CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 1: Characteristics & Classification Of Living Organisms: Movement: Action by an organism or part of an organism causing a change of position or place. Respiration: Chemical reactions in cells that break down nutrients and release energy for metabolism. Sensitivity: Ability to detect and respond to changes in the internal or external environment. Growth: Permanent increase in size and dry mass. Excretion: Removal of waste products of metabolism and substances in excess of requirements. _________________________________________________________________________________ Species: Group of organisms that can reproduce to produce fertile offspring. Monocotyledons: Petals in multiples of 3 and have parallel leaf veins. Dicotyledons: Petals in multiples of 4 or 5 and have reticulated (branched) veins. Unit 2: Organization Of The Organism: Tissues: Group of same cells working together to perform specific function. Magnification = Image Size Actual Size (1 mm = 1000 m) Unit 3: Movement Into & Out Of Cells: Diffusion: • Net movement of particles from region of higher concentration to a region of lower concentration. • Down a concentration gradient because of their random movement. • Some substances diffuse across a cell membrane. • Factors influencing diffusion: Surface Area, Temperature, Concentration Gradient, Distance. Osmosis: • Net movement of water from region of higher water potential to region of lower water potential. • Water moves from dilute solution to concentrated solution. • Across a partially permeable membrane. • If plants do not receive enough water, they wilt due to plasmolysis of cells. • Water entering plant cells pushes cell membrane to cell wall, becoming turgid and strong. Active Transport: • Net movement of particles from region of lower concentration to region of higher concentration. • Against concentration gradient. • Requires energy, released from mitochondria. • Protein carriers push specific molecules and ions across cell membrane. Unit 4: Biological Molecules: Test For Reducing Sugars: Benedicts reagent; turns from blue to brick-red (heat is required). Test For Starch: Iodine solution; turns from brown to blue-black. Test For Protein: Biuret solution; turns from blue to purple. Test For Lipids: Ethanol, forms cloudy emulsion. Test For Vitamin C: DCPIP solution, turns from blue to colourless. DNA: (A-T) and (C-G). Double Helix made of two strands coiled together. Strands have bases, bonds hold together. Carbohydrates & Fats: C, H, O Proteins: C, H, O, P CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 5: Enzymes: • Catalyst which increases rate of chemical reaction. • Involved in all metabolic processes. • Active site complementary to substrate which bind to form enzyme-substrate complexes. • High temperature denatures active site, so no ezyme-substare complexes can be formed; irreversible. Unit 6 AND Unit 8: Plant Nutrition & Transport: Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 (in presence of sunlight and chlorophyll). Chlorophyll (green pigment in chloroplast) converts light energy to chemical energy for photosynthesis. Describe Uses Of Carbohydrates In Plants: [5] • Starch as an energy source. • Cellulose to build or strengthen cell walls. • Glucose used in respiration to provide energy. • Sucrose for transport in phloem. • Nectar to attract insects for pollination. Hydrogencarbonate Indicator: • Increase in CO2 → turns from red to yellow. • Decrease in CO2 → turns from red to purple. Translocation: • Movement of sucrose and amino acids from source to sink. • Different parts can act as source or sink at different times. How & Why Wilting Occurs: • More water evaporates from surfaces of plant. • Less water being taken in by roots by osmosis. • When cells are not full of water, they become flaccid. • Cell walls cannot support plant and begin to collapse Limiting Factor: • Something present in the environment in such short supply that it restricts life processes. • CO2 concentration, light intensity and temperature are the limiting factors for plants. State And Explain The Features And Adaptations Of Plants For Photosynthesis: [5] • Large surface area allows more light to be absorbed. • Network of veins allow transport of water to leaf and transport of carbohydrates from leaf. • Thin waxy cuticle protects leaf without blocking sunlight. • Palisade layer at top of leaf to maximize absorption of sunlight by hitting chloroplasts directly. • Spongy layer has air spaces to allow CO2 to diffuse through the leaf. Xylem provides support, transports water and mineral ions. Phloem transport sucrose and amino acids. Adaptations & Functions Of Xylem Vessel: [3] • Cells joined end to end with no cross-walls to form long, continuous tube. • Cells have no organelles (dead) to allow free flow of water. • Xylem walls thickened with lignin to provide support and waterproofing. Pathway Of Water From Root To Leaf: • Root hair cells (movement of water from higher water potential to lower water potential by osmosis). • Root cortex cells. • Xylem vessels (by transpiration pull to the lead and forces of adhesion). • Enters mesophyll cells. Transpiration: • Loss of water vapour from plant leaves. • Evaporation of water at surfaces of mesophyll cells followed by diffusion of water vapour through stomata. • Provides water to keep cells turgid, for photosynthesis and mineral ions for growth (by transpiration pull in xylem). • Transpiration rate increases with high temperature and high wind speed but decreases with high humidity. