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Factors affecting the the growth of molds or yeast

Factors affecting the the growth of molds or yeast

Introduction: (Initial Observation)

Molds are varieties of multi-cellular organisms that grow on bread, fruits, cheese and almost any other dead organic matter.

Learning about the factors that affect the growth of mold and yeast can help us to control reproduction of these micro organisms.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

What you will see in this project is just an example of information and experiments about growing mold and Yeast. You need to read this information and then come up with your own procedures. First you will decide which one you want to study on. Mold is an easy one, but you may select yeast as well. The next step is growing the organism that you select in order to make yourself familiar with what is involved. In your final step, you will repeat growth experiment at different conditions of light, moisture, and temperature. Finally, you will compare the results and draw a conclusion.

Information Gathering:

Find out about mold, yeast or other types of fungi, how they grow, and where they grow. Read books, magazines or ask professionals who might know in order to learn about different types of fungi. Keep track of where you got your information from.

Click here to see a sample project related to mold growth.

Mold if a fungi. Click here for a good source of information about fungi.


The material that supports the growth of a fungus is called its substrate. A commercially prepared medium like potato agar is one kind of substrate, but any organic material can be used.

The simplest method of growing molds is to put a substrate like bread in a moist chamber. The substrate provides nutrients, and the chamber maintains the high humidity that favors the growth of fungi. Placing a slice of bread, fruit or vegetable, or a leaf in a plastic sandwich bag is a simple way to use this method. The small plastic bag must have a tie, a fold-over top or another way of sealing it. Mold growth should be visible after 3 to 5 days. If you want to try this experiment, follow the directions below.

You will need the following items:

  • Substrate material
  • Sandwich bags with a tie, fold top or “zip lock”.
  • A marker to label the bags.
  • Damp, NOT WET, paper towels.

Making the moist chambers

  • Label the bags with a number so you can tell them apart.
  • Place a damp towel in each bag.
  • Place a slice of bread or other substrate on top of the damp towel.
  • Seal the bags.
  • Record the substrate put in each bag.
  • Place the bags in a warm area out of direct sunlight where they will not be disturbed.
  • Check the bags each day. Fungal growth should be visible in 3 to 5 days. Fungi are fuzzy or hairy and may be green, white, black, yellow, etc. Bacterial colonies are shiny or slimy and may also be different colors.
  • Record the number, color, and size of the fungal colonies. One very fast growing fungus, the Galloping Grey Ghost (Rhizopus stolonifer), may completely cover bread in just a couple of days.

Questions to help design experiments

  • Does the amount of light affect the growth of mold?
  • Does moisture affect the mold growth?
  • Does temperature affect the mold growth?
  • Are there differences in the numbers and kinds of fungi growing on different kinds of bread?
  • Does preservative in some bread affect the numbers and kinds of molds?
  • Are there differences in the numbers and kinds of fungi growing on bread compared to carrots?


The yeasts are one very important group of fungi. The common yeast used in baking bread grows very fast. You can complete an experiment in two days! The basic idea in this method is to measure the amount of carbon dioxide (CO2) released during the growth of yeast. The growth of the yeast stops when one of the nutrients required by the yeast is gone, or when the liquid gets too acid (low pH) and kills the yeast. If you want to try this experiment, follow the directions below.


You will need the following items:

  • A teaspoon measure
  • A permanent marker
  • Active dry yeast (used in baking bread–do not use quick-rising varieties.) This yeast is available in jars if you are planning on doing a large experiment.
  • Bottled soda pop or water in equal amounts. Different items contain different ounces per container. Shake each soda bottle and let the foam settle before opening, or open and allow to go flat overnight.
  • Identical round, thin latex balloons–“water balloons” are slow to expand. Non-Mylar® “helium-quality” balloons give good results.

