Chapter 5: Photosynthesis and Cellular Respiration Notes

5.1 Matter and Energy Pathways in Living Systems

• Photosynthesis: Organisms trap solar energy in chloroplasts.
• Cellular respiration: Energy-rich compounds break down to generate ATP in mitochondria.
• ATP: Energy source for chemical reactions in cells.

5.2 Photosynthesis Stores Energy in Organic Compounds

• Light-dependent reactions: Chloroplasts trap solar energy and transform it to NADPH (reducing power) and ATP (chemical energy).
• Chemiosmosis: Energy stored in a concentration gradient generates ATP.
• Light-independent reactions: ATP and NADPH reduce carbon dioxide to synthesize glucose.

5.3 Cellular Respiration Releases Energy from Organic Compounds

• Aerobic cellular respiration: Glycolysis, Krebs cycle, and electron transport system.
• Aerobic cellular respiration: Complete oxidation of glucose to release energy.
• Fermentation: Incomplete oxidation of glucose to release energy.

Phytoplankton and Oxygen Production

• Phytoplankton produce over half of Earth's oxygen.
• Phytoplankton blooms may indicate impending earthquakes due to nutrient upwelling from ocean floor shifts.

Launch Lab: Seeing Green

• Chlorophyll absorbs light energy to synthesize carbohydrates using carbon dioxide and water.
• Chlorophyll fluorescence: When a pigment molecule absorbs light, its electrons become excited and move to a higher energy state and emit energy as light of a longer, lower-energy wavelength.

Section 5.1: Photosynthesis and Cellular Respiration – Capturing and Converting Light Energy

• Life on Earth is possible because the sun provides energy in the form of light.
• Living organisms trap, store, and use energy to maintain and sustain cells.
• Green plants and other photosynthesizing organisms (autotrophs) have chloroplasts that contain molecules that trap the Sun’s energy and convert it to chemical energy.
• Non-photosynthesizing organisms (heterotrophs) must consume photosynthetic organisms or other heterotrophs to obtain the chemical energy they need.
• Photosynthesis converts solar energy into chemical energy stored in sugars and carbohydrates; byproducts are oxygen, ATP, and heat.
• Cellular respiration uses mitochondria to break down carbohydrates (and fats) to generate ATP, which fuels cellular activities.
• ATP is the "energy currency" of cells; cells "spend" ATP when they need energy.

ATP and Cellular Activity

• ATP supplies energy for active transport, chromosome movement, cilia/flagella movement, muscle contraction, and synthesis of compounds.
• Cells maintain a constant ATP supply despite its rapid use.
• When the bond to the third phosphate group in ATP breaks, energy is released to form ADP and a free phosphate group which is represented by P.
• ATP is regenerated by adding a free phosphate group represented by P to ADP, which requires an input of energy.
• Molecules of ATP are broken down and regenerated thousands of times each day.

Chloroplasts: Site of Photosynthesis

• Chlorophyll, the main photosynthetic pigment is contained within cell organelles called chloroplasts.
• Most photosynthetic cells contain 40-200 chloroplasts
• A typical leaf may have 500,000 chloroplasts per square millimeter!
• Chloroplasts are bound by an outer and inner membrane.
• Stroma: Fluid in the inner space with proteins and chemicals for carbohydrate synthesis.
• Thylakoids: Interconnected flattened sacs within the stroma.
• Grana: Stacks of thylakoids.
• Chlorophyll molecules are located in the thylakoid membranes.

Mitochondria: Site of Cellular Respiration

• Eukaryotic cells (plants, animals, fungi, protists) contain mitochondria for energy extraction.
• Mitochondria are smaller than chloroplasts; range from 0.5 \mu m-1.0 \mu m in diameter and 2 \mu m-5 \mu m in length.
• Mitochondria are bounded by two membranes.
• Matrix: Fluid-filled space of the inner membrane with proteins and chemicals to break down carbohydrates and high-energy molecules.
• Cristae: Folds in the inner membrane that provide a large surface area for ATP production.

Metabolic Pathways and Energy for Cellular Reactions

• Photosynthesis: 6CO2(g) + 6H2O(l) + energy \rightarrow C6H{12}O6(s) + O2(g)
• Cellular respiration: C6H{12}O6(s) + O2(g) \rightarrow 6CO2(g) + 6H2O(l) + energy
• Photosynthesis uses respiration products as reactants, and cellular respiration uses photosynthesis products as reactants.
• Cellular respiration releases energy and is similar to combustion, but occurs in controlled, step-by-step metabolic pathways.
• Metabolic pathway: Product of one reaction becomes the reactant for another.

