Bioenergetics

• What do plants use as their source of energy

  Plants use light from the sun as their source of energy, in order to grow
• What is photosynthesis


  Photosynthesis is the process of converting light energy into glucose using carbon dioxide and water, releasing a byproduct of oxygen
• Where does photosynthesis take place & Why

  It takes place in the green chemical chlorophyll, inside the leaves because chlorophyll can absorb light energy
• Explain the process of photosynthesis


  1. The plant takes in carbon dioxide, which diffuses through the air into the leaves via the stomata and water which diffuses from the soil into the root hair cells by osmosis
  2. Light energy is then absorbed by chlorophyll
  3. The light energy is then used to convert the carbon dioxide and water (which are chemically reacted using light energy) into glucose, producing a byproduct of oxygen
• Explain how light intensity effects the rate of photosynthesis & what it tells us

  The more light intensity, the faster the rate of photosynthesis. However, if the rate of photosynthesis is increasing with the light intensity, it tells us that the light intensity is a limiting factor. This is because the rate of photosynthesis increasing means there wasn't enough light intensity before. Furthermore, once the rate of photosynthesis stops increasing with the light intensity, it tell us that light intensity is no longer the limiting factor, as it is no longer effecting the rate of photosynthesis
• Explain how carbon dioxide effects the rate of photosynthesis & what it tells us

  The more carbon dioxide, the faster the rate of photosynthesis. However, if the rate of photosynthesis is increasing with the carbon dioxide, it tells us that the carbon dioxide is a limiting factor. This is because the rate of photosynthesis increasing means there wasn't enough carbon dioxide before. Furthermore, once the rate of photosynthesis stops increasing with the carbon dioxide, it tell us that carbon dioxide is no longer the limiting factor, as it is no longer effecting the rate of photosynthesis
• What factors effect the rate of photosynthesis

  1. The amount of chlorophyll in the leaf
  2. The temperature
  3. The light intensity
  4. The amount of carbon dioxide in the air
• Explain how the amount of chlorophyll effects the rate of photosynthesis

  Chlorophyll absorbs light energy, thus the more chlorophyll, the faster the rate of photosynthesis, as light is needed to convert carbon dioxide & water into glucose.
• Explain how temperature effects the rate of photosynthesis

  Increasing the temperature causes the enzymes involved in photosynthesis to work faster, thus increasing the rate of photosynthesis. However, if the temperature gets to high, enzymes may denature, causing the rate of photosynthesis to fall
• Where does respiration take place

  Respiration takes place continually in all living cells but more specifically in the mitochondria
• What are the uses of glucose from reactions in metabolism

  1. Energy released from glucose is used to respire
  2. Glucose can be used to produce insoluble storage molecule starch, which can be converted back to glucose by plants when they need to respire at night & cannot photosynthesise for glucose
  3. Glucose is converted to (glycogen) fats and oil as storage form of glucose, which can release energy (animals only)
  4. Glucose makes cellulose, which give plant's cell walls strength
  5. Glucose produces amino acids, which react with nitrate ions absorbed from the soil to synthesise (produce) proteins in plants
• Describe the steps of investigating the effect of light intensity on the rate of photosynthesis (step 1-5)

  1. Place a boiling tube 10 cm away from a LED light (use a ruler to measure the distance)
  2. If your using a light bulb instead of a LED light, then place a water filled beaker between the light bulb and the boiling tube to absorb the heat
  3. Fill the boiling tube with sodium hydrogen carbonate solution
  4. place a pondweed in the boiling tube with the cut end facing up
  5. Let the pondweed acclimatise to the conditions of the boiling tube for 5 minutes
• Describe the steps of investigating the effect of light intensity on the rate of photosynthesis (step 6-8)

  6. Start a stop watch and count the amount of gas bubbles (oxygen made by photosynthesis) produced at the end of the pondweed for 1 minute

  7. Repeat the prior steps 2 times and find the mean amount of bubbles produced in 1 minute

  8. Repeat the whole experiment at 20, 30 & 40cm distance
• Why is a LED light convenient to use when investigating the effect of light intensity on the rate of photosynthesis

  LED lights don't release much heat, therefore it wont change the temperature of the experiment
• Why do we fill the boiling tube with sodium hydrogen carbonate solution when investigating the effect of light intensity on the rate of photosynthesis


