Biology Study Notes - Cell Membrane & Structure PDF

Biology study notes Unit 1 Topic 1: Cell Membrane 1. Structure of the Cell Membrane: Fluid Mosaic Model: o Describes the cell membrane as a dynamic structure where various proteins float in or on the fluid lipid bilayer. o Phospholipids: Form the fundame...

Biology study notes Unit 1 Topic 1: Cell Membrane 1. Structure of the Cell Membrane: Fluid Mosaic Model: o Describes the cell membrane as a dynamic structure where various proteins float in or on the fluid lipid bilayer. o Phospholipids: Form the fundamental structure; hydrophilic heads face outward (toward the aqueous environment), while hydrophobic tails face inward, away from water, creating a bilayer. o Proteins: Integral proteins span the membrane, providing pathways for transport, while peripheral proteins are attached to the surface, playing roles in signaling and structural support. o Cholesterol: Embedded within the phospholipid bilayer, cholesterol molecules help maintain membrane fluidity and stability across varying temperatures. o Glycoproteins: Carbohydrate chains attached to proteins that serve as recognition sites for cell signaling and immune responses. 2. Homeostasis via Passive Transport: Diffusion: The movement of molecules from an area of higher concentration to lower concentration. Small nonpolar molecules (e.g., O₂, CO₂) can diffuse freely across the membrane. Osmosis: A specific type of diffusion that refers to the movement of water through a selectively permeable membrane. It occurs through special channels called aquaporins and is driven by water potential differences (concentration gradients). 3. Homeostasis via Active Transport: Active Transport: Requires energy (ATP) to move substances against their concentration gradient. o Example: The sodium-potassium pump moves Na⁺ out of the cell and K⁺ into the cell, crucial for maintaining cellular potential and volume. 4. Endocytosis: Endocytosis: A process that engulfs large molecules or particles by enclosing them in a membrane vesicle. o Phagocytosis: A type of endocytosis where the cell engulfs solid particles (e.g., immune cells engulfing pathogens). 5. Predicting Movement Across Membranes: Factors influencing movement include:  o Concentration gradient (steeper gradients increase movement rates). o Size and polarity of molecules (small, nonpolar molecules diffuse more easily). o Membrane permeability (affected by temperature and membrane composition). 6. Surface Area to Volume Ratio: As cells increase in size, volume grows faster than surface area, reducing the surface area to volume ratio. A higher ratio facilitates more efficient diffusion of materials. Cells adapt by staying small or developing specialized structures (e.g., microvilli). 7. Mandatory Practical: Conduct experiments to observe how changes in surface area to volume ratio affect diffusion rates and overall cell size, such as using agar cubes to study diffusion rates of dyes. Unit 1 Topic 1: Prokaryotic and Eukaryotic Cells 1. Cell Requirements for Survival: Energy Sources: o Organisms require energy to fuel cellular processes; can be obtained from sunlight (photosynthesis) or chemical compounds (respiration). Matter: o Essential gases (O₂ for aerobic respiration, CO₂ for photosynthesis), nutrients (monosaccharides, amino acids), and minerals are necessary for cellular functions. Waste Removal: o Cells produce metabolic waste (e.g., CO₂, ammonia) that must be efficiently removed to maintain homeostasis. 2. Common Features: Both prokaryotic and eukaryotic cells possess DNA, ribosomes for protein synthesis, and a plasma membrane, reflecting their common evolutionary ancestry. 3. Prokaryotic Cells: Characterized by their simplicity: o Lack a true nucleus; DNA is located in the nucleoid region. o Typically have a single circular chromosome and are smaller (1-10 µm). o Often possess plasmids (small DNA circles) and can have structures like flagella for movement. 4. Eukaryotic Cells:  More complex and larger (10-100 µm): o Contain membrane-bound organelles (e.g., nucleus, mitochondria) that compartmentalize cellular functions. o Specialized organelles include: § Chloroplasts: Sites of photosynthesis in plant cells. § Mitochondria: Powerhouses of the cell for ATP production via cellular respiration. § Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; Smooth ER synthesizes lipids. § Lysosomes: Contain digestive enzymes to break down waste materials. 