Factors affecting the growth of bacteria

Introduction: (Initial Observation)

If we don’t brush our teeth, next day we will have a bad breath. In our mouth, bacteria will find food, water and warm environment that they need to live and reproduce. By learning about the factors affecting bacteria growth, we will be able to keep ourselves safe from invading harmful bacteria. In this project we will investigate on favorable conditions for bacteria growth.

Among the factors that you may study are light, temperature, water or moisture, nutrients in general or any specific nutrient.

Information Gathering:

Find out about bacteria and the environment that they grow. Study about different types of bacteria. Not all bacteria are bad and harmful. Read books, magazines or ask professionals who might know in order to learn about good bacteria and bad bacteria (pathogens). Keep track of where you got your information from.

Search the Internet for “Good Bacteria” to learn about helpful and beneficial bacteria. For many years humans have used these good bacteria, such a lactobacillus, to ferment and preserve milk and plant product. Good bacteria in our body digest our food and fight with bad bacteria. (Actually this fight is only in the form of consuming all existing food, so nothing will be left for bad bacteria to eat. This will stop or limit the growth of bad bacteria, so the body will have time to defend)

Search the Internet for “Bad Bacteria”. Contamination of food and drinking water by ‘bad’ bacteria can result in serious illness and even death, especially in children and senior citizens. Examples of bad bacteria, include strains of E. coli, Salmonella and Campylobacter species.

Finally search for “bacteria growth” or “bacteria growth conditions”.

In order to grow, a bacterium must have an energy source, a source of carbon and other required nutrients, and a permissive range of physical conditions such as food, temperature, and pH. Sometimes bacteria are referred to as individuals or groups based on their patterns of growth under various chemical (nutritional) or physical conditions. For example, phototrophs are organisms that use light as an energy source; anaerobes are organisms that grow without oxygen; thermophiles are organisms that grow at high temperatures.

In the laboratory, bacteria are grown in culture media which are designed to provide all the essential nutrients in solution for bacterial growth. Picture on the right, shows a petri-dish with agar culture media and bacteria colonies on that. Every spot (large or small) is a bacteria colony)

Simple Bacteria Growth experiments

Procedures: (using agar or gelatin culture media)

You need to be prepared and conduct each step accurately to get results. Keep in mind bacterium live everywhere and most strains can grow easily under a favorable conditions already exist in your home, given water and food. Once you grow them, you can easily cross contaminate your environment if care is not taken. Consult an adult prior to conducting these experiments.

Prior to collecting bacterium sample you need to prepare the culture media. Culture media is where bacteria can grow. In previous experiments we used chickpeas and sponges with broth as culture media, but in advanced level and in chemistry or biology laboratories, we can not use those as a culture media.

A good culture media must be clear liquid or solid. If solid, we can grow the bacteria on it’s surface and observe the bacteria colony from different angles and also we must be able to take samples from bacteria without them being mixed with chickpeas or any other things.

Gelatin can be a good culture media for starters. It is available as a dessert with different flavors such as strawberry and Lemon. There are some problem with gelatin however that makes it unusable for serious laboratory use. One problem is that it is solid only in cold temperature. So if you place it in a warm location, it will change to liquid again. The other problem is that manufacturers add some preservatives and flavors that slows down or prevents the growth of bacteria.

In laboratories another gelatinous substance is used called “Agar Agar”. Even though it’s name is “agar agar”, we usually call it agar. Agar gel will remain solid in warm temperatures too.

You can buy agar culture media from laboratory suppliers or online stores such as MiniScience.com.

Dissolve the gelatin or agar in hot water according to its instruction on the package and pure about 30 ml (few table spoons) into each petri dish until the bottom of the dish is covered with liquid. Notice that agar is not a food for most bacteria. So you normally add sugar and broth to it as foods.

Two different types of mold grow in two of our dishes (above pictures, left and right). In one dish we have indications of some bacteria growth (above middle picture). Images are taken about 2 weeks after the preparation of culture media and keeping them at room temperature. Bacteria and mold are obviously entered from the air, because we did not add them to the plate.

For pH experiment you can add a few drops of vinegar to lower PH or add a few drops of baking soda solution to increase the PH. Add these in a separate test tube or small beaker, mix it with hot liquid gel (agar or gelatin with nutrients such as chicken broth) and then pure it into the petri-dish.