Directions for growing yeast

  • Label each bottle with a number to keep track of what each one contains–control, treatment and contents, so that you can tell bottles containing the same solution (replicates) apart. Color is not a reliable means of identification–the caramel color used in cola is a carbohydrate and the yeast can eat it.
  • Put a teaspoon of dried yeast in each bottle.
  • Seal the bottles tightly and shake the bottle.
  • Remove the lids and stretch a balloon over the mouth of each bottle. The balloon should fit very tightly so that the carbon dioxide does not leak into the air.
  • Place each container in a warm area out of direct sunlight (top of refrigerator or clothes dryer) where they will not be disturbed.
  • Record the diameters of the balloons, time since start of experiment, etc. for each bottle. One good method of measurement is to wrap a string around each bottle at its widest point, and then measure the length of the wrapped string against a yardstick. Record any other things you see happen. Did the color change? Did one balloon have a hole in it?
  • Calculate the average diameter of the balloons in each treatment and the controls. The average is calculated by adding all the diameters of all the balloons in a treatment then dividing by the number of balloons in the treatment.
  • Compare the results (average balloon diameters) of the experiment.
  • A graph of the averages might help show your results.

Questions to help design experiments

  • Is the average of the treatments larger than the average of the controls?
  • Is the average of one treatment larger than the averages of the other treatments?
  • Is carbonated water a better control than non-carbonated water in experiments with different kinds of soda pop?
  • Is the amount of sugar used in a bottle related to the amount of carbon dioxide released into the balloon? Hint: graph sugar concentration versus average balloon size.

An Alternative to the Balloon Method for Measuring Yeast Respiration

The apparatus shown in the picture permits more accurate measurement of yeast respiration than the balloon approach. The carbon dioxide respired by the yeast is trapped in an upside down graduated cylinder. The milliliters marked on the graduated cylinder let you read directly the amount of carbon dioxide trapped.


You will need:

  • graduated cylinder (100 ml shown).
  • beaker or bowl.
  • rubber or plastic tubing.
  • one hole rubber stopper. A number 3 stopper fits most 1 liter plastic soda bottles.
  • short glass or plastic tube. A medicine dropper or piece of a 1 ml plastic pipette might work. The tube should not touch the liquid culture in the flask or bottle.
  • Erlenmeyer flask or soda bottle (500 ml flask shown).

Directions for assembly:

  • Buy one-hole rubber stoppers that fit your bottles or flasks. Your teacher may be able to help or hobby stores that sell chemistry sets often have the supplies you will need.
  • Insert a short piece of glass or plastic tubing in the hole in the stopper. It will be easier to insert the tube if you put salad oil on the outside of the tube. BE CAREFUL. If you break the glass tube you may cut yourself.
  • Measure and cut a piece of rubber tubing long enough to reach from the flask to the lower part of the graduated cylinder.
  • Slide one end of the rubber tubing over the tube in the rubber stopper.
  • Fill the beaker or bowl with water.
  • Fill the graduated cylinder all the way to the top with water.
  • Cover the top of the graduated cylinder with your hand and quickly turn it over and put it in the beaker filled with water.
  • Remove your hand. There should not be any air in the graduated cylinder. If there is a small amount of air, record the amount (ml). You will need to subtract this amount from the total in the cylinder when you take respiration measurements.
  • Fill the flask or bottle with your liquid yeast culture.
  • Insert stopper in the flask or bottle.
  • Insert the end of the rubber tube in the graduated cylinder. Do not lift the end of the graduated cylinder out of the bowl or it will fill with air.

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.

Temperature, moisture and light are among the factors that may be studied for their effect on the growth of mold, yeast, or any other fungi.

These are samples of how you may define a question or purpose for your project.

The purpose of this project is to identify the effect of light on the growth of mold.

Note that instead of light you may choose other factor and modify your experiments accordingly. You can also substitute mold with yeast. This is another example:

The purpose of this project is to find out “How does the type of substrate affect the growth of yeast?”.

Substrate is a combination of food and growth media. Substrates such as water, sugar water, starch solution, flat soda,.. may be compared.

You may be much more specific and have a purpose like this:

Does yeast need air to grow?

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.

This is a sample of how you define the variables:

  • Independent variable (also known as manipulated variable) is light.
  • Dependent variable (also known as responding variable) is the mold growth.
  • Controlled variables are temperature, substrate type (type of bread), moisture.
  • Constants are all other experiment conditions such as the source of bread, type and size of the plastic bag.

You may want to study other factors (Independent variables) as well. Just make sure that the independent variables must be tested ONE at a time.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample of hypothesis:

My hypothesis is that molds grow best in a dark environment. Possibly light or certain radiations in the light spectrum can slow down or prevent mold growth.

This hypothesis is based on my personal observation on where mold is usually found at home.

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.”

