Bioenergetics

• The equation for photosynthesis is:

  carbon dioxide + water -> glucose + oxygen
• Photosynthesis takes place in chloroplasts that contain green pigments like chlorophyll that absorb light.
• Photosynthesis is endothermic.
• Plants use glucose in five main ways:

  • For respiration
  • Making cellulose
  • Combined with nitrate ions for making amino acids
  • Stored as fats and oils (lipids) in seeds
  • Stored as insoluble starch
• The rate of photosynthesis is affected by the light intensity, concentration of carbon dioxide and temperature.
• Chlorophyll can also be a limiting factor of photosynthesis: if the plant has a disease, the chloroplasts can be damaged and not absorb as much light.
• If the temperature is too warm, the enzymes in the plant will denature. This happens at about 45 degrees celsius.
• Light intensity is proportional to 1/distance squared.
• The most common way to create the the ideal environment for plants is to grow them in a greenhouse.
• Keeping plants in a greenhouse allows farmers to control the limiting factors for photosynthesis. It also makes it easier to keep them free from pests and disease.
• All living things respire.
• Respiration is exothermic.
• The energy from respiration is used for:

  • Building larger molecules from smaller ones (eg. proteins)
  • Allowing muscles to contract
  • To maintain a constant body temperature
• The total of all of the reactions that happen in a cell or the body is known as its metabolism.
• Aerobic respiration uses oxygen. It happens all the time in plants and animals.

  glucose + oxygen -> carbon dioxide + water
• Anaerobic respiration takes place when there isn't enough oxygen. It isn't as efficient as aerobic respiration.

  glucose -> lactic acid
• Plant and yeast cells respire anaerobically too, but they produce different things.

  glucose -> ethanol + carbon dioxide
• Anaerobic respiration in yeast cells is called fermentation. It is important for making things like bread and beer.
• When you exercise, you respire more. Your breathing rate and volume increases, and so does your heart rate.
• If you do really vigorous exercise, your muscles start respiring anaerobically and lactic acid builds up, which is painful. You also create an 'oxygen debt', which is the amount of oxygen your body needs to react with the lactic acid and remove it.
• Blood also transports lactic acid to the liver, where it is converted back to glucose.