Photosynthesis & Cellular Respiration - 2025 revised PDF

PHOTOSYNTHESIS & CELLULAR Biology 20 RESPIRATION LEAF ANATOMY REVIEW COMPARISON BETWEEN PHOTOSYNTHESIS AND CELLULAR RESPIRATION Definitions: Autotroph: (Self feeder) – organism that produces its own food from inorganic raw materials using light or chemical energy. Heterotroph: (Oth...

PHOTOSYNTHESIS & CELLULAR Biology 20 RESPIRATION LEAF ANATOMY REVIEW COMPARISON BETWEEN PHOTOSYNTHESIS AND CELLULAR RESPIRATION Definitions: Autotroph: (Self feeder) – organism that produces its own food from inorganic raw materials using light or chemical energy. Heterotroph: (Other feeder) – Organism that cannot produce its own food, therefore; must consume other organisms for nutrition  COMPARISON BETWEEN PHOTOSYNTHESIS AND CELLULAR RESPIRATION Photosynthesis Cellular respiration Description of the Conversion of solar energy to chemical Glucose is broken down in a series of reactions to produce reaction energy, which is stored as glucose and other ATP (energy) organic compounds General reaction Types organisms Autotrophs (plants) Heterotrophs (animals) and autotrophs (plants) that use this process  Photosynthesis Cellular respiration Why is this process used? To produce a food source (glucose) To convert the chemical energy stored in which can be used for cellular glucose into useable energy (ATP) respiration or converted to other organic compounds for storage. Site of this process Chloroplasts Mitochondria  MATTER AND ENERGY PATHWAYS IN LIVING SYSTEMS Both cellular respiration and photosynthesis are examples of biological processes that involve matter & energy – these are called metabolic pathways. During photosynthesis, energy from the sun is stored in the chemical bonds of glucose This energy is released during cellular respiration. THE CHLOROPLAST The chloroplast is the site of photosynthesis They consist of a series of membranes Chloroplasts are found in plant cells. The inner and outer membranes surround the stroma The stroma is a yellowish fluid that contains the proteins and chemicals required for photosynthesis. A third type of membrane is the thylakoid, which creates a series of flattened sac-like structures. These thylakoids are stacked in structures known as grana. Singular is granum. THE MITOCHONDRIA The mitochondria is the site of cellular respiration They are found in both plant and animal cells. The mitochondria has two membranes The fluid-filled space within the inner membrane is known as the matrix. This matrix contains many of the chemicals and proteins required to break down carbohydrates and create ATP. ATP MOLECULE ADENOSINE TRIPHOSPHATE ( ATP) An ATP molecule is made of three components: A 5 Carbon sugar (Ribose) A nitrogen containing base (Adenine) 3 Phosphate molecules When the body requires energy, the ATP molecule is decomposed. It breaks down into adenosine diphosphate (ADP + P) (Releasing a phosphate also releases energy) ATP ATP can be broken down TWICE to release energy. The reactions are: ATP → ADP + P ADP → AMP + P These reactions are exothermic (releasing energy). The decomposition of ATP releases more energy than the decomposition of ADP. ATP The resynthesis of ATP (choose the correct response): Releases energy / absorbs energy Requires adding a phosphate molecule / requires removing a phosphate molecule METABOLIC PATHWAYS The common chemical equations that represent both photosynthesis and cellular respiration are only net reactions. Both of these processes use a series of pathways that are set up in step-by-step sequences. METABOLIC PATHWAYS Metabolism (the sum of the processes within a cell) can be broken into two distinct types of reactions. Anabolic reactions & pathways create larger molecules from small subunits Catabolic reactions & pathways break down large molecules into smaller pieces TYPES OF REACTIONS There are many important reactions that are involved in cellular respiration and photosynthesis. They include: Redox reactions Decarboxylation Phosphorylation Lysis OXIDATION & REDUCTION??? Oxidation is a reaction where an atom or molecule loses electrons (LEO – Loses Electrons = Oxidation)…this is a LOSS of