Mark Scheme answers Flashcards
1
Q
Describe how a polypeptide chain is formed during translation
A
- Specific amino acid is attached to the amino acid binding site on the tRNA molecule
- Amino acids form peptide bonds using ATP
- mRNA codon binds to complimentary anticodon on tRNA
- Ribosome attaches to mRNA molecule
- Amino acids join together via a condensation reaction
2
Q
Describe how mRNA is formed by transcription in eukaryotes
A
- Hydrogen bonds between DNA bases break
- Only one strand acts as a template
- Free RNA nucleotides align by complimentary base pairing
- In RNA uracil base pairs with adenine on DNA
- RNA polymerase joins adjacent RNA polynucleotides
- Phosphodiester bonds between adjacent nucleotides
3
Q
Describe how a polypeptide is formed by translation of mRNA
A
- mRNA attaches to ribosomes
- tRNA anticodons bind to complimentary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- Amino acids are joined together using ATP
- tRNA is released after amino acid is joined to the polypeptide
- The ribosome moves along the mRNA to form a polypeptide
- Ribosome moves to find start codon
4
Q
What does degenerate mean?
A
More than one codon can code for several amino acids
5
Q
List four principles of mutations
A
- Mutations are spontaneous/ random
- Only the rate of mutation is affected by the environment
- Different species do not interbreed/ produce fertile offsprings
- So mutation cannot be passed on from one species to another
6
Q
Apart from genetic factors, what other type of factors cause variation within a species
A
Environment
7
Q
How can DNA from species that have been hunted and killed years ago
A
- Museums
- Bones
- Skin
- Preserved remains
8
Q
What are the effects of hunting on genetic diversity
A
- Genetic bottleneck
- Few alleles left
- Reduced population
9
Q
How can breeding experiments determine if two populations are of the same species
A
- Breed two of the population together
- same species produce a fertile offspring
10
Q
What comparisons can be used to determine similar genetic characteristics of the same species
A
- Amino acid sequence of proteins
- Base sequence of mRNA
- Order of base sequence of DNA
11
Q
Give two points of evidence that mitosis is happening
A
• The individual chromosomes will be visible because they have condensed
• Each chromosome is made up of two chromatids because DNA replication has taken place
12
Q
Suggest one way the structure of chromosomes could differ along its length to result in a stain binding more in some areas
A
Differences in base sequences/ differences in histones
13
Q
What is a homologous pair of chromosomes
A
Two chromosomes that carry the same genes
14
Q
How can a student accurately measure the change in mass of cubes put in a concentrated solution?
A
• Control the temperature
• Dry the cubes before measuring
• Measure the mass of cubes at stated time intervals
15
Q
Define species richness
A
A measure of different species in an environment
16
Q
Suggest one consideration scientists take into account when sampling bees
A
• Must not harm bees, must allow the bees to be released
• Photographs can be used to identify the species of bees
17
Q
What does it mean to suggest and explain?
