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alevel bio > Alevel past papers > Flashcards

Alevel past papers Flashcards

1
Q

Describe the acrosome reaction (1)

A
  • when the sperm cell releases an enzyme that digests the zona pellucida
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2
Q

Describe the events of fertilisation that occur after the acrosome reaction. (3)

A
  • sperm cell fuses with egg cell membrane
  • cortical granules release contents
  • fusion of sperm and egg nuclei
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3
Q

Explain how phospholipids form a cell surface membrane. (3)

A
  • hydrophilic parts associate with water
  • hydrophobic parts repel water
  • bilayer forms with hydrophobic parts pointing towards each other
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4
Q

Describe the movement of osmosis. (1)

A
  • against a solute concentration gradient, through a partially permeable membrane
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5
Q

Which part of the cell surface membrane allows facilitated diffusion of glucose? (1)

A

protein

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6
Q

Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency. (3)

A
  • Cl ions leave cells
  • Na ions leave cells
  • water moves out of cells via osmosis
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7
Q

Explain the nature of the genetic code. (3)

A
  • triplet code: when 3 bases code for 1 amino acid
  • non-overlapping code: each base is only read once e.g. ATT = I , AAA = K
  • degenerate code: when multiple codons can code for the same amino acid
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8
Q

Describe how DNA is organised in a bacterial cell. (3)

A
  • small plasmids
  • circular DNA
  • located in cytoplasm
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9
Q

Explain why the experiment would be improved if all the bases were provided but only the thymine was radioactive. (2)

A
  • because thymine is found only in DNA
  • only DNA would be measured
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10
Q

Define: bacteriostatic

A

stops bacteria dividing

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11
Q

Define: bactericidal

A

kills bacteria

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12
Q

Describe the LDR of photosynthesis. (5)

A
  • use of light energy to excite electrons in chlorophyll
  • photolysis to produce: O, e- and H ions
  • electrons used in the ETC
  • generation of ATP
  • reduction of NADP
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13
Q

In which parts of the chloroplast do the light-independent reactions take place. (1)

A

stroma

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14
Q

What enzyme is used by plants to fix carbon dioxide. (1)

A

RUBISCO

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15
Q

What is an immediate product of the LIR of photosynthesis? (1)

A

GP

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16
Q

Explain how studying pollen grains in peat bogs can provide evidence of climate change. (4)

A
  • pollen is preserved in peat bogs
  • plant species can be identified from pollen
  • climate effects type of plants growing
  • change in pollen over time indicates a change in climate
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17
Q

Explain the effect of changes in the initial rate of reaction on the time taken for a blood clot to form. (2)

A
  • slower initial rate of reaction means it takes longer for a clot to form
  • because fibrin is produced more slowly
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18
Q

Explain how changes in fibrinogen concentration might be a risk factor of CVD. (3)

A
  • increased fibrinogen concentration leads to increased fibrin
  • which increases risk of blood clotting
  • blocking lumen of arteries
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19
Q

Describe the structure of collagen. (3)

A
  • 3 polypeptide chains
  • chains coiled around each other
  • cross-linking between chains
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20
Q

Give a function for collagen in the blood-gas barrier. (1)

A
  • to provide strength
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21
Q

Explain how the blood-gas barrier of the chicken is adapted to give more efficient gas exchange than the blood-gas barrier of the fog. (3)

A
  • thinner blood-gas barrier
  • therefore reduced diffusion distance
  • so faster rate of diffusion
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22
Q

Analyse the data to explain why the Guardasil vaccine is preferred to the Cervarix vaccine. (4)

A
  • Guardasil developed from 4 HPV strains, Cervarix only developed from 2
  • Guardasil provides protection against all 4 strains, Cervarix only 2
  • both provide immunity against HPV 16 & 18 viruses that cause cervical cancer
  • Guardasil also provides immunity against HPV 6 & 11 that cuase genital warts
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23
Q

Which type of immunity is developed by vaccines. (1)

A
  • artificial active immunity
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24
Q

A person who has been vaccinated becomes infected with HPV-16.
Explain the role of the T cells in the body of this person. (3)

A
  • vaccinated person has memory T cells
  • T helper cells activate T killer cells
  • T killer cells destroy virus-infected cells
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25
Q

Define: sex-linkage. (2)

A
  • gene responsible for a trait is located on a sex chromosome
  • expression of the trait is related to gender
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26
Q

Comment on the effect of adding cow dung to composting coffee husks. (3)

