Standard Grade Science

Pollution

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

As the amount of organic waste, such as raw sewage, in a river increases the oxygen level in the water , the number of bactera and the number of invertebrates living in the water .