^8o How Living Things Affect One Another unit vii 



Exercises 



1. Give other examples of food chains. 



2. Demonstration. The frog and the butterfish are the victims of many 

 parasites. Examine hver, lungs, and intestinal canal of a freshly killed frog 

 or the teased out muscle of a butterfish for parasites. Describe what you 

 find. 



3. Denwnstratiofi. If green hydras are available they can be studied 

 under the microscope. What makes the hydra green? What kind of re- 

 lationship does this illustrate? 



4. Draw an oxygen and hydrogen cycle without consulting the book. 

 Or draw a different type of oxygen cycle. 



5. {a) Draw a circle and by writing words and drawing pictures on it 

 show how carbon may go from the air through the seeds of plants into 

 a bird, and back again into the air. This is called a carbon cycle, (b) Show 

 how carbon goes from the air into grass and into a pig where large 

 amounts are stored. 



6. (a) If you bought an old farm and the land was poor, what kinds of 

 crops would you plant first? (b) Explain how the same bacteria of decay 

 may be useful in one place and harmful in another. 



7. Suppose a sealed balanced aquarium contained green plants, a small 

 goldfish, a snail, decay bacteria, and nitrifying bacteria. Explain how the 

 aquarium might remain in balance for many months. Be sure to use the 

 carbon and oxygen cycle in your explanation. What might happen if 

 the aquarium were to be placed in light that was too dim? 



Further Activities in Biology 



1. Are bacteria more numerous in sand or in humus (the dark top soil)? 

 If you have Petri dishes, you can find out. 



2. Start and maintain a balanced aquarium. Turtox leaflets should be 

 of help. 



3. If you draw well you could make interesting and original charts to 

 illustrate the carbon, oxygen, and nitrogen cycles. 



4. If you live near a farming section, find out what the farmers are 

 doing to keep the necessary soil compounds from becoming exhausted. 



5. Read up and report about commercial, large-scale nitrogen fixation. 



6. Cut open and examine a nodule on a fresh leguminous plant. Use a 

 microscope. 



