## GCSE Biology Paper 1 Study Notes This guide covers cells, infection and response, organization, and bioenergetics. ### 1. Cells #### 1.1 Eukaryotic Cells: Animal and Plant Cells Both animal and plant cells are eukaryotic, meaning their DNA is contained within a nucleus. They share several organelles: * **Nucleus:** Contains DNA. Think of it as the cell's control center. * **Cytoplasm:** Watery gel where organelles are suspended. Imagine it as the cell's internal environment. * **Mitochondria:** Site of respiration (energy production). Often called the "powerhouse" of the cell. * **Ribosomes:** Site of protein synthesis. These are the protein factories of the cell. * **Cell Membrane:** Controls what enters and leaves the cell. Acts like a selectively permeable gatekeeper. Plant cells have additional organelles: * **Vacuole:** Large, central sac storing sap. Think of it as a storage tank for water and nutrients. * **Cell Wall:** Rigid outer layer made of cellulose, providing structural support. This is what gives plants their shape and rigidity. * **Chloroplasts:** Contain chlorophyll, the pigment that absorbs light for photosynthesis. These are the sites of photosynthesis, where plants make their food. #### 1.2 Prokaryotic Cells Prokaryotic cells (e.g., bacteria) lack a nucleus; their DNA is found in a plasmid (a circular loop of DNA). #### 1.3 Cell Division * **Mitosis:** Produces two identical daughter cells from a single parent cell. Chromosomes are copied, line up in the middle of the cell, and are then separated. Humans have 23 pairs (46 total) chromosomes in each cell except gametes. * **Meiosis:** Produces four genetically different gametes (sex cells – sperm and egg) each with half the number of chromosomes (23 in humans). DNA is copied, and genetic material is exchanged between chromosomes before cell division. #### 1.4 Cell Specialization and Organization Stem cells can differentiate into specialized cells with specific functions (e.g., brain cells, muscle cells). Specialized cells form tissues, tissues form organs, and organs work together in organ systems. #### 1.5 Microscopy * **Magnification:** Magnification = Image size / Object size. * **Units:** Nanometers (nm) and micrometers (µm) are used to measure cell sizes. 1 µm = 1000 nm; 1 mm = 1000 µm. * **Microscopes:** Light microscopes can view cells; electron microscopes (SEM and TEM) have higher resolution and can view organelles. ### 2. Infection and Response #### 2.1 Pathogens Infectious diseases are caused by pathogens: bacteria, viruses, fungi, and protists. Malaria is caused by a protist. #### 2.2 Non-Specific Defenses * **Skin:** Acts as a barrier. * **Platelets:** Involved in blood clotting. * **Cilia and mucus:** Trap and remove pathogens from the respiratory system. * **Stomach acid:** Kills pathogens. #### 2.3 Specific Defenses: White Blood Cells * **Phagocytes:** Engulf and destroy pathogens (non-specific). * **Lymphocytes:** Produce antibodies that target specific antigens on pathogens. Antibodies are like "smart bombs" targeting specific invaders. The body remembers the antibodies produced, leading to immunity. #### 2.4 Vaccination Vaccination introduces a weakened or inactive form of a pathogen to stimulate antibody production, providing immunity. #### 2.5 Antibiotics Antibiotics kill bacteria; they do not affect viruses. Overuse can lead to antibiotic resistance. It's crucial to complete the entire course of antibiotics. #### 2.6 Drug Development Drug development involves discovery, development (tissue and animal testing, then human trials – blind and double-blind), manufacturing, and review. #### 2.7 Plant Diseases Plants can be affected by viruses (e.g., tobacco mosaic virus), fungi (e.g., rose black spot), and mineral deficiencies (e.g., nitrate deficiency leading to stunted growth, magnesium deficiency causing chlorosis). Plants have defenses such as cell walls, waxy cuticles, and antibacterial chemicals. ### 3. Organization #### 3.1 Root Hair Cells Root hair cells have a large surface area to maximize water and nutrient absorption. #### 3.2 Leaf Structure * **Waxy cuticle:** Prevents water loss. * **Upper epidermis:** Transparent to allow light penetration. * **Palisade mesophyll:** Site of most photosynthesis. * **Spongy mesophyll:** Facilitates gas exchange. * **Stomata (and guard cells):** Control gas exchange and water loss. * **Lower epidermis:** Contains stomata. #### 3.3 Stem Structure * **Xylem:** Transports water and minerals. * **Phloem:** Transports sugars (produced during photosynthesis). #### 3.4 Transpiration Transpiration is the evaporation of water from leaves, creating a pull that draws water up the xylem. Factors affecting transpiration rate include temperature, wind, and humidity. #### 3.5 Food Tests * **Starch:** Iodine solution (turns purple/black). * **Fats:** Ethanol (turns cloudy). * **Glucose:** Benedict's solution (turns from blue to orange/brick red). * **Protein:** Biuret reagent (turns from blue to purple). #### 3.6 Enzymes Enzymes are biological catalysts (proteins) that speed up chemical reactions. They work through a lock-and-key mechanism. Temperature and pH affect enzyme activity; extreme conditions can denature enzymes. #### 3.7 Gas Exchange in the Lungs The lungs facilitate gas exchange between the air and the blood. Alveoli provide a large surface area for efficient gas exchange. #### 3.8 The Heart The heart is a double circulatory system, pumping blood to the lungs and the body. Arteries carry blood away from the heart (thick walls, high pressure), veins carry blood to the heart (thin walls, valves to prevent backflow), and capillaries facilitate gas exchange (thin walls). Oxygen binds to hemoglobin in red blood cells; carbon dioxide dissolves in plasma. ### 4. Bioenergetics #### 4.1 Respiration Respiration is the process of releasing energy from glucose. Aerobic respiration (with oxygen): $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$. Anaerobic respiration (without oxygen) produces lactic acid in animals and releases less energy. Oxygen debt is the extra oxygen needed to break down lactic acid after anaerobic respiration. #### 4.2 Photosynthesis Photosynthesis is the process of making glucose from carbon dioxide and water using light energy. It's an endothermic reaction. Glucose is used to make starch, cellulose, proteins, and lipids. #### 4.3 Factors Affecting Photosynthesis Light intensity, temperature, and carbon dioxide concentration affect the rate of photosynthesis. A limiting factor prevents the rate from increasing further, even if other factors are increased. #### 4.4 Metabolism Metabolism is the sum of all chemical reactions in the body. The liver plays a key role in metabolic processes. #### 4.5 Non-Communicable Diseases Non-communicable diseases (NCDs) include atheroma, coronary heart disease (CHD), aneurysms, diabetes, and cancer. Risk factors include diet, smoking, exercise, and exposure to carcinogens. Correlation does not equal causation; research is needed to establish cause-and-effect relationships.