For example, in one experiment you may study the effect of light on growing mold. You may take three pieces of bread in three identical plastic bags and keep one of them at normal light to be your control and place two others, one in a dark place, and the other exposed to more than normal light. For a more reliable result you may use more samples. For example you may place 5 samples in a dark place, 5 samples in normal room light and 5 samples under a strong light source such as fluorescent light.

About Mold Experiment

As you know, we keep food in refrigerators so it will last longer. But still, sometimes you open a bag of bread or a jar of spaghetti sauce and what do you find? Mold!!

Ever wonder exactly what mold is? And how did it get there? And why sometimes it’s green and other times black or white? Did you know mold is a fungus and is alive and growing?

In this experiment, you’ll find out all about those colorful, fuzzy fungi by growing your own crop. Print out these pages and follow the directions to do this experiment at home. When you’re done, try answering
the questions below.

Note: This is a long-term activity. It will take several days for the mold to grow. The first day should take you about 30 minutes to one hour to prepare everything. For safety reasons, don’t eat or drink while doing this experiment. And don’t taste or eat any of the materials used in this activity.

You’ll Need:

  • 3 eye droppers
  • small cup filled with 4 teaspoons or 20 mL of sugar water (see directions for preparing sugar water below)
  • small cup filled with 4 teaspoons or 20 mL lemon juice
  • small cup filled with 4 teaspoons or 20 mL tap water
  • 4 slices of plain white bread*
  • 4 slices of assorted bread, such as wheat, rye, sourdough, etc.*
  • 8 resealable plastic sandwich bags
  • marker
  • masking tape

*It’s best if you use newly bought, fresh bread to make this experiment as accurate as possible.

Preparing sugar water

Note: Young people who don’t have experience operating a stove or microwave oven should get help and supervision from an adult. Parents or supervisors of young children may consider doing this step themselves.

Microwave: Stir 1/4 cup of sugar into 1/4 cup of water in a microwave-safe container and heat at one-minute intervals until sugar dissolves. Water will not need to reach boiling. Use potholders or oven mitts to handle container. Allow the mixture to cool for about five minutes before using.

Stovetop: Stir 1/4 cup of sugar into 1/4 cup of water in a small saucepan. Heat over medium heat until the sugar is dissolved. Use potholders to handle hot saucepan. Allow the mixture to cool for about five minutes before using.

What To Do:

1. Using masking tape and marker, make labels for four sandwich bags. Label the first bag “Dry White Bread.” Label the second “Water on White Bread,” the third “Lemon Juice on White Bread,” and the fourth “Sugar Water on White Bread.”

2. Wash your hands. Place a slice of white bread in the bag labeled “Dry White Bread” and seal the bag. Using one eye dropper, sprinkle 20 drops of tap water on another slice of white bread. (Don’t overdo it; the bread should be moist, not wet. If your bread is dripping, you’ve definitely done way too much. Throw away that slice and try again.) Place the moist bread in the bag marked “Water on White Bread” and seal the bag. Using a different eye dropper, sprinkle 20 drops of lemon juice on another slice of white bread and put it in the bag marked “Lemon Juice on White Bread” and seal the bag. Using your third eye dropper, sprinkle 20 drops of sugar water on the last slice of white bread and place it in the bag labeled “Sugar Water on White Bread” and seal. Try to keep your fingers off moist spots when handling each slice of bread.

3. Repeat steps 1 and 2, but this time use a different kind of bread in the remaining four bags. Your labels should note what kind of bread you’re using. Wash your hands when you’re done.

4. Make sure all of your bags are tightly sealed. Place all eight bags in a dark, warm place (about 86 degrees Fahrenheit, 30 degrees Celsius). Check with your parents or supervisor about where to store the bags. Check the bags each day for two weeks and record the results in a notebook. You may wish to draw or take pictures of the bread slices. Don’t open the bags!

5. Make a graph recording the total growth of mold on each of the four white bread slices at the end of two weeks (see sample graph on right). Make a similar graph for the other four bread slices. Compare the results. At the end of the two weeks, throw out all the bags unopened.


  1. From this activity can you tell what helps mold to grow best?
  2. Does it matter what kind of bread you use?
  3. What causes the different colors you see?
  4. What would happen if you left the bags in a well-lit place instead of a dark place?
  5. What would happen if you changed the temperature?

