AQA A LEVEL BIOLOGY PAPER 2 MIDTERM EXAM 2025

Air spaces between them = rapid diffusion, long and narrow and are packed with chloroplast the thin tissue of the leaf allows light to reach mesophyll - -name three advantages of mesophyll in the leaf Stroma in the fluid filled matrix - -where does the lir occur? 100 stacked discs of thylakoids - -what is the grana? Chlorophyll absorbs light energy, excite electrons, move along carriers etc releasing energy, used to join adp and pi to form atp, photolysis of water produces protons electrons oxygen, nadp reduced by electrons - -describe the light dependent reaction starting with photolysis Electron is oxidised that reduces nadp, carries out series of redox reactions along the electron transport chain that is then accepted by oxygen that is the terminal electron receptor which oxidises nadph back to nadp - -describe the electron transport chain Contain both dna and rna so proteins can be manufactured quickly, thylakoid membrane has a large sa for rapid df and a network of proteins in the grana to maximise the absorbance of light - -name three advantages of the structure of a chloraplast Co2 combines 5 carbon ribulose-bi-phosphate to make 6 carbon molecule that is then catalysed by rubisco to create two 3 phosphate glycerate molecules that are then reduced via nadp and energy from atp from ldr to triose phosphate that will eventually turn into glucose, nadp reformed and goes back to ldr - -describe the process of the lir Phosphorylated glucose is broken down in two 3 carbon molecules called pyruvate (happens in the matrix mitochondria - -what is glycolysis and where does it happen? Pyruvate is decarboxylated and dehydrogenated to acetate nad is reduced - -what happens in the link reaction after glycolysis? Acetyl coenzyme a combines with oxaloacetate to form citrate which is decarboxylated and dehydrogenated to form 5 carbon molecule which is then dehydrogenated and decarboxylated to form 4 carbon atp made by substrate-level phosphorylation and fad is reduced, oxalacetate is then regenerated to restart the cycle - -what happens in the krebs cycle after the link reaction? AQA A LEVEL BIOLOGY AQA A LEVEL BIOLOGY H+ from oxidized reduced nad and fad, splits into p and e travels down electron transport chain via oxidation-reduction reactions losing energy each carrier used pump p from matrix into intermembrane space creating high concentration forming electrochemical gradient move down into matrix by atp synthase drives synthesis atp chemiosmosis, matriz end transport chain p,e, and o combine form water. O final electron acceptor. - -what is oxidative phosphorylation? Hydrolysed to glycerol that is phosphorylated into into triose phosphate that becomes glucose and thus glycolysis can occur - -how does the respiration of lipids occur? Where no oxygen is available to accept the h+ ion and so reduced nad builds up and cannot take anymore h+ from glyolysis thus pyruvate is now reduced and produces lactate and oxdidised nad and produces ethanol in plants - -what is anaerobic respiration? The dry weight of the total mass of living material in a specific area at a given time - what is biomass? Gross primary production - respiratory losses = the chemical energy left - -what is the calculation for net primary production? And what is it? Total chemical plant biomass - -what is gross primary production? Net production = chemical energy of ingested plants - (energy lost in faeces + energy lost in respiration) - -what is the calculation for net production? Nitrogen from atmosphere is fixed by nitrogen-fixing bacteria to ammonium ions via ammonification, also nitrogen from atmosphere is fixed by mutualistic bacteria to ammonium containing compounds, then fed on by saprobionts that causes ammonification, ammonium ions that undergo nitrification by nitrifying bacteria twice into nitrite and nitrate ions that are then absorbed by producers or lost to the atmosphere - describe the nitrogen cycle Phosphates from rocks are eroded into oceans and running water that is absorbed by plants and excreted into the soil via death that then taken up by water to form new rocks - -describe the phosphorus cycle Algae build up on surface of water due to nitrogen from water that limits light to lower level plants that can no longer photosynthesise and die that are fed on by saprobiants that multiply and take up oxygen in the water so that o2 becomes the limiting factor and larger organsims die as a result that are also fed on by saprobiants that release toxins into the water - -what is eutrophication? Natural = dead decomposing plants and artificial = mined from rocks t provides nutrients to plant - -what is an example of a natural and artificial fertiliser? AQA A LEVEL BIOLOGY AQA A LEVEL BIOLOGY The change of speed of direction in response to a stimulus - -what is kinesis? Response to a stimulus where the direction is determined by the stimulus itself that is moving the entire organism away or towards - -what is taxis? The detectable change in the external or internal environment - -what is a stimulus? Iaa moves down a concentration gradient to the dark side of the shoot that then increases the growth of that side to increase more than that of the light side so the plant curves towards the light (phototrophism) ,in roots however, iaa inhibits growth and so builds up on the underside of the root so the plant can more on the top so that it bends towards gravity (gravitrophsim) - -what is the base movement of iaa in plants and roots? Where the active transport of h+ ions from cytoplasm into the spaces in the cell wall casuing the cell wall to become more plastic - -what is the acid growth hypothesis? Brain and spinal cord - -what does the cns consist of? Provides a voluntary/autonomic nervous system to provide a quick response with a thought process to avoid overloading the brain so that it can carryout other actions at the same time - -what does the pns do? Stimulus - receptor - sensory neurone - coordinator - motor neurone - effector - response - -name the pathway of the detection of a stimulus Chemoreceptors detect change in ph from the increase of co2 in the blood that sends a nerve impulse to the medulla oblongata, nerve impulse sent to san via the sympathetic nervous system that initiates a wave of excitation across the atria, causing it to contract, there is a short delay by non conducting tissue while the ventricles fill and then the avn releases another wave of excitation down the purkinje tissue and bundles of his to the apex of the heart that then contracts from the base up, the more impulse to san = faster contraction of the heart to increase the heart rate, opposite = reduced impulse via parasympathetic - -describe the cardiac cycle with reference to increase heart rate Contraction within the muscle itself - -what does myogenic mean? Pressure in pc is transfixed to chemical energy from mechanical pressure that causes the stretch mediated sodium channels to become distorted and change shape to allow sodium to diffuse down a concentration gradient that causes the opening of more sodium ion channels to open on a neurone that stimulates the depolarisation of an axon as a threshold has been met of the micro voltage - -describe the generating of a action potential via the pacinian corpuscle Receptors in eye that found at the periphery, detect low intensity light, have low visual acuity, can't detect colour and have more than one linking to the same neurone - -what are rods? AQA A LEVEL BIOLOGY AQA A LEVEL BIOLOGY Found in fovea, detects colour, only one connected to the same neurone so multiple colours can be detected, detects high intensity light to produce rhodopsin - -what is a cone? Cell body, dendrons, axon, schwann cell, myelin sheath and nodes of ranvier - -name the six parts of a motor neurone? Transport of hormones via blood plasma to target cells that is more slower and general - -what is the hormonal system? Transport of nervous impulses that is faster and in a more localised region - -what is the nervous system? Has a cell body in the middle of the axon that is a dorsal root ganglian - -what is the distinguishable feature of a sensory neurone? Long axon, cell body at the end, short den-trites - -distinguishable features of a motor neurone? No threshold has been reached by stimulus so sodium potassium pump occurring where 3 molecules of sodium go in and 1 potassium goes out via active transport - describe what is happening in resting potential?