biology paper 1

• Photosynthetic reaction


  Light energy is absorbed by chlorophyll (pigment) in chloroplasts in plant / algal cells, and this energy is used to convert carbon dioxide and water into glucose (sugar) and oxygen (by-product)

  
• Photosynthesis


  Endothermic reaction - energy transferred from environment to chloroplast by light
• Photosynthesis


  1. Light energy absorbed

  2. By chlorophyll in chloroplasts

  3. Convert carbon dioxide and water into glucose and oxygen

  
• Oxygen is made in photosynthesis, but it is only a by-product. The aim of photosynthesis is to make glucose.

  
• Limiting factor


  Restricts rate of photosynthesis (stops from increasing) if in low levels
• As temperature increases


  Rate of photosynthesis increases
• Above an optimum temperature

  Rate of photosynthesis decreases
• As light intensity increases

  Rate of photosynthesis increases
• Above a certain light intensity

  Rate of photosynthesis stops increasing
• As CO2 concentration increases

  Rate of photosynthesis increases
• Above a certain CO2 concentration

  Rate of photosynthesis stops increasing
• Chlorophyll


  Affects how much light energy can be absorbed
• Inverse square law describes the relationship between distance of a light source from a plant and light intensity
• Interpreting graphs of photosynthesis rate showing two or three factors

  If increasing a particular factor increases rate of photosynthesis, that factor is the limiting factor
• Removing limiting factors


  Gain maximum rate of photosynthesis, increase plant yield
• Water is not considered a limiting factor in photosynthesis as the volume needed is very small and water shortages affect other processes in the plant before affecting photosynthesis
• Factors limiting rate of photosynthesis

  • Carbon dioxide concentration
  • Temperature
  • Light intensity
• Factors affecting CO2 concentration in a greenhouse

  • Respiration (releases CO2) occurs when no photosynthesis
  • Photosynthesis rate greater than respiration rate

  
• Optimum temperature for lettuce growth in a greenhouse in winter is 21.5-22°C
• Investigating effect of light intensity on rate of photosynthesis

  1. Vary distance of white light source from pondweed

  2. Control temperature, CO2 concentration, pondweed type/length

  3. Measure volume of O2 released or count O2 bubbles produced per minute
• Independent variable


  Distance of pondweed from light source (light intensity)
• Dependent variable


  Volume of O2 released / number of O2 bubbles produced per minute (photosynthesis rate)

  
• Control variables


  Temperature, CO2 supply/concentration, pondweed type/length, light colour
• Placing pondweed in sodium hydrogen carbonate solution provides carbon dioxide so it is not a limiting factor
• Counting bubbles is not an accurate way of measuring volume of oxygen produced as bubbles are different sizes and can be easy to miss
• Using an LED light source does not emit a lot of infrared/thermal radiation, so temperature is controlled
• Modifying the experiment


  Investigate effect of CO2 concentration, temperature, wavelength of light on rate of photosynthesis

  
• Uses of glucose from photosynthesis

  • Used for respiration to release energy
  • Converted into insoluble starch for storage
  • Used to produce fat/oil (lipids) for energy storage
  • Used to produce cellulose to strengthen cell wall
  • Used to produce amino acids for protein synthesis

  
• Glucose is not used directly for growth, but is used for the specific purposes of starch, cellulose, amino acids, respiration, and fat/oil production

  
• Leaf left in cupboard with no light for 2 days

  Starch converted to glucose, glucose used for respiration as no photosynthesis to make new glucose
• TMV causes plants to produce less chlorophyll


  Lack of chlorophyll reduces photosynthesis, leading to stunted growth
• Uses of glucose in photosynthesis

  • Used for respiration to release energy
  • Converted into insoluble starch for storage
  • Used to produce fat/oil (lipids) for energy storage
  • Used to produce cellulose to strengthen cell wall
  • Used to produce amino acids for protein synthesis

  
• Glucose is combined with nitrate ions from soil to form amino acids
• Glucose is not used for growth, this is a common misconception
• Example application questions


  • Explain why a leaf left in a cupboard with no light for 2 days did contain glucose but did not contain starch
  • Explain why plants with TMV have stunted growth
• Cellular respiration


  A series of chemical reactions that release/transfer energy from glucose, occurs continuously in all living cells, exothermic reaction

  
• Energy released in respiration

  Used for chemical reactions to build larger molecules, keeping warm, movement
• Aerobic respiration


  1. Oxygen + glucose

  2. Complete oxidation

  3. High energy transferred

  
• Anaerobic respiration in animal cells

  1. Glucose only, no oxygen

  2. Incomplete oxidation

  3. Low energy transferred

  4. Lactic acid produced

  
• Anaerobic respiration in plant