biology module 3

• volume


  determines number of substances that need to be taken in and transported out
• surface area to volume ratio

  • organism inc in size vol inc bc there are more cells
• adaptions to surface area to volume ratio

  • large sa allows more of a substance to diffuse at the same time - prokaryotic organisms have enourmous SA:V so can meet cells energy requirements through diffusion that occours across the plasma membrane - eukaryotic cells are larger so have smaller SA:V so needs specialist organelles for repiration
• thin membrane adaption


  reduces diffusion distance
• transport systems 


  allow a higher concentration gradient to be maintained steeper concentration gradient increases rate of transport
• single celled organisms


  exchange directly with their external environment
• single celled organisms body surface exchange

  can exchange gases and other substances using their cell membrane, rate of gas exchange is increased by a larger surface area to volume ratio
• diffusion rate for single-celled organisms 


  rapid for single-celled organisms as substances only have to move across one cell surface membrane
• insects


  multicellular organisms that use gas exchange surfaces
• gas exchange surfaces


  parts of the body that are specialised for gas exchange
• tracheal system - insects

  • tracheal system consists of tracheoles that carry oxygen around the body - tracheoles branch into cells and contain tracheal fluid which gases can dissolve into
• what happens to tracheal fluid when the insect is more acitive

  tracheal fluid moves further into the tissue meaning gas exchange happens closer to respiring cells
• spiracles 


  openings along the thorax and abdomen gases diffuse through spiracles into the tracheoles gases also diffuse out
• fish


  multicellular organisms that use gas exchange surfaces
• gills


  filaments of thin tissue that are highly branched and folded the structure creates a large surface area for gas exchange gill filaments are highly folded into lamellae which are responible for the high surface area
• diffusion of oxygen in fish

  mouth opens water enters buccal cavity bc the buccal cavity inc in vol the opercula remain closed. when the mouth closes internal volume decreases and operculum open forcing water across the gills when water flows through he gills oxygen in the water diffuses quickly into the bloodstream
• why can oxygen diffuse from water into the bloodstream in water

  counter current system
• counter current system


  blood flows through the lamellae in the opposite direction of the flow of water through the gills the counter current system ensures there is always a steep concentration gradient between water and blood
• features of the gills

  counter current system, folding of gills by lamellae, large surface area, presence of an operculum
• mammalian gas exchange


  takes place in speciallised organs (lungs) which are speciallised for quick exchange of oxygen and carbon dioxide
• structure of mammalian gas exchange system

  structure of lungs is designed for efficient gas exchange air enters the body through the trachea and travels through a highly branched system where surface area is maximised for exchange of oxygen and carbon dioxide
• trachea 


  when you breathe in air flows through the trachea ridges of cartilage surround the front of the trachea to provide protection and structure no cartilage at the back of the trachea so that the oesophagus is not constricted
• bronchi

  trachea divides into two bronchi air flows along each bronchus to a lung bronchi are made from cartilage and smooth muscle
• bronchioles

  each bronchus divides into many smaller bronchioles many bronchioles branch into small air sacs called alveoli
• alveoli


  sacs that fill with air when you breathe in, oxygen in alveoli diffuses into the bloodstream and carbon dioxide in the bloodstream diffuses into the alveoli the alveoli provide a large surface area for gas exchange
• control of ventilation

  controlled by the ribcage, intercostal muscles, and the diaphragm, when you breathe in these structures allow lungs to fill with air
• capillaries alveoli


  each alveolus is surrounded by a network of capillaries, these provide a large surface area for gas exchange between alveoli and the bloodstrem
• alveolar epithelium

  • made up of a single layer of epithelial cells that walls the alveoli
  • the epithelium provides a short diffusion distance from the alveoli to the capillaries which maximises the rate of gas exchange
• concentration gradient

  • capillaries supply co2 to the alveoli and oxygen is rapidly carried away from the alveoli
  • the quick transport of gases in the bloodstream maintains a steep concentration gradient of oxygen and carbon dioxide
  • steep concentration gradient allows quick diffusion of gases into and out of the bloodstrem
• alveoli 


  air sacs - fill with air when you breathe in

  damage- smoking can damage alveoli smokers often have difficulty breathing

  numerous- millions of alveoli in the lungs that provide a large surface area for gas exchange

  capillaries - alveoli are surrounded by capilaries so oxygen can easily diffuse into the bloodstream
• breathing in

  muscle contraction, thoracic activity, lung pressure decreases, air flow
• inspiration

  • externam intercostal muscles contract
  • diaphragm contracts and moves down
  • energy is required to power the muscle contraction
  • volume of the thoracic cavity increases
  • this causes pressure in lungs to decrease
  • pressure gradient between outside of the lungs and inside of lungs is created
  • air flows inside the lungs down the pressure gradient
  • air flows down the trachea into the alveoli
• breathing out

  • muscle relaxation
  • thoracic cavity
  • lung pressure increases
  • air flow
• expiration

  • external intercostal muscles relax
  • internal intercostal muscles contract
  • diaphragm relaxes and moves up
  • volume of thoracic cavity decreases
  • this causes pressure in the lungs to increase
  • pressure gradient between outside of the lungs and inside of the lungs is created
  • air flows out of the lungs down the pressure gradient
  • air flows out of the alveoli and up the trachea
• measuring lung function

  using a spirometer measuting gas exchange allows doctors to identify problems in lungs
• spirometer


  peice of apparatus that measures gas exchange in the lungs measures the volume of air that is inspired and expired by an individual

  an individual breathes into and out of a spirometer to measure lung function
• tidal volume

  volume of air in a normal breath at rest

  average 0.4dm^3-0.5^3
• breathing rate

  number of breaths a person takes per minute at rest

  average is about 15 breaths per minute
• forced expiratory volume

  • maximum volume an individual can expire in one second
  • cannot be more than the total volume of gas in the lungs
  • always a small amount of air that cannot be respired this residual air ensure alveoli do not close
• vital capacity

  maximum volume of air that can be breathed in and out of the lungs