energy. When a reaction occurs where an atom or molecule gains electrons, it is known as Reduction (GER – Gains Electrons = Reduction)…this is a GAIN of energy. So…the reduced form actually has MORE energy! However, free electrons from oxidation cannot exist on their own. As a result, the electrons that are lost through oxidation of one substance cause the reduction of another compound Therefore, oxidation and reduction must occur at the same time A HALF reaction plus a HALF reaction! REDOX Examples: NAD+ + H+ →NADH (REDUCTION) NADH → NAD+ + H+ (OXIDATION) We will see both of these later in the unit! OTHER TYPES OF REACTIONS: Phosphorylation Decarboxylation Lysis PHOTOSYNTHESIS –Most animals are classified as heterotrophs due to their ability to ingest their food source, however plants are classified as autotrophs as they produce their food source. Autotroph means self feeder. –Plants facilitate food production through the process of photosynthesis, where light energy is transformed into glucose using inorganic raw materials (CO2 from the air and H2O from the soil). This occurs in a series of reactions and thus is referred to as a Metabolic Pathway. One of the key by-products of this process is Oxygen.  The Generalized formula for photosynthesis is light 6 CO2 + 6 H2O Chlorophyll C6H12O6 + 6 O2 –Photosynthesis takes place mainly in the leaf cells of plants in specialized organelles called chloroplasts. Light energy is trapped by the green pigment inside the organelle, this pigment is called chlorophyll. Through a series of reactions the trapped light energy is transformed into chemical energy in the form of glucose and ATP.  OVERVIEW OF PHOTOSYNTHESIS https://www.youtube.com/watch?v=g78utcLQrJ4 PHOTOSYNTHETIC PIGMENTS AND ABSORPTION Light exists in various wavelengths, which represents their energy content and absorptive potential. The following is the Electromagnetic Spectrum of various wavelengths.  Pigments in plants absorb wavelengths in the visible light spectrum. When all wavelengths in this spectrum are present simultaneously they combine to form white light. When seen separately they appear as various colours. Wavelengths may be absorbed or reflected it depends on the pigment within the plant. The colour of the plant is indicative of the wavelength of light that was reflected. Ex. Grass is green b/c chlorophyll (the main pigment in grass) absorbs wavelengths other than green & reflects green light  TYPES OF PIGMENTS Chlorophyll A: is the most important pigment in photosynthesis since it plays a direct role in obtaining the best type of wavelengths for photosynthesis. Chlorophyll B: absorbs in a similar spectrum of wavelengths to chlorophyll A, but in lower amounts. Carotenoids: one of the main groups of accessory pigments. They serve to broaden the spectrum of absorption by absorbing other wavelengths, then pass the energy received to chlorophyll A. Carotene Chlorophyll Carotenoïds ABSORPTION AND ACTION SPECTRA Absorption spectrum: Amount of each wavelength absorbed Action spectrum: Effectiveness of a wavelength in the action of photosynthesis ABSORPTION SPECTRA OF VARIOUS PIGMENTS Chlorophyll A Chlorophyll B Carotenoids Amt of Absorptio n 400 500 600 700 Wavelength (nm) ACTION SPECTRUM OF PHOTOSYNTHESIS Amt O2 produced 400 500 600 700 Wavelength (nm) Which colours of the spectrum are best absorbed by chlorophyll a? How does an action spectrum compare and contrast to an absorption spectrum? Which wavelengths are ideal for photosynthesis? Which pigments of the spectrum are not well absorbed by accessory pigments?  