Download Dissolved Oxygen AP Lab Write-up Guidelines For

DISSOLVED OXYGEN AP LAB WRITE-UP GUIDELINES FOR AP EXAM NON-TEST-TAKERS
Due Mon, 5/1 or Sun, 4/30 by 5 for 5!
Title
I. Introduction
 Explain the importance of oxygen availability to aquatic ecosystems including reasons it’s often a limiting factor
 Research & describe the effect of temperature, altitude, water movement on dO2
 Explain the purpose of the lab, including a discussion of the relevance of each environmental factor tested.
II. Materials & Methods
 Description of procedure
o Summary (written in past tense) of the procedure used
o Include a brief explanation of the principle (not the specific steps) of the procedure used to determine DO.
 For a complete listing of materials & methods, see lab protocol titled “Dissolved Oxygen AP Lab” posted by Mrs. Rice
III. Data
 Hypothesis - Completed & stamped
 Data Table
 Graph showing DO for each set-up
IV. Data Interpretation – Primary Productivity in Varying Amounts of Light
 http://www.phschool.com/science/biology_place/labbench/lab12/intro.html
 Background
o Light is a limiting factor in any aquatic ecosystem because of its importance to primary producers, the 1st trophic level of
virtually any food chain. Because producers themselves use a portion of the products for cellular respiration, an important
consideration in evaluating the biomass potential of any ecosystem is the availability of the products of photosynthesis to
consumers. This is accounted for by further defining primary productivity as gross primary productivity versus net
primary productivity.
o Gross Primary Productivity
 Sum Total of Organic Molecule Formation
 Rate of Photosynthesis
o Net Primary Productivity
 (Total of Organic Molecules Formed) – (Organic Molecules Used by Producers for Cellular Respiration)
 (Rate of Photosynthesis) – (Rate of Cellular Respiration in Producers)
 In other words, net primary productivity represents availability of organic molecules, O2 available to consumers
 Data
o An AP Biology class of Hoppy Learners set up an experiment in which pure cultures of Chlorella algae were placed in
BOD bottles. One BOD bottle was fixed immediately to represent the initial DO concentration. The remaining BOD bottles
were exposed to varying amounts of light for 24 hours. The varying amounts of light represented different depths in an
aquatic ecosystem. Following incubation, the BOD bottles were fixed, and DO was determined using the Winkler titration
method.
 One BOD bottle was fixed immediately to represent the initial DO concentration.
 Five BOD bottles were covered with varying numbers of screens, allowing different percentages of light through
to the culture.
 One BOD bottle was covered completely in foil to represent a dark environment with 0% light.
 Class data was collected and the means were calculated for each set-up.
% Light
Initial
100%
65%
25%
10%
2%
0%

DO (mg/L)
5.37
10.75
9.10
6.21
4.26
3.11
2.52
Interpretation – Please answer questions 4 & 5 in complete sentences.
1. Determine the respiration rate of the Chlorella by completing the following calculation. Show your work.
 (Initial DO) – (Dark DO)
2. Construct a Data Table to show the gross primary productivity and net primary productivity for each depth (%light).
 Net Primary Productivity

 (Light DO) – (Initial DO)
 Light DO = DO in each % Light bottle
Gross Primary Productivity
 Net Productivity + Amount Lost to Producer Cell Respiration
 (Light – Initial) + (Initial – Dark) = Light – Dark
Set-Up
(% Light)
100%
65%
25%
10%
2%
3.
4.
5.
DO
(mg/L)
Net Productivity
(mg/L)
Gross Productivity
(mg/L)
Construct a graph showing Net vs Gross Productivity for the varying light percentages.
Refer to the line on your graph that represents Net Productivity. Provide an explanation for its direction and slope. What
is occurring when the line crosses the x-axis?
What is the significance of this point in an aquatic ecosystem? Significance of values above this point? Below this point?
IV. Questions – Please answer in complete sentences.
1. In this lab, DO was measured after a period of several days and the results were graphed. If instead, DO was measured
every 12 hours, how would the results differ?
2. The graph below depicts an abundance curve for two species in a community. One species is a primary consumer and the
other is a secondary consumer. After examining the graph,
a) Identify the trophic level of each species. Explain.
b) Explain the cause of the pattern found on the graph.
c) Explain how and why the curves would change if producer concentration decreased dramatically in this
community.
3.
4.
5.
6.
Two researchers, one at Toolik Field Station in northern Alaska and the other at LaSelva Biological Station in Costa Rica,
are studying populations of aquatic arthropods in freshwater pools during July. The researcher in Alaska determines an
average of 280 arthropods per m3 of water in the pools she is studying. The researcher in Costa Rica determines an
average of 125 arthropods per m3 at his study site. What are two factors that account for this difference? Explain.
The diagram to the right represents a terrestrial food web.
a) Which organism represents the primary producer? Explain.
b) Which organism is most likely a decomposer? Explain.
c) To which two kingdoms would the decomposer most likely belong?
d) Identify all organisms that could represent secondary consumers.
e) Batesian mimicry describes an adaptation in which a harmless species
has evolved to mimic the warning signals of a harmful species.
Species C makes its predators sick … which species would benefit from
being a mimic of C? Explain.
Eutrophication is created by large run-offs of nitrogen and phosphorus into an aquatic ecosystem. Although it can occur
naturally, it is typically a man-made problem and it is the reason detergents high in phosphates were banned years ago.
The enriched concentrations of N and P stimulate a) algal blooms, leading to b) explosions in bacterial populations,
followed by c) decreases in populations of larger aquatic plants and fishes. Explain this 3-part sequence of events . . . why
does each event occur?
Although there are negative consequences when too much N and P are available, they can also be limiting factors in a
community. Describe why all organisms need these two minerals and how they are naturally recycled in an ecosystem.
V. Conclusion
 Re-address the purpose of the lab … in other words, was the purpose accomplished?
 Evaluate your hypothesis based on your data.
 Identify at least three controlled variable from the experimental design.
 Explain at least three plausible sources of error.
Academic Pledge