A
Suggest a point and give reason for your point
18
Q
Another word for index of diversity
A
Species richness diversity
19
Q
Describe how a gene is a code for the production of a polypeptide
A
• Base/nucleotide sequence
• In triplets
• Determines order/sequence of amino acid sequence/ primary structure in polypeptide
20
Q
Describe and explain the difference in structure of mRNA and pre-mRNA
A
• Pre-mRNA contains introns and exons
• mRNA contains only exons
• Because of splicing
21
Q
Note
A
SPECIFIC amino acid
22
Q
What enzyme is used when an amino acid is added to a polypeptide
A
ATP
23
Q
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide
A
• mRNA associates with a ribosome/ribosome attaches to mRNA
• Ribosome moves to/finds the start codon
• tRNA brings/carries specific amino acid
• Anticodon on tRNA complementary to codon on mRNA
• Ribosome moves along to the next codon
• Amino acids join by peptide bonds via a condensation reaction
24
Q
Describe the role of a ribosomes in the production of a polypeptide
A
• mRNA binds to ribosome
• Moves along (mRNA to the next codon)
• catalysed the formation of peptide bonds between amino acids
25
How does a mutation in introns affect a protein
• Prevents splicing
• Different amino acid sequence
• Faulty mRNA formed
26
Explain why percentages of bases from the middle part of the chromosome and the end part are different
• Pre-mRNA contains introns
27
Why would a gene have more number of bases than calculated
Some regions are non coding
28
Give two other measurements he made to calculate the rate of water movement in a plant
• initial and final mass of beaker and all contents
• Number of groups of xylem vessels
29
Give the reason for adding a layer of oil to the water in the beaker
• Prevent evaporation/water loss
30
Describe how one can ensure they should handle a scalpel safely during this procedure
• Cut away from the body
• Cut on flat surface
31
Give two other ways in which genetic diversity between species is measured
• Comparing features/characteristics
• Comparing sequence of amino acid/ primary structures
32
Why is a students T-test used?
For comparing mean of data sets/histograms/ data that are normally distributed
33
List the principles of natural selection in the evolution of populations
• Variation due to mutations
• Change in environment
• Different selective pressures
• Organisms with favourable alleles will survive and breed
• Changes in allele frequency
34
Explain how random mutations can result in new alleles of a gene
• Mutations can change the primary structure of the protein. This then alters the secondary and tertiary structure. A protein with a different 3D shape is formed
35
Many mutations are harmful but in certain environments, explain how the new allele of a gene might benefit its possessor, leading to an increased reproductive success?
Change in coat colour to become more camouflaged, run faster to escape predators
36
Describe stabilising selection and give an example
• The curve becomes narrower and taller. The alleles at the extremes are lost and the alleles in the middle increase frequency. Birth weights of babies
37
Give another difference between DNA in the chloroplast and in the nucleus
• Introns are absent in DNA in chloroplast but present in nuclear DNA
38
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why?
• Triplet code is degenerate
• Occurs in the introns/non-coding sequence
39
Explain why it is more useful to calculate an index of diversity than to record species richness
• Index of diversity measures abundance/number/population size of each species
• So useful because there may be many of some species/ few of other species
40
Data logging device
Can be used to measure the rate of flow in the river
41
Name an organelle found in both a chloroplast and prokaryotic cell
70s ribosomes
42
How can the population size be calculated
• Determine the area of the field
• Calculate the total area of meadow
• Divide the area of meadow by the area of plot
• Multiply the answer by the number of individuals of a species
43
Suggest and explain advantages and disadvantages to a farmer of replanting hedges on their farmland
Advantages
• Greater biodiversity so increase in predators of pests
• Increase in predators of pests so more yield/ income/less pesticides/less damage to crops
• Increase in pollinators so more income
• May attract tourists to their farm so more income
Disadvantages
• Reduced land area for crop growth/income
• Greater biodiversity so increases pest population
• Increased interspecific competition so less yield/income
• Increase pest population so less yield/income/need for more pesticides
44
Suggest why the plant population in an open grassland is undergoing a different type of selection to a dense forest
The environmental conditions in the grass land and dense forest is different
45
Explain why proteins can be analyzed to help classify organisms
- Protein consists of amino acids which are encoded by DNA sequences.
- The more similar proteins are, the more similar the DNA is between the two species and
- so the more closely related they are
46
What is the characteristic selected for in directional selection?
An extreme phenotype
47
What is the function of a t-test
To compare two mean values
48
What is the formula for the area of a circle
Pie r2
49
Function of autoclaving
- To sterilize
- To prevent contamination of the investigation which could affect the results
50
The mass flow hypothesis is used to explain the movement of substances through phloem.
