Bioenergetics

• Where does photosynthesis take place?

  Photosynthesis takes place in the leaves, in the palisade mesophyll layer. This layer is close to the top of the leaf, and thus has a high light intensity. Specifically, within cells, photosynthesis takes place in the chloroplasts, which contain chlorophyll - a green pigment necessary for the absorption of light.
• Is photosynthesis an endothermic or exothermic reaction?

  Photosynthesis is an endothermic reaction, since it transfers energy from the environment in the process.
• What is the word equation for photosynthesis?

  Carbon dioxide + water -> glucose + oxygen.

  
  

  Do not include sunlight or chlorophyll.
• What is the symbol equation for photosynthesis?

  The symbol equation for photosynthesis is:

  
  

  6CO2 + 6H2O → C6H12O6 + 6O2

  
  

  Do not include sunlight or chlorophyll.
• Is photosynthesis exothermic or endothermic?

  Photosynthesis is endothermic since energy is transferred from the environment in the process.
• State 5 ways that plants use glucose.


  1) Respiration (aerobic or anaerobic): the breakdown of glucose to release energy.

  2) Making cellulose for cell walls.

  3) Making amino acids when combined with nitrate ions from the soil, which are then made into proteins.

  4) Stored as oils or fats in seeds.

  5) Stored as starch and stored in roots, stems and leaves, ready for use when photosynthesis is not happening (e.g. in the winter or at night).
• Why do plants store energy as starch and not glucose in the long term?


  Starch is insoluble, which makes it better for storing than glucose - a cell with lots of glucose would draw in lots of water and swell up.
• Define limiting factor.


  A limiting factor is a factor that determines the maximum rate of a reaction, even if other factors change to become more favourable.
• What limiting factors can affect the rate of photosynthesis?


  The rate of photosynthesis is affected by light intensity, carbon dioxide concentration, temperature and chlorophyll (e.g tobacco mosaic virus or not enough magnesium).
• Describe how light intensity affects the rate of photosynthesis.

  As the light intensity increases, the rate of photosynthesis will also increase, but only up to a certain point. Beyond that point, the light intensity will no longer affect the rate of photosynthesis, as light intensity will no longer be the limiting factor. To further increase the rate of photosynthesis, the carbon dioxide concentration or temperature would need to be increased.

  
• Describe how carbon dioxide concentration affects the rate of photosynthesis.


  Carbon dioxide is one of the raw materials that are needed for photosynthesis. However, eventually the carbon dioxide concentration will no longer be the limiting factor, and either light intensity or temperature must be increased to further increase the rate of photosynthesis.

  
• Describe how temperature affects the rate of photosynthesis.


  If the temperature is too low, it will be the limiting factor, since the enzymes needed for photosynthesis work more slowly at low temperatures. However, if the plant gets too hot (usually above 45°C), then the enzymes will begin to denature, which will decrease the rate of photosynthesis.

  
• Describe how to use Canadian pondweed to measure the effect of light intensity on the rate of photosynthesis.


  1) Place a source of white light at a specific distance from the pondweed.

  2) Leave the Canadian pondweed to photosynthesise for a specific amount of time. The oxygen released will collect in the capillary tube.

  3) Use the syringe to draw the gas bubble in the tube up alongside a ruler and measure the length of the gas bubble. This will be proportional to the volume of oxygen produced.

  4) Repeat the experiment twice with the light source at the same distance, and calculate the mean volume of oxygen produced.

  5) Repeat the experiment with the light source at different temperatures.

  
• State the variables in the Canadian pondweed experiment.


  In the Canadian pondweed experiment:

  
  

  Control variables = temperature, time provided for the pondweed to photosynthesise.

  
  

  Independent variable = distance of light source from the pondweed.

  
  

  Dependent variable = volume of oxygen produced.
• How could the Canadian pondweed experiment be altered to measure the effect of temperature or carbon dioxide on photosynthesis?

  In order to investigate the effect of temperature on the rate of photosynthesis, the plant could be placed in a water bath at different temperatures.

  
  

  In order to investigate the effect of carbon dioxide on the rate of photosynthesis, the plant could be placed in a solution of water and sodium hydrogencarbonate, which emits carbon dioxide.
• In the Canadian pondweed experiment, explain why distance cannot be placed on a graph against the volume of oxygen produced, instead of light intensity.


  In the Canadian pondweed experiment, when the lamp is moved away from the pondweed, the light intensity decreases. Therefore, the distance of the light source from the plant is inversely proportional to the light intensity.
• State the inverse square law.


  The inverse square law states that the intensity of radiation (including light) at a given distance from the point source is inversely proportional to the square of the distance.
• What are the units for light intensity, using the inverse square law?


  When the inverse square law, the answer must be given using arbitrary units (a.u.)
• How can you artificially create the ideal conditions for farming?


