Hypothesis testing: Oxygen and water temperature
What sort of questions can science answer? What can't it answer?
What steps do we need to answer a question scientifically? [make hypotheses, make
predictions, test hypotheses, draw conclusions]
If we ask the question whether water holds more oxygen at some temperatures than at others, how can we answer it?
What are the 3 hypotheses (guesses)?
[Draw - unit-less graph of 3 possibilities: positive, negative, and no correlation]
When we try to force more air into the water than it can hold, what happens?
[Demonstrate- Use straw or squeeze bottle, make bubbles]
If the hypothesis is true, what should we see? Make predictions for each.
If warm water holds more, what should happen as it cools off? [oxygen leaves]
Can we see the oxygen as it comes out of the water?
If cold water holds more, what should happen when the cold water warms up?
[List - hypotheses and predictions in table form]
Activity-Water temperature and Oxygen
Put hot, cold, and room temperature water in 3 separate vials. Why use equal volumes?
Measure starting temperature and write it on the inside of the cap. Why the inside?
Tap vials and tilt to remove visible bubbles from all.
Set aside for later examination and discussion.
| Hypothesis | Prediction |
|---|---|
| Temperature doesn't effect | All vials same |
| Warm holds more | More bubbles in water starting out hot |
| Cold holds more | More bubbles in water starting out cold |
Discussion-The water cycle
How do we use water? [drinking, washing, flushing, cooking, recreation, irrigation, fighting
fires, cooling engines, etc.]
How much do we use per day? [500 l/125 gal]
How much is used for you (farming, manufacturing)? [7200 l/1800 gal]
Where does water come from and where does it go when we've used it?
[Draw water cycle showing precipitation, flow, condensation, evaporation]
How much rainfall do we get in a year here? [average 17 inches, but lots of variation]
Where does our local water come from? [other places-Cachuma Reservoir, the Feather River]
Where does our local water go? [treatment plants, aquifer, ocean, atmosphere]
What is carried in water as it flows to the sea?
Which substances will dissolve in water?
Activity - What dissolves in water?
Lab Safety - Keep stuff away from eyes and mouth, use things only as directed, ask if you're unsure.
Put some of test substance in bottle with water. Label the bottle. Shake it up. Did it
dissolve? [soil, sand, oil, acid (vinegar), etc.]
Discussion-What is carried by runoff and why is that important?
What dissolved and what didn't?
What floated ? Why?
Are things settling out now? Why?
What is runoff?
What else would water pick up? [sewage, "germs", large objects,
animals and plants]
Where will these things end up?
What happens when a lot of rain falls in a short time?
Will more things be picked up?
Streams can be constant or "flashy".
Which is ours? Does this mean more stuff in runoff?
What effects can runoff have?
Dirt [clog gills and reduce light for plants, channel erosion]
Oil [clogs gills, mats fur and feathers, blocks surface, hurts eyes, etc.]
Trash, Acid, Fresh Water
What happens when it reaches the sea? [relative density, dilution]
Acids and bases
Discussion - Acidic things and bitter things
Name some sour things. Name some bitter-tasting things.
[Draw- pH scale with examples battery acid, stomach acid, oven cleaner, ammonia, etc.]
Which things are dangerous? Which things are neutral?
Activity - What is acidic and what is basic?
Lab safety - Keep stuff away from eyes and mouth, use things only as directed, ask if
you're unsure. Don't taste anything!
Test a substance by dipping a test strip in the labeled vial. [detergent, lemon juice,
soap, cola, fertilizer, vinegar, tap water, distilled water, etc.]
Compare it with the color chart.
Write the substance and its pH on the strip. Tape it to the scale.
Discussion-Acids and bases in our water
Where did things fall on the scale?
Which things could end up in our streams and ocean?
How would this affect our water?
How would it affect plants and animals?
Can rain pick up things on its way to the ground? [dust, acid, "smog"]
Smog can produce acid rain. How would this affect runoff and the life in the stream and sea?
How much water do you have to add to raise pH by one step? [Each "step" multiplies by 10]
Discussion - Temperature and water
What's your body temperature?
How do you control it?
How do plants and fish control theirs?
[Draw- F and C temperature scale showing boiling and freezing point for water, range for oceans, life processes range, human body temperature]
Which varies more, land or water temperature?
What temperature is the ocean around here?
Does the stream's temperature matter?
Activity-Water temperature and oxygen content
[Review hypotheses and predictions]
Look at vials filled earlier.
Have one person secretly label the tops of the vials with a 1, 2, or 3,
being careful not to disturb them. Rearrange vials to hide their identity.
Which has the most bubbles? Why? [Go back to earlier predictions and evaluate them]
If cold water holds more oxygen, what does this mean to fish?
What things affect stream water temperature?
Discussion - Nutrients, "building blocks" of life
All living things are made of similar "building blocks" called nutrients.
Where do we get them?
Where do plants get them?
Where do wastes go?
Where do they go when we die?
[Draw simple nutrient cycle: consumption, fertilizer, sewage, decomposition, erosion, removal, harvest]
How much is enough?
What happens if we have too few or too many nutrients?
Duck weed is a small plant that lives in ponds.
We will try to grow it under different conditions.
Make hypotheses about how much fertilizer your plant needs. Is any needed? Is more better?
Is too much bad? Is too little bad? Make predictions.
Activity - How much fertilizer do plants need?
Lab Safety - Keep stuff away from eyes and mouth, use things only as directed, ask if
you're unsure.
Label a clear plastic cup with your group name and type of water
(0, 0.5%, 1%, 2% fertilizer; pond water; tap water; sea water, etc.).
Add duckweed until you have 10 leaves (not 10 plants).
Set cups in appropriate light.
Observe cups daily and record changes by counting leaves and noting other things.
Why do we need more than one cup of each type?
Do all cups need to start with the same number of leaves? Why?
Think about what questions you have about our local creek. In our next
class we will design an experiment to try to answer them.