Answer 1: Unless you used bread that had been sitting out for many days, you probably didn’t get much or any mold growth on the dry bread. Clearly, water is important for the growth of mold. The mold grew best on bread sprinkled with sugar water because the sugar serves as food for the fungi. The more food that’s available, the more fungi cells can grow. The mold also grew pretty well on the bread with plain tap water because the fungi could use the sugar and starch in the bread as food. The mold didn’t grow as well on the bread sprinkled with lemon juice because lemon juice is acidic. Acids hinder the growth of many common fungi and bacteria.

Answer 2: Molds grow better on some kinds of breads than others depending on the ingredients used and how the bread was made. Some breads are dry and some are moist. The amount of the sugar in different breads varies; some have sugar, honey or molasses added. Some breads are even acidic, such as sourdough. Some may have fruit or nuts or other ingredients added. Many commercial breads are made with preservatives that hinder the growth of molds and bacteria to prevent or delay spoilage. Bread baked fresh in a bakery that doesn’t use preservatives will more likely become moldy faster. All of these factors can influence how much mold will grow on a particular kind of bread.

Answer 3: Many of the colors you see on the moldy bread are due to the spores the fungi have produced. Molds reproduce by making spores at the end of stalks that rises above the surface of the bread, giving molds a fuzzy appearance. Spores are like seeds—they spread molds to new places so that they can continue to grow. Spores are usually colorful. Some fungi, such as Rhizopus nigricans (rye-zoh-puss neye-grih-cans) and Aspergillus niger (As-per-jill-us neye-jer), make black spores. Neurospora crassa (new-rah-spore-ah crah-sah) produces spores that appear pink. And the Penicillium (pen-ih-sill-ee-um) molds, the molds that make penicillin, are blue-green.

Some of the colors on your bread may be the result of growing colonies of bacteria, which also sometimes grow on old food. For example, a bacterium called Serratia marcescens (ser-ay-shuh mar-seh-sens) forms reddish colonies. You can tell bacteria colonies apart from molds because bacteria colonies appear smooth while molds look fuzzy.

Answer 4: Molds grow best in the dark, so not as much mold would be present on bread slices kept in a well-lit place.

Answer 5: Most fungi grow best around room temperature. But they can grow at a range of temperatures from cold (like in a refrigerator) to quite warm (body temperature). At temperatures colder or warmer than their favorite temperature, they usually do not grow as rapidly. If the temperature is too cold or too hot, they will not grow at all, and may even be killed.

Yeast growth experiment


As you probably know from eating numerous meals, all breads are not the same. Tortillas and pitas are flat and dense, while loaves of sandwich bread and dinner rolls are puffy and lighter. In fact, if you look closely at a piece of sandwich bread, you can see a honeycomb texture in it where bubbles formed and burst. Why these differences? Aren’t all breads made of the same basic ingredients? What made those bubbles?

The differences are caused by a microbe called yeast, pictured here. Yeast is a kind of fungus. If you open up a package of baker’s yeast bought from the supermarket and sprinkle some out, you’ll see tiny brownish grains.

These are clumps of dehydrated yeast cells (dehydrated means most of the water has been removed). Let them sit there for a while and watch them and you’ll soon get bored. They don’t exactly do much, do they? But put them in bread dough and after a while you can definitely see that they must be doing something. But what exactly are they doing?

You’ll find out in this activity in which you’ll make your own bread dough.

Note: This activity can be done within one hour, though you could stretch it over a few hours if you wish, depending on how many different sweeteners you want to try.

You’ll Need:

  • 2 cups of flour (plus a little extra)
  • 4 medium-sized bowls
  • 2 packages of rapid-rise yeast
  • access to warm water
  • 6 teaspoons of sugar
  • a sweetener besides sugar such as honey or artificial sweetener
  • 24 clear drinking straws (must be clear)
  • 24 clothespins
  • measuring spoons
  • ¼ cup measuring cup
  • spoon
  • metric ruler
  • permanent marking pen
  • notebook and pen or pencil
  • clock, watch or timer

What To Do:

1. Using the ruler, measure the point 3 centimeters from one end of each straw and mark that point with a line using the permanent marker.

2. Put ¼ cup of flour into each of your bowls. Mark the first bowl as the “Control.” Mark the others as 1, 2, and 3. (Just imagine that the dough in the illustration below is in four separate bowls.)

