4 - Bioenergetics

• What type of reaction is photosynthesis?

  - photosynthesis takes in light energy => endothermic
• Why does photosynthesis occur in the leaves of plants?

  - leaves contain chloroplasts which contain chlorophyll which can absorb light energy
• What is the equation for photosynthesis?

  carbon dioxide + water → glucose + oxygen

  
  

  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy absorbed by clorophyll)
• What are the factors affecting the rate of photosynthesis?

  - temperature (enzymes)

  - light intensity

  - carbon dioxide concentration

  - chlorophyll concentration
• What are the 5 uses of glucose from photosynthesis?

  - used for respiration

  - converted into the insoluble storage molecule, starch (converted back to glucose when needed)

  - converted to fats and oils (used as storage form of energy)

  - used to produce cellulose which strengthens the cell wall

  - used to combine with nitrate ions to produce amino acids for protein synthesis
• What is the method for investigating the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed?

  1) Take a boiling tube and place it 10cm away from an LED light source (these do not release very much heat and too much heat would change the temperature of the experiment => affect the rate of photosynthesis). (we can also place a beaker with water (to absorb the heat produced

  by the bulb)in between the light source and boiling tube if we do not have an LED light source)

  2) Fill the boiling tube with sodium hydrogen carbonate solution (releases CO₂ which is needed for photosynthesis).

  3) Put a piece of pondweed into the boiling tube with the cut end at the top.

  4) Leave for 5mins to acclimatise to the conditions in the boiling tube.

  5) Start a stopwatch and count the number of oxygen bubbles produced in 1min.

  6) Repeat this 2 more times and calculate the mean number of bubbles produced.

  7) Repeat the whole experiment again but at 20cm, then 30cm, then 40cm. Calculate the mean for each after doing it 3 times in total.
• What are some problems with the photosynthesis experiment?

  - number of bubbles can be too fast to count accurately

  - bubbles are not the same size => can have different volumes
• How can we solve the problems identified with the photosynthesis experiment?

  - place the pondweed under a funnel and catch the bubbles in a measuring cyclinder => use this to measure the volume of the oxygen gas produced
• What does the inverse-square law show in regards to the photosynthesis experiment?

  
  

  What is the equation for light intensity?

  - if multiply the distance by 2, the number of bubbles/min decreases by a factor of 2²=4

  
  

  light intensity = 1/distance²
• What does it mean if light intensity is the limiting factor in photosynthesis?


  - the light intensity is the factor that limits the rate of photosynthesis
• What happens if we increase the temperature in photosynthesis?

  - as the temperature increases, the enzymes get more energy so the rate increases

  
  

  - if the temperature is too hight, the enzymes vibrate too much, and this changes the shape of their active site => substrate can no longer fit => enzymes is denatured => rate of photosynthesis decreases
• Why would farmers want to use greenhouses?

  - can manually adjust the factors that affect the rate of photosynthesis => higher rate => grearer crop yield
• How can farmers adjust the factors that affect photosynthesis in greenhouses?

  - increase light intensity

  - porivde optimum wavelengths of light

  
  

  - use paraffin heaters/oil burners (provide both heat and CO₂) (efficient)

  
  

  - can sometimes use fungi, grown as mycelium in bags around the greenhouse, that add carbon dioxide through their respiration

  
  

  - irrigation systems

  - grow plants in hydroponics (system that allows plants to grow in a porous material (other than soil)

  
  

  - temperature regulation
• In a greenhouse, why must growers find a balance in humidity?

  - high humidity will promote the growth of pathogenic fungi
• What must be justified in greenhouses?

  - the extra cost has to be justified by the increase in crop yield
• Why is energy important to a living organism?

  - movement

  - to keep warm

  - for chemical reactions to build larger molecules
• How is the energy we need supplied?

  (cellular) respiration
• What type of reaction is respiration?

  respiration releases energy => exothermic reaction
• What is the equation for aerobic respiration?

  glucose + oxygen → carbon dioxide + water (→energy)

  
  

  C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
• Why does aerobic respiration release more energy?

  - the glucose molecule has been fully oxidised
• What happens if there is insufficient oxygen for aerobic respiration?

  - cells carry out anaerobic respiration
• Where does anaerobic respiration in the body usually take place? Why?

  - muscle cells

  - they need a lot of energy for contraction but the oxygen supply is limited
• What is the equation for anaerobic respiration in muscle cells?

  glucose → lactic acid (→energy)
• What are some differences between the two types of respiration?

  - anaerobic respiration does not require oxygen

  - anaerobic respiration releases much less energy than aerobic respiration (the oxidation of glucose is incomplete)
• What is the equation for anaerobic respiration in plant cells and yeast cells?

  glucose → ethanol + carbon dioxide (→energy)
• What is anaerobic respiration in yeast cells called?


  fermentation
• Why is anaerobic respiration in yeast cells useful?

  - ethanol produced can be used to make alcoholic drinks

  - carbon dioxide produced can be used as a rising agent for bread
• What happens to the body during exercise?

  - a lot of energy needed for muscle contraction => increased demand for energy

  
  

  - heart rate, breathing rate & breathing volume ↑↑↑ to supply the muscles with more oxygenated blood

  
  

  - insufficient oxygen => anaerobic respiration
• What happens to muscles during long periods of vigorous activity?

  - insufficient supply of oxygen => anaerobic respiration takes place

  
  

  - oxidation of glucose is incomplete => build up of lactic acid (toxic) => muscles become fatigued & stop contracting efficiently => creates an oxygen debt
• What is oxygen debt?

  - the amount of extra oxygenthe body needs after exercise to react with the accumulated lactic acid &

  remove it from the cells
• How does the body remove lactic acid from the muscle cells?

  - blood flowing through the muscles transports the lactic acid out of the muscles and to the liver

  - in the liver, the lactic acid is converted back into glucose in a series of chemical reactions (which requires oxygen)
• What is required by people to do to convert the lactic acid back into glucose?


  - people continue to breathe rapidly for some time after finishing exercise to receive the extra oxygen required
• What is metabolism?

  - the sum of all the reactions in a cell or the body
• What is the energy transferred by respiration in cells used by the organism for?

  - the energy transferred is used by the organism for the continual enzyme controlled processes of metabolism that synthesis new molecules
• In humans, what are examples of metabolism?

  - the conversion of glucose into the storage form of glycogen

  - the formation of lipid molecules from a molecule of glycerol + 3 fatty acid molecules

  - respiration

  - the breakdown of excess proteins to form urea for excretion by the kidneys