AQA AS BIOLOGY Exam Questions and Answers |Complete Solutions Graded A+ |100%
Correct
Describe and explain what the student should have done when counting cells to make sure that
the mitotic index he obtained for this root tip was accurate.
[2 marks] Description;
Explanation;
E.g,
1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
OR
3. Repeat count;4. To ensure figures are correct; OR
Method to deal with part cells shown at edge /count only whole cells;
To standardise counting;
What is the name given to the division of cytoplasm during the cell cycle.
[1 mark] Cytokinesis
A scientist treated growing tips of onion roots with a chemical that stops roots growing. After
24 hours, he prepared a stained squash of these root tips.
Figure 3 is a drawing showing the chromosomes in a single cell observed in the squash of one of
these root tips in anaphase. This cell was typical of other cells in anaphase in these root tips.
Figure 3
Use all of this information to suggest how the chemical stops the growth of roots.
[3 marks] 1. Stops anaphase / cell division / mitosis;
2. (By) stopping / disrupting / spindle fibres forming /
attaching / pulling;
3. Preventing separation of (sister) chromatids;
4. (So) no new cells added (to root tip);
,What is digestion?
[2 marks] 1. Hydrolysis (of);
2. (Large / insoluble substances) to small(er) / soluble substances;
One species of fungus digests cellulose using two types of enzyme, endocellulases and
exocellulases.
Endocellulases act in the middle of the cellulose molecule and exocellulases act at the ends of
the cellulose molecule.
Endocellulases and exocellulases act at different places on cellulose molecules.
Suggest why.
[2 marks] 1. Active sites are different shapes;
2. So different enzyme-substrate complexes (are formed);
OR
So complementary to different parts of cellulose / substrate;
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 marks] Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 101 dilution);
Mix (well);
Repeat using 9 parts fresh (sterile) liquid and 1
part of 101 and 102 dilutions to make 103 dilution;OR
Add 1 part 101 (suspension) to 99 parts (sterile) liquid (to make 103 dilution);
The scientist could have expressed her results as the percentage loss in mass of cellulose.
In the space, write the equation for calculating the percentage loss in mass.
,Turn over for the next question
[1 mark] (Initial Mass - Final Mass / Initial Mass) x 100
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.
[5 marks] COMPARISONS
1.Nucleotide structure is identical;
2.Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3.DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
CONTRASTS
4.Eukaryotic DNA is longer;
5.Eukaryotic DNA contain introns, prokaryotic
DNA does not;
6.Eukaryotic DNA is linear, prokaryotic DNA is
circular;
7.Eukaryotic DNA is associated with / bound to
protein / histones, prokaryotic DNA is not;
Haemoglobins are chemically similar molecules found in many different species. Differences in
the primary structure of haemoglobin molecules can provide evidence
of phylogenetic (evolutionary) relationships between species. Explain how.
[5 marks] 1.Mutations change base / nucleotide (sequence);
2.(Causing) change in amino acid sequence;
3.Mutations build up over time;
4.More mutations / more differences (in amino acid
/ base / nucleotide sequence / primary structure) between distantly related species;
, OR
Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary
structure) in closely related species;
5. Distantly related species have earlier common ancestor;
OR
Closely related species have recent common ancestor;
Name the type of bond between the deoxyribose and the phophate in DNA
[1 mark] Phosphodiester (bond)
The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe the function of each of these enzymes.
[2 marks] 1. DNA helicase - (unwinding DNA and) breaking hydrogen bonds / bonds between
chains / bases / strands;
2. DNA polymerase - joins (adjacent) nucleotides OR forms phosphodiester bond / sugar-
phosphate backbone;
Adenosine triphosphate (ATP) is a nucleotide derivative.Contrast the structures of ATP and a
nucleotide found in DNA to give two
differences.
[2 marks] 1.ATP has ribose and DNA nucleotide has deoxyribose;
2.ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group);
3.ATP- base always adenine and in DNA nucleotide base can be different / varies;
A student investigated the effect of three types of disinfectant on the growth of Lactobacillus
bacteria.