5. Identification of Structures: Recognize key organelles in electron micrographs and their functions: o Chloroplasts: Green due to chlorophyll, essential for photosynthesis. o Mitochondria: Double membrane, involved in energy production. o Rough ER: Studded with ribosomes, important for protein synthesis. o Lysosomes: Membrane-bound vesicles for waste processing. 6. Comparing Cell Types: Key differences include: o Prokaryotes: No membrane-bound organelles, single chromosome. o Eukaryotes: Multiple chromosomes, organelles present. 7. Mandatory Practical: Prepare wet mount slides from various organisms and use microscopy to identify cell structures such as nuclei and cell walls. Calculate total magnification and observe field of view. Unit 1 Topic 1: Energy and Metabolism 1. ATP Production: Organisms convert energy stored in glucose into ATP via cellular respiration, a series of enzyme-mediated reactions that release energy. 2. Photosynthesis Overview: Chemical Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Occurs in two main stages: o Light-dependent Reactions: § Occur in the thylakoid membranes; convert solar energy into chemical energy (ATP and NADPH) using water, releasing oxygen as a byproduct. o Light-independent Reactions (Calvin Cycle):  § Occur in the stroma; use ATP and NADPH to convert CO₂ into glucose. 3. Cellular Respiration: A series of metabolic processes converting glucose into ATP, with three main stages: o Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate, producing a small amount of ATP and NADH. o Krebs Cycle: Takes place in mitochondria; further breaks down pyruvate into CO₂, generating ATP, NADH, and FADH₂. o Electron Transport Chain: Uses NADH and FADH₂ to generate ATP through oxidative phosphorylation. 4. Anaerobic Respiration: Occurs in the absence of oxygen; less efficient than aerobic respiration. Produces lactic acid (in animals) or ethanol and CO₂ (in yeast) via fermentation pathways. 5. Energy Transfer Diagrams: Analyze pathways of energy transformation through diagrams illustrating glycolysis, the Krebs cycle, and photosynthesis to understand where and how energy is stored and released. Unit 1 Topic 2: Cell Differentiation and Specialisation 1. Stem Cells: Unspecialized Cells: Capable of dividing indefinitely and can differentiate into various cell types, crucial for development and repair. Potency: o Totipotent (can become any cell type, including placental cells), pluripotent (can become almost any cell type, excluding placental), and multipotent (limited to specific lineages). 2. Differentiation Process: Involves gene expression changes leading to specialized functions, influenced by intrinsic and extrinsic factors (e.g., signaling molecules, environmental conditions). 3. Hierarchical Structure: Organization from single cells to complex multicellular organisms: o Cells: Basic unit of life. o Tissues: Groups of similar cells performing a specific function (e.g., muscle, nerve). o Organs: Composed of different tissues working together (e.g., heart, lungs). o Organ Systems: Groups of organs that perform related functions (e.g., circulatory system). Unit 1 Topic 2: Gas Exchange and Transport 1. Gas Exchange Surfaces: Alveoli in Lungs and Gills: o Features such as a large surface area (many folds), thin walls (one or two cells thick), and moist surfaces facilitate efficient gas exchange. o Surrounded by a dense capillary network for rapid diffusion of gases (O₂ uptake and CO₂ release). 2. Capillary Function: Structure and Role: o Thin-walled vessels (one cell thick) allow easy exchange of materials (water, gases, nutrients) between blood and interstitial fluid, maintaining tissue homeostasis. 