Notes to Teachers and Volunteers

Answers to Questions for Each Topic

10 October 2013

The following represents a complete list of answers to questions in all four of the topics covered in the Cell Bio Lab sessions for weeks 1 through 3. Answers to some of the experiments for Topic Bacterial Growth are not provided yet, until students complete gathering of data on Friday of week 2 and also for both days of week 3. Teachers can decide how to share these answers with students. Some topics have many more questions than others and time is not available in the lab sessions for students to answer all of the questions. Since these topics are part of an enrichment experience for the students, we would suggest that students be provided answers to questions once they have attempted to answers the questions or after the three-week session is completed and during the time they are preparing for their PowerPoint presentations. Copies of this handout will be made available to volunteers in week 2 F lab sessions and also during week 3 lab sessions on W and F.

Questions for Topic A World in a Drop of Water

Questions for Experiment 1 and 2:

1. What are the three forms of nutrition observed in the four different protists observed in the lab? See bottom of page 2: ingestion, absorption, and photosynthesis.

2. Which one of these organisms is able to obtain its nutrition in two different ways? What advantage do these options provide to this organism? Euglena – photosynthesis in light and ingestion if in total darkness; this dual approach allows the organism to survive in the absence of light.

3. How do the pseudopods of the Amoeba aid this single-celled organism in obtaining its nutrition? There could be two answers to this question -- name both of them? They allow the cell to move into regions of nutrition, and they allow the cell to engulf another microorganism, like a bacterium, or another food particle.

4. Do cilia have a dual purpose in the way a paramecium lives in an aquatic environment. The answer to this question is similar to # 3, above. Yes. Cilia provide allow the cell to be motile, and some of the cilia are present in the oral groove which aids the cell in funneling food particles including other smaller microorganism into the cell.

5. Were you able to observe contractile vacuoles in the protozoans you observed? What might happen to these aquatic organisms if contractile vacuoles were absent? These should be visible at the higher magnifications, but seeing them contract was difficult to see in the microscopes we used. They probably would burst, because water is constantly moving into the cells from the surrounding solution, e.g., pond water, because the concentration of water in the pond is greater than the concentration of water inside the cell, so a water gradient favors movement into the cell. The contractile vacuoles aide in the discharge of the excess water back into the aquatic environment

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6. Can you think of another experiment you performed in your classroom recently, where water movement into and out of a cell was observed? What is the name for this process? Why does it occur? Yes, the lab topic “Cells are a Bag of Goo” completed in the classroom during recently, where the egg shell was dissolved away from the egg cell membrane. Osmosis. Osmosis occurs whenever the concentration of water on one side of a semi-permeable membrane is different from the other side – either higher or lower in concentration. Water will always move from region where there is more water to a region where there is less water regardless of the reason for the differences in water concentration.

7. Now that you have summarized the similarities and difference among the four protists in Table 1, what do you think is the most unique feature of each of them? Amoeba – pseudopods; Paramecium – cilia; Euglena – flagellum and the ability to either produce food by photosynthesis or ingest it; Spirogyra – nonmotile when compared to these protozoans and multicellular.

Questions for Experiment 3:

Topic 1

1. Was your group able to demonstrate that Euglena is attracted to light? If so, what part of your procedure was most important in demonstrating this attraction? The answer to this question will depend on the outcome of their experiment; the part of the procedure that might turn out to be the most important is their ability to develop a method to focus the light so it is clearly coming from only one direction, and then being able to observe the movement of the cells to the light source. Results will be known after student groups have completed their experimental procedures in week 3.

2. Were you able to demonstrate using filters of different wavelengths that Euglena’s attraction to light is influenced by the color of the light used? If so, which color was the most effective of the ones you tested? See Topic1, 2), top of p. 9 where the light sensory system is discussed. Blue and red light in the visible spectrum are the two wavelengths of light most involved or contributing to photosynthesis. It will be interesting to see if these two light sources used alone or in combination are more effective than say green light. Blue light is at the short end of the visible spectrum; red light is at the longer end of the spectrum; green is intermediate in wavelength. Filters will be available for the students to use in their experiments. Results of experiments published in the literature indicate that Euglena migrates toward blue light.

3. If you were unable to demonstrate whether Euglena is attracted to light, what additional changes in procedure would you recommend as the next best approach to demonstrate this attraction? There is no completely right answer to this question. This question gives a student or the group an opportunity to hypothesize about what might have worked better. Three possibilities: being able to insure the light is unidirectional and still be able to observe movement; having sufficient light intensity so the cells are attracted to the light; using light of the most favorable wavelength in the visible spectrum.

