ap bio 9-26 do lab

18
Eddy Egan September 26, 2008 Mrs. Contreras AP Biology Pd. ¾ Even The Concentration of Dissolved Oxygen (DO) at Varying Temperatures (4ºC, 19ºC, 30ºC) and the Primary Productivity of Elodea at Various amounts of Light Primary productivity of an ecosystem is defined as the amount of light energy converted to chemical bond energy (glucose) by an ecosystem autotroph’s during a given amount of time. (Goldberg) The total primary production within an environment is often called Gross Primary Production (GPP) and can be measured in three different ways: the rate of carbon dioxide utilization, the rate of oxygen production (which we will use in this lab), and the rate of formation of organic compounds. (Primary Production: Wikipedia) GPP is the amount of solar radiation converted into chemical energy by the light processes of photosynthesis. (Goldberg) That means that this productivity supports all of the life in an ecosystem. The ways that the primary producers make this energy available are through two separate processes; photosynthesis and cellular respiration. The equation for

Upload: edward-egan

Post on 13-Nov-2014

1.105 views

Category:

Documents


4 download

TRANSCRIPT

Page 1: AP Bio 9-26 DO LAB

Eddy EganSeptember 26, 2008Mrs. ContrerasAP Biology Pd. ¾ Even

The Concentration of Dissolved Oxygen (DO) at Varying Temperatures (4ºC, 19ºC, 30ºC) and the Primary Productivity of Elodea at Various amounts of Light

Primary productivity of an ecosystem is defined as the amount of light energy

converted to chemical bond energy (glucose) by an ecosystem autotroph’s during a given

amount of time. (Goldberg) The total primary production within an environment is often

called Gross Primary Production (GPP) and can be measured in three different ways: the

rate of carbon dioxide utilization, the rate of oxygen production (which we will use in this

lab), and the rate of formation of organic compounds. (Primary Production: Wikipedia)

GPP is the amount of solar radiation converted into chemical energy by the light

processes of photosynthesis. (Goldberg) That means that this productivity supports all of

the life in an ecosystem. The ways that the primary producers make this energy available

are through two separate processes; photosynthesis and cellular respiration. The equation

for photosynthesis is 6CO2 + 6H2O C6H12O6 + 6CO2 but that also must include sunlight

and ATP for the process to work. That is why I believe that if plants were introduced to

varying amounts of light, then 100% light would prove to be most productive in oxygen

production and the more oxygen production means more primary production has taken

place. Cellular respiration is required by all living organisms and the equation is C6H12O6

+ 6CO2 6CO2 + 6H2O. (Duedall) Only a small portion of the energy produced by

primary production will be used in secondary production by the organism, the rest will be

excreted or used in aerobic respiration.

Page 2: AP Bio 9-26 DO LAB

Of course, these processes cannot be preformed under such simple circumstances.

Without proper nutrition of the plant or organism the process turns into nothing. In order

to overcome these problems, photosynthesis must include water and carbon dioxide as

well. (Duedall) On top of the need for water and carbon dioxide, the right atmosphere

must also be present for the process to take place. Photosynthesis is known to not work

very well in the dark. This is due to the fact that chlorophyll is not absorbing sunlight and

in turn, not producing glucose. Temperature has an effect similar to the lack of water. If

the temperature is too high or too low then water absorption will become increasingly

difficult to the point where glucose production comes to stop.

Cellular respiration can also drive photosynthesis. Secondary products of cellular

respiration, such as the carbon dioxide we exhale, are reactants to photosynthesis. This

cycle is a large part to our survival and the containment of greenhouse gases. The cycle

repeats itself since cellular respiration requires oxygen when the aerobic form is used.

(Duedall)

The oxygen that is required for cellular respiration then has problems to encounter

as well. The kind that we breathe gets thinner and colder as altitude increases and air

pressure decreases. Under water there is something comparable to that lack of oxygen.

Organisms such as fish that live underwater don’t breathe the oxygen that is in H20 but

rather the dissolved oxygen (DO) in the water that is in a free state. (Lab 12. P 136) As

the water gets colder, the oxygen is more readily available since more oxygen is

dissolved in the water. This allows for more organisms to survive and flourish in the

richly oxygenated water. Warm water has the opposite affect and can effectively

suffocate species if the concentrations are too low.

