ES5

Water is practically everywhere on Earth. It is the only known substance that can naturally exist as a gas, a liquid, and solid within the relatively small range of air temperatures and pressures found at the Earth’s surface.

Water, in both liquid and frozen forms, covers approximately 75% of the Earth’s surface. The water cycle describes how water evaporates from the surface of the earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation (usually rain in

Ireland). The water falling on land collects in rivers and lakes, soil, and porous layers of rock, and much of it flows back into the oceans, where it will once more evaporate. The ocean holds 97% of the total water on the planet; 78% of global precipitation occurs over the ocean and it is the source of 86% of global evaporation Plants absorb water through their roots and release water through their leaves in transpiration. Water is a product of respiration when organisms get energy from food.

Carbon can be found in various forms in a pure state such as soot, graphite and diamond. Compounds of carbon are found as minerals and rocks such as in limestone and marble. Carbon is found in biomolecules such as carbohydrates, fats and proteins.

Photosynthesis takes carbon from the air as carbon dioxide. This carbon becomes used in starch for the plant. Feeding passes carbon molecules between organisms. Respiration converts starches and sugars back to carbon dioxide. Burning releases carbon dioxide into the atmosphere.

Acid rain can release carbon dioxide when reacting with limestone. Increased burning and less photosynthesis is leading to increased carbon dioxide in the atmosphere which is affecting our climate globally. Carbon dioxide in the atmosphere prevents heat escaping from earth and is leading to global warming. The carbon cycle shows how carbon can be passed from one form to another.