5.1.1

• all living things need :

  • a suitable temperature
  • a suitable pH
  • an aqueous environment that keeps substrates + products in solution
  • freedom from toxins + excess inhibitors

  → without these the cells become inactive + die as cells are specialised + rely on each other they must be able to communicate in order to coordinate their activities
• The threat from changing environments

  Changing external environments

  could place stress on living organisms

  • if the organism is to remain active + survive , the change in environment must be monitored + the organism must change its behaviour or physiology to reduce stress, environmental change affects its response
  • environment may change slowly in seasons pass - these changes elicit a gradual response
  • environment may change quicker
• Changing internal environments

  Many cells and tissues are not exposed to the external environment - they are protected by epithelial tissues such as skin or bark

  • animals the internal cells and tissues are bathed in tissue fluid
  • as cells undergo metabolic reactions, they use up substrates + create new products

  → some may be unwanted or toxic so the substances move out of the cells into the tissue fluid + the activities of the cells alter their own environment
• Changing internal environments 2

  • Carbon dioxide is a waste product that, if allowed to build up in tissue fluid, lowers pH and can disrupt enzymes and proteins
  • Accumulated waste stimulates its own removal; for example, lower blood pH triggers increased breathing to expel carbon dioxide
  • Excess waste can also reduce cell activity, which may not be beneficial for the organism as a whole
• Maintaining internal environment

  compilation of tissue fluid is maintained by the blood

  • blood flows throughout the body + transports substances to and from the cells
  • any wastes or toxins accumulating in the tissue fluid are likely to enter the blood + be carried

  → in order to prevent their accumulation in the blood they must be removed from the body by excretion
• Maintaining internal environment 2

  • important to monitor closely concentration of waste products + other substances in blood

  → ensuring the body doesn’t excrete too much of useful substances but remove enough of waste products to maintain good health so cells in body are supplied with substrate they need
• A good communication system will :

  • cover the whole body enable cells to communicate with each other
  • enable specific communication
  • enable rapid communication
  • enable both long term + short term responses
• Cell Signalling

  neuronal system

  an interconnected network of neurones that signal to each other across synapse junctions

  • neurones can conduct a signal very quickly and enable rapid response to stimuli that might be changing quickly

  hormonal system

  a system that uses blood to transport its signals

  • cells in an endocrine organ release the signal (a hormone) directly from the blood

  →the hormone is transported throughout the body, but only recognised by specific target cell

  • enable long-term responses to be coordinated
• Cell Signalling

  hormonal system

  a system that uses blood to transport its signals

  • cells in an endocrine organ release the signal (a hormone) directly from the blood

  →the hormone is transported throughout the body, but only recognised by specific target cell

  • enable long-term responses to be coordinated