Excel A-level biology exam with 100% Approved solutions

Describe the events of fertilization that occur after the acrosome reaction. - -Membrane of sperm and egg cell fuse together -cortical granules release contents into zona pellucid -Zona pellucid thickens -Haploid nuclei fuse Explain how phospholipids form a cell surface membrane - -Hydrophilic parts associate with water -Hydrophobic parts repel water -a bilayer forms with hydrophobic parts pointing in towards the center of the bilayer Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency - -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 organized in a bacterial cell - -Circular DNA that is not associated with histones -Plasmids -located in the cytoplasm Describe the light-dependent reactions of photosynthesis - -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 - - Drop in body temperature is linked to time after death -Factors affect it (egg. 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 - -Body decomposes in a specific sequence -Factors affect it (egg. environmental temperature, wounds) -Not useful if body has fully decomposed Why can human DNA polymerase not be used in PCR - 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 - It is made from dead material, there is no DNA present Describe how the production and action of interferon differs from lysozyme - Interferon 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 - -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 - -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 edema Suggest why reducing inflammation could help reduce a patient's immune response - -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 - -Increased concentrations of fibrinogen leads to increased fibrin -Increases the risk of blood clotti