During the investigation, the student:
boiled the agar before pouring the agar plates
transferred 0.5 cm3 of a diluted liquid culture of Lactobacillus onto each agar
Correct
Describe and explain what the student should have done when counting cells to make sure that
the mitotic index he obtained for this root tip was accurate.
[2 marks] Description;
Explanation;
E.g,
1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
OR
3. Repeat count;4. To ensure figures are correct; OR
Method to deal with part cells shown at edge /count only whole cells;
To standardise counting;
What is the name given to the division of cytoplasm during the cell cycle.
[1 mark] Cytokinesis
A scientist treated growing tips of onion roots with a chemical that stops roots growing. After
24 hours, he prepared a stained squash of these root tips.
Figure 3 is a drawing showing the chromosomes in a single cell observed in the squash of one of
these root tips in anaphase. This cell was typical of other cells in anaphase in these root tips.
Figure 3
Use all of this information to suggest how the chemical stops the growth of roots.
[3 marks] 1. Stops anaphase / cell division / mitosis;
2. (By) stopping / disrupting / spindle fibres forming /
attaching / pulling;
3. Preventing separation of (sister) chromatids;
4. (So) no new cells added (to root tip);
,What is digestion?
[2 marks] 1. Hydrolysis (of);
2. (Large / insoluble substances) to small(er) / soluble substances;
One species of fungus digests cellulose using two types of enzyme, endocellulases and
exocellulases.
Endocellulases act in the middle of the cellulose molecule and exocellulases act at the ends of
the cellulose molecule.
Endocellulases and exocellulases act at different places on cellulose molecules.
Suggest why.
[2 marks] 1. Active sites are different shapes;
2. So different enzyme-substrate complexes (are formed);
OR
So complementary to different parts of cellulose / substrate;
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 marks] Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 101 dilution);
Mix (well);
Repeat using 9 parts fresh (sterile) liquid and 1
part of 101 and 102 dilutions to make 103 dilution;OR
Add 1 part 101 (suspension) to 99 parts (sterile) liquid (to make 103 dilution);
The scientist could have expressed her results as the percentage loss in mass of cellulose.
In the space, write the equation for calculating the percentage loss in mass.
,Turn over for the next question
[1 mark] (Initial Mass - Final Mass / Initial Mass) x 100
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.
[5 marks] COMPARISONS
1.Nucleotide structure is identical;
2.Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3.DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
CONTRASTS
4.Eukaryotic DNA is longer;
5.Eukaryotic DNA contain introns, prokaryotic
DNA does not;
6.Eukaryotic DNA is linear, prokaryotic DNA is
circular;
7.Eukaryotic DNA is associated with / bound to
protein / histones, prokaryotic DNA is not;
Haemoglobins are chemically similar molecules found in many different species. Differences in
the primary structure of haemoglobin molecules can provide evidence
of phylogenetic (evolutionary) relationships between species. Explain how.
[5 marks] 1.Mutations change base / nucleotide (sequence);
2.(Causing) change in amino acid sequence;
3.Mutations build up over time;
4.More mutations / more differences (in amino acid
/ base / nucleotide sequence / primary structure) between distantly related species;
, OR
Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary
structure) in closely related species;
5. Distantly related species have earlier common ancestor;
OR
Closely related species have recent common ancestor;
Name the type of bond between the deoxyribose and the phophate in DNA
[1 mark] Phosphodiester (bond)
The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe the function of each of these enzymes.
[2 marks] 1. DNA helicase - (unwinding DNA and) breaking hydrogen bonds / bonds between
chains / bases / strands;
2. DNA polymerase - joins (adjacent) nucleotides OR forms phosphodiester bond / sugar-
phosphate backbone;
Adenosine triphosphate (ATP) is a nucleotide derivative.Contrast the structures of ATP and a
nucleotide found in DNA to give two
differences.
[2 marks] 1.ATP has ribose and DNA nucleotide has deoxyribose;
2.ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group);
3.ATP- base always adenine and in DNA nucleotide base can be different / varies;
A student investigated the effect of three types of disinfectant on the growth of Lactobacillus
bacteria.
During the investigation, the student:
boiled the agar before pouring the agar plates
transferred 0.5 cm3 of a diluted liquid culture of Lactobacillus onto each agar