Page 3: AP Bio 9-26 DO LAB

Warm water can also have significantly low dissolved oxygen rates due to the

environment in which it’s in. In warm summer months, the sunlight evaporates a vast

amount of water. The water that evaporates gets sucked out of streams, ponds, and lakes.

Because there is so much water loss, the ponds, streams, and lakes are shallower and less

turbulent. That lack of turbulence means that less air is circulating to the water and the

dissolved oxygen is lessened. Water falls and other turbulence then plays a large role in

dissolved oxygen. The more there are, then the more oxygen can be dissolved in the

water. In stagnant ponds and lakes, the dissolved oxygen rates are extremely low due to

the fact that only the top of the water is being oxygenated by the air. On top of that, the

water might also be being heated which lowers the dissolved oxygen rate. That leaves

relatively no dissolved oxygen in the pond or lake if it is shallow enough. I believe that if

the water temperature is cool or cold, then the highest saturation will be present. I came

to this hypothesis by realizing how cold the ocean is and how well so many things live in

it; I may think it is freezing but the vast amount of organisms and life forms favor lots of

oxygen. Many factors can then affect photosynthesis and that does not even incorporate

human involvement with things like pesticides and herbicides.

An ecosystem is a natural unit consisting of all plants, animals and micro-

organisms (biotic factors) in an area functioning together with all of the non-living

physical (abiotic) factors of the environment (Wikipedia). When it says functioning

together, this refers to all of the cycles and processes working together to make a

community. Previously stated, a cycle can be observed in nature and that cycle consists of

plants producing oxygen, which is used by organisms in cellular respiration, and then

cellular respiration produces carbon dioxide. When organisms happen to die off, then

Page 4: AP Bio 9-26 DO LAB

their carcasses lie on the ground to decompose. That decomposition then provides the

ground with nutrients that can be reused by other organisms and plants.

The same thing can be observed in aquatic environments. In the book Survival of

the Sickest they refer to the extremely rich deposit of nutrients that sits on the ocean

bottom. Scientists have even tried to construct experiments in which they surface these

nutrients and then growth flourishes upon them. The dissolved oxygen in the water

thanks to the decomposition promotes the life of plants that live in the water. Those

plants must then live within the photic zone, where sunlight reaches, in order to keep the

process of photosynthesis going and keeping the dissolved oxygen levels at a regulated

rate.

Procedure

1. Obtain three beakers

2. Measure 5 cm from the bottom of the beakers and fill them with distilled water to

that line.

3. Leave the first beaker at room temperature (19ºC)

4. Measure the amount of dissolved oxygen in the sample with the dissolved oxygen

meter. In order to keep the water moving when measuring the Dissolved oxygen,

place the beaker on a mixing tray and insert a mixing magnet, set the mixing

setting to low. Record the data that you receive from the dissolved oxygen meter

5. The next beaker will need to be chilled to 4ºC. To do this, fill a large beaker up

half way with water and then add about 10 cubes of ice. Place the original beaker

in the large one and insert a thermometer to make sure that the temperature is

correct.

Page 5: AP Bio 9-26 DO LAB

6. Repeat step 4

7. The final beaker will need to be slightly heated to 30ºC. Place beaker on warming

tray and put the setting very low. We do not want to overheat the water. Place a

thermometer in the beaker and wait until the temperature reaches 30ºC.

8. Repeat step 4

9. Clean up your station.

1. On the first day, prepare your set up for the lab.

1. Obtain three sample jars with overflow lids.

2. Cover one jar completely with aluminum foil, this will be

your dark jar that allows 0% light

3. Cover the second jar with nothing, this will be you 100%

light jar

4. Cover the third jar with three screens, allowing only 25%

light to enter the bottle.

2. On the next day, obtain Elodea from the class store of it.

3. Make sure that the elodea is as dry as possible and then measure out exactly one

gram.

4. Add one gram of Elodea to each of the three jars

5. Fill the jars with water completely; there should be no air bubbles present.

6. Once the jars are filled, empty them back out into separate beakers.

7. Record the dissolved oxygen content

8. Return the water back to the jars again. If air bubbles are present then top off the

bottles with more distilled water.

Page 6: AP Bio 9-26 DO LAB

9. Place the dark bottle in a very dark cabinet away from all light.

10. Place both the 100% and the 25% bottles underneath a light source.

11. After about 24 hours, measure the dissolved oxygen content again.

12. Clean up your station.

Discussion

Our initial samples of water showed to be differing in amounts of dissolved

oxygen, that finding should have been the same throughout everyone’s experiment.