Enzymes Catalyze Cellular Metabolism and Energy Production

• Metabolism: All chemical reactions within a cell to support life functions.
• Anabolic pathways: Synthesize larger molecules from smaller ones and require energy.
• Catabolic pathways: Break down larger molecules into smaller ones and release energy.
• Metabolic reactions are catalyzed by enzymes specialized proteins that lower the energy needed to activate biological reactions.. Each reaction has a specific enzyme.

Linking Reactions through Oxidation and Reduction

• Oxidation: Atom or molecule loses an electron.
• Reduction: Atom or molecule gains an electron.
• Electrons lost by one atom or molecule must combine with another; when one compound is oxidized, another must be reduced.
• Reduced compounds contain more energy than oxidized compounds.
• Reducing power: Molecules that, in their reduced form, contain a large amount of available energy.

Section 5.2 Photosynthesis Stores Energy in Organic Compounds

• Photosynthesizing organisms synthesize about 1.4 \times 10^{15} kg of glucose and other sugars each year.
• Glucose produced can be converted to cellulose, other sugars, or storage forms like starch.
• Sugars produced by photosynthesis are involved in the synthesis of other essential cellular substances such as amino acids, which are needed to make proteins
• Products of photosynthesis account for nearly 95 percent of the dry weight of green plants and humans depend on them for survival.

Process of Photosynthesis

• Photosynthesis can be summarized as: 6CO2(g) + 6H2O(l) + energy \rightarrow C6H{12}O6(s) + O_2(g). The arrow represents over 100 distinct chemical reactions that lead to the end products.
• Two sets of reactions: light-dependent and light-independent reactions.
• Light-dependent reactions: Solar energy is trapped and used to generate ATP and NADPH (reducing power).
• Light-independent reactions: Energy of ATP and reducing power of NADPH are used to reduce carbon dioxide to make glucose, which can be converted into starch for storage.

The Light-Dependent Reactions of Photosynthesis

• Pigments within the thylakoid membranes absorb light energy. Pigment absorbs certain wavelengths of visible light, while reflecting others that give the pigment its specific color.
• Photosynthetic pigment traps light energy and passes it on to other chemicals, which use the energy to synthesize high-energy compounds; Chlorophyll is the main pigment.
• Chlorophyll absorbs red and blue light while it transmits or reflects green light.
• Absorbance spectrum: A graph that shows the relative amounts of light of different colors that a compound absorbs.
• Beta-carotene absorbs blue and green light, so it is yellow, orange, and red in color; it is responsible for the orange color of carrots and can be converted into vitamin A, then retinal for visual pigment.
• Action spectrum: Shows the relative effectiveness of different wavelengths of light for promoting photosynthesis, linking oxygen production (as a response) to selected wavelengths and specific pigments that absorb them.
• Having a variety of pigments enables a plant to use a greater percentage of the Sun’s light.

The Path of Electrons in the Light-Dependent Reactions

• Chlorophyll is bound to the membranes of the thylakoids inside the chloroplasts.
• Chlorophyll and other pigments are arranged in the thylakoid membranes in clusters called photosystems
• Chloroplasts of plants and algae have two photosystems: Photosystem I (PSI) and Photosystem II (PSII).
• Photosystems are named for order of discovery, not function sequence.
• Each photosystem is made up of pigment molecules including one dozen or more chlorophyll molecules, as well as a few carotenoid molecules.
• Photosystem also contains a molecule that accepts electrons.
• All the pigment molecules in each photosystem can absorb light energy of various wavelengths, but they always pass the energy along to one specialized, electron- accepting chlorophyll a molecule called the reaction centre.

Part 2: Steps After Electrons Reach Acceptor

• When electron leaves reaction center in photosystem II and goes to electron-acceptor, reaction center is missing an electron. New electron comes from splitting water molecule in reactions that release electrons, hydrogen ions, and oxygen atoms so a water molecule is the source.
• Energized electron is transferred along an electron transport system, with each transfer releasing a small amount of energy to push hydrogen ions from the stroma, across the thylakoid membrane, and into the thylakoid space.
• Light energy absorbed by photosystem I, energy transferred to a reaction center, where an electron becomes excited.
• Electron that was received by electron-acceptor from photosystem I is used to reduce NADP^+ to form NADPH (reducing power), will be used in the light-independent reactions.

