Exchange surfaces & substances

• What effects how easily stuff moves between an organism and its environment?

  Surface area to volume ratio
• Why does diffusion occur?

  Cells take in substances they need and get rid of waste products
• Why do multicellular organisms need exchange surfaces?

  Their surface area is small compared to their volume
• Give 4 ways exchange surfaces are adapted

  *Thin membrane

  *Large surface area

  *Lots of blood vessels (in animals)

  *Ventilated
• As living organisms get larger and more complex, their surface area to volume ratio _________

  Decreases
• What does a decrease in surface area to volume ratio make it more difficult to do?


  Exchange of important substances
• Why can larger organisms no longer rely on diffusion of oxygen?

  As it will not reach cells deep within the body
• What are there in larger organisms to aid the exchange of substances?

  Surfaces adapted to effective exchange
• Where are exchange surfaces found?

  In plants and animals
• What are the features that maximise the effectiveness of an exchange surface?

  *Large surface area

  *Thin

  *Good blood supply

  *Ventilated
• How does a thin exchange surface increase the rate at which materials are exchanged?

  It means there is less distance for the substance to travel through the surface
• What are the effects of poor diffusion in an organism?

  Gases and food molecules cannot reach every single cell by simple diffusion and metabolic waste cannot be removed fast enough to avoid cell poisoning
• Where are the lungs located?

  The thorax
• What is the job of the lungs?

  To transfer oxygen to the blood and to remove waste carbon dioxide
• What system do the lungs make up part of?

  The respiratory system
• What does the lung contain as an exchange surface?

  Alveoli
• What are the alveoli rich in?

  Blood supply
• What does an exchange surface rich in blood supply mean?

  The rate of diffusion will be maximised
• How are alveoli adapted for gas exchange?

  • large surface area

  • good blood supply

  • thin - short diffusion pathway

  • moist - dissolve gases
• What are villi?


  Small finger-like structures that increase the surface area of the intestinal wall
• How are villi adapted?


  Single layer of surface cells

  Good blood supply
• How are leaves structured to assist gas exchange?

  *The underneath of the leaf is an exchange surface, it is covered in little holes called stomata which the carbon dioxide diffuses in through.

  *Flattened shape of the leaf increases the area of exchange surface so that it is more effective

  *The air spaces inside the leaf increase the area of this surface so there's more chance for CO2 to get into the cells.
• What are the roles of stomata?

  CO2 diffuses through, water vapour diffuses out
• What is an exchange surface of a fish?

  Gills
• What are gills made up of?

  Gill filaments which are stacked up in a pile
• What are gill filaments covered in?

  Lamellae, which increase surface area
• How do gills work in a fish?

  Water containing oxygen enters and passes through gills

  Oxygen diffuses from the water into the blood

  Carbon dioxide diffuses from the blood to the water
• how are lamallae adapted for gas exchange?

  Lots of blood capillaries

  Thin surface area
• Where does gas exchange occur in the lungs?

  Across the alveoli
• Where does an exchange of substance occur in the small intestine?

  Across the villi
• Whats one adaptation of alveoli for diffusion?

  One cell thick thus short diffusion path
• What structure allows diffusion in plant leaves?

  Stomata
• Give one unique adaptation of villi

  Folds in the cell membrane called microvilli increase surface area
• What is the size of stomata controlled by?

  Guard cells which surround them
• Give an adaptation of leaves for diffusion

  Air spaces increase surface area
• What maintains a high concentration gradient in lamellae?

  Water and blood flow in opposite directions
• How are roots adapted to exchange materials via diffusion?

  Large surface area and large permanent vacuole which increases the concentration gradient