Topic 2

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1. Of the three motile protozoans you measured through the microscope, which one was the longest? The shortest? The widest? Is this what you expected? Explain. The sizes will depend on the species used in the lab; Amoeba may range up to 600+ µm in lengths when pseudopods are fully extended; Paramecium species may range in length from about 70 to 300 µm in length; Euglena is the shortest and smallest ranging in length from about 30-60 µm in length. Amoeba will be the widest because of the extending pseudopods.

2. Which of the three different measurement techniques using the stage micrometer did you find to be the easiest to do? The most difficult? The most accurate? The answer will depend on how successful the students are in being able to observe specimens. All of the approaches will work. The most accurate could be either calibrating the tick marks on the pointer in the eyepiece or ocular if they have a microscope where the pointer has tick marks --- the calibration could be done using the stage micrometer; photographing a portion of the stage micrometer and a specimen at the same magnification also should be accurate, but requires more steps to get the information to determine the measurements.

3. Is the length of an individual Spirogyra cell similar in length to that of the protozoans you measured? What about the width of an individual cell compared to the width of the protozoan cells. Length may vary depending on growing conditions. Usually the cells within a filament are many times longer than their width. Width may be 30-50 µm; length may be 100-200 µm.

Topic 3

1. Were you able to observe the ingestion of individual yeast cells by a Paramecium? What about the Amoeba – did it ingest a yeast cell? Answers to this question will depend their success in observing these cells ingesting a yeast cell and being able to identify a yeast cell because it may be too transparent.

2. Did staining some yeast cells with 1 % neutral red aid in your observations of ingestions? It should have, depending on how intense the cells were stained. Student Groups on Wed of week 2 tried 1 % neutral red, but the yeast cells did not take up the stain very well. Student Groups on Fri of week 2 will try yeast cells stained in 1% congo red, which is the preferred stain to use. Wed students observed large numbers of food vacuoles in paramecia in the field of view suggesting the cells were ingesting yeast cells, but this is only an anecdotal observation at present until more observations are made by students in Friday’s sessions.

3. If you were unable to observe ingestion by either protozoan, which change in procedure would you recommend to increase the likelihood of observing ingestion? Being able to see yeast cells will be important – greater intensity of staining would aide in seeing them. Being able to observe either an Amoeba or Paramecium continuously for a period of time to observe ingestion or engulfment by pseudopods will be critical.

Topic 4

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1. How many different microorganisms did you observe in the pond water when you initially observed it at the beginning of the Week 2 lab session? What was your basis for considering them as different from one another? The number will vary based on the source of the pond water and the influence of the timothy grass in stimulating more growth. Their basis for considering them to be different organisms may be based on their size differences, whether they are motile or non-motile, whether they have chloroplasts, etc. They may observe some small invertebrate animals such as worms, and perhaps some fungi. They won’t be expected to know the names of the organisms in the pond water and neither should the volunteers be expected to know their names, but they can hypothesize that they are different based on cellular characteristics including shape, motility, presence or absence of cell walls, chloroplasts, etc.

2. Did filtering the pond water change or have any effect on the total number of different microorganisms in the Week 3 when compared to the unfiltered pond water treatment? If no differences between treatments were observed then what conclusions can you draw from this result? Filtering could have reduced the number and types of organisms depending on how many organisms were present in the pond water at the beginning, and also how effective the filter paper was in screening out organisms that could not pass through it. If the filter paper was porous enough that most of the organisms passed through it, then it would not have had any difference.

3. Did Timothy had infusion contribute to an increase in the number or diversity of microorganisms present? How can you explain why dry grass blades would change either the number or diversity of microorganisms present? We expect that timothy hay infusion will increase the number of organisms and also the number of different types of organisms.

4. Did you observe any organisms in the pond water that probably would not be considered either protists (including protozoans) or bacteria? Why do you believe these organisms were different than protists or bacteria? What other group(s) of organisms do you think are most closely related to these organisms you observed? It is possible that they will observe different fungi in the water, and also some microscopic or near microscopic small animals lacking a backbone that are generally called invertebrates. Some of these may appear segmented and are motile, but usually move rather slowly through the water. These organisms are considered different than bacteria because they are multicellular, and they are different from protists in beginning much more complex.

