Exam Questions by Topic Chapter 1 Biology

Question 1

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. (2)

Answer 1

1) A condensation reaction joins two monomers together, forms a chemical bond and releases water.
2) A hydrolysis reaction splits two monomers apart by breaking the chemical bond and uses water.

Question 2

What is a monomer? (1)

Answer 2

1) A repeating unit that forms polymers.

Question 3

A biochemical test for reducing sugar produces a negative result with raffinose solution.
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar. (3)

Answer 3

1) Heat with acid and neutralise.
2) Heat with Benedict’s solution.
3) Red precipitate forms.

Question 4

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. (2)

Answer 4

1) Filter and dry the precipitate.
2) Find the mass.

Question 5

Use of a colorimeter in this investigation would improve the repeatability of the student’s results. Give one reason why

Answer 5

1) Colorimeter is quantitative.

Question 6

Describe three differences between the structure of a cellulose molecule and a glycogen molecule.

Answer 6

1) Cellulose is made up of beta glucose, glycogen is made up of alpha glucose.
2) Cellulose is a straight chain, glucose is branched.
3) Glycogen has 1,4 and 1,6 glycosidic bonds, cellulose has only 1,4 glycosidic bonds.

Question 7

Describe and explain five features of starch that make it a good storage molecule.

Answer 7

1) Insoluble so it doesn’t affect the water potential.
2) Branched so it is more compact.
3) Polymer of alpha glucose so it provides glucose for respiration.
4) Branched so more ends for enzyme action.
5) Large so can’t cross the cell membrane.

Question 8

Describe the structure of glycogen. (3)

Answer 8

1) Polysaccharide of alpha glucose.
2) Joined by glycosidic bonds.
3) Branched.

Question 9

Suggest how glycogen acts as a source of energy. (2)

Answer 9

1) Hydrolysed into glucose.
2) Glucose is used in respiration.

Question 10

Explain the difference in the structure of the starch molecule and the cellulose molecule. (2)

Answer 10

1) Cellulose is made up of beta glucose, starch is made up of alpha glucose.
2) Position of the hydrogen and hydroxyl group are inverted on carbon 1.

Question 11

Explain how cellulose molecules are adapted for their function in plant cells. (3)

Answer 11

1) Long and straight chains.
2) Joined by hydrogen bonds to form fibrils.
3) Provides strength to cell wall.

Question 12

Describe how a triglyceride molecule is formed. (3)

Answer 12

1) One glycerol and three fatty acids.
2) Condensation reaction and removal of 3 water molecules.
3) Ester bonds formed.

Question 13

Describe how an ester bond is formed in a phospholipid molecule. (2)

Answer 13

1) Condensation reaction
2) Between glycerol and fatty acid.

Question 14

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

Answer 14

1) Substrate binds to active site.
2) Active site changes shape so it is complementary to the substrate.
3) Reducing the activation energy.

Question 15

A competitive inhibitor decreases the rate of an enzyme-controlled
reaction. Explain how. (3)

Answer 15

1) Inhibitor is similar in shape to the substrate.
2) Binds to active site.
3) Prevents enzyme-substrate complex from forming.

Question 16

Describe how the structure of a protein depends on the amino acids it contains. (5)

Answer 16

1) Structure is determined by R groups.
2) Primary structure is the sequence of amino acids.
3) Secondary structure formed by hydrogen bonding.
4) Tertiary structure formed by ionic bonds, hydrogen bonds and disulfide bridges.
5) Quaternary structure contains more than one polypeptide.

Question 17

Explain how the active site of an enzyme causes a high rate of reaction. (3)

Answer 17

1) Lowers activation energy.
2) Induced fit causes active site of enzymes to change shape.
3) So enzyme-substrate complex causes bonds to form.

Question 18

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end. (2)

Answer 18

1) One amine group joins to a carboxyl group to form a peptide bond.
2) So in the chain there is a free amine group on one end and a free carboxyl group on the other end.

Question 19

Describe two other ways in which all dipeptides are similar and one way in which they might differ. (3)

Answer 19

Similarities:
1) Amine group at one end.
2) Carboxyl group at the other end.