  Because sodium hydrogen carbonate solution releases carbon dioxide which is needed for photosynthesis
• What are the main problems faced when investigating the effect of light intensity on the rate of photosynthesis


  1. The number of bubbles can be too fast to count accurately
  2. Bubbles aren't always the same size, e.g. a large bubble consists more oxygen then a small bubble
• How do we fix the problems faced when investigating the effect of light intensity on the rate of photosynthesis


  We can measure the volume of oxygen produced by the pondweed instead of the amount of bubbles:

  1. To do this we place the pondweed under a funnel & catch the bubbles in a measuring cylinder filled with water
  2. Use the measuring cylinder to measure the volume of oxygen produced
• How are results effected by the inverse square law when investigating the effect of light intensity on the rate of photosynthesis

  The effect of the inverse law can be identified as if we double the distance of the boiling tube from the light, the light intensity falls by 4 times. This causes the number of oxygen bubbles to also decrease by 4 times, as we need light for photosynthesis
• What is the word & symbol equation for photosynthesis

  (Look at diagram below)

  
• How do farmers increase their yield (amount) of crops they produce

  Farmers will light, heat and add extra carbon dioxide to their greenhouses to increase the rate of photosynthesis by preventing limiting factors, resulting in a higher yield of crops:

  1. Using oil burners as these release heat & carbon dioxide at the same time
• What is the disadvantage with farmers increasing their yield (amount) of crops they produce

  The methods are expensive, so the extra cost has to be justified by the increase in yield. In other words, the large amount of crops make up for the loss of money.
• Give examples of why we need energy

  1. Energy is needed for movement
  2. Humans & other mammals need energy to keep warm
  3. Energy needed for chemical reactions to build larger molecules, e.g. proteins are made by amino acids chemically joining
• What does cellular respiration (or respiration for short) provide


  It supplies us with energy
• What type of reaction is respiration

  It's chemical exothermic reaction because respiration releases energy from glucose
• What type of reaction is photosynthesis

  It's an endothermic reaction because it takes in energy from the sun
• What happens in aerobic respiration

  Glucose reacts with oxygen to produce carbon dioxide and water, also releasing energy
• Why does aerobic respiration release a great deal of energy

  Because the glucose molecules have been fully oxidised
• What's the symbol/word equation for aerobic respiration


  (shown in diagram)

  
• What do muscle cells need energy for

  Energy is needed for contraction
• When do cells undergo anaerobic respiration

  When there's a shortage of oxygen cells go through anaerobic respiration as it requires not oxygen
• What happens during anaerobic respiration for animals, including humans

  Glucose is converted into lactic acid and releases energy
• What is the problem with anaerobic respiration

  It releases much less energy than aerobic respiration because the oxidation of glucose is incomplete
• What happens in anaerobic respiration for plants and yeast cells

  Glucose is converted into ethanol, carbon dioxide and releases energy
• What is anaerobic respiration called for yeast cells & give an example of its purpose

  1. Anaerobic respiration in yeast cells are called fermentation, e.g. this reaction is used to make alcoholic drinks like beer. The alcohol in these drinks is ethanol, which is produced by fermentation.
  2. Yeast is also used to make bread, as the carbon dioxide, produced by the fermentation, creates bubbles in the dough, causing the bread to rise
• By which process is all the energy humans need provided by

  All the energy humans need are provided by respiration
• What is the effect on our body when the oxidation of glucose is incomplete

  1. It causes a build up in lactic acid, leading to muscle fatigue (especially from long period of vigorous activity).
  2. This ultimately causes the muscles to stop contracting efficiently
  3. A condition called oxygen debt occurs as our body needs oxygen to get rid of lactic acid build up
• How is lactic acid removed from our body

  1. Lactic acid is transported out of our muscles via our blood
  2. Lactic acid is taken to the liver and converted back into glucose in a series of chemical reactions
  3. Reacting with the accumulated lactic acid & and removing it from cells requires oxygen
• What is oxygen debt & why is oxygen needed

  Oxygen debt, is the amount of extra oxygen the body needs, after exercise, to get rid of the accumulated lactic acid build up. This explains why people still breathe rapidly even after completing exercise. Oxygen is needed to react with the accumulated build up of lactic acid & removing it from the cells requires oxygen.
• What is energy from respiration used for

  Energy from respiration is used by enzymes to synthesise new molecules in the cell
• Define metabolism


  Metabolism is the sum of all the chemical reactions in a cell or the body