Plant chromatography overview: Pigments in a plant can be separated through a technique called chromatography. We rub a sample of pigment from a plant onto chromatography paper and place it in a solvent. The solvent travels up the paper and pigments that are very soluble will travel a larger distance on the paper. What can we conclude about the solubility of carotene compared to chlorophyll a when we look at the chromatography results to the left? Bozeman biology demo: http://www.youtube.com/watch?v=6Z-SpXUeKr0  PHOTOSYNTHESIS – THE REACTIONS Photosynthesis actually involves many chemical reactions that work together. These reactions can be summarized in two groups: 1. Light-Dependent Reactions 2. Light-Independent Reactions  SYNOPSIS OF THE REACTIONS OF PHOTOSYNTHESIS The Light - Dependent Reactions – When: Day time – Where: In the thylakoids – What: light is absorbed, this causes electrons to “jump” and this energy is used to make ATP and NADPH The Light - Independent Reactions ( Aka: _Carbon-Fixation or Calvin-Benson Cycle_) – When: All the time – Where: Stroma of a chloroplast – What: Carbon is fixed (added) to a molecule and eventually glucose is formed LIGHT-DEPENDENT REACTIONS During these reactions, the pigments contained inside the thylakoid absorb light energy. Although plants have a number of pigments, the most important for photosynthesis is chlorophyll. THE PHOTOSYSTEMS In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into photosystems. A photosystem acts like a light-gathering “antenna complex” consisting of a few hundred chlorophyll A, chlorophyll B, and carotenoid molecules. There are two – Photosystem I and Photosystem II.  THE PHOTOSYSTEMS There is a reaction center in the photosystems that contains a chlorophyll A molecule. When the electron in the reaction center is “excited” by the addition of energy, it travels to the electron-acceptor molecule. This reduces the electron acceptor and puts it at a high energy level. A series of steps then takes place: STEP 1 The electron leaves the reaction center of photosystem II and joins with the electron acceptor This leaves an “electron hole” in photosystem II…a place with no electron. Enzymes break down a water molecule, which releases H+ ions, electrons, and oxygen (this is the step in photosynthesis that produces oxygen gas).This process is called photolysis. STEP 2 The electron acceptor transfers the energized electron to a series of electron-carrying molecules (known as the electron transport system)…like a staircase going down… As the electron moves through this system, it loses energy. The “lost” energy from the electrons are used to push H+ ions across the stroma, across the thylakoid membrane and into the thylakoid space. The movement of the H+ ions into the thylakoid space produces a concentration gradient (the pH within the thylakoid space is about 5, while the pH in the stroma is about 8). This concentration gradient serves as a source of potential energy. STEP 3 While steps 1 & 2 are taking place, photosystem I is absorbing light. Again, an electron is released from the action center and is passed to a high-energy electron-acceptor. The electron lost from photosystem I is replaced by the electron arriving through the electron transport system from Photosystem II. STEP 4 The electron from photosystem I is used to reduce NADP+ to form NADPH. These are membrane-bound enzyme complexes a.k.a coenzymes. NADPH’s reducing power is then used later in the light-independent reactions NADP+ = Nicotinamide adenine dinucleotide phosphate NADPH = Nicotinamide adenine dinucleotide phosphate (reduced).  ATP PRODUCTION IN THE LD REACTIONS - CHEMIOSMOSIS The energy from the electrons in photosystem II is used to produce ATP indirectly. As previously mentioned, the energy of the electrons is used to push H+ ions against the concentration gradient into the thylakoid space. WHAT HAPPENS DURING CHEMIOSMOSIS? 1. H+ ions move into the thylakoid space through active transport. 2. To return to the stroma, the H+ ions must move through a special molecule known as ATP synthase. 3. ATP synthase uses the movement of the H+ ions to run a mechanism that bonds together ADP and free phosphates to form ATP.  CHEMIOS MOSIS Thylakoid + H H+ H+ ATP Synthase Space H+ Molecule F r H+ Mvmt – Thylakoid Memb. e activates the e molecule P ADP + P ATP H+ Stroma H+ End result…ATP LIGHT DEPENDENT REACTIONS NOTE NOTE  The light reactions use solar energy absorbed by both photosystem I A SUMMARY OF THE LIGHT and photosystem II to provide chemical energy in the form of DEPENDENT REACTIONS ATP and reducing power in the form of the electrons carried by NADPH.  