Bioenergetics

• Photosynthesis


  A fundamental process that makes our existence possible
• Without photosynthesis, plants wouldn't grow and ecosystems would fail
• You can use the bioenergetics workbook alongside this video to get the most out of your revision time
• Photosynthesis is a fundamental process that has already come up in lots of earlier topics like cell biology
• Photosynthesis


  The process by which plants harness the sun's energy to make food
• Photosynthesis happens in the green parts of the plant like the leaves and the stem, in the chloroplasts
• Photosynthesis


  Carbon dioxide + Water -> Glucose + Oxygen
• Light is a condition needed for photosynthesis to happen, not a chemical
• Carbon dioxide


  Comes from the air around the leaf and diffuses in through the stomata
• Water


  Comes from the soil and is absorbed by osmosis
• Chemical symbols


  • Carbon dioxide (CO2)
  • Water (H2O)
  • Glucose (C6H12O6)
  • Oxygen (O2)
• Photosynthesis


  An endothermic reaction, meaning light needs to be taken into the chloroplasts
• Chloroplasts contain chlorophyll, the green pigment that absorbs light
• Leaf adaptations to maximize photosynthesis

  • Large surface area to absorb more light
  • Thin to allow gases to diffuse in and out easily
  • Veins containing xylem to transport water and phloem to transport glucose
  • Lots of guard cells on the underside to regulate gas exchange
  • Spongy mesophyll with air spaces to allow gases to diffuse easily
  • Palisade mesophyll with many chloroplasts to maximize photosynthesis
• Water is taken up by the roots through osmosis and transported by the xylem to the leaves
• The loss of water from the stomata in the leaves causes more water to be drawn up through the xylem, creating the transpiration stream
• Aquatic plants like pond weeds obtain carbon dioxide from the water around them, as it can dissolve into water
• Photosynthesis


  A reaction that can be sped up or slowed down by certain factors
• Four main factors affecting photosynthesis


  • Light intensity
  • Carbon dioxide concentration
  • Temperature
  • Amount of chlorophyll
• Light intensity increases


  Rate of photosynthesis increases
• Limiting factor


  A factor that prevents the rate of photosynthesis from increasing further
• Light intensity increases


  Rate of photosynthesis increases, but plateaus when another factor becomes limiting
• Carbon dioxide concentration increases

  Rate of photosynthesis increases
• Temperature increases


  Rate of photosynthesis increases until optimum temperature, then decreases as enzymes become denatured
• Chlorophyll


  The green pigment in chloroplasts that can absorb light for photosynthesis
• Reduced chlorophyll


  Rate of photosynthesis is reduced
• Limiting factors can interact with each other
• High light intensity but low carbon dioxide concentration


  Overall rate of photosynthesis is low due to carbon dioxide being the limiting factor
• Increasing carbon dioxide concentration


  Rate of photosynthesis increases until another factor becomes limiting
• Increasing temperature


  Rate of photosynthesis increases when carbon dioxide is not limiting
• Comparing results requires keeping independent variables the same
• Inverse square law applies to light intensity affecting photosynthesis
• High greenhouse temperatures


  Enzymes become denatured, reducing rate of photosynthesis and plant growth