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 7: Human Nutrition: Mechanical Digestion: Breakdown of food into smaller pieces. Increases surface area of food. Chemical Digestion: Breakdown of large, insoluble molecules to smaller, soluble molecules. Assimilation: Uptake and use of nutrients by cells. Absorption: Movement of nutrients from intestines into blood. Emulsification: • Larger fat globules to smaller fat globules, by bile (secreted by liver, stored in gallbladder). • Increases surface area of fat globules for quicker chemical digestion. Bile: Emulsification of fats and neutralizing acidic mixture of food and gastric juices entering duodenum. Pepsin (stomach) and Trypsin (small intestine) break down proteins to amino acids. Lipase is produced by pancreas and acts in small intestine to digest fats to fatty acids and glycerol. Amylase produced in mouth and pancreas, digests starch to maltose (simple reducing sugars). HCl in gastric juice kills pathogens in food and provides acidic optimum pH for stomach enzymes. Explain The Adaptations & Functions Of Villus In Absorption: [4] • Microvilli present on the surface increase surface area for faster absorption of nutrients. • Villus wall is one cell thick, provides short distance for diffusion and active transport of molecules. • Large network of capillaries that transport glucose and amino acids in the blood. • Lacteal present in center of villus to transport fatty acids and glycerol away from small intestine. Unit 9: Transport In Animals: Circulatory System: System of blood vessels with a pump and valves to ensure one-way flow of blood. Fish have single-circulation and two-chambered heart. Blood passes through heart once per cycle. Humans have double-circulation and four-chambered heart. Blood passes through heart twice per cycle. Advantages Of Double Circulation: • Oxygenated and deoxygenated blood remain separated. • Cells supplied with blood faster and more frequently. Left ventricle has thicker wall to sustain very large pressure. Arteries: Thick wall, narrow lumen, high pressure from heart. Veins: Thin wall, large lumen, low pressure to heart, valves. Capillaries: Low pressure supply of blood within tissues. Coronary Heart Disease: • Build-up of plaque from cholesterol blocking arteries. • Caused to lack of exercise, poor diet, stress, genetics. Heart rate remains high after physical activity to pay off oxygen debt and ensure muscles still receive extra oxygen. Blood Clotting: (To Prevent Blood Loss): • Involves platelets. • Fibrinogen converted to fibrin. • Forms a mesh / barrier (prevents pathogen entry). CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 10: Diseases & Immunity: Pathogens: • Disease-causing organism. • Caused directly by blood and other body fluids. • Caused indirectly by contaminated surfaces, particles in air, in food. • Control spread by hygienic food preparation, good personal hygiene, clean water supply. • Gives active immunity after infection. Describe How Vaccines Work: [6] • Weakened, dead or attenuated pathogens injected into body. • Immune response triggered. • Lymphocytes secrete antibodies which are specific and complementary to antigen. • Antibody binds to antigen, clumps up pathogens and marks for phagocytosis. • Active immunity attained after memory cells created. • In case of infection with same pathogen, antibodies produced quicker. Describe The Effect Of Cholera Bacterium On The Gut: [4] • Cholera bacterium produces toxin which causes secretion of chloride ions into gut. • Water potential of gut decreased, great osmotic movement of water from cells into gut. • Diarrhea, dehydration, loss of salts and ions from blood. Potential death if untreated. • Oral rehydration therapy, drinking solutions of water and mineral ions, salts. Unit 11 AND Unit 12: Gas Exchange & Respiration: Process Of Inspiration: • Diaphragm contracts. • External intercostal muscles contract, internal intercostal muscles relax. • Ribs move up and out. Volume of thorax increases, pressure decreases. • Air moves into the lungs to equalize pressure. Cartilage in trachea prevents collapse. Outline How Oxygen Debt Is Removed: [3] • Breathing rate remains high after exercise to supply oxygen for aerobic respiration. • Faster heart rate allows lactic acid to diffuse into blood and transported to Liver. • Aerobic respiration of lactic acid in liver, broken down to CO2 and water. Adaptive Features Of Gas Exchange Surfaces: • Large surface area to allow quicker diffusion of gases. • Thin walls to ensure short diffusion distances. • Good air ventilation to maintain concentration gradients. • Good blood supply to maintain high concentration gradient and more diffusion. Uses Of Energy In Living Organisms: • Active transport. • Passage of nerve impulses. • Protein synthesis. • Muscle contraction. • Homeostasis. