As Paper 1 A-Level Biology Flashcards
Explain how the considerable length of a DNA molecule is compacted into a chromosome
The double helix is tightly coiled around histone proteins.
What is the function of a histone protein?
To associate with the DNA to assist in the tightly coiling of DNA to fit chromosomes into the nucleus.
Suppose the total length of all the DNA in a single human muscle cell is 2.3m
a) If all the DNA were distributed equally between the chromosomes calculate the mean length of DNA in each one
b) Calculate in mm the length of DNA in a human brain cell
a) 2.3m / 46 = 0.05m
b) 2.3m DNA in muscle and brain cell
Convert m to mm = x1000
2.3 x 1000
= 2300mm
The human genome contains approximately 3 billion base pairs, which reside in the 23 pairs of chromosomes within the nucleus of all our cells. If all the base pairs were equally distributed between the chromosomes, calculate how many base pairs each chromosome would have. Write your answer in standard form.
3 x 10^9 base pairs in 23 pairs (all 46 chromosomes)
3x 10^9 / 46
= 6.5 x 10^7
Give two structures found in all prokaryotic cells and in all eukaryotic cells [2]
- Cell(-surface) membrane;
- Ribosomes;
Ignore 70S - Cytoplasm;
- DNA;
All prokaryotic cells contain a circular DNA molecule and some prokaryotic cells
contain plasmids.
(b) Scientists have found that the rate of plasmid replication is faster in cells
growing in a culture with a high concentration of amino acids than in a
culture with a lower concentration of amino acids.
Suggest one explanation for the faster rate of plasmid replication in cells
growing in a culture with a high amino acid concentration. [2]
Mark in pairs: 1 and 2 OR 3 and 4
1. (Amino acids used in) protein synthesis;
Accept for ‘protein synthesis’, translation
2. (So) more enzymes (for DNA/plasmid replication)
OR
(So) more DNA polymerase;
3. (Amino acids used in) respiration;
4. (So) more energy/ATP (for DNA/plasmid replication);
Describe how a sample of chloroplasts could be isolated from leaves. [4]
- Break open cells/tissue and filter
OR
Grind/blend cells/tissue/leaves and filter;
Accept homogenise and filter - In cold, same water potential/concentration, pH controlled solution;
Accept for ‘same water potential/ concentration’,
isotonic
Accept for ‘pH controlled’, buffered - Centrifuge/spin and remove nuclei/cell debris;
- (Centrifuge/spin) at high(er) speed, chloroplasts settle out;
Scientists grew two groups of plants:
* control plants with all the inorganic ions needed
* iron-deficient plants with all the inorganic ions needed but without
iron ions.
After 1 week, the scientists measured the mass of protein and the mass of
chlorophyll in the chloroplasts isolated from samples of leaves of these two
groups of plants.
The table below shows the scientists’ results.
Mass of protein /
percentage of control = 40
Mass of chlorophyll /
percentage of control = 10
Some proteins found inside the chloroplast are synthesised inside the
chloroplast.
Give one feature of the chloroplast that allows protein to be synthesised
inside the chloroplast and describe one difference between this feature in
the chloroplast and similar features in the rest of the cell.
Feature:
Structural
difference:
[2]
The ratio of protein to chlorophyll in control plants is 9:1
Use the information in the table above to calculate the ratio of protein to
chlorophyll in iron-deficient plants.
[1]
Mark in pairs, 1 and 2 OR 3 and 4
1. DNA;
2. Is not associated with protein/histones but nuclear DNA is
OR
Is circular but nuclear DNA is linear
OR
Is shorter than nuclear DNA
3. Ribosomes;
4. Are smaller than cytoplasmic ribosomes;
Accept: 70S ribosomes in chloroplast, but 80S
ribosomes in cytoplasm
36:1
A scientist determined the volume of a plant cell and the volume of
organelles it contained.
They found:
* 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.
Answer = µm3
Correct answer of 7455 = 2 marks;;
Accept for 1 mark answers in range:
7717.5 to 7718 (44.1% of 17500)
If incorrect answer, accept for 1 mark working
shows an attempt to subtract 262.5
Describe the chemical reactions involved in the conversion of polymers to
monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to
illustrate your answer.
[5]
Ignore reference to dimers.
1. A condensation reaction joins monomers together and forms a
(chemical) bond and releases water;
2. A hydrolysis reaction breaks a (chemical) bond between
monomers and uses water;
3. A suitable example of polymers and the monomers from which
they are made;
3. and 4. Polymers must contain many monomers.
3. and 4: suitable examples include
* amino acid and polypeptide, protein, enzyme,
antibody or specific
example
* nucleotide and polynucleotide, DNA or RNA
* Alpha glucose and starch/glycogen
* Beta glucose and cellulose.
If neither specific carbohydrate example is given, allow
monosaccharide/glucose and polysaccharide.
3. and 4. Reject (once) reference to triglycerides.
4. A second suitable example of polymers and the monomers
from which they are made;
5. Reference to a correct bond within a named polymer;
Reject reference to ester bond
Lactulose is a disaccharide formed from one molecule of galactose and
one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference
between the structures of lactulose and lactose.
Similarity
1. Both contain galactose / a glycosidic bond;
Ignore references to hydrolysis and / or
condensation
Difference
2. Lactulose contains fructose, whereas lactose contains glucose;
Ignore alpha / beta prefix for glucose
Difference must be stated, not implied
Explain five properties that make water important for organisms [5]
- A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
- A solvent so (metabolic) reactions can occur
OR
A solvent so allowing transport of substances; - High (specific) heat capacity so buffers changes in temperature;
For ‘buffer’ accept ‘resist’. - Large latent heat of vaporisation so provides a cooling effect (through
evaporation);
Reject latent heat of evaporation - Cohesion (between water molecules) so supports columns of water
(in plants);
For ‘columns of water’ accept ‘transpiration stream’.
Do not credit ‘transpiration’ alone but accept
description of ‘stream’.
For ‘columns of water’ accept ‘cohesion-tension
(theory)’. - Cohesion (between water molecules) so produces surface tension
supporting (small) organisms;
For cohesion accept hydrogen bonding
Ignore reference to pH. Allow other suitable
properties but must have a valid explanation.
For example
* ice floating so maintaining aquatic habitat beneath
* water transparent so allowing light penetration for
photosynthesis
State and explain the property of water that helps to prevent temperature
increase in a cell. [2]
- High (specific) heat capacity;
- Buffers changes in temperature;
Accept ideas such as a lot of energy needed/gained
to change temperature
State and explain the property of water that can help to buffer changes in
temperature. [2]
- (water has a relatively) high (specific) heat capacity;
Ignore numbers relating to heat capacity - Can gain / lose a lot of heat / energy without changing temperature;
OR
Takes a lot of heat / energy to change temperature;
Accept due to H bonding between water molecules
Describe how an ATP molecule is formed from its component molecules [4]
- and 2. Accept for 2 marks correct names of three components adenine,
ribose/pentose, three phosphates;;
Accept for 1 mark, correct name of two components
Accept for 1 mark, ADP and phosphate/Pi
Ignore adenosine
Accept suitably labelled diagram - Condensation (reaction);
Ignore phosphodiester - ATP synthase;
Reject ATPase
