Chapter 9: Plants as Organisms

• Plants make their own food using photosynthesis
• The food that plants produce is important, not only for the plants themselves, but for the other organisms that feed on the plants
• Photosynthesis


  The process by which plants use light energy, carbon dioxide and water to produce glucose and oxygen

  
• Photosynthesis


  1. Light energy absorbed by chlorophyll in chloroplasts

  2. Light energy drives chemical reaction

  3. Carbon dioxide and water react to produce glucose and oxygen

  
• Photosynthesis is an endothermic reaction

  
• Chlorophyll


  • Green pigment in leaves that absorbs light energy for photosynthesis
  • Located in chloroplasts in plant cells
• Without enough light, a plant cannot photosynthesise very quickly
• Increasing light intensity


  Increases the rate of photosynthesis
• Carbon dioxide is one of the reactants in photosynthesis
• Increasing carbon dioxide concentration


  Increases the rate of photosynthesis
• The rate of photosynthesis is affected by temperature as it is an enzyme-controlled reaction

  
• At low temperatures


  The rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates

  
• At high temperatures


  Enzymes are denatured
• Water and carbon dioxide are reactants in photosynthesis

  
• Symbol Equation

  6CO2 + 6H2O → C6H12O6 + 6O2

  
• The gas produced in photosynthesis is oxygen
• A glowing splint relighting indicates the gas produced is oxygen
• Limiting factors


  Factors that can limit the rate of photosynthesis

  
• Limiting Factors

  1. Light intensity

  2. Carbon dioxide level

  3. Temperature

  4. Amount of chlorophyll

  
• Light intensity increases


  Rate of photosynthesis increases
• Carbon dioxide level increases


  Rate of photosynthesis increases

  
• Temperature decreases


  Rate of photosynthesis decreases

  
• Temperature increases


  Rate of photosynthesis increases, then eventually stops due to enzyme denaturation

  
• Greenhouses


  • CO2 levels increased during high light levels to avoid being a limiting factor
  • Optimum temperature for enzyme activity maintained
  • Artificial lighting used to prolong photosynthesis and increase light intensity
• Glucose is the starting point for the biosynthesis of materials that plants need to live

  
• Some of the glucose produced by photosynthesis is used for respiration

  
• The glucose not used for respiration is used for starch storage

  
• Test for starch


  Blue-black stains show presence of starch
• Mineral ions

  Dissolved in the soil water and absorbed through the roots by active transport.
• Minerals needed by plants

  • Magnesium ions
  • Nitrate ions
• Magnesium ions


  • Needed for making chlorophyll
  • Deficiency causes leaves to turn yellow
• Nitrate ions


  • Needed for making amino acids
  • Deficiency causes stunted growth
• Bogs have wet and peaty soil


  Contain very few minerals, especially nitrates
• Plants need nitrates from the soil


  To make amino acids and build into proteins
• Carnivorous plants trap insects and digest their bodies


  Provides a good supply of nitrates and other minerals
• Carnivorous plants can grow and thrive in bogs


  While relatively few other plants can
• Transpiration


  The evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapour through the stomata

  
• Water movement in a plant

  Root (xylem) → Stem (xylem) → Leaf

  
• Transpiration stream


  Constant movement of water molecules through the xylem from the roots to the leaves

  
• Functions of the transpiration stream

  • Transporting mineral ions
  • Providing water to keep cells turgid
  • Providing water to leaf cells for photosynthesis
  • Keeping the leaves cool by evaporation