The Unseen World Life in the Hidden Realm

Exercise 5: The Unseen World Part 2: Life in the Hidden Realm

Take a drop of water from a pond and look at it under a microscope and you will enter a whole new universe that you probably never suspected existed. You will use todays lab exercise to learn about that realm, and on the way, you will learn to use an important tool in biology, the compound microscope.Remembertousetheinformationinthepre-labtothinkaboutthequestionsposedhere.

The Scenario

Youareascientistwhoisstudyingtheecosystemofasmallpondnearyourhome.Youhavedecided toexaminethepondatintervalsoverthenextyeartofindouthowthecompositionoforganismsliving in the pond changes over the year. This will be your initial set of observations about the pond. Your objectives will be to examine some of the pond water to observe and classify the different types of organisms that are growing there, and to speculate about the overall structure of the ecosystem.

You should work with a partner in this exercise. Each of you should have a compound microscope, a stereomicroscopetoshareandshouldberesponsibleforfindingatleast2differentmicroscopicand2 different macroscopic organisms. As you look for organisms, you are trying to find a cross section of organismsthatrepresentbothproducersandconsumersoftheecosystem.Inthesecondactivity,you willworkwithotherstudentsintheclasstotryandfindthewidestpossiblecross-sectionoforganisms that may exist in the ecosystem.

Activity 1

Youwillneedtomakewetmountslidesofthepondwater.Todothis,placeasmalldropofthepond water on the center of a clean glass slide. Add a glass cover slip over the drop of water. If the cover slipseemstofloatonthewaterdrop,youhaveaddedtoomuchwaterandshouldmakeanotherslide with a smaller drop of water.

1. Observe the drop of water under 10X to scan and find the organisms. The higher power objective(40X)shouldbeusedonceyouhavefoundanorganismandwanttoseethedetails.

2. If youfindthattheorganismsaremovingtooquicklyandaredifficulttoobserve,addonedrop of Protosloto the drop of water on the slide. Allowit tomix, and then gently add the cover slip to the slide.

3. You should be patient looking for these organisms. You may need to make a number of different slides in order to find different organisms. Take your slide samples from different areasofthemainpondwatersample;differenttypesoforganismsmaytendtocongregatein different areas.

4. You and your partner should locate and draw a pictureof at least 4 different organisms, two microscopicones,andtwomacroscopicones.Whenyouhavefinisheddrawinganorganism, let your partner see and draw it before moving onto the next one. Use the Skill Check worksheet for your drawings. Underneath each sketch you should write the following information:

& ThenameoftheorganismifyoucandetermineitusingtheKeytoPondWaterOrganismsor the Wards Dichotomous Key to Pond Life or one of the following web sites.

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Key to Pond Water Organisms

Thiswebsiteisadichotomouskeythatcanbeusedforidentificationofmanyoftheorganisms that might befound in pond water. There will be copies of this key available in the lab for you to use during the identification process.

Organism identification Sites

The Smallest Page on the Web: This site has drawings, photos and descriptions of the differenttypesoforganismsthatcanbefoundinpondwaterecosystems.Therearegood descriptionsoftheorganismsandthevarioustypesofphysicalstructuresyouwillseeon them.

uk.org.uk/mag/wimsmall/smal1.html

The Molecular Expressions Digital Video Gallery:Pond Life. Thissitehasdescriptions and photos of a wide variety of organisms found in pond water ecosystems

The Pond Life Identification Kit:Thissitehasorganismsgroupedbytype,including bacteria, protozoa (a group of animal-like protests), algae (also protists) and larger animals such as worms

& Writeabriefdescriptionofthecolorandshape,anymovementpattern,whetheritusesciliaor flagella to move

& Recordanybehavioralactionsthatyousee,forexample,responsestolight,responseto obstacles in its path

Estimatethesizeoftheorganism(referbacktotheExercise3prelabifnecessary)

Howmanyorganismsofthistypedidyoufind?Arethereafewofthem,oraretherealotof them? Estimate how heavily populated this ecosystem is with this organism.

Activity 2

One job of scientists is to communicate information in order to build a more complete picture of the scientific endeavor. In order to arrive at a more complete understanding of the types of organisms in thepondwaterecosystem,youshouldnowcompareyourresultswiththoseofothermembersofyour class. Each person in class should have observed two organisms, and it is now your task to talk with yourfellowbiologistsinclasstoseeifthereareotherorganismspresentintheecosystemthatyoudid not directly observe. You should find at least four additional organisms, to add to your observations. Record the information you obtain from your peer researchers on the Skill Check worksheet in the areaforActivity 2. Besuretorecordthenameof thepersonfrom whomyouobtainedyour datainthe area marked Source of Data.

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Activity 3

Now that you have data about at least 8 pond water organisms, is time to write about what you have learned. Write a paragraph or two describing the organisms you have seen and their behaviors. How do you think these organisms might contribute to the overall activity of the pond? For example, which organismsareplantsoralgae(producers)andwhichareprotistsoranimals(consumers)?Howdoyou think these organisms might fit together to form an inter-dependent community in the pond? Draw a proposed food chain based upon the organisms you have observed or obtained information about.

Thisinformationshouldbetyped(althoughyoumaydrawyourproposedfoodchainbyhand)and attached to the Skill Check worksheet that you turn in next week.

Activity 4

Theorganismsthatyouhaveobservedareprobablyonlyasmallpartoftheoverallpondecosystem.It islikelythatthereareotherlargerorganismsthatarealsopartofthesystem.Taketheinformationthat you described in Activity 3, and speculate how it would change if you were to add the following list of organisms into the ecosystem. How would feeding relationships change? If you were to speculate on thepopulationsofeachofthedifferentorganisms(thoseyouhaveobserved,andthosepresentonthe list below), which of the organisms would you expect would be present in the greatest numbers?

Whichwouldbepresentinthelowestnumbers(thinkabouttheenergypyramidfromthepre-lab)?Add a paragraph or two to the information from Activity 3 that describes these modifications and hand this in attached to the Skill Check worksheet next week.