B4

• Photosynthesis

  1. Takes place in the leaves

  2. Takes place in chloroplasts

  3. Chlorophyll absorbs light energy

  4. Converts carbon dioxide and water into glucose and oxygen
• Photosynthesis is an endothermic reaction, where energy is transferred from the environment to chloroplasts by light
• Carbon dioxide and water supply for photosynthesis

  1. Carbon dioxide diffuses into leaves through stomata

  2. Water is taken up from soil by roots and transported to leaves via xylem
• Products of photosynthesis

  • Glucose is the main product
  • Oxygen is also produced but not as important
• Uses of glucose produced by photosynthesis

  • Cellular respiration
  • Making cellulose
  • Making starch
  • Making amino acids
  • Making oils and fats
• Plant growth rate is often dependent on the rate of photosynthesis
• Factors affecting the rate of photosynthesis are light intensity, temperature, carbon dioxide concentration, and the amount of chlorophyll
• Factors affecting photosynthesis

  • Light intensity
  • Temperature
  • Concentration of carbon dioxide in the air
  • Amount of chlorophyll in plants
• Chlorophyll

  Pigment within chloroplasts that absorbs the light energy needed for photosynthesis
• Plants have less chlorophyll


  They won't be able to carry out as much photosynthesis
• Different plants will naturally have different amounts of chlorophyll
• The level of chlorophyll within an individual plant can vary due to disease, environmental stress or lack of nutrients
• Factors that damage chloroplasts and reduce chlorophyll production include disease, environmental stress, and lack of nutrients
• Limiting factors for photosynthesis

  • Light
  • Carbon dioxide
  • Temperature
• Graphing limiting factors for photosynthesis

  1. Plot light intensity on x-axis

  2. Plot rate of photosynthesis on y-axis
• As light intensity increases

  Rate of photosynthesis increases
• The line flattens out when something else becomes the limiting factor, such as carbon dioxide concentrations or temperature
• As carbon dioxide concentration increases

  Rate of photosynthesis increases
• As temperature increases initially

  Rate of photosynthesis increases
• As temperature increases further

  Rate of photosynthesis decreases as enzymes denature
• At around 45 degrees, enzymes are fully denatured and the rate of photosynthesis falls to zero
• Graphs can show multiple limiting factors, such as light intensity at different temperatures or carbon dioxide concentrations
• How farmers can create optimal conditions for photosynthesis

  • Use greenhouses to trap heat and provide artificial light
  • Pump in carbon dioxide
  • Use fertilizers to provide essential minerals
  • Use pesticides to control pests
• Creating optimal conditions for photosynthesis can be costly for farmers, so they have to weigh the extra cost against the expected yield increase
• What is the inverse square law?

  • The inverse square law states that the intensity of light decreases proportionally to the square of the distance from its source.
  • For example, if the distance is doubled, the light intensity decreases to 1/4 of its original value.

  Where:

  I = light intensity

  d = distance between light source and object

  
• temperature graph

  
• photosynthesis + temperature

  • Rate initially increases with temperature...
  • ...because particles have more energy and move faster, so react more frequently
  • Highest rate is at optimum temperature for enzyme
  • At higher temperatures the rate decreases as bonds holding the enzyme together begin to break, and so the enzyme changes shape
  • Rate falls to zero as enzymes denature 
• Paraffin heaters have two benefits. As the paraffin (a type of fuel) is burned it releases lots of heat, and also lots of carbon dioxide
• Cellular respiration is an exothermic reaction which transfers energy from glucose and is continuously occurring in living cells
• Cellular respiration

  Breaking apart glucose molecules to release the energy that's trapped inside
• How organisms use their energy

  • Building up larger molecules from smaller ones (e.g. combining amino acids to form proteins)
  • Muscular contraction for movement
  • Maintaining body temperature
• Energy is needed for loads of reactions in our cells, most of which are catalyzed by enzymes
• Metabolism

  All the chemical processes that occur within a living organism in order to maintain life
• Aerobic respiration

  • More common type
  • Takes place whenever there's enough oxygen
  • Most efficient way to transfer energy from glucose
  • Takes place continuously in both plants and animals
  • Takes place within mitochondria
• Aerobic respiration

  Glucose + Oxygen → Carbon dioxide + Water
• The equation for aerobic respiration is the opposite of the equation for photosynthesis
• Anaerobic respiration

  • Respiration without oxygen
  • Used when there is not enough oxygen to keep up with the demands of aerobic respiration
  • Incomplete breakdown of glucose
  • Leads to lactic acid buildup
• Anaerobic respiration

  Glucose → Lactic acid
• Anaerobic respiration in plants and yeast

  • Glucose is converted to ethanol and carbon dioxide instead of lactic acid
  • In yeast, this process is called fermentation
  • Used in industry to make bread, beer, and wine
• Exercise

  Requires our bodies to carry out more cellular respiration