SYMBIOSIS 



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en 



body of an insect, with the lower epidermis of a leaf show that living things breathe? 



being (22) in the body is passed into the air again as 



(23) (24), thus completing the cycle. 



i PROBLEM III. WHAT IS SYMBIOSIS AND HOW DOES IT DIFFER 

 FROM PARASITISM? 



Symbiosis. Plants and animals are seen in a general way to 

 i be of mutual advantage to each other. Some plants, called 

 i lichens, show this mutual partnership in the following interesting 

 way. A lichen is composed of two kinds of plants, one of which 

 at least may live alone, but the two plants have formed a partner- 

 j ship for life, and have divided the duties of such life between them. 

 In most lichens the alga, a green plant, forms starch and nourishes 

 the fungus. The fungus, in turn, produces spores, by means of 

 I which new lichens are started in life ; moreover, the alga is 

 > usually protected by the fungus, which is stronger in structure 

 \ than the green part of the combination. This process of living 

 together for mutual advantage is called symbiosis (sim-bi-o'sis). 

 Some animals also combine with plants ; for example, the hydra 

 I with certain of the one-celled algae. 

 Animals also frequently live in 

 i this relation to each other, the 

 tiny protozoans living in the diges- 

 tive tracts of the termites or white 

 ants. These little animals act as 

 digestive cells for the termites, 

 making it possible for them to 

 digest the wood fibers on which they live. In return these proto- 

 zoans are protected by their hosts. A somewhat similar situa- 



Algae and fungi in a lichen, 

 relationship. 



fungus 



Explain this 



