1
Q
Describe the structure of a virus
A
- nucleic acid - DNA or RNA inside
- surrounded by a capsid (protein coat)
- attachment proteins
- proteins in capsids - eg enzymes like reverse transcriptase.
2
Q
Describe the structure of a bacterium
A
- Cell wall and cell membrane
- Plasmids and free floating DNA
- smaller ribosomes than eukaryotes.
- flagella (some)
- Pilli
- slime capsule
3
Q
Describe How HIV would enter, then exit from a host cell.
A
- attaches to receptors on lymphocyte/host cell.
- injects RNA into host cell.
- Uses host cell resources to replicate itself
- cell becomes saturated and copies of HIV leave the cell, killing it (Lysis)
4
Q
Name some entry routes of pathogens
A
- breaks in skin
- mucosal surfaces
- Respiratory system
- Digestive system
5
Q
What are physical non-specific defenses against pathogens?
A
- Skin: physical barrier and sebum. Also has bacterial coating which can out-compete pathogens that are no adapted to skin conditions.
- cillia: digestive and respiratory systems
- gut and genital flora: bacteria
- enzymes in tears and saliva (Lysozyme) - causes pathogens to lyse.
6
Q
What are some non-specific immune responses?
A
- inflammation
- interferons
- phagocytosis
- gut and skin flora
7
Q
Explain how inflammation occurs.
A
- histamines released by mast cells.
- causes vasodilation, increasing blood flow to the area. (red appearance)
- increases permeability of capillaries: increases water in the area (swelling)
8
Q
Describe 3 ways in which interferons act.
A
- increase non-specific immune response
- inhibit production of viral proteins.
- activate WBCs to specific immune response.
9
Q
What are interferons?
A
Anti-viral proteins that prevent viruses from spreading to uninfected cells.
10
Q
Describe the stages of phagocytosis
A
- Pathogen is ingulfed by phagocyte.
- it then gets enclosed in a vesicle, called a phagosome.
- Phagosome then binds to a lysosome, hydrolysing the pathogen. (formed a phagolysosome)
- phagocyte will then present the pathogen’s antigens on its surface, meaning it has become an APC.
11
Q
Describe the structure of an antibody.
A
- light chain (short) (top)
- heavy chain (long) (bottom)
- antigen binding site (variable with different antibodies)
- Constant region (not variable, the same for all antibodies)
- Hinge region - gives flexibility to bind to an antigen at different angles.
12
Q
Describe what is meant by splicing
A
- Introns (non-coding) are ‘cut out’ from pre-RNA, then exons are rearranged by spliceosomes in different combinations to form mature functional RNA.
13
Q
Describe the stages of the cell-mediated response
A
- T cells look for non-self antigens, triggering clonal selection.
- they mature inside the thymus
- they then divide through mitosis - (clonal expansion)
- they can either give rise to Killer, Helper or memory T cells
- Helper T cells: produce cytokines to attract Macrophages and B cells to the area.
- Killer T cells: bind to receptors on infected cell, puncture holes and release toxins to destroy infected cells (lysis)
- Memory T cells: stay behind to remember the pathogen, allowing for a faster immune response upon reinfection.
14
Q
Describe the humorol response.
A
- Involves B cell responses
- mature in bone marrow
- clonal selection and clonal expansion
- 2 types: plasma and memory (can arise during expansion)
- Plasma cells: produce antibodies, and therefore have plenty of mitochondria and ReR. This causes agglutination, causing immobility of pathogens and an inability to reproduce, attracting macrophages and neutrophils to the area to destroy the pathogens.
- Memory cells: stay behind, faster response upon re-infection because of remembering the pathogen.
14
Q
Explain how changes in the blood vessels result in the redness and swelling seen at the site
of inflammation.
A
- histamines are released
- leads to vasodilation, resulting in redness in the area due to more blood flow to the area.
- Swelling caused by capillaries becoming more permeable, allowing plasma fluid to flood the area.
15
Q
Describe how HIV particles are able to enter T helper cells
A
- Attach to CD4 receptor protein on surface of T helper cell
- injects viral RNA into T helper cell through viral envelope fusing with cell membrane of T helper cell.
16
Q
Explain why the destruction of T helper cells causes the symptoms of AIDS.
A
- reduces cytokine production
- so less B cells are activated, producing less antibodies against HIV
- increasing risk of opportunistic infections.
17
Q
Explain why the presence of microorganisms on the skin and in the gut helps to
prevent pathogenic organisms multiplying in the body
A
- bacteria on skin and in gut more well-adapted to conditions
- so bacteria on skin and gut out-competes pathogenic organisms for resources
- bacteria in the gut secrete lactic acid which also destroys pathogens.
