Ecosystem: Comes from the Grek word OIKOS which means home and system.
- A community together with its nonliving surroundings.
- Interaction of biotic and abiotic factors.

 Abiotic factors: Nonliving components.

There are two kinds of abiotic factors:

1. Physical:  sunlight and shade, amount of precipitation, altitude and latitude, nature of soil and wind. 
2. Chemical:  salinity of water, level of dissolved O2 and other gases, level of plant nutrients, pH of solid and water and level of natural and artifitial toxic substances.   

 Biotic factors: Living components in an ecosystem. 

1. Autotrophs: photoautotrophic and chemoautotrophic. 

                Photoautotrophs: has clorophyll and carry on photosyntesis.

                Chemoatotrophs: bacteria that obtain energy from the oxidation of inorganic compounds. 

      2. Heterotrophs: 

• Need a source of pre formed nutrients 
• consume tissues of the other organisms
• consumers are classified according to the type of food they eat  

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