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Bio AQA A-Level > Topic 4 > Flashcards

Topic 4 Flashcards

1
Q

Define the term exon.

A

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

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2
Q

Give three differences between the DNA in the nucleus of a plant and the DNA in a prokaryotic cell

A
  • associated with histones v no histones
  • linear v circular
  • no plasmids v plasmids
  • introns v no introns
  • longer v shorter
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3
Q

DNA - Structure related to function (7)

A
  1. 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
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4
Q

DNA - Degenerate and Non-overlapping (2)

A
  1. Degenerate: more than one (base) triplet for each amino acid;
  2. Non-overlapping: each base is part of only one triplet;
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5
Q

DNA - Comparing DNA and mRNA (6)

A
  1. 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;
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6
Q

Comparing mRNA and tRNA
(3)

A
  1. mRNA longer;
  2. mRNA is a straight molecule but tRNA is a folded molecule/clover-leaf shaped
    molecule;
  3. mRNA doesn’t not contain hydrogen bonds but tRNA has hydrogen bonds;
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7
Q

Which two molecules are ribosomes made from? (2)

A
  1. 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
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8
Q

Define the term exon.

A

Base sequence coding for polypeptide/sequence of amino acids

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9
Q

Name the proteins associated with DNA

A

Histone

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10
Q

Differences between prokaryotic DNA and Eukaryotic DNA (5)

A

eukaryote v prokaryote
1. (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);

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11
Q

Transcription - Describe transcription (7)

A
  1. 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
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12
Q

Translation - Describe translation (7)

A
  1. 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. ERNA 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);
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13
Q

Translation - Role of ribosome (5)

A
  1. 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
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14
Q

Translation - Role of tRNA (4)

A
  1. 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;
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15
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.

A
  1. Condensation (reaction)/loss of water;
    2 between phosphate and deoxyribose;
    3 (catalysed by) DNA Polymerase
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16
Q

What is a gene

A

A sequence of DNA
nucleotides that codes for a polypeptide;

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17
Q

The genome is…..

A

(The) complete set of genes in a cell. OR (All) the DNA in a cell/organism;

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18
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;

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19
Q

Meiosis - Process of Crossing
Over (4)

A
  1. 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
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20
Q

Describe how the process of meiosis results in haploid cells.

A
  1. 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;
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21
Q

Define mutation

A
  1. DNA replication (in interphase) creates two identical chromatids;
  2. (meiosis has) to nuclear divisions;
  3. (first division) Homologous pairs separated
  4. (second division) sister chromatids separated
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22
Q

What is meant by the degenerate code?

A

More than one codon codes for a single amino acid;

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23
Q

Mutation - How does mutation cause change in protein (receptor) structure? (4)

A
  1. 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);
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24
Q

Mutation - Mutation leading to evolutionary changes/phylogenetic relationships

A
  1. 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
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25
Q

Define the term mutagenic agent.

A

(A factor that) increases (the rate of mutations;

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26
Q

Name ways which increase genetic variation in a population

A
  1. Mutation;
  2. Meiosis - crossing over and independent segregation
  3. Random fertilisation/random fusion of gametes
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27
Q

Define how a mutation can have a positive effect on an individual and no effect on a individual

A

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

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28
Q

Define genetic diversity

A

the number of different alleles of genes in a population.

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29
Q

Describe how a student made a 1 in 10 dilution and then usedthisto make a 1 in 1000 dilution of the original liquid culture of bacteria.

A
  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;
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30
Q

Why would a 1 in 10 dilution not be appropriate to use to determine cell numbers?

A
  1. Count unlikely to be accurate / repeatable / reproducible / reliable
  2. Because too many cells; Or cells will be overlapping
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31
Q

Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria.

A
  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
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32
Q

Describe the aseptic techniques used to transfer bacterial culture onto an agar plate.

A
  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
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33
Q

Describe the principles of natural selection in the evolution of a population.

