Title: Dissolved Oxygen

Discipline: Life Science

Ability: 7th Grade, 8th Grade

NJ Core Curriculum Content Standards:

5.1, 5.5, 5.3

 

Objective:

Students will gain an understanding of the effect of temperature change on dissolved oxygen (D.O) content of the water.  The goal was for the students to understand that removal of vegetation on a stream bank and around a pond increases the temperature and decreases the D.O. of water.  The students will understand why monitoring the D.O. of their fish tanks in important.

 

Materials:

8 feeder goldfish

6 beakers

Hot plate

6 thermometers

Clock with a second hand

 

Preparation:

Goldfish should be bought in advance of the lesson and plans should be made for how they will be kept in the classroom.  The water can be heated during discussion with the students on D.O.  It helps if one teacher is warming the water and putting the fish into beakers for observation while the other teacher is leading the class discussion.  The goldfish should be observed in cold water and then warm water should be added.  The water temperature should not be increased more than 4-5 degrees.

            Create a table for class data on the board.  Once the students have documented their breathing rates they should fill in the information on the board for all the students to copy.  The data should be graphed for homework.

 

Class Discussion:

Today we will discuss how pollution and temperature influences the amount of oxygen in the water.

 

  1. Is there oxygen in water? Yes, it is called Dissolved Oxygen (mg/L of water)
  2. What are some ways oxygen gets into water?
    1. Air- when water comes into contact with air it absorbs oxygen from air.  When water moves around a lot (turbulence) this adds more oxygen to the water.

Healthy stream, DO=5mg/L or above

When water cannot hold any more oxygen=Saturation Concentration-#of mg of O2 dissolved in 1 liter of water before water can hold no more

                        Summer –Sat. Conc can be as low as 8mg/L

                        Winter- Sat. Conc goes up to 9mg/L

                        Anaerobic condition- water has no oxygen in it.  Bacteria used all up.

                   2. Plants- photosynthesis

  1. Scientists- dissolved oxygen is one of the best indicators of the health of a stream.
  2. Why is oxygen so important in a stream?? What types of aquatic organisms need oxygen?

 

All aquatic organisms need oxygen to live.  Aerobic bacteria need oxygen to break down organic material= decomposition

  1. What affects the amount of oxygen in a stream or lake??

-Nutrients-Eutrophication

Algal blooms.  Too much nutrients cause algae to grow out of control.  When algae die, oxygen is used up by bacteria (aerobic bacteria) that decomposes all that algae

-Temperature

Does the amount of oxygen in the water change when temperature rises?

Create a hypothesis to predict whether the amount of oxygen in the water decrease or increase as the temperature rises.

Hypothesis is a statement that you test.

 

Activity:

The student instructions are on the accompanying handout.  They are do count the breathing rate for 3 trials before and after the water is heated.  Stress to the students to be respectful of living organisms and do not stress out the fish anymore then they already are (i.e. Tapping the glass, moving the beaker around)

 

Student Assessment:

Student data should be recorded on the board and they should graph their data for homework. Make sure to discuss the types of graphs that would be appropriate to display the data.

 

Questions:

What kinds of things in nature cause a river creek to have warmer water?

Removal of riparian zone, factories or power plants that dump warm water into streams.

 

Assessment:

This lesson went well in both 7th and 8th grade classes.  Enough time should be given to allow the students to copy down the class data.  We could have gone over what type of graph would be appropriate to display the data more thoroughly than we did.