Biology A-Level Questions & Answers

Biology A-Level Questions & Answers abiotic factors - Answer- non-living conditions in a habitat activation energy - Answer- the energy required to initiate a reaction. active site - Answer- area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity. active transport - Answer- movement of particles across a plasma membrane against a concentration gradient. Energy is required. (ATP) adenosine diphosphate (ADP) - Answer- a nucleotide composed of a nitrogenous base (adenine), a pentose sugar and two phosphate groups. Formed by the hydrolysis of ATP, releasing a phosphate ion and energy. adenosine triphosphate (ATP) - Answer- a nucleotide composed of a nitrogenous base (adenine), a pentose sugar and three phosphate groups. The universal energy currency for cells. agglutinins - Answer- chemicals (antibodies) that cause pathogens to clump together so they are easier for phagocytes to engulf and digest.(caused by cross linking by antibodies that have a number of binding sites) alleles - Answer- different versions of the same gene. amino acids - Answer- monomer used to build polypeptides and thus proteins anabolism (anabolic) - Answer- reactions of metabolism that construct molecules from smaller units. These reactions require energy from the hydrolysis of ATP. analogous structures - Answer- structures that have adapted to perform the same function but have a different origin. anaphase - Answer- third stage of mitosis when chromatids are separated to opposite poles of the cell. antibiotic-resistant bacteria - Answer- bacteria that undergo mutation to become resistant to an antibiotic and then survive to increase in number. antibiotics - Answer- a chemical or compound that kills or inhibits the growth of bacteria antibodies - Answer- Y-shaped glycoproteins made by B cells of the immune system in response to the presence of an antigen. antigen - Answer- identifying chemical on the surface of a cell that triggers an immune response antigen−antibody complex - Answer- the complex formed when an antibody binds to an antigen. antigen-presenting cell (APC) - Answer- a cell that displays foreign antigens complexed with major histocompatibility complexes on their surface plasma membranes, so it can be recognised by other cells antisense strand 'lagging strand' - Answer- the strand of DNA that runs 3' to 5' and is complementary to the sense strand. It acts as a template strand during transcription. anti-toxins - Answer- chemicals (antibodies) that bind to toxins produced by pathogens so they no longer have an effect. apoplast - Answer- the cell walls and intercellular spaces of plant cells. apoplast route - Answer- movement of substances through the cell walls and cell spaces by diffusion and into cytoplasm by active transport. arrhythmia - Answer- an abnormal rhythm of the heart. artefacts - Answer- objects or structures seen through a microscope that have been created during the processing of the specimen. artificial active immunity - Answer- immunity which results from exposure to a safe form of a pathogen, for example, by vaccination. artificial passive immunity - Answer- immunity which results from the administration of antibodies from another animal against a dangerous pathogen. asexual reproduction - Answer- the production of genetically identical offspring from a single parent. assimilates - Answer- the products of photosynthesis that are transported around a plant, e.g., sucrose atrial fibrillation - Answer- an abnormal rhythm of the heart when the atria beat very fast and incompletely. atrio-ventricular node (AVN) - Answer- stimulates the ventricles to contract after imposing a slight delay to ensure atrial contraction is complete.