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A-level Biology mock paper 1 Dec 2020
Terms in this set (26)
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus.
1. DNA shorter;
2. Fewer genes;
3. DNA circular not linear;
4. Not associated with protein/histones, unlike
5. Introns absent but present in nuclear DNA;-Nuclear
Some DNA nucleotides have the organic base thymine, but RNA nucleotides do not have thymine. RNA nucleotides have uracil instead of thymine.
Give one other difference between the structure of a DNA nucleotide and the structure of an RNA nucleotide.
NA nucleotides contain
as their pentose sugar whereas
NA nucleotides contain
sugar as their pentose sugar in the molecule.
-DNA nucleotides are mainly involved in
storage of genetic information.
-RNA nucleotides are mainly involved in
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why.
1. Triplets code for same amino acid
2. Occurs in introns /non-coding sequence;
What is a monoclonal antibody?
(Antibodies with the) same tertiary structure
Monoclonal antibodies are artificial antibodies that are produced from a single clone of cells by fusing B-lymphocytes to myeloma cells.
a disease is diagnosed, monoclonal antibodies are used in some medical treatments.
Give one example of using monoclonal antibodies in a medical treatment.
Monoclonal antibodies have been developed which can prevent rejection of organ donors.->
Block antigens/receptors on cells;
OR *Targets/binds/carries drug/medicine to specific
-[They combine with and inactivate helper T cells, without which the lymphocytes that produce antibodies against the transplanted organ won't work.]
Describe the role of antibodies in producing a positive result in an ELISA test. (4 marks)
1.First antibody binds to the antigen
2.Second antibody with enzymes attached is added.
3.Second antibody attaches to the antigen
4.Substrate is added and colour changes indicating a positive result.
A precipitate is produced in a positive result for reducing sugar in Benedict's test.
A precipitate is solid matter suspended in solution.
A student carried out Benedict's test. Suggest a method, other than using a colourimeter, that this student could use to measure the quantity of reducing sugar in a solution.
-Filter and dry the precipitate
-Find the mass/weight using scales
Use of a colourimeter in this investigation would improve the repeatability of the student's results.
Give one reason why.
(Colour change is) subjective;
2. Standardises (the) method;
In Test 1, the student used a measuring cylinder to measure 15 cm3 of solution from a beaker. The measuring cylinder gives a volume with an uncertainty of ±1 cm3
She used a graduated syringe to measure 5.0 cm3 of Benedict's solution. The graduated syringe gives a volume with an uncertainty of ± 0.5 cm3. She mixed these volumes of liquid to do the biochemical test.
Calculate the percentage error for the measurements used to obtain a 20 cm3 mixture of the solution from the beaker and Benedict's solution. Show your working.
(1/15 + 0.5/5) x 100= 16.67%
Explain why it is more useful to calculate an index of diversity than to record species richness.
-It measures the abundance of each species because there may be many of 1 species or very few of one species.
[1. (Index of diversity also) measures abundance /
number / population (size) of each species;
2. (So useful because) may be many of some
(So useful because) may be few of other
Suggest how the scientist measured the rate of water flow in the river.
1. *Movement of (floating) object over known
distance and over given time*
It was important that the sampling procedure was standardised when collecting the Slate Drake mayflies from the two sites.
Give one way in which the sampling procedure could be standardised.
Same size of area (sampled)
Same size net/mesh
Same sampling time
Samples taken at same time of day/on same day;
The detail shown in "Figure 3" would not be seen using an optical microscope.
-Light has a longer wavelength and therefore has a lower resolution.
-limit to magnification
A scientist determined the volume of a plant cell and the volume of organelles it
- the volume of a plant cell is 17 500 μm3
- the volume of all the mitochondria in a plant cell is 262.5 μm3
- the volume of all the mitochondria and all the chloroplasts in a plant cell is 44.1% of
the volume of a plant cell.
Use this information to calculate the volume of all the chloroplasts in a plant cell.
Name an organelle found in both a chloroplast and a prokaryotic cell.
A biologist separated cell components to investigate organelle activity. She prepared a suspension of the organelles in a solution that prevented damage to the organelles.
Describe three properties of this solution and explain how each property prevented damage to the organelles.
1. COLD- to
reduce enzyme activity
that might break down the organelles
2.SAME WATER POTENTIAL AS TISSUE- to
prevent lysis of organelles as a result of osmotic gain or loss of water
3.BUFFERED- so that the
pH does not fluctuate
-prevents denaturing of enzyme/proteins.
Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill. (3 marks)
1. Water and blood flow in opposite
2. Maintains diffusion/concentration gradient
Oxygen concentration always higher (in
It allows maximum oxygen to be absorbed by the blood from the water, by
maintaining the concentration gradient the whole length through the gills.
[-->This means fish can get enough oxygen without having to push large amounts of water through their gills.]
Explain how the active site of an enzyme causes a high rate of reaction. (3 marks)
1. Lowers activation energy;
2. Induced fit causes active site (of enzyme) to
3. (So) enzyme-substrate complex causes bonds
Describe a biochemical test to confirm the presence of protein in a solution.
-The test solution needs to be alkaline so first you add a few drops of
sodium hydroxide solution
- Then add some
copper (II) sulphate solution
Positive result= solution turns
A dipeptide consists of two amino acids joined by a peptide bond. Dipeptides may differ in the type of amino acids they contain.
Describe two other ways in which all dipeptides are similar and one way in which they might differ.
1. Amine/NH2 (group at end);
2. Carboxyl/COOH (group at end);
3. Two R groups;
4. All contain C and H and N and O;
5. Variable/different R group(s);
Suggest why preventing the formation of spindle fibres (lines 2-3) stopped the cell cycle.
1. Chromosomes/centromeres cannot attach (to
Chromosomes cannot line up (on spindle);
2. (So, no) metaphase;
3. Chromatids cannot separate (on spindle);
4. (So, no) anaphase;
Suggest and explain why "ABZ" could be used as a treatment for cancer even though it affects some healthy cells (lines 3-4).
1. Cancer cells divide more/uncontrollably/rapidly
Healthy cells divide less/slowly;
Scientists investigated the response of the roots of pea seedlings to gravity.....The pea seedlings were kept in the dark after each treatment. Explain why this was necessary.
Because (Seedlings) respond to light / are phototropic;
Suggest two advantages of simple reflexes.
-Protect against damage to body tissues
-Do not have to be learnt
-Help escape from predators
-Enable homeostatic control
Name the process by which IAA moves from the growing regions of a plant shoot to other tissues.
When a young shoot is illuminated from one side, IAA stimulates growth on the shaded side.
Explain why growth on the shaded side helps to maintain the leaves in a favourable environment.
Causes plant to grow towards light- positively phototropic;
Light is required for photosynthesis
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