B4 - Bioenergetics

  • Created by: Benny52
  • Created on: 21-02-19 13:40

Photosynthesis & Limiting Factors

  • Occurs in chloroplasts in green plant cells - contain pigments - chlorophyll, etc. - absorb light. Energy transferred to chloroplasts from environment by light. Photosynthesis - endothermic - energy transferred from environment.
  • Carbon Dioxide + Water --> Glucose + Oxygen - 6CO2 + 6H2O --> C6H12O6 + 6O2
  • Plant use glucose for:
    • Respiration - transfers energy from glucose, enabling plant to convert rest into other useful substances.
    • Making cellulose - for making strong plant cell walls.
    • Making amino acids - then made into proteins.
    • Stored as oils or fats - for storing in seeds.
    • Stored as starch - stored in roots, stems & leaves for use when photosynthesis isn't happening - winter. Starch - insoluble - better for storing than glucose - cell with lots of glucose would draw in lots of water & swell up.
  • Rate of photosynthesis affected by light, CO2 concentration & temp. Any can become limiting factor - stopping photosynthesis happening faster. Which factor is limiting depends on environmmental conditions - night - light. Winter - temperature. Warm & bright enought - CO2. Chlorophyll - also limiting factor - amount can be affected by disease or environmental stress - lack of nutrients, etc. Cause chloroplasts to be damaged or not make enough chlorophyll - rate of photosynthesis reduced as plant can't absorb much light.
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The Rate of Photosynthesis

  • As light level increases, rate of photosynthesis increases steadily but only to certain point. Beyond - no difference - temp. or CO2 limiting factor.
  • Amount of CO2 only increases rate of photosynthesis to a point. Graph then flattens out - CO2 no longer limiting factor.
  • If temperature is limiting factor, it's usually because it's too low - enzymes needed for photosynthesis work slower at low temps. If plant gets too hot, enzymes needed - damaged. Usually at 45 degrees celsius.
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The Rate of Photosynthesis 2

  • As distance increases from light source, light intensity decreases. Distance & light intensity inversely proportional. Inverse square law = light intensity inversely proportional to the square of the distance.
  • Most common way to artificially create ideal environment for plant growth is to grow them in greenhouse - help to trap sun's heat - ensures temperature doesn't become limiting. Winter - heater used to keep temperature at ideal level. Summer - too hot - shades & ventilation used to cool things down.
  • Artificial light often supplied after sunset - more quality photosynthesis time for plants.
  • CO2 level can be increased - e.g. paraffin heater - heats greenhouse, and as paraffin burns, CO2 is made.
  • Plants enclosed in greenhouse makes it easier to keep them pest & disease free. Fertilisers added to soil to provide all minerals needed.
  • Expensive to set up greenhouse, but if conditions kept right for photosynthesis, plants grow faster and high yield can be harvested more often & sold. Important that right amount of conditons are supplied, but not too much - waste of money.
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Respiration & Metabolism

  • Respiration = the process of transferring energy from glucose, which goes in every cell. Exothermic - transfers energy to environment.
  • How oragnsism use energy:
    • To build up larger molecules from smaller ones.
    • To allow muscles to contract in animals.
    • To keep body temperature steady in colder environments in mammals & birds.
  • Metabolism = All the chemical reactions in an organism. In a cell - lots of chemical reactions happening constantly - controlled by enzymes. Reactions linked together to form bigger reactions: Reactant --> (enzyme) Product --> Product --> Product. In some of these reactions, larger molecules made from smaller ones:
    • Lots of glucose molecules joined together to form starch, glycogen & cellulose.
    • Lipid molecules made from one molecule of glycerol & 3 fatty acids.
    • Glucose combined with nitrate ions to make amino acids, then made into proteins.
  • Other reactions - larger molecules broken down into smaller ones:
    • Glucose broken down by respiration.
    • Excess protein broken down to produce urea - excreted in urine.
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Aerobic & Anaerobic Respiration

  • Aerobic - using O2. Most efficient way to transfer energy from glucose. Constant. Most aerobic respiration reactions happens in mitochondria.
  • Glucose + Oxygen --> Carbon Dioxide + Water   C6H12O6 + 6O2 --> 6CO2 + 6H2O
  • Vigorous exercise - body can't supply enough O2 to muscles - anaerobic + aerobic. Anaerobic - incomplete breakdown of glucose, making lactic acid. Doesn't transfer as much energy as aerobic - glucose isn't fully oxidised. Only used in emergencies.
  • Glucose --> Lactic Acid.
  • Plants & yeast cells - anaerobic respiration produces ethanol & CO2
  • Glucose --> Ethanol + Carbon Dioxide
  • Anaerobic respiration in yeast cells - fermentation - uesd to make bread - CO2 makes bread rise - and alcoholic drinks - process produces alcohol.
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  • Exercise - some muscles contract more frequently - need more energy - increased respiration - need more O2. Breathing rate & breath volume increase and heart rate increases to pump oxygenated blood round body faster. Also removes CO2 faster. 
  • Vigorous exercise - anaerobic respiration - lactic acid builds up in muscles - painful. Long periods of exercise - muscle fatigue - stop contracting efficiently.
  • Anaerobic respiration leads to oxygen debt - amount of extra O2 body needs to react with build up of lactic acid & remove it from cells. Forms CO2 & H2O. Need to keep breathing hard for while after stopping exercise to get more O2 into blood to muscle cells. Pulse & breathing rate stay high whilst there are high levels of lactic acid & CO2
  • Blood entering muscles also transports lactic acid to liver - converted back to glucose.
  • Can measure breathing rate by counting breaths, & heart rate by taking pulse.
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