Growing Yeast Activity

GROWING YEAST ACTIVITY

Prior Knowledge:

In grade 5, you learned about the structure and function of the major organs in the major body systems. You also explored how the skeletal, muscular, and nervous systems work together.

In previous years you have also explored the characteristics of life, as well as identifying variables, observation skills, recording data, and precise use of vocabulary.

Did You Know?

Living cells require oxygen and nutrients (food) and produce waste products. This is true of unicellular organisms such as yeast and multi-cellular organisms such as humans. 

Did You Know?

Yeasts are unicellular fungi. There are yeasts living in a wide variety of natural habitats. For example they live on plant leaves, flowers, soil, water, and skin surfaces. The yeast used in baking and alcohol fermentation is usually a strain of Saccharomyces cerevisiae.

Yeast cells require both food (a source of nutrients) and water for survival, reproduction and growth. The growth of yeast is also influenced by the pH and temperature of the environment. The presence or absence of oxygen and the presence of metabolic products that they make through fermentation (acids or alcohol) will also affect yeast growth.

When yeast metabolizes sugar one of the waste products is carbon dioxide gas. In an anaerobic (without oxygen) environment, it also produces ethanol (alcohol) as a waste product.

As unicellular organisms are in direct contact with their environment they can absorb nutrients and release waste products directly to the environment. However, most cells of multi-celled organisms are isolated from the environment and so receive nutrients and release waste through systems with specialized functions (e.g. circulatory, digestive, and excretory).

Each system of the human body groups organs that work together. Each organ is made up of two or more different kinds of tissue, and each type of tissue is made up of similar cells working together.

Has anyone made bread from scratch? An important step of making bread is

letting the dough “rise”. What ingredient makes the dough “rise”?

(Yeast) What is yeast? Is yeast alive? What do you know about yeast?”

Place Mat Activity Fold a sheet of paper is into four sections

diagonally. In groups of four, each student has a

separate section in which to write what they know about yeast.

pH pH is a measure of the acidity or basicity

of a solution. Pure water is said to be neutral. The pH

for pure water at 25 °C (77 °F) is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.

In this activity, you will grow yeast. The first step is to prepare your lab write-up. Be sure to include:

TitleHypothesisApparatus/MaterialsProcedureObservationConclusion

Introduction In this lab you will be using 2 water

bottles. In each bottle you will be placing a spoonful of yeast, a spoonful of sugar and a scoop of water. A balloon will be used to seal the mouth of each bottle.

Make a Hypothesis about what you think will happen.

Materials Yeast Sugar Water 2 containers per group (plastic water bottle) Balloons or Ziploc baggies Masking tape Marker Timing device Spoons of various sizes

Procedure Using the 2 water bottles provided, in each bottle: Place 1 spoonful of yeast Add 1 spoonful of sugar Pour 1 scoop of water (some groups will get warm

water and some will get cool water.) Place the balloon over the mouth of each bottle and

observe for 5 minutes What do you notice? Are both of your bottles the same? Look at results from other groups. Which group has

completely different results from what you found? Talk to them to see what they did differently.

Observations Make observations on what is happening

inside the bottle. Discuss with you table partners how to

measure and record your observations. Did you notice if the two bottles have

similar results? Compare your results to those of other

groups.

Reflection: In small groups

In your group discuss: What did you notice? Rotate around room to look at other

results. Find the group with results most unlike

yours and talk with that group to figure out what they did differently. Make a note of your findings at the end of you Lab Report under the heading: Reflection

Reflection: Class Discussion

What factors may have contributed to the variety of results?

Possible Factors amount of yeast, sugar, water temperature of the water, temperature

of the room – especially if they were left overnight

How fast the balloon was put on or the baggie sealed, if there was a tight seal between the neck of the bottle and the balloon or the baggie

Questions to Consider What is happening to the sugar?

Why does the balloon or bag inflate?

Look at list of facts about yeast that we completed last class. Are there any items that should be added to or revised? Is there other information we could add?

Reflection: Journaling

In your notebook create a journal entry, describe the variability in experimental results observed in your classroom. Suggest reasons for the variability.

Part II

Factors That Affect Yeast Activity

From the last activity you learned that yeast needs food (sugar) and water.

Based on the similarities and differences between the experiments done earlier, you will design and carry out some experiments to see what has an effect on yeast growth.

Next you are going to design your own experiments.

Be sure that you are only changing one variable at a time. Check with the teacher before completing the experiment.

You will use a rubric to assess your work, it will be provided for you.

Rubric BreakdownGot it Nearly There Not yetQuestion is stated clearly and in a testable form

Question is clear but not in a testable form.

Question is unclear.

Materials list includes all necessary and appropriate items.

Materials list incomplete.

Materials list incomplete and contains unnecessary items.

Written steps are detailed and in sequential order. Steps are detailed enough that variables are controlled. Procedure could be replicated.

Some steps are unclear or missing and/or steps are out of order. Missing some details that would control one or more variables during the replication.

Steps are not accurate or there is not enough detail to replicate procedure.

Spelling and grammar errors are absent or rare.

Some spelling and grammar errors.

Spelling and grammar errors common.

Materials Ziploc bags or containers (water bottles) and balloons Liquids such as water, apple juice, and/or pop (Root Beer

and Orange Soda) Salt, sugar Ice, hot water Teaspoons, tablespoons,measuring spoons, measuring

cups Yeast Pepper Corn Starch Baking Soda Vinegar

What to do In small groups write a question

concerning the growth of yeast that you could test.

You should outline your procedure with projected amounts, how you will make measurements and record them, and/or time and make a prediction that reinforces your choice of variable.

Try it out Perform your experiments using the

procedures you created earlier. Record your results paying close

attention to the measurements you used and the observations you made.

Check to see what other groups are testing if you are struggling to design an experiment.

Some Ideas to Help Possible experiments may include

altering the amount of sugar such as doubling or halving; adding salt; using different liquids such as juice, Five Alive, vinegar; adding carbon dioxide by blowing into the container with a straw; using hot water; or ice water; adding food colouring...

You should write up your question, materials and procedure to hand in.

Reflection: Class Discussion Share your results with the class and

what that tells us about yeast.

What factors seemed to make the yeast produce the most gas? The least?

Explain why these factors affect yeast the way they do.