GCSE BIOLOGY PAPER 1

Topic 1: Cell Biology

1.1 Microscopes

• Light Microscope:

  • Developed in the mid-17th century.

  • Uses light to form an image.

  • Can view live specimens.

  • Relatively cheap and easy to use.

  • Maximum magnification: up to $\times 2000$.

  • Resolving power (resolution): approximately $200\,nm$ (low resolution).

• Electron Microscope:

  • Developed in the 1930s.

  • Uses electrons fired through specimens to form an image.

  • Requires dead specimens.

  • Expensive and requires specific conditions.

  • Maximum magnification: up to $\times 2000000$.

  • Resolution: approximately $0.2\,nm$ (high resolution, allows visualization of subcellular structures).

• Key Terms:

  • Magnification: How many times larger the image is compared to the real object.

  • Resolution: The ability to distinguish between two separate points; higher resolution shows clearer detail.

1.2 Animal and Plant Cells

• Animal Cell Organelles:

  • Nucleus: Controls cell activities and contains genetic material ($DNA$).

  • Cell Membrane: Controls the movement of substances into and out of the cell.

  • Cytoplasm: Gel-like liquid where chemical reactions take place.

  • Mitochondria (singular: Mitochondrion): Site of aerobic respiration, releasing energy for the cell.

  • Ribosomes: Site of protein synthesis.

• Plant Cell Organelles:

  • Contains all animal cell organelles plus:

  • Chloroplasts: Contain chlorophyll to absorb light energy for photosynthesis.

  • Permanent Vacuole: Filled with cell sap to keep the cell rigid and structural.

  • Cell Wall: Made of cellulose; strengthens and supports the cell.

1.3 Eukaryotic and Prokaryotic Cells

• Eukaryotic Cells (Animals, Plants, Fungi, Protists):

  • Contain a cell membrane, cytoplasm, and genetic material enclosed within a nucleus.

• Prokaryotic Cells (Bacteria):

  • Much smaller in size.

  • Contain cell membrane, cytoplasm, ribosomes, and a cell wall (not made of cellulose).

  • Genetic material is not in a nucleus; present as a single loop of $DNA$ in the cytoplasm.

  • May contain small additional rings of $DNA$ called plasmids.

  • May have a protective slime layer or flagella (singular: flagellum) for movement.

  • Lack mitochondria and chloroplasts due to their small size.

1.4 Specialized Cells

• Cell Differentiation: The process by which an undifferentiated cell develops specific subcellular structures to perform a specific function.

• Animal Specialized Cells:

  • Sperm Cell: Fertilizes an egg cell.

  • Tail (flagellum) for motility.

  • Midpiece packed with mitochondria to supply energy.

  • Acrosome containing digestive enzymes to penetrate the egg membrane.

  • Large nucleus carrying genetic material.

  • Muscle Cell: Contracts and relaxes to cause movement.

  • Abundant mitochondria for energy release.

  • Special sliding protein filaments for contraction.

  • Stores glycogen to be broken down into glucose for respiration.

  • Nerve Cell: Carries electrical impulses throughout the body.

  • Long axon to cover large distances.

  • Dendrites to connect with adjacent nerve cells.

  • Nerve endings filled with mitochondria to produce chemical neurotransmitters.

• Plant Specialized Cells:

  • Root Hair Cell: Absorbs water and mineral ions from soil.

  • Large surface area extension.

  • Large permanent vacuole to speed up osmosis.

  • Abundant mitochondria for active transport of mineral ions.

  • Xylem Cell: Transports water and minerals upwards from roots.

  • Hollow continuous tubes with hollow ends (cell walls removed).

  • Strengthened by spirals of lignin to withstand pressure.

  • Phloem Cell: Transports dissolved food (sugars) up and down the plant.

  • Sieve plates with pores to allow easy translocation.

  • Companion cells filled with mitochondria to supply energy for transport.

1.5 Transport Mechanisms

• Diffusion:

  • The net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient (passive process, requires no energy).

  • Factors affecting rate:

  1. Temperature: Higher temperature increases kinetic energy and diffusion rate.

  2. Concentration Gradient: Steeper gradient yields faster diffusion.

  3. Surface Area: Larger surface area provides a greater area for diffusion.

• Osmosis:

  • The diffusion of water from a dilute solution (high water concentration) to a concentrated solution (low water concentration) across a partially permeable membrane (passive process).

