Photosynthesis & Cellular Respiration PDF

PHOTOSYNTHESIS & Biology 20 CELLULAR 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) –...

PHOTOSYNTHESIS & Biology 20 CELLULAR 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 C 6H12O6 + 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 Absorption 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.  CHEMIOSM OSIS Thylakoid H+ H+ H+ ATP Synthase Space H+ Molecule F Thylakoid r H+ Mvmt – activates e Memb. e the 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 ATP DEPENDENT REACTIONS 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).