Instead of remeasuring the dissolved oxygen in each sample, we simply took the average

of two samples that were gathered. Our results after 24 hours were in good display and

the correlation can be seen on Graphs 1&2. The skew that had been seen is at 2% light

in relation to both Gross Productivity and Net Productivity. The explanation for this

could be attributed to human error. For the most part, a positive correlation is present in

our samples and it can be understood that the more light that is present, then the more

gross and net productivity is also present. This almost confirms that primary productivity

is dependent on light. 100% light had almost the highest productivity, while 2% had the

lowest productivity. With further investigation and repetition of the experiment, a more

conclusive correlation can be found since the 25% light is most likely due to human error.

Graphs 1&2 show a positive correlation but there is actually no net gain that was

produced. If this is the actual case then organisms would not be able to easily survive

around elodea since it is just soaking up nutrients and not giving anything back. The data

represented may again be due to human error. Net productivity should be more than 0%.

Looking at it a different way, 100% light may not be suitable for Elodea. This plant

grows in the depths of water and therefore never really receives 100% of light. If it did

Page 7: AP Bio 9-26 DO LAB

happen to, then Elodea would thrive to out of control numbers, and lead to the thriving of

many other organisms as well. The growth of lots of plants and organisms also mean that

there is going to be a lot of death of lots of plants and organisms. This leads to what is

known as eutrophication, or a natural process that occurs in an aging lake or pond as that

body of water gradually builds up its concentration of plant nutrients and thus depletes

the amount of dissolved oxygen. (Eutrophication: Wikipedia) Eventually, this process

will choke off the life in the pond and algal blooms will be prevalent.

If out results were absolutely true, then all of our light environments would not be

able to support life. Like stated before, a negative net productivity means that there is less

than no productivity. The sources of food and oxygen would be depleted at astronomical

rates and nothing would ever survive.

As the temperature increases, as our graph indicates, the saturation of dissolved

oxygen also increases; this clearly goes against my hypothesis that states the complete

opposite. Outside sources, including LabBench, clearly and concisely stated that when

temperature increases then the amount of dissolved oxygen decreases. (LabBench) Our

experiments somewhere went awry and should be redone many times in order to properly

use the part of the scientific method that states that repetition must take place.

When organisms respire outside of water, they only use 1 to 2 percent in the

process. Air encompasses the earth and is very easily attainable since it is such large

abundance. Oxygen diffuses 300,000 times faster in air than water. That information

provides the basis for the hypothesis that the reason fish spend 15% of their energy to

move water over their gills is because oxygen is so much harder to access under water.

Page 8: AP Bio 9-26 DO LAB

The density of water compared to air, is incredibly higher, meaning that more energy

must be used to push through the liquid and acquire air.

Different sources of water provide much different results in the dissolved oxygen

content. It mainly depends on the environment that the water is in to provide the

explanation of why the dissolved oxygen is so much or so little. Lakes are huge, slow

moving bodies of water that are quiet and serene. These adjectives are not good for

dissolved oxygen. Since they are so slow moving and untouched, the rate of water mixing

with the air is incredibly low. When looking at a stream, one notices the small waterfalls,

all of the rocks that get in the way of the watery path and other sticks and obstacles the

water must get around. Every one of those things provides the water with another

aeration technique and allows the water to have a higher dissolved oxygen reading.

If the readings for dissolved oxygen concentration of water samples were taken at

various times in the day, I would expect the water samples taken at 7:00 a.m. to be the

least saturated with oxygen. At night, when photosynthesis is not taking place, plants

must use cellular respiration to survive. While doing that, they suck up the dissolved

oxygen in the water since it is required for cellular respiration. At 5:00 p.m.,

photosynthesis has been happening all day which means high dissolved oxygen rates.

When looking at the two fish in the separate jars with varying amounts of water, I

notice that A looks like it is pretty well off. The downfall of choice A is the surface area

to volume ratio. He may survive for longer without much movement but when his oxygen

resources are used up it would be hard for him to overcome the oxygen debt that the

water is in. Choice B is much more promising. The surface area to volume looks to be

about 1:1 and that is great for the diffusion of oxygen in the water. If the oxygen starts to

Page 9: AP Bio 9-26 DO LAB

run out, then the natural tendency of a fish is to flop around. The flopping around

stimulates the water and provides even more surface area for the diffusion of water, just

like the rocks and waterfalls in a stream.

