Download Biological_Molecules worksheet - answers

Biological Molecules: Carbohydrates
1. Carbohydrates (also called starch/saccharides) are molecular compounds made from just three
elements: hydrogen, oxygen and carbon.
2. Glucose is a monosaccharide. Monosaccharides are the simplest carbohydrates and are often called
single sugars. They are the building blocks from which all bigger carbohydrates are made
3. Give the chemical formula of glucose C6H12O6
4. Sucrose, maltose and fructose are disaccharides. What is a disaccharide?
These form when two monosaccharides react. Examples of disaccharides are
sucrose, lactose and maltose.
5. A polysaccharide is a long chain, large sugar molecule.
Examples of polysaccharides are starch and glycogen and cellulose.
6. Carbohydrates are one of the most important biological molecules because:
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a source of fuel for the body e.g. glucose and a store of energy, e.g. starch in plants
building blocks for polysaccharides (giant carbohydrates), e.g. cellulose in plants and glycogen in
the human body
components of other molecules e.g. DNA, RNA
7. If many simple sugars join together, we call this a polysaccharide. Most of these are insoluble,
meaning they don’t dissolve in water. Humans get most of the carbohydrates in our diet from starch,
which is found as a storage carbohydrate in many plants. Animal cells contain glycogen, which can be
found in the liver and muscle, where it acts as a store of energy. Another carbohydrate which is a
polysaccharide is found in plant cell walls: cellulose. Humans cannot digest this, as our gut does not
make the enzyme required to break it down. Instead it forms part of our diet as fibre.
8. Describe how you would test for the presence of starch?
Iodine (yellow) turns blue-black in the presence of starch.
9. Describe how you would test for the presence of glucose (a reducing sugar) and what result you would
expect to see. Called the Benedict’s test – Benedict’s solution is blue and turns red/orange when heated
if reducing sugars present.
Biological Molecules: Proteins
1. What are proteins made from? Amino acids.
2. How many different types of the above are there? 20
3. Which 4 chemical elements does protein contain?
a. nitrogen
b. carbon
c. oxygen
d. hydrogen
3. Why are proteins such an important biological molecule?
It is used for growth and repair, to make new cells. Humans must obtain nine essential amino acids
through their food because our bodies are not capable of manufacturing them. A missing amino acid
restricts the protein synthesis and may lead to a protein deficiency, which is a serious type of
malnutrition.
4. Proteins come in many different shapes. The shape is important because most enzymes are proteins and
therefore their function is specific to their structure.
5. Humans must obtain 9 essential amino acids through their food because our bodies are not capable of
manufacturing them.
5. Describe how you would test for the presence of protein?
Use Biuret solution (copper sulphate and sodium hydroxide), this is blue in colour. If this solution
turns purple/violet/lilac this is a positive test for protein.
Biological molecules: Lipids
1. Lipids contain the 3 elements: carbon+ hydrogen + oxygen. However the proportion of oxygen is
much lower than in carbohydrates.
2. The picture below is a simple picture of a lipid (fat) molecule. Label X and Y.
X = glycerol
Y = fatty acids
3. Fats are made up of fatty acids and glycerol.
Fats are large molecules that are composed of three fatty acid molecules bonded to a glycerol molecule.
3. Most animal fats are solid at room temperature, but will melt if you warm them up. Plant lipids are
usually liquid at room temperature and are called triglycerides.
3. Fat molecules are insoluble, meaning that they don’t dissolve in water. They are, however, soluble in
alcohol/ethanol
4. List 3 functions of fats in the human body:
a. They make up cell membranes
b. Long term energy source – they release as twice as much energy as carbohydrates/protein.
c. Good thermal insulators, reducing heat loss.
5. Describe how you would test for the presence of lipids?
They will dissolve in ethanol, if a solution of fat in ethanol is added to water it goes cloudy.
7. Fats are broken down into fatty acids and glycerol by the enzyme lipase.
Biological molecules: Cellulose
1. Cellulose is made from sugars (carbon, hydrogen and oxygen).
2. Cellulose is a polysccharide, a long chain molecule or natural polymer which makes it incredibly
strong.
3. It is the main component of plant cell walls.
4. Although potentially a major food source, humans lack the enzymes to break it down.