles C) Intense activity such as sprinting quickly depletes oxygen in muscles. Under anaerobic conditions, ATP is produced mainly by lactate fermentation in white muscle fibers. Fermentation does not make enough ATP to sustain this type of activity for long.

5.8 Alternative Energy Sources in Food  In humans and other organisms, simple sugars from carbohydrate breakdown, glycerol and fatty acids from fat breakdown, and carbon backbones of amino acids from protein breakdown may enter aerobic respiration at various reaction steps

Complex Carbohydrates  Complex carbohydrates are broken down into monosaccharide subunits and broken down by glycolysis  High concentration of ATP causes sugars to be diverted from glycolysis and into a pathway that forms glycogen  Between meals, the liver maintains blood glucose level by converting stored glycogen to glucose

Fats  Fats are broken down into glycerol and fatty acids  Fatty acids enter the Krebs cycle as acetyl-CoA  Glycerol enters glycolysis  Fatty acids yield more energy (ATP) than carbs  When blood glucose is high, acetyl–CoA is diverted from the Krebs cycle and into a pathway that makes fatty acids

Proteins  Proteins are broken down into amino acids  Amino acids can be used for energy by removing the amino group (as ammonia) and converting the carbon backbone to acetyl-CoA, pyruvate, or an intermediate of the Krebs cycle

starch (a complex carbohydrate)glucose Alternative Energy Sources in the Body

a fat glycerol head fatty acid tails Food Fats Complex Carbohydrates Proteins fatty acidsglycerolglucose, other simple sugarsamino acids 3 acetyl–CoAPGALacetyl–CoA Glycolysis NADH pyruvate Intermediate of Krebs cycle Krebs Cycle NADH, FADH 2 Electron Transfer Phosphorylation 1234 Alternative Energy Sources in the Body

alanine (an amino acid)pyruvate Alternative Energy Sources in the Body

5.9 A Burning Concern (revisited)  Air and dust trapped in ancient Antarctic ice reveal the composition of the atmosphere millions of years ago  Due to human activities, the atmospheric CO 2 level today is higher than it has been for 15 million years  The increase in CO 2 is contributing to global climate change

Air bubbles trapped in Antarctic ice

Digging Into Data: Energy Efficiency of Biofuel Production