Ordinary Level Biology Study notes - Form 3 & 4

SAFETY IN THE LABORATORY

• Causes of Accidents in the Laboratory:

  • Fires resulting from the use of Bunsen gas burners or methylated spirit burners.
  • Hazardous fumes such as $Cl_{2}$ (chlorine) and $NH_{3}$ (ammonia) produced during chemical reactions.
  • Skin burns caused by contact with strong acids and bases.
  • Infections resulting from the improper handling of microorganisms.
  • Cuts and punctures from improper handling of apparatus such as glassware, razor blades, and needles.
  • Electrical shocks from faulty or misused equipment.
  • Burns from handling hot liquids, such as boiling water.

• Laboratory Safety Rules:

  • Students must never be in the laboratory without a teacher present.
  • Always follow the teacher’s instructions meticulously.
  • Eating or drinking in the laboratory is strictly prohibited.
  • Running or horseplay is forbidden to avoid accidents.
  • All breakages or chemical spills must be reported immediately.
  • Students must know the safe procedures for accidents like fires.
  • Never touch, smell, or taste chemicals without specific permission.
  • Never mix chemicals for fun, as this may cause explosions.
  • Dispose of all chemicals exactly as instructed by the teacher.
  • Wash hands thoroughly after handling chemicals or microorganisms.

• Fire Drills and Equipment:

  • A fire drill is a practice session for evacuating a building during a fire; it must be practiced several times a year.
  • When the alarm rings, everyone must stop work and walk in a calm, orderly manner along a predetermined route to a safe place.
  • A roll call must be taken by the teacher at the safe assembly point to ensure everyone is out.
  • Essential safety items in the lab: A bucket of sand (to douse fires), a fire extinguisher, a fire guard around the laboratory, and a First Aid kit (with knowledge of how to use it).
  • Local emergency numbers for fire fighters and doctors must be displayed clearly on the wall.

• Safety Regarding Fumes:

  • Experiments producing poisonous fumes (e.g., $Cl_{2}$) or acidic fumes must be performed in a fume cupboard.
  • Windows should be closed or the experiment should be conducted outside if a cupboard is unavailable.
  • Gas tapes must remain closed when not in use.

CAREERS AND BRANCHES IN BIOLOGY

• Definition of Biology: The study of living organisms. Due to its breadth, it is divided into various specialized fields.
• Careers in Biology:
  • Medicine: Doctors, laboratory scientists, clinicians, and nurses.
  • Research Scientist: Conducting experiments to expand biological knowledge.
  • Ecologist: Studying the relationships between organisms and their environment.
  • Dietician: Specializing in nutrition and diet planning.
  • Conservationist: Working to protect natural habitats and species.
  • Botanist: A scientist specializing in the study of plant life.

SAFETY LABELS AND SYMBOLS

• Purpose: These are universally recognized symbols that communicate potential hazards immediately.
• Chemical Hazard Symbols Explained:
  • Poisonous: Dangerous if ingested, inhaled, or even touched.
  • Environmental Hazard: Rare in labs; indicates the chemical requires specialized disposal to protect the environment.
  • Corrosive: Avoid skin contact; can rust chemical storage cupboards.
  • Stow Away From Foodstuffs: Harmful materials that must not contact edible items.
  • Dangerous When Wet: Reacts violently upon contact with water.
  • Flammable Gas/Liquid: Used for storage/transport of materials that ignite easily. Volatile solvents must be kept in flame-resistant cupboards.
  • Explosive: Includes materials triggered by noise, movement, sparks, or flames.
  • Irritant or Harmful: Covers a range of hazards; requires precautions like avoiding skin contact or inhalation.
  • Oxidising Chemical: Materials that evolve oxygen spontaneously or promote combustion; must be kept away from flammable chemicals.
  • Non-Flammable Gas: Used for transport of gases that do not ignite.
  • Organic Peroxide: Symbol for the transport/storage of organic peroxides.
  • Inhalation Hazard: Specific symbol for materials dangerous to breathe.
  • Marine Pollutant: Must not be disposed of in sewer systems.
  • Miscellaneous Danger: A catch-all symbol for dangers not covered by other specific labels.