A
  • adding cow dung doesn’t change decrease in organic carbon
  • adding cow dung causes a slight increase in Nitrogen
  • adding cow dung has no significant effect on composting
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27
Q

Define: allele

A

alternative form of a gene

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28
Q

Explain how two species of African elephant could evolve from common ancestor. (3)

A
  • two populations geographically isolated from one another
  • therefore reduced gene flow between the two populations
  • leading to allopatric speciation
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29
Q

Does an increased magnesium ion intake increase or reduce the chance of getting CVD. (1)

A

reduce

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30
Q

Describe the role of LDLs in the development of atherosclerosis. (3)

A
  • LDLs carry cholesterol in blood
  • cholesterol is deposited to form atheroma
  • in endothelium of artery
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31
Q

Explain how atherosclerosis can result in damage to a heart muscle. (3)

A
  • narrowing of coronary arteries
  • reduces blood flow to cardiac muscle
  • which reduces aerobic respiration
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32
Q

Explain the effect of temperature on the rate of growth of blowfly maggots. (3)

A
  • temperature affects enzymes
  • increased temperature increases kinetic energy
  • leading to more frequent collisions between enzymes and substrates
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33
Q

Describe the role of decomposers, such as microorganisms, in the carbon cycle. (2)

A
  • respire
  • release CO2
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34
Q

Which cell produces antibodies? (1)

A

plasma cell

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35
Q

Which type of immunity does a newborn baby obtain from the mother’s milk. (1)

A

natural passive immunity

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36
Q

Explain how changes in the blood vessels result in the redness and swelling seen at the site of inflammation. (4)

A
  • histamine released
  • causes vasodilation
  • which increases blood flow
  • allowing blood plasma to enter tissue, causing swelling
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37
Q

Explain why the interferon made by genetically modified bacteria is different from the interferon made my animal cells. (2)

A
  • polypeptide chain is not modified properly
  • therefore protein is incorrectly folded
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38
Q

Describe the role of tRNA in the production of leptin. (3)

A
  • tRNA molecules
  • have anticodons that bind to mRNA codons
  • each tRNA carries a particular amino acid
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39
Q

Describe how the primary structure of leptin enables it to be soluble in water. (3)

A
  • primary structure determines folding
  • forming globular structure
  • water forms hydrogen bonds with protein
40
Q

Describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures. (2)

A
  • introduces a new stop codon
  • coding for a shorter amino acid sequence
41
Q

Define: stem cell. (2)

A
  • a cell that is undifferentiated
  • that can give rise to specialised cells
42
Q

Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells. (4)

A
  • both: increase number of cells
  • mitosis produces diploid cells, meiosis produces haploid cells
  • mitosis produces genetically identical cells, meiosis: genetically different to each other
  • mitosis results in 8 spermatocytes from each stem cell, meiosis results in 4 sperm cells from each spermatocyte
43
Q

Explain how the primary structure of trypsin molecules can be used to produce a phylogenetic tree. (3)

A
  • determine amino acid sequence
  • determine number of differences in sequences between species
  • the higher the number of differences, the less closely related the species are
44
Q

Explain how this calcium ion binding site could have evolved in vertebrates. (3)

A
  • variation in trypsin gene
  • calcium ion binding site offers advantage
  • vertebrates survive, reproduce and pass on allele
45
Q

Explain how reforestation of tropical rainforests can be used to minimise climate change. (3)

A
  • new trees uptake CO2
  • reducing CO2 in atmosphere
  • therefore, slowing rate of global warming
46
Q

Describe what needs to be measured in order to compare the biodiversity of two rainforests. (2)

A
  • number of different species
  • number of individuals per species
47
Q

Explain why the value for GPP is lower than the light energy available to the ecosystem. (3)

A
  • some light is reflected
  • some light misses the chloroplast
  • some light not absorbed by chlorophyll
48
Q

Define: species (1)

A
  • a group of organisms that can interbreed to produce fertile offspring
49
Q

Explain how these two species of snake could have arisen from a common ancestor. (4)

A
  • mutation leads to variation within grass snake population
  • better camouflaged snakes survived and reproduced
  • therefore, giving rise to 2 populations with differing allele frequencies
  • leading to sympatric speciation
50
Q

Compare and contrast the structure of chitin with that of a cellulose molecule. (3)

A

both:
- have glycosidic bonds
- every other glucose is inverted

  • chitin contains nitrogen, cellulose does not
51
Q

Describe how a peptide bond is formed. (2)

A
  • via a condensation reaction
  • between the amine group and carboxyl group of the adjacent amino acid
52
Q

What does a bacteriostatic antibiotic do? (1)

