4 Exam Questions

Question 1

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 1

Base sequence of nucleotides
In triplets
Determines order of amino acids

Question 2

Define the term exon. [1]

Answer 2

Base sequence coding for polypeptide

Question 3

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. [3]

Answer 3

Condensation reaction
Between phosphate and deoxyribose
Catalysed by DNA polymerase

Question 4

The nucleus and a chloroplast of a plant cell both contain DNA.

Give five ways in which the DNA in a chloroplast is different from DNA in the nucleus. [5]

Answer 4

DNA shorter in chloroplasts
Fewer genes in chloroplasts
DNA circular in chloroplasts, linear in nucleus
Not associated with histones in chloroplast unlike nuclear DNA
Introns absent but present in nuclear DNA

Question 5

Give two differences between the structure of a DNA nucleotide and
the structure of an RNA nucleotide. [2]

Answer 5

DNA have base thymine but DNA have uracil instead
Deoxyribose in DNA and ribose in RNA

Question 6

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 6

Different triplets can code for same amino acid
Occurs in introns

Question 7

Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells. [6]

Answer 7

Nucleotide structure is identical
Nucleotides joined by phosphodiester bond
Eukaryotic DNA is longer
Eukaryotic DNA contains introns, prokaryotic does not
Eukaryotic DNA is linear, prokaryotic DNA is circular
Eukaryotic DNA is associated with histones, prokaryotic DNA is not

Question 8

Suggest two ways the structure of the chromosome could differ along its length to result in the stain binding more in some areas. [2]

Answer 8

Differences in base sequences
Differences in coiling

Question 9

What is a homologous pair of chromosomes? [1]

Answer 9

Two carry chromosomes that carry the same genes

Question 10

Describe four differences between the structure of a tRNA molecule and the structure of an mRNA molecule. [4]

Answer 10

tRNA is clover leaf shape, mRNA is linear
tRNA has hydrogen bonds, mRNA does not
tRNA has amino acid binding site, mRNA does not
tRNA has anticodon, mRNA has codon

Question 11

Describe and explain a difference in the structure of mRNA and pre-mRNA molecules. [2]

Answer 11

mRNA fewer nucleotides - no introns
Because of splicing

Question 12

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

Answer 12

tRNA brings specific amino acid to ribosome
Anticodon on tRNA binds to codon on mRNA
Amino acids join by condensation reaction using ATP

Question 13

Describe how mRNA is produced from an exposed template strand of DNA. [3]

Answer 13

Free RNA nucleotides form complementary base pairs
Phosphodiester bonds form
By RNA polymerase

Question 14

Describe how mRNA is formed by transcription in eukaryotes. [6]

Answer 14

Hydrogen bonds between DNA bases break
One DNA strand acts as a template
Free RNA nucleotides align by complementary base pairing
RNA polymerase joins adjacent RNA nucleotides
By phosphodiester bonds between adjacent nucleotides
Pre-mRNA is spliced to remove introns and form mRNA

Question 15

Describe how a polypeptide is formed by translation of mRNA. [6]

Answer 15

mRNA attaches to ribosomes
tRNA anticodons bind to complementary mRNA codons
tRNA brings a specific amino acid
Amino acids join by peptide bonds
With the use of ATP
tRNA released after amino acids form polypeptide

Question 16

What is the proteome of a cell? [1]

Answer 16

The number of different proteins that a cell is able to produce at a given time

Question 17

Describe how mRNA is produced in a plant cell. [6]

Answer 17

The DNA strands separate by breaking the H bonds
One strand acts as a template
Complementary base pairing
RNA nucleotides joined by RNA polymerase
pre-mRNA formed
Splicing, introns removed to form mRNA

Question 18

Give the two types of molecule from which a ribosome is made. [1]

Answer 18

RNA
Proteins

Question 19

Describe the role of a ribosome in the production of a polypeptide. [5]

Answer 19

mRNA binds to ribosome
Two codons
Allows tRNA with anticodons to bind
Catalyses formation of peptide bond between amino acids held by tRNA
Moves along mRNA to next codon

Question 20

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.

