Download Protein foods - Deans Community High School

West Lothian Council
Lorna C. Webster
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Protein foods
Proteins are important food chemicals that we can get
from plants and animals. Our bodies need protein for
growing and repairing damage. We can get protein
into our bodies by eating the foods shown below.
The foods shown above have all come from animals but some
people are vegetarians and do not eat food that has come from
animals. Vegetarians still need to eat protein because they still
need to grow and repair their bodies.
They need to eat lots of different
plants to make sure they get enough
protein. Soya is a protein that comes
from a plant and it is used in different
foods for example soya milk. Beans also
contain protein.
Write a heading and try the work below.
1. Why do our bodies need protein?
2. Make a list of foods that contain high levels of protein.
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3. Do vegetarians need to eat protein – explain your answer?
4. How do people who are vegetarians make sure they have
enough protein in their diet?
5. List two foods that contain protein that comes from plants.
6. Copy and complete the table below.
Name of food
name of animal or
plant it came from
Steak
Bacon
Eggs
Cheese
Beans
Milk
Chicken
Soya
7. Collect a data book and answer the questions below.
a) What page would you look at to find out about how much
protein there is in food?
b) Which food contains the most protein per 100g?
c) Which food contains the most fat per 100g?
d) Which food contains the most carbohydrate per 100g?
e) Which food contains no fat but 6g of carbohydrate per
100g?
f) Which two foods contains no fat but 20g per 100g
carbohydrates?
g) Which food contains approximately the same amount of
all three food chemicals?
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Testing foods for protein
Read
You may already know about testing foods:
 the benedict’s test turns from blue to orange if sugar is in
food.
 the iodine test turns from brown to black if starch is in food.
 the filter paper test goes transparent if fat is in food.
Chemists also have a way to test whether foods contain protein.
This test is called the soda lime test.
Watch your teacher demonstrate (demo 3.40) what happens in
the soda lime test. Remember the pH paper must be moist
because we need water present to test the pH of a substance.
substance
+ soda lime
moist pH paper
Write a heading and try the work below.
1. What test is used to find out if
a) sugar is in food?
b) starch is in food?
c) fat is in food?
2. What is the name of the test that is used to find out if
protein is present in a substance?
3. Draw a diagram to show what is done in the soda lime test.
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4. Why does pH paper need to be moist?
5. What happened to the pH paper if the substance contained
protein?
6. Does this mean that the gas made was acid, alkaline or
neutral?
7. Copy and complete the sentences below.
To test if a substance contains protein we add s____- l____
to it and heat it. If the pH paper turns _________ we know
that protein is present. This means that an a__________
gas has been made in the reaction.
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Protein chemistry
Read
The diagram below shows the elements that are present in all
proteins.
N
C
H
O
Remember we are made of mainly water (60%) with some
protein so our bodies contain the same elements as proteins.
You may already know that starch is a very large molecule called
a polymer made by joining lots of glucose molecules together.
glucose
glucose
glucose
glucose
glucose
glucose
Proteins are also very large molecules called polymers. Proteins
are made by joining lots of molecules called amino acids
together.
Amino
acid
Amino
acid
Amino
acid
Amino
acid
Amino
acid
Amino
acid
The reaction to join small molecules into polymers is called a
polymerisation reaction.
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Write a heading and try the work below.
1. Use a data book and the chicken diagram on page 6 to make a
list of the elements that you would find in a protein.
2. What elements do our bodies contain? Explain your answer.
3. Is a polymer a large molecule or a small molecule?
4. Explain how starch is made.
5. What are the small molecules called that join together to
make a protein molecule?
6. Are proteins large or small molecules? Explain your answer.
7. Copy the diagram to show how a protein is made from amino
acids joining together.
8. What is the name of the reaction that makes polymers like
starch and protein?
9. Go to the amino acids display and look at the models of amino
acids. Draw a picture of each molecule and beside it write
the formula.
Hint:
Black = carbon
Red = oxygen
Blue = nitrogen
White = hydrogen
10. Copy the revision box below and colour it in to make it
stand out in your jotter.
Polymerisation is the name of a chemical reaction to make
large molecules by joining small molecules together. A
polymerisation reaction is used to make proteins, starch
and also plastics.
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The Protein problem
Our bodies need certain amino acids to keep us healthy. We get
these amino acids by eating protein in animal and plant foods.
We have the same problem with eating protein as we do with
eating starch. Protein molecules are too big to get into our
blood. This means that our bodies have to break the proteins
up into small amino acids. This is called digestion.
amino protein
acid
The amino acids are small enough to get into our blood and
travel to places where they are needed to make new proteins
for example muscle protein, skin protein, nerve protein, kidney
protein, enzyme protein.
Write a heading and try the work below.
1. Why can protein molecules not get into our blood?
2. What is the process called that breaks big protein molecules
up into amino acids?
3. Why can amino acids get into our blood?
4. Copy the blood and guts diagram.
5. What happens to the amino acids once they get into our
blood?
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