Exam Questions by Topic Chapter 4 Biology

Question 1

Name the fixed position occupied by a gene on a DNA molecule. (1)

Answer 1

Locus

Question 2

Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer. (3)

Answer 2

1) Because the nucleotide sequence.
2) In triplets
3) Determines the primary structure.

Question 3

Define the term exon. (1)

Answer 3

1) Nucleotide sequence coding for amino acids.

Question 4

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

Answer 4

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

Question 5

Name the protein associated with DNA in a chromosome. (1)

Answer 5

Histone.

Question 6

What are five differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Answer 6

1) Linear v Circular
2) Introns v No introns
3) Longer v Shorter
4) Associated with histones v Not.
5) No plasmids v Plasmids

Question 7

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome. (2)

Answer 7

1) DNA that doesn’t code for amino acids.
2) Positioned between genes.

Question 8

Give five ways in which the DNA in a chloroplast is different from DNA in the nucleus.

Answer 8

In chloroplasts:
1) DNA is shorter
2) Fewer genes
3) DNA is circular
4) Not associated with histones
5) No introns

Question 9

Give two differences between the structure of a DNA nucleotide and
the structure of an RNA nucleotide.

Answer 9

1) Deoxyribose in DNA and ribose in DNA.
2) RNA has Uracil, DNA has thymine.

Question 10

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why. (2)

Answer 10

1) Triplets code for the same amino acid.
2) Occurs in introns.

Question 11

What is a homologous pair of chromosomes? (1)

Answer 11

1) Two chromosomes that carry the same genes.

Question 12

Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells. (6)

Answer 12

Comparisons:
1) Nucleotide sequence is identical.
2) Nucleotide joined by phosphodiester bond.
3) DNA in chloroplasts is similar to DNA in prokaryotes.

Contrasts:
1) Eukaryotic DNA is longer
2) Eukaryotic DNA contains introns, prokaryotic DNA doesn’t.
3) Eukaryotic DNA is linear, prokaryotic DNA is circular.

Question 13

Describe four differences between the structure of a tRNA molecule and the structure of an mRNA molecule.

Answer 13

1) tRNA is clover leaf shape, mRNA is linear.
2) tRNA has hydrogen bonds, mRNA doesn’t.
3) tRNA has an amino acid binding site, mRNA doesn’t.
4) tRNA has anticodon, mRNA has codon.

Question 14

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. (3)

Answer 14

1) tRNA brings specific amino acid.
2) Anticodon on tRNA binds to codon.
3) Amino acids join by condensation reaction using ATP.

Question 15

Describe how mRNA is produced from an exposed template strand of DNA. Do not include DNA helicase or splicing in your answer. (3)

Answer 15

1) Free RNA nucleotides form complementary base pairs.
2) Phosphodiester bonds form.
3) By action of RNA polymerase.

Question 16

Describe how mRNA is formed by transcription in eukaryotes. (6)

Answer 16

1) DNA helicase breaks hydrogen bonds.
2) One strand acts as a template.
3) Free RNA nucleotides align by complementary base pairing.
4) RNA polymerase joins joins adjacent RNA nucleotides.
5) By phosphodiester bonds
6) Pre-mRNA is spliced to form mRNA.

Question 17

Describe how a polypeptide is formed by translation of mRNA. (6)

Answer 17

1) mRNA attaches to ribosomes.
2) tRNA anticodons bind to complementary mRNA codons.
3) tRNA brings a specific amino acids.
4) Amino acids join by peptide bonds.
5) Amino acids join with the use of ATP.
6) tRNA released after amino acid joined to polypeptide.

Question 18

Give the two types of molecule from which a ribosome is made. (2)

Answer 18

1) RNA
2) Protein

Question 19

What is the proteome of a cell? (1)

Answer 19

1) The proteome is the full range of proteins that a cell is able to produce.

Question 20

Define the term mutagenic agent. (1)

Answer 20

1) A factor that increases the rate of mutations.

Question 21

Apart from mutation, explain one other way genetic variation within a species is increased. (2)

Answer 21

1) Random fertilisation
2) Produces new allele combinations

Question 22

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual. (6)

Answer 22

Gene mutation:
1) Change in the nucleotide sequence.
2) Results in the formation of new allele.

Has no effect because:
3) Genetic code is degenerate.
4) Changes amino acid but has no effect on tertiary structure.

Has positive effect because:
1) Results in change in polypeptide positively changes the properties of protein.
2) May result in increased survival.

Question 23

Give six differences between mitosis and meiosis.

Answer 23

1) Mitosis is one division, meiosis is two divisions.
2) Daughter cells are genetically identical in mitosis, daughter cells are genetically different in meiosis.
3) Crossing over in meiosis only.
4) Independent segregation in meiosis only.
5) Separation of homologous chromosomes in meiosis only.
6) Two cells produced in mitosis, four cells produced in meiosis.

Question 24

Explain how the chromosome number is halved during meiosis. (2)

Answer 24

1) Homologous chromosomes
2) One of each pair goes to opposite poles.

Question 25

Describe the process of crossing over and explain how it increases genetic diversity. (4)

Answer 25

1) Homologous pairs of chromosomes form a bivalent. 2) Chiasmata form. 3) Alleles are exchanged. 4) Producing new combinations of alleles.

Question 26

Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity.

Answer 26

1) Genetic Bottleneck 2) Inbreeding