A
  1. Random mutation can result in new alleles of a genes.
  2. Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.
  3. The advantageous allele is inherited by members of the next generation.
  4. over many generations, the new allele increases in frequency in the population.
34
Q

Explain what is meant by a phylogenetic group?

A

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

35
Q

What is species richness

A

(A measure of) the number of (different) species in a community;

36
Q

Why is calculation of index of diversity more reliable than species richness?

A

(Index of diversity also) measures abundance / number / population (size) of each species;
(So useful because) may be many of some species

37
Q

Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity.

A

Individual organisms could not be identified/ separated OR
Too small/numerous to count individuals

38
Q

Outline a method the ecologists could have used to determine the plant species richness at one site.

A
  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)
39
Q

Farming Techniques - Pros and Cons to farmer for Planting Hedges

A

(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

40
Q

Suggest one ethical argument for maintaining biodiversity.

A

Prevent extinction / loss of populations / reduction in populations / loss of habitats

41
Q

Suggest one economic argument for maintaining biodiversity.

A

Medical or pharmaceutical uses of plants
Tourism
Agriculture
Saving forest communities

42
Q

How many hydrogen bonds does adenine form with thymine?

A

2 hydrogen bonds

43
Q

How many hydrogen bonds does cytosine form with guanine?

A

3 hydrogen bonds

44
Q

What does the deoxyribose-phosphate backbone do?

A

Protects the more chemically reactive bases

45
Q

What is a non-overlapping genetic code?

A

Each base is only read once

46
Q

What is a universal genetic code?

A

Triplets of bases code for same amino acids in all organisms

47
Q

Give structural adaptations of DNA

A
  • many hydrogen bonds give stability and allow it to separate easily for replication
  • extremely large so carries a lot of genetic information
  • double helix protects bases and makes molecule more stable
  • complementary bases allow DNA to be copied accurately
48
Q

What are introns

A

Parts of a gene that don’t code for amino acids

49
Q

Describe DNA replication

A
  • DNA helipads breaks weak hydrogen bonds between complementary base pairs to unzip and uncoil the double helix
  • each original strand acts as a template for each new strand
  • free nucleotides align next to complementary bases on the template strands- hydrogen bonds
  • DNA polymerase joins nucleotides in new strand via condensation reactions forming phosphodiester bonds
  • this is known as semi conservative replication as each newly formed DNA molecule contains 1 of the original polynucleotide strands
50
Q

Describe and explain the evidence for semi conservative replication

A
  • cells of the bacterium E. coli were grown in medium in which the normal isotope of N14 was replaced with heavier Ns
  • cells were allowed to divide until it was certain that the heavy nitrogen had been incorporated into the entire DNA
  • bacteria was transported to a medium containing only N14s to divide and sample was taken after each division (generation)
  • are allowed to divide for 3 generations
  • each time the bacteria divide, the new nucleotides will contain N14
  • after each generation, the DNA is spun in a centrifuge and the heaviest will settle to the bottom
51
Q

What increases the chance of mutations?

A
  • high energy radiation - X-rays, gamma, UV light
  • high energy particles - alpha, beta, gamma
  • chemicals - nitrous oxides, benzene, tar
52
Q

Define community

A

All the organisms of all the species that live in a habitat

53
Q

Define habitat

A

A place where an organism lives

54
Q

What two things do you need to calculate biodiversity?

A
  • the number of different species
  • the number of individuals of each species
55
Q

Describe woodland clearance and its effects

A
  • reduces number of trees
  • reduces variety of habitats and food sources
  • animals migrate/die
  • reduces biodiversity
56
Q

Describe hedgerow removal

A
  • reduces number of small trees and plants
  • reduces variety of habitats and food sources
  • animals migrate and die
  • reduces biodiversity
57
Q

Describe the use of herbicides and its impacts

A
  • kills unwanted plants (weeds)
  • reduces number of plant species
  • reduces variety of habitats and food sources
  • reduces biodiversity
58
Q

Describe the use of pesticides and its impacts

A
  • kills organisms (pests) that feed on crops
  • reduced number of pests
  • reduced biodiversity
59
Q