Making ATP: Chemiosmosis

• Hydrogen ions are forced from the stroma to the thylakoid space and cannot diffuse back across the membrane because the membrane is impermeable to these charged particles.
• ATP synthase, embedded in the thylakoid membrane, provides the only pathway for hydrogen ions to move down their concentration gradient, which bonds a free phosphate group to an ADP molecule to form ATP.
• Chemiosmosis: Linking of the movement of hydrogen ions to the production of ATP.

Mimicking Nature

• Scientists and engineers are using chlorophyll to trap solar energy and convert it into chemical energy.
• The amount of electrical energy that can be produced by solar cells at Earth’s surface is not enough to supply much of the energy that society needs.
• Scientists are looking closely at hydrogen as an alternative source of energy to reduce CO_2 emmissions.
• Plants release oxygen gas but not hydrogen gas. The hydrogen from the water becomes part of the concentration gradient or is added to NADP^+ to reduce it to NADPH.
• Teams of scientists are now looking for a way to produce an artificial system similar to photosystem II that will use solar energy to split water but convert the released ions and electrons into hydrogen gas instead of using them for reducing power.

The Light-Independent Reactions of Photosynthesis

• Energy from NADPH and ATP can be used synthesize glucose in the presence or absence of light through the Calvin-Benson cycle.

1. Fixing Carbon Dioxide: carbon atom in CO_2 is chemically bonded to a pre-existing molecule (RuBP), which is unstable and immediately breaks down into two 3-carbon compounds.

• Plants demonstrating this process are called C3 plants because the three-carbon compounds that are the first stable products of the process
• CO_2 + RuBP → unstable C6 → 2 C3

1. Reduction: The newly formed three-carbon compounds are activated by ATP and then reduced by NADPH to form two molecules of PGAL (glyceraldehyde-3-phosphate). In their reduced (higher-energy) state, some of the PGAL molecules leave the cycle and may be used to make glucose.
2. Replacing RuBP: Most of the reduced PGAL molecules are used to make more RuBP. Energy, supplied by ATP, to make the five-carbon RuBP from PGAL, Calvin-Benson cycle must be completed six times to synthesize one molecule of glucose. Of the 12 PGAL molecules that are produced in sic cycles, 10 are used to regenerate RuBP, and 2 are used to make glucose.

Photosynthesis Efficiency

• The maximum efficiency of photosynthesis is estimated at 30 percent, with actual field efficiency ranging from 0.1 percent to 3 percent.
• Photorespiration counteracts photosynthesis because rubisco can catalyze reactions involving oxygen as easily as carbon dioxide, removing carbon from carbon-related reactions.

Section 5.3 Cellular Respiration Releases Energy from Organic Compounds

• Cellular respiration releases energy of glucose molecules by oxidizing glucose to carbon dioxide.
  C6H{12}O6(s) + O2(g) \rightarrow 6CO2(g) + 6H2O(l) + energy (ATP)

Three Pathways for Energy Release

• Aerobic cellular respiration: Requires oxygen to produce ATP; Animals, plants, fungi, protists, and bacteria.
• Anaerobic cellular respiration: Does not require oxygen to produce ATP; Oxygen may be lethal; bacteria carry out anaerobic cellular respiration, as do members of archae.
• Fermentation: Anaerobic process (not technically anaerobic cellular respiration). Fermentation occurs in the muscle cells of mammals; yeasts and the bacteria that cause milk to sour (Lactobacillus bulgaricus) are examples of organisms that carry out fermentation

Examining Aerobic Cellular Respiration

• Aerobic cellular respiration: Enzymze-catalyzed reactions transfer electrons from high-energy molecules such as glucose to oxygen, main mean sof releasing energy and happens mainly in the mitochondira of eukaryotic cells; begins with glycolysis in the cytoplasm of cells- an anaerobic process
• Glycolysis: splitting glucose(a six-carbon molecule) to two molecules of pyruvate(three-carbon molecule) and a small amount of ATP. Pyruvate still contains a large amount of chemical energy.If oxygen is not available to eukaryotic cells, pyruvate goes to the process of fermentation
• With sufficient oxygen, pyruvate is transported from the cytoplasm into the mitochondrion.Then, pyruvate prepares itself for entry into Krebs cycle.
• Krebs cycle transforms energy of glucose into reducing power of molecules called NADH and FADH_2. These supply high-energy electrons to electron transport system that produces a large amount of ATP. Water is the final end product of this process

