Study Guide

Photosynthesis

Definition: The process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, utilizing carbon dioxide and water. This process is crucial for life on Earth as it is the primary source of organic matter for nearly all organisms.

Overall Equation: 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂This equation summarizes the conversion of light energy into chemical energy, resulting in the formation of glucose and the release of oxygen as a byproduct.

Stages:

  • Light-dependent Reactions:Occur in the thylakoid membranes of chloroplasts, where light energy is captured by chlorophyll and converted into chemical energy in the form of ATP and NADPH. Water is split, releasing oxygen as a byproduct.

  • Calvin Cycle (Light-independent Reactions):Takes place in the stroma of chloroplasts, where ATP and NADPH produced from the light-dependent reactions are used to convert CO₂ into glucose through a series of reactions known as Carbon Fixation, Reduction Phase, and Regeneration of RuBP.

Cellular Respiration

Definition: The process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water. This process is essential for cellular functions and energy production in both aerobic and anaerobic organisms.

Overall Equation: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATPThis equation represents the aerobic breakdown of glucose in the presence of oxygen to produce energy.

Stages:

  • Glycolysis:The first step of cellular respiration that occurs in the cytoplasm, where one molecule of glucose is broken down into two molecules of pyruvate, yielding approximately 2 ATP and 2 NADH.

  • Krebs Cycle (Citric Acid Cycle):Occurs in the mitochondria, where each pyruvate is further oxidized. This cycle produces NADH, FADH₂, ATP, and CO₂ as waste products, contributing electrons for the electron transport chain.

  • Electron Transport Chain:Located in the inner mitochondrial membrane, this stage uses electrons from NADH and FADH₂ to create a proton gradient that drives ATP synthesis through chemiosmosis. Oxygen acts as the final electron acceptor, forming water as a byproduct.

Structure and Function of Chloroplasts

Structure:

  • Outer and Inner Membranes:A double membrane structure that protects the chloroplast and regulates entry and exit of molecules.

  • Thylakoids:Membrane-bound compartments stacked in structures called granum; the site of the light-dependent reactions, containing chlorophyll and other pigments.

  • Stroma:The fluid-filled space surrounding thylakoids; site of the Calvin Cycle, containing enzymes, DNA, and ribosomes specific to chloroplasts.

Function:Chloroplasts are the organelles where photosynthesis occurs, converting light energy into chemical energy. They play a vital role in converting carbon dioxide into organic compounds, sustaining the energy needs of nearly all living organisms on Earth.

C3, C4, and CAM Plants

C3 Plants:Use the Calvin Cycle for the fixation of CO₂. They are the most common type of plants (e.g., wheat and rice) and generally perform best in moderate climates. Less water-efficient under hot and dry conditions due to photorespiration, where oxygen is fixed instead of CO₂.

C4 Plants:Evolved mechanisms to minimize photorespiration, utilizing a C4 pathway to initially fix CO₂ into a four-carbon compound. This allows them to efficiently perform photosynthesis under bright sunlight and high temperatures (e.g., corn and sugarcane).

CAM Plants:Adapted to arid conditions by opening their stomata at night to fix CO₂ and storing it as malate until daytime. This strategy helps minimize water loss (e.g., cacti and succulents).

Fermentation

Definition:An anaerobic process that enables the conversion of glucose into energy when oxygen is not available. It allows cells to generate ATP through alternative pathways.

Types:

  • Lactic Acid Fermentation:Occurs in muscle cells and some bacteria, converting pyruvate into lactic acid while producing 2 ATP. This process is crucial during intense exercise when oxygen levels are low.

  • Alcoholic Fermentation:Occurs in yeast and some bacteria, converting pyruvate into ethanol and CO₂, also producing 2 ATP