Unit 4 mark scheme flashcards
(48 cards)
1
Q
DNA – How is Structure of DNA related to its function (7)
A
- stable due to numerous hydrogen bonds so can be passed on from generation to generation; 2. weak hydrogen bonds between strands are easily broken for DNA replication or protein synthesis; 3. large so can carry a lot of genetic information; 4. base pairs are contained within the helix and held in place by the strong sugar-phosphate backbone; 5. complementary base pairs allow the synthesis of an identical daughter molecule; 6. 2 strands so both can act as templates; 7. helical shape means that it can be coiled so compact for storage
2
Q
DNA – define Degenerate and Non-overlapping and universal (3)
A
- Degenerate: more than one (base) triplet for each amino acid; 2. Non-overlapping: each base is part of only one triplet; 3. the same in all living things
3
Q
DNA – Compare DNA and mRNA (6)
A
- DNA double stranded/double helix and mRNA single-stranded; 2. DNA (very) long and RNA short; 3. Thymine/T in DNA and uracil/U in RNA; 4. Deoxyribose in DNA and ribose in RNA; 5. DNA has base pairing and mRNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t; 6. DNA has introns/non-coding sequences and mRNA doesn’t;
4
Q
Compare mRNA and tRNA (3)
A
- mRNA longer; 2. mRNA is a straight molecule but tRNA is a folded molecule/clover-leaf shaped molecule; 3. mRNA contains hydrogen bonds but tRNA has hydrogen bonds;
5
Q
Which two molecules are ribosomes made from? (2)
A
- One of RNA/ribonucleic acid(s)/nucleotide(s)/nucleic acid(s)/rRNA/ribosomal RNA/ribosomal ribonucleic acid; 2. One of protein(s)/polypeptide(s)/amino acid(s)/ peptide(s)/ribosomal protein
6
Q
Define the term exon.
A
Base sequence coding for polypeptide/sequence of amino acids
7
Q
Name the proteins associated with DNA
A
Histone
8
Q
What are the Differences between prokaryotic DNA and Eukaryotic DNA (5)
A
- (Associated with) histones/proteins v no histones/proteins; 2. Linear v circular; 3. No plasmids v plasmids; Do not credit if suggestion that prokaryotic DNA only exists as plasmids. 4. Introns v no introns; 5. Long(er) v short(er);
9
Q
Transcription – Describe transcription (7)
A
- DNA strands separate by breaking hydrogen bonds; 2. (Only) one of the strands is used as a template (to make mRNA); 3. Complementary base pairing so A to U, T to A, C to G, G to C; 4. (RNA) nucleotides joined by RNA polymerase; 5. Forms phosphodiester bonds 6. Pre-mRNA formed; 7. Splicing/ introns removed to form mRNA
10
Q
Translation – Describe translation (7)
A
- mRNA binds to ribosome; 2. ribosome moves to start codon/AUG 3. Idea of two codons/binding sites; 4. (Allows) tRNA with anticodons to bind/associate with codon on mRNA; 5. tRNA brings specific amino acid; 6. mRNA moves along to the next codon; 7. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules);
11
Q
Translation – Role of ribosome (5)
A
- mRNA binds to ribosome; 2. Idea of two codons/binding sites; 3. (Allows) tRNA with anticodons to bind/associate; 4. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules); 5. Moves along (mRNA to the next codon)/translation described
12
Q
Translation – Describe the Role of tRNA (4)
A
- anticodon complementary to codon/reads message on mRNA; 2. specific amino acid; 3. carried/transferred (to ribosome); 4. correct sequence of amino acids along polypeptide;
13
Q
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.
A
- Condensation (reaction)/loss of water; 2 between phosphate and deoxyribose; 3 (catalysed by) DNA Polymerase
14
Q
What is a gene
A
A sequence of DNA nucleotide bases that codes for amino acid sequence of a polypeptide;
15
Q
The genome is…..
A
(The) complete set of genes in a cell. OR (All) the DNA in a cell/organism
16
Q
The proteome is…..
A
(The full) range/number of different proteins that a cell is able to produce (at a given time); OR (The full) range/number of different proteins the genome/DNA is able to code for;
17
Q
Meiosis – Causes of Variation (6)
A
- Homologous chromosomes pair up; 2. Chiasmata formed 3. Independent segregation; 4. Maternal and paternal chromosomes are re-shuffled in any combination; 5. Crossing over leads to exchange of parts of (non-sister) chromatids/alleles between homologous chromosomes; 6. (Both) create new combinations of alleles
18
Q
Meiosis – Process of Crossing Over (4)
A
- Homologous pairs of chromosomes associate / form a bivalent; 2. Chiasmata(ta) form; 3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged; 4. Producing new combinations of alleles;
19
Q
Describe how the process of meiosis results in haploid cells.
A
- DNA replication (in interphase) creates two identical chromatids; 2. (meiosis has) two nuclear divisions; 3. (first division) Homologous pairs separated 4. (second division) sister chromatids separated
20
Q
Define mutation
A
A change in the base sequence of DNA, results in a new allele
21
Q
What is meant by the degenerate code?
