We speak of the balance of nature． Biologists talk about biotic pyramids and the web of life． Both are referring to the same phenomenon or existing fact : the many complex ( 复杂的）relationships among organisms and their environment or surroundings．

　　The pyramid is the biologist’s attempt and try to sketch and describe the energy relationships in nature． You could call it a catalogue or describing record of who eats whom． The land forms the base of the pyramid, and upon it rests a layer or covering or a thickness of plants． Insects such as ants and worms, and herbivores or plant-eating animals, then birds and rodents such as rats and mice, and finally, at the top of the pyramid, the large carnivores or flesh-eating animals, and predatory birds which hunt and eat other animals． Organisms at each level of the pyramid exist by eating those in the layers below, and so are dependent for their survival on the existence of the members of the lower layers．

　　From the base of the pyramid to the top, populations of organisms decrease． There are always, for example, fewer hawks than gophers, a kind of rats, their prey, and always fewer insects than the plants they eat． But most species of organisms exist on more than one kind of food;each organism forms only one link or ring in a chain of energy transfer or change． These pathways by which energy is cycled through organisms are called food chains． The relationships between organisms form a complex network through which energy from the soil is passed into living things and then, through death and decay or rotting, is returned to the soil． Some energy is always lost in the process or course, and is continually replaced or take the place of by energy from the air and sun through plants, during the process of photosynthesis． But in spite of these gains and losses, the total system does not change much unless interfered with, by man or if man is not in the way． This system is the web of life, a tangle of' food chains, so complicated that we do not yet understand all its workings．

　　But man's interference has changed many of the relationships． For example, the food chain formed by the soil, bunch-grass, deer, and cougar has been changed to the chain: soil, alfalfa, cow, farmer． Will such changes have serious effects or influence upon the existence of other organisms forming part of the web? If so, what will these effects be, and will they be good or bad? Can we change the web of life without losing something of value in the process? These are some of the questions which the ecologist tries to answer．

　　Our understanding of the energy relationships in nature is still very limited, but what we have learned so far tells us clearly that when we change the web of life, we run the risk of or we are in danger of losing something which cannot be replaced．

　　The following story is a true one, and is happening in British Columbia today． It is a dramatic illustration of the energy relationships between organisms, and of the effect man’s intervention has had on the web of life．

1．What is the passage mainly about?

A．Organisms and life．

B．Energy and the balance of nature．

C．A catalogue of who eats whom．

D．Biotic pyramids, webs of life and food chains．

2．The word organisms refers to 　　　　　　 ．

A．life B． energy C． attempt D． relationships

3．A grasshopper is 　　　　　　　　 ．

A．an insect B． a herbivore　　C． a rodent D． a carnivore

4．Vegetation is 　　　　　　　　 ．

A．birds B． animals　　C． plants D． organisms

5．Look at the picture below． How many food chains can you find in it?

A．2 ． B． 4．　　C． 5． D． 6．

6．The _____is a rodent like a ______．

A．weasel, frog　　B． grasshopper, rabbit C． frog, rat D． rabbit, mouse

7．If we change the picture of the passage into a pyramid, the _____ is at the top, the ____ at the second layer and the ______ is at the 3rd layer while _____are at the base．

A．hawk, weasel, mouse, plants

B．hawk, grasshopper, rabbit, mice

C．grasshopper , weasel, rabbit , plants

D．hawk, plants, grasshopper, rabbits

8．The population of grasshoppers is always _____ that of frogs．

A．smaller than B． greater than C． the same as D． different from

9．According to the passage, which of the following sayings is true?

A．Food chains are a death and decay process．

B．Photosynthesis is an energy losing process．

C．Each kind of living thing eats only one kind of food．

D．Most kinds of living thing live on more than one kind of organism．

10．What is the passage following this passage most probably about? It is about ______．

A．British Columbia

B．a dramatic illustration

C．man’s influence on the web of life in a certain place

D．the energy relationships between organisms and man’s influence on the web of life