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AQA AS Biology Exam With Complete Solution
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AQA AS Biology Exam With Complete Solution...
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AQA AS Biology Exam WithComplete Solution
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells -
Answer 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 - Answer 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
Explain why students were unable to make a conclusion from the table? - Answer -
missing information -so cannot compare all stages -no statistical comparison of
standard deviations given or no measure of significant differences
Why do we press down firmly on the cover slip? - Answer To form a thin layer of cells so
light passes through making cells visible
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 - Answer • Examine
large number of fields of view to ensure representative sample
• Repeat count to ensure figures are correct
• Count only whole cells to standardise counting
Where do hydrogen bonds form? - Answer Hydrogen bonds form between NH and C=O
groups in a protein's secondary structure
, Scientists looking for extra-terrestrial life are looking for planets with evidence of free
water. Explain why water is considered so important for life to occur. - Answer Life
evolved in water. Water provides support (for bodies of organisms). Water is a major
component of cytoplasm. Metabolic reactions occur in aqueous solutions (solvent).
Water is a metabolite/reactant is many cell reactions. Water stabilises temperature (high
specific heat capacity). Important in cooling (high latent heat).
Limiting water loss in insects - Answer -Small surface area to volume ratio, to minimise
the area over which water is lost.
-Exoskeleton covered with a waterproof cuticle.
-Spiracles remain closed to minimise water loss.
Describe the difference between the structure of a triglyceride molecule and the
structure of a phospholipid molecule (1 mark) - Answer In phospholipids, one of the fatty
acid chains are *replaced* by a phosphate group
Explain why it is more useful to calculate an index of diversity than to record species
richness. - Answer Measures abundance of each species because there may be many
of 1 species or very few of one species.
Suggest how scientists measured the rate of water flow in the river. - Answer measured
time to fill a container of a known volume.
slow water flow leads to... - Answer less oxygen dissolved in water so less respiration
for aquatic life
How to standardise a sampling procedure. - Answer use same size measuring object
same size of area sampled
same sampling time
Not all mutations in the nucleotide sequence of a gene cause a change in the structure
of a polypeptide. Give two reasons why. - Answer degenerate code
could happen in introns/non coding
Suggest a method that could be used to measure the quantity of reducing sugar in a
solution. - Answer Filter and dry the precipitate
Weigh/find mass
Why using a colorimeter improves the repeatability of the student's results. - Answer
quantitative
colour change is subjective
standardises values
Explain how the active site of an enzyme causes a high rate of reaction. - Answer
Enzyme lowers the activation energy.
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