Use your understanding of the mass flow hypothesis to explain how pressure is generated inside the phloem
- Sucrose is actively transported into the phloem
- Lowers the water potential in the phloem
Water moves into the phloem by osmosis from the xylem
51
Suggest two reasons why the rate of water uptake by a plant might not be the same as the rate of transpiration
• Water used for support/turgidity
• Water used in photosynthesis
• Water used in hydrolysis
• Water produced during respiration
52
What other measurement is required to calculate an index of diversity for dung beetles when the mean number of species and total number of dung beetles is given.
The number of INDIVIDUAL dung beetles in each species
53
In the intensive farms, the farmers had removed hedges to increase land for grazing. This resulted in a decrease in the diversity of birds on these farms.
Explain why the removal of hedges caused a decrease in the diversity of birds.
• Removes species/types of plant/ insects
• Fewer food sources
• Fewer HABITATS/ NICHES
54
The chilling requirement (exposure to low temperatures) of seeds of certain plant species is considered to be an adaptation for survival in countries with seasonal changes in environmental conditions.
Suggest how this adaptation may enable these plant species to survive and respond to seasonal changes
• Seeds/embryo remain dormant/inactive in winter/cold
• Seeds/plants develop in spring/summer
• Plant photosynthesise in spring/when warm
• Produce (more) seeds/offspring in spring/growing season
55
A student researched information on a disinfectant before carrying out a zone of inhibition investigation. On the basis of this research, the student used a maximum concentration of disinfectant of 40%. Explain why?
• Clear zone would be too large
• Clear zones would overlap/merge
• Could kill all bacteria (on the plate)
56
Describe the processes involved in the transport of sugars in plant stems (6)
• At source sucrose is actively transported into the phloem/sieve tube element
• By companion/transfer cells
• Lowers water potential in phloem/sieve element/tube and water enters by osmosis
• Produces high hydrostatic pressure
• Mass flow/transport towards sink/roots/storage tissue
• At sink/roots sugars are removed/unloaded
57
What is one more way to improve collected data
• Take random samples until you’ve achieved a stable running mean
58
Suggest why biodiversity increases when farmers use larger fields
Fewer species
59
Give advantages and disadvantages of farmers replanting hedges in their farms
ADVANTAGE
• Greater biodiversity so increase in predators of pest
• Increase in predators of pest do more yield/income/ less pesticides to damage crops
• Increase in pollinators so more yield/income
• May attract tourists so more income
DISADVANTAGES
• Reduced land area for crop growth
• Greater biodiversity so increase in pest population
• Increase in pest population so less yield
• Increase interspecific competition so less income
60
Sunflowers are not xerophytic plants. The scientists repeated the experiment with xerophytic plants.
Suggest and explain one way the leaf growth of xerophytic plants would be different from the leaf growth of sunflowers
• Low/slow growth
• Due to smaller number of stomata
• Growth may continue at lower water potentials
• Due to adaptations in enzymes involved in photosynthesis/metabolic reactions
61
Use your knowledge of gas exchange in leaves to explain why plants growth in soil with very little water grow only slowly
• Closed stomata
• Less carbon dioxide (uptake) for less photosynthesis/ glucose production
62
Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome
• Non-functional protein
• Change in tertiary structure of the protein
63
Why is there a time lag before the appearance of a species that is resistant
• Initially one/ few insects with favourable mutation
• Individuals with favourable mutation/ allele will have more offspring
• Takes many generations for favourable mutation/ allele to become the most common allele
64
One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect and that this mutation had spread to other species of insect. Was he correct. Explain your answer
No
• Mutations are spontaneous/ random
• only the rate of mutation is affected by the environment
• Different species do not interbreed/do not produce a fertile offspring
• Takes many generations for favourable mutation/allele to become the most common allele of this gene
65
Describe how mRNA is produced in the nucleus (7)
* Action of DNA helicase to break hydrogen bonds between complimentary base pairs causing the DNA helix to unwind
* one strand acts as a template
* Free-floating rna bases bind to complimentary dna bases on template strand
* Adenine binds to uracil, guanine binds to cytosine, thymine binds to adenine, cytosine binds to guanine
* RNA polymerase forms phosphodiester bonds between adjacent rna nucleotides via a condensation reaction (negative sugar phosphate backbone)
* Pre-mRNA is formed
* Splicing removes introns to form mRNA
66
Describe the action of tRNA
• Another tRNA with a complimentary anticodon to the next codon on mRNA
• tRNA attaches and collects another amino acid
• 2 codons fit into ribosome at the same time
67
What are the kingdoms in biology
• Animalia
• Plants
• Fungi
• Protists
• Prokaryotes
68
What is the role of independent segregation in meiosis
• To provide genetic variation
• Allows different combinations for f maternal and paternal chromosomes/alleles
69
Why is percentage used to display results
• Number in sample varies
• Allows a valid comparison
70
The population number of both species of lizard varied at different times of the year. **Suggest five reasons** why
• Breeding of lizards
• Food source/prey
• Predator
• Temperature variation
• Availability of water
71
What effect might a mutation in an intron lead to?
