igcse biology definitions

• Diffusion


  Movement of particles from high to low concentration down the concentration gradient as a result of random motion
• Osmosis


  Movement of water from high to low water potential down the water potential gradient through a semipermeable membrane
• Active Transport


  Movement of substances from low to high concentration through a semipermeable membrane against a concentration gradient using energy from aerobic respiration
• Translocation


  Movement of sucrose and amino acids in the phloem from source to sink via active transport
• Enzyme


  Biological catalysts made out of proteins that increases rate of reaction while remaining unchanged at the end of reaction
• Transmissible Disease


  Disease where pathogens can be transferred from one host to another
• Species


  A group of organisms that can reproduce to make fertile offspring
• Pathogen


  Microorganisms that cause diseases
• Excretion


  Removal of waste products and excess material produced by metabolic processes from the body through excretory organs
• Sensitivity


  Ability to detect and respond to changes in the internal or external environment
• Drugs


  Any chemical substance consumed that alters/modifies chemical reactions in the body
• Hormone


  A chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Sexual reproduction


  Process where the nuclei of two gametes fuse to form a zygote (and the production of offspring that are genetically different)
• Fertilisation


  Fusing of nuclei from a male and female gamete
• Variation


  Difference between different individuals of a species
• Genetic Mutation


  Random change in base sequence of DNA
• Gene


  Length of DNA that codes for a protein
• Allele


  Alternate form of gene
• Organ


  A structure made up of groups of different tissues, working together to perform a specific function
• Sense organ


  A group of receptor cells that work together to detect and respond to specific stimuli
• Pollination


  Transfer of pollen grain from one plant to another from anther to stigma
• Deamination


  Removal of the nitrogen-containing part of amino acid to form urea and amino acids by the breakdown of amino acids by enzymes in liver
• Homeostasis


  Maintenance of constant internal environment
• Codominance


  When both alleles for a gene equally contribute to the phenotype
• Genotype


  Genetic makeup of an organism in terms of alleles
• Phenotype


  Observable features of an organism
• Species


  Group of organisms that have similar genetic coding with minimal variations and can reproduce to produce fertile offspring
• Population


  Group of animals of the same species living together in the same area at the same time
• Community


  Population of all species in an area
• Assimilation


  Absorption of nutrients for cell usage
• Limiting factor


  Factor that is not in excess
• Transpiration


  Loss of water vapour via evaporation on the surface mesophyll cells followed by diffusion of water vapour through the stomata
• Meiosis


  The nuclear division of cells to produce daughter cells with half the number of chromosomes, so haploid cell. The daughter cells are genetically different and are gametes
• Artificial Insemination.

  • Used when animal is reluctant to mate in captivity
  • Sperm samples are collected from the males
  • These samples are then artificially introduced into the female reproductive system.
  • These samples can also be frozen and stored for later use.
• In Vitro Fertilization

  • Females are given fertility drugs
  • Their ovaries releases multiple mature ova, collected by laparoscopy
  • Ova are mixed with the male seminal fluid in a petri dish/test tube, allowing some sperm to fuse with them
  • Fertilisation takes place outside the body/in petri dish or test tubes
  • The embryos are introduced into the female’s uterus by inserting a tube into the cervix
• Blood flow into the kidney

  1. Flows from renal artery with high blood pressure

  2. Branches into tiny coiled capillaries called glomeruli (glomerulus)
• Glomerulus


  • Acts as a filtration medium
  • Has microgaps and is one cell thick
  • Blood plasma is filtered into (H2O, glucose, urea, amino acids) except for blood cells and large proteins
• Filtrate collection


  Collected in the Bowman's capsule
• Reabsorption in proximal convoluted tubule (PCT)

  1. Responsible for reabsorption of most ions and water

  2. Located in the cortex (outer part) of the kidney

  3. Useful substances like glucose, amino acids and some water and ions are selectively reabsorbed back to the blood
• Selective reabsorption


  Due to the need of the body for these substances that have been filtered