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 13: Excretion: Kidneys regulate water content of blood and excrete toxic waste products of metabolism. Glomerulus: Filters blood of water, glucose, urea and ions. Forms ultrafiltrate. Nephron: Reabsorbs all glucose, most water and some ions to form urine (urea, excess water and ions). Deamination: Removal of nitrogen-containing part of amino acids to form urea, excreted because toxic. Unit 14: Coordination & Response: Describe The Events At Synapse: [4] • Impulse stimulates release of neurotransmitter molecules from vesicles into synaptic gap. • Neurotransmitter molecules diffuse across the synaptic gap. • Neurotransmitter molecules bind with receptor proteins on the next neurone. • Impulse is stimulated into next neurone. Nervous System & Reflexes: • Coordinates and regulates body functions, allows response to surroundings. • Reflex is an involuntary action that rapidly integrates coordinating stimuli with responses of effectors. • Reflex Arc: Sensory Neurone → Relay Neurone → Motor Neurone → Effector (gland or muscles). Functions Of Parts Of Eye: • Cornea refracts light. • Iris controls how much light enters pupil. • Lens focuses Light on retina. • Retina contains light receptors. Bright Light: Circular muscles contract, radial muscles relax. (Pupil becomes smaller). Far Object: Ciliary muscles relax, suspensory ligaments tighten, lens is thinner so less light is refracted. Hormone: Chemical substance produced by endocrine gland, carried in blood, alters activity of organs. Negative Feedback From Homeostasis (When Blood Glucose High): • Insulin secreted by pancreas, converts soluble glucose to insoluble glycogen. • Causes decrease in blood glucose (brings back to normal level). • Turned back to glucose after levels drop further, using glucagon also secreted from pancreas. Homeostasis: (When Feeling Hot): • Vasodilation of arterioles (wider), more blood supplied to capillaries to radiate more heat. • Sweat gland stimulated to secrete sweat, which evaporates, causes cooling effect. • Hairs lie flat against skin to allow free circulation. (Maintenance of constant internal environment). Auxin made in shoot tip, diffuses across stem, collects in one side to stimulate cell elongation to tropics. Type 1 Diabetes Treatment & Symptoms: • Insulin pumps / injections, healthy diet. • Constant monitoring of blood glucose. • Symptoms include weight loss, thirst, fatigue. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 15: Drugs: Drugs: Substance taken into body that modifies or affects chemical reactions in the body. Antibiotics: Work only on bacteria by destroying cell wall and metabolism. Viruses are non-living. Unit 16: Reproduction: Asexual Reproduction: Genetically identical offspring, very quick process, only 1 parent needed. Female Hormones: FSH released by pituitary gland, so egg matures. FSH stimulates ovaries to release oestrogen. Pituitary gland releases LH when oestrogen peaks. LH stimulates ovaries to cause ovulation. LH stimulates ovaries to produce progesterone. Sexual Reproduction: Genetically different, better ability to adapt to new changes in environment. Adaptations Of Reproductive Cells: Fertilization: Fusion of gametes male nuclei and female nuclei to form zygote to ball of cells to embryo. Placenta acts as a barrier to toxins, provides glucose, water and O2. Removes CO2 and urea. After pollination, pollen tube grows, fuses with ovum nucleus in fertilization. Seed grows within ovule. Amniotic Sac and Amniotic Fluid cushions fetus from bumps. Fluid made from plasma. Umbilical cord connects placenta to fetus. Substances diffuse across and has blood vessels to carry nutrients. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 17 AND Unit 18: Inheritance & Variation And Selection: Inheritance: Transmission of genetic information from generation to generation. Gene: Length of DNA that codes for a protein. Found on a chromosome. Allele: Alternative form of a gene. Chromosomes: Thread-like structures of DNA, carrying genetic information in form of genes. Father is responsible for determining sex of child as father passes on Y chromosome. (Males: XY) Describe The Process Of Protein Synthesis: [4] • Genetic information in DNA copied on to mRNA (transcription). • mRNA moves out of nucleus towards cytoplasm. • mRNA attaches to ribosomes. • Base sequences of DNA codes for sequences of amino acids to make protein (translation). Mitosis: Nuclear