Biology - Bioenergetics
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Eton Academy**We aren't endorsed by this school
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BIOLOGY LEVEL
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Biology
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Jan 6, 2025
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27
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Head to savemyexams.co.uk for more awesome resourcesPage 1 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersGCSE Biology AQA4. BioenergeticsCONTENTS4.1 Photosynthesis4.1.1 Photosynthetic Reaction4.1.2 Rate of Photosynthesis4.1.3 Interactions of Limiting Factors4.1.4 Required Practical: Photosynthesis Rate4.1.5 Uses of Glucose from Photosynthesis4.2 Respiration4.2.1 Aerobic & Anaerobic Respiration4.2.2 Response to Exercise4.2.3 MetabolismYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 2 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersPhotosynthesisPlants are autotrophs– this means that they can make their own food using light,water and carbon dioxideThis is why they are called producersin food chainsPhotosynthesis is an endothermic reaction in which energy is transferred from theenvironment to the chloroplasts by lightThe leaves of the plant are where most photosynthesis takes place, in specialisedmesophyll cells which are packed with chloroplasts containing chlorophyll toabsorb as much light energy as possibleThe sugars produced by photosynthesis are used to make all the substances a plantneeds, as well as being used in respiration to release energyThese reactions can be summarised into a simple equationWord equation for photosynthesisBalanced symbol equation for photosynthesisThe reactants for photosynthesis are obtained by a plant as follows:4.1 Photosynthesis4.1.1 Photosynthetic ReactionYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 3 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersPlants obtain the materials they need for photosynthesis from the environmentPhotosynthesis is essential for the majority of all food chains on Earth, solearning the equation above is essential!YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 4 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersFactors that Affect PhotosynthesisIn order to photosynthesise a plant needs light, water and carbon dioxideThe availability of light and carbon dioxide can affect how much and how quickly (therate) photosynthesis occursAlthough water is necessary for photosynthesis, it is not considered a limitingfactoras the amount needed is relatively small compared to the amount of watertranspired from a plant so there is hardly ever a situation where there is notenough water for photosynthesisOther environmental factors such as temperature and the amount of chlorophyll in thechloroplasts can also affect the rateof photosynthesisThe temperature of the environment affects how much kinetic energyall particleshave – so temperature affects the speed at which carbon dioxide and water movethrough a plantThe lower the temperature, the less kinetic energy particles have, resulting in fewersuccessful collisionsoccurring over a period of timeIncreasing temperature increases the kinetic energy of particles, increasing thelikelihood of collisions between reactants and enzymes which results in the formationof productsAt higher temperatures, however, enzymes that control the processes ofphotosynthesis can be denatured(where the active site changes shape and is nolonger complementary to its substrate) – this reduces the overall rate4.1.2 Rate of PhotosynthesisYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 5 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersGraph showing the effect of temperature on the rate of photosynthesisThe intensityof the light available to the plant will depend on the amount of energythat it has to carry out photosynthesisThe morelighta plant receives, the fasterthe rate of photosynthesisThis trend will continue until some other factor required for photosynthesis preventsthe rate from increasing further because it is now in short supplyYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 6 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersGraph showing the effect of light intensity on the rate of photosynthesisAt low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At acertain point, increasing the light intensity stops increasing the rate. The rate becomes constantregardless of how much light intensity increases as something else is limiting the rate.Carbon dioxide is one of the raw materials required for photosynthesisThis means the more carbon dioxidethat is present, the faster the reactioncan occurThis trend will continue until some other factor required for photosynthesis preventsthe rate from increasing further because it is now in short supplyYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 7 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersA graph showing the effect of the concentration of carbon dioxide on the rate ofphotosynthesisThe number of chloroplasts(as they contain the pigment chlorophyll which absorbslight energy for photosynthesis) will affect the rate of photosynthesisThe more chloroplasts a plant has, the faster the rate of photosynthesisThe amount of chlorophyll can be affected by:diseases (such as tobacco mosaic virus)lack of nutrients (such as magnesium)loss of leaves (fewer leaves means fewer chloroplasts)Make sure you know that the effect of low temperature is a reduced rate ofcollisions occurring, and the effect of high temperatures is that enzymesdenature.YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 8 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersInteractions of Limiting FactorsMore than one limiting factor can have an effect on the rate of photosynthesisGraphs may show the effect of two factors interacting:The rate of photosynthesis increases with increasing light intensity, temperature andcarbon dioxideAt the start of the graph, the rate of photosynthesis is limited by the light intensity so both linesare showing the same rate.As the light intensity increases the rate of photosynthesis at 15℃is lower than 25℃.Both lines level off, this shows that light intensity is no longer the limiting factor.Graphs may show the interactions between three different factors, the graph belowshows the relationship between temperature, carbon dioxide as light intensity isincreased:4.1.3 Interactions of Limiting FactorsYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 9 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersThe rate of photosynthesis increases with increasing