Photosynthesis Biology Notes PDF

Introduction to **[PHOTOSYNTHESIS]** From the Greek word "**PHOTO**" means produced by light, and "**SYNTHESIS**" which means a whole made of parts put together. **PHOTOSYNTHESIS** - is the process whereby plants, algae, some bacteria, use the energy of the **sun** to synthesize organic com...

Introduction to **[PHOTOSYNTHESIS]** From the Greek word "**PHOTO**" means produced by light, and "**SYNTHESIS**" which means a whole made of parts put together. **PHOTOSYNTHESIS** - is the process whereby plants, algae, some bacteria, use the energy of the **sun** to synthesize organic compounds (**sugars**) from inorganic compounds (**CO~2~ and water**). **WHY IS PHOTOSYNTHESIS SO IMPORTANT?** PHOTOSYNTHESIS is one of the most important biological process on earth! - Provides the oxygen we breathe - Consumes much of the CO~2~ - Food - Energy - Fibers and materials **GENERAL FORMULA FOR PHOTOSYNTHESIS** light 6 CO~2~ + 12 H~2~O \-\-\-\-\-\-\-\--\> C~6~H~12~O~6~ + 6 O~2~ + 6 H~2~O pigments, enzymes - Oxygen on earth allowed for the evolution of aerobic respiration and higher life-forms. - Respiration: extracting energy from compounds (sugars) C~6~H~12~O~6~ + O~2~ 6 CO~2~ + ATP II. **PROPERTIES OF LIGHT** - Light moves in waves, in energy units called PHOTONS - Energy of a PHOTON inversely proportional to its wavelength - Visible light (between UV and IR) occurs in a spectrum of colors Visible light contains just the right amount of energy for biological reactions.  Light is absorbed by **pigments** - The primary pigment for photosynthesis is ***chlorophyll a*** - It absorbs blue and red light, not green (green light is - **Absorption spectrum** of *chlorophyll a*: BLUE & RED - **Action spectrum** of photosynthesis closely matches absorption **Accessory pigments** like ***chlorophyll b*** and carotenoids (beta-carotene, lycopene): - absorb light at different wavelengths, (extending the absorption range) - help transfer some energy to *chlorophyll a* - protect cell from harmful byproducts ***Chlorophyll a*** is the primary photosynthetic pigment that drives photosynthesis. **Accessory pigments** absorb at different wavelengths, extending the range of light useful for photosynthesis. **WHERE DOES PHOTOSYNTHESIS OCCUR? PLANT CELL** III. **CHLOROPLAST STRUCTURE AND FUNCTION: SOLAR CHEMICAL FACTORY** - Football shaped - Double membrane - Stroma - Thylakoid\ membrane - Grana (stacks) - Lumen (inside thylakoid) **Inside a Chloroplast** IV. **The Light REACTIONS** 1. Light dependent 2. Occur in the **thylakoid membrane** of chloroplast 3. **Water** is split into **oxygen gas** (O~2~) and **H^+^** 4. Use **light energy** (photons) to generate two **chemical energy** compounds: ATP & NADPH **CHEMICAL ENERGY COMPOUNDS MADE IN THE LIGHT REACTIONS** **SEQUENCE OF EVENTS IN THE [LIGHT REACTIONS]** **SUMMARY OF THE LIGHT REACTIONS** **[LIGHT REACTIONS]**: Chemical energy compounds are made from light energy, water is split into O~2~ and protons V. **THE "DARK" OR CARBON REACTIONS** 1. Light independent (can occur in light or dark; some enzymes require activation by light) 2. Occur in the **stroma** of chloroplasts. 3. Use the **chemical energy** produced in Light Reactions (ATP; NADPH) to reduce CO~2~ to carbohydrate (sugar). 4. CO~2~ is converted to sugar by entering the Calvin Cycle.  **THE CALVIN CYCLE** - CO~2~ enters the **Calvin Cycle** - First product is a 3-carbon molecule: 3-PGA (**phosphoglyceric acid**). That's why it's also called C-3 cycle. - Enzyme RUBISCO (ribulose bisphosphate carboxylase/oxygenase) is the main enzyme that catalyzes the first reactions of the Calvin Cycle. - **RUBISCO**: Is the most abundant protein on earth! **Most plants use the Calvin Cycle to Convert CO~2~ into sugars.