As Biology Revision Notes Unit 1 Core Principles

As Biology Revision Notes Unit 1 Core Principles AS Biology Revision Notes Unit 1 Core Principles This document provides a comprehensive set of revision notes for Unit 1 of AS Biology focusing on the core principles that underpin the study of life These notes aim to guide you through the key concepts definitions and applications of the unit ensuring a thorough understanding of the fundamental building blocks of biology 1 Cells as the Fundamental Unit of Life 11 The Cell Theory States All living organisms are composed of cells Cells are the basic structural and functional unit of life All cells arise from preexisting cells Evidence Microscopes have allowed us to observe cells in various organisms Cell division mitosis and meiosis demonstrates the origin of new cells from existing ones Exceptions Viruses while not considered living organisms do contain genetic material and can replicate Some tissues like muscle are multinucleated 12 Prokaryotic and Eukaryotic Cells Prokaryotic cells Lack a membranebound nucleus and other organelles Have a single circular chromosome located in the nucleoid region Found in bacteria and archaea Eukaryotic cells Possess a membranebound nucleus and other organelles Have multiple linear chromosomes contained within the nucleus Found in plants animals fungi and protists 13 Organelles and their Functions Nucleus Contains genetic material DNA controls cell activities 2 Ribosomes Sites of protein synthesis Endoplasmic Reticulum ER Network of membranes involved in protein and lipid synthesis transport and detoxification Golgi apparatus Processes and packages proteins lipids and other molecules Mitochondria Site of cellular respiration producing ATP Chloroplasts plant cells only Site of photosynthesis Vacuoles plant cells mainly Storage of water nutrients and waste Lysosomes Contain enzymes for intracellular digestion 2 Biological Molecules 21 Macromolecules Carbohydrates Composed of carbon hydrogen and oxygen Provide energy and structural support Monosaccharides Simple sugars glucose fructose Disaccharides Two monosaccharides joined sucrose lactose Polysaccharides Long chains of monosaccharides starch glycogen cellulose Lipids Insoluble in water serve as energy stores insulation and cell membrane components Fatty acids Building blocks of lipids Triglycerides Store energy provide insulation Phospholipids Form cell membranes Steroids Hormones cholesterol Proteins Composed of amino acids perform a wide range of functions Primary structure Amino acid sequence Secondary structure Alpha helices and beta sheets Tertiary structure Threedimensional shape Quaternary structure Multiple polypeptide chains interacting Nucleic Acids Carry genetic information DNA Deoxyribonucleic acid doublestranded contains genetic code RNA Ribonucleic acid singlestranded involved in protein synthesis 22 Water as a Biological Solvent Polar molecule Unequal sharing of electrons making it a good solvent Hydrogen bonding Forms between water molecules giving it high cohesion and adhesion properties Importance Solvent for biological reactions transport medium temperature regulation 3 Enzymes and Biological Reactions 3 31 Enzyme Structure and Function Proteins Act as biological catalysts Active site Specific threedimensional region where the substrate binds Lock and key model Substrate fits precisely into the active site Induced fit model Active site changes shape slightly to accommodate the substrate 32 Factors Affecting Enzyme Activity Temperature Enzymes have an optimal temperature range pH Enzymes have an optimal pH range Substrate concentration Increased substrate concentration leads to increased reaction rate until saturation Enzyme concentration Increased enzyme concentration leads to increased reaction rate Inhibitors Substances that reduce enzyme activity competitive and noncompetitive 33 Applications of Enzymes Industrial processes Food production detergents biofuels Medical applications Diagnostic tests drug development Environmental applications Bioremediation waste treatment 4 Cell Membranes and Transport 41 Structure of the Cell Membrane Phospholipid bilayer Hydrophilic heads face outwards hydrophobic tails inwards Proteins Embedded within the membrane performing various functions transport receptors enzymes Cholesterol Provides membrane fluidity and stability 42 Movement Across Membranes Passive transport Does not require energy Diffusion Movement of molecules from high to low concentration Osmosis Movement of water from high to low water potential Facilitated diffusion Movement aided by transport proteins Active transport Requires energy ATP Pumping Movement of molecules against their concentration gradient 43 Importance of Cell Membranes Regulates cell contents Controls what enters and leaves the cell 4 Maintains cell shape Provides structural support Cellular communication Facilitates signaling between cells 5 Cellular Respiration 51 Process Breakdown of glucose to release energy ATP Occurs in Mitochondria of eukaryotic cells Overall equation C6H12O6 6O2 6CO2 6H2O ATP 52 Stages of Cellular Respiration Glycolysis Occurs in the cytoplasm breaks down glucose into pyruvate Link reaction Converts pyruvate to acetyl CoA Krebs cycle Occurs in the mitochondrial matrix produces ATP NADH and FADH2 Electron transport chain Occurs in the inner mitochondrial membrane generates the majority of ATP through oxidative phosphorylation 53 ATP Production ATP Adenosine triphosphate the energy currency of cells Phosphorylation Addition of a phosphate group to a molecule Chemiosmosis Movement of protons across the membrane to drive ATP synthesis 6 Photosynthesis 61 Process Conversion of light energy into chemical energy glucose Occurs in Chloroplasts of plant cells Overall equation 6CO2 6H2O C6H12O6 6O2 62 Stages of Photosynthesis Lightdependent reactions Capture light energy produce ATP and NADPH Lightindependent reactions Calvin cycle Use ATP and NADPH to fix carbon dioxide into glucose 63 Importance of Photosynthesis Primary producer of organic molecules Provides food for most ecosystems Oxygen production Essential for respiration in most living organisms 7 Genetic Material 5 71 DNA Double helix Two strands of nucleotides linked by hydrogen bonds Nucleotide structure Sugar deoxyribose phosphate group nitrogenous base adenine guanine cytosine thymine Base pairing Adenine pairs with thymine guanine pairs with cytosine 72 DNA Replication Semiconservative replication Each new DNA molecule contains one original strand and one new strand Steps Unwinding separation base pairing joining 73 Protein Synthesis Transcription DNA is copied into mRNA Translation mRNA is translated into a polypeptide chain Genetic code Triplet codons on mRNA code for specific amino acids Conclusion This set of revision notes provides a comprehensive overview of the core principles of biology covered in Unit 1 of AS Biology By understanding these fundamental concepts you will be wellequipped to tackle more advanced biological topics and deepen your appreciation for the complex and fascinating world of life