Prepare 3 identical petri-dishes, one neutral PH (7), one acid PH and one basic PH.

For more accurate tests, you can not do any of the above methods, because there is no guarantee that the amount of bacteria in all of your test samples are the same. So do this instead.

Once you inoculate all your plates, you need to cover them store them upside down. It is important to store them up side down because the culture media is moist and will lose moisture quickly and becomes dry if placed face up. If you keep it upside down, the moisture will not evaporate so quickly and media will remain moist for a longer time. (If you used gelatin, just cover them. Gelatin will remain moist while covered. )

For the temperature experiment you have to use agar and gelatin can not be used. For this experiment place one sample at room temperature (remember always store all your plates upside down), but somewhere that no body can easily touch it. It should not be disturbed during the incubation period. Place another plate in a plastic zip log bag, seal it and place it in the fridge, in one corner isolated from other food items. Place another one in the bag and put in the freezer. Finally, place one in a warm location (beside the water hater, behind the fridge, inside the warmed up oven….)

After 2 days, collect them all and open them and write down your observation from each plate in your note book. Count the colony of bacteria in each place. Compare the plates, type of bacterial, growth rate, size of the colonies, etc….

NOTE: You eventually need to dispose of your all plates. Collect them all and place them in aluminum or metal container, cover and place in oven. Heat them up for 2-3 hours above 350F. Ideally, you want to kill all the bacteria with heat prior to disposing them.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to find out how different environmental factors such as light, temperature, food, water and pH may affect bacteria growth.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Variables that may affect the growth of bacteria are food or nutrients, light, temperature, PH, Moisture and other possible environmental variables. In this project we will investigate on the effect of Food, light, temperature and PH on bacteria growth. Each of these factors is an independent variable and we study them ONE AT A TIME. The rate of bacteria growth is the dependent variable.

For each independent variable that we study, all other variables must be constant. For example if we are testing the effect of light on the growth of a specific bacteria, then pH, temperature, food and moisture must remain constant.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the growth of bacteria. Identifying variables is necessary before you can make a hypothesis. You need to come up with one hypothesis for each variable that you want to test. Followings are some examples:

1. I think food and water are required for bacteria to grow and reproduce. Without food and water bacteria may die or become dormant. Dormant bacteria are inactive bacteria, waiting for proper conditions to wake up.
2. Bacteria can live or grow in low temperatures (above freezing point of water) and high temperatures (close to the boiling point of water). Freezing temperature will not kill bacteria and boiling also can not kill all bacteria.

Usually after each hypothesis, you also describe why do you think your hypothesis is correct. Following is a sample:

My hypothesis is based on my observation of other live animals and plants. I have not seen any live organism that can survive without food.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

I can suggest three different methods for testing bacteria growth. Some of these methods are not scientific methods, however traditionally they have been used for many years. One method is to let the bacteria grow on a food and determine the bacteria growth by the bad odor of gases released from certain bacteria. This simple method is suggested for younger students. Second method is letting the bacteria grow in a clear solution of nutrients. As bacteria grow, solution will lose its clarity and becomes cloudy. The rate of cloudiness indicates the population of bacteria or the rate of bacteria growth. Third method is growing bacteria on nutrient agar plates and counting the bacteria colonies. Following are sample experiments. Learn from them and design your own experiments.

Experiment 1: (effect of temperature on bacteria growth)

Cook some chickpeas, empty any excess water and let them cool in a tray for a few hours. Don’t cover the peas so bacteria from the air will get to them. Now take 5 samples of the peas in five cups. Try to put same amount of peas in each cup. Cover each cup with a small peace of paper towel and secure the paper towel with the rubber band. Place each cup in a different location in your home with a different temperature.

I suggest to put one in the freezer, one in refrigerator, one in a normal room temperature, one in a slightly warm place and the last one in a warm place. Place a thermometer next to each cup so you will know the temperature in each location. Visit your samples every day and smell them. Bacteria grow will cause chickpeas to create bad odors. Write the results of your experiment in a table like this.

