Alevel past papers Flashcards
1
Q
Describe the acrosome reaction (1)
A
- when the sperm cell releases an enzyme that digests the zona pellucida
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
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
4
Q
Describe the movement of osmosis. (1)
A
- against a solute concentration gradient, through a partially permeable membrane
5
Q
Which part of the cell surface membrane allows facilitated diffusion of glucose? (1)
A
protein
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
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
8
Q
Describe how DNA is organised in a bacterial cell. (3)
A
- small plasmids
- circular DNA
- located in cytoplasm
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
10
Q
Define: bacteriostatic
A
stops bacteria dividing
11
Q
Define: bactericidal
A
kills bacteria
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
13
Q
In which parts of the chloroplast do the light-independent reactions take place. (1)
A
stroma
14
Q
What enzyme is used by plants to fix carbon dioxide. (1)
A
RUBISCO
15
Q
What is an immediate product of the LIR of photosynthesis? (1)
A
GP
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
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
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
19
Q
Describe the structure of collagen. (3)
A
- 3 polypeptide chains
- chains coiled around each other
- cross-linking between chains
20
Q
Give a function for collagen in the blood-gas barrier. (1)
A
- to provide strength
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
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
23
Q
Which type of immunity is developed by vaccines. (1)
A
- artificial active immunity
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
25
Define: sex-linkage. (2)
- gene responsible for a trait is located on a sex chromosome
- expression of the trait is related to gender
26
Comment on the effect of adding cow dung to composting coffee husks. (3)
- 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
27
Define: allele
alternative form of a gene
28
Explain how two species of African elephant could evolve from common ancestor. (3)
- two populations geographically isolated from one another
- therefore reduced gene flow between the two populations
- leading to allopatric speciation
29
Does an increased magnesium ion intake increase or reduce the chance of getting CVD. (1)
reduce
30
Describe the role of LDLs in the development of atherosclerosis. (3)
- LDLs carry cholesterol in blood
- cholesterol is deposited to form atheroma
- in endothelium of artery
31
Explain how atherosclerosis can result in damage to a heart muscle. (3)
- narrowing of coronary arteries
- reduces blood flow to cardiac muscle
- which reduces aerobic respiration
32
Explain the effect of temperature on the rate of growth of blowfly maggots. (3)
- temperature affects enzymes
- increased temperature increases kinetic energy
- leading to more frequent collisions between enzymes and substrates
33
Describe the role of decomposers, such as microorganisms, in the carbon cycle. (2)
- respire
- release CO2
34
Which cell produces antibodies? (1)
plasma cell
35
Which type of immunity does a newborn baby obtain from the mother's milk. (1)
natural passive immunity
36
Explain how changes in the blood vessels result in the redness and swelling seen at the site of inflammation. (4)
- histamine released
- causes vasodilation
- which increases blood flow
- allowing blood plasma to enter tissue, causing swelling
37
Explain why the interferon made by genetically modified bacteria is different from the interferon made my animal cells. (2)
- polypeptide chain is not modified properly
- therefore protein is incorrectly folded
38
Describe the role of tRNA in the production of leptin. (3)
- tRNA molecules
- have anticodons that bind to mRNA codons
- each tRNA carries a particular amino acid
39
Describe how the primary structure of leptin enables it to be soluble in water. (3)
- primary structure determines folding
- forming globular structure
- water forms hydrogen bonds with protein
40
Describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures. (2)
- introduces a new stop codon
- coding for a shorter amino acid sequence
41
Define: stem cell. (2)
- a cell that is undifferentiated
- that can give rise to specialised cells
42
Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells. (4)
- 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
Explain how the primary structure of trypsin molecules can be used to produce a phylogenetic tree. (3)
- 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
Explain how this calcium ion binding site could have evolved in vertebrates. (3)
- variation in trypsin gene
- calcium ion binding site offers advantage
- vertebrates survive, reproduce and pass on allele
45
Explain how reforestation of tropical rainforests can be used to minimise climate change. (3)
- new trees uptake CO2
- reducing CO2 in atmosphere
- therefore, slowing rate of global warming
46
Describe what needs to be measured in order to compare the biodiversity of two rainforests. (2)
- number of different species
- number of individuals per species
47
Explain why the value for GPP is lower than the light energy available to the ecosystem. (3)
- some light is reflected
- some light misses the chloroplast
- some light not absorbed by chlorophyll
48
Define: species (1)
- a group of organisms that can interbreed to produce fertile offspring
49
Explain how these two species of snake could have arisen from a common ancestor. (4)
- 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
Compare and contrast the structure of chitin with that of a cellulose molecule. (3)
both:
- have glycosidic bonds
- every other glucose is inverted
- chitin contains nitrogen, cellulose does not
51
Describe how a peptide bond is formed. (2)
- via a condensation reaction
- between the amine group and carboxyl group of the adjacent amino acid
52
What does a bacteriostatic antibiotic do? (1)
-prevents the multiplication of bacteria
53
Describe the infection control practices hospitals have introduced. (3)
- hand wash stations
- increased disinfection of bedding
- doctors not to wear long sleeves
54
Describe the role of thrombin in blood clotting. (3)
- thrombin is an enzyme
- catalyses conversion of: fibrinogen to fibrin
- mesh of fibrin traps red blood cells to form a clot
55
Explain why a mutation in the gene coding for the protein factor V may increase the risk of VTE. (3)
- changes amino acid sequence
- overactive factor V increases thrombin production
- increasing blood clotting
56
Describe the possible impact of climate change on the effects of leaf rust on the yield of wheat crops. (4)
