Gas exchange

• features of specialised exchange surfaces

  • movement of the environmental medium- maintains concentration gradient
  • large surface area to volume ratio- increases rate of diffusion
  • thin- shortens diffusion pathway
  • selectively permeable- constant concentration gradient
  • movement of the internal movement- waste can be removed
• small, inactive organisms don't need specialised gas exchange surfaces because they have

  • larger surface area to volume ratio
  • lower metabolic rate
  • meet needs via diffusion
• Large organisms require a circulatory system to meet metabolic requirements

  • higher demand for nutrients
  • higher metabolic rate
  • mass transport creates a quicker route for transport
• gas exchange in single celled organism

  • large surface area to volume ratio
  • short diffusion pathway
  • lower metabolism- can maintain metabolism through simple diffusion
• Gas exchange in insects

  • to reduce water loss insects have a large surface area to volume ratio and a waterproof cuticle over their exoskeleton
• Parts of the insects exchange system

  • Waxy cuticle
  • Spiracle- maintains humidity and water gradient by opening and closing
  • trachea- lined with rings of chitin
  • tracheoles
  • muscle tissue
• Gas exchange in fish

  • fish need a large surface area to absorb oxygen because oxygen is not concentrated in water
  • gas exchange happens in the gills which are located behind the head
• What is the counter-current exchange system?

  water and blood flow in opposite directions to maintain a concentration gradient along the gills allowing for constant gas exchange
• Adaptations of lamella for gas exchange

  • rich blood supply- maintain concentration gradient
  • thin- short diffusion pathway
  • lots of gill filaments- large surface area to volume ratio
• Gas exchange in plants

  • surfaces of mesophyll in contact with air spaces
  • large surface area and a small diffusion distance
  • oxygen/carbon dioxide only travels a short distance to get to chloroplast
• Adaptations of terrestrial insects and plants in limiting water loss

  • small SA:VOL- gases can be exchanged via simple diffusion
  • waterproof covering- prevents water loss
  • spiracles- opens for gas exchange when closed water loss is limited
  • stomata in plants- work the same as spiracles
• How are xerophytes evolved to live in areas of short water supply to minimise water loss

  • extensive roots- maximise uptake
  • thick cuticle- stops uncontrollable evaporation
  • sunken stomata- maintains humid air around stomata
  • rolled leaves- maintains humid air
• Structure of the human gas exchange system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Trachea

  • flexible airway supported by cartilage
  • collapse slightly to allow food down throat
  • walls made from ciliated epithelial cells and goblet cells which produce mucus
• Bronchi

  • two divisions each leading to a lung
  • have goblet cells and ciliated epithelial cells and cartilage
• Bronchioles

  • branching subdivisions of the bronchi
  • walls made from smooth tissue
  • smooth tissue allows them to constrict so they can control the flow of air in and out of the alveoli
• Alveoli

  • mini air sacs at the end of the bronchioles
  • contain collagen and elastic fibres and are made from a single layer of flattened epithelial cells
  • elastic fibres allow them to stretch as they fill with air during inhalation
  • recoil during exhalation so that carbon dioxide rich air can be expelled
• mechanism of breathing

  Inspiration- air pressure inside the lungs is reduced, lowing atmospheric pressure so air moves into the lungs

  Expiration- air pressure inside the lungs is increased above atmospheric pressure so air moves out the lungs
• Inspiration

  • External intercostal muscles- contract
  • Internal intercostal muscles- relax
  • Diaphragm- contracts- flatterns
  • Thorax volume- increases
  • air pressure- reduces
  • result- air is forced in
• Expiration

  • external intercostal muscles- relax
  • internal intercostal muscles- contract
  • diaphragm- relax- domes
  • thorax volume- reduces
  • air pressure- increases
  • result- air is forced out
• pulmonary ventilation- volume of air moved into the lungs in one minute

  ventilation rate- number of breaths in a minute

  tidal volume- volume of air taken in at each breath when at rest

  TV X VR = PV
• Adaptations of the alveoli

  • selectively permeable- only allows certain molecules in
  • thin walls- maintain concentration gradient
  • pulmonary capillary is narrow so blood flow slows down meaning more time for diffusion