	Bacteria growth spoiled the peas after this hours
Sample in Freezer
Sample in refrigerator
Sample in room temperature
Sample in a little warm place
Sample in a very warm place

Experiment 2: (Effect of light in bacteria growth)

Repeat the previous experiment with 4 cups of chick peas. Place two cups under a bright light (From window or a desk lamp), place the other two in the dark, but under exact same conditions (For example same room temperature). If you want to use a desk lamp, use fluorescent bulbs or modern energy saving lamps that do not create heat. Smell all cups every day and record the results in a table like this:

	Bacteria growth spoiled the peas after this hours
First sample under light
Second sample under light
First sample in the dark
Second sample in the dark

Experiment 3: (Effect of pH on bacteria growth)

Repeat the experiment 1 with 3 sample cups of chickpeas. Before you cover the cups with paper towel, add 10 drops of vinegar to one cup and mix it toughly so the chickpeas will become slightly acidic. In the other cup add 10 drops of a saturated solution of baking soda and mix it toughly so the chickpeas will become slightly basic (Alkali). Place them somewhere in room temperature and normal light. Smell the 3 samples every day and record the results in a table like this.

	Bacteria growth spoiled the peas after this hours
No pH change (control)
Acidic Sample
Basic sample

Experiment 4: (Effect of food on bacteria growth)

Preparation:

In this experiment we will use three regular sponges as a bacteria growth media.

We will use plain regular sponges, not those that have anti-bacteria chemicals.

Cook some chicken wings (or any other part of chicken) with some chickpeas. When it is well cooked filter the broth and use it as a liquid food for bacteria.

Procedure:

Place three sponges in 3 different plastic plates and number them from 1 to 3.

Let sponge number 1 remain dry as a control. Add water to sponge number 2 until it is saturated and absorbs no more water. Add some liquid food to the sponge number 3 until it is saturated and absorbs no more liquid.

Leave all dishes exposed to the air (uncovered) for about 1 hour. This will give enough time for bacteria to get to the sponges.

Cover the plates with 3 other plastic plates.

Inspect and smell all plates every day for up to 2 weeks. Bacteria growth will create a bad odor that can be identified by smelling the sponges.

Record the results in a table like this:

Record the results in a table like this:

	Plate 1 (Control)	Plate 2 (water)	Plate 3 (broth)
Smelled after	………. hours	………. hours	………. hours

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Main Experiment:

Introduction:

If you are a senior student, you need to perform all your experiments with a scientific method. Following steps can be your guideline for your experiment procedures. These procedures consist of 6 main steps.

1. Collect bacteria.
2. Dilute bacteria
3. Grow dilutions on nutrient agar petri-dishes to get bacteria colonies.
4. Get a sample from one colony and grow it in a flask containing clear liquid nutrients. The result must be a liquid containing a uniform distribution of only one type bacterium.
5. Get certain amount of this sample for growth in different growth conditions (heat, water, pH,…)
6. dilute each sample and grow it on petri-dishes for bacteria count.

Does it seem complex? Read this example (sample procedure)

1. You wet a sterile swab with distilled water and then rub it against your refrigerator door handle to get samples of bacteria.
2. Put this swab in a test tube and add about 4 ml distilled water and stir it. By now about 2000 bacteria from the refrigerator handle are in the distilled water in the test tube. Remove the swab and dispose it. Add another 6 ml water to the test tube to bring the total volume to 10ml. If the entire tube has 2000 bacteria, 0.1 ml of that must have about 20 bacteria. This is a good number of bacteria that can grow on each nutrient agar petri-dish.
3. Prepare some nutrient agar petri-dishes (instructions follows) and place 0.1 ml of the test tube solution in each dish. Spread the liquid over the surface of agar. Then place the agar plates in an incubator or warm place. After 2 days you should see bacteria colonies on the agar plates. If you have had different bacteria on your refrigerator door, you will see bacteria colonies with different shapes, colors and sizes. Each colony consists of many bacteria of the same type.
4. Make some fat free chicken broth with mushroom and filter it to get a clear solution. This solution is a good nutrient media for growing bacteria. use a sterile spatula to remove some bacteria from one colony and transfer it to the nutrient solution. Keep the solution in a warm place for two days. By now you should have millions of identical bacteria in your solution. This uniform solution can be used for testing bacteria growth with scientific method. You know that there is only one type of bacteria in this solution. You also know that the bacteria are distributed uniformly. So if you get ten 1 ml samples of this solution, all of them will have the same amount of bacteria.
5. For example imagine you want to test the effect of temperature on bacteria growth. You can make another liquid nutrient solution. Add 0.1 ml of this bacteria solution to your fresh nutrient solution and stir it to make a new uniform solution. Then split your new solution into 5 parts and keep each part in a different temperature. After 24 hours, you test these 5 samples to see which one has more bacteria.
6. To do that you make two dilution of each solution. One is 1:1000 and the other is 1:10000 dilution. Spread 0.1 ml of each dilution on one nutrient plate. So you will have 10 plates for 5 samples (2 plates for each sample). Place the plates in an incubator for 48 hours and then count bacteria colonies in each plate.