  • Effects on animal cells (e.g., Red Blood Cells):

  • Hypotonic solution (more dilute outside): Water enters cell, causing it to swell and potentially burst (lysis).

  • Isotonic solution (same concentration): No net movement of water.

  • Hypertonic solution (more concentrated outside): Water leaves cell, causing it to shrivel (crenation).

• Active Transport:

  • The movement of substances from a more dilute solution to a more concentrated solution against a concentration gradient.

  • Requires energy supplied by cellular respiration in mitochondria.

  • Examples: Absorption of mineral ions into plant root hair cells; absorption of glucose from the lumen of the small intestine into the blood.

1.6 Mitosis and the Cell Cycle

• Chromosomes:

  • Located inside the nucleus, made of $DNA$ molecules carrying genes.

  • Body cells contain $23$ pairs of chromosomes ($46$ total).

• Stages of the Cell Cycle:

  • Stage 1 (Interphase): Longest phase. Cell grows in size, increases number of subcellular structures (mitochondria, ribosomes), and replicates its $DNA$ (forming $92$ chromosomes temporarily).

  • Stage 2 (Mitosis): One set of chromosomes is pulled to each end of the cell, and the nucleus divides.

  • Stage 3 (Cytokinesis): Cytoplasm and cell membranes divide to yield two genetically identical daughter cells.

• Functions of Mitosis: Growth, development, and tissue repair.

1.7 Stem Cells

• Stem Cell Definition: An undifferentiated cell capable of giving rise to more stem cells and differentiating into specialized cell types.

• Types of Stem Cells:

  • Embryonic Stem Cells: Derived from early embryos; can differentiate into almost any cell type. Used to treat conditions like paralysis and Type 1 diabetes.

  • Adult Stem Cells: Found in tissues like bone marrow; limited to forming specific cell types (e.g., blood cells).

  • Plant Meristem Stem Cells: Found in root and shoot tips; can differentiate into any plant cell type throughout life.

  • Uses: Fast and cheap cloning of plants, preservation of rare species, production of disease-resistant crop strains.

• Issues & Risks:

  • Risk of viral infection transfer.

  • Immunological rejection (mitigated by therapeutic cloning using the patient's own $DNA$).

  • Ethical and religious objections regarding embryo usage.

1.8 Culturing Microorganisms

• Binary Fission: Simple cell division in bacteria.

  • Calculation for bacterial growth:
    $\text{Number of Divisions} = \frac{\text{Total Time}}{\text{Mean Division Time}}$
    $\text{Final Population} = 2^{\text{Number of Divisions}}$

• Aseptic Technique:

  • Sterilize culture media and petri dishes before use to kill unwanted microbes.

  • Sterilize inoculating loops by passing through a hot Bunsen burner flame.

  • Secure petri dish lid lightly with adhesive tape to prevent airborne contamination without creating anaerobic conditions.

  • Store petri dishes upside down to avoid condensation dripping onto agar.

  • Incubate at maximum $25\,^{\circ}C$ in school laboratories to prevent growth of harmful human pathogens.

Topic 2: Organisation

2.1 Principles of Organisation

• Hierarchy: Cells $\rightarrow$ Tissues $\rightarrow$ Organs $\rightarrow$ Organ Systems $\rightarrow$ Organism.

• Definitions:

  • Tissue: A group of cells with similar structure and function working together.

  • Organ: Aggregations of tissues performing specific functions.

  • Organ System: Group of organs working together to perform key bodily functions.

2.2 Digestive System

• Organs and Functions:

  • Mouth: Mechanical breakdown via teeth; mixes food with saliva.

  • Salivary Glands: Produce saliva containing amylase.

  • Esophagus: Transports food to stomach.

  • Stomach: Churns food; secretes hydrochloric acid ($HCl$) and protease.

  • Small Intestine: Digestion of food and absorption of soluble nutrients into blood.

  • Adaptations: Large surface area via villi and microvilli, rich blood supply to maintain concentration gradient, short diffusion pathway ($1$ cell thick).