light intensity, temperature andcarbon dioxideAll three experiments level off when light intensity is no longer the limiting factor.In the top line, this has the highest temperature and concentration of carbon dioxide so the rate ofphotosynthesis is much higher.In experiment 2, the concentration of carbon dioxide is the limiting factor.In this graph, the rate of photosynthesis is controlled by carbon dioxide levels.YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 10 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersLight IntensityTheinverse square lawshows the relationship between light intensity and distance.As the distance increases the light intensity decreases. This means that they areinversely proportionalto each otherLight intensity and distance are inversely proportional to each otherThis means that as the distance doubles you decrease the intensity of the light will befour times lessThis is called the inverse square lawand shown by the equation below:Calculate the light intensity when the distance of the plant is 30cm from the lamp1. Use the equation:Light intensity = 1/d2. Fill in the values you know:Light intensity = 1/303. Calculate the light intensity:Light intensity = 0.001 auRemember that ‘au’ stands for arbitrary units.22YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 11 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersGrowing in a GreenhouseCommercial horticulturistswill grow their plants in a greenhouseThis means that they are able to controlas many of the limiting factors ofphotosynthesis as possibleLimiting factors are important in the economics of enhancing the conditions ingreenhouses to gain the maximum rate of photosynthesis while still maintaining profitKeeping plants in a greenhouse has associated costs, but the increased yield of thecrop and fact that the crop can be harvested more frequently, means that thefarmer will make more moneyThe levels of heat, light, water, carbon dioxide and nutrients are carefully controlled soonly the smallest amounts needed are used so that farmers are not wasting moneyEg. spending money on increasing the concentration of carbon dioxide beyond apoint when some other factor limits the rate of photosynthesis is a wasteThe farmers can increase yield in a greenhouse but this does have an increased costYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 12 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersYou should be able to use data in the exam to relate limiting factors to the cost-effectiveness of adding heat, light or carbon dioxide to greenhouses.Rememberthat spending money on increasing a factor above the point at which it has aneffect on the rate of photosynthesis will be a waste of money.YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 13 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersInvestigating PhotosynthesisAim: Investigate the effect of light intensity on the rate of photosynthesis using anaquatic organism such as pondweedYou will:measure the volume of oxygen produced by the pondweed as the light intensitychanges as the light source is movedmeasure and calculate rates of photosynthesisextract and interpret graphs of photosynthesis rate involving one limiting factorThe most commonly used method to measure the rate of photosynthesis is to measureor observe the oxygen released from aquatic plantsDiagram showing the setup for the investigation using aquatic plantsPlace a piece of pondweed (Elodeaor Cabombaare often used), into a beaker of waterUse a light a set distance from the plantRecord the number of bubbles observed in three minutesRepeat steps for different distancesUse a gas syringe to collect the volume of gas produced4.1.4 Required Practical: Photosynthesis RateYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 14 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersRepeat the experiment at least twice for each distance and calculate the mean numberof bubblesUse of a glass tank between lamp and plant to prevent heating of the plant, or using anLED bulb that releases very little heat energyDifferent variables can be investigated using this method. The three diagrams showthe setup for 3 independent variables: light, carbon dioxide and temperatureA graph of the independent variable used against the number of bubbles produced perminute can be drawn to see the pattern or trendA graph of distance from the lamp against number of bubbles per minuteYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 15 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersUses of GlucoseThe glucoseproduced in photosynthesis may be:Used for respiration(both aerobic and anaerobic)Converted into insoluble starchfor storage in the stems, leaves and rootsUsed to produce fator oilfor storage (especially in seeds)Used to produce cellulose, which strengthens the cell wallCombined with nitrate ions absorbed from the soil to produce amino acids forprotein synthesisThe fate of glucoseA test to show that a plant is photosynthesising is to test the leaf for the presence ofstarch using iodine4.1.5 Uses of Glucose from PhotosynthesisYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 16 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersThis can be used to show the effect of light on photosynthesisYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 17 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersStarch testing of leaves shows that photosynthesis has been taking placeRemember that plants always respire to release energy – but they onlyphotosynthesise during the day if conditions are right.YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 18 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersRespiration: PrinciplesCellular respiration is an exothermic reactionwhich is continuously occurring in livingcellsThe chemical process of cellular respiration releases energyThe energy transferred supplies all the energy needed for living processes to occurwithin cells and organisms as a wholeOrganisms need energy for:Chemical reactionsto build larger molecules from smaller moleculesMuscle contractionto allow movementKeeping warm(to maintain a constant temperature suitable for enzyme activity)Uses of the energy released from respiration4.2 Respiration4.2.1 Aerobic & Anaerobic RespirationYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 19 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersAerobic RespirationRespiration in cells can take place aerobically(using oxygen) to transfer energy;glucose is reacted with oxygen in this processThe equations that summarise the chemical reactions of respiration that releaseenergy from glucose are:Word equation for aerobic