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Edexcel A-level biology exam questions and answers(2022 exam graded A)
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Edexcel A-level biology exam questions and answers(2022 exam graded A)
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Edexcel A-level biology exam questionsand answers(2022 exam graded A)
Describe the events of fertilisation that occur after the acrosome reaction. Ans-
Membrane of sperm and egg cell fuse together
-cortical granules release contents into zona pellucida
-Zona pellucida thickens
-Haploid nuclei fuse
Explain how phospholipids form a cell surface membrane Ans-Hydrophilic parts
associate with water
-Hydrophobic parts repel water
-a bilayer forms with hydrophobic parts pointing in towards the centre of the bilayer
Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs
has the right consistency Ans-Chloride ions move out of the cells through the CFTR
protein
-Sodium ions then also move out of the cells
-The concentration of the solute increases in the mucus
-Water moves out of the cell by osmosis
Describe how DNA is organised in a bacterial cell Ans-Circular DNA that is not
associated with histones
-Plasmids
-located in the cytoplasm
Describe the light-dependent reactions of photosynthesis Ans-Light energy excites a
pair of electrons in PSII
-Electrons used in the electron transport chain
-Photolysis of water to produce H+, O2 and electrons
-Generation of ATP (phosphorylation)
-Reduction of NADP
Suggest how useful body temperature is in determining time of death Ans-Drop in body
temperature is linked to time after death
-Factors affect it (eg. environmental temperature, body size etc)
-Time of death can be calculated if ambient temperature is known.
-However it's only useful for a short amount of time after death.
Suggest how useful state of decomposition is in determining time of death Ans-Body
decomposes in a specific sequence
,-Factors affect it (eg. environmental temperature, wounds)
-Not useful if body has fully decomposed
Why can human DNA polymerase not be used in PCR AnsHuman enzymes will not
work at high temperatures as they will be denatured
Why species of plants cannot be identified from xylem material using PCR and DNA
profiling AnsIt is made from dead material, there is no DNA present
Describe how the production and action of interferon differs from lysozyme
AnsInterferon produced by infected cells to inhibit the replication of viruses, whereas
lysozyme present in macrophages to destroy bacteria.
Suggest why the protein structure of lysozyme is important to the way in which it acts
against pathogens Ans-Enzyme, that has an active site of a specific shape
-Acts on the cell wall of bacteria
Explain why an insect bite, which breaks the surface of the skin, may lead to
inflammation Ans-Histamine released from mast cells as a result of damaged tissue
-Arterioles dilate causing increased blood flow and capillaries become more permeable
-Resulting in an oedema
Suggest why reducing inflammation could help reduce a patient's immune response
Ans-There will not be such an increase in blood flow to the wound.
-Will not be such an increase in macrophages to the area
-Fewer macrophages to present antigen to T-helper cells
-Without T-helper cell activation B cells cannot be activated etc
Explain how changes in the fibrinogen concentration might be a risk factor for CVD Ans-
Increased concentrations of fibrinogen leads to increased fibrin
-Increases the risk of blood clotting
-Which blocks the lumen of arteries
Describe the structure of collagen Ans- Primary structure is a repeating amino acid
sequence
-3 Polypeptide chains
-Chains coiled around each other
-Cross-links between chains
State what is meant by the term sex-linkage Ans-The allele responsible for a trait is
located on a sex chromosome
-The expression of the trait is linked to gender
Explain how studying pollen grains in peat bogs can provide evidence of climate change
Ans-Pollen is preserved in peat bogs
-A plant species can be identified by its pollen
, -Climate affects the type of plant growing
-Depth of peat correlates with period of time since pollen was produced
-Changes in pollen over time indicate changes in climate
Describe the role of mRNA in protein synthesis Ans-mRNA is a copy of the DNA
-To take information out of the nucleus for translation
-Post transcriptional modification to enable more than 1 gene to code for a peptide
Explain why it is important that a tRNA molecule can only attach to one amino acid Ans-
tRNA is specific for an amino acid
-To ensure that the primary structure of the peptide is correct
-Otherwise folding will be incorrect
Explain why some amino acids can attach to more than 1 type of tRNA molecule Ans-
Genetic code is degenerative
-Some amino acids have more than one code
-There will be a different tRNA for each codon on the mRNA
Explain why there are fewer possible anticodons than codons AnsThere are stop
codons that tRNA do not bind to
State the meaning of the term bacterial infection AnsWhen bacteria are inside cells
Describe an investigation, that could be carried out in a laboratory, to determine a
suitable combination of antibiotics to use against Mycobacterium tuberculosis Ans-
Culture bacteria with agar using aseptic techniques
-Different antibiotics used in a number of different combinations
-Apply antibiotics using filter paper soaked in antibiotic
-Incubate bacteria with antibiotic for a period of time (greater than 12 hours)
-Most suitable combination will have the largest zone of inhibition
State the meaning of the term species AnsGroups of organisms that can breed together
to produce fertile offspring
Explain how gel electrophoresis can be used to determine the father of a cub Ans-
Collect DNA samples, from blood, skin, etc., from mother, cub and all possible fathers.
-Use restriction endonucleases, load onto gel and apply a current.
-Visualise through southern blotting, adding fluorescent probes
-Match DNA bands
Describe the structure of a cell wall in a xylem vessel Ans-cellulose molecules as
microfibrils held together by hydrogen bonds
-mesh of microfibrils
-lignified
-Lignin distributed in spirals
-Presence of pits
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