  The ideal conditions for farming can artificially be created by growing plants in a greenhouse. This works because greenhouses ensure that temperature never becomes a limiting factor for photosynthesis by trapping the heat of the Sun. The level of heat can also be altered by using a heater or shades and ventilation. Moreover, commercial farmers often supply artificial light after the Sun goes down to ensure that plants are still photosynthesising and growing during the night, as well as the day. In addition, farmers and gardeners can also increase the level of carbon dioxide in a greenhouse by using a paraffin heater to heat the greenhouse, as it produces carbon dioxide as a by-product. Also, keeping plants enclosed in a greenhouse also makes it easier to keep them free from pests and diseases. Finally, farmers can also add fertilisers to the soil as well, to provide all the minerals needed for healthy growth.
• What is the difference between respiration, breathing and ventilation?


  Ventilation is the act of oxygen moving in and out of lungs by a mechanical force.

  
  

  Breathing is the exchange of oxygen and carbon dioxide by taking breaths.

  
  

  Respiration is the process of transferring energy from glucose, which occurs in every cell.
• Do plants respire?


  Yes, plants respire, but during the day, the respiration is masked by a higher rate of photosynthesis.
• Is respiration endothermic or exothermic?

  Respiration is exothermic, as it transfers energy to the environment.
• State 3 ways in which organisms use the energy transferred by respiration.

  Organisms can use the energy transferred from respiration to build larger molecules from smaller ones (e.g. proteins from amino acids), to allow muscles to contract in animals, and to keep body temperature warm in mammals and birds.
• Define metabolism.


  Metabolism is all the chemical processes and reactions that occur within a living organism in order to maintain life.
• Give three examples of reactions wherein larger molecules are made from smaller ones.


  Examples of reactions wherein larger molecules are made from smaller ones include:

  
  

  1) The construction of starch, glycogen and cellulose from glucose molecules.

  2) The construction of lipid molecules from one molecule of glycerol and three fatty acids.

  3) The construction of proteins from amino acids, which in turn have been constructed from the combination of glucose and nitrate ions.See an expert-written answer!We have an expert-written solution to this problem!
• Give two examples of reactions wherein smaller molecules are formed from larger ones.


  Examples of reactions wherein smaller molecules are formed from larger ones include:

  
  

  1) The breakdown of glucose in respiration (alongside oxygen) to form water and carbon dioxide molecules.

  2) The breakdown of protein to produce urea.
• Define aerobic respiration.


  Aerobic respiration is the complete breakdown of glucose to form water and carbon dioxide. It is the most efficient way to transfer energy from glucose.
• Where does aerobic respiration take place?

  Aerobic respiration takes place in the mitochondria of the cell.
• What is the symbol equation for aerobic respiration?

  The symbol equation for aerobic respiration is:

  
  

  C6H12O6 + 6O2 -> 6CO2 + 6H2O
• What is the word equation for aerobic respiration?


  The word equation for aerobic respiration is:

  
  

  glucose + oxygen -> carbon dioxide + water

  
  

  Do not include energy.
• Define anaerobic respiration.


  Anaerobic respiration is the incomplete breakdown of glucose to form lactic acid. It does not use oxygen, which means that the glucose is not fully oxidised. Therefore, it is not as efficient at transferring energy from glucose as aerobic respiration.
• Where does anaerobic respiration take place?

  Anaerobic respiration takes place in the cytoplasm of the cell.
• When is anaerobic respiration used?


  Anaerobic respiration is used when there is not enough oxygen available, during emergencies such as exercise.
• Give the word equation for anaerobic respiration in muscle cells in animals.


  The word equation for anaerobic respiration in muscle cells in animals is:

  
  

  glucose -> lactic acid

  
  

  Do not include energy.
• Give the symbol equation for anaerobic respiration in muscle cells in animals.


  The word equation for anaerobic respiration in muscle cells in animals is:

  
  

  C6H12O6 -> 2C3H6O3

  
  

  Do not include energy.
• Give the word equation for anaerobic respiration in plants and yeast.


  The word equation for anaerobic respiration in plants and yeast is:

  
  

  glucose -> ethanol + carbon dioxide

  
  

  Do not include energy.
• Give the symbol equation for anaerobic respiration in plants and yeast.


  The symbol equation for anaerobic respiration in plants and yeast is:

  
  

  C6H12O6 -> 2C2H5OH + 2CO2

  
  

  Do not include energy.
• In yeast cells, what is anaerobic respiration called?


  In yeast cells, anaerobic respiration is known as fermentation.
• How can fermentation be useful?


  Fermentation has many uses. For example, fermentation is used in the food and drinks industry to make bread and alcoholic drinks, such as beer and wine. In bread making, the carbon dioxide from fermentation makes bread rise, and in beer- and wine-making, the fermentation process produces alcohol.
• What are the disadvantages of anaerobic respiration?


  The disadvantages of anaerobic respiration include that it is not a very efficient way to transfer the energy from glucose (i.e. it produces a relatively small amount of energy compared to aerobic respiration).

  
  

  Furthermore, anaerobic respiration creates lactic acid, which is poisonous and can cause cramps.