Topic 2 - Organisation

• Cells


  The basic building blocks that make up all living organisms
• Specialised cells carry out a particular function
• Differentiation

  The process by which cells become specialised for a particular job
• Differentiation occurs during the development of a multicellular organism
• Formation of organ systems

  1. Cells form tissues

  2. Tissues form organs

  3. Organs form organ systems
• Large multicellular organisms

  • Have different systems inside them for exchanging and transporting materials
• Tissue

  A group of similar cells that work together to carry out a particular function
• A tissue can include more than one type of cell
• Examples of tissues in mammals (like humans)

  • Muscular tissue
  • Glandular tissue
  • Epithelial tissue
• Muscular tissue

  • Contracts (shortens) to move whatever it's attached to
• Glandular tissue


  • Makes and secretes chemicals like enzymes and hormones
• Epithelial tissue


  • Covers some parts of the body, e.g. the inside of the gut
• Organ

  A structure made up of different tissues that work together to perform a specific function
• Organ system

  A group of organs working together to perform a particular function
• Organ system

  • Digestive system
• Digestive system

  • Breaks down and absorbs food
  • Made up of glands, stomach, small intestine, liver, large intestine
• Digestive system function

  1. Glands produce digestive juices

  2. Stomach and small intestine digest food

  3. Liver produces bile

  4. Small intestine absorbs soluble food molecules

  5. Large intestine absorbs water from undigested food, leaving faeces
• Organ systems work together to make entire organisms
• Enzymes

  Catalysts produced by living things
• Living things have thousands of different chemical reactions going on inside them all the time
• These reactions need to be carefully controlled to get the right amounts of substances
• Raising the temperature

  Speeds up the useful reactions but also the unwanted ones
• There's a limit to how far you can raise the temperature inside a living creature before its cells start getting damaged
• Enzymes

  Biological catalysts that reduce the need for high temperatures and only speed up the useful chemical reactions in the body
• Catalyst

  A substance which increases the speed of a reaction, without being changed or used up in the reaction
• Enzymes

  • They are all large proteins and all proteins are made up of chains of amino acids
  • These chains are folded into unique shapes, which enzymes need to do their jobs
• Enzymes have special shapes so they can catalyse reactions
• Chemical reactions usually involve things either being split apart or joined together

  Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction

  Enzymes are really picky - they usually only catalyse one specific reaction

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