18
Q
A small number of people have been identified who are resistant to HIV.
They have a mutation in a gene coding for a protein in the cell membrane.
(i) Deduce why this mutation makes these people resistant to HIV infection
A
- glycoprotein unable to bind to receptor on host cell.
- meaning that viral RNA cannot enter the cell.
19
Q
Stem cell therapy can be used to treat patients infected with HIV.
The bone marrow of these patients can be destroyed using radiotherapy.
The patients can then be given stem cells from the bone marrow of a donor who has this
mutation.
Explain why these stem cells may prevent HIV causing AIDS.
A
- stem cells can differentiate into specialised cells.
- so they differentiate into T cells that have the mutated gene
- so mutated CD4 prevents HIV entering the T cell
- prevents destruction of T cells, so HIV virus doesn’t stay in blood.
20
Q
) Scientists have isolated these new antibiotics and tested their effectiveness against
bacteria that are resistant to other types of antibiotic.
Devise a laboratory procedure to compare the effectiveness of penicillin with one of the
new antibiotics.
A
- have at least 2 petri dishes with agar jelly
- prepare solutions of the same concentration of the new antibiotic and penicillin
- soak paper disks in these solutions, placing them in the petri dishes.
- making sure they are close to a bunsen flame.
- incubate at same temperature and moisture, for the same period of time.
- measure zone of inhibition of both disks.
- repeat procedure for different strains of resistant bacteria.
- use t-test to measure if results are statistically significant. (eg the zones of inhibition)
21
Q
Human papilloma virus (HPV) is a DNA virus.
Cervarix and Guardasil have been used in national vaccination programs.
A person who has been vaccinated becomes infected with HPV-16. Explain the role of the T
cells in the body of this person.
A
- memory T cells will have been present after vaccination
- they will differentiate into T killer cells to destroy pathogens.
- helper T cells produce cytokines to activate B cells.
22
Q
The human gut contains more than a thousand species of bacteria. Only 30 to 40 of these
species are found in the stomach.
Explain why there are relatively few species of bacteria in the stomach.
A
- only some bacteria are adapted to stomach conditions
- as pH is too low for some bacterial enzymes to function
23
Q
Compare and contrast the structure of Ebola virus with that of the human immunodeficiency
virus (HIV).
A
- both have RNA strands
- both have a capsid
- HIV is spherical
24
Explain why the interferon made by genetically modified bacteria is different from the
interferon made by animal cells.
- bacteria don't have an RER or golgi body
- therefore can't modify proteins properly
- leading to incorrect folding of the protein.
25
Explain the role of T cells in the immunity to the Ebola virus that develops following the
use of this vaccine.
- T memory cells arise from vaccine
- they remember antigen on pathogen surface
- so differentiate into helper and killer T cells quicker, activating B plasma cells faster, and therefore producing antibodies quicker omm reinfection.
26
) Scientists are developing methods that use microorganisms to break
down plastics.
Some of the products produced are being used for other purposes, such as
vanilla flavouring.
Explain why some microorganisms can break down plastics.
- produce enzymes
- that can hydrolyse bonds within plastics.
27
State two precautions that should be taken to ensure that only one type of
bacteria is grown in this culture.
- work near a bunsen burner flame
- disinfect all equipment
28
One type of bacteria, Pseudomonas, uses half of the plastic it breaks down to
produce its own biomass, with the rest released as carbon dioxide.
Explain how the breakdown products become biomass and carbon dioxide.
- breakdown of bacteria absorbed by bacteria
- breakdown products are converted to biomass (organic molecules)
- respiration of bacteria produces CO2.
29
GALP is produced in the light-dependent reactions in the leaves.
Explain how the cells in the trunk are able to synthesise the molecule in the
diagram using GALP produced in the leaves.
Use the information in the diagram and your own knowledge to support
your answer.
- GALP converted to glucose.
- glucose converted sucrose to use in plant cells.
- phosphates used in rubber.
- glucose is respired for energy.
30
Explain how dendrochronology could be used to determine the age of a tree that
is still producing rubber.
- Tree trunk can be collected.
- each ring is equivalent to one year.
- rings counted, and that is the number of years.
31
) It has been estimated that because humans have planted more trees and crops,
the leaf area increased by 0.5 million km2
between 2019 and 2000.
China accounts for 25% of this increase. It planted forests and crops, in
equal proportions.
India accounts for 7% of this increase. It planted mostly crops.
Discuss the possible impacts of planting forests or crops on global warming,
biodiversity and the local population.(6)
- increasing the number of plants may increase biodiversity
- as it provides a source of habitat for wildlife,
- meaning that there might be an increase in the herbivore population.