CHEMICALS OF LIFE

• Water ($H_{2}O$):

  • Makes up approximately $70\%$ of the human body.
  • Structure: Composed of two positively charged hydrogen atoms and one negatively charged oxygen atom.
  • Polarity: The uneven distribution of charges makes it a polar molecule; adjacent molecules form hydrogen bonds.
  • Properties and Uses:
    1. Transparency: Allows light to penetrate for aquatic plant photosynthesis and helps aquatic animals see.
    2. Solvent: Dissolves and transports food molecules and solutes; acts as a medium for enzymatic reactions.
    3. Reagent: A reactant in photosynthesis and the hydrolysis of food during digestion.
    4. High Specific Heat Capacity: Absorbs significant heat to raise $1\,kg$ by $1\,^{\circ}C$. This stabilizes body and environmental temperatures.
    5. High Latent Heat of Vaporization: Absorbs massive heat to evaporate. Cooling occurs as sweat evaporates from the skin.

• Carbohydrates:

  • Organic molecules containing Carbon ($C$), Hydrogen ($H$), and Oxygen ($O$).
  • Classification:
    1. Monosaccharides: Simplest sugars (e.g., glucose, fructose, galactose).
    2. Disaccharides: Two units joined via a condensation reaction (elimination of water). Examples: Maltose ($glucose + glucose$), Sucrose ($glucose + fructose$), Lactose ($galactose + glucose$).
    3. Polysaccharides: Long chains of glucose units (e.g., starch, glycogen, cellulose).
  • Functions: Respiration substrate (energy), supporting structures (cell walls), synthesis of lubricants and nucleic acids.
  • Testing:
    • Reducing Sugars: Benedict’s test (heat with Benedict's solution; color change indicates presence).
    • Non-Reducing Sugars (e.g., Sucrose): Heat with dilute $HCl$ (hydrolysis), neutralize with $NaHCO_{3}$, then perform Benedict’s test.

• Fats (Lipids):

  • Contains $C, H, O$; composed of one glycerol and three fatty acids joined by condensation.
  • Hydrolysis: Adding $3$ water molecules with enzymes breaks fats into glycerol and fatty acids.
  • Functions: Energy storage, cell membrane components, hormone/steroid synthesis, thermal insulation, solvent for fat-soluble vitamins, and a source of metabolic water for desert animals.
  • Test: Ethanol emulsion test (precipitates into a cloudy white emulsion when added to water).

• Proteins:

  • Polymers of amino acids linked by peptide bonds. Contain $C, H, O, N$ (sometimes $S$).
  • Functions: Cell growth and repair, formation of enzymes, hormones, and antibodies, and can be used for energy during starvation.

• Nucleic Acids:

  • Polymers made of nucleotides ($DNA$ and $RNA$). Contain $C, H, O, N, P$.
  • DNA (Deoxyribonucleic acid): Found in the nucleus; carries genetic information. Genes are segments of DNA.
  • RNA (Ribonucleic acid): Made from DNA; moves to the cytoplasm to synthesize proteins.

CELLS AND CELLULAR ACTIVITIES

• Basic Unit: The cell is the smallest structural and functional unit of life.

• Cell Parts and Functions:

  • Cytoplasm: Jelly-like medium for chemical reactions; contains organelles.
  • Cell Membrane: Partially permeable boundary; controls substance entry/exit.
  • Nucleus: Contains DNA in chromosomes; controls cell activities, development, and division.
  • Cell Wall: (Plants only) Rigid cellulose layer; prevents bursting and allows free passage of water/salts.
  • Vacuole: Fluid-filled; contains cell sap (salts/sugars) and maintains plant firmness.
  • Chloroplast: (Plants only) Contains chlorophyll for trapping light energy for photosynthesis.
  • Mitochondria: Site of aerobic respiration and energy production.

