5.1 — Introduction to Carbon Compounds

Carbon Compounds in Nature

• A carbon compound is a compound that contains the element carbon, C.
• Carbon compounds are divided into two groups:

Group	Origin and examples
Organic carbon compounds	Originate from living things; examples: petroleum, silk and charcoal
Inorganic carbon compounds	Originate from non-living things; examples: limestone and carbon dioxide

Carbon Cycle

• The carbon cycle shows how carbon elements are recycled through the formation or decomposition of carbon compounds in living things and organic substances in the environment.
• Main processes: respiration, combustion, decomposition and photosynthesis.

Movement of carbon

1. Carbon dioxide in the atmosphere is absorbed by green plants during photosynthesis.
2. Carbon compounds pass from green plants to organisms when the plants are eaten.
3. Respiration by plants, animals and microorganisms releases carbon dioxide into the atmosphere.
4. Dead organisms undergo decomposition; decomposers such as bacteria and fungi release carbon dioxide.
5. Some dead organisms form fossil fuels—petroleum, natural gas and coal.
6. Combustion of fossil fuels releases carbon dioxide into the atmosphere.
7. Natural phenomena such as volcanic eruptions and forest fires also release carbon dioxide.

Role and importance of photosynthesis

• Enables green plants to make their own food.
• Provides food for animals.
• Increases the oxygen content in the air.
• Removes excess carbon dioxide from the air and maintains its carbon dioxide content.

Carbon-cycle diagram cues

• Atmosphere → green plants: photosynthesis.
• Green plants → organisms: feeding.
• Green plants / organisms → atmosphere: respiration.
• Dead organisms → atmosphere: decay or decomposition.
• Dead organisms → fossil fuels: formation of petroleum, natural gas and coal.
• Fossil fuels → atmosphere: combustion.