Investigate - Life processes in a Unicellular Organism
The word organism is used to describe any life form that can live independently and carry out all seven life
functions.
Unicellular organisms are only _ _ _ cell big – their single cell carries out all life processes including:

Responding to changes in their environment (which life process? ______________)

Moving food into the cell (which life process? ______________)

The food absorbed by unicellular organisms is broken down to produce energy for the cell
(which life process? ______________)

The energy that is produced through respiration is used to increase cell size (which life process?
______________) and to reproduce.

Respiration produces waste products that must be transported out of the cell (which life process?
_____________)
Yeasts are unicellular fungi. Like all living things they carry out all seven MRS GREN life processes, many
of which can be easily and safely observed.
Yeasts - True or False
1. One yeast cell is approximately the same size as one red blood cell
2. One gram of baker’s yeast contains around 30 billion yeast cells
3. Yeast is often taken as a vitamin supplement because it is 50 percent
protein and is a rich source of B vitamins, niacin, and folic acid.
4. Wild yeast spores are constantly floating in the air and landing on
uncovered foods and liquids
5. Yeasts carry out a form of respiration called fermentation
6. Louis Pasteur first proposed the production of carbon dioxide from yeast as
responsible for raising a loaf of bread in 1859
7. Yeasts are unicellular organisms
8. Yeasts can cause infections
9. The ancient Egyptians used yeast for brewing and baking over 4,000 years ago
10. Yeasts grown naturally on the skin, in the mouth, gut, and other mucus membranes.
1
Yeast – life processes
Reproduction
Baker’s yeasts reproduce by budding - a form of asexual reproduction that doesn’t involve the production of
sex cells or the combination of genetic material from two parents. Asexual reproduction produces offspring
that are genetically identical to the ‘parent’ organism.
Use the Power point presentation “Reproduction in yeasts” to answer these questions:
1. How do yeasts reproduce?
2. What is budding?
3. What does asexual reproduction mean?
4. How does budding occur?
5. How quickly does budding occur?
6. What are the advantages of this kind of reproduction?
7. What are the disadvantages of this kind of reproduction?
8. Which picture doesn’t represent budding?
2
Cut out the yeast pictures below. Glue them in the correct place to complete the diagram showing budding
in yeasts.
Chromosomes
Separate
Nucleus
divides
DNA is
copied
Bud
emerges
Cell
division
Start
Growth
3
Using a microscope to make a Biological Drawing
1. Use A4 unlined paper.
2. Draw in pencil.
3. Avoid unnecessary details and shading – use clear solid lines without
gaps
4. Make your drawing large (at least 1/3 of an A4 page) and centre it in
the middle of the page
5. Your drawing should have an identifying title at the top of the page (use the scientific name if you know
it)
6. The magnification used should be written at the bottom of the page
7. Labels should be used to identify details. Label lines (not arrows) must be ruled, must touch the object,
should be drawn horizontally and should not cross over each other
Check your Understanding
How many rules have been broken? – How many mistakes in this biological drawing can you identify?
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Experiment
Aim: To observe and record budding in yeasts
Method:
1. Use a pipette to place on drop of a rapidly growing yeast culture onto a
clean microscope slide
2. Carefully lower a coverslip onto the droplet
3. If there are bubbles under the coverslip remove the coverslip and lower it gently again
4. Place the slide under the microscope and focus
5. Make a detailed biological drawing of the yeast cells under the highest power objective lens
6. Use the diagram below as a guide to labelling your drawing
5
Make your biological drawing of the yeast cells in the space below.
Describe the yeast features or structures that can be observed in your biological drawing
______________________________________________________________________________
______________________________________________________________________________
Relate the presence of these structures to their relevant life process (which MRS GREN function
do these structures carry out?)
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Yeast Respiration and Excretion
Like all other living things yeasts carry out respiration – breaking down sugar molecules in their food to
release chemical energy. When oxygen is used to break down glucose this process is described as
aerobic respiration. Humans can only carry out aerobic respiration – this is why breathing is necessary!
Yeasts carry out aerobic respiration like most other living things, acquiring ____________by using
_____________ to break down simple _____________ and excreting __________ ___________ and
______________ as the waste products of this process:
C6H12O6 + 6 O2
6 CO2 + 6 H2O + ENERGY
glucose + oxygen
carbon dioxide + water
However, if not enough oxygen is available, yeasts can carry out anaerobic (without oxygen) respiration. In
yeasts this process is called fermentation. When carrying out fermentation, yeasts acquire less energy
and excrete alternative waste products - _____________ ______________ and _____________.
C6H12O6
2 C2H5OH + 2 CO2 + (LESS) ENERGY
Questions:
1. What is C6H12O6 ?
2. What is C2H5OH ?
3. Suggest a use for each of these waste products of fermentation
o
o
4. Humans have been exploiting the life processes of yeasts for thousands of years. The word that
describes the deliberate use of living organisms to produce new products is biotechnology. What
kind of biotechnology is shown in this ancient Egyptian hieroglyphic?
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1. Observing Yeast Respiration and excretion - Bread making
A bread maker recipe tells you to measure these ingredients into the
machine.
- Yeast
- Sugar
- Salt
- Flour
- Warm water
- Oil
The machine mixes these ingredients together and then warms the
bread dough.
1. Which ingredient provides food for the yeasts?

