Photosynthesis PPT PDF

PHOTOSYNTHESI S PHOTOSYNTHESIS the process in which light energy is converted to chemical energy in the form of sugars PHOTOSYNTHESIS In a process driven by light energy, glucose...

PHOTOSYNTHESI S PHOTOSYNTHESIS the process in which light energy is converted to chemical energy in the form of sugars PHOTOSYNTHESIS In a process driven by light energy, glucose molecules (or other sugars) are constructed from water and carbon dioxide, and oxygen is released as a byproduct. PHOTOSYNTHESIS the glucose molecules provide organisms with two crucial resources: energy and fixed— organic—carbon Energy The glucose molecules serve as fuel for cells: their chemical energy can be harvested through processes like cellular respiration and fermentation, which generate adenosine triphosphate – a small, energy-carrying molecule— for the cell’s immediate energy needs. Fixed Carbon Fixed Carbon are the carbon in organic molecules. The carbon that's fixed and incorporated into sugars during photosynthesis can be used to build other types of organic molecules needed by cells. Site of Photosynthesis  All green plant tissues can photosynthesize, but in most plants, the majority of photosynthesis usually takes place in the leaves. The cells in a middle layer of leaf tissue called the mesophyll are the primary site of photosynthesis.  Small pores called stomata— singular, stoma—are found on the surface of leaves in most plants, and they let carbon dioxide diffuse into the mesophyll layer and oxygen diffuse out.  Each mesophyll cell contains organelles called chloroplasts, which are specialized to carry out the reactions of photosynthesis.  thylakoids are disc-like structures inside the chloroplast thylakoids arranged in piles like stacks of pancakes are known as grana—singular, granum The fluid-filled space around the grana is called the stroma  the space inside the thylakoid discs is known as the thylakoid space Photosynthesis in the leaves of plants involves many steps, but it can be divided into two stages: LIGHT-DEPENDENT REACTIONS CALVIN CYCLE take place in the thylakoid membrane also called the light-independent require a continuous supply of light reactions energy. takes place in the stroma Chlorophylls absorb this light energy, uses ATP and NADPH from the light- which is converted into chemical energy dependent reactions to fix carbon through the formation of two dioxide and produce three-carbon compounds, ATP—an energy storage sugars—glyceraldehyde-3- molecule—and NADPH—a reduced phosphate, or G3P, molecules— (electron-bearing) electron carrier. which join up to form glucose. Water molecules are also converted to oxygen gas—the oxygen we breathe!  PHOTOSYNTHESIS CELLULAR RESPIRATION starts in water and winding up electrons flow from in glucose—an energy- glucose to oxygen, requiring process powered by forming water and light releasing energy. photosynthesis and cellular respiration both involve a series of redox reactions (reactions involving electron transfers) SEATWORK Identify the following as reactants or products in photosynthesis. 1. Glucose 2. Water 3. Oxygen 4. Carbon dioxide 5. What organelle is the site of photosynthesis in plants? 7. Photosynthesis can be divided into two steps: the light- dependent reactions and the Calvin cycle. Which of the following is true regarding these two steps? A. The Calvin cycle converts water molecules into oxygen gas as a byproduct of its reactions. B. The light-dependent reactions use ATP from the Calvin cycle, and the Calvin cycle uses energy from absorbed sunlight. C. During the light-dependent reactions, carbon dioxide is fixed to produce sugars that form glucose. D. The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma. 8. Which of the following are true regarding photosynthesis and cellular respiration? A. Photosynthesis and cellular respiration are near-opposite processes. B. Photosynthesis and cellular respiration are performed by all plants and animals. C. Photosynthesis produces carbon dioxide, and cellular respiration uses carbon dioxide D. Both photosynthesis and cellular respiration occur in the chloroplasts of a cell.  LIGHT-DEPENDENT REACTIONS Takes place use light makes ATP in thylakoid energy and NADPH membranes PHOTOSYSTEMS large complexes of proteins and pigments (light- absorbing molecules) that are optimized to harvest light has light-harvesting complexes that contain proteins, 300-400 chlorophylls, and other pigments contain many pigments that help collect light energy, as well as a special pair of chlorophyll molecules found at the core (reaction center)  When a pigment absorbs a photon, it is raised to an excited state. Most of the pigments in a photosystem act as an energy funnel, passing energy inward to a main reaction center. When one of these pigments is excited by light, it transfers energy to a neighboring pigment through direct electromagnetic interactions in a process called resonance energy transfer.  