Difference:
1) Different R group.

Question 20

Describe how a non-competitive inhibitor can reduce the rate of an
enzyme-controlled reaction. (3)

Answer 20

1) Attaches to the allosteric site.
2) Changes shape of active site.
3) Substrate is no longer complementary so no substrate can bind.

Question 21

Describe how a peptide bond is formed between two amino acids to form a dipeptide. (2)

Answer 21

1) Condensation reaction
2) Between amine group and carboxyl group.

Question 22

The secondary structure of a polypeptide is produced by bonds between amino acids. (2)

Answer 22

1) Hydrogen bonds.
2) Forming alpha helix or beta pleated sheets.

Question 23

Two proteins have the same number and type of amino acids but different tertiary structures. (2)

Answer 23

1) Different sequence of amino acids.
2) Forms ionic, hydrogen and disulfide bonds in different places.

Question 24

Formation of an enzyme-substrate complex increases the rate of reaction. Explain how. (2)

Answer 24

1) Reduces activation energy.
2) Due to bending bonds.

Question 25

Describe the structure of DNA. (5)

Answer 25

1) Polymer of nucleotides. 2) Each nucleotides is formed from a phosphate group, a deoxyribose and a nitrogenous base. 3) Phosphodiester bonds form between adjacent nucleotides. 4) Double helix held by hydrogen bonds. 5) Hydrogen base pairing between complementary bases - A and T or C and G.

Question 26

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (3)

Answer 26

1) Condensation reaction 2) Between phosphate and deoxyribose 3) Catalysed by DNA polymerase.

Question 27

Describe how the separation of strands occurs.

Answer 27

1) DNA helicase. 2) Breaks hydrogen bonds between complementary base pairs.

Question 28

Describe the role of DNA polymerase in the semi-conservative replication of DNA. (3)

Answer 28

1) Joins adjacent nucleotides. 2) By condensation reactions. 3) Forming phosphodiester bonds.

Question 29

Use your knowledge of semi-conservative replication of DNA to suggest: 1. the role of the single-stranded DNA fragments (2) 2.the role of the DNA nucleotides. (1)

Answer 29

1: 1)Template. 2) Determines the order of bases. 2: 1) Forms complementary base pairs between A and T or C and G.

Question 30

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. (3)

Answer 30

1) Two strands so both can act as templates. 2) Complementary base pairing allows for accurate replication. 3) Weak hydrogen bonds so two strands can easily separate.

Question 31

Describe the role of two named enzymes in the process of semiconservative replication of DNA.

Answer 31

1) DNA helicase breaks hydrogen bonds between the DNA strands. 2) DNA polymerase joins the DNA nucleotides. 3) Forming phosphodiester bonds.

Question 32

Describe the function of each of these enzymes: DNA helicase (1) DNA polymerase (1)

Answer 32

DNA helicase: 1) Breaks hydrogen bonds between bases. DNA polymerase: 1) Joins adjacent nucleotides.

Question 33

Contrast the structures of ATP and a nucleotide found in DNA to give three differences.

Answer 33

1) ATP has ribose, DNA has deoxyribose. 2) ATP has 3 phosphate groups, DNA has 1 phosphate group. 3) ATP base is always adenine, DNA base can be ACGT.

Question 34

Use your knowledge of enzyme action to explain why the arrows point in opposite directions in a double helix of DNA. (4)

Answer 34

1) DNA has antiparallel strands. 2) Nucleotides are aligned differently. 3) Enzymes have active sites with specific shape. 4) Only substrates with complementary shape can bind to the active site of the enzyme.

Question 35

Explain why new nucleotides can only be added in a 5’ to 3’ direction.

Answer 35

1) DNA polymerase 2) Is specific. 3) Only complementary with the 5' end. 4) Shapes of 5' end and 3' end are different.

Question 36

Describe how an ATP molecule is formed from its component molecules. (3)

Answer 36

1) ATP is made up of adenine, 3 phosphate groups and ribose. 2) Condensation reaction 3) Catalysed by ATP synthase.

