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AP Lab 12

Completing the Research Notebook for AP Biology Lab #12.....Dissolved Oxygen and Primary Productivity

Resource: Lab Twelve, Dissolved Oxygen and Primary Productivity

Page 136 in the AP Biology Lab Manual

 

Note: You will be using a student guide from the Carolina Biological kit for this lab.

Note: The lab preparation will take TIME. This is one of the most involved laboratories of the twelve lab topics.

Start early and spend as much time as needed to develop your prelab. Spend time READING THE METHOD to

understand what you are supposed to do. This lab involves a lot of materials that need to be rinsed and stored.

This is not a lab that you can start 30 minutes before the lab to prepare. Please have a positive, committed “AP Bio

Style” attitude in preparing for the DO Lab.

Time Projection: three 45 min time periods. We will do Exercise 12A and the first part of Exercise 12B on Wed the

14th (notice we may go over a bit, please plan accordingly), and we will do day 2 of Exercise 12B on Thursday (you

have to incubate algae cultures overnight).

 

Before the lab (set up your research notebook) 

Title: Develop a title in the form of a question after completing the pre-lab.

 

Objectives for the lab: refer to Student Guide

 

Prelab Q&A: Refer to the Background included on the Student Guides.

1. How is the DO concentration often used, and mention a few minimum requirements for survival of sample species.

2. How does oxygen enter water?

3. Discuss physical factors (temp, salinity, winds, currents) that affect solubility of gases (oxygen) in water. Be

specific with concepts.

4. Discuss the two biological processes that affect DO concentration, and consequential influences on aquatic

ecosystems.

5. Discuss how pollutants can decrease dissolved oxygen in water (very important: read for complete

understanding; page 9 of Student Guide)

6. Define primary productivity (include a chemical equation which is pertinent).

7. Name three ways primary productivity can be measured AND the method that will be used in this laboratory for

measuring primary productivity.

8. Quantitatively relate “oxygen production” and “carbon assimilation”.

9. What indicates “net productivity”? (Last two paragraphs in Primary Productivity section).

10. Use the information copied to briefly describe the chemistry of the Winkler method of measuring DO

concentration.

 

Method:

Exercise 12A To determine the effect of temperature on dissolved oxygen concentration, a graphical device called

a “nomograph” will be used to determine percent oxygen saturation of three samples of water at different

temperatures. Usually, the amount of oxygen dissolved in a water sample is often only part of what the water could

hold. The nomograph will be used after DO concentration is measured using the Winkler Method.

Exercise 12B Water samples containing a green alga
Chlorella will be utilized to measure changes in dissolved

oxygen concentration after overnight incubation. Temperature will be held constant, but light intensity will be varied.

Fiberglass screens will be used to filter light, and different light intensities will be set up to simulate increasing aquatic

depth. By calculating differences in bottles kept in darkness (respiration only) and bottles exposed to varying

amounts of light (respiration and photosynthesis occurring), an estimate of gross productivity can be made.

 

Data Tables.

Table 12.1 Temperature and Dissolved Oxygen

This table will be used to enter group DO data and for Class data.

Table 12.2 DO Conversion

The DO, mg/L will be read directly from the syringe scales.

On Thursday, after we titrate the bottles that have been incubated, we will finish lab discussion and directions will be

given for final preparations for lab report submission (Lab Questions/Answers, Themes, Conclusions)

 

Dissolved Oxygen and Primary Productivity-Post Lab Guide

Part 1

Graph

Independent variable (x axis): Temperature

Dependent variable (y axis) Percent saturation

(percent saturation is dependent on temperature)

Questions (Refer to the questions on the student guide; the following information is given to help you think critically)

1. Temperature vs Solubility

The higher the temperature, the lower the solubility of oxygen

The lower the temperature, the higher the solubility of oxygen (inversely proportional)

Kinetic Theory (kinetic energy of molecules increases with Kelvin temperature)

The colder sample could have less saturation (which means it could have more DO)

Even though cold water contains more DO, the DO concentration would represent low saturation since it could hold

more water.

2. This is a “design an experiment” question:

Hypothesis: If salinity is related to solubility of oxygen, then ____________________

(reread the intro to find out if salinity affects DO)

Your experiment should include a method.

The controlled variables (temp. MUST be controlled)

The experimental variable ( how would you test salinity?)

Repeated trials necessary.

Statistics (take averages of trials)

Graphing and analysis of data

Part 2

The effect of light intensity on the primary productivity in samples of Chlorella

 

Graph

Independent variable: (light intensity see chart on page 13 for percents)

Dependent variables Net productivity values in mL / L in one color and Gross productivity values in another color.

 

Questions (see the questions on the student guide; the following information is to help you think critically)

 

1. Page 17 You will have to analyze your graph carefully to see if growth (primary productivity) was limited by light

intensity.. Provide evidence (data)

 

2. You have to use your graph and data to answer this question: where would you expect no gross productivity?

and no net productivity? (which intensity) ??

 

3. Read question 3.

Think about a mammal: it gets oxygen from the air; it is endothermic which means that it respires (uses oxygen) to

make ATP which is used for energy; and because heat is released during metabolism, it is able to maintain a

constant internal temp.

Think about a fish: it gets oxygen from water; it is ectothermic (does not rely on metabolism for heat to maintain

internal temp)

Think about air vs. water: Air contains a lot more oxygen that water; air is less dense than water; fish

constantly move the operculum (gill cover) so that water constantly bathes the gills where diffusion of oxygen occurs

into the blood).

These concepts should help you develop an answer to this question. Read the question carefully to see that you

understand what it is asking.

 

4. Read question 4.

You take two water samples.

Think about where you are collecting. Riffles refers to the fact that the stream is “running” and bubbles are forming.

Turbulence in water causes an increase in DO. Lake water would have less turbulence and thus less DO. Use

these ideas in your discussion.

 

Question #5 

Read question #5

OK, at 7 am, all of the organisms in the water have been respiring all night (that includes heterotrophs and

autotrophs, all organisms in the water). What would this do to the DO? At 7 am, is there much light for

photosynthesis to occur in autotrophs? At 5 pm, after the autotrophs have been in the light of the day, what

process would have taken place? What would have happened to the DO?

 

Question #6

Read question #6

Think volume!!!! The more water, the more oxygen that can be dissolved!!! Which bowl??

(Now, further analysis: Which bowl of water would sustain the fish over time? Over time, the fish would utilize the

oxygen for respiration. Which bowl would more efficiently gain oxygen from the air?????

 

Question #7

Read question #7

You need to find a good definition of eutrophication (it is the increase of nutrients, which nutrients??? from

where?)

What does that increase in nutrients do to the biomass?

Let’s say there is a tremendous algal bloom because of eutrophication. How could the algal bloom affect the other

organisms in the body of water in terms of DO concentration? Light availability for other autotrophs? Algal death

and decomposition of it by bacteria?

 

Themes:

Energy transfer: How are photosynthesis and respiration exemplary of energy transfer?

Interdependence in nature: Plants and animals depend on each other. Think about the biological processes that

were occurring in the bottles.

Science as a Process: How was this experiment controlled?

 

Conclusion Topics:

Temperature of water vs. DO.

Effect of light intensity on primary productivity: Be sure to define net productivity and gross productivity and explain

how you calculated these. What was the purpose of dark bottle? of the initial bottle? Purpose of screens? Use

data to discuss outcomes. What does the data show you?

Importance of DO in bodies of water; factors that affect DO concentration; examples of human interferences with

nature that affect DO levels.

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