If one of the plates made from a 1:1000 solution has 35 colonies, that means 35 bacteria have entered this plate and each bacteria has grown to a colony.

If 0.1 ml of a 1:1000 solution contains 35 bacterium, as simple calculation shows that 1 ml of sample has had 350000 bacterium at the time we spread the samples on the nutrient agar plate. Similar calculation can be done for every other sample and finally we can compare the results to see in which temperature the rate of bacteria growth is higher.

How to prepare a culture media?

In order to grow bacteria, you will need culture media, plates or petri-dishes and some laboratory supplies and an incubator.

Culture Media: Culture media is a moist or liquid matter that contains nutrients for bacteria. Almost any nutrient food may be considered a culture media for general bacteria, however if you want to grow a specific bacteria or prevent growing some other bacteria, you will need to use a fine tuned recipe for your culture media.

Chicken broth and beef broth are among nutrients that most bacteria can use. In some recipes you may also add some mushroom extract. Sugar can also be added to some culture media. Small amounts of some minerals such as potassium phosphate and calcium carbonate may also be added to the culture media. Note that there are many foods that are good for growing bacteria, but they are not good as culture media. For example bacteria can easily grow on milk, but milk is not a good culture media because it will change by the activity of bacteria. Part of milk will solidifies when bacteria produce acids. A good culture media must be clear and must remain liquid and should not easily change pH. If we need to solidify our culture media, we use agar to do that. Agar is a gelatinous substance that is extracted from sea weeds. If we need to grow bacteria for the purpose of identification or counting, we need to grow bacteria in nutrient agar plates. These are petri-dishes containing a mixture of agar and nutrients.

Incubator: Incubator is a warm cabinet that you can set it’s temperature to a proper temperature for bacteria growth. About 35º C is a good temperature for most bacteria. This is close to the body temperature. If you are able to create such a temperature in any other way, it is as good as an incubator. You may find warm places behind your refrigerator, next to the radiator or inside an oven that is off.

You may also make an incubator by placing a small desk lamp inside a wooden or metal box. Or you may put a Styrofoam cooler upside down over a desk lamp. A small lamp (15 watts) should be able to create enough heat to warm up a small space. Prepare your incubator in advance and use a thermometer to test it a day before starting your experiment.

* Chicken broth or beef broth can be purchased from supermarkets and health food stores or you may make them at home. (It must be fat free). Filter paper is coffee filter or you may substitute it with any clean cotton cloth.

How to prepare nutrient agar plates?

Prepare the nutrients such as chicken broth or beef broth and boil it with some mushroom. Let it cool off to the room temperature and filter it to be clear. Add water to bring it to 800ml to 1000 ml. Add agar and stir it to make an emulsion. Reheat the emotion while stirring until it boils for about one minute. Your nutrient agar is now ready. Let it cool to about 45ºC. At this time you can pour the nutrient agar solution in petri-dishes and place the lid. The amount of nutrient agar in each plate must be enough to cover the bottom of the plate. Agar will solidify in plates.

Note that boiling does not kill all the bacteria and your agar and your plates may not be sterile at this time. If you have access to an autoclave, place your plates in autoclave for about one hour at the temperature of 135ºC. Without autoclave your results will not be reliable and some unexpected bacteria may grow in your nutrient agar.

