UID:0
Carbon dioxide (chemical formula CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas being only 0.038% of the atmosphere. Carbon dioxide is used by plants during photosynthesis to make sugars, which may either be consumed in respiration or used as the raw material to produce other organic compounds needed for plant growth and development. It is produced during respiration by plants, and by all animals, fungi and microorganisms that depend either directly or indirectly on plants for food. It is thus a major component of the carbon cycle. Carbon dioxide is generated as a by-product of the combustion of fossil fuels or the burning of vegetable matter, among other chemical processes. Small amounts of carbon dioxide are emitted from volcanoes and other geothermal processes such as hot springs and geysers and by the dissolution of carbonates in crustal rocks. As of March 2009[update], carbon dioxide in the Earth's atmosphere is at a concentration of 387 ppm by volume. Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Carbon dioxide is a greenhouse gas as it transmits visible light but absorbs strongly in the infrared and near-infrared. Carbon dioxide has no liquid state at pressures below 5.1 atmospheres. At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below −78 °C and the solid sublimes directly to a gas above −78 °C. In its solid state, carbon dioxide is commonly called dry ice. CO2 is an acidic oxide: an aqueous solution turns litmus from blue to pink. It is the anhydride of carbonic acid, an acid which is unstable and is known to exist only in aqueous solution. CO2 + H2O ⇌ H2CO3 CO2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy.Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.
UID:1818
引用第1樓狂虎ex於2009-11-01 18:53發表的 :唔BO 氣想玩死D金魚咩= =
UID:23118
UID:37131
UID:21215
引用第6樓千草於2009-11-01 18:58發表的 :匿名 點用
引用第4樓廁所為上於2009-11-01 18:56發表的 :可憐的金魚
UID:37172
UID:31395
引用第10樓-hp-於2009-11-01 19:26發表的 :魚都會respiration -.-你唔換水之類的你個度既水冇哂氧姐係一獲熟
引用第11樓匿名於2009-11-01 19:28發表的 :英文天才=0=respiration喎
UID:27700
引用第12樓匿名於2009-11-01 19:31發表的 : respiration渣嘛 f.2有教呀
UID:17175
引用第12樓匿名於2009-11-01 19:31發表的 :respiration渣嘛 f.2有教呀
UID:20111
UID:27058
引用第16樓omegah4400於2009-11-01 19:58發表的 :佢有無講Chemistry and Biology, CO2都唔識 =.=
UID:37165