Sugar
2. Why is the dough warmed before it is baked?

To provide the correct environmental conditions for the yeast to reproduce
3. Like all living things, yeasts break down their food to produce energy – what is the general name for this
life process?

Respiration
4. Some living things must use oxygen to carry out this process – what is this called?

Aerobic respiration
5. Other living things (like yeasts) can extract energy from food without using oxygen – what is this called?

Anaerobic respiration
6. Yeast cells break down food, and acquire energy – this energy is used to help them carry out another
important life process – what is it?

Reproduction
7. Breaking down food produces waste products that must be removed from the yeast cells – what is the
name of the life process that does this?

Excretion
8. Name these waste products

Carbon dioxide and water
9. Explain how one of these waste products is useful in the bread making process

Carbon dioxide – it creates the bubbles that make the bread rise
10. Write the word formula that summarises this entire process

Glucose + Oxygen  Carbon dioxide + Water
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2. Observing Yeast Respiration and Excretion - Ginger Beer
EQUIPMENT
INGREDIENTS
Clean 2 litre plastic soft drink bottle with cap
Funnel
1 cup measuring cup
1/4 tsp and 1 Tsp measuring spoons
1 cup table sugar
Dried ginger
Lemon juice
Baker's yeast (1/4 teaspoon)
Water
Use a funnel to add 1 cup sugar, ¼ teaspoon yeast and 1 tsp dried
ginger to the 2 litre bottle
Add a tablespoon of lemon juice to the mixture
Fill the bottle to the neck with clean water, leaving about an inch of
head space, securely tighten the lid. Tip upside down repeatedly to
thoroughly dissolve the sugar.
Place in a warm place for 24 to 48 hours.
Test to see if the drink is ready by squeezing the bottle with your
thumb. If it dents (like in the picture), it is not ready.
Once the bottle feels hard to squeeze, refrigerate overnight to
thoroughly chill before serving.
OPEN THE BOTTLE CAREFULLY!
NOTE: There will be a ginger and yeast
9 sediment at the bottom of the
bottle, pour carefully if you wish to avoid drinking this!
Biology Ideas
This assessment requires you to investigate how life processes are affected by changing
environment factors, and how this impacts on an organism’s survival.
To do this you must know a few facts about the biology of the organism you are experimenting
with (facts about an organism’s life style that explain how it responds in a changing environment).
Response to temperature
Most organism’s bodies (including unicellular organisms such as yeasts), function best at an
optimal temperature
Question: What does the term “optimal temperature” mean?
__________________________________________________
The reasons for this involve enzymes - proteins that control life
processes.
Enzymes are catalysts – chemicals that speed up chemical
reactions. Without the help of enzymes, all the chemical reactions
that occur during life processes would occur too slowly and
organisms would die.
Enzymes work best at optimal temperatures. These temperatures often reflect the temperature of
the environment in which the organism lives naturally.
Check your understanding:
What is the optimal temperature for the action of the
enzyme shown in the diagram opposite?
_______________________________________
Fill in the missing words below:
If temperatures are too low – enzymes work too slowly
If temperatures are too high – enzymes become damaged and stop working
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Experiment – measuring respiration rate in yeasts
You will be using a software programme to carry out a simulated Biology experiment.
1. Open the program using this pathway
2. Click OK
3. Use the dropdown menu to find the Biology experiment “Yeast respiration”
Background
In the absence of large amounts of oxygen (anaerobic respiration), yeast cells break down glucose to
produce ethyl alcohol and carbon dioxide - a process called fermentation.
Glucose
Alcohol + Carbon dioxide
This computer simulation allows you to investigate
anaerobic respiration in yeasts by changing either of
two variables - the temperature or the strength of the
glucose solution. The reaction is gauged by measuring
the volume of carbon dioxide produced by the yeast
cells over a fixed period of time.
In this experiment you will be keeping the glucose
concentration constant, while changing the
temperature the experiment is carried out at.
To do this drag the sliding bars

