Dissolved Oxygen Quiz - Answers

1. What percent of the atmosphere we breathe is composed of oxygen gas?
   1. 78% (Incorrect. Nitrogen gas makes up 78% of the air.)
   2. 21% (Correct! Oxygen makes up 21% of the air we breathe.)
   3. .03% (Incorrect. Carbon dioxide makes up .03% of the air.)
   4. 50% (Incorrect. By the way, is half a glass of water 50% filled or 50% empty? )

2. Trace amounts of dissolved oxygen are measured in...
   1. percent (Incorrect. Oxygen gas in the air is measured in percent.)
   2. mg/L (Correct! Dissolved oxygen is measured in milligrams per litre.)
   3. grams (Incorrect. The fat content of food is measured in grams per serving.)
   4. mL (Incorrect. Cans of soda pop are measured in milliliters.)

3. Oxygen is an essential element for...
   1. photosynthesis (Incorrect. Carbon dioxide is essential for photosynthesis.)
   2. protein synthesis (Incorrect. Nitrogen is essential for protein synthesis.)
   3. cellular respiration (Correct! Oxygen is used to "burn" calories and produce energy.
   4. bones and teeth (Incorrect. Phosphorus is essential for bones and teeth.)

4. High dissolved oxygen levels in a river indicate...
   1. low flow rates (Incorrect. Low flow rates can result in low dissolved oxygen levels.)
   2. high turbidity (Incorrect. High dissolved oxygen levels are more likely with low turbidity.)
   3. excessive aquatic plants and/or algal blooms (Incorrect. Excessive aquatic plant growth and algal blooms result in low oxygen levels during decay.)
   4. better water quality (Correct! High dissolved oxygen levels indicate good to excellent water quality.)

5. An acceptable level of dissolved oxygen (mg/L) for cold water trout is...
   1. 2-4 (Incorrect. Very low oxygen levels of 2-4 mg/L seldom supports life.)
   2. 5-7 (Incorrect. Dissolved oxygen levels of 5-7 mg/L may support warm-water fish such as pike.)
   3. 7-9 (Correct! Trout survive well in water with dissolved oxygen levels of 7-9 mg/L.)
   4. 11-15 (Incorrect. Dissolved oxygen levels rarely reach as high as 11-15 mg/L.)

6. High dissolved oxygen levels can result from...
   1. mixing and splashing (Correct! Moving water and turbulence adds dissolved oxygen to water.)
   2. the decay of dead animal and plant matter (Incorrect. Decomposition of organic matter results in high levels of carbon dioxide.)
   3. warm water discharge from wastewater and power plants (Incorrect. Warm, nutrient-rich water results in excessive plant growth, decay and eventually, lower dissolved oxygen levels.)
   4. excessive nutrients that increase aquatic plant and algae growth (Incorrect. Excessive nutrients and increased plant growth eventually leads to decomposition and low dissolved oxygen levels.)

7. Low dissolved oxygen levels can result from...
   1. mid-day photosynthesis (Incorrect. Sunlight increases the amount of photosynthesis and produces more dissolved oxygen.)
   2. run-off from cattle feedlots (Correct! Cattle manure increases the amount of organic material in a river, resulting in more decomposition and lower dissolved oxygen levels.)
   3. keeping trees along stream banks (Incorrect. Streamside trees produce shade, cooler water and higher dissolved oxygen levels.)
   4. faster river velocities (Incorrect. Moving water contains higher dissolved oxygen levels.)

8. One effect of low oxygen concentrations is...
   1. water levels drop (Incorrect. Snowmelt, rain and irrigation determine water levels.)
   2. temperature increases (Incorrect. River temperatures are determined by shade, season and nearness to the source.)
   3. water becomes clear (Incorrect. Cloudy or turbid water can cause low oxygen levels by blocking sunlight needed for photosynthesis.)
   4. trout can't survive (Correct! Trout cannot survive at oxygen levels below 5 mg/L.)

9. During a dissolved oxygen test, the fuzzy orange material that gradually settles to the bottom of the round DO bottle is called a...
   1. scum (Incorrect. Scum is a layer of material that floats on the surface of a liquid.)
   2. floc (Correct! Floc or flocculant is a precipitate that settles to the bottom of a liquid.)
   3. film (Incorrect. Film is a thin layer on the surface of a liquid.)
   4. filtrate (Incorrect. Filtrate is the liquid that has passed through a filter.)

10. The organism responsible for low oxygen levels during the decay of excessive plant and algae growth is...
    1. fish (Incorrect. Fish cannot survive in low oxygen levels.)
    2. bacteria (Correct! Large populations of bacteria use oxygen when decomposing organic material.)
    3. macroinvertebrates (Incorrect. Invertebrates like mayflies and stoneflies require very high levels of dissolved oxygen for survival.)
    4. snails (Incorrect. Just because snails are slow doesn't mean that they cause problems!)

Congratulations!

You've finished the dissolved oxygen quiz. You can now breathe a sigh of relief!

How did you do?

0-4 (A score of 0-4 suggests that you're a bit sketchy on the details of dissolved oxygen. You'll need to re-read the material or ask questions before trying the quiz again.)

5-7 (A score of 5-7 shows that you have a basic understanding of dissolved oxygen. You might like to review some of the material and try the quiz again.)

8-10 (A score of 8-10 shows that you have a very good understanding of dissolved oxygen. Take a bow!)