A

-prevents the multiplication of bacteria

53
Q

Describe the infection control practices hospitals have introduced. (3)

A
  • hand wash stations
  • increased disinfection of bedding
  • doctors not to wear long sleeves
54
Q

Describe the role of thrombin in blood clotting. (3)

A
  • thrombin is an enzyme
  • catalyses conversion of: fibrinogen to fibrin
  • mesh of fibrin traps red blood cells to form a clot
55
Q

Explain why a mutation in the gene coding for the protein factor V may increase the risk of VTE. (3)

A
  • changes amino acid sequence
  • overactive factor V increases thrombin production
  • increasing blood clotting
56
Q

Describe the possible impact of climate change on the effects of leaf rust on the yield of wheat crops. (4)

A
  • climate change could result in increased temperature
  • which could increase leaf rust growth
  • increased humidity may increase the spread of leaf rust
  • period of drought could decrease the leaf rust spreading
57
Q

Explain why anthropogenic emissions of greenhouse gases are affecting the climate. (3)

A
  • burning fossil fuels
  • increases CO2 emissions
  • causing more heat energy to be trapped in the atmosphere
58
Q

Define: inherited recessive disorder. (2)

A
  • caused by a faulty allele
  • that is only expressed in the homozygous condition
59
Q

Evaluate genetic screening. (4)

A

Advantage:

  • allows you to identify risk of developing a particular disease so choices can be made e.g. termination of pregnancy, preventative mastectomy

Disadvantages:

  • finding out you are a carrier can cause emotional stress
  • tests are not always 100% accurate
  • prenatal testing: risk of miscarriage
60
Q

Explain why incorrectly folded enzymes cannot carry out their function. (3)

A
  • the tertiary structure would be different
  • so wouldn’t be able to form substrate-enzyme complex
  • therefore, not able to catalyse reaction
61
Q

Define: endemic. (1)

A
  • found only in one geographical location
62
Q

Explain why the presence of microorganisms on the skin and gut help prevent pathogenic organisms multiplying in the body. (3)

A
  • flora in the gut and on skin are better adapted to the conditions
  • and so can outcompete pathogenic organisms
  • bacteria in the gut secretes lactic acid that helps destroy pathogen
63
Q

Explain why there are relatively few species of bacteria in the stomach. (2)

A
  • pH inside stomach is too low for enzymes of most bacteria to function
  • bacteria living in stomach have adaptations that enable them to survive
64
Q

Explain why this mutation affects the function of the haemoglobin molecule. (3)

A
  • could change an amino acid
  • causing change in tertiary structure
  • haemoglobin no longer able to bing to oxygen
65
Q

Describe how the pre-mRNA may be modified before being translated on the ribosome. (2)

A
  • pre-mRNA contains exons and introns
  • introns are removed and exons are spliced together to produce mRNA strand
66
Q

Explain why modification of pre-mRNA enables one gene to give rise to more than one protein. (2)

A
  • the different exons can be removed
  • therefore, producing different amino acid sequence
67
Q

Describe the role of the acrosome in fertilisation. (3)

A
  • fuses with cell surface membrane of sperm cell
  • digestive enzyme released
  • to break down zona pellucida
68
Q

Explain how breeding programmes in zoos maintain the genetic diversity of captive populations. (3)

A
  • animals selected to prevent inbreeding depression
  • stud book used to keep record of all breeding events
  • exchange of animals between zoos
69
Q

Compare and contrast the structure of Ebola virus with that of HIV. (3)

A

both:
- contain RNA
- have glycoproteins

  • HIV = spherical, Ebola virus = elongated
70
Q

Describe how clinical trials of a vaccine would be conducted. (3)

A
  • healthy volunteers given vaccine to test for side effects
  • group of people at risk of conducting disease given vaccine
  • number of people who develop viral disease are monitored
71
Q

Justify the use of the Ebola vaccine. (4)

A
  • large number of people died from the disease
  • vaccine side effects not worse than contracting Ebola
  • vaccinating immediate family will help reduce disease spreading
  • if health care workers vaccinated, they can care for more people
72
Q

Explain how microorganisms in the soil break down the stems. (3)

A
  • stems contain starch
  • enzymes secreted by microorganism
  • which break down glycosidic bonds
73
Q

Name the plant organelle that fixes carbon dioxide from the atmosphere. (1)

A

chloroplast

74
Q

Explain why burning wood chips does not increase carbon dioxide to the atmosphere in the long term. (4)