- Intron non-coding (DNA) / only exons coding;
- (So) not translated / no change in mRNA produced / no
effect (on protein) / no effect on amino acid sequence;
Accept does not code for amino acids
OR
- Prevents / changes splicing;
- (So) faulty mRNA formed;
Accept exons not joined together / introns not
removed
- Get different amino acid sequence
72
The genetic code uses four different DNA bases. What is the maximum number of
different DNA triplets that can be made using these four bases?
64
73
Some populations of animals that have never been hunted show very low levels of
genetic diversity. Other than hunting, suggest two reasons why populations might show
very low levels of genetic diversity.
- Population might have been very small / genetic bottleneck;
- Population might have started with small number of individuals /
by one pregnant female / founder effect;
- Inbreeding.
74
The number of amino acids coded for could be fewer than your answer to part ai, give one reason why
- introns
- Start and stop codon
75
Application
- Sources/ less variety of food
- Fewer habitats/ niches
- Lower diversity of insects (be specific)
76
Stabilising selection
- Range is reduced
- Higher proportion of populations becomes well adapted to the environment
77
Describe how amino acids join to form a polypeptide so there is always NH2 at
one end and COOH at the other end (2)
1. One amine/NH2 group joins to a
carboxyl/COOH group to form a peptide
bond;
2. (So in chain) there is a free amine/NH2 group
at one end and a free carboxyl/COOH group
at the other
OR
Each amino acid is orientated in the same
direction in the chain
78
Describe how mRNA is formed by transcription in eukaryotes. (5)
1. Hydrogen bonds (between DNA bases) break;
2. (Only) one DNA strand acts as a template;
3. (Free) RNA nucleotides align by complementary
base pairing;
4. (In RNA) Uracil base pairs with adenine (on
DNA)
OR
(In RNA) Uracil is used in place of thymine;
5. RNA polymerase joins (adjacent RNA)
nucleotides;
6. (By) phosphodiester bonds (between adjacent
nucleotides);
7. Pre-mRNA is spliced (to form mRNA)
OR
Introns are removed (to form mRNA);
79
Describe how a polypeptide is formed by translation of mRNA (6)
1. (mRNA attaches) to ribosomes
OR
(mRNA attaches) to rough endoplasmic
reticulum;
2. (tRNA) anticodons (bind to) complementary
(mRNA) codons;
3. tRNA brings a specific amino acid;
4. Amino acids join by peptide bonds;
5. (Amino acids join together) with the use of ATP;
6. tRNA released (after amino acid joined to
polypeptide);
7. The ribosome moves along the mRNA to form
the polypeptide;
80
Complete Table 2 to show three differences between DNA in the nucleus of a
plant cell and DNA in a prokaryotic cell. (5)
Plant v prokaryote
1. (Associated with) histones/proteins v no
histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
4. Introns v no introns;
5. Long(er) v short(er);