• Plant vs. Animal Cells:

  • Plant: Fixed shape (cell wall), large central vacuole, presence of chloroplasts.
  • Animal: Varying shape, no cell wall, small temporary vacuoles, no chloroplasts.

• Cell Specialization (Division of Labour):

  • Palisade Cells: Columnar, packed with chloroplasts for photosynthesis.
  • Root Hair Cells: Long projections to increase surface area for water/mineral absorption; thin walls and large vacuoles for osmosis.
  • Neurones: Long fibers for conducting electrical impulses.
  • Muscle Cells: Contain actin/myosin for contraction; high mitochondria count for energy.
  • Sperm Cells: Tail for movement; mitochondria for energy; acrosome with enzymes to penetrate the egg; haploid nucleus.
  • Ovum: Large with nutrient-rich cytoplasm; specialized membrane to prevent multiple sperm entry; haploid nucleus.
  • Red Blood Cells (RBCs): Contain haemoglobin; biconcave shape (surface area); no nucleus (oxygen capacity); flexible to fit capillaries.
  • White Blood Cells (WBCs): Macrophages (engulf pathogens); Lymphocytes (produce antibodies).

• Cellular Transport:

  • Diffusion: Net movement of molecules from high to low concentration. Affected by: Surface area to volume ratio, temperature, concentration gradient, particle size, and membrane thickness.
  • Osmosis: Movement of water from high to low water potential through a semi-permeable membrane.
  • Plant Osmosis: Turgidity (firm state in dilute solutions) vs. Plasmolysis (membrane pulls from wall in concentrated solutions).
  • Animal Osmosis: Cytolysis (bursting in high water potential) vs. Crenation (shrinking/spiking in low water potential).
  • Active Transport: Movement against a concentration gradient using energy from respiration (e.g., mineral uptake by roots).

ENZYMES

• Properties: Biological catalysts made of proteins; specific in action; affected by $pH$ and temperature; remain unchanged; lower activation energy.
• Mode of Action (Lock and Key):
  • Substrate (key) fits into the enzyme's active site (lock) to form an enzyme-substrate complex.
  • Anabolic: Joining molecules.
  • Catabolic: Splitting molecules.
• Environmental Effects:
  • Temperature: Rate doubles every $10\,^{\circ}C$ until optimum (approx. $40\,^{\circ}C$); denaturation occurs at high temperatures as weak bonds break.
  • pH: Enzymes have a narrow optimum range. Extremes cause denaturation as ionic/hydrogen bonds are disrupted.
• Applications: Biological washing powders use proteases (break down blood/sweat proteins) and lipases (remove fats), allowing for effective cleaning at lower temperatures.

PLANT SCIENCE

• Photosynthesis: $6CO_{2} + 6H_{2}O \rightarrow C_{6}H_{12}O_{6} + 6O_{2}$ (using light/chlorophyll).
  • Testing for Starch: Kill leaf in hot water, remove chlorophyll with boiling alcohol (water bath), soften in water, add iodine (blue-black = starch).
  • Leaf Adaptations: Broad/flat (surface area), thin (short diffusion path), spongy mesophyll (gas exchange spaces), many stomata.
• Mineral Nutrients:
  • Nitrogen: For proteins, DNA, and chlorophyll. Deficiency: Stunted growth and yellow leaves.
  • Phosphorus: For ATP, cell membranes, and DNA. Deficiency: Purplish leaves and poor root growth.
  • Potassium: Operates $Na/K$ pumps, regulates stomata. Deficiency: Brown leaf margins.
• Productivity: Rate of biomass increase. Affected by light, water, minerals, and pests.
  • Pests: Tissue eating (caterpillars) and sap sucking (aphids). Controlled by Cultural (rotation), Biological (predators), or Chemical (pesticides) methods.
• Plant Transport Systems:
  • Xylem: Dead, lignified tubes; transport water/minerals via Transpiration Pull (suction) and Capillarity (hydrogen bonding).
  • Phloem: Living cells (sieve tubes/companion cells); transport sugars (sucrose) and amino acids via Translocation.
  • Transpiration: Loss of water vapor from leaves. Factors: Humidity (decreases rate), Temperature (increases), Wind (increases), Light (increases).
• Plant Reproduction:
  • Asexual (Vegetative): Tubers (potatoes), Rhizomes (grass), Runners (strawberries), Bulbs (onions). Artificial: Cuttings, Grafting (Scion on Stock).
  • Sexual: Flower structure includes Stamen (male) and Carpel (female). Pollination can be Self or Cross. Fertilization involves the pollen tube growing through the style into the micropyle to fuse with the ovum nucleus.
  • Seed Dispersal: Wind (dandelions), Animal (blackjack/guava), Water (coconut), Self/Explosive (beans).