  • Large Intestine: Absorbs water from undigested material to form feces.

  • Liver: Produces bile.

  • Gallbladder: Stores bile.

  • Pancreas: Produces amylase, protease, and lipase.

2.3 Enzymes and Metabolism

• Enzyme Definition: Biological catalysts (proteins) that speed up metabolic reactions without being consumed.

• Lock and Key Theory:

  • Active site has a unique 3D shape complementary to a specific substrate molecule.

• Metabolism: The sum of all chemical reactions in a cell or organism.

• Factors Affecting Enzymes:

  • Temperature: Increasing temperature increases kinetic energy up to the optimum ($\approx 37\,^{\circ}C$ in humans). Temperatures above optimum break internal bonds, changing active site shape (denaturation).

  • pH: Enzymes have an optimum pH. Extreme pH levels alter charges on amino acids and denature the active site.

• Bile:

  • Alkaline liquid produced by liver, stored in gallbladder.

  • Neutralizes stomach $HCl$ to create optimal alkaline conditions in small intestine.

  • Emulsifies fats into smaller droplets, increasing surface area for lipase action.

• Digestive Enzymes Summary:

  • Amylase (Carbohydrase):

  • Breaks down Starch $\rightarrow$ Simple Sugars (Glucose).

  • Produced in: Salivary glands, Pancreas, Small intestine.

  • Works in: Mouth, Small intestine.

  • Protease:

  • Breaks down Proteins $\rightarrow$ Amino Acids.

  • Produced in: Stomach, Pancreas, Small intestine.

  • Works in: Stomach, Small intestine.

  • Lipase:

  • Breaks down Lipids (Fats) $\rightarrow$ Fatty Acids + Glycerol.

  • Produced in: Pancreas, Small intestine.

  • Works in: Small intestine.

2.4 Blood and Blood Vessels

• Components of Blood:

  • Plasma: Fluid transport medium ($\approx 55\%$) carrying $CO_2$, urea, hormones, and blood cells.

  • Red Blood Cells: Transport oxygen. Adaptations: contain hemoglobin, no nucleus, biconcave disc shape for high surface area to volume ratio.

  • White Blood Cells: Defend against pathogens; contain a nucleus.

  • Platelets: Cell fragments that aid blood clotting at wound sites.

• Blood Vessels:

  • Arteries: Carry blood away from heart under high pressure. Thick muscular/elastic walls, narrow lumen.

  • Capillaries: Exchange substances at tissues. Thin walls ($1$ cell thick), very narrow lumen.

  • Veins: Carry blood to heart under lower pressure. Thinner walls, wide lumen, valves to prevent backflow.

2.5 Heart and Gas Exchange

• Gas Exchange System:

  • Air enters via Nose/Mouth $\rightarrow$ Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli.

  • Alveoli Adaptations: Large surface area, thin walls ($1$ cell thick), surrounded by dense capillary network, ventilated to maintain concentration gradients.

  • Fish Gills: Gill filaments provide large surface area, short diffusion path, and counter-current exchange mechanism (blood and water flow in opposite directions).

• The Heart Structure and Pathway:

  • Double circulatory system.

  • Right side pumps deoxygenated blood to lungs; Left side has thicker muscle to pump oxygenated blood to body.

  • Pathway: Vena Cava $\rightarrow$ Right Atrium $\rightarrow$ Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs $\rightarrow$ Pulmonary Vein $\rightarrow$ Left Atrium $\rightarrow$ Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Body.

  • Resting heart rate controlled by pacemaker cells in right atrium.

2.6 Cardiovascular Diseases

• Coronary Heart Disease (CHD): Buildup of fatty material inside coronary arteries, reducing blood flow and oxygen supply to heart muscle.

• Treatments:

  • Stents: Metal mesh tubes inserted into arteries to keep them open. Risk: Blood clotting.

  • Statins: Drugs reducing blood cholesterol levels. Advantage: Non-invasive. Disadvantages: Requires daily intake, potential side effects.

  • Valve Replacement: Faulty valves replaced with Mechanical valves (durable, requires anti-clotting medication) or Biological valves (from donors/animals, limited lifespan of $10\text{--}15$ years).

  • Artificial Pacemaker: Electrical device implanted to correct heart arrhythmias.