Give some disadvantages of planting hedgerows

A
  • compete with crops for light, ions, water, CO2 so it can decrease crop productivity
  • are tall so block sunlight from reaching the crops
  • maintenance costs
  • may act as a habitat for pests
60
Q

Describe some economic reasons for maintaining biodiversity

A
  • tourism
  • agriculture
  • saving local forest communities
  • commercial products/medicines
61
Q

Define inter specific variation

A

Differences between species

62
Q

Define intraspecific variation

A

Differences within the same species

63
Q

A large sample size is important as…

A
  • mean will be more representative
  • mean will be more reliable as outliers will be reduced
64
Q

Describe what the results of standard deviation mean?

A
  • when standard deviation bars overlap it indicates the difference between the means is not significant
  • when the standard deviation bars don’t overlap, it indicates the difference between the means is significant but not due to chance
65
Q

Define taxonomy

A

The study of classification

66
Q

Define classification

A

The organisation of living organisms into groups

67
Q

Define phylogenetic classification

A

Organisation of organisms according to their evolutionary history, shows how species are related over time

68
Q

Describe the problems in defining species

A
  • species are not fixed, they can evolve over time
  • there can be considerable variation within a species
  • many species are extinct and have left no fossil record
  • some species are sterile
69
Q

what is the binomial system?

A

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

70
Q

How would you compare DNA between organisms?

A
  • randomly collect a large sample of organisms of a specific species to make it representative and avoid bias
  • extract the DNA and compare the base sequence
  • DNA sequencing, the greater the similarities the more closely related they are
71
Q

Courtship behaviour allows animals to…

A
  • recognise members of own species
  • attract a mate of the opposite sex
  • identify a male that is capable of breeding
72
Q

Describe the gene pool

A
  • collection of all the different alleles of a gene in a population of a species
73
Q

Describe some causes of variation

A
  • gene mutation - spontaneous changes to DNA base sequence producing new alleles
  • meiosis - crossover and independent segregation of homologous chromosomes
  • random fertilisation - gametes are genetically unique and which fuse are random
  • environmental factors - influence how genes are expressed
74
Q

Describe some beneficial adaptations

A
  • behavioural - ways an organism acts in order to increase survival
  • physiological - processes inside an organism that increased its chance of survival
  • anatomical - features an organism’s body has that increased chance of survival
75
Q

Describe the process of natural selection

A
  • population has genetic variation due to mutations
  • Some individuais have favourable alleles and some won’t
  • A change in the environment occurs
    → predators, temperature
  • Individuals with favourable alleles will survive. Individuals without may die.
  • Individuals with favourable alleles survive and reproduce. They pass on their favourdble alleles to their
    Offspring.
  • Allele frequency of favourable allele increases
76
Q

Describe directional selection

A
  • selection of alleles for the extreme characteristics
  • change in environment
  • change in mean
  • range stays the same
77
Q

Describe and explain an example of directional selection

A

ANTIBIOTIC. RESISTANCE:
1 Bacterial population has variation due to mutations
3 antibiotic given, better adapted individuals survive
2 Bacteria have different alleles-some have resistance, some don’t.
4 Bacteria with resistance survive and pass on resistance alleles to the next gereration
5 Frequency of antibiotic resistance allele increases

78
Q

Describe stabilising selection

A
  • alleles for middle range of characteristics
  • no change in environment
  • no change in mean
  • range narrows
79
Q

Describe and explain an example of human birth weight

A

• Humans have a range of weights
• v. Small babies have an increased SA:Vol so are less likely to survive as they find it hard to maintain a body temperature - can be fat as there’s lots or pressure on respiratory and cardiac systems
- v. Large babies are less likely to survive as it can be difficult to fit through mothers pelvis and lead to complications
- conditions are favourable for medium sized babies

80
Q

What separates during the first division in meiosis?

A

Bivalents/ homologous pairs

81
Q

What separates during the second division in meiosis?

A

Sister chromatids

Bio AQA A-Level (5 decks)

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