As I had explained before, Eutrophication is the overabundance of nutrients

within a given environment (AquaPlant). As seen with the jalapeno and tomato outbreak

of salmonella, bacteria and fertilizers run off into water supplies including streams and

lakes (Science In the News). This runoff provides the grounds for Eutrophication. When

the nutrients are low, and phosphorus is high, algal blooms start to form and choke the

life out of the organisms that use aerobic respiration. (Eutrophication: Wikipedia)

With mistakes found in the experiment, sources of error are prevalent. The errors

that occur the most are from human interaction but are usually going to be that way many

experiments. Other sources of error are small but can play a large role in our experiments.

The elodea that had been used in our experiments was not all from the same source. They

had been collected and then put into a container where we had to sift through them and

find random pieces of elodea to equal a gram in each bottle. That method was not very

scientific for a couple of reasons. The first is that the leaf size had not been the same

throughout the bottles and could have lead to increased photosynthesis in one jar that had

big leaves and little photosynthesis in another jar because the leaves were small and the

stem was large. The stem does not perform photosynthesis.

A source of error in the dissolved oxygen lab had to do with temperature. We

were supposed to measure the dissolved oxygen while it was at specific temperatures.

This could not be accomplished because as soon as the beaker had been removed from

Page 10: AP Bio 9-26 DO LAB

the ice or the hot plate, they migrated rapidly towards room temperature, even by as

much as 5ºC.

The light regulation in our experiments did not seem fitting to me. There was no

way to be certain that 2% of the light was actually penetrating to the Elodea plant. An

idea for a future experiment would be regulating the actual light source instead of

regulating the coverage of a bottle where there is no way to know how much actual light

is getting to the plant. We would also need a light gauge to be absolutely sure that the

light is at the correct intensity for our experiment and to be very precise with our

measurements.

For another experiment, we could step up the previous one but with more

variables to consider. We would set up the different light intensities, but with a multitude

of different color lights. This would show us which light color is the most easily

absorbable by the chlorophyll pigment that photosynthesis uses and at what intensity the

light has to be for the most effective photosynthesis.

References

"Biological Oxygen Demand." 2008. Stevens Institute of Technology, Center for

Innovation in Engineering and Science Education (CIESE). 26=5 Sept. 2008

<http://www.ciese.org/curriculum/dipproj2/en/fieldbook/bod.shtml>.

Campbell, Neil A., and Jane B. Reece. Biology: AP Edition. 7th ed. San Francisco, CA:

Pearson Education, Inc., 2005. 1186-188.

"Dissolved Oxygen." AquaPlant. 2008. Texas Agrilife Extension Service. 25 Sept. 2008

<http://aquaplant.tamu.edu/contents/dissolved_oxygen.htm>.

Page 11: AP Bio 9-26 DO LAB

"Dissolved Oxygen." 2007. Institute of Ecosystem Studies. 25 Sept. 2008

<http://www.ecostudies.org/images/education/chp/dissolved_oxygen.pdf>.

Duedall. "Lecture Notes." OCN-1010 Oceanography. 11 Sept. 2002. 25 Sept. 2008

<http://duedall.fit.edu/ocn1010eng/week13-2bio3.htm>.

"Eutrophication." WikiPedia. 25 Sept. 2008. 25 Sept. 2008

<http://en.wikipedia.org/wiki/eutrophication>.

Goldberg, Deborah T. How to Prepare for the AP Advanced Placement Exam.

Hauppauge, NY: Barron's Educational Series, 2008. 364-65. Google. 2008. 25

Sept. 2008 <http://books.google.com/books?

id=7cobl_npga4c&printsec=copyright&dq=lab+12+dissolved+oxygen#ppp4,m1>

.

Lab 12: Dissolved Oxygen and Aquatic Primary Productivity. Pg 136-139

Pearson Prentice Hall. "Primary Productivity." LabBench. 2002. 25 Sept. 2008

<http://www.phschool.com/science/biology_place/labbench/lab12/primary.html>.

Saskatchewan Learning curriculum. "Unit 2: Ecological Organization." Biology 20

Online. 18 Feb. 2003. 25 Sept. 2008

<http://www.saskschools.ca/curr_content/biology20/unit2/unit2module1lesson3.h

tm>.