ErinPrice-APLabDissolvedOxygen

8/6/2019 ErinPrice-APLabDissolvedOxygen

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The effect of light intensity and temperature on the primary productivity of natural water.

Conducted By: Price, E.

Assisted By: Powell, R.

Date(s) of Experiment: 5/10/2011-5/12/2011

AP Bio 1st Block

Ms. Umscheid


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I. Introduction

The purpose of this lab is...to analyze the effect of temperature and light intensity on the primary

productivity of pond water samples.

Background Information

In an ecosystem carbon and oxygen are important in every ecosystem. As oxygen and

carbon cycle throughout the system, the organisms use the mineral to create necessary

molecules throughout the body. Carbon is taken from the atmosphere in the form of carbon

dioxide by plants, the plants then use the carbon to make their sugars and release oxygen. The

oxygen in the atmosphere is breathed in by living organisms or captured in between the water

molecules of aquatic environments. Primary productivity is the rate at which organic materials

are stored, carbon is necessary to make organic compounds within cells. Primary productivity

relates the the metabolism of organisms in an ecosystem because as the metabolism increases

so does the primary productivity because as metabolism uses energy and creates molecules

more energy is needed so more organic molecules are made so the primary productivity

increases.

The amount of oxygen stored in between water molecules can be affected by several

factors. The temperature of the affects the amount of oxygen because as the temperature rises

the ability of water to hold oxygen decreases due to the more frequently breaking hydrogen

bonds between molecules. The amount of photosynthesis occurring in the water, due to sun

exposure and presence of plants will increase the amount of oxygen in the water. The amount

of decomposers and dead organisms will decrease the amount of oxygen because

decomposers consume oxygen as organic material is broken down. The amount of turbulence

through the water will also decrease the amount of oxygen since the hydrogen bonds break

more easily with the movement and oxygen cannot be stored between the bonds. Lastly theamount of salt within the water causes it to be unable to hold oxygen decreasing oxygen in a

body of water.

Dissolved oxygen in the water can be affected by photosynthesis and cellular

respiration. The amount of photosynthesis throughout the body of water increases oxygen

because oxygen is released s a bi product during photosynthesis. Cellular respiration decreases

the amount of oxygen because it is taken during the process while carbon dioxide is released.

Photosynthesis will increase the amount of primary productivity because organic materials are

made in the form of glucose. Respiration decreases primary productivity because it break down

the organic molecules having the opposite effect of photosynthesis and therefore, primary

productivity.

The independent variable(s) are temperature as defined by 10*C, 25*C, and 50*C and light

intensity as defined by 100%, 65%, 25%, 10%, and 2%.


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The dependent variable is the primary productivity of the pond water samples as defined by the

percent saturation of dissolved oxygen and mean productivity between the gross productivity

and net productivity.

The control is the primary productivity of the pond water sample at standard temperature and

light intensity as defined by 100% light and room temperature.

The hypothesis is as temperature increases the amount of dissolved oxygen will decrease; As

light intensity increases the gross and net productivity will increase

II. Procedure

Materials

1 Flask

1 spoonful- sulfamic acid

8 drops- Manganous Sulfate

8 drops- Alkaline Solution

5 BODs with caps

10 mL Thiosulfate

15 screens

3 Lamps

1 Titrater

6 rubber bands

Square of foil

Experimental Design

Refer to procedure on page 137-138, 140-141 of lab packet with the following

modifications:

1. Use the WINKLER Method for determining Dissolved Oxygen

a. Fill the sampling bottle fully with the pond water sample

-make sure no air bubbles are trapped inside

b. Add 8 drops of Manganous Sulfate to the sampling bottle

c. Add 8 drops of Alkaline (potassium-iodide-azide) to the sampling bottle

d. Cap and mix thoroughly by inverting the bottle several times

-a precipitate will form

e. Allow the precipitate to settle below the shoulder of the bottle ~ way

f. Add 1 spoonful of Sulfamic Acid (or 8 drops of sulfuric acid)

g. Cap and mix thoroughly by inverting the bottle several times

-the solution will be yellow to orange

h. Transfer 20mL to the BOD and cap

-if sample is pale yellow skip to step J


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i. Titrate the BOD from yellow-orange to pale yellow with Thiosulfate

j. Add 8 drops of Starch Indicator to the BOD sample

-the pale yellow solution should turn blue

k. Titrate the BOD from blue to colorless with Thiosulfate

-record as ppm where each drop is equivalent to 1mg O2/L

Other procedural modifications include:a) Amount of drops were recorded instead of mg or ppm

b) The sample started in the BOD and was not moved

Constants

The following three variables must be held constant:

The amount of sample in each BOD should stay the same

The amount of chemicals used in each sample; sulfamic acid, manganous sulfate and

alkaline solution

The dark bottle DO should stay the same for each gross productivity population

III. Results - Exercise 12A Dissolved Oxygen and Temperature

Data Table 1:

Temperature Lab Group DO Class Mean DO Lab Group %DOSaturation

Class Mean%DO Saturation

Cold 7 40 35 150% 146.5%

Cold 9 30 143%

Warm 22.3 29 29 141% 141%

Hot 35 15 10.5 120% 92.5%

Hot 35 6 65%


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Data Graph 1:

III. Results - Exercise 12B: Model of Productivity as Function of Depth of Lake in 24 Hours

Data Table 2:

Individual Data Class Mean

Initial DO 25 32.4

Dark Bottle DO 0 0

Respiration Rate(Initial - Dark)

25 32.4


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Data Table 3: Mean Productivity

# of screens % Light Gross Productivity(Light - Dark)

Net Productivity(Light - Initial)

0 100% 10.5 -21.9

5 10% 0 -32.4

10 2% 0 -32.4

Data Graph 2:

IV: Conclusions

The hypothesis was supported because the data shows that as temperature increases the

ability to hold oxygen in the water decreases, when the water was hot the oxygen percentage

was 120% and when it was cold the oxygen was at 150%. As light intensity increased so did the

gross and net productivity, the data shows that at 100% light intensity the gross productivity was

10.5 and at 1% the gross productivity was 0.

The results may be inconclusive because of the following errors.

The data in the third data table is inconsistent and skewed when compared to the constants

given by LabBench.


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At 10% light with with 5 screens the gross productivity, during trial one, was not measured drop

by drop so the measurements were off. Trial two at 1% with 10 screens there was air bubbles in

the titration so the specimen could have had oxygen added to it skewing the results.

The results indicated that (what I learned)...

Primary productivity can be measured several different ways, the amount of carbon

dioxide consumed, the amount of sugar formed, and the amount of oxygen released. The

carbon dioxide and oxygen production are related in that as carbon is consumed by organisms,

during photosynthesis, to make sugars oxygen is released. The temperature of a water sample

effects the amount of water it a hold because as the water heats up the weak hydrogen bonds

break more quickly due to the more rapid motion of the molecules, with the bonds breaking

more quickly less oxygen is stored between the bonds.

It would be expected, at 0% light intensity, that there would be no gross productivity

because there would be no light energy powering the production of organic molecules and

therefore there is no gross productivity. At 0% light intensity there would also be no net

productivity because net productivity is the amount of energy stored between bonds of organic

materials but if no organic materials are being made there is no energy stored in the bonds.

Mammals obtain the oxygen needed to allow for respiration from the atmosphere they

live in. They only have to use 1-2% of its energy because the oxygen is readily available in

gaseous, breathable form in the atmosphere. Fish, on the other hand, have to use 15% of there

energy underwater to breathe through its gills. The process by which fish breathe takes much

longer; fish take in water by their mouths, by opening and closing their mouths they pump water

through their gills, oxygen and carbon dioxide are exchanged across the gill structure called the

lamellae, thin disk shaped membranes filled with capillaries, allowing for the gas exchange. This

takes much more energy than mammal because the fish must constantly be pumping water andits blood while mammals only have to pump their blood. If there were two containers of fish, one

with a volume of water at 90% and another with a volume of water at 50% the fish in the 90%

full tank would have more oxygen available. There would be more oxygen because there is

more water, with more water comes more hydrogen bonds and more chances to catch water

between in them, so a fish with more water have more oxygen.

The dissolved oxygen of stream entering a lake would be much lower than that of the

lake because a lake has much less movement than a stream does. More movement means

more breaking of he hydrogen bonds and less ability to store water, when a stream is constantly

moving, flowing into a lake it is breaking those bonds. The concentration of dissolved oxygen in

water samples would be greater at 7am because the water would have had less exposure to the

sun. The sun gives the molecules energy and the energy causes more motion of the molecules

breaking the hydrogen bonds like movement does. At 5pm the water would have been exposed

to sunlight all day and the water molecules would be excited and moving more rapidly frequently

breaking the bonds allowing for less holding of oxygen.

Eutrophication is the excessive accumulation of nutrients that cause dense growth of

organisms, the decay of the organisms cause a decrease in oxygen concentration of shallow

waters. Excessive runoff from fertilizers can cause eutrophication, the chemicals given by


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fertilizes help plants grow but when they make it into ponds they cause an excessive amount of

algae growth. Algae can absorb large amount of oxygen and when it dies it decreases the

amount of oxygen in the water then suffocating the organisms living within the water.

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