Edexcel A Level Biology Topic 6 Exam Questions

Describe how DNA profiling could be carried out to show that these snakes are different species. (4)

• M1: DNA obtained from two types of snakes

• M2: {PCR/ restriction enzymes} used to produce fragments of DNA

• M3: Gel electrophoresis used to analyse the DNA

• M4: Gel electrophoresis used to separate the fragments of DNA

• More differences in the patterns of bands produced would indicate that the snakes are different species

Describe the changes that occur inside a body in the first week after death. (3)

M1: Body temperature falls

M2: Rigor mortis/ stiffening of the muscles

M3: Autolysis/ breakdown of cells by enzymes in the body

M4: Putrefaction/ discolouration/ bloating (allow: accumulation of gases)

Microorganisms are also found on a dead body.

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

• M1: Decomposers break down organic material

• M2: Decomposers respire

• M3: releasing CO₂ into the atmosphere

Devise a procedure, using electrophoresis, to compare the amplified DNA from these two types of human.

• M1: {restriction enzymes/ endonuclease} used to cut DNA into fragments

• M2: DNA samples are loaded into agarose gel

• M3: {electric current is passed through/ potential difference is applied across} the gel

• M4: Markers are added to visualise the gel

• M5: The positions of the bands produced can be compared

Explain the effect of ambient temperature on the rate of decomposition. (3)

• M1: An increase in temperature will increase the rate of {decay/ decomposition}

• M2: An increase in temperature increases enzyme activity

• M3: An increase in temperature increases growth rate of {bacteria/ fungi/ decomposers}

Describe how one PCR cycle would increase the quantity of DNA present. (3)

• M1: heat to 90-98 C {to break hydrogen bonds between DNA strands/ separate the strands of DNA} - denaturation

• M2: {joining of primers/ annealing} at 50-75 C

• M3: {elongation/ extension/ addition of nucleotides}/ DNA polymerase involved in formation of phosphodiester bonds

• M4: To double the quantity of the DNA

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

• M1: Hand wash stations

• M2: doctors/ nurses not to wear {ties/ watches/ long sleeves}

• M3: Testing patients for antibiotic resistant bacteria before admission/ {isolation/ quarantine} of infected patients

• M4: Increased washing of bedding/ disinfection of {beds/surfaces}

Inflammation is a non-specific response to an infection. Explain how changes in the blood vessels result in the redness and swelling seen at the site of inflammation. (4)

• M1: Histamines are released

• M2: Histamines cause {arterioles to dilate/ vasodilation}

• M3: Which increase the blood flow to the site causing redness

• M4: Histamines also cause the permeability of the membranes to increase

• M5: Allowing blood plasma to {leave the capillary/ enter the tissues} causing oedema/ swelling

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

• M1: {glycoproteins/ GP120} on the surface of the virus

• M2: bind to CD4 receptors on the surface of the T-helper cells

• M3: Viral envelope fuses with the cell membrane of the T-helper cell

• M4: Viral RNA enters the cell

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

• M1: Lack of T-helper cells reduce cytokine production

• M2: Therefore reducing {cloning/ activation} of B cells

• M3: Reducing antibody production

• M4: There is an increased risk of opportunistic infections(eg TB)

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

• M1: Flora in the gut and skin are better adapted to the conditions

• M2: Therefore they can outcompete pathogenic organisms

• M3: Bacteria in the gut secrete {chemicals/ lactic acid} which help to destroy pathogens

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)

• M1: A vaccinated person will have memory T-cells

• M2: Memory T cells recognise antigens specific to the HPV-virus

• M3: T-helper cells that activate {B-cells/ T killer cells}

• M4: Formation of T-killer cells destroy cells infected with the virus

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

• M1: Because pH in the stomach is too low for the enzymes of most bacteria to suffer

• M2: Bacteria that live the the stomach have adaptations that enable them to survive.

State what is meant by the term bacteriostatic. (1)

• A substance which can {inhibit the growth/ prevent multiplication} of bacteria

Explain the role of T cells in the immunity to the Ebola virus that develops following the use of this vaccine. (3)

• M1: T helper cell bind to {protein/ antigen} on the APC

• M2: Therefore leading to production of {active T helper cells/ T memory cells}

• M3: The T helper cells activate the B cells to {divide/ become} cells capable of producing antibodies

• M4: The memory cells cells remain in the body so antibodies can be produced quickly on re-infection

Explain how a bone marrow stem cell can give rise to red blood cells. (4)

• M1: By differentiation

• M2: Due to certain stimuli

• M3: Which causes {some genes genes of haemoglobin} to be activated

• M4: {mRNA/ haemoglobin} produced from activated genes

• M4: Removal of nucleus/ produce a biconcave shape

M. tuberculosis bacteria can remain dormant in the body after infection.

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

• M1: the bacteria are inside {macrophages/ phagocytes}

• M2: This bacterium has a thick waxy cell wall

• M3: Lysosomes cannot fuse with phagocytic vacuole/ bacteria not destroyed by enzymes

• M4: Bacteria within tubercles cannot be destroyed

Describe how amplified samples of DNA can be prepared for analysis using gel electrophoresis. (3)

• M1: DNA is cut into fragments

• M2: {radioactive tracers/ fluorescent tags} attached to DNA (allow stains such as dye)

• M3: Fragments of DNA loaded onto agarose gel/ samples placed in wells

• M4: Electric current passed through the gel/ potential difference set up through buffer/ across gel

Explain why antibiotics cannot be used to treat influenza. (2)

• M1: Because influenza is (caused by) a virus

• M2: Antibiotics target {prokaryotes / bacteria} (ALLOW: treat bacterial infections)

• M3: Structure of a virus is different to that of a {prokaryote / bacteria}

Devise a procedure to determine the similarities of the RNA of a particular virus which has many strains (hence differences in its RNA) in saliva collected from different people. (4)

• M1: {isolate / extract} RNA from (saliva) samples

• M2: Amplify the {RNA/DNA/nucleic acid} by PCR (ALLOW (reverse) transcribe RNA to DNA and amplify DNA)

• M3: Cut the {RNA/DNA/nucleic acid} into fragments (using restriction enzymes)

• M4:(separate fragments using) gel electrophoresis

• M5: More similar the {banding / profile} (of the fragments) the more closely related the strain

Describe how M. tuberculosis bacteria evade the immune system. (2)

• M1: (M tuberculosis) survive inside macrophages

• M2: (M tuberculosis) {survive / remain dormant} in tubercles

• M3: (M tuberculosis) {inhibit T helper cells / supress the (acquired) immune response}

State what is meant by the term transcription factor. (1)

• Is a protein that controls {activation/ transcription} of gene