You can keep your nutrient agar plates in a refrigerator for later use. When you are ready to use a plate, remove it from the refrigerator and keep it in room temperature for a few hours.

To grow bacteria, use a pipette to drop 0.1 ml of infected water or any other sample on one agar plate and spread it on the surface of the agar using an sterile glass rod or spoon. Place the plate in an incubator or any other place with a temperature of about 35ºC. Within 24 to 48 hours you should be able to observe bacteria colonies.

In order to grow bacteria, you will need culture media, plates or petri-dishes and some laboratory supplies and incubator.

Culture Media: Culture media is a moist or liquid matter that contains nutrients for bacteria. Almost any nutrient food may be considered a culture media for general bacteria, however if you want to grow a specific bacteria or prevent growing some other bacteria, you will need to use a fine tuned recipe for your culture media.

Chicken broth and beef broth are among nutrients that most bacteria like. In some recipes you may also add some mushroom extract. Sugar can also be added to most culture media. Small amounts of some minerals such as potassium phosphate and calcium carbonate may also be added to the culture media. Note that there are many foods that are good for growing bacteria, but they are not good as culture media. For example bacteria can easily grow on milk, but milk is not a good culture media because it will change by the activity of bacteria. Part of milk will solidifies when bacteria produce acids. A good culture media must be clear and must remain liquid and should not easily change pH. If we need to solidify our culture media, we use agar to do that. Agar is a gelatinous substance that is extracted from sea weeds. If we need to grow bacteria for the purpose of identification or counting, we need to grow bacteria in nutrient agar plates. These are petri-dishes containing a mixture of agar and nutrients.

Peteri-dishes: Petri-dishes are disposable clear plastic dishes with a cap that are used for many science experiments and bacteria growth. A thin layer of nutrient agar in a petri-dish is enough for growing bacteria. You can see the bacteria colony shapes and count them without opening the lead of the petri-dish. Since petri-dishes are clear, you can see the bacteria from either side of the dish.

Incubator: Incubator is a warm cabinet that you can set it’s temperature to a proper temperature for bacteria growth. About 35º C is a good temperature for most bacteria. This is close the body temperature. If you be able to create such a temperature in any other way, it is as good as an incubator. You may find warm places behind your refrigerator, next to the radiator or inside an oven that is off.

You may also make an incubator by placing a small desk lamp inside a wooden or metal box. Or you may put a Styrofoam cooler upside down over a desk lamp. A small lamp (15 watts) should be able to create enough heat to warm up a small space. Prepare your incubator in advance and use a thermometer to test it a day before starting your experiment.

Material:

• Agar (dry powder)*
• 10 petri-dishes (100 mmx 15mm)*
• 1 ml Pipette*
• 10 ml pipette*
• 2 transfer pipette*
• 2 test tubes with cap*
• Glass beaker or steel pan *
• Chicken broth or beef broth *
• Filter Paper *

* These material are included in a kit from MiniScience.com or you may buy them individually from a local laboratory supplier.

* Chicken broth or beef broth can be purchased from supermarkets and health food stores or you may make them at home. (It must be fat free). Filter paper is coffee filter or you may substitute it with any clean cotton cloth.

Procedure:

If you are making your own chicken broth, one small chicken can give you enough broth for this experiment. (Half a pound beef can be used instead). Boil the chicken for one hour. Separate the broth by transferring it to another pot. remove any fat from the top of the broth. Filter the broth using a clean piece of cloth or coffee filter. If you are buying chicken or beef broth from a super market, it comes in small bags of about 4 grams each. Use two bags in about 300 ml water and boil it. Then filter it and transfer the filtered broth to another clean pan.

Add water to the broth to bring it to about 650 ml and boil it again. Start adding the Agar powder while stirring. (If you are using a MiniScience kit, entire agar tube must be used, otherwise use 8 grams of dry agar powder). You will add agar gradually while stirring. Adding agar will take 30 seconds to one minute. If you don’t stir it good, agar solidifies at the bottom of the pan and burns. Continue stirring for another two minutes or until the agar solution is fully dissolved and the solution is clear.

At this time you may optionally add a calcium carbonate tablet and some mushroom extract. (You could also boil mushroom with beef or chicken broth).