3. Predicting Exchange Directions: Use diagrams to illustrate gradients and predict the movement of gases based on partial pressures, concentrations, and solubility factors: o Alveoli to Capillaries: O₂ moves from alveoli (high concentration) to blood (low concentration), while CO₂ moves in the opposite direction. o Capillaries to Muscle Tissue: O₂ and nutrients diffuse from blood into muscle cells, while waste products like CO₂ diffuse into the bloodstream. Unit 1 Topic 2: Plant Systems — Gas Exchange and Transport Systems 1. Stomata and Guard Cells: Function and Regulation: o Stomata are pores on leaf surfaces that facilitate gas exchange (O₂, CO₂, water vapor). o Guard cells regulate stomatal opening and closing in response to light, humidity, and CO₂ concentration, balancing photosynthesis and transpiration. 2. Leaf Structure and Function: Composed of layers: o Palisade Mesophyll: Packed with chloroplasts, maximizing light absorption for photosynthesis. o Spongy Mesophyll: Loosely arranged cells allowing gas diffusion. o Cuticle: Waxy layer that minimizes water loss. 3. Xylem and Phloem: Xylem: Transports water and dissolved minerals from roots to leaves via transpiration pull and root pressure.  Phloem: Transports organic nutrients (e.g., sugars) produced during photosynthesis from source (leaves) to sink (roots and growing tissues). 4. Water Movement in Xylem: Mechanisms: o Root pressure pushes water upward. o Transpiration creates negative pressure, drawing water through cohesion and adhesion properties in xylem vessels. 5. Factors Influencing Transpiration: Environmental factors include: o Light: Increases photosynthesis, leading to more open stomata. o Temperature: Higher temperatures increase evaporation rates. o Humidity: Lower humidity enhances water loss. o Wind: Can increase evaporation by removing moisture around the leaf surface. 6. Translocation in Phloem: The process of moving nutrients from source to sink, utilizing osmotic pressure differences and companion cells that facilitate loading/unloading of sugars. Unit 2 Topic 1: Homeostasis 1. Homeostasis Concept: Definition: The process of maintaining a stable internal environment despite external changes, vital for optimal functioning. Stimulus-response Model: Involves detecting changes (stimuli) and initiating responses to restore balance. 2. Sensory Receptors: Specialized cells that detect environmental changes: o Chemoreceptors: Respond to chemical changes (e.g., blood pH). o Thermoreceptors: Detect temperature changes. o Mechanoreceptors: Respond to mechanical pressure or distortion (e.g., touch, sound). o Photoreceptors: Detect light. o Nociceptors: Respond to pain stimuli. 3. Effectors: Organs or cells that act upon receiving signals from the control center (e.g., muscles contracting, glands secreting hormones) to restore homeostasis. 4. Feedback Control Diagrams: Illustrate feedback loops, including: o Negative Feedback: A response that counteracts a change (e.g., thermoregulation). o Positive Feedback: A response that enhances a change (less common, e.g., childbirth). 5. Metabolism: Total of all biochemical reactions in an organism, including: o Catabolism: Breakdown of molecules for energy (e.g., cellular respiration). o Anabolism: Synthesis of complex molecules from simpler ones (e.g., protein synthesis). 6. Enzyme Activity and Metabolism: Enzymes are proteins that catalyze biochemical reactions; their activity can be affected by temperature, pH, and substrate concentration, which can influence overall metabolic rates. Unit 2 Topic 1: Hormonal Homeostatic Control Pathways 1. Hormones as Messengers: Chemical signals produced by endocrine glands (e.g., pancreas, thyroid) that regulate physiological processes. Hormones travel through the bloodstream to target tissues, influencing metabolism, growth, and homeostasis. 2. Receptor Sensitivity: Upregulation and Downregulation: o Upregulation occurs when hormone levels are low, increasing receptor numbers and sensitivity. o Downregulation occurs when hormone levels are high, decreasing receptor numbers to maintain balance. 3. Signal Transduction: The process by which hormone binding to its receptor initiates a cascade of biochemical events inside the cell, often involving second messengers (e.g., cAMP), altering cellular functions. Unit 2 Topic 1: Thermoregulation 1. Thermoregulation in Endotherms:  Mechanisms: o Structural adaptations include insulating layers (fur, feathers) and vasodilation/vasoconstriction to manage heat loss. o Behavioral responses include seeking shade or water and hibernation to conserve energy during extreme conditions. o Physiological controls include sweating, shivering, and altering metabolic rates to regulate body temperature. Unit 2 Topic 1: Osmoregulation 1. Water Balance in Animals: Mechanisms: o Excretory systems (e.g., kidneys in mammals) play a crucial role in filtering blood, reabsorbing water, and excreting excess solutes. o Hormones (e.g., antidiuretic hormone [ADH]) regulate water reabsorption in the kidneys. 