Drag the glucose bar to the maximum 

Drag the temperature bar to the minimum 
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1. Complete the Aim for your experiment
AIM: To measure the effects of changing _______________ on the rate of anaerobic respiration in yeasts.
2. Try to predict what your results will show: - What would you expect to happen to the rate of
respiration in yeasts as you increase temperature from minimum to maximum?
3. How you can ensure that this experiment is a fair test?
4. List some of the controlled variables (the variables that you will keep constant)
5. What is the Dependent variable in this experiment? (What will you measure?)
6. In an actual experiment are there any other factors that might affect the results?
7. If the yeast and sugar were mixed at room temperature and then placed in the water-bath, how
might this affect the results?
12
Carry out your experiment
1. Don’t adjust the glucose levels
2. Gradually increase temperature from
minimum to maximum
3. Use the zoom button to get a closer look at
the levels of CO2 accumulating in the burette
RESULTS:
Use the table below to record your results:
Table Showing ________________________________
Temperature oC
Amount of CO2 produced (cm3)
13
Graph your results as a scatter graph. Draw a line of best fit
(cm3)
Amount of CO2 produced
Graph Showing ________________________________
14
What was the aim of this experiment?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
What was your initial prediction?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Was your prediction correct? – Describe the results of this experiment
______________________________________________________________________________
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15
Use biology ideas to discuss your results. Your discussion should:




Name the independent variable (the environmental factor that was changed in this
experiment)
Describe your observations (in what way did the yeast cells respond to their changing
environment?)
Explain how this response and the environmental factor relate to the life processes of
this organism
Discuss how the results of this experiment relate to the survival of yeasts in their natural
habitat.
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Mark schedule Achievement standard 1.10
Evidence
Judgement For achieved
Judgement For Merit
Judgement For Excellence
(The answers or performance expected from the
students)
Investigates life processes
and environmental factors
that affect them.
Investigates in depth life
processes and environmental
factors that affect them
Comprehensively investigates
life processes and
environmental factors that
affect them.
Task
1

Describes observations of structures related
to the life processes of this organism
Uses observations and biological ideas to
explain how structures relate to the life
processes of this organism

Produces a recognisable
biological drawing of
budding yeast that has
at least three accurate
labels.

Links structural features
(buds) to the life process of
reproduction

Describes observations of response and the
environmental factor related to this
behaviour



Uses observations to explain how this
response and the environmental factor
relate to the life processes of this organism
Uses observations and biological ideas to
make significant links between structures,
behaviours and environmental factors related
to life processes of the organism, including
the survival implications for the organism
Production of bubbles of
carbon dioxide
described. Temperature
identified as the stimulus
for this response.
Links production of bubbles
of carbon dioxide with
increased temperature to
the life processes of
respiration and excretion

Task
2

Sufficiency
All judgements in this
column met for Achieved
17
All judgements in this column
met for Merit

Survival implications are
discussed (enzyme action
limits the range of
tolerance of yeasts to
changing temperature.
Yeasts respire most
efficiently at their optimum
temperature – the
temperature in their natural
habitat ).
As for Merit plus judgement in
this column met for Excellence
18