exchange surfaces

• Adaptations for substance exchange

  • Single-celled organisms have large surface area to volume ratio
  • Multicellular organisms have small surface area to volume ratio, so need specialised organ systems and cells to allow enough molecules in and out.
  • large SA:V ratio allowing more of one substance to diffuse at once.
  • Thin membrane, shorter diffusion distance.
  • Good blood supply to maintain concentration gradients of oxygen and carbon dioxide.
  • Moist surfaces for gases to dissolve in to form a solution to pass through thecell membrane
• Multi-cellular organisms (plants and mammals)

  • Very small surface area to volume ratios, their surface area is small in comparison to their volume and distance between the surface and centre of the organism is large.
  • Meaning, they require highly adapted exchange surfaces and transport systems to provide the cells with everything they require.
• Single-celled organisms (like bacteria)

  • Have a very large surface area to volume ratios, their outer surface area is large in comparison to its volume.
  • Don't have to travel far to get where they need to be within the cell and simple methods of diffusion, osmosis and active transport are sufficient to keep the cell alive.
• Small Intestine:

  The small intestine is adapted for efficient absorption of food into the blood stream.

  • It is lined with lots of of finger-like projections (villi) which increase the surface area of the small intestine walls and therefore provide quick absorption.
  • Each villus has a single layer of surface cells and a vast network of capillaries which means molecules from the small intestine have a short diffusion distance into the blood and the concentration gradient is constantly maintained.

  
• • Large organisms rely on specialised exchange surfaces to supply all of their cells with the required substances and remove waste products.
  • They typically have large surface areas, a short diffusion path and methods to maintain a concentration gradient. 
• The structure of the gills allows for efficient exchange:

  • Each gill has many thin gill filaments which are covered in lamellae which provides a large surface area.
  • Lamellae have excellent blood supply and a thin layer of surface cells, short diffusion distance.
  • Blood flows in the opposite direction to the water so a large concentration gradient is maintained and maximum oxygen is absorbed from water.
• Fish have gills that allow them to carry out gas exchange while in water.

  The water flows in through the fishes mouth and over the gills where oxygen diffuses into the blood from the water and carbon dioxide does the reverse. 

  
• Lungs: responsible for taking in oxygen from the air so it can be carried by the blood to cells that require it for aerobic respiration. They also remove carbon dioxide from the blood and send it back out into the air.

  They have lots of tiny air sacs called alveoli which allow for efficient gas exchange.

  • Many alveoli provide a massive surface area for the exchange of gases.
  • They have a moist lining for dissolving gases.
  • They have very thin walls so a short diffusion distance.
  • capillaries provide a good blood supply to maintain the concentration gradient.

  
• Root hair cells: adapted for efficient absorption of water and mineral ions from the soil, necessary for survival.

  • The root hair structures provide a large surface area.
  • The vacuole full of concentrated cell sap creates a steep water potential gradient.
  • They contain lots of mitochondria for the active transport of mineral ions.

  
• Underside of the leaf

  • Covered in tiny holes called stomata
  • Allow for carbon dioxide to enter and oxygen and water vapor to be expelled from the leaf, down concentration gradients
  • Stomata are controlled by guard cells that can close the stomata when the plant is losing more water than it is receiving, to prevent wilting
• Cell walls (inside the leaf)

  • CO₂ diffuses into cells for photosynthesis
  • Oxygen and water vapour diffuse out
  • Air spaces surrounding the leaf cells increase the area in which this gas exchange can take place
• Leaves are structured in a way that allows oxygen and water vapor to diffuse out of the cells and carbon dioxide to diffuse into the cells.