organisms interaction with the environment

• nervous system


  enables humans to react to their surroundings and to coordinate their behaviour
• information from the receptors passes along cells (neurones) as impulses to the central nervous system (cns) cns is the brain and spinal cord brain coordinates the responds
• reflex actions


  automatic and rapid. often involve sensory, relay and motor neurones
• simple reflex action process

  • impulses from a receptor pass along a sensory neuron to cns
  • at a junctions (synapse) between a sensory neutron and a relay neurone in the cns a chemical is released that causes an impulse to be sent along a relay neurone
  • a chemical is then release at the synapse between a relay neurone and motor neurone in the cns causing impulses to be sent along a motor neurone to the effector
  • the effector is either a muscle or a gland
  • muscle - contracts
  • glands - secreting chemical substances
• stimulus -> receptor -> coordinator -> effector -> response
• automatic control systems in the body keep conditions inside the body relatively constant
• control systems:


  • cells called receptors - detect stimuli
  • coordination centres that receive and process information from receptors
  • effectors - bring about responses
• receptors found in:


  • eyes - light
  • ears - sound and changes in position
  • tongue and nose - sensitive to chemicals
  • skin - touch, pressure, pain, temperature
  • brain - blood temperature and concentration of water in blood
  • pancreas - concentration of glucose in the blood
• coordination centres include the brain and spinal cord and the pancreas
• internal conditions controlled:


  • temperature
  • water content
  • ion content
  • blood glucose levels
• water leaves the body via lungs (breathing) and skin (sweat). excess water is removed via kidneys (urine)
• urea and ions are lost via the skin (sweat). excess ions are removed via the kidneys (urine)
• liver


  • excess amino acids are deaminated to form ammonia, which is converted into urea for excretion
  • poisonous substances are detoxified and the breakdown products are excreted in the urine via the kidneys
  • old blood cells are broken down and the iron is stored
• healthy kidney


  • blood is filtered
  • all the glucose is reabsorbed
  • the dissolved ions needed by the body are reabsorbed
  • as much water as the body needs is reabsorbed
  • urea, excess ions and excess water is released as urine
• if the water content of the blood is too low the pituitary gland released hormone called ADH into the blood. this causes the kidneys to reabsorb more water and results in a more concentrated urine
• if the water content of the blood is too high less ADH is released into the blood. less water is reabsorbed in the kidneys resulting in a more dilute urine
• the production of ADH is controlled by a negative feedback mechanism
• body temperature is monitored and controlled by the thermoregulatory centre in the brain. it has receptors sensitive to the temperature of the blood flowing through the brain
• temperature receptors in the skin send impulses to the thermoregulatory centre giving information about skin temperature
• if core body temp too high:

  • blood vessels supplying skin capillaries dilate so that more blood flows through the capillaries and more energy is transferred from the skin to the environment
  • sweat glands release more sweat which cools the body as the sweat evaportates
• sweating helps to cool the body. more water is lost when it is hot and more fluids has to be taken through drink or food to balance this loss
• if core body temp too low:

  • blood vessels supplying the skin capillaries constrict to reduce the flow of blood through the capillaries
  • muscles may shiver - their contractions needs respiration which transfers some energy to warm the body
• blood glucose concentration is monitored and controlled by the pancreas. much of the glucose is stored as glycogen in the liver and muscles. when these stores are full, excess glucose is stored as lipid
• if blood glucose levels are too high the pancreas produces the hormone insulin which allows the glucose the move from the blood into the cells
• when blood glucose levels fall the pancreas produces a second hormone glucagon. this causes glycogen to be converted into glucose and released into the blood
• type 1 diabetes


  a persons blood glucose level may be too high because the pancreas does not produce enough insulin

  controlled - careful diet, exercise, injecting insulin
• type 2 diabetes


  the body does not respond to its own insulin. obesity is a significant factor in the development.

  controlled - careful diet, exercise, drugs that help the cells to respond to insulin
• animals different mating strategies:

  • mate for life
  • several mates over a life time
  • a mate for a breeding season
  • several mates over one breeding season
• some animals have developed special behaviours for rearing their young, parental care can be a successful evolutionary strategy, including:

  • increased chance of survival of offspring
  • increased chance of parental genes being passed on by the offspring
• different behaviours in animals:

  • innate behaviour
  • imprinting
  • habituation
  • classic conditioning
  • operant conditioning
• use of animals when conditioned:

  • sniffer dogs
  • police horses
• animals use variety of types of signals to communicate
• microorganisms that cause infectious disease are called pathogens
• bacteria and viruses may reproduce rapidly inside the body. bacteria may produce poisons (toxins) that make us feel ill. viruses live and reproduce inside cells, causing damage
• white blood cells defend against pathogens:

  • ingesting pathogens (phagocytosis)
  • producing antibodies, which destroy particular bacteria or viruses
  • producing antitoxins which counteract the toxins released by the pathogens
• the immune system of the body produces specific antibodies to kill a particular pathogen.

  this leads to immunity from that pathogen. in some cases, dead or inactive pathogens stimulate antibody production (vaccines).

  if a large proportion of the population is immune to a pathogen the spread of the pathogen is very much reduced
• people can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination).

  vaccines stimulate the white blood cells to produce antibodies that destroy the pathogen. this makes the person immune to future infections by the microorganism, because the body can respond by rapidly making the correct antibody in the same way as if the person had previously had the disease
• the mmr vaccine is used to protect children against measles, mumps and rubella
• antibiotics


  eg. penicillin

  they are medicines that help to cure bacterial disease by killing infective bacteria inside the body. it is important that specific bacteria should be treated by specific antibiotics.

  the use of antibiotics has greatly reduced deaths from infectious bacterial diseases
• antibiotics cannot kill viral pathogens (viruses)