Question 37

Name the two products of ATP hydrolysis.

Answer 37

1) Adenosine diphosphate 2) Inorganic phosphate

Question 38

ATP is an energy source used in many cell processes. Give five ways in which ATP is a suitable energy source for cells to use.

Answer 38

1) Does not leave cell. 2) Releases energy instantaneously. 3) Releases small amounts of energy. 4) Phosphorylates other compounds making them more reactive. 5) Can be rapidly re-synthesised.

Question 39

Describe how ATP is resynthesised in cells. (3)

Answer 39

1) From ADP and inorganic phosphate. 2) By ATP synthase. 3) During respiration.

Question 40

Give two ways in which the hydrolysis of ATP is used in cells.

Answer 40

1) Provides energy for reactions. 2) To add phosphate to other substances and make them more reactive.

Question 41

Explain five properties that make water important for organisms

Answer 41

1) A metabolite in photosynthesis. 2) A solvent so reactions can occur. 3) HSHC so buffers changes in temperature. 4) LLHOV so provides a cooling effect. 5) Cohesion provides surface tension supporting small organisms.

Question 42

State and explain the property of water that helps to prevent temperature increase in a cell. (2)

Answer 42

1) High specific heat capacity. 2) Buffers changes in temperature.

Question 43

State and explain the property of water that can help to buffer changes in temperature.

Answer 43

1) High specific heat capacity. 2) Takes a lot of energy to change temperature.

Question 44

Give two properties of water that are important in the cytoplasm of cells. For each property of water, explain its importance in the cytoplasm.

Answer 44

1) Polar molecule - universal solvent. 2) Reactive - takes place in condensation.

Question 45

Describe the structure of proteins.

Answer 45

1) Polymer of amino acids. 2) Primary structure is the sequence of amino acids in the polypeptide. 3) Secondary structure is the folding of the polypeptide chain due to hydrogen bonding. 4) Tertiary structure is 3D folding due to hydrogen bonding, ionic bonding and disulfide bridges. 5) Quaternary structure is made up of more than one polypeptide chain.

Question 46

Describe the roles of iron ions, sodium ions, and phosphate ions in cells

Answer 46

Iron ions: 1) Haemoglobin associates with oxygen. Phosphate ions: 1) Phosphorylates other compounds making them more reactive. 2) Used to produce ATP. Sodium ions: 1) Co-transport of glucose and amino acids. 2) Because sodium is moved out by active transport.

Question 47

Give five ways in which the structure of starch is similar to cellulose. (5)

Answer 47

1) Both are polymers of polysaccharides. 2) Both contain C H O. 3) Both contain glycosidic bonds. 4) Both have 1,4 glycosidic bonds. 5) Both have hydrogen bonding.

Question 48

Give two ways in which the structure of starch is different from cellulose.

Answer 48

1) Starch has alpha glucose, cellulose has beta glucose. 2) Starch has 1,6 glycosidic bonds whereas cellulose doesn't. 3) Starch doesn't have fibrils. 4) Starch is helical whereas cellulose is straight. 5) Starch doesn't have hydrogen bonds BETWEEN molecules.

Question 49

Hydrogen bonds are important in cellulose molecules. Explain why. (2)

Answer 49

1) Holds chains together. 2) Hydrogen bonds are strong in large numbers.

Question 50

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. (1)

Answer 50

1) Compact

Question 51

Maltose is hydrolysed by the enzyme maltase. Explain why maltase catalyses only this reaction. (3)

Answer 51

1) Active site of enzyme has specific shape. 2) Only maltose can bind to it. 3) To form enzyme-substrate complex.

Question 52

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

Answer 52

1) ATP can't be stored. 2) ATP only releases a small amount of energy at a time.

Question 53

Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells.

Answer 53

1) Made up of beta glucose. 2) Joined by condensation reactions. 3) Has 1,4 glycosidic bonds. 4) Hydrogen bonds join long straight chains. 5) Cellulose provides structural support to the cell wall. 6) Can resist turgor pressure.