topic 4

Question 1

Non-overlapping

Answer 1

Each base is part of only one triplet.

Question 2

Degeneracy

Answer 2

More than one codon codes for a single amino acid;

Question 3

Codon

Answer 3

1. Triplet / three bases on mRNA;
2. Accept nucleotide for base
3. That code for an amino acid;

Question 4

Transcription

Answer 4

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);

Question 5

Translation

Answer 5

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;

Question 6

Ribosome structure

Answer 6

RNA And protein

Question 7

Gene mutation

Answer 7

1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;

Question 8

Gene mutation with no effect

Answer 8

3. Genetic code is degenerate (so amino acid sequence may not change);
   OR
   Mutation is in an intron (so amino acid sequence may not change);
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype

Question 9

Gene mutation with positive effect

Answer 9

6. Results in change in polypeptide that positively changes the properties (of the protein)
   OR
   Results in change in polypeptide that positively changes a named protein;
7. May result in increased reproductive success
   OR
   May result in increased survival (chances);

Question 10

Genome definition

Answer 10

(All) the DNA in a cell/organism;

Question 11

Proteome definition

Answer 11

(The proteome is the full) range of / number of different proteins that a cell is able to produce (at a given time);
OR
(The proteome is the full) range of / number of different proteins the genome / DNA is able to code for

Question 12

mRNA compared to tRNA

Answer 12

1. mRNA does not have hydrogen bonds / base pairing, tRNA does;
   OR
   mRNA is linear / straight chain, tRNA is cloverleaf;
2. mRNA does not have an amino acid binding site, tRNA does;
   Accept mRNA cannot carry an amino acid, tRNA can
3. mRNA has more nucleotides;
4. (Different) mRNAs have different lengths, all tRNAs are similar / same length;
5. mRNA has codons, tRNA has an anticodon;

Question 13

Pre-mRNA compared to mRNA

Answer 13

1. Introns (in pre-mRNA);
2. Removal of sections of (pre-mRNA) / splicing

Question 14

Exon definition

Answer 14

Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure

Question 15

Homologous chromosomes

Answer 15

(Two chromosomes that) carry the same genes;

Question 16

Non-coding base sequences and location

Answer 16

1. DNA that does not code for protein/polypeptides
   OR
   DNA that does not code for (sequences of) amino acids
   OR
   DNA that does not code for tRNA/rRNA;
2. (Positioned) between genes

Question 17

Meiosis and genetic variation

Answer 17

1. Homologous chromosomes pair up;
2. Independent segregation;
3. Maternal and paternal chromosomes are re-shuffled in any combination;
4. Crossing over leads to exchange of parts of (non-sister) chromatids / alleles between homologous chromosomes;
5. (Both) create new combinations of alleles;

Question 18

Causes of genetic variation

Answer 18

1. Crossing over;
2. Independent segregation/assortment (of homologous chromosomes);
3. Random fusion of gametes OR Random fertilisation;

Question 19

Comparing mitosis and meiosis

Answer 19

1.   One division, two divisions in meiosis;
2.   (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
3.   Two cells produced, (usually) four cells produced in meiosis;
4.   Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
Accept same number chromosomes in mitosis, but half the number in meiosis
5.   Separation of homologous chromosomes only in meiosis;
6.   Crossing over only in meiosis;
7.   Independent segregation only in meiosis;

Question 20

Substitution mutation

Answer 20

Replacement of a base by a different base (in DNA);

Question 21

Natural selection

Answer 21

1. Characteristic due to mutation
   OR
   Allele due to mutation;
2. Characteristic provides named advantage
3. Individuals with characteristic more likely to survive and reproduce
   OR
   Individuals with advantageous allele more likely to survive and reproduce
4. Directional/Stabilising selection;
5. Frequency of allele increases (in the offspring/next generation);
   Must be applied to the context of the question

Question 22

Directional selection

Answer 22

One extreme selected/removed/favoured/chosen
OR
One extreme allowed to breed

Question 23

Stabilising selection

Answer 23

Mean selected for/chosen/favoured

Question 24

Aseptic technique

Answer 24

1.   Wash hands to remove/kill microbes
OR
Wear gloves/apron to prevent contamination;
2.   Burning Bunsen close by to create upward current of air;
3.   Disinfect bench/work on disinfected cloth to kill microbes/prevent contamination;
Accept use sterile/ antiseptic/bleach for ‘disinfect’
4.   Flame instrument/equipment to sterilise/kill microbes/prevent contamination;
Accept autoclave/ use alcohol/steam/boil for flame
Accept scalpel/ inoculating loop/wire loop/loop/forceps/ spreader for instrument
5.   Lift lid slightly to prevent entry of microbes;

Question 25

Mutations and evolutionary relationships

Answer 25

1. Mutations change base / nucleotide (sequence); Reject if mutation in amino acid 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;

Question 26

Measuring genetic diversity

Answer 26

1.   Comparing (measurable/observable) features/characteristics; 2.   Comparing amino acid sequences/primary structures (of a/named/the same protein); 3. comparing differences in the base sequence of DNA 4. Comparing differences in the base sequence of mRNA

Question 27

Importance of courtship behaviour

Answer 27

1. Recognise / identify / attract same species; 2. Stimulates / synchronises mating / production / release of gametes; 3. Recognition / attraction of mate / opposite sex; 4. Indication of (sexual) maturity / fertility / receptivity / readiness to mate; 5. Formation of a pair bond / bond between two organisms (to have / raise young).

Question 28

Taxa

Answer 28

Kingdom, phylum, class, order, family, genus, species

Question 29

Hierarchy

Answer 29

1.Groups within groups; 2.No overlaps between groups

Question 30

Phylogeny

Answer 30

(Grouped according to) evolutionary links/history/relationships / common ancestry

Question 31

Species

Answer 31

1. Able to reproduce; 2. To produce fertile offspring

Question 32

Species richness

Answer 32

(A measure of) the number of (different) species in a community; For ‘community’ accept ‘habitat/ecosystem/one area/environment’ Reject ‘in a population’

Question 33

Index of diversity calculation

Answer 33

D = N(N-1) En(n -1)

Question 34

Genetic diversity

Answer 34

Number of different alleles of each gene

Question 35

Farming – removal of hedges

Answer 35

More centre OR Less edge OR Less hedge OR Fewer species;

Question 36

Farming – Advantages of hedges

Answer 36

Advantage - 1.   Greater (bio)diversity so increase in predators of pests OR Increase in predators of pests so more yield/income/less pesticides/less damage to crops OR Increase in pollinators so more yield/income OR May attract more tourists/subsidies to their farm so more income (from diversification);

Question 37

Farming – disadvantages of hedges

Answer 37

Disadvantage - 2.   Reduced land area for crop growth/income OR Greater (bio)diversity so increase pest population OR Increase pest population so less yield/less income/(more) need for pesticides/(more) damage to crops OR Increased (interspecific) competition so less yield/income OR More difficult to farm so less income;