Lesson Title: Yeast – digestion, respiration and rising of the bread
Activity: Keep the yeast alive
Grade:
9-10
Content Areas: Science
Lesson’s Time Block: 1 hour in class and 1 weekend for the activity
Grouping: Students will work individually and participate in class discussions. The
activity will be done individually.
-------------------------------------------------------------------------------------------- Pre-planning tasks
EALRs/GLEs/PEs
9-11 PS2I The rate of a physical or chemical change may be affected by factors such as
temperature, surface area, and pressure.
9-11 LS1B The gradual combustion of carbon-containing compounds within cells, called
cellular respiration, provides the primary energy source of living organisms; the
combustion of carbon by burning of fossil fuels provides the primary energy source for
most of modern society.
9-11 LS1F All of the functions of the cell are based on chemical reactions. Food molecules
are broken down to provide the energy and the chemical constituents needed to
synthesize other molecules. Breakdown and synthesis are made possible by proteins
called enzymes.
Some of these enzymes enable the cell to store energy in special chemicals, such
as ATP, that are needed to drive the many other chemical reactions in a cell.
Objectives (Learning Targets):
The student will be able explain the optimum conditions for yeast activity and demonstrate
that knowledge by keeping yeast alive for several days. If they fail to keep the yeast alive,
they will be able to explain what went wrong.
Rationale:
Living organisms, including yeast, require certain conditions to stay alive. A narrower set
of conditions are required for the optimum performance of those organisms. By having the
student actively keep some yeast alive over two to three days, they will practice this
knowledge.
Essential Question: What conditions are required to keep an organism such as yeast
alive.
Academic Language and Pre-requisite Knowledge: The student should already know
the functions of the individual components within yeast cells. Those were covered in the
eukaryotic and prokaryotic cell lesson.
Academic Language Target: By the end of the lesson, students will be able to explain
the optimum conditions for yeast activity and demonstrate that knowledge by keeping
yeast alive for several days.
---------------------------------------------------------------------------------------------------- Lesson Setup
Unit: Bread
Lesson: Milling the Seed
Page: 1
Lesson Opening:
1. Focus question/ Anticipatory set: What conditions are required to keep an organism
alive? That depends on the organism. Ask: What does a person require to stay
alive? (food, water, shelter - temperature, oxygen) We will be exploring the
optimum conditions to keep yeast alive and then put that into practice over the
weekend.
2. After the lesson about optimum yeast conditions, students will be given a sample of
yeast and will create a plan to keep the yeast alive over the weekend. They will
write a short description of what went well or did not go well. This will include
whether the yeast survived or did not survive.
----------------------------------------------------------------------------------------------------- Lesson Body
Lesson: (can be: I do it – you do it – we do it)
YEASTS
from: http://www.delaval.com.tr/Dairy_Knowledge/EfficientCooling/Why_Cool_Milk.htm#Fungi
Yeasts are single-cell organisms of spherical or cylindrical shape and the size of yeast cells varies
considerably. For example, brewer’s yeast, saccharomyces cerevisiae, has a diameter in the order of 2 – 8
mm, and a length of 3 – 15 mm. Yeast cells of certain other species may be as large as 100 mm.
Structure of the yeast cell (adapted from Tetra Pak 1995)
Yeast cells normally reproduce by budding, though there are other methods. Budding is an asexual process.
A small bud develops on the cell wall of the parent cell. The cytoplasm is shared for a while by parent and
offspring, but eventually the bud is sealed off from the parent cell by a double wall. The new cell does not
always separate from its parent, but may remain attached to it while the latter continues to form new buds.
The offspring cell also form fresh buds of its own, which can result in large clusters of cells attached to each
other. Some types of yeast reproduce by forming spores (these are quite different from bacterial spores).

Nutrients
Yeast has the same need for nutrients as other living organisms, such as
bacteria.

Moisture
As for bacteria, although yeast needs less water; some can grow with very little
water.
Unit: Bread
Lesson: Milling the Seed
Page: 2

Acidity
Yeast can grow in a PH value range of between 3 and 7 (optimum is between 4.5
and 5).

Temperature
The optimum temperature is normally between 20 and 30º C.

Oxygen
Yeast can grow both with and without the presence of atmospheric oxygen.
Yeast cells are facultatively anaerobic, which means that in the present of
oxygen they grow better.
Conditions for the growth of yeast.
--------------------------------------------------------------------------------------------- Extended Practice
In Class Practice or work:
After being shown what the optimum conditions are for a yeast cell, the students will
develop a plan in class for keeping a sample of yeast alive over the weekend. The lesson
should include rough times for feeding and the temperature.
Homework:
The students will each be given a sample of yeast mixed in water. A good sample would
be 1 Tsp of yeast in ½ cup water with ½ cup flour. When the students return the following
week, they will write a description about how everything went and whether the yeast
sample stayed alive or died. If it died, they should describe what may have gone wrong.
--------------------------------------------------------------------------------------------------- Lesson Closing
Closure:
Review:
 Review the conditions needed to keep yeast alive. If you already have a sample of
yeast you are keeping alive, you could show this. Sourdough is an example of this
same process.
Back to bread
 This is directly related to bread, especially sourdough bread.
--------------------------------------------------------------------------------------------------------- Evaluation
Assessment:

The students need to prepare a plan that will be used to keep the yeast alive over
the weekend.
Unit: Bread
Lesson: Milling the Seed
Page: 3

The students will keep a sample of yeast alive over the weekend and will be
assessed on their description of how things went.
Family Interactions:
A few cups of all purpose, whole wheat or bread flour will be needed for the weekend
activity. They will need to be notified a few days ahead in case they need to purchase
some.
Accommodations:
If the students can’t afford flour or do not have the ability to fully participate in the weekend
activity on their own, they should be encouraged to do their best with what they have. The
are being assessed on how well they document what they were able to do. If the yeast
dies because it was not cared for, the conditions that caused the yeast to die or fail to
thrive should be documented. A lot can be learned from what did not go well.
Extension:
When beer is made, the sugar is slowly broken down by the yeast as food. Eventually no
sugars are left. The optimum conditions do not exist, because the food has been depleted.
In order to get the carbonation in the beer, a little extra sugar is added to the solution,
which reactivates the yeast still alive. The extra sugar allows the yeast cells to produce
CO2 which carbonate the beer during the final stages.
Materials:
Yeast sample – 1 Tsp + ½ cup water + ½ cup flour
References:
DeLaval (2011). Why cool milk - fungi. Retrieved 31 October, 2011 from
http://www.delaval.com.tr/Dairy_Knowledge/EfficientCooling/Why_Cool_Milk.htm#Fungi
This site is focused on milk production, but the specific link above describes the
optimum conditions for yeast.
Unit: Bread
Lesson: Milling the Seed
Page: 4