THE LIGHT-INDEPENDENT REACTIONS Once enough ATP and NADPH has been produced by the chloroplasts, glucose can be synthesized – this is the end goal of photosynthesis. This involves a series of reactions known as the Calvin-Benson Cycle. LIGHT INDEPENDENT REACTIONS (CARBON FIXATION / CALVIN – BENSON CYCLE) The reactants are: (1) CO2 (2) NADPH & ATP from the light dependant reactions (3) Raw inorganic compounds The products are: Two G3P (three carbon sugar molecules) that combine to make Glucose THE CALVIN-BENSON CYCLE The Calvin cycle regenerates its starting material after molecules enter and leave the cycle…that’s why it’s called a CYCLE. CO2 enters the cycle and leaves as a sugar. The cycle spends the energy of ATP and the reducing power of electrons carried by NADPH to make the sugar. The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P) (Also known as PGAL – Phosphoglyceraldehyde) Each turn of the Calvin cycle “fixes” one carbon. This is CARBON FIXATION - The process by which plants turn inorganic carbon into organic compounds ▪ For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO2. ▪ To make one glucose molecule would require six turns of the cycle and the fixation of six CO2 molecules. ▪ There are THREE phases to the cycle… PHASE 1 – CARBON FIXATION In the carbon fixation phase, each CO2 molecule becomes attached to a five-carbon sugar called ribulose bisphosphate (RuBP). This is catalyzed by an enzyme called RuBP carboxylase or rubisco. The resulting six-carbon intermediate splits in half to form two molecules of 3-phosphoglycerate per CO2. PHASE 1 – CARBON FIXATION PHASE 2 - REDUCTION During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3 bisphosphoglycerate. A pair of electrons from NADPH reduces each 1,3 bisphosphoglycerate to G3P. Some of the G3P molecules leave to make glucose, the rest go to phase 3. PHASE 2 - REDUCTION PHASE 3 - REGENERATION In the last phase, regeneration of the CO2 acceptor (RuBP), the five G3P molecules are rearranged to form 3 RuBP molecules. To do this, the cycle must spend three more molecules of ATP (one per RuBP) to complete the cycle and prepare for the next. PHASE 3 - REGENERATION The WHOLE DEAL…  OVERALL COSTS: For the net synthesis of one G3P molecule, the Calvin recycle consumes nine ATP and six NAPDH. It “costs” three ATP and two NADPH per CO2. The G3P from the Calvin cycle is the starting material for the metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.  FACTORS AFFECTING PHOTOSYNTHESIS The three main things affecting the rate of photosynthesis are: 1.Light 2.Temperature 3.Carbon dioxide These three factors are called LIMITING FACTORS.  LIGHT The rate of photosynthesis increases linearly with increasing light intensity (from point A to B on the graph). Gradually the rate falls of and at a certain light intensity the rate of photosynthesis stay constant. TEMPERATURE ⚫ The higher the temperature then typically the greater the rate of photosynthesis, photosynthesis is a chemical reaction and the rate of most chemical reactions increases with temperature. However, for photosynthesis at temperatures above 40°C the rate slows down. This is because the enzymes involved in the chemical reactions of photosynthesis are temperature sensitive and destroyed at higher temperatures.  CARBON DIOXIDE LEVELS The rate of photosynthesis increases linearly with increasing carbon dioxide concentration (from point A to B on the graph). Gradually the rate falls of and at a certain carbon dioxide concentration the rate of photosynthesis stays constant (from point B to C on the graph).  CELLULAR RESPIRATION RELEASES ENERGY FROM ORGANIC COMPOUNDS During photosynthesis electrons and hydrogen ions are chemically bonded to carbon dioxide reducing it to produce chemical energy in the form of glucose molecules Cellular respiration is the reverse of this… Glucose is oxidized to carbon dioxide while releasing energy and water  RELEASING STORED ENERGY There are three ways of releasing the energy stored in food: 1. Aerobic cellular respiration is carried out by organisms that live in oxic (oxygen containing) environments 2. Anaerobic cellular respiration is carried out by organisms that live in anoxic (no-oxygen containing) environments A subcategory of anaerobic respiration that happens in microorganisms such as yeast is calles fermentation. This process allows these microorganisms to produce ATP.  