Questions for Topic Multicellular Magic

Questions regarding leaf cell structure and function

1. What is a stoma? Two guard cells and pore or opening between them.

2. What cellular component is present in guard cells, but absent in other epidermal cells? Chloroplasts

3. What is the purpose of a stoma? Gas exchange between the inside of the leaf and the atmosphere. Oxygen and water vapor exit the leaf and carbon dioxide enters the leaf.

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4. How do stomates carry out their function? By either opening or closing thus allowing gases to escape or enter or if closed they limit the entry and exit of gases.

5. Can you name the three gases that pass through stomates? See no. 3, above

6. Are all of these gases essential for the survival of animals and humans on this planet? Explain. Yes. Oxygen is required of all respiring organisms including animals and humans. The latter also give off carbon dioxide via respiration, which can be used by plants during photosynthesis.

Questions regarding root cell structure and function:

1. Are root hairs single cells or multicellular? Unicellular. What is unique about them is the way they grow out away from the main axis of the root.

2. What is the primary function of root hairs? They have two functions. Their primary function is absorption of water and minerals from the soil. Their other function is to anchor the root in the soil.

3. Why are root hairs so sensitive to drying out when exposed to the air (atmosphere) in the room? What cell feature makes leaf cells like guard cells more resistance to drying out when exposed to the same atmosphere as root hairs? Root hairs are not covered by a waxy cuticle like guard cells in a stoma. Thus, they lose water very rapidly when exposed to the atmosphere. In soil, root hairs exist in a very humid environment except when soil dries out due to a lack of rainfall or moisture.

4. What are the primary cellular differences between root hairs and guard cells found in the leaf? Their cell shape is very different; guard cells have chloroplasts and root hairs do not; guard cells have a protective covering over their surface to protect them from drying out, root hairs do not; their functions are very different as discussed in question 2.

5. Do you believe that some of the water vapor molecules that pass out of the stomates of the leaf were absorbed from the soil by root hairs? Explain. Yes. Most of the water that passes out of stomates was absorbed by root hairs.

Questions regarding specialized cells of the circulatory system in animals/humans

1. Describe unique cellular features of red blood cells. RBCs do not have a nucleus. This makes them uniquely different from white blood cells. The absence of a nucleus is related to their function described in question 2.

2. What is the primary function of red blood cells? RBCs transport oxygen molecules throughout the circulatory system. The oxygen molecules attach to RBCs in the lungs and then these molecules are transported throughout the body. RBCs also transport carbon dioxide molecules from tissues where they are given off back to the lungs where the carbon dioxide is released into the atmosphere.

3. How are white blood cells different in cellular features from red blood cells? All WBCs have prominent nuclei. There are five main types of WBCs – each type has a unique nucleus; some WBCs appear to have granules in their cytoplasm whereas others have a non-granular cytoplasm.

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4. Is there more than one type of white blood cell? What about red blood cells? Were you able to observe all types of white blood cells on the microslide? Yes, see the answer to question 3. No, there is only one type of RBC. There are many fewer WBCs than RBCs. They are also quite small, and can be difficult to observe in the microscope unless you are patient and look very carefully. You should have been able to observe at last three or four of the different types. If you had more time, then you would be able to find all different types.

5. What is the primary function of white blood cells? Their primary function is to fight the entrance of foreign particles or organisms into the body. They do this by attacking these agents and destroying them.

6. Can white blood cells be found outside of the circulatory system? What might their function be if found outside of this system? Yes, several types can migrate outside of the circulatory system where they fight infection by bacteria and other organisms or substances.

7. Are there more white blood cells or red blood cells in the human body? Can you propose an explanation for any differences in numbers? There are many, many more RBCs than WBCs. The requirement for oxygen by living organisms including humans requires trillions of RBCs whereas fighting infection requires only a small percentage of the total cells in the blood.

Questions comparing cells of multicellular organisms to bacteria, protozoans and other protists

1. What is a primary difference in the cellular structure of the plant and animal cells that you observed? Plant cells are surrounded by a cell wall; animal cells do not have a cell wall. Plant cells may have chloroplasts; animal cells never have chloroplasts. Plant cells have vacuoles; animal cells do not have vacuoles. There are other differences but these are major differences.

2. How are plant and animal cells different from bacteria, protozoans, and protists? All bacteria and protozoans are single celled organisms; some protists are single celled, and some are multicelled. All plant and animal cells are part of a multicellular organism. Plant and animal cells are more specialized in cellular structure and function than most bacteria, protozoans, and protists.