Your nutrient agar is ready at this time. Turn off the heat and let it cool down. While it is still warm set your petri-dishes on a table. Open the lead of each petri dish and pour some nutrient agar in each dish (enough to cover the bottom of the dish) and immediately put the lead back. Repeat this for all petri-dishes. Leave the dishes where they are until they solidify.

Note: The nutrient agar should be free from all bacteria, however boiling usually is not enough to kill all the environmental bacteria that have entered our nutrient agar. For school experiments, it may not matter but in real biology laboratories, nutrient agar plates are transferred to an autoclave for sterilization. Hot, under pressure steam of autoclave can kill all bacteria in about 30 minutes. Advanced students may use a pressure cooker to do the same.

Prepare your test sample:

For counting bacteria, you will prepare different dilutions of your original sample. For example you will make 1:10, 1:100, 1:1000 and 1:10000 dilutions. You will then grow each dilution on a different nutrient agar plate.

Use a 1 ml pipette to place 0.1 ml of each dilution in each dish. Spread the liquid all over the plate surface using a sterile spoon. Cover the plate. Turn it upside down and place it in an incubator. Nutrient agar will remain moist when the plate is upside down. Check back within 36 hours to see the result of bacteria growth.

When the bacteria grow, each bacteria will become a bacteria colony that can be seen as a small spot on the petri dish. By counting bacteria colonies, you will know how many bacteria existed in the sample.

In order to test the effect of food, light, PH and temperature (Or any other possible factors) in bacteria growth, we must make some preparations as described here:

• We need a nutritious culture media, where bacteria can grow. In laboratories agar based culture media is being used. Varieties of culture media are available from laboratory suppliers. These culture media consists of agar (A gelatinous material derived from certain marine algae) and some nutrients such as sugar, minerals and more. We may as well invent our own culture media. Fresh milk for example is very nutritious and bacteria may easily grow on that. Also gelatin that can almost be found in every supermarket may be used as a culture media. You may need to add some more nutrients to that to get the best result.
• We need some bacteria to grow. Fortunately bacteria can be found everywhere. On your hand, in your mouth, on the door handle and many other places you may find samples of bacteria to grow. Just use a clean Q-tip to collect them and transfer them to your culture media.
• We need an incubator. Incubator is a warm cabinet with adjustable temperature. A few empty cardboard box can be used with similar results. You can simply place each box in a different place in your house with different temperature. You may use a desk lamp to keep your sample warm. Covering the box with black paper will make it to absorb more light energy and become warmer.
• After a few days (1 to 5 days) we need to see the growth rate of bacteria in our samples. If we use good quality culture media, we can visually observe bacteria colonies. Otherwise we may need some test methods or other indications for bacteria growth. One that may work is using hydrogen peroxide. Hydrogen peroxide will fizz when added to an infected media.
• The reason for this fizz is that the hydrogen peroxide decomposes into water and oxygen when in contact with anaerobic bacteria. The bubbles you see are oxygen bubbles. We may use the rate of bubbles as an indication for the rate of bacteria growth.

Materials and Equipment:

Material that you can use for this experiments are:

• Perti dishes
• clean Q-tips or cotton swabs
• gelatin (A solidifying agent)
• soil sample (good source of bacteria)
• water
• vinegar (Acidic pH)
• baking soda (Alkaline pH)
• paper pH indicator
• zip log bag
• Agar (A solidifying Agent like gelatin)
• broth (contains nutrients)
• filter paper

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

For bacteria count you need to calculate the number of bacteria in each milliliter of solution.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

http://seafood.ucdavis.edu/Pubs/pathogen.htm

http://www.bact.wisc.edu/Bact303/NutritionandGrowth

http://www.wested.org/werc/earthsystems/biology/microbes.html

http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap4.html

http://helios.bto.ed.ac.uk/bto/microbes/shape.htm

http://www.glue.umd.edu/~nsw/ench485/lab8b.htm

http://www.familyhealthnews.com/27.html (The effect of Hydrogen Peroxide on Bacteria)

http://www-micro.msb.le.ac.uk/LabWork/bact/bact1.htm (Bacteria growth curve)

http://www.bact.wisc.edu/Bact303/NutritionandGrowth (Nutrition and growth of bacteria)