SYNOPSIS OF AEROBIC VS ANAEROBIC Reactions of Aerobic Reactions of Anaerobic Cellular Respiration Cellular Respiration Glycolysis Glycolysis Link Reaction Fermentation Krebs Cycle Oxidative Phosphorylation GLYCOLYSIS The first step of cellular respiration (aerobic or anaerobic) is glycolysis In glycolysis, a glucose molecule is converted into two molecules of pyruvic acid. ATP and NADH are also produced This takes place in the cytoplasm (outside the mitochondria) Oxygen is not required for this step  STEPS IN GLYCOLYSIS 1. 2 ATP are used to change glucose to fructose diphosphate 2. The fructose molecule is split into two molecules of G3P. 3. The G3P molecules are oxidized and their electrons are donated to NAD+ to form 2 NADH 4. Finally, the molecules are converted to pyruvate and 4 molecules of ATP are produced GLYCOLYSIS (glucose) Splitting of the 6C sugar Recall that NADH is nicotinamide adenine PYRUVATE and dinucleotide ATP are produced…  GENERAL NOTES REGARDING GLYCOLYSIS Note that oxygen is NOT required for glycolysis Glycolysis occurs in the cytosol of cells, not in the mitochondria. Glycolysis produces 4 ATP while consuming 2 ATP, providing a net outcome of 2 ATP 2 reduced NADH molecules are also produced Alone, glycolysis does not produce much energy (most of it is still stored in pyruvate and NADH) Some microorganisms ONLY need to perform glycolysis to meet their energy demands, but it isn’t enough to meet the energy demands of multicellular organisms. THE FATE OF PYRUVATE… After glycolysis, if there is enough oxygen present, the pyruvate will be converted to acetyl CoA and then move to the Krebs Cycle in the mitochondria If there is not enough oxygen present, the pyruvate undergoes fermentation lactate fermentation in animals and some unicellular organisms Ethanol fermentation in plants, yeast, some bacteria AEROBIC CELLULAR RESPIRATION There are 4 steps to aerobic cellular respiration: 1. Glycolysis 2. Oxidation of pyruvate (links reaction) 3. Krebs Cycle 4. Oxidative phosphorylation (electron transport chain and chemiosmosis) The products of aerobic respiration are: 36 ATP CO2 H2O PYRUVATE & COENZYME A Pyruvate loses a carbon in the form of carbon dioxide…this process is called decarboxylation. When this occurs, another molecule of NAD+ is reduced to form NADH. The remaining 2 carbon atoms from pyruvate attach to a molecule called Coenzyme A. Coenzyme A “tows” the acetyl group into the Krebs cycle (in the form of Acetyl-CoA)  THE KREBS CYCLE Occurs in the matrix of the mitochondria During this cycle ATP and reduced compounds are formed (NADH & FADH2) https://www.youtube.com/watch?v=-_8aYKcQZ_Q STEPS IN THE KREBS CYCLE 1. Acetyl CoA binds with a 4-carbon molecule to form a 6-carbon molecule. 2. The 6-carbon molecule loses a carbon in the form of CO2. This releases an electron and a hydrogen atom to form NADH from NAD+. 3. This new 5-carbon molecule loses a carbon in the form of CO2. This releases an electron and a hydrogen atom to form NADH from NAD+. As well, ATP is formed. 4. This new four-carbon molecule undergoes a series of structural changes that release more electrons, allowing the production of 1 FADH2 molecule from FAD, and the production of another NADH molecule from NAD+ 5. The four-carbon molecule is now the same as the original molecule that started the cycle binding to acetyl-coA Krebs Cycle Animation THE KREBS CYCLE It’s called a The pyruvate loses cycle because C in the form of the 4C CO2 that’s released compound gets into the regenerated to atmosphere. The pick up more leftover carbon carbon groups bonds to become CoA which “tows” The role of the the C into the cycle cycle is to transfer the energy from the glucose to NADH and FADH2  OXIDATIVE PHOSPHORYLATION: THE ELECTRON TRANSPORT TakesCHAIN place in the cristae (inner membrane of the mitochondria) Oxidative phosphorylation has two parts: 1. The electron transport chain (using the products of the Krebs cycle - NADH and FADH2) 2. Chemosmosis (ATP