3. Why do think cells of plants and animals have become very specialized in function compared to what you observed in simpler organism? Many of these simpler organisms live in an aquatic (fresh or salt water) environment whereas many plants and animals live on land. In order to live on land, plants and animals have adapted to an environment that is much harsher than living in water. Thus, many different types of cells have evolved in multicellular plants and animals in order to survive in this harsher environment.

4. Can you hypothesize why particular cells in a multicellular organism develop into guard cells vs root hair or why bone marrow cells develop into red blood cells vs white blood cells? Part of the difference may be related to where the cell types are found in the body of the organism. For example, the environment where root hairs grow is very different than the one where guard cells and stomates differentiate. A second reason may be related to how specific cell types in plants and animals have

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adapted to carry out their functions within the plant or animal body.

5. The term differentiation is defined as the process by which a cell becomes different from the cells it originated from and different from other cells within a multicellular organism ( e.g., plant or animal). Do you think that differentiation is controlled within the cytoplasm or nucleus of a specific cell or both? Can it also be influenced by the location of the cell in the multicellular body of the organism within which it is found? Both the nucleus and cytoplasm play a role in differentiation so that one cell type in a plant or animal body becomes different form other cell types. Location can also influence how a cell differentiates. You will learn more about how differentiation is controlled as you continue to study biology in more advance grades, and perhaps also in high school and college.

Questions for Topic Yucky Poo

1. How is Physarum different in cell structure from the other two fungi that you observed in the lab? No cell walls. The body of the organism consists of a plasmodium of protoplasm with many nuclei included in the cytoplasm. The other two fungi consist of filaments of cells with cell walls.

2. Are Physarum, Rhizopus, and Penicillium able to produce food? If not how do they obtain their food or nutrition? No, they do not have chloroplasts for production of food by photosynthesis. They absorb their food directly from the substrate they grow upon.

3. Why are these organisms called decomposers? Did you observe their action as decomposers in the lab? In what way? Because they break down the substrate they grow upon and over time return the decomposed parts back into the soil as minerals and nutrients that can be used by other organisms.

4. Why did you observe growth of Rhizopus on the store bakery bread but not on the brand-named bread? How are these two breads different from one another? The brand-named bread contains a preservative, whereas the bakery bread has no preservative in it. If you examined the label on the brand-named bread where it lists the ingredients, then near the end of that list the chemical calcium propionate was listed as a preservative. Many brand-named food products contain preservatives.

5. Where did the Rhizopus come from that infected the bread slices you placed in the zip lock bag? Where did they come from in the bag of bread slices that remained after slices were removed for experiments? Rhizopus spores floating in the atmosphere of the bakery at the time the bread was baked, could have been baked into the bread when it was made. Also, Rhizopus spores could have landed on the bread after it had been taken out of oven in the bakery and before it was placed inside a plastic bag. Finally, Rhizopus spores could have entered the bag when it was opened to remove a slice of bread to conduct the experiment. That would mean the Rhizopus spores were floating in the air within the Science Lab.

6. Is Rhizopus a harmful or beneficial organism? Defend your answer. Rhizopus generally is regarded as a harmful organism in that it grows on bread and other bakery products, and limits their useful life of eating. However, it could be thought of as beneficial in that it can cause the decomposition of old bread and other similar products that will not be eaten.

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7. Did you observe any other mold growing on the store bakery bread other than Rhizopus? If so, do you think it was Penicillium? Yes, it appears the colonies were Penicillium, but we would have to make a wet mount slide to positively confirm it was Penicillium.

8. Do you think that you could limit the growth of Penicillium on oranges or other fruits if you kept them refrigerated until you ate them? Unfortunately, some kinds of Penicillium grow very well at colder temperatures such as you find in a refrigerator, so it doesn’t always work to refrigerate food items such as cheeses, cold meats, some fruits, etc., in hopes that they will not be substrates for Penicillium growth.

9. Why do you think Penicillium frequently grows in a round patch on the surface of an orange rather than in a different pattern? Many Penicillium colonies originate from a single spore or a small cluster of spores that tend to grow out in all directions or radially from the point where a spore or cluster of spores came in contact with the surface of an orange. Therefore, the colony appears as a round patch.

10. What are the green splotchy areas in the sample of Roquefort cheese that you observed in the lab? Do you think they are harmful to your health? Explain. They are Penicillium spores. Note they are green in color similar in color to the Penicillum colonies that you saw growing on the orange or bread. They are not harmful and actually impart a particular flavor to the cheese, unless you are allergic to Penicillium.

