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Biological Molecules Exam Questions with Complete Answers
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Biological Molecules Exam Questionswith Complete Answers
What is a monomer? - Answer-Monomers are small units which are the components of
larger molecules, examples include monosaccharides such as glucose, amino acids
and nucleotides.
What is a polymer? - Answer-Polymers are molecules made from many monomers
joined together through a condensation reaction.
What happens in a condensation reaction? - Answer-A chemical bond forms between 2
molecules & a molecule of water is produced. Glyosidic bonds formed.
What happens in a hydrolysis reaction? - Answer-A water molecule is used to break a
chemical bond between 2 molecules.
What is a monosaccharide? Give examples. - Answer-The simplest carbohydrates,
consisting of only one sugar molecule. Some examples include galactose, fructose and
glucose.
What formula do monosaccharides have? - Answer-(CH2O)n
What is a disaccharide? Give an example. - Answer-2 monosaccharides joined together
in a condensation reaction, forming a glycosidic bond and forming a water molecule. An
example is maltose.
Name the disaccharides and which mono's make up the disaccharides. - Answer-
Maltose - two glucose molecules
Sucrose - glucose and fructose
Lactose - glucose and galactose.
What is a polysaccharide? Give an example. - Answer-Formed from many glucose units
joined together. Examples include glycogen and starch, formed by the condensation of
alpha glucose and cellulose which is formed by the condensation of beta glucose.
Draw the structure of alpha glucose. - Answer-
Draw the structure of beta glucose. - Answer-
Describe the function of glycogen. - Answer-Main storage molecule in animals.
- Large number of side branches so energy can be released quickly as enzymes can
simultaneously act on these branches.
- Large but compact molecule maximising the energy stored.
- Insoluble so won't affect water potential.
, Describe the structure of glycogen. - Answer-It is formed from many molecules of alpha
glucose joined together by 1, 4 and 1, 6 glyosidic bonds. It has many branches and is
compact.
Describe the structure of starch. - Answer-Made up of amylose and amylopectin.
Amylose - amylose is an unbranched chain of glucose molecules joined by 1, 4
glycosidic bonds, and as a result amylose is coiled and thus a very compact molecule
storing a lot of energy. • Amylopectin is branched and is made up of glucose molecules
joined by 1, 4 and 1, 6 glycosidic bonds. Due to the presence of many side branches
these can be acted upon simultaneously by many enzymes and thus broken down to
release its energy.
How is starch adapted to its function? - Answer-It stores energy in plants. It is insoluble
so wont affect the cells water potential. It is compact so can store a lot of energy in a
small space. When hydrolysed the glucose can be transported easily.
Describe the function of cellulose. - Answer-Cellulose is a component of cells walls in
plants and is composed of long, unbranched chains of beta glucose which are joined by
glycosidic bonds.
How is cellulose adapted for its function. - Answer-Microfibrils are strong threads which
are made of long cellulose chains running parallel to one another that are joined
together by hydrogen bonds forming strong cross linkages. Cellulose is important in
stopping the cell wall from bursting under osmotic pressure. This is because it exerts
inward pressure that stops the influx of water. This means that cells stay turgid and
rigid, helping to maximise the surface area of plants for photosynthesis.
Describe how you could test for reducing sugars. - Answer-The Benedicts test.
1. Add 2cm3 of your liquid food sample.
2. Add 2cm3 of Benedicts reagent.
3. Heat gently. If the solution turns from blue to brick red a reducing sugar is present.
Describe how you could test for non-reducing sugars. - Answer-1. Complete the
Benedicts test and get a negative result.
2. Add 2cm3 of dilute HCl to 2cm3 of the food sample and heat. This will hydrolyze
di/polysaccharides.
3. Add sodium hydrogencarbonate to neutralize the test as it will not work in acidic
conditions.
4. The solution can now be retested by adding 2cm3 of Benedict's Reagent to the
solution and placing in a water bath for 5 minutes.
5. If a non reducing sugar is present in the original sample then a colour change from
the blue Benedict's Reagent to brick red (orange-brown) will be observed.
Chemical test for starch. - Answer-A chemical test for starch is iodine/potassium iodide.
If the solution turns blue/black in colour from orange-brown then starch is present.
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