2. Plant Water Balance: Structural adaptations include: o Stomata: Open and close to regulate gas exchange and water loss. o Cuticle: Reduces transpiration. o Root Systems: Extensive root systems enhance water uptake. 3. Hormonal Responses: Abscisic Acid (ABA): A plant hormone that helps reduce water loss by closing stomata during drought conditions. 4. Mandatory Practical: Compare stomata distribution in leaves from various environments (e.g., dry vs. humid) to understand adaptation strategies. Unit 2 Topic 2: Infectious Disease 1. Infectious vs. Non-infectious Diseases: Infectious diseases are caused by pathogens (bacteria, viruses, fungi) and can be transmitted between hosts; non-infectious diseases result from genetic factors or environmental influences and are not contagious. 2. Pathogen Types: Various pathogens have unique characteristics and modes of transmission: o Prions: Infectious proteins causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).  o Viruses: Require host cells to replicate (e.g., influenza, HIV). o Bacteria: Prokaryotic cells that can be beneficial or pathogenic (e.g., E. coli, Streptococcus). o Fungi: Eukaryotic organisms that can cause infections (e.g., athlete's foot). o Protists: Single-celled eukaryotes that can be parasitic (e.g., malaria). o Parasites: Organisms that live on or in a host, deriving nutrients at the host's expense (e.g., tapeworms). 3. Virulence Factors: Characteristics that enable pathogens to establish infections and cause disease, including: o Adhesion Factors: Proteins allowing attachment to host tissues. o Invasive Enzymes: Break down host barriers (e.g., hyaluronidase). o Toxins: Harmful substances produced by pathogens (e.g., endotoxins and exotoxins). 4. Modes of Disease Transmission: Various routes include: o Direct Contact: Person-to-person transmission (e.g., colds). o Airborne: Transmission through droplets in the air (e.g., influenza). o Vector-borne: Carried by organisms (e.g., mosquitoes transmit malaria). o Fomite Transmission: Contact with contaminated surfaces (e.g., doorknobs). 5. Mandatory Practical: Conduct experiments to assess the antimicrobial effects of substances (e.g., antibiotics) on microbial growth using agar plates. Unit 2 Topic 2: Immune Response and Defence Against Disease 1. Immune Responses: The immune system has two main components: o Innate Immune Response: Non-specific, immediate defense mechanisms (e.g., physical barriers, phagocytic cells). o Adaptive Immune Response: Specific, slower response involving B cells and T cells, leading to long-lasting immunity. 2. Physical and Chemical Defenses: Barriers include skin, mucous membranes, and secretions (e.g., lysozyme in tears). Inflammation is a response that recruits immune cells to sites of infection and facilitates healing. 3. Adaptive Immune Responses:  Involves: o Humoral Immunity: B cells produce antibodies specific to antigens, marking pathogens for destruction. o Cell-mediated Immunity: T cells directly kill infected cells and help activate other immune cells. 4. Immunity Types: Active Immunity: o Natural (exposure to pathogens) or artificial (vaccination), leading to long- lasting protection. Passive Immunity: o Transfer of antibodies (e.g., maternal antibodies to infants), providing short- term protection. Unit 2 Topic 2: Transmission and Spread of Disease (Epidemiology) 1. Disease Transmission: The spread of infectious diseases is influenced by factors like: o Population Mobility: Travel can facilitate outbreaks. o Immunity Levels: Herd immunity can protect vulnerable populations. o Pathogen Persistence: Some pathogens can survive outside hosts for extended periods. 2. Predicting Outbreaks: Analyze risk factors, transmission patterns, and environmental influences to model potential outbreaks. 3. Prevention Strategies: Vaccination, sanitation, vector control, and education are key in reducing disease transmission.