11. Is Penicillium a decomposer? Why do you say that? Is it a beneficial or harmful microorganism or both? Yes – because it causes the decomposition or breakdown of the substrate it grows upon, and in the process it returns useful nutrients and minerals into the environment that can be used by other growing organisms. Some species of Penicillium can be regarded as beneficial if they cause decomposition of substrates that are not intended to be eaten. If they destroy fruits or other foodstuffs that we could eat, then they would be regarded as harmful. However, one or more species of Pencillium produces penicillin, an antibiotic that has saved millions of human lives since its discovery – thus, in this case it is very beneficial.

Questions for Topic Bacterial Growth

Questions for Experiment 1:

1. Do the results shown in Table 1-2 indicate which treatment was the most favorable for colony growth? Is this what you expected? Why or why not? Some groups did not observe any bacterial colony growth on the petri dishes that they prepared for any of the treatments. Some groups observed colony growth only on the control. There could be several reasons for these outcomes, and you are learning by performing this experiment, that results do not always turn out as expected. If no growth was observed on any treatment dishes, then perhaps the triple mixture of bacteria that was used was not viable. Alternatively, perhaps the way the dishes were inoculated where the inoculated sterile water was poured into the dishes and then decanted or poured off was not effective. Perhaps the sterile water inoculum should have been left on the plates longer in order for the inoculated water to soak into the water. Or perhaps, the inoculum placed in the sterile water did not have enough bacterial cells to establish colonies. Generally speaking for this triple mixture of bacteria, we would have expected that the 1 % sucrose solution would have been most favorable for growth and that the higher sucrose and salt

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concentrations would have limited or inhibited growth.

2. Did the incubation of the triple mixture on the agar plates permit you to distinguish the three bacterial species in the triple mix from one another? In what way? If a reasonable number of colonies are observed and are distinct from one another, then the shape and color of the colonies could serve as two markers that could be used to distinguish one bacterium from another. A gram stain procedure to be performed in week 3 could provide proof for which colony was which.

3. If you can distinguish the three species from one another as asked in questions # 2, then did the three species respond in the same way or differently from one another when grown on these sugar and salt solutions? Explain your answer. The answer to this question will depend on whether sufficient colonies were formed on plates and also whether the colonies were different enough in appearance to recognize them as distinct from one another.

4. Is colony counting an effective way to determine measure the growth of bacteria in a quantitative way? Can you think of a better way to measure quantitative growth other than colony counting? Explain. Colony counting is one way to establish quantitative differences in colony growth. Another way would be to measure the cloudiness or turbidity of a solution if bacteria were grown in a liquid medium. This approach would require the use of a special instrument that currently is not available in the MPE Science Lab.

Answers to questions for Experiments 2-4 will be provided once we have an opportunity to review the outcome of experiments for the Friday session of week 2 and the W and F sessions of week 3.

Questions for Experiment 2

1. Did you observe a difference in colony counts for the triple mixture bacteria and the salt resistant bacterium, Halobacterium NRC-1 when these colonies were grown on nutrient agar vs high salt agar? Is this what you expected? Explain.

2. Can you think of an advantage for a bacterial species to be able to grow in a high salt environment? Explain.

3. If you were going to search for a salt “loving” bacterium, where would you look? For example: high up in the mountains, in a fresh water lake, in a marsh near the seashore, or somewhere else? Explain your choice?

Questions for Experiment 3

1. Did you observe a difference in colony counts for the three different treatments in this experiment? Is this what you expected? Explain.

2. Would you have expected greater differences in colony counts if you had counted the colonies more frequently, e.g., on day 1, 3, 5, and 7 rather than just on day 7? Explain.

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3. If the plates were left for a longer period of time, e.g., 14 days, what might you observe in terms of numbers of colonies?

4. Can you think of a better way to determine the quantitative growth of bacteria other than using colony counting?

5. Which temperature was the most favorable for bacterial growth based on colony counts? Is this what you expected? Explain.

6. Refrigerator temperatures are usually between 4 and 6 degrees Centigrade. Why do you think this temperature range has been selected for storing food?

Questions for Experiment 4

1. Were you able to distinguish between the three different forms or shapes of the bacterial species in the triple mixture using the bacterial smear and gram negative staining techniques? Which of the three forms was the most visible in the microscope? The least? Can you explain why one form is easier to see than the others?

2. What is the basis for identifying a bacterium as being either gram + or gram -? Which of the three bacterial species in the triple mixture is/are gram + and which is gram -?

AnstoQuest10.01.13wp+whd

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