effects – pollution causes smog which can cause lung cancer if exposed over time if smog is bad enough. also think about the Black Lung disease that plagued many in England over a century ago. (pollution can be indoors too)

places – the most common would be in any urban city (Mexico City, LA, Atlanta, NYC, London, Beijing, Lagos etc)

reduce – CONSERVE ENERGY! that's the simplest answer but it's not that easy especially since alot of the world is so dependent on oil. stop cutting down trees, use less oil, use renewable energy (wind, solar, hydro)

%age – I don't know about the percentage of polluted air but I do know that in the IPCC report it says that CO2 is currently at about 370ppb; in the natural cycles throughout Earth's lifespan it has never gone over 270ppb and that was during interglacial periods. In 100 years it is projected to increase to over 500 ppb. If CO2 keeps increasing, the atmosphere will probably become poisonous. You might want to look up the most recent IPCC report for this one (and possibly impress your teacher)

1) proteins: are used for building muscles, they are also found in hair and nails. they are very important

hint* the 20 essential amino acids which we need to live combine with each other to form proteins thats why the chemical formulas of proteins is very complex, you can look them up on google

DNA: the genetic code, sepertes us from the animals and each other, something wrong in the code can cause major defects in the body leading to very serious and untreatable diseases
whats DNA made of is the combing part of it i guess, the ribose sugar and phosphates group combine and the base pairs actg combine so look up the composition of DNA wont be too bad

water: very essential to life, helps with the chemical reactions and really doesnt need a whole lot of explanation. i am sure you know how important water is