Gas Exchange - Insects and Amphibians
Insects
Amphibians
Circulatory system
water loss
most adult insects are terrestrial
water evaporates from their bodies - risk of dehydration
Water loss is reduced by rigid exoskeleton made of thisk waxy layer (waterproof epicuticle) over a thicker layer of chitin and protein (strong procuticle)
Insects have an insufficient, open circulatory system
Insect blood, called haemolymph, flows freely throughout the body with no blood vessels
Insects do not have blood circulation to carry oxygen
Spiracles
located on each segment of the abdomen
Gas exchange occurs hear
air entry/exit point of the tracheal system
can open so gas exchange can take place and close to reduce water loss
sometimes have hair covering spiracles to reduce water loss
Tracheal system
branch into smaller & smaller tubes = tracheoles
Tracheoles terminate on the plasma membrane of all cells in body
Air enters tracheae through spiracles and travels through the tracheoles to the fluid filled tips
here O2 dissolves in fluid and diffuses directly into the cell. CO2 diffuses into tracheoles
When active
Ventilation
fluid levels increase as O2 demand increases
Water moves by osmosis out of the tracheoles due to build up of lactic acid in cells
this exposes more surface area surface area of tracheoles for diffusion to occur
At rest
insects rely on diffusion through spiracles, tracheae and tracheoles for gas exchange
Air sacs are tiny sacs off the tracheae where they increase raspatory efficiency by providing a large surface area for gas exchange
when active
e.g. in flight insects forcibly ventilate by their tracheae by contracting and relaxing abdominal muscles to push air in and out
when very active - lactic acid accumulates in cells decreasing water potential - water in tracheoles is drawn into cells by osmosis so more air enters tracheoles
characteristics
frogs have smooth moist skin and long stripy legs - found in damp habitats
Toads have warty skin, golden eyes and prefer to crawl rather than hop. if threatened puff themselves up to appear bigger. found in dryer habitats
Amphibians have moist permeable skin
They have a well-developed capillary network just below the surface
Gas exchange takes place in the skin but also in lungs when active
