A. what organic compounds is carbon found in? b. what organic compounds is oxygen found in? c. carbon dioxide and oxygen comprise approximately what percent of gases in the troposphere? d. identify the two processes which have the greatest influence on tropospheric concentrations of co2 e. name the two largest sinks (storage areas) for carbon. f. discuss how oceans play a major role in regulating co2 levels in the troposphere g. describe two ways that people impact the carbon cycle. h. describe the two major biological processes that carbon and oxygen are involved in.

1.Generally, any chemical compounds that contain carbon in its structure are considered as organic compounds. More specifically, organic compounds  are molecules  the are found in living organisms and contain carbon. All known life is based on organic compounds. These include carbohydrates, lipids and fatty acids, nucleic acids, proteins (enzymes, hormones, neurotransmitters).

2.Oxygen found in organic compounds is in the oxidation state -2, otherwise it might be very reactive. The most important organic compound of oxygen is water (H2O) in which oxygen is covalently bonded with hydrogen atoms. Oxygen is component of many organic molecules: alcohols, ethers, ketones , aldehydes ,carboxylic acids, esters amides…It is also in glycerol, formaldehyde, citric acid, acetamide. When it comes to biomolecules, it is the main component of all of them: proteins, lipids, nucleic acids and sugars.

3.Oxygen is about 21 percent and Carbon dioxide about 0.04 percent of all gases in the troposphere (the lowest layer of Earth's atmosphere). Other gases are nitrogen about 78 percent, argon about 0.93 percent. The mixture of gases not only contains the air that we breathe but also protects us from the heat and radiation e from the sun. Gases of troposphere control the temperature day-to day (warms the planet by day and cools it at night).

4.Two processes which have the greatest influence on tropospheric concentrations of CO2:

•Photosynthesis-process in plants in which CO2 is used for the production of organic compounds-sugars. This is one of the main processes by which carbon dioxide is removed from the atmosphere.

•Precipitation- carbon dioxide dissolves in raindrops (during the rainfall) , reacts with water molecules and forms carbonic acid, which contributes to ocean acidity.

5.The largest sinks for carbon are:  

•ocean sediments-  the largest active carbon sink on Earth are oceans that absorb carbon dioxide via physicochemical and biological processes (quarter of the carbon dioxide)

•continental rocks - carbon can be trapin the form of solid carbonate salts

These two are considered as sinks because the carbon from these areas is cycled very slowly.

6.Carbon enters the ocean mainly through the dissolution of atmospheric carbon dioxide which occurs during the rainfall. Carbon dioxide from the atmosphere reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. Ocean acidity affects biosystems. Also, increased CO2 in ocean can increase the ocean temperature.

7.Human activities have a huge influence on carbon cycle mostly because they directly add carbon to the atmosphere. They do that through emissions of carbon dioxide and removal of carbon dioxide from sinks. Two most common ways on affecting carbon cycle are:

•Burning of fossil fuels-burning of oil or coal increase the amount of carbon dioxide in the atmosphere (carbon is released)

•Deforestation- permanent removal of trees from forests (trees are no longer absorbing carbon dioxide).

8.Two major biological processes that carbon and oxygen are involved in are:

•photosynthesis-  the process by which plants convert sunlight energy into chemical energy (create energy-rich carbohydrate molecules such as glucose).The process uses CO2 and releases O2.

•Cellular respiration-the process opposite of photosynthesis in which food molecules are broken down to obtain energy and store it in the form of ATP. Occurs in all living cells, uses O2 and releases CO2.