A
More than one codon codes for a single amino acid;
22
Q
Mutation - How does mutation cause change in enzyme function? (3)
A
- Change in amino acid / (sequence of) amino acids / primary structure; 2. Change in hydrogen / ionic / disulphide bonds alters tertiary structure / active site (of enzyme); 3. Substrate not complementary / cannot bind (to enzyme / active site) / no enzyme- substrate complexes form;
23
Q
Mutation - How does mutation cause change in protein (receptor) structure? (4)
A
- Change in DNA base (sequence); 2. Change in amino acid (sequence)/primary structure; 3. Alters (position of) hydrogen/ionic/disulfide bonds; 4. Change in tertiary structure (of receptor);
24
Q
Mutation – Mutation leading to evolutionary changes/phylogenetic relationships
A
- Mutations change base / nucleotide (sequence); 2. (Causing) change in amino acid sequence; 3. Mutations build up over time; 4. Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary structure) in closely related species; 5. Closely related species have recent common ancestor
25
Define the term mutagenic agent.
(A factor that) increases (the rate of) mutations;
26
Name 3 ways which increase genetic variation in a population
1. Mutation; 2. Meiosis – crossing over and independent segregation 3. Random fertilisation/random fusion of gametes
27
Define how a mutation can have a positive effect on an individual and no effect on an individual
No effect because: 1. Genetic code is degenerate/codon codes for the same amino acid 2. Mutation is in an intron 3. Creates a recessive allele which does not affect phenotype
Positive effect because: 4. (new allele) increases chance of survival
28
Define genetic diversity
the number of different alleles of genes in a population.
29
Describe how a student made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria.
1. 1 part bacterial culture to 9 parts water 2. Mix 3. Repeat using 9 parts fresh (sterile) liquid and 1 part of 10–1 and 10–2 dilutions to make 10–3 dilution;
30
Why would a 1 in 10 dilution not be appropriate to use to determine cell numbers?
1. Count unlikely to be accurate / repeatable / reproducible / reliable 2. Because too many cells; Or cells will be overlapping
31
Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria.
1. Some bacteria have alleles for resistance 2. Exposure to antibiotics creates a selection pressure 3. Antibiotics kill bacteria that are not resistant 4. Resistance strains survive and reproduce
32
Describe the aseptic techniques used to transfer bacterial culture onto an agar plate.
1. Use sterile pipette/syringe 2. Flame top of the bottle 3. Lift lid of agar plate at an angle 4. Use sterile spreader 5. Place pipette/spreader onto disinfectant
33
Describe the principles of natural selection in the evolution of a population.
Random mutation can result in new alleles of a genes. Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success. The advantageous allele is inherited by members of the next generation. over many generations, the new allele increases in frequency in the population.
34
Define Species
a group of similar organisms that Can interbreed to produce fertile offspring
35
Give the taxonomic levels of classification
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
36
Describe how genetic diversity between species can be measured
1. Comparing observable characteristics/features 2. Comparing base sequences of DNA 3. Comparing Base sequences of mRNA 4. Comparing amino acid sequences (of the same protein)
37
Classification is hierarchical – what does this mean?
smaller groups are placed within larger groups, with no overlap between groups.
38
Which two taxa make up an organisms binomial name?
Genus species
39
Explain what is meant by a phylogenetic group?
(Grouped according to) evolutionary links/history/relationships /common ancestry;
40
Courtship Behaviour – The importance (3)
1. enables male I female to recognise opposite sex; 2. enables recognition of own species; 3. synchronises mating behaviour
41
Courtship Behaviour – How it increases probability of mating (4)
1. Attracts mate of the same species; 2. Indication of sexual maturity / fertility / synchronises mating; 3. Stimulates release of gametes; 4. Formation of a pair bond / bond between two organisms (to have / raise young)
42
What is species richness
(A measure of) the number of (different) species in a community;
43
Why is calculation of index of diversity more reliable than species richness?
(Index of diversity also) measures abundance / number / population (size) of each species; (So useful because) may be many of some species
44
Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity.
Individual organisms could not be identified/separated OR Too small/numerous to count individuals
45
Outline a method the ecologists could have used to determine the plant species richness at one site.
1. A method of selecting sampling sites at random e.g. random number generator 2. Use of quadrat; 3. Identify (plant) species (at site / in each quadrat)
46
Farming Techniques – Pros and Cons to farmer for Planting Hedges
(Pros) 1. Greater (bio)diversity so increase in predators of pests 2. Increase in predators of pests so more yield/income 3. Increase in pollinators so more yield/income
(Cons) 1. Reduced land area for crop growth/income 2. Greater (bio)diversity so increase pest population 3. Increase pest population so less yield/income 4. Increased competition so less yield/income
47
Suggest one ethical argument for maintaining biodiversity.
Prevent extinction / loss of populations / reduction in populations / loss of habitats
48
Suggest one economic argument for maintaining biodiversity.
Medical or pharmaceutical uses of plants Tourism Agriculture Saving forest communities
