Skin Breathers

Skin Breathers - Earthworms  What happens when it rains?

 These animals use their skin as their gas exchange organ.

 To maintain a moist surface area they secret mucus. If they dry out they will suffocate.

  What happens when it is dry?

Where did we find them? (our soapy water investigation)

Skin Breathers  Gases such as oxygen and carbon dioxide can only diffuse about 1 mm into an organism. That puts a limit to how big an organism can get.

 Worms are clearly bigger than that. How have worms managed to grow to such sizes?

Skin Breathers   How have earthworms managed to obtain:    A large surface area?

A thin membrane?

A moist surface area?

How is the earthworms' gas exchange system suited to their way of life?

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What about those critters living in water?

Segmented worms found in marine environments  Class Polychaeta. = "many bristles.“  The bristles are filled with blood vessels.They increase the worm's surface area for gas exchange.  The circulatory systems of many polychaetes contain haemoglobin … allows the worms to live in stagnant mud where food is plentiful but oxygen is scarce.

Diffusion across a membrane  Hydra   Animals with central cavity filled with water.

Their bodies are only two cell layers thick

Diffusion across a membrane Simple animals that lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans, which are the most efficient for gas exchange. However, these simple animals are rather small in size.

Single celled organism  Single celled organisms exchange gases directly across their cell membrane. However, the slow diffusion rate of oxygen and carbon dioxide limits the size of single-celled organisms.

Biozone p190