** **These plants are called C-3 plants** **SUMMARY OF CARBON REACTIONS** **[CARBON REACTIONS]:** Use CO~2~ and chemical energy (ATP & NADPH) to produce sugars by means of the Calvin Cycle **LIMITATIONS ON PHOTOSYNTHESIS** - Photosynthesis is not perfect in C-3 plants, it is only 1 - 4 % efficient. - Low efficiency due to **photorespiration.** - **Photorespiration** occurs when internal CO~2~ concentration becomes [too low] (drought); rubisco begins fixing oxygen. **C-4 plants are more efficient** - C-4 plants first product is a 4-carbon molecule. - The C-4 plants (sugar cane, corn, etc.), are more efficient than C-3 plants -- they grow in hotter climates with more light. - For example, sugar cane's photosynthetic efficiency is 7%. - C-4 plants have a different leaf anatomy. VI. **SUMMARY OF PHOTOSYNTHESIS:** 1. Light energy absorbed by *chlorophyll a* drive the reactions of photosynthesis. 2. Converts light energy into chemical energy to make organic compounds. 3. CO~2~ and H~2~O used to produce C~6~H~12~O~6~ (glucose) and O~2~ (gas). 4. Light Reactions occur in thylakoids of the chloroplasts; ATP and NADPH are formed; water is split to O~2~ (gas) and protons. 5. Carbon Reactions occur in stroma -- Calvin Cycle fixes CO~2~ to produce C~6~H~12~O~6~ (glucose). 6. Low efficiency, about 1- 4% in C-3 plants. 7. Nevertheless, PHOTOSYNTHESIS is still the most important biological process on earth. ***Importance of photosynthesis and the impact that it has in all our lives. Without photosynthesis, virtually all plants and animals would become extinct.*** **\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--** **RESPIRATION, ENERGY & CARBON CYCLE** - **Energy** - **Virtually all organisms require energy of food for**: - Making chemicals (proteins, carbs, etc.) - Movement - Cell division - Heat, electricity and light production - The way living organisms obtain energy is through Cell respiration **RESPIRATION** - Process of making energy of food available in the cell. Involves breaking down: **Complicated molecules into simple molecules** **(C~6~H~12~O~6~, sugars) (CO~2~, water)** **RESPIRATION** The energy held by complicated molecules is held temporarily as ATP (energy currency) **C~6~H~12~O~6~ + 6 O~2~ 6CO~2~ + 6 H~2~O + 36 ATP**  **(glucose) (energy)** Respiration occurs mainly in Mitochondria and Cytoplasm. **STAGES OF RESPIRATION** Cellular Respiration has **three main stages:** - Glycolysis - Krebs Cycle - Electron transport system 3 STAGES OF CELLULAR RESPIRATION - **Glycolysis**: Splitting of glucose -- 2 net ATP generated - **Krebs Cycle**: Energy of glucose molecule is harvested as ATP (2) -- it occurs in the mitochondria (matrix) - **Electron Transport System**: also happens in the mitochondria, more ATP are generated (32). - For each glucose molecule, total ATP = 36 - Only 39% efficient, rest is lost as heat. **PHOTOSYNTHESIS AND RESPIRATION** - **Photosynthesis and respiration are complimentary reactions**  **ENERGY** - ability to do work. **Newton's First Law of Thermodynamics:** **"Energy cannot be created or destroyed, it can only be transformed from one form to another"** - Once a cell has used energy to do work, it cannot be used again by any organism. **ENERGY FLOW IS LINEAR** Sun Earth Producers 1^o^ consumers 2^o^ consumers heat resp, heat resp, heat resp, heat Energy flows into ecosystem from the sun. Energy travels in a straight line by way of food chains. However, much energy is lost as **heat** along the way -- as a result of respiration. Approximately 90% energy is lost on each step! **Newton's Second Law of Thermodynamics:** **"In any transfer of energy there is always a loss of useful energy to the system, usually in the form of heat"** **FOOD CHAINS** - Food chains demonstrate linear nature of energy - **Producers** are the base of the food chain, they include photosynthetic organisms like: - Plants - Algae - Certain Bacteria - **PRIMARY CONSUMERS** -- all plant eaters (herbivores). - **SECONDARY CONSUMERS** -- Eat primary consumers (carnivores). - **DECOMPOSERS** -- obtain energy by breaking down remaining organic material of the other members of the food chain (Fungi and bacteria). **THE CARBON CYCLE** - Carbon from the atmosphere (CO~2~) enters the biosphere by way of [plants]! - CO~2~ used in photosynthesis - Carbon moves into food chain - Carbon is released to the physical environment by respiration - Release CO~2~ during respiration - Amount CO~2~ fixed in photosynthesis = the amount released by respiration - Carbon moves from atmosphere to plants to animals and back to atmosphere.  **CELLULAR RESPIRATION** - the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (**ATP**), and then release waste products.  **AEROBIC** - respiration occurs in the [presence of oxygen]. **ANAEROBIC RESPIRATION / FERMENTATION** -- respiration occurs without oxygen; another path is taken. **There are three stages of cellular respiration:** 1\.  Glycolysis 2\.  Kreb\'s Cycle (Citric Acid Cycle) 3\.  Electron Transport Chain **1. GLYCOLYSIS** - can occur without oxygen - \"glyco - lysis \" is the splitting of a 6-carbon glucose into two pyruvates, each having 3 carbons. - Energy Requiring Phase - Energy Releasing Phase net yield of 2 ATP per glucose molecule\ net yield of 2 NADH per glucose molecule **ENERGY REQUIRING PHASE** **Step 1.** A phosphate group is transferred from ATP to glucose, making **glucose-6-phosphate.** **Step 2.** Glucose-6-phosphate is converted into its isomer, **fructose-6-phosphate.** **Step 3.** A phosphate group is transferred from ATP to fructose-6-phosphate, producing fructose-1,6-bisphosphate. **Step 4.1.** Fructose-1,6-bisphosphate splits to form two three-carbon sugars: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate. **Step 4.2.** They are isomers of each other, but **only** one---glyceraldehyde-3-phosphate---can directly continue through the next steps of glycolysis. **Step 5.** DHAP is converted into glyceraldehyde-3-phosphate.  **Step 6.** Two half reactions occur simultaneously: 1) Glyceraldehyde-3-phosphate is oxidized, and 2) NAD+ is reduced to NADH and H+. **Step 7.** 1,3-bisphosphoglycerate donates one of its phosphate groups to ADP, making a molecule of ATP and turning into 3-phosphoglycerate. **Step 8.** 3-phosphoglycerate is converted into its isomer, 2-phosphoglycerate. **Step 9.** 2-phosphoglycerate loses a molecule of water, becoming phosphoenolpyruvate (PEP). **Step 10.** PEP readily donates its phosphate group to ADP, making a second molecule of ATP. As it loses its phosphate, PEP is converted to pyruvate, the end product of glycolysis. **BREAKING DOWN OF PYRUVATE** - A carboxyl group is removed from pyruvate, releasing a molecule of **carbon dioxide** into the surrounding medium. - The hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD+, forming NADH. - The enzyme-bound acetyl group is transferred to CoA, producing a molecule of **acetyl CoA.** **2. CITRIC ACID OR KREBS CYCLE** - occurs in the mitochondria - an aerobic process; will proceed only in the presence of O2 - net yield of 2 ATP - net yield of 6 NADH and 2 FADH2  \--\> sent to ETC - in this stage of cellular respiration, the oxidation of glucose to CO~2~ is completed. (this is why we exhale carbon dioxide) **CITRIC OR KREB'S CYCLE:**     **3. ELECTRON TRANSPORT SYSTEM** \- consists of a series of enzymes on the inner mitochondrial membrane \- electrons are released from NADH and from FADH2 and as they are passed along the series of enzymes, they give up energy which is used to fuel a process called [chemiosmosis] which drives ATP synthesis. - net yield of 32 or 34 ATP per glucose molecule \- 6 H~2~O are formed when the electrons unite with O~2~\* at the end of electron transport chain.  Without oxygen to serve as the final electron acceptor, the process shuts down. **FERMENTATION** - This happens when the Krebs cycle cannot occur due to lack of oxygen - Byproducts of fermentation include lactic acid and alcohol - Lactic Acid in muscle cells can cause muscle cramps.