3. Measure 1 teaspoon of sugar and add it to the flour in the bowl marked 1. Put 2 teaspoons of sugar into bowl 2. Put 3 teaspoons of sugar into bowl 3.

4. Pour ¼ of a package of yeast (or ¼ teaspoon) into each of the four bowls. Using the spoon, stir together the ingredients in each bowl starting with the Control bowl.

5. Fill a cup with warm water from your faucet. The water should be warm, not hot and steaming. Dust your hands with a little flour. Carefully add the water to the Control bowl about a teaspoonful at a time and begin to knead the mixture. Your dough should eventually feel kind

of like Play-Doh—it should be damp, not wet. It’ll be sticky at first, but should eventually reach a point where it’s just damp enough that it no longer really sticks to the bowl or your hands. If it’s too sticky still, add a little bit more flour. Form the dough into a ball.

6. Repeat step 5 with each of the remaining bowls, working as quickly as you can. (If you have friends or classmates or parents helping out, each person should take a bowl and everyone should do step 5 at the same time.)

7. Working quickly, push three straws into the Control dough until the dough inside the straw reaches the 3-centimeter mark. Lay these straws by the Control bowl. Repeat this step with each of the remaining bowls.

Be sure to keep the straws beside the right bowls and don’t mix them up. (Again, if you’ve got more people working with you on this activity, each person should take a ball of dough and everyone should do this step all at the same time.)

8. Now pinch the bottoms of each of your Control dough straws, pushing the dough up from the bottom enough to clip a clothespin to the end of each straw. Mark the new height of the dough on each straw. Stand the straws upright using the clothespins as bases. Do the same with the rest of the straws. Label the batches of straws as Control, 1, 2 and 3.

9. Mark the time on your clock or watch or set your timer for 10 minutes. Wait 10 minutes. Then measure and mark the heights of the dough in each straw and record these heights and the time in your notebook. Repeat this step 10 minutes later. Repeat after another 10 minutes has passed.

10. During the 10-minute intervals while waiting for the dough in the straws to do its thing, discard your first batches of dough from each bowl and wash the bowls out. Dry them thoroughly. Be sure to keep an eye on the clock while you’re doing this so that you don’t miss the 10-minute deadline to check and measure your straws.

11. Repeat the dough making process only this time use a different kind of sweetener than sugar. Repeat the steps of filling and marking the straws. Label the new batch of straws and set them away from your first batch. Repeat the process of measuring the dough height in the straws at 10-minute intervals and recording the results in your notebook. Be sure to record the heights of this new batch of straws separately from the first batch.

12. Graph your results. First, calculate the average final height for each set of three straws in your first batch. Make a bar graph showing these average heights with the number of teaspoons of sugar (0, 1, 2, 3) on the horizontal axis and the height in centimeters on the vertical axis. Make a similar bar graph for your second batch of straws. See the sample graph on the right.

13. Throw away all the straws when you’re done. You might want to save the clothespins for another project in the future. Discard the dough in the bowls and wash them out. Clean up any spilled flour, sugar or yeast.


  1. In the first batch of straws you made, which straws showed the greatest change in dough height? Why?
  2. Can you guess what effect the sugar had and why?
  3. Did the Control dough rise at all or not? Why or why not?
  4. Did your dough made using a different sweetener besides sugar show the same results?

Answer 1: The straws containing dough from bowl 3 showed the highest rising. Since everything—the amount of flour, the amount of yeast, the temperature of the water—stayed the same except for the amount of sugar, you have probably already rightly guessed that the height of the dough rising is connected to the larger amount of sugar in this dough. Why is that? See the next question.

Answer 2: You will notice that the dough from the other bowls also rose some in their straws, the height connected to how much sugar was in the flour. The more sugar, the higher the dough rose. What can you figure out from this? Well, you’ve already read that yeast makes bread rise and become puffy instead of flat and this has something to do with yeast activity. What makes living things active? Food energy. The sugar is food for the yeast cells. The more sugar there is, the more active the yeast cells are.

Yeast cells chow down on the sugar molecules, breaking them apart in a chemical reaction and turning them into simpler elements and compounds including carbon dioxide. Carbon dioxide is a gas. Bubbles of carbon dioxide released by the yeast get trapped in the dough as bubbles. As more and more of these bubbles build up, the dough puffs up or rises. When the dough is put in the oven and baked, the carbon dioxide vaporizes in the heat, leaving spaces where the bubbles once and giving bread its honeycomb texture.