Explain why. [2]

Answer 20

Introns in pre-mRNA
Removal in splicing

Question 21

Define the term mutagenic agent. [1]

Answer 21

A factor that increases the rate of mutations

Question 22

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

Answer 22

Random fertilisation
Produces new allele combinations

Question 23

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

Answer 23

Change in the base sequence of DNA
Results in the formation of new allele

Genetic code is degenerate or mutation is in intron so amino acid sequence may not change
New allele is recessive so does not influence phenotype

Results in change that positively changes the properties of the protein
May increase chance of survival

Question 24

Give two differences between mitosis and meiosis. [2]

Answer 24

Mitosis produces genetically identical daughter cells, meiosis produces genetically different daughter cells
Two cells produced in mitosis, four cells produced in meiosis

Question 25

Explain how the chromosome number is halved during meiosis. [2]

Answer 25

Homologous chromosomes in pairs
One of each pair goes to opposite pole for each daughter cell

Question 26

Describe the process of crossing over and explain how it increases genetic diversity. [4]

Answer 26

Homologous chromosomes form pairs
Chiasmata gorm
Equal lengths of alleles are exchanged
Producing new combinations of alleles

Question 27

A student used a dilution series to investigate the number of cells present in a liquid culture of bacteria.

Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria. [3]

Answer 27

Add 1 part bacteria culture to 9 parts distilled water to make 1 in 10 dilution
Mix well
Add 1 part 1 in 10 dilution to 99 parts distilled water to make 1 in 1000 dilution

Question 28

What term is used to describe this method of naming organisms? [1]

Answer 28

Binomial

Question 29

There are many different species of AnimalX in Europe. Using a
phylogenetic classification, all of these species have names that start with NameY.
What information does this give about AnimalX?

Answer 29

Same genus
Same evolutionary origin

Question 30

Describe how breeding experiments could determine whether the two populations are from the same species. [2]

Answer 30

Breed the two mice together
Same species will produce fertile offspring

Question 31

The scientists obtained DNA from AnimalX that were alive before hunting started.

Suggest one source of this DNA. [1]

Answer 31

Preserved remains

Question 32

Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity. [2]

Answer 32

Population might have started with a small number of individuals
Inbreeding

Question 33

Explain why it is more useful to calculate an index of diversity than to record species richness. [2]

Answer 33

Index of diversity also measures population size of each species
Useful as may be more/less of some species

Question 34

Suggest how the scientist measured the rate of water flow in the river. [1]

Answer 34

Movement of object over known distance

Question 35

Give one way in which a sampling procedure could be standardised. [1]

Answer 35

Same size area sampled

Question 36

What data would students need to collect to calculate an index of
diversity in each habitat? [1]

Answer 36

Number of species and number of individuals in each species in each habitat

Question 37

Give two ways the students would have ensured their index of diversity was representative of each habitat. [2]

Answer 37

Random samples
Large number of samples

Question 38

What is meant by ‘species richness’? [1]

Answer 38

A measyre of the number of different species in a community

Question 39

Outline a method the ecologists could have used to determine the plant species richness at one site. [3]

Answer 39

Coordinates and a random number generator
Use of quadrat
Count number of different plant species in each quadrat

Question 40

Describe how you would investigate the effect of an invasion by a
non-native species of plant (a biotic environmental factor) over many years on the abundance of a native species of plant in a community. [4]

Answer 40

Set up grid of coordinates
Place large number of quadrats at random coordinates
Estimate percentage cover of native plant in quadrats
Repeat at same time each year

Question 41

Give two other ways in which genetic diversity between species is
measured.

Answer 41

Comparing features
Comparing differences in base sequence of DNA
Comparing amino acid sequence