Biology

• Organisms


  Microscopic units known as cells
• Simplest organisms


  • Made from single cells
• Complex plants and animals

  • Composed of millions of cells
• Multicellular organisms


  • May have hundreds of different types of specialized cells
• Eight life processes


  • Require nutrition
  • Respire
  • Excrete
  • Respond to stimuli
  • Move
  • Control internal conditions
  • Reproduce
  • Grow and develop
• Cell structure


  Nucleus, cytoplasm, cell membrane
• Cells of bacteria


  • Simpler in structure than 'higher' organisms
• Cytoplasm


  The living material that makes up a cell, with a texture like sloppy jelly
• Nucleus


  The largest organelle, controls the activities of the cell and contains chromosomes with genetic material
• Ribosomes


  Tiny structures where proteins are assembled
• Enzymes


  Proteins that control the chemical reactions in the cytoplasm
• Cell membrane


  Surrounds the cell, partially and selectively permeable
• Mitochondria


  Organelles that carry out respiration and release energy
• Plant cells


  • Have a cell wall, permanent vacuole, and chloroplasts
• Cell wall


  Layer of non-living material made of cellulose, gives plant cells shape and support
• Vacuole


  Large central space in plant cells, filled with cell sap
• Chloroplasts


  Organelles in plant cells that contain chlorophyll and carry out photosynthesis
• Nearly all cells contain cytoplasm, a nucleus, a cell membrane and mitochondria. Plant cells also have a cell wall, permanent vacuole, and chloroplasts.
• Enzymes


  Biological catalysts that control the chemical reactions in a cell
• Catalyst


  A chemical that speeds up a reaction without being used up itself
• Cells contain hundreds of different enzymes, each catalysing a different reaction
• Genes


  Control the production of enzymes, which then catalyse reactions in the cytoplasm
• Enzymes are necessary because the temperatures inside organisms are low, and without catalysts most reactions would be too slow
• Metabolic reactions


  The chemical reactions taking place in a cell
• Metabolism


  The sum of all the metabolic reactions in a cell
• Extracellular enzymes


  Enzymes secreted onto food to break it down, outside cells
• Intracellular enzymes


  Enzymes that carry out their function inside cells
• Secretion


  The release of a fluid or substance from a cell or tissue
• Substrate


  The molecule that an enzyme acts on
• Active site


  The small area on an enzyme's surface where the substrate attaches
• Lock and key model

  The substrate fits into the active site of the enzyme like a key fitting into a lock
• Enzymes are specific, an enzyme will only catalyse one reaction
• Factors affecting enzymes


  • Concentration of enzyme or substrate, temperature, pH
• Optimum temperature


  The temperature at which the reaction takes place most rapidly
• Kinetic energy increases as the molecules of enzyme and substrate move faster
• Optimum pH


  The pH at which an enzyme works best, most are neutral but some are below or above pH 7
• Respiration


  1. Breakdown of food molecules to release stored chemical energy, using oxygen

  2. Produces carbon dioxide and water as waste

  3. Releases energy that is used to make ATP
• Respiration is an oxidation reaction, as oxygen is used to break down food molecules
• ATP


  The energy 'currency' of the cell, energy released from respiration is used to make ATP
• Each step in the respiration process is catalysed by a different enzyme