Biology IGCSE Definitions

• Movement:

  • An action by an organism or part of an organism causing a change of position or place
• Respiration:

  • The chemical reactions in cells that break down nutrient molecules and release energy for metabolism
• Sensitivity:

  • The ability to detect and respond to changes in the internal or external environment
• Growth:

  • Permanent increase in size and dry mass
• Reproduction:

  • The processes that make more of the same kind of organism
• Excretion:

  • The removal of the waste products of metabolism and substances in excess of requirements
• Nutrition:

  • The taking in of materials for energy, growth, and development
• Species:

  • A group of organisms that can reproduce to produce fertile offspring
• Binomial System of Naming Species:

  • An internationally agreed system in which the scientific name of an organism is made up of two parts, showing the genus and species
• Organization of the organism:

  • Cell: Basic functional and structural units in a living organism
  • Tissue: Group of cells with similar structures that work together to perform a specific function
  • Organ: Different tissues working together to perform specific functions
  • Organ System: Group of organs with related functions, working together to perform body functions
  • Organism: Various organ systems together make up the entire body of an organism
• Movement into and out of cells:

  • Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration
  • Osmosis: The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
  • Active Transport: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, using energy from respiration
• Enzymes:

  • Catalyst: A substance that increases the rate of a chemical reaction and is not changed by the reaction
  • Enzymes: Proteins that are involved in all metabolic reactions, where they function as biological catalysts
• Plant Nutrition:

  • Photosynthesis: The process by which plants synthesize carbohydrates from raw materials using energy from light
• Human Nutrition:

  • Balanced Diet: A substance that increases the rate of a chemical reaction and is not changed by the reaction
  • Physical Digestion: The breakdown of food into smaller pieces without chemical change to the food molecules
  • Chemical Digestion: The breakdown of large insoluble molecules into small soluble molecules
• Transport in Plants:

  • Transpiration: The loss of water vapor from leaves
  • Translocation: The movement of sucrose and amino acids in phloem from sources to sinks
  • Sources: Parts of plants that release sucrose or amino acids
  • Sinks: Parts of plants that use or store sucrose or amino acids
• Transport in Animals:

  • Circulatory System: System of blood vessels with a pump and valves to ensure one-way flow of blood
  • Clotting: Conversion of soluble fibrinogen to insoluble fibrin to form a mesh
• Diseases and Immunity:

  • Pathogen: Disease-causing organism
  • Transmissible Disease: Disease in which the pathogen can be passed from one host to another
  • Active Immunity: Defense against a pathogen by antibody production in the body
  • Antibodies: Proteins that bind to antigens, leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes
  • Cholera: Disease caused by a bacterium which is transmitted in contaminated water
• Respiration:

  • Aerobic Respiration: Chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
  • Anaerobic Respiration: Chemical reactions in cells that break down nutrient molecules to release energy without using oxygen
• Excretion:

  • Deamination: The removal of the nitrogen-containing part of amino acids to form urea
• • Gravitropism: A response in which parts of a plant grow towards or away from gravity
  • Phototropism: A response in which parts of a plant grow towards or away from the direction of the light source
• Coordination and Response:

  • Reflex Action: A means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)
  • Synapse: Junction between two neurons
  • Sense Organs: Groups of receptor cells responding to specific stimuli: light, sound, touch, temperature, and chemicals
  • Hormone: Chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
  • Homeostasis: The maintenance of a constant internal environment
• Drugs:

  • Drug: Any substance taken into the body that modifies or affects chemical reactions in the body
• • Cross-pollination: The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
  • Sexually Transmitted Infection (STI): An infection that is transmitted through sexual contact
• Reproduction:

  • Asexual Reproduction: The process resulting in the production of genetically identical offspring from one parent
  • Sexual Reproduction: The process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other
  • Fertilization: The fusion of the nuclei of gametes
  • Pollination: The transfer of pollen grains from an anther to a stigma
  • Self-pollination: The transfer of pollen grains from an anther of a flower to a stigma on the same flower or a different flower in the same plant
• Inheritance:

  • Gene: Length of DNA that codes for a protein
  • Allele: An alternative form of a gene
  • Haploid Nucleus: Nucleus containing a single set of chromosomes
  • Diploid Nucleus: There is a pair of each type of chromosome and in a human diploid cell, there are 23 pairs
  • Mitosis: Nuclear division giving rise to genetically identical cells
  • Stem Cells: Unspecialized cells that divide by mitosis to produce daughter cells that can become specialized for specific functions
• • Meiosis: Reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
  • Inheritance: The transmission of genetic information from generation to generation
  • Genotype: The genetic make-up of an organism and in terms of the alleles present
  • Phenotype: The observable features of an organism
  • Homozygous: Having two identical alleles of a particular gene
  • Heterozygous: Having two different alleles of a particular gene
  • Dominant Allele: An allele that is expressed if it is present in the genotype
• • Recessive Allele: An allele that is only expressed when there is no dominant allele of the gene present in the genotype
  • Codominance: Situation in which both alleles in heterozygous organisms contribute to the phenotype
  • Sex-linked characteristic: Feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other
• Variation and Selection:

  • Variation: Differences between individuals of the same species
  • Mutation: Genetic change (change in the structure of a gene or in the chromosome number)
  • Gene Mutation: Random change in the base sequence of DNA
  • Adaptive Feature: An inherited feature that helps an organism to survive and reproduce in its environment
  • Natural Selection: The process, resulting from natural selection, by which populations become more suited to their environment over many generations
• • Trophic Level: Position of an organism in a food chain, food web, or ecological pyramid: producers, primary consumers, secondary consumers, tertiary consumers, and quaternary consumers
  • Population: A group of organisms of one species, living in the same area, at the same time
  • Community: All of the populations of different species in an ecosystem
  • Ecosystem: A unit containing the community of organisms and their environment, interacting together
• Organisms and Their Environment:

  • Food Chain: Showing the transfer of energy from one organism to the next, beginning with a producer
  • Food Web: A network of interconnected food chains
  • Producer: An organism that makes its own organic nutrients, usually using energy from sunlight through photosynthesis
  • Consumer: An organism that gets its energy by feeding on other organisms
  • Herbivore: An animal that gets its energy by eating plants
  • Carnivore: An animal that gets its energy by eating other animals
  • Decomposer: An organism that gets its energy from dead or waste organic material
• Human Influences on Ecosystems:

  • Biodiversity: The number of different species that live in an area
  • Sustainable Resource: A resource which is produced as rapidly as it is removed from the environment so that it does not run out