Collectively, the pigment molecules collect energy and transfer it towards a central part of the photosystem called the reaction center. The reaction center of a photosystem contains a unique pair of chlorophyll a molecules, often called special pair. The special pair can actually lose an electron when excited, passing it to another molecule in the complex called the primary electron acceptor.  TYPES OF PHOTOSYSTEMS PHOTOSYSTEM II PHOTOSYSTEM I (PSII) (PSI) Special Pairs P680 P700 Primary Receptor Pheophytin A0 electrons flow down electrons came from an electron Source of Electrons water transport chain from PSII  ASSIGNMENT IN A SHORT BONDPAPER, WRITE THE DIFFERENCES BETWEEN CYCLIC AND I NON-CYCLIC PHOSPHORYLATION NON-CYCLIC PHOTOPHOSPHORYLATION  Electrons are removed from water and passed through PSII and PSI before ending up in NADPH. This process requires light to be absorbed twice, once in each photosystem, and it makes ATP.  “photophosphorylation” it involves using light energy (photo) to make ATP from ADP (phosphorylation)  Electrons are removed from water and passed through PSII and PSI before ending up in NADPH. This process requires light to be absorbed twice, once in each photosystem, and it makes ATP. LIGHT ABSORPTION OF PSII When light is absorbed by one of the many pigments in photosystem II, energy is passed inward from pigment to pigment until it reaches the reaction center. LIGHT ABSORPTION OF PSII There, energy is transferred to P680, boosting an electron to a high energy level. LIGHT ABSORPTION OF PSII The high-energy electron is passed to an acceptor molecule and replaced with an electron from water. This splitting of water releases the oxygen we breathe. ATP SYNTHESIS The high-energy electron travels down an electron transport chain, losing energy as it goes. ATP SYNTHESIS Some of the released energy drives pumping of H+ ions from the stroma into the thylakoid interior, building a gradient. LIGHT ABSORPTION OF PSI The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. LIGHT ABSORPTION OF PSI When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an acceptor molecule. LIGHT ABSORPTION OF PSI The special pair's missing electron is replaced by a new electron from PSII (arriving via the electron transport chain). NADPH FORMATION The high-energy electron travels down a short second leg of the electron transport chain. NADPH FORMATION At the end of the chain, the electron is passed to NADP+ (along with a second electron from the same pathway) to make NADPH. ATP SYNTHESIS Protons "want" to diffuse back down the gradient and into the stroma, and their only route of passage is through the enzyme ATP synthase. ATP SYNTHESIS ATP synthase harnesses the flow of protons to make ATP from ADP and phosphate. ATP SYNTHESIS This process of making ATP using energy stored in a chemical gradient is called chemiosmosis. In some cases, electrons break the pattern in non-cyclic photophosphorylation and instead loop back to the first part of the electron transport chain, repeatedly cycling through PSI instead of ending up in NADPH. CYCLIC PHOTOPHOSPHORYLATION After leaving PSI, cyclically flowing electrons travel back to the first leg of the electron transport chain. The electrons then flow down the chain to PSI as usual, driving proton pumping and the production of ATP. The cyclic pathway does not make NADPH, since electrons are routed away from NADP+ reductase.  CALVIN CYCLE REACTIONS not directly fueled by takes place driven by ATP and in stroma light NADPH In plants, carbon dioxide CO2 enters the interior of a leaf via pores called stomata and diffuses into the stroma of the chloroplast—the site of the Calvin cycle reactions, where sugar is synthesized. Reactions of the Calvin Cycle The Calvin cycle reactions can be divided into three main stages: carbon fixation reduction regeneration of the starting CARBON FIXATION A CO2 molecule combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-PGA). This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase, or rubisco. REDUCTION In the second stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P). This stage gets its name because NADPH donates electrons to, or reduces, a three-carbon intermediate to make G3P. REGENERATION Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor. Regeneration requires ATP and involves a complex network of reactions.