- Since crops also provide food, the human population may have less food insecurity.
- however, new crops may replace already growing crops
- there may also be need to invest in fertilisers which are expensive
- Global warming may decrease, as more crops take in more CO2 for photosynthesis.
- so effects of extreme temp or drought may decrease.
32
The body temperature of a fish changes with the temperature of
its surroundings.
Explain why the survival time of fish is reduced at temperatures lower and
higher than those in the zone of tolerance.
- enzyme activity may be reduced at high and low temps
- because at lower temps, there is not enough kinetic energy for collisions to dorm enzyme-substrate complexes
- at high temps, enzymes may denature.
33
Explain why the optimum temperature for this enzyme is affected by
storage time.
- as storage time increases, the optimum temperature decreases
- so the active site changes shape
- therefore, the longer the active site is changed in shape, the less likely it is that it will go back to normal.
34
Another group of scientists showed that an extract from the leaves of the papaya
plant helped in recovery from dengue virus infection.
They showed that the platelet and white blood cell counts were higher in people
treated with the extract than in people given a placebo.
Explain how these changes may have helped in recovery from dengue
virus infection.
- more blood flow to the area due to the extract
- allows more wbcs to flow to area to increase immune response.
- allows for more phagocytosis by macrophages, so more becoming APCs
- so more T cells can be activated, activating B cells to produce antibodies
- so more agglutination happens, preventing dengue from multiplying.
35
Another group of scientists infected the eggs of mosquitoes with
Wolbachia bacteria.
The Wolbachia do not harm the mosquitoes but compete with the virus so that it
is harder for it to replicate.
The bacteria can also be passed on to future generations of mosquitoes.
One study in Indonesia showed a 77% reduction in new cases of dengue infection
after the introduction of Wolbachia into the mosquito population.
Describe two advantages of this method of disease control.
- less people may die of dengue
- treatment has to be done only once.
36
Explain how infection with Mycobacterium tuberculosis may result in death.
- reduces gas exchange in lungs
- so insufficient oxygen for respiration
- this may result in organ failure and death.
37
Explain why the macrophages had to be treated to stimulate IL-1β release in
this investigation.
Use the information in the graph to support your answer.
- because they did not already release 1L-1b
- so that the effect of inhibition couldve been seen to show affect on TB
38
Enzymes that cut the DNA at a specific base.
restriction endonucleases
39
what is needed in a PCR?
- primer (base sequence attached at a certain end)
- nucleotides
- DNA polymerase.
40
why is the temp change first so high for PCR?
what is the value of this temp?
- Hydrogen bonds breaks
- 95 degrees celcius.
41
What temp is the PCR cooled down to after the hydrogen bonds breaking?
what does this cause.
- 55
- causes the primer to anneal (attaches)
42
what are the methods to find time of death?
- body temp
- rigor mortis
- decomposition
- forensic entomology
43
name 3 factors that affect post mortem cooling
Body size
air movement
humidity
44
Describe the changes that occur inside the body the first week of death.
- body temp decreases
- rigor mortis
- autolysis - breakdown of cells by enzymes in the body.
45
Explain the effect of temperature on the rate of growth of blowfly maggots.
- higher the temp, the faster the growth.
- since temp effects rate of enzyme action.
- higher temp = more kinetic energy
- so higher frequency of enzyme-substrate complexes.
46
Explain the effect of ambient temperature on the rate of decomposition.
- higher the ambient temp, higher the rate of decomposition, as higher temp means more enzyme action
- increase in temp also therefore increases growth rate of decomposers.
47
After grain is harvested, farmers plough the stems (straw) from wheat plants into the
soil.
This improves the quality of the soil. These stems contain polysaccharides.
Explain how microorganisms in the soil break down the stems.
- hydrolyse using enzymes
- breaking the glycosidic bonds
- so produce glucose used by microorganisms in respiration.
48
Body farms use the bodies of pigs to study the changes in insect species on a body after
death.
Explain how the results of this study could be used to help to establish the time of death
of a human.
- record species of insect present on the body
- take its life cycle into account
- environmental factors need to be taken into account when using stages of succession- like temp.
49
describe how PCR worksin stages
- Mixture is heated to 95 degrees to break H bonds between strands
- cooled back down to 50-65 degrees to help with annealing
- temp increased to 70 degrees to help DNA polymerase join free nucleotides onto the strand.
50
Suggest why data around HIV infections are often estimates.
- HIV does not always produce symptoms
- only people who suspect they have contracted HIV will get a test.
- a new strain of HIV might arise