  • Artificial Heart: Temporary mechanical pump used while awaiting donor heart transplant.

2.7 Non-Communicable Diseases and Health

• Health: State of physical and mental well-being.

• Risk Factors & Causal Mechanisms:

  • Diet, smoking, and lack of exercise $\rightarrow$ Cardiovascular disease.

  • Obesity $\rightarrow$ Type 2 diabetes.

  • Alcohol consumption $\rightarrow$ Liver cirrhosis and brain damage.

  • Smoking $\rightarrow$ Lung disease and lung cancer.

  • Smoking and alcohol during pregnancy $\rightarrow$ Fetal developmental damage.

  • Carcinogens (e.g., UV light, ionizing radiation, tar) $\rightarrow$ Cancer.

• Cancer:

  • Result of uncontrolled cell growth and division forming tumors.

  • Benign Tumors: Contained in one area within a membrane; non-invasive.

  • Malignant Tumors: Invasive cells that spread via blood to form secondary tumors elsewhere.

2.8 Plant Tissues, Transport, and Transpiration

• Leaf Tissues:

  • Epidermal Tissue: Covered with waxy cuticle to reduce water evaporation.

  • Palisade Mesophyll: Upper layer packed with chloroplasts for photosynthesis.

  • Spongy Mesophyll: Contains air spaces to facilitate gas exchange.

  • Stomata & Guard Cells: Regulate gas exchange and water loss on leaf underside.

• Transport Systems:

  • Xylem: Transports water and mineral ions upwards from roots (transpiration stream). Non-living hollow tubes reinforced with lignin.

  • Phloem: Transports dissolved sugars up and down plant (translocation). Living tissue with sieve plates and companion cells.

• Transpiration:

  • Loss of water vapor from leaf surface via stomata by evaporation.

  • Factors Increasing Transpiration Rate: Increased light intensity, increased temperature, increased air movement (wind), decreased humidity.

  • Potometer: Equipment used to measure rate of transpiration:
    $\text{Rate} = \frac{\text{Distance Moved by Air Bubble}}{\text{Time}}$

Topic 3: Infection and Response

3.1 Pathogens and Communicable Diseases

• Pathogen Definition: Microorganisms that cause infectious disease (Bacteria, Viruses, Protists, Fungi).

• Transmission Methods: Direct contact, water, air (droplet infection).

• Pathogen Actions:

  • Bacteria: Reproduce rapidly inside body; produce toxins that damage tissues.

  • Viruses: Live and replicate inside host cells, causing cell damage/bursting.

• Viral Diseases:

  • Measles: Droplet infection; causes fever and red skin rash; prevented by MMR vaccine.

  • HIV: Sexual contact or exchange of body fluids; flu-like symptoms initially; damages immune system leading to AIDS; controlled by antiretroviral drugs.

  • Tobacco Mosaic Virus (TMV): Affects plant leaves creating a mosaic pattern; reduces photosynthesis and crop yield.

• Bacterial Diseases:

  • Salmonella: Food poisoning from raw/undercooked food; causes fever, abdominal cramps, vomiting, diarrhea; controlled by vaccinating poultry in UK.

  • Gonorrhea: STD causing thick yellow/green discharge and painful urination; treated with antibiotics; prevented by barrier contraception (condoms).

• Fungal and Protist Diseases:

  • Rose Black Spot (Fungal): Purple/black spots on leaves; leaves turn yellow and drop early; treated with fungicides and burning infected leaves.

  • Malaria (Protist): Transmitted by female mosquito vectors; causes recurrent fever episodes; prevented using mosquito nets and insecticides.

3.2 Human Defense Systems

• Non-Specific External Defenses:

  • Skin: Physical barrier; produces antimicrobial secretions.

  • Nose: Traps pathogens with hairs and mucus.

  • Trachea and Bronchi: Produce mucus trapped by ciliated cells that waft mucus upwards.

  • Stomach: Produces Hydrochloric Acid ($HCl$) to destroy ingested pathogens.

• Immune System Functions (White Blood Cells):

  1. Phagocytosis: Engulfing and digesting pathogens.

  2. Antibody Production: Producing specific proteins that bind to complementary antigens on pathogens to mark them for destruction.