division, makes genetically identical diploid cells. Chromosomes copied before division. Meiosis: Reduction division, makes genetically different haploid cells (become diploid upon fertilization). Stem Cells: Unspecialized cells divide by mitosis to produce daughter cells that can become specialized. Heterozygous: Two different alleles of a particular gene. Codominance: Both alleles in heterozygous organism contribute to phenotype. Sex-Linked Characteristic: Gene responsible is located on sex chromosome, more common in one sex. Continuous Variation: Large number of phenotypes between two extremes. (Examples: Mass, Height). Discontinuous Variation: Limited phenotypes with no intermediates. Caused only by genes. Genetic Mutation: Random change in base sequence of DNA. Responsible for variation in populations. Adaptive Feature: Helps organism to survive and reproduce in its environment. Hydrophytes Xerophytes Large air spaces in leaves. Thick waxy cuticle. Small, shallow roots. Sunken stomata. Stomata on upper epidermis. Small, rolled leaves. Describe How Bacteria Become Resistant To Antibiotics And How To Manage The Problem: [5] • Bacteria become mutated (get resistive gene). • Mutation is change in base sequence of DNA. • Natural selection occurs; resistant bacteria survive and reproduce rapidly. • Bacteria that reproduce pass on resistive allele to more bacteria. • Only use antibiotics when essential, complete full course of prescribed antibiotics. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 19 AND Unit 20: Organisms And Their Environment & Human Influences On Ecosystems: Describe Why More Than Five Trophic Levels Cannot Be Sustained: [4] • Energy is lost as trophic levels increase, usually by 10%. • Not all energy is transferred, used in respiration, movement, nerve impulses, excretion. • Entire organism still containing energy is not consumed, so energy not passed on. • Majority of energy organisms receive is lost also as undigested waste and heating. Trophic Level: Position of organism in food chain or food web. Humans get more energy from eating crops than eating livestock because energy is lost in livestock. Population: • Group of organisms of same species. • Living in the same area at the same time. Community: All populations of different species in an ecosystem. Ecosystem: • Community of organisms and their environment. • Interacting with each other. Carbon Cycle: • Respiration, combustion of fuels release CO 2. • Photosynthesis takes in CO2 (trees as carbon stores). How To Conserve Endangered Species: • Monitoring and protecting habitats. • Education of people. • Captive breeding programmes. • Develop seed banks. Reasons Of Conservation Programmes: • Maintaining / increasing biodiversity. • Reducing extinction. • Protecting vulnerable ecosystems. How Forests Can Be Conserved: • Replanting trees and protected areas. • Education of people and quotas. How Fish Stocks Can Be Conserved: • Closed seasons and protected areas. • Controlled net type, mesh size. • Quotas and monitoring. Effects Of Deforestation: • Habitat loss and loss of soil. • Loss of biodiversity and extinction. • Increased CO2 in atmosphere. • Trees as carbon stores removed. • Areas more prone to flooding. Explain How Eutrophication Affects Marine Life: [6] • Leaching of fertilizers / nutrients from agriculture to river. • Nutrient enrichment causes algal bloom. • Blocked sunlight, aquatic producers cannot photosynthesize, die. • Bacterial decomposition increases, less oxygen in water. • Due to decreased oxygen, marine life dies. • Disrupts the food chain, loss of marine biodiversity. Explain How Bacteria Can Be Used In Biotechnology: [6] • DNA containing human gene is cut out using restriction enzymes. • DNA of bacterial plasmid is cut using same restriction enzyme. • Sticky ends are formed which are complementary to each other. • DNA of human gene inserted into the bacterial plasmid DNA. • New plasmid containing human gene is put back into bacterium. • Bacteria with human gene divides rapidly to make the protein. Why Bacteria Are Useful In Biotechnology: • Rapid reproduction rates. • No ethical concerns. • Can make complex molecules. • Contain plasmids. (Have same genetic code as other organisms). Effects Of Non-Biodegradable Plastics On Marine Ecosystems: • Animals can get stuck and die due to restricted movement. • Animals ingest toxic chemicals present in plastic. • Enters the food chain, causes bioaccumulation, biomagnification. • Disruption to food chain, extinction, loss of biodiversity. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series Unit 1: Characteristics & Classification Of Living Organisms: • Sensitivity: Ability to detect stimuli in environment and make appropriate responses. • Excretion: Removal of waste products of metabolism and toxic substances from the body. • Growth: Permanent increase in growth and dry mass by increase in cell number and cell size. • Species: Group of organisms that can reproduce to produce fertile offspring. • Prokaryotes: Unicellular. Have cell wall and cytoplasm but no nucleus and mitochondria. Unit 2: Organisation Of The Organism: • Magnification = Image Size ÷ Actual Size • Cell → Tissue → Organ → Organ System → Organism Unit 3: Movement Into & Out Of Cells: • Diffusion: Movement of particles from higher concentration to lower concentration. Down a concentration gradient as a result of their random movement. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series • Osmosis: Movement of water from higher concentration to lower concentration. Across semi-permeable membrane down concentration gradient. • Active Transport: Movement of ions from lower concentration to higher concentration. Against concentration gradient, requires energy from cells. Moves across cell membrane (notably in roots). • Water entering plant cell makes cell rigid and firm. • If cells don’t get enough water, cell becomes turgid and wilting occurs. Unit 4: Biological Molecules: • Composition Of Carbohydrates & Lipids: C, H, O. • Composition Of Proteins: C, H, O, N. • Test For Reducing Sugars: Benedicts Solution, turns from blue to brick-red. • Test For Protein: Biuret Solution, turns from blue to purple. • Test For Lipids: Ethanol, cloudy emulsion formed. • Test For Vitamin C: DCPIP, turns from blue to colourless. • DNA: Individual units called nucleotides. Two strands form a double helix. A-T and C-G. Unit 5: Enzymes: • Enzymes are made of proteins. Denatures after 37C. • Substrate and active site are complementary to each other. • If temperature exceeds 37C, active site changes shape and substrate cannot fit. Plants: (Units 6 & 8): • Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 • Chlorophyll more concentrated in palisade layer for absorption of sunlight. • Molecules like H2O, O2 and CO2 diffuse through air spaces in leaf. • Translocation of sucrose and amino acids done by Phloem. (Source To Sink). • Limiting Factors: Light intensity, humidity, temperature and carbon dioxide concentration. Humans (Units 7 & 9): • Emulsification: Increase in surface area of fats to allow quicker absorption. Done by bile. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series • Chemical Digestion: Done in stomach by HCl, pepsin. Starch digested in mouth by amylase. • Mechanical Digestion: Teeth in mouth tear and grind food to provide large surface area. • Villi: Have microvilli, thin walls with large surface area to allow for quicker and absorption. • Advantages Of Double Circulation: Oxygenated and deoxygenated blood remain separated. Ensure body always has supply of oxygen. • The left ventricle contracts to send oxygenated blood through the left atrium to the aorta. • Arteries are thicker than veins to withstand the intense pressure required to pump blood. Unit 10: Diseases & Immunity: • Active immunity produces memory cells, long term immunity. • Antibodies are complimentary to antigens on the pathogens. • Phagocytes engulf pathogens by the process of phagocytosis. • Direct Contact: Transfer of body fluids. • Indirect Contact: Respiratory droplets in air, contaminated surfaces. Unit 11 & 12: Gas Exchange & Respiration: • Alveoli: Large surface area, moist, surrounded by network of capillaries. • Capillaries have very thin walls (1 cell thick) to allow for quicker diffusion of gases. • C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP • Breathing rate remains high after exercise because: Oxygen debt needs to be repaid. Done by aerobic respiration in liver. Lactic acid broken down to H2O. Unit 13: Excretion: • Filters in kidney allow small substances to pass through but larger molecules are blocked. • Deamination: Removal of nitrogen-containing part of amino acids to form urea. Done in Liver. Unit 14: Coordination & Response: • Reflex: Involuntary action, very quick response. • Neurons conduct electrical impulses to brain, very long cells. CAIE IGCSE Biology Revision Sheet – May June 2023 Examination Series • Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector • Synaptic gap between neurons allows neurotransmitters to diffuse and attach to receptors. • Hormone: Substance secreted by an endocrine gland to alter the activity of the target organs. • Cornea allows for light to be refracted onto the retina, protects the eye. • Nearby Object: Pupil becomes smaller, circular muscle contracts, radial muscles relax. • Gravitropism makes shoot move upwards and roots move downwards. COMMON [3] Marks To [6] Marks Questions: 1 Describe the stages of genetic engineering. • • • • • • The DNA containing human gene is cut out using restriction enzymes. The DNA of bacterial plasmid is cut open using the same restriction enzyme. Sticky ends are formed which are complementary to each other. DNA of human gene inserted into the bacterial plasmid DNA. New plasmid containing human gene is put back into bacterium. The bacteria with human gene divides rapidly make the human protein.
