Bioenergetics

• Photosynthesis uses energy to change carbon dioxide and water into glucose and oxygen


  it takes place in chloroplasts, which contain green pigments called chlorophyll that can absorb light

  photosynthesis is endothermic, which means energy is transferred from the environment
• carbon dioxide + water -(light)- glucose + oxygen


  6CO2 + 6H2O -(LIGHT)- C6H12O6 + 6O2
• plants use glucose in five main ways


  -respiration

  -making cellulose

  -making amino acids

  -stored as oils or fats

  -stored as starch
• plants use glucose for respiration


  this transfers energy from glucose which enables the plant to convert the rest of the glucose into other useful substances
• plants use glucose for making cellulose


  glucose is converted into cellulose for making strong plant cell walls
• plants use glucose for making amino acids


  glucose is combined with nitrate ions to make amino acids, which are then made into proteins
• plants store glucose as oils and fats


  glucose is turned into lipids for storing in seeds
• plants store glucose at starch


  glucose is turned into starch and stored in roots, stems, and leaves, ready for use when photosynthesis isn't happening

  starch is insoluble which makes it better for storing than glucose, a cell with lots of glucose would draw in more water and swell up
• limiting factors affect the rate of photosynthesis


  -light

  -temperature

  -co2 concentration

  -chlorophyll
• not enough light slows down the rate of photosynthesis


  light provides the light needed for photosynthesis

  as the light level is raised, photosynthesis increases steadily but only up to a certain point

  as light intensity increases, the rate will no longer increases because it is being limited by another factor
• too little carbon dioxide slows down photosynthesis


  co2 is one of the materials needed for photosynthesis

  the amount of co2 will only increase the rate of photosynthesis up to a point

  after this the graph will plateau because another factor is limiting the rate of photosynthesis
• the temperature has to be just right


  temperature affects the rate of photosynthesis because it affects the enzymes involved

  enzymes needed for photosynthesis work more slowly at low temperatures

  if the plant gets too hot, the enzymes will be damaged and denature

  this happens at about 45C
• measuring the rate of photosynthesis RP


  pondweed can be used to measure the effect of light intensity on the rate of photosynthesis

  a source of white light is set at a distance from the pondweed

  the pond weed is left to photosynthesise for a 1min- count the bubbled produced

  change the distance of the light source and repeat

  repeat for valid results
• a test tube of pondweed can be put in a water bath- effect of temperature


  a measured amount of sodium hydrogencarbonate can be dissolved in the water which gives off co2
• the inverse square law links light intensity and distance


  as distance increases, light intensity decreases- inversely proportional
• greenhouses create ideal conditions for farming


  -temperature

  -light

  -co2

  -free from diseases
• greenhouses trap the sun's heat


  this ensures the temperature doesn't become limiting

  in winter a heater may be used to heat the greenhouse up while in summer shades and ventilation to cool things down
• greenhouses keep the light intensity high


  often artificial light is supplied after the sun goes down to ensure the plant can continue to photosynthesise
• greenhouses increase the levels of co2


  a paraffin heater can be used to heat the greenhouse, which releases co2 as a by-product
• keeping plants enclosed reduces disease in a greenhouse


  pests can be trapped reducing the diseases plant get

  fertilisers can be added to the soil easily, to ensure the plant has the minerals needed for growth
• greenhouses cost money


  if the conditions are kept just right, plants will grow faster and a decent crop can be harvested more often, which can be sold

  it is important the farmer supplies the right amount of heat/light, enough to make the plants grow well but not more than the plants need, as this would waste money
• respiration involves many reactions


  respiration is NOT breathing in and out

  respiration is the process of transferring energy from the breakdown of glucose, which goes on in every cell

  all living things respire

  respiration is exothermic- it transfers energy to the environment
• respirations transfers energy for lots of things


  -to build up larger molecule from smaller ones

  -in animals- to allow the muscles to contract

  -in mammals and birds- to keep the body temperature constant in cold surroundings
• metabolism is ALL the chemical reactions in an organism


  in a cell there are lots of chemical reactions happening all the time, controlled by enzymes- many link together to form bigger reactions

  in some larger molecules are made from smaller ones, larger molecules are broken down into smaller ones

  METABOLISM IS THE SUM OF ALL REACTIONS THAT HAPPEN IN A CELL/BODY
• Larger molecules can be made from smaller ones


  lots of small glucose molecules are joined together in reaction to from starch, glycogen, and cellulose

  lipid molecules are made from ONE molecule of glycerol and THREE fatty acids

  glucose is combined with nitrate ions to make amino acids, which are then made into proteins
• larger molecules can be broken down into smaller ones

  glucose is broken down in respiration, respirations transfers energy to power all the reactions in the body that make molecules

  excess protein is broken down in a reaction to produce urea, urea is excreted in urine
• aerobic respiration 


  aerobic respiration takes place in the presence of oxygen- it is the most efficient way of transferring energy from glucose

  most of the aerobic respiration reactions happen in the mitochondria
• glucose + oxygen - carbon dioxide + water


  C6H12O6 + 6O2 - 6CO2 + 6H20
• Anaerobic respiration

  takes place in the absence of oxygen- incomplete breakdown of glucose, making lactic acid

  anaerobic respiration does not transfer as much energy as aerobic respiration, because glucose isn't fully oxidised
• glucose - lactic acid

  glucose - ethanol + carbon dioxide
• plant and yeast cells can respire without oxygen but produce ethanol and carbon dioxide


  anaerobic respiration in yeast cells is fermentation

  fermentation is used to make bread and alcoholic drinks

  in bread- the carbon dioxide makes the bread rise

  in alcoholic drinks (beer + wine)- the fermentation produces alcohol
• muscles need energy from respiration to contract


  when exercising, the muscles are contracting more frequently and so need more energy from respiration

  the increase in respiration increases the demand for oxygen
• during exercise, minute ventilation and heart rate increases


  minute ventilation increases to get more oxygen into the blood

  heart rate increases to pump more blood around the body faster
• when doing vigorous exercise, the body cannot supply oxygen to the muscles fast enough


  this means anaerobic respiration takes place

  this is not the best way to produce energy as lactic acid is produced, which causes a painful burning sensation in the muscles

  long periods of exercise also cause muscle fatigue- the muscles get tired and stop contracting efficiently
• anaerobic respiration creates an oxygen debt


  anaerobic respiration produces lactic acid

  lactic acid needs to be broken down by oxygen which means that after exercise there is still a high demand for oxygen in order to remove lactic acid from the cells

  blood can also transport lactic acid to the liver, where it is converted back into glucose
• the effect of exercise on the body can be investigated


  you can measure breathing rate by counting breaths, and heart rate by taking a pulse

  you could take your pulse after, sitting, walking, jogging, and running for five minutes

  you pulse rate will need to increase more, the more vigorous the exercise as there will be a higher demand for oxygen