Answer 3: You probably saw some rising happen in the straws containing Control dough. This is because flour is a starch. Starches contain glucose, a form of sugar (this is why a saltine cracker tastes a little sweet if you let it sit on your tongue for a while; the enzymes in your saliva break the cracker starch down into glucose and other simpler molecules). So even though you didn’t add any sugar to the Control dough, it already contained some for the yeast to much on. However, because the amount of sugar in this dough was much less than in the others, less carbon dioxide could be made by the yeast in this batch and the dough couldn’t rise as much in comparison.

Answer 4: Different sweeteners will have similar or lesser effects on dough rising as sugar. You could try this experiment with as many different types of sweetening agents as you want to compare the results. Then you could do some research on the types of sugars in these different sweeteners to determine which ones work best as food for yeast.

Stop the Mold: A Bread Mold Study

This experiment examined how alcohol, pickle juice and mercurochrome affect mold growth. Mercurochrome and ethanol were selected because each stops wounds from infection. Pickle juice, a weak acid, was chosen to examine whether decreasing pH would inhibit mold growth. Method: Mold was grown on bread allowing enough growth so that mold type could determined. The most common mold growing was used to inoculate other four slices of bread. Three drops of mercurochrome, pickle juice, alcohol were each added to a slice, leaving the fourth slice as a control. Mold growth was recorded daily. Results: Pink, green, yellow and black molds grew on the bread. The green mold was used for this study. None of the agents tested totally inhibited mold growth although pickle juice worked the better than the other agents.

The main types of mold inhibitors are (1) individual or combinations of organic acids (for example, propionic, sorbic, benzoic, and acetic acids), (2) salts of organic acids (for example, calcium propionate and potassium sorbate), and (3) copper sulfate. Solid or liquid forms work equally well if the inhibitor is evenly dispersed through the feed. Generally, the acid form of a mold inhibitor is more active than its corresponding salt.

Any other chemical substance may also be tested for its effect on mold.


To experiment with fungi, mycologists often need to grow them. Simply allowing bread to become moldy is not an experiment. An experiment is the test of an idea. Often, this idea is expressed in the form of the question: what? What if…? What happens when…? What kind of effect…? Experiments are designed to use the methods and materials that will give the most complete and accurate answer to an inquiry.



Fungi break down and absorb organic material for their nourishment, so any experiment must first provide them with food. Oxygen and moisture are also necessary. A material for the growth of fungi for experiments is called a medium.

Most commercially prepared media for growing fungi are extracts of plant materials like potatoes. A medium that is specially prepared to contain only the exact nutrients required by one species of fungus is called a “minimal medium”.

The choice of growth medium depends on the question that is being asked. If the question is “What kinds of fungi grow naturally on bread?” the choice of medium is simple. You could just put a slice of bread in a plastic bag, close it to retain moisture and await mold growth.

However, observing only one slice of bread would not make an effective experiment. Your chosen slice may not have any mold spores on it, or contain spores of all the species present in the loaf. It might be too dry to allow growth. You would have to use a number of bags to account for all reasonably possible growth failures and successes. The slices of bread would be replicates. Replicates allow the treatment to be repeated often enough to allow you to determine if the results are significant or the product of random chance..

You will also need to decide how to record your results. Do you identify each species of mold by its scientific name, or do you just describe them (fluffy red colonies, white fuzzy spots, blue-green velvet, etc.?)

A more complicated question requires the design of a more complicated experiment. At first glance, “What effect does the preservative in some breads have on mold growth?” seems as if it could be answered with a loaf of bread and some plastic bags, like the first experiment. However, the best experiment on the effect of a preservative on mold growth would use two loaves of bread. These loaves would be identical in preparation and ingredients, except for the presence or absence of the preservative. The bread without the preservative would be the control and the bread containing the preservative would be the treatment. Replication of both treatment and control gives the experimenter a way to understand the effect of substance by showing what happens when it is both present and absent.

Materials and Equipment:

Can be extracted from experiment design.

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.


No calculation is required for this project.

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.


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.


Visit your local library and find some books and publications related to mold or fungus. Following are some online resources.

About Mold: http://www.e-tulsa.net/mold1.html