Biology Semester 2 Quiz 1.docx

Biology Semester 2 Quiz 1 **Overview of Photosynthesis:** Photosynthesis is the biological process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen as byproducts. It consists of two main stages: 1. **Light-Dependent Reactions**: Ca...

Biology Semester 2 Quiz 1 **Overview of Photosynthesis:** Photosynthesis is the biological process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen as byproducts. It consists of two main stages: 1. **Light-Dependent Reactions**: Capture solar energy and convert it into ATP and NADPH. 2. **Calvin Cycle (Light-Independent Reactions)**: Utilize ATP and NADPH to fix CO₂ into organic molecules like glucose. **Overall Equation of Photosynthesis** 6CO2+6H2O+light→C6H12O6+6O2 **Light Reactions (Light-Dependent Reactions)** - **Location**: Thylakoid membranes of the chloroplast. (Chloroplasts are solar-powered chemical factories. Their thylakoids transform light energy into the chemical energy of ATP and NADPH.) The Thylakoid Membrane has chlorophyll, absorbs red and green wavelengths, and reflects green. - **Purpose**: Convert light energy into chemical energy (ATP and NADPH) while releasing O₂ as a byproduct. **Step 1: Light Absorption & Electron Excitation** - **Photosystem II (PSII)** absorbs light energy, exciting electrons in **chlorophyll a** molecules. - Excited electrons are transferred to the **primary electron acceptor**. - **Photolysis of water** occurs to replenish lost electrons: 2H2O→4H++4e−+O2 - enter the **electron transport chain (ETC)**. **Step 2: Electron Transport Chain & ATP Synthesis** - Electrons travel through the **ETC** (plastoquinone (PQ), cytochrome complex, plastocyanin (PC)). - The **energy released** pumps **H⁺ ions into the thylakoid lumen**, creating a **proton gradient**. - **ATP Synthase** utilizes this gradient to convert phosphorylate **ADP + Pᵢ → ATP** (**chemiosmosis**). **Step 3: Photosystem I (PSI) & NADPH Formation** - Electrons reach **Photosystem I (PSI)** and are **re-excited** by light. - High-energy electrons are transferred to **ferredoxin (Fd)**, then to **NADP⁺ reductase**, which forms **NADPH**: NADP++2e−+H+→NADPH A screenshot of a black and white list Description automatically generated **Calvin Cycle (Light-Independent Reactions) The Calvin cycle is anabolic;** - **Location**: Stroma of the chloroplast. - **Purpose**: Use ATP and NADPH to incorporate CO₂ into organic molecules. - **Three Phases**: Carbon Fixation, Reduction, and Regeneration of RuBP. **Step 1: Carbon Fixation** - **Enzyme Involved**: RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase). - **CO₂ combines with RuBP (5-carbon molecule)** → forming an unstable **6-carbon compound**. - The compound immediately splits into **two 3-phosphoglycerate (3-PGA) molecules**. **Step 2: Reduction** - **6 ATP molecules** phosphorylate 3-PGA into **1,3-bisphosphoglycerate (1,3-BPG)**. - **6 NADPH molecules** donate electrons to convert 1,3-BPG into **glyceraldehyde-3-phosphate (G3P)**. - **Net Product**: 1 G3P exits the cycle; the remaining 5 regenerate RuBP. **Step 3: Regeneration of RuBP** - **5 G3P molecules (3-carbons each) rearrange into 3 RuBP (5-carbons each).** - **3 ATP molecules** are consumed in the process. **Glucose Formation & Cycle Turns** - **1/3 Turns of the Cycle** produce **1 G3P**. - **2/6 Turns** produce **2 G3P**, which combine to form **1 glucose (C₆H₁₂O₆).**  **Photosynthesis as a Redox Process** - **Electron Flow**: Photosynthesis **reverses** the electron flow of cellular respiration. - **H₂O is oxidized( Lose Electrons) to O₂**, and **CO₂ is reduced (Gain Electrons) to glucose**. - Light energy drives this **endergonic** reaction. **Key Experimental Insights** - **Water Splitting Experiment**: Used **Oxygen-18 isotope tracing** to confirm that O₂ comes from H₂O, not CO₂. - **Photosynthesis as a Chemical Factory**: Thylakoids use light to generate ATP and NADPH, while the Calvin Cycle assembles sugars. Sugar is transported to nonphotosynthetic cells throughout the plant as sucrose Excess sugar is stored as starch in chloroplasts or in the cells of roots, tubers, seeds, and fruits. In addition to food production, photosynthesis produces the O2 in our atmosphere. **Lab** **Key Vocabulary:** - **Aerobic respiration**: A process by which cells use oxygen to break down glucose and produce energy (ATP), carbon dioxide, and water. - **Bromothymol blue (BTB)**: A pH indicator that changes color based on the presence of carbon dioxide. It turns yellow in acidic conditions (high CO2) and blue in basic conditions (high O2). - **Carbon dioxide-oxygen cycle**: The process by which animals and plants exchange carbon dioxide and oxygen. Animals release carbon dioxide, and plants use it for photosynthesis, releasing oxygen in the process. - **Indicator**: A substance that changes color to show the presence or amount of a particular substance. - **Interdependence**: The mutual dependence between two organisms or systems, such as plants and animals relying on each other for gases like oxygen and carbon dioxide. - **Photosynthesis**: The process by which plants use sunlight, carbon dioxide, and water to produce glucose (a sugar) and oxygen. **Gizmo Warm-up:** - **Objective**: Understanding how BTB (Bromothymol blue) indicates the presence of different gases (O2 and CO2) in water and how it changes color. 