- 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
Explain why anthropogenic emissions of greenhouse gases are affecting the climate. (3)
- burning fossil fuels
- increases CO2 emissions
- causing more heat energy to be trapped in the atmosphere
58
Define: inherited recessive disorder. (2)
- caused by a faulty allele
- that is only expressed in the homozygous condition
59
Evaluate genetic screening. (4)
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
Explain why incorrectly folded enzymes cannot carry out their function. (3)
- the tertiary structure would be different
- so wouldn't be able to form substrate-enzyme complex
- therefore, not able to catalyse reaction
61
Define: endemic. (1)
- found only in one geographical location
62
Explain why the presence of microorganisms on the skin and gut help prevent pathogenic organisms multiplying in the body. (3)
- 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
Explain why there are relatively few species of bacteria in the stomach. (2)
- 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
Explain why this mutation affects the function of the haemoglobin molecule. (3)
- could change an amino acid
- causing change in tertiary structure
- haemoglobin no longer able to bing to oxygen
65
Describe how the pre-mRNA may be modified before being translated on the ribosome. (2)
- pre-mRNA contains exons and introns
- introns are removed and exons are spliced together to produce mRNA strand
66
Explain why modification of pre-mRNA enables one gene to give rise to more than one protein. (2)
- the different exons can be removed
- therefore, producing different amino acid sequence
67
Describe the role of the acrosome in fertilisation. (3)
- fuses with cell surface membrane of sperm cell
- digestive enzyme released
- to break down zona pellucida
68
Explain how breeding programmes in zoos maintain the genetic diversity of captive populations. (3)
- animals selected to prevent inbreeding depression
- stud book used to keep record of all breeding events
- exchange of animals between zoos
69
Compare and contrast the structure of Ebola virus with that of HIV. (3)
both:
- contain RNA
- have glycoproteins
- HIV = spherical, Ebola virus = elongated
70
Describe how clinical trials of a vaccine would be conducted. (3)
- 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
Justify the use of the Ebola vaccine. (4)
- 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
Explain how microorganisms in the soil break down the stems. (3)
- stems contain starch
- enzymes secreted by microorganism
- which break down glycosidic bonds
73
Name the plant organelle that fixes carbon dioxide from the atmosphere. (1)
chloroplast
74
Explain why burning wood chips does not increase carbon dioxide to the atmosphere in the long term. (4)
- 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
Explain how results of electrophoresis could provide evidence for interbreeding between the two types oh human. (2)
- by comparing number of bands produce by the 2 types of DNA
- similarities indicate interbreeding
76
Describe how the Hardy-Weinberg equation can be used to provide evidence for changes in the elephant population in Mozambique. (2)
- calculate allele frequency in population in Mozambique
- regularly sample over period of time
77
Define: totipotent cell. (2)
- cell that has ability to differentiate
- into all cell types
78
Describe how cells become specialised. (3)
- chemical signals cause some genes to activate
- only activates genes that produce mRNA
- mRNA causes synthesis of specific proteins which cause cell modification
79
Explain how epigenetic changes affect the development of tissues in the embryo. (3)
- DNA is wrapped around histones
- methylation of DNA affects gene transcription
- therefore, gene expression is altered
80
Describe the role zoos play in animal conservation. (3)
- protection from poeachers
- important role in education
- contribute to research e.g. developing better nutrition
81
Define: habitat. (1)
- the area inhabited by a particular organism
82
Describe the structure of a cell surface membrane. (3)
- cell membrane consists of phospholipids and proteins
- phospholipids form a bilayer
- proteins float in phospholipids
83
Explain the effect of spherocytosis on the uptake of oxygen by r.b.cs. (3)
- oxygen enters cells via diffusion
- change in shape increases diffusion distance
- therefore, gas exchange decreases
84
Explain why these antibiotics could affect the production of proteins in bacteria. (3)
- ribosome shape altered
- so translation cannot occur
- and polypeptide is not synthesised
85
Describe how HIV particles are able to enter T helper cells. (3)
- glycoproteins on virus surface
- bind to receptors on T helper cells
- viral RNA enters cell
86
Explain why the destruction of T helper cells causes the symptoms of AIDS. (4)
- reduces cytokine production
- which reduces activation of B cells
- reducing antibody production
- therefore, increasing risk of opportunistic infections
87
Explain why farming of beet cattle on deforested land produces more greenhouse gas emissions. (3)
- trees are carbon sinks
- burning them releases CO2 into atmosphere
- without trees, there is less photosynthesis to remove CO2 from the atmosphere
88
State how the age of the layers in a peat bog can be determined. (1)
- using carbon dating
89
Explain why the conditions in peat bogs prevent decomposition. (3)
- conditions are anaerobic
- so less respiration by decomposers
- therefore, enzymes cannot break down organic material
90
Describe the primary structure of a protein. (1)
- sequence of amino acids
- joined via peptide bonds
91
Describe the role of the organelles involved in these processes. (5)
- 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
Deduce how siRNA may be used to prevent the development of porphyria. (4)
- 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
Explain why a fertilised egg cell would only contain maternal mitochondria. (2)
- only nucleus of sperm enters ovum
- so all mitochondria comes from egg cell
94
Explain why resulting embryo doesn't develop mitochondrial disease. (2)
- bcs all mitochondria in embryo came from donor
- which does not carry mutation
95
Following an infection, why is repeating vaccinations advised? (3)
- need to repeat vaccinations to produce more memory cells
- so antibodies can be produced quickly
- so that there is a secondary immune response
96
Explain why these dormant bacteria are not destroyed by the immune system. (3)
- bacteria inside microphages
- this bacterium has waxy cell wall
- bacteria not destroyed by enzymes
97
Explain which population is more likely to adapt to changing conditios. (4)
- 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