ANIMAL SCIENCE AND NUTRITION

• Balanced Diet: Includes Carbohydrates (energy), Lipids (insulation/energy), Proteins (growth/repair), Vitamin A (vision), Vitamin C (healing/immunity), Vitamin D (bones/calcium), Iron (haemoglobin), Calcium (bones/teeth), Fiber (peristalsis), and Water (solvent).
• Malnutrition:
  • Obesity: Excess fats/carbs stored as adipose tissue.
  • Marasmus: Severe lack of energy (carbs).
  • Kwashiorkor: Severe protein deficiency; causes swollen belly and poor growth.
  • Deficiency Diseases: Scurvy (Vit C), Rickets (Vit D), Anemia (Iron).
• The Digestive System:
  • Mouth: Mechanical (teeth) and chemical (Amylase digests starch).
  • Stomach: Gastric juice ($HCl$ for $pH\,2$ and bacteria kill, Pepsin for proteins).
  • Small Intestine (Duodenum/Ileum): Bile (emulsifies fats), Pancreatic juice (Trypsin, Amylase, Lipase), and intestinal enzymes (Maltase, Sucrase, Lactase, Peptidase).
  • Villi Adaptations: Large surface area, one-cell thick, rich capillary network, and lacteals for fat absorption.
  • Liver Functions: Regulates glucose (via Insulin/Glucagon), deaminates amino acids (urea), stores Vitamins A/D/Glycogen, detoxifies alcohol, and produces bile.
• Teeth: Incisors (cutting), Canines (tearing), Premolars/Molars (grinding).

GASEOUS EXCHANGE AND RESPIRATION

• Breathing Mechanism:
  • Inhalation: External intercostals and diaphragm contract (diaphragm flattens); volume increases, pressure decreases, air enters.
  • Exhalation: Muscles relax; volume decreases, pressure increases, air is pushed out.
• Alveoli Efficiency: Millions of sacs (surface area), thin membrane, moist, and extensive capillary network for diffusion.
• Smoking Effects:
  • Nicotine: Addictive; increases heart rate/BP.
  • Carbon Monoxide: Forms carboxy-haemoglobin (reduces oxygen transport).
  • Tar: Carcinogenic; causes lung cancer and paralyses cilia.
• Respiration:
  • Aerobic: $Glucose + Oxygen \rightarrow CO_{2} + Water + Energy$ (38 ATP).
  • Anaerobic: In animals ($Glucose \rightarrow Lactic\,acid + Energy$); In plants ($Glucose \rightarrow Alcohol + CO_{2} + Energy$). Lactic acid causes fatigue and creates an "Oxygen Debt."

THE CIRCULATORY SYSTEM

• Heart Structure: Four chambers; thick muscle (left ventricle is thickest to pump to the whole body); valves prevent backflow.
• Cardiac Cycle: Deoxygenated blood enters Right Atrium (Vena Cava) -> Right Ventricle -> Pulmonary Artery -> Lungs -> Pulmonary Vein -> Left Atrium -> Left Ventricle -> Aorta -> Body.
• Blood Vessels:
  • Arteries: Thick walls, high pressure, no valves.
  • Veins: Thinner walls, low pressure, have valves.
  • Capillaries: One-cell thick, permeable for exchange.
• Blood Components: Plasma ($55\%$), RBCs (oxygen), WBCs (phagocytes/lymphocytes), Platelets (clotting).
• Coronary Heart Disease (CHD): Blockage of coronary arteries (atherosclerosis/thrombosis); caused by high-fat diet, smoking, stress, and lack of exercise.

