Edexcel A-level biology exam questions / Edexcel A Level Biology Question Paper 3 June 2023 (Salters Nuffield) ALREADY GRADED A

Edexcel A-level biology exam questions / Edexcel A Level Biology Question Paper 3 June 2023 (Salters Nuffield) ALREADY 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 why genes found on the sex chromosome pair have a different pattern of inheritance - ANS--X chromosome carries genes not on y -Therefore males only have 1 copy of some genes -If only one inherited then it will be expressed Describe how low serotonin levels can affect transmission of impulses in the brain - ANS--Less neurotransmitter -Less depolarisation -Less chance of action potential occurring in post synaptic membrane 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 - ANS-Human 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 - ANS-It is made from dead material, there is no DNA present Describe how the production and action of interferon differs from lysozyme - ANS-Interferon produced by infected cells to inhibit the replication of viruses, whereas lysozyme present in macrophages to destroy bacteria. 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 why genes found on the sex chromosome pair have a different pattern of inheritance - ANS--X chromosome carries genes not on y -Therefore males only have 1 copy of some genes -If only one inherited then it will be expressed Describe how low serotonin levels can affect transmission of impulses in the brain - ANS--Less neurotransmitter -Less depolarisation -Less chance of action potential occurring in post synaptic membrane 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 - ANS-Human 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 - ANS-It is made from dead material, there is no DNA present Describe how the production and action of interferon differs from lysozyme - ANS-Interferon produced by infected cells to inhibit the replication of viruses, whereas lysozyme present in macrophages to destroy bacteria.