A
  • the CO2 produced from burning wood is replaced by CO2 absorbed by the trees
  • trees absorb CO2 for photosynthesis
  • new trees grown to replace those that are cut down
  • therefore, no net increase in CO2
75
Q

Explain how results of electrophoresis could provide evidence for interbreeding between the two types oh human. (2)

A
  • by comparing number of bands produce by the 2 types of DNA
  • similarities indicate interbreeding
76
Q

Describe how the Hardy-Weinberg equation can be used to provide evidence for changes in the elephant population in Mozambique. (2)

A
  • calculate allele frequency in population in Mozambique
  • regularly sample over period of time
77
Q

Define: totipotent cell. (2)

A
  • cell that has ability to differentiate
  • into all cell types
78
Q

Describe how cells become specialised. (3)

A
  • chemical signals cause some genes to activate
  • only activates genes that produce mRNA
  • mRNA causes synthesis of specific proteins which cause cell modification
79
Q

Explain how epigenetic changes affect the development of tissues in the embryo. (3)

A
  • DNA is wrapped around histones
  • methylation of DNA affects gene transcription
  • therefore, gene expression is altered
80
Q

Describe the role zoos play in animal conservation. (3)

A
  • protection from poeachers
  • important role in education
  • contribute to research e.g. developing better nutrition
81
Q

Define: habitat. (1)

A
  • the area inhabited by a particular organism
82
Q

Describe the structure of a cell surface membrane. (3)

A
  • cell membrane consists of phospholipids and proteins
  • phospholipids form a bilayer
  • proteins float in phospholipids
83
Q

Explain the effect of spherocytosis on the uptake of oxygen by r.b.cs. (3)

A
  • oxygen enters cells via diffusion
  • change in shape increases diffusion distance
  • therefore, gas exchange decreases
84
Q

Explain why these antibiotics could affect the production of proteins in bacteria. (3)

A
  • ribosome shape altered
  • so translation cannot occur
  • and polypeptide is not synthesised
85
Q

Describe how HIV particles are able to enter T helper cells. (3)

A
  • glycoproteins on virus surface
  • bind to receptors on T helper cells
  • viral RNA enters cell
86
Q

Explain why the destruction of T helper cells causes the symptoms of AIDS. (4)

A
  • reduces cytokine production
  • which reduces activation of B cells
  • reducing antibody production
  • therefore, increasing risk of opportunistic infections
87
Q

Explain why farming of beet cattle on deforested land produces more greenhouse gas emissions. (3)

A
  • trees are carbon sinks
  • burning them releases CO2 into atmosphere
  • without trees, there is less photosynthesis to remove CO2 from the atmosphere
88
Q

State how the age of the layers in a peat bog can be determined. (1)

A
  • using carbon dating
89
Q

Explain why the conditions in peat bogs prevent decomposition. (3)

A
  • conditions are anaerobic
  • so less respiration by decomposers
  • therefore, enzymes cannot break down organic material
90
Q

Describe the primary structure of a protein. (1)

A
  • sequence of amino acids
  • joined via peptide bonds
91
Q

Describe the role of the organelles involved in these processes. (5)

A
  • folding of protein inside rER
  • bonds formed between R groups
  • rER packages proteins in vesicles
  • vesicles transport protein to Golgi Apparatus
  • Golgi Apparatus modifies protein
92
Q

Deduce how siRNA may be used to prevent the development of porphyria. (4)

A
  • siRNA binds to mRNA
  • mRNA cannot bind to ribosome
  • polypeptide isn’t synthesised
  • so no development of porphyria as faulty enzyme is not produced
93
Q

Explain why a fertilised egg cell would only contain maternal mitochondria. (2)

A
  • only nucleus of sperm enters ovum
  • so all mitochondria comes from egg cell
94
Q

Explain why resulting embryo doesn’t develop mitochondrial disease. (2)

A
  • bcs all mitochondria in embryo came from donor
  • which does not carry mutation
95
Q

Following an infection, why is repeating vaccinations advised? (3)

A
  • need to repeat vaccinations to produce more memory cells
  • so antibodies can be produced quickly
  • so that there is a secondary immune response
96
Q

Explain why these dormant bacteria are not destroyed by the immune system. (3)

A
  • bacteria inside microphages
  • this bacterium has waxy cell wall
  • bacteria not destroyed by enzymes
97
Q

Explain which population is more likely to adapt to changing conditios. (4)

A
  • North america has higher heterozygosity index so their population is more genetically diverse
  • so more likely to have advantageous alleles
  • those with advantageous allele more likely to survive and breed
  • frequency of allele will increase

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