L1 - the need for communication

• why do cells need to communicate with each other:

  -most organisms are multicellular

  -made of many specialised cells

  -cells that need to interact may be far away from one another

  -environmental conditions change

  -stable internal environment must be maintained for cells to survive

  -enable the organism to survive
• distances over which cells need to communicate:

  -no distance (a cell targets a cell connected by gap junctions)

  -short distance (a cell targets a nearby cell)

  -long distance (a cell targets a distant cell through the bloodstream)
• cells need to communicate if the environment changes because cell metabolism relies on enzymes
• what conditions need to be maintained in cells:

  -temperature

  -pH

  -substrate concentration

  -enzyme concentration

  -concentration of cofactors and coenzymes
• what happens if cell conditions change drastically:

  -if these change drastically, enzyme action becomes inefficient, and cells may die. tertiary structure of active site is denatured, and the rate of enzyme reaction may be reduced or stopped
• changing internal and external conditions:

  -external environments and internal environments may change placing stress on an organism

  -to survive, an organism must change its behaviour or physiology to reduce the stress
• internal example of environment change; increased CO2:

  -during exercise or other activity, cell metabolism increases and produces more CO2

  -more CO2, dissolves in blood, forming carbonic acid which lowers blood pH slightly

  -receptors in the brain sense the drop in pH and send nerve signals to increase breathing rate

  -increased breathing rate quickly removes more CO2 from blood. blood pH rises slightly, returning to normal
• multicellular organisms have a range of tissues and organs, and most are not exposed to external environments but are rather bathed in tissue fluid - giving the cells an "extra" environment to interact with

  cells undergo many metabolic activities and use substrates and create products - altering the cells internal environment. the substances must interact with the tissue fluid and one such example is carbon dioxide
• features of a good communication system in a multicellular organism:

  -covers the whole of the body

  -allows specific communication between individual cells

  -allows general communication between all cells

  -enables rapid communication in emergency situations

  -enables both short term and long term responses

  -has cells that can detect information and other cells that respond and a coordination centre that enables a coordinated response
• stimulus:

  -any change in the environment
• response:

  -a change in the organism's physiology (the way it functions) or behaviour because of the stimulus

  -responding to a stimulus requires a method of monitoring changing stimulus levels
• cells communicate by cell signalling
• what is cell signalling:

  -1st cell releases a signal (chemical)

  -2nd cell detects the signal (this is the target cell), and creates a response
• communication systems:

  -neuronal system

  -hormonal system
• nervous system:

  -route message takes; along nerves

  -information speed; fast

  -length of response; short lived response

  -area of body affected; can be small area or widespread effects

  -similar to a telephone call
• hormonal system:

  -route message takes; in the bloodstream

  -information speed; slow

  -length of response; long lasting response

  -area of body affected; widespread effects

  -similar to the postal service
• situations caused by hormonal system:

  -high blood glucose levels

  -control of growth

  -puberty

  -dilation of cervix during labour
• situations caused by neuronal system:

  -the sensing of pain

  -the movement of muscle in response to pain

  -being able to see

  -shivering
• neuronal responses:

  -uses interconnected cells called neurones

  -contains synaptic junctions

  -signals are conducted very quickly

  -neurotransmitters are released

  -signals travel by diffusion

  -response is usually short term
• hormonal responses:

  -uses blood to transport signals

  -cells release signals directly into the blood

  -signal is carried all over the body

  -signal is recognised by target cells

  -response is usually long term