IMMUNITY AND HEALTH

• Defense Layers: Skin (barrier), Tears (lysozyme), Mucus (traps), Clotting (seals).
• Immunity Types:
  • Active: Body makes its own antibodies (Natural infection or Vaccination).
  • Passive: Antibodies introduced from elsewhere (Natural via breastmilk/placenta or Artificial via serum).
• HIV/AIDS: Virus attacks CD4 lymphocytes, disabling the immune system and leading to opportunistic infections (TB, Pneumonia).
• Common Diseases:
  • Cholera: Bacterial ($Vibrio$); water-borne; severe diarrhea; treated with rehydration/antibiotics.
  • Malaria: Protozoan ($Plasmodium$); female Anopheles mosquito vector; fever/chills.
  • Tuberculosis (TB): Bacterial; spread by droplets; affects lungs; BCG vaccine prevention.
  • Bilharzia: Flatworm ($blood\,fluke$); enters thru skin in water; blood in urine/faeces.

GENETICS AND SELECTION

• Terms: Chromosome (DNA structure), Gene (DNA segment), Allele (gene version), Genotype (genetic makeup), Phenotype (physical trait).
• Dominance: Dominant alleles mask recessive ones; Co-dominance (e.g., AB blood type).
• Sex Determination: Males ($XY$), Females ($XX$).
• Selection:
  • Natural Selection: Survival of the fittest; favorable traits accumulate over generations.
  • Artificial Selection (Selective Breeding): Humans choose parents with desirable traits (higher yield, disease resistance).
• Variation: Discontinuous (distinct categories like blood type) vs. Continuous (range like height, bell curve).

ECOSYSTEMS AND BIODIVERSITY

• Components: Physical (soil, water, air) and Biological (producers, consumers, decomposers).
• Trophic Levels: Energy flows from Sun -> Producers -> Primary Consumers -> Secondary Consumers -> Tertiary Consumers. energy is lost ($90\%$) at each level as heat/movement.
• Nutrient Cycles:
  • Carbon Cycle: Driven by photosynthesis, respiration, combustion, and decomposition.
  • Nitrogen Cycle: $N_{2}$-fixing bacteria (roots), Nitrifying bacteria (ammonia to nitrates), Denitrifying bacteria ($N_{2}$ release).
• Conservation: Afforestation, urban planning, recycling, and government policies to combat threats like deforestation and pollution.

COORDINATION, RESPONSE, AND HOMEOSTASIS

• Nervous System: CNS (Brain/Spinal Cord) and PNS. Neurones: Sensory (from receptors), Motor (to effectors), Relay (connections).
• Reflex Arc: Rapid, involuntary path ($Receptor \rightarrow Sensory \rightarrow Relay \rightarrow Motor \rightarrow Effector$).
• Brain Regions: Cerebrum (intelligence/voluntary), Hypothalamus (homeostasis/temp), Medulla Oblongata (involuntary: heart/breath), Cerebellum (balance/posture).
• The Eye: Focuses via the lens and ciliary muscles (accommodation). Pupils contract/dilate via circular and radial muscles.
• Homeostasis: Maintenance of constant internal environment (e.g., Body temp at $37\,^{\circ}C$).
  • When Hot: Vasodilation, sweating, hair layers flat.
  • When Cold: Vasoconstriction, shivering, hair erection (goosebumps).
• Endocrine System: Ductless glands.
  • Adrenaline: Flight-or-fight; increases HR, blood sugar, and pupil size.
  • Insulin/Glucagon: Secreted by Islets of Langerhans (Pancreas) to control blood glucose.
• Excretion: Removal of metabolic wastes. Kidney removes urea/salts via nephrons; ureter carries urine to bladder.
• Skeletal System: Functions in support, protection, and movement. Synovial joints (Ball and Socket, Hinge) allow for movement via antagonistic muscle pairs (Biceps/Triceps).