respirationBalanced symbol equation for aerobic respirationAerobic respiration uses oxygen and most of the reaction takes place in themitochondria(these are shown above the arrow in the equations)YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 20 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersAnaerobic Respiration in AnimalsRespiration in cells can take place anaerobically (without oxygen), to transfer energy; itsimply involves the incomplete breakdown of glucose into lactic acidThis occurs when the body can’t supply enough oxygen for aerobic respiration, such asduring vigorous exerciseAnaerobic respiration is represented by the equation:Word equation for anaerobic respiration in animals – some bacterial cells respire in thisway tooAs the oxidation of glucose is incomplete in anaerobic respiration much less energy istransferred than in aerobic respirationAnaerobic respiration takes place without the need of oxygenYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 21 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersAnaerobic Respiration in Plants & YeastPlants and yeast can respire without oxygen as well, breaking down glucose in theabsence of oxygen to produce ethanol and carbon dioxideAnaerobic respiration in yeast cells is called fermentationFermentation is economically important in the manufacture of bread (where theproduction of carbon dioxide makes dough rise) and alcoholic drinks (as ethanol is atype of alcohol)The process outlined above is the same in plantsYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 22 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersComparing Anaerobic & Aerobic RespirationYou need to be able to compare the processes of aerobic and anaerobic respirationwith regard to the need for oxygen, the differing products and the relative amounts ofenergy transferred:Remember that cellular respiration is not breathing; it is a chemical process oftransferring energy from glucose in all living cells.YOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 23 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersEffect of ExerciseIn order for an individual to be able to move, their muscles need to contract, whichrequires energy from respirationWhen exercising, the number of muscle contractions increases, therefore there is agreater energy demand, which means that the muscles need a greater supply ofoxygen for aerobic respirationThe human body reacts to the increased demand for oxygen in a number of ways:The breathing rate and breath volume increase during exercise to increase theamount of oxygen absorbed into the bloodstream by diffusion, and the amount ofcarbon dioxide removedThe heart rate increasesThese reactions increase the supply of oxygenated blood to the musclesIf exercising vigorously, the body may not be able to supply sufficient oxygen to themuscles to meet the demand for energyIn this situation, some of the energy supplied to the muscles comes from anaerobicrespiration, which is the incomplete breakdown of glucose without oxygenThis releases much less energy than aerobic respiration and results in the formation oflactic acidas glucose is incompletely oxidisedAn “oxygen debt” is created after exercising in this way; it is a debt as “extra” oxygen isneeded to react with the lactic acid produced via anaerobic respirationThis is why an individual still breathes heavily at an increased rate (with a higher heartrate than usual) after exercising vigorously“Extra” carbon dioxide also has to be removed from the bodyDuring long periods of vigorous activity, muscles become fatigued and stop contractingefficiently as a result of increased levels of lactic acid building upIt is relatively simple to investigate the effects of exercise on the body in the classroomBreathing rate can be measured by counting the number of breaths per minute, whileheart rate can be measured by taking a pulseEither can be measured before and after an activity is performed and the resultsplotted on a bar chartIt is important that the time over which breathing rate and pulse rate aremeasured is consistent, and that individuals fully recover (rest) before starting anew activity4.2.2 Response to ExerciseYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 24 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersOxygen DebtThe body can deal with lactic acid in one of two waysIt can be oxidised (reacted with oxygen) to form carbon dioxide and water – the sameproducts formed in aerobic respirationAlternatively, blood flowing through the muscles transports the lactic acid to the liverwhere it is converted back into glucoseRemember the “oxygen debt” is the amount of extra oxygen the body needs afterexercise to react with the accumulated lactic acid and remove it from the cellsYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 25 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersMetabolism: BasicsMetabolism is thesum of all the reactionsin a cell or the body – these reactionshappen all of the timeThe energy transferred by respiration in cells is used by the organism for the continualenzyme controlled processes of metabolism that synthesise new moleculesEnzymes control all of the reactions occurring in cells; often the products of onereaction are the reactants for another (and so on)4.2.3 MetabolismYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 26 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersMetabolic SubstratesThe products of digestion are used to build substances, and some of these are then brokendown – this is metabolismYOUR NOTES
Head to savemyexams.co.uk for more awesome resourcesPage 27 of 27© 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past PapersYou should be able to explain the importance of sugars, amino acids, fatty acidsand glycerol in the synthesis and breakdown of carbohydrates, proteins andlipids.Use of MetabolitesMetabolism includes:Conversion of glucoseto cellulose in plants to build and strengthen cell wallsConversion of glucoseinto glycogenin animals and starchin plants for storageThe formation of lipidmolecules from a molecule of glyceroland three moleculesof fatty acidsto form triglycerides which are used for energy storage and asinsulation in animalsIn plants: the use of glucoseand nitrateions to form aminoacidswhich in turnare used to synthesise proteins required by cells (such as enzymes)Glucoseis broken down in the process of respirationto release energyin all cellsIn animals, the breakdown of excessproteinsto form ureafor excretionAll of the features of metabolism listed are covered in more detail in the relevanttopics but you should be aware of how they all link together here.YOUR NOTES