1. **Experiment Setup**: - **Snail test tube**: The tube containing the snail turned yellow after 24 hours, indicating the presence of high levels of carbon dioxide (CO2). - **Plant test tube**: The tube with the plant stayed blue, indicating a high concentration of oxygen (O2). 2. **Gas Levels**: - **Blue water**: Indicates that oxygen (O2) is the dominant gas. - **Yellow water**: Indicates that carbon dioxide (CO2) is the dominant gas. - **Green water**: Equal levels of O2 and CO2 in the water. **Activity A: Gases In and Gases Out** **Objective**: Investigating what gases plants and animals take in and release under different conditions (light and dark). 1. **Data Collection**: - Various combinations of plants and snails in both light and dark conditions. - **Results**: - In the dark (plants alone), the water turned pale green with a decrease in O2 levels. - In the light (snails alone), the O2 level dropped, and the water turned yellow as CO2 increased. - In the light (plants alone), O2 increased, and water became very blue with bubbles. The plants eventually turned brown due to lack of proper conditions. - A combination of plants and snails (off lights) caused both O2 levels to drop to zero and the snails and plants to die due to the absence of light. 2. **Analysis of Gas Release**: - **Plants in light**: Release oxygen (O2). - **Plants in dark**: Release carbon dioxide (CO2). - **Animals (snails) in light and dark**: Release carbon dioxide (CO2) continuously. 3. **Carbon Dioxide-Oxygen Cycle**: - Animals breathe in oxygen (O2) and exhale carbon dioxide (CO2). - Plants take in carbon dioxide (CO2) and release oxygen (O2) in sunlight. **Activity B: Interdependence** **Objective**: To explore how plants and animals depend on each other for survival. 1. **Observations with Elodea (plant) and snail**: - In light conditions, the levels of O2 and CO2 in the test tube remained stable (close to 6.0 ppm). - Without light, the CO2 level increased, and the O2 level decreased due to the absence of photosynthesis by the plant. 2. **Interdependence**: - Animals need oxygen (O2) and produce carbon dioxide (CO2). - Plants need carbon dioxide (CO2) for photosynthesis and produce oxygen (O2). - The survival of each is dependent on the other---animals rely on oxygen produced by plants, and plants rely on the carbon dioxide produced by animals. 3. **Stable Environment**: - A balanced number of plants and snails (4 plants and 1 snail) creates a stable environment, where oxygen and carbon dioxide levels remain stable over time. **Activity C: The Carbon-Oxygen Balance** **Objective**: Understanding how oxygen (O2) and carbon dioxide (CO2) levels are related during photosynthesis and aerobic respiration. 1. **Observations with Elodea**: - In light conditions, the oxygen level increases, and the carbon dioxide level decreases due to photosynthesis. - In the dark, the oxygen level decreases, and the carbon dioxide level increases due to aerobic respiration. 2. **Total Gas Levels**: - In both light and dark conditions, the total amount of oxygen and carbon dioxide remains constant (12 ppm). This is because the amount of oxygen produced by photosynthesis is balanced by the amount consumed during respiration, and vice versa. 3. **Photosynthesis and Aerobic Respiration**: - Photosynthesis: **6CO2 + 6H2O + light energy → C6H12O6 + 6O2** - Aerobic Respiration: **C6H12O6 + 6O2 → 6CO2 + 6H2O + energy** - The processes are complementary. The oxygen produced by plants during photosynthesis is used by animals for respiration, and the carbon dioxide released by animals is used by plants for photosynthesis. **Conclusion:** - The balance between oxygen and carbon dioxide in the environment is maintained through the interconnected processes of photosynthesis in plants and aerobic respiration in animals. Both systems rely on each other, creating a stable cycle essential for life. Plants contribute oxygen, and animals contribute carbon dioxide, demonstrating interdependence. **Important Diagrams**