production) Oxidative phosphorylation is similar to the light-dependent reactions in photosynthesis. Oxidative phosphorylation produces large amounts of ATP during cellular respiration  OXIDATIVE PHOSPHORYLATION: THE ELECTRON TRANSPORT CHAINNADH and The high-energy FADH2 molecules are oxidized. NADH and FADH2 lose their H+ ions, and electrons are released. Electrons are transported through a chain inside the mitochondria's inner membrane (the cristae). This energy is used to pump H+ ions across the membrane into the intermembrane space. This pumping of hydrogen creates a concentration gradient…remember particles move down the gradient. This can be used to power the formation of ATP from ADP in chemiosmosis. OXYGEN & ELECTRON TRANSPORT ▪ The electron transport chain requires oxygen in aerobic respiration. ▪ As electrons move down the electron transport chain they eventually reach the final and the strongest electron acceptor, which is oxygen. ▪ The oxygen is reduced, picking up hydrogen & its electrons and forming water If oxygen were not present at this final point, it would prevent electrons from passing from the previous electron receptor Without it the reaction would cease, much like a traffic jam backing up the freeway  OXIDATIVE PHOSPHORYLATION: CHEMIOSMOSIS Hydrogen atoms follow another pathway (chemiosmosis) Protons (H+) accumulate in the intermembrane space - between the two mitochondrial membranes, and then pass through ATP synthase to exit. ATP synthase facilitates the phosphorylation of ADP to produce ATP. SUMMARY OF AEROBIC CELLULAR RESPIRATION CO2 ATP NADH FADH2 Glycolysis 0 2(net) 2 0 Link rxn (con. of pyruvate into 2 (1/Pyruvate) 0 2 0 Acetyl-COA Krebs Cycle 4 (2/cycle) 2 (1/cycle) 6 (3/cycle) 2 (1/cycle) Oxidative 0 32 (net) 0 0 Phosphorylation Total ATP Made in Aerobic Cellular Respiration= 36 ANAEROBIC RESPIRATION Anaerobic respiration (or fermentation) has two stages: Glycolysis Fermentation Products are 2 ATP molecules and either ethanol (ex: in plants) or lactate (ex: in animals' muscles) Takes place in the cytoplasm, without oxygen This pathway produces only the ATP that is generated during glycolysis, therefore, it is less efficient than aerobic respiration. WHAT CARRIES OUT FERMENTATION? Many single-celled organisms carry out fermentation…yeast, bacteria for example. Fermentation can also occur deep within tissues that are not near an oxygen source such as submerged plant tissue There are two types of fermentation: 1. Lactate fermentation 2. Ethanol fermentation FERMENTATION NADH is produced by glycolysis and its H atom is transferred either to acetaldehyde to produce ethanol, or to pyruvate to produce lactate. The goal of the second step is to regenerate NAD+ so the process can start again (like a cycle)  LACTATE FERMENTATION ⚫ Cells that are temporarily without oxygen carry out lactate fermentation. ⚫ The cells convert pyruvate to a molecule called lactate or lactic acid. ⚫ This lactate is then stored. ⚫ When the oxygen content increases the lactate is converted to pyruvate which continues in the Krebs cycle in the aerobic pathway. ⚫ Lactate is formed in bacteria and animal muscle cells. ETHANOL FERMENTATION Some organism can function both aerobically and anaerobically When they function anaerobically they carry out ethanol fermentation Produced in yeast, plants and some bacteria. This process involves two steps: 1. After glycolysis produces pyruvate the pyruvate is converted into a two carbon compound by the release of CO2. 2. This two carbon compound is then reduced by NADH to form ethanol. ETHANOL FERMENTATION The everyday products formed by ethanol fermentation are: Beer Wine Bread Carbonated drinks Cheese Soy sauce LACTATE FERMENTATION During strenuous exercise, muscle cells need more ATP than the body can produce with aerobic cellular respiration alone. Our body uses lactate fermentation to produce more ATP. The effects of lactate fermentation are: Muscle cramps muscle pain Muscle stiffness Fatigue Lactate is then picked up by the blood and transported to the liver, where it is converted into glucose. Fitness and health have a big effect on cellular respiration!