English for

Reading #3: 
Energy flow
 
The fundamental source of energy in almost all ecosystems is 
radiant energy
from the Sun. 
The energy of sunlight is used by the ecosystem’s 
autotrophic
, or self-sustaining, organisms (that is, 
those that can make their own food). Consisting largely of green vegetation, these organisms are 
capable of photosynthesis—i.e., they can use the energy of sunlight to convert carbon dioxide and 
water into simple, energy-rich carbohydrates. The autotrophs use the energy stored within the simple 
carbohydrates to produce the more complex organic compounds, such as proteins, lipids, and starches, 
129
: (
https://www.britannica.com/science/ecological-restoration/Implementation
 ) 
130
: (
https://www.britannica.com/science/ecosystemic-approach
) 

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that maintain the organisms’ life processes. The autotrophic segment of the ecosystem is commonly 
referred to as the producer level.
Trophic levels
Together, the autotrophs and heterotrophs form various 
trophic (feeding) levels
in the 
ecosystem: the producer level (which is made up of autotrophs), the primary consumer level (which 
is composed of those organisms that feed on producers), the secondary consumer level (which is 
composed of those organisms that feed on primary consumers), and so on. The movement of organic 
matter and energy from the producer level through various consumer levels makes up a food chain. 
For example, a typical food chain in a grassland might be grass (producer) → mouse (primary 
consumer) → snake (secondary consumer) → hawk (tertiary consumer). Actually, in many cases the 
food chains of the ecosystem’s 
biological community overlap
and interconnect, forming what 
ecologists call a food web. The final link in all food chains is made up of 
decomposers
, those 
heterotrophs (such as scavenging birds and mammals, insects, fungi, and bacteria) that break down 
dead organisms and organic wastes into smaller and smaller components, which can later be used by 
producers as nutrients. A food chain in which the primary 
consumer
feeds on living plants is called 
a grazing pathway, and a food chain in which the primary consumer feeds on dead plant matter is 
known as a