Gas Exchange - Amoeba, Flatworms and Earthworms
Amoeba
Flatworms
Earthworms
Unicellular organisms allow for large SA:V ratio
general characteristics
3 cell layers
Outer - Ectoderm
Middle - Mesoderm
Inner - Endoderm
bilaterally symmetrical - left and right side of body are mirror images
flattened dorsoventrally
distinctive head and tail
aquatic organism
Gas exchange system
lacks a special circulatory or gas exchange system
Flat body provides
Large surface area
Small diffusion distance
easy gas exchange by diffusion across body walls directly to the cells and tissues
Limitations to body adaptation
large surface area for gas exchange means large surface area for desiccation (drying)
found only in moist areas
parasites - tapeworm and liver flukes
Non-parasites - freshwater and marine ecosystems, less often in moist soil
Gas exchange surface
uses the cell wall as a gas exchange surface
diffusion can occur through a membrane if it is:
thin
moist
permeable
short diffusion pathway
Structure of Amoeba
there is a higher concentration of oxygen in water than in the ameoba
Multicellular, terrestrial animals restricted to damp areas
Cylindrical, segmented body with no specialised respiratory organs
Take in oxygen and expel carbon dioxide directly through their skin = gas exchange surface
Oxygen diffuses through the earthworm's body surface by dissolving in the moisture on the surface and diffuses inward to the network of capillaries just under the surface
too large for diffusion through body alone
body adaption
Slow moving and low metabolic rate - low oxygen requirement
Haemoglobin present in blood carries oxygen around the body in blood vessels
Carrying oxygen from the boy surface maintains a diffusion gradient at the respiratory surface (the skin)
Carbon dioxide is also carries in the blood and diffuses out through the skin
they need to keep their skin moist to absorb oxygen and give off carbon dioxide
epithelial cells produce slimy mucus to keep moist and trap and dissolve oxygen in the air
behaviour - in dry weather the earthworm will burrow deeper into the ground to stop skin from drying out (+death)