Scientist____________________ Date_________ College____________________________ #______
C.21 Unit Assessment
Level 1-Multiple Choice (50% Correct= +.5) (75% correct= +1)
1. Which extrinsic factors are needed for microbes to multiply rapidly?
A. Cold
B. Dry
C. Oxygen-rich
D. Warm
2. The factors that impact microbial growth are called:
A. Internal & External
B. Intrinsic & Extrinsic C. Outside & Inside
D. Hot & Cold
3. What are some of the best ways to prevent microbial growth in food?
A. dehydrating, irradiating, pickling, freezing
B. sealing, hydrogenating, microscoping, chromatherapy
C. salting, cooking, blanching, distilling
D. generating, fermenting, sublimating, evaporating
4. What are the three types of microbes?
A. disease, germs, bacteria
B. curdles, mushrooms, fungi
C. viruses, germs, rotillum
D. bacteria, viruses, fungi
5. Bacteria that can survive without oxygen are described as
A. aerobic
B. anaerobic
C. heterotrophic
D. saprophytic
6. Single-celled organisms that can grow in food and may cause people to get sick. Can be shaped like a
rod or cocci.
A. Pathogen
B. Molds
C. Viruses
D. Bacteria
7. Bacteria that live in intestines. Grow in undercooked hamburgers.
A. S. aureus
B. E. coli
C. Listeria
D. Molds
8. Use the pictures below to answer the following question.
9-10 List the OPTIMAL conditions for bacteria growth
___Instrinsic: Microbes multiply most rapidly in moist, nutritionally rich, pH neutral foods, no biological
barrier (no rind or thick skin)
___Extrinsic: Microbes multiply rapidly in warm, oxygen-rich environments
11-12 List some everyday activities that could cause food contamination in your home.
___Not cleaning food, leaving food out, not washing hands before or after touching, leaving counters
dirty______
#_____
Level 2-Short answer
Scoring: Both answers correct=+.5
Base your answer(s) to the following question(s) on the information below and on your knowledge of
biology.
Where is the Beef? Out Being Irradiated
E. coli bacteria in food cause an estimated 73,000 cases of infection leading to some deaths in
the United States each year. Until recently, the only way to guarantee meat free of E. coli was to heat it
to 160 degrees Fahrenheit, which kills E. coli. The rare hamburgers preferred by many people are not
heated to this temperature, and just a few E. coli may cause severe illness.
Recently, ground beef has been decontaminated by irradiation using electron beam technology.
The packaged ground beef is scanned by an electron beam that disrupts the genetic structure of the
pathogens. This kills them or leaves them unable to reproduce.
This process is considered safe and has been endorsed by various governmental groups in this
country as well as the World Health Organization. Irradiation is effective in preserving only certain
foods, such as herbs, wheat flour, fresh fruits, vegetables, and some meats. Although some methods of
irradiation can change the taste of some foods, this is not an effect of electron beam technology on
ground beef.
Opponents of irradiating food are concerned that the process may result in the formation of
chemicals that may be harmful or result in a loss of vitamins. Supporters claim that irradiation is safe
and should be considered as just another technique for preservation of food.
A. Identify the specific group of molecules in bacteria whose function would be interfered with by
heating them to 160 degrees Fahrenheit.
E. Coli
B. What are the pros and cons of irradiation? At least 3 of each.
Pros: Kills E. Coli, allows you to have rare ground beef, preserves popular foods, considered safe,
endorsed by World Health Organization, does not change the taste of ground beef
Cons: may cause loss of vitamins, may form harmful chemicals, changes taste of some foods
#_____
Level 2-Table
Fill in the table below, by selecting the preferred method of preservation, and why that would keep food
from spoiling due to microbes. Be sure to mention what microbes need to grow!
P=Pickling
Scoring:
F=Freezing
75% of method & Reasoning correct= +.5
D=Dehydrating
I=Irradiation
Food
Method
Reasoning
Plums
D
Very juicy fruit, dehydrating removes excess fluid that microbes need
to grow
Grapes
D
Very juicy fruit, dehydrating removes excess fluid that microbes need
to grow
Raw whole beef
D/F
Cucumber
P
Meat has liquid in it, dehydrating removes excess liquid that microbes
need to grow and seals the meat against other microbes entering
Microbes grow best in room temperature and needs liquid in meat to
survive, freezing crystallizes the water so the microbes can’t use it and
lowers the temperature so they die
Microbes do not like very acidic environments and putting cucumbers
in a sanitary environment with a brine that is very acidic, pickling the
cucumber increases acid level
Ground Beef
I
Irradiation kills the microbes that are already on meat or makes it
unable for them to reproduce, chosen because it does not need special
packaging
Bread
F
Bread does not have a lot of moisture, but the moisture that is in it
gets crystalized so the microbes can’t use it
Strawberries
D/F
Very juicy fruit, dehydrating removes excess moisture that the
microbes need to survive
Freezing crystallizes the water so that microbes can’t use it
Bananas
D/F
Moisture in bananas, dehydrating removes excess moisture that the
microbes need to survive and creates a seal around the fruit
Freezing crystallizes the water in the bananas and makes it unusable to
microbes
#_____
Level 3-Open-Ended Response
Identify a food that could be pickled. Describe the process of pickling (what happens to the food AND
how to do it). Explain how pickling prevents food spoilage due to microbes.
___Cucumbers can be pickled. The food is treated with an acidic brine and sealed. In order to do it you
sanitize canning jars, make a brine that consists of vinegar water and salt, cut and clean the food to be
pickled, place in jars with brine, clean and seal. __
Identify a food that could be irradiated. Describe the process of irradiation. Explain how irradiation
prevents food spoilage due to microbes.
____Ground beef can be irradiated. The process is that the meat is packaged as normal and then
scanned with electron beam technology. This kills the microbes in the ground beef or alters their DNA,
making them unable to reproduce. It doesn’t really keep the food from spoiling, but makes it safer to
eat.____
Identify a food that could be dehydrated. Describe the process of dehydrating (what happens to the
food AND how to do it). Explain how dehydrating prevents food spoilage due to microbes.
___A food that can be dehydrated is grapes. The dehydrator removes excess moisture from the food by
heating it very slowly at very low temperatures. While dehydrating, the process also creates a seal
around the food. This prevents food spoilage due to microbes because microbes need water to grow
and dehydrating removes excess moisture. ____
Identify a food that could be frozen. Describe the process of freezing (what happens to the food AND
how to do it). Explain how freezing prevents food spoilage due to microbes.
___A food that can be frozen is strawberries. When a food is frozen the molecules slow down and water
molecules are crystallized. When they are in crystallized form, the microbes cannot use the water and
therefore, cannot grow. This prevents spoilage because the microbes can’t grow.___
Proficient (+.5)
Identified a food that
would be a good
candidate for each
method
Described the
processes completely.
Mastery (+1)
Identified a food.
Described process.
Explained how the
method prevents
spoilage & how it limits
microbe growth
Above Mastery (+1.5)
Met Mastery
On the back, create a
T-Chart that identifies
the pros and cons of
each method
Advanced (+2)
Met above mastery
Explained three other
methods of food
preservation that were
not taught in class