Outside of Mitochondria: Glycolysis

• Glycolysis is the only source of energy because it can proceed anaerobically for some cells.Glycolysis splits glucose( six-carbon molecule) into two molecules of pyruvate (three-carbon molecule).
• ATP molecules are used at the start of glycolysis because more energy must be added to start series of reactions even though glucose is high-energy molecule.
• Glycolysis is complete, there are two identical three-carbon molecules of pyruvate.
• When oxygen is available species that cannot utilize pyruvate must be processed through fermentation.When sufficient oxygen is present in call, pyruvate is transported into the matrix of the mitochondria in preparation for the Krebs cycle.

Inside the Mitochondria: Krebs cycle Preparation

• Before portions of it can enter krebs cycle: pyruvate loses a carbon atom in the form of carbon dioxide, and the other two carbon atoms are bonded to molecule called coenzyme A(CoA). Another NAD^+ is reduced to NADH.
• CoA attaches to the two carbon compound (acetyl group) and “tows” its to the Krebs cycle

The Krebs Cycle

• Krebs cycle is a cycle meaning that the four carbon compound that picks up a group of two carbons from Acetyl-CoA must be regenerated the carbon in carbon dioxide because carbon is fully oxidized.
• Most of the energy released when carbon molecules are oxidized are transformed into reducing power in the form of reduced NADH and another molecule called FADH_2( very similar to NADH and NADPH).
• ATP molecules is generated during the Krebs Cycle

Electronn Transport

• The vast majority of the ATP molecules in aerobic cellular respiration are produced during electron tranport.
• High energy electrons are passed on to chain of electron-carrying molecules that are attached to the inner membrane of the mitochondrion.
• Energy is released and controls amounts as electron pass from one carrier to another.
• Energy is used to pump hydrogen ions across the membrane from the matrix to intermembrane space.
• Build up of ions in intermembrane space creates ahydrogen ion concentration gradient.
• Enzyme ATO synthase uses the energy of the concentratin gradient to bind a phosphate grouo to ADP, forming ATP>>this process is chemiosmosis.In chlorplast chemiosmosis in the mitochondrion couples the movement of hydrogen ions down their concentation gradient to the synthesis of ATP from ADP and phosphate.
• Oxygen is the final electron-accepting molecule in electron transport system and the results produces water molecules.

The Role of Oxygen in Aerobic Cellular Respiration

• If oxygen where not present to receive electrons, the whole process would ultimately fail.
• The last electron carrier would not be able to release its electron.No oxidized NAD^+ of FAD to pick up electrons and all reactions would seize.
• Therefore glycolysis would be the only process done without oxygen but it doesn't produce enough energy to sustain needs of most eukaryotic cells
• The electron gradient produce by chemiosmosis is where the energy to carry out every tak is derived.

Anareobic Cellular Respiration Uses a Different Final Electron-Acceptor

• Some organisms use anaerobic cellular respiration for their energy needs in environments of anoxic.
• Like aerobic respiration anaerobic includes ETC and concentration gradient to generate molecules of ATP.
• Anaerobic cellular respiration gives less energy because it is not as efficient as aerobic
• Final accepting molecule is inorganic chemical because oxygen is not available as the final accepting molecule

Fermentation

• Anaerobic organisms, some cells withoy oxygen perform ETC without oxygen
• Fermentation- metabolic pathway (glycolysis that occurs in the cytoplasm along with one or two with electron transport sysrem)
• It is far less effective at supplying energy compared to the supply of aerobic energy
• Single celled organisms(yeast, bacteria)

Lactate Fermentation

• Some singe-celled, animal cells with no oxygen go though lactate fermentation.
• NADH to convert pyruvate to lactate
• This process occur in muscle cells that are working strenuously. Demand greater then production aerobically.
• If lactate buildup muslce fatigue and can cause crammps:when oxygen present lacetate to convert for pyruvate and go through aerobic

Ethanol Fermentation

• When function anaerobically they carry out Entanol fermentation; yeast and some bacteria convert Pyruvate to ethanol
• Steps fermentation happens in figure 5.22
• Brewers yeast(saech
• Brewing and Alcoholic bev use ethanol production