  3. Antitoxin Production: Neutralizing toxins released by pathogens.

3.3 Vaccination and Drug Development

• Vaccination: Injection of small quantities of dead or inactive pathogens to stimulate antibody production by white blood cells. Memory cells respond rapidly upon re-exposure.

• Herd Immunity: High proportion of vaccinated population prevents pathogen spread, protecting unvaccinated individuals.

• Drugs:

  • Antibiotics (e.g., Penicillin): Kill bacteria inside body; ineffective against viruses.

  • Painkillers: Relieve symptoms without killing pathogens.

• Drug Origins:

  • Digitalis (heart drug): Derived from foxgloves.

  • Aspirin (painkiller): Derived from willow bark.

  • Penicillin (antibiotic): Discovered by Alexander Fleming from Penicillium mold.

• Testing and Trialing:

  • Tested for Toxicity, Efficacy, and Dosage (TED).

  • Preclinical Testing: Done in labs on cells, tissues, and live animals.

  • Clinical Trials: Tested on healthy human volunteers at low doses, then on patients to determine optimum dosage.

  • Double-Blind Placebo Trials: Neither doctor nor patient knows who receives active drug or placebo to prevent bias.

3.4 Monoclonal Antibodies

• Production:

  1. Mouse immunized with target antigen to stimulate lymphocyte antibody production.

  2. Lymphocytes extracted and fused with myeloma (tumor) cells to form hybridoma cells.

  3. Hybridoma cells cloned to produce identical antibodies, which are collected and purified.

• Uses:

  • Pregnancy testing kits (bind to $hCG$ hormone).

  • Diagnostic assays for disease detection.

  • Fluorescent tagging in cell research.

  • Targeted cancer therapies (delivering toxic drugs directly to tumor antigens).

3.5 Plant Defenses

• Detection Indicators: Stunted growth, spots on leaves, decay, malformed stems, discoloration, presence of pests.

• Defenses:

  • Physical: Cellulose cell walls, tough waxy cuticle, bark layers.

  • Chemical: Antibacterial chemicals, poisons to deter herbivores.

  • Mechanical: Thorns, leaf hairs, drooping/curling response when touched, mimicry.

Topic 4: Bioenergetics

4.1 Photosynthesis

• Process: Endothermic chemical reaction taking place in chloroplasts.

• Word Equation:
  $\text{Carbon Dioxide} + \text{Water} \xrightarrow{\text{Light}} \text{Glucose} + \text{Oxygen}$

• Symbol Equation:
  $6CO<em>2 + 6H</em>2O \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2$

• Limiting Factors:

  • Light intensity.

  • Carbon dioxide concentration.

  • Temperature.

  • Amount of chlorophyll.

• Uses of Glucose (FOSRAC):

  • F: Fats and oils storage.

  • O: Oils.

  • S: Starch storage (insoluble).

  • R: Respiration to release energy.

  • A: Amino acid synthesis (combined with nitrate ions).

  • C: Cellulose production for cell walls.

4.2 Respiration

• Process: Exothermic reaction occurring continuously in living cells.

• Aerobic Respiration (with oxygen, occurs in mitochondria):
  $\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water}$
  $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O$

• Anaerobic Respiration (without oxygen):

  • In Animals:
    $\text{Glucose} \rightarrow \text{Lactic Acid}$
    (Releases significantly less energy due to incomplete oxidation of glucose).

  • In Yeast and Plants (Fermentation):
    $\text{Glucose} \rightarrow \text{Ethanol} + \text{Carbon Dioxide}$
    (Used commercially in bread making and alcoholic beverage production).

4.3 Exercise and Metabolism

• Body Responses to Exercise:

  • Heart rate, breathing rate, and breathing volume increase to supply extra oxygen and glucose to muscular tissues.

• Oxygen Debt:

  • Amount of extra oxygen required after exercise to react with accumulated lactic acid in the liver and convert it back to glucose.

• Metabolism Summary Examples:

  • Conversion of glucose to starch, glycogen, and cellulose.

  • Formation of lipid molecules from one glycerol and three fatty acid molecules.

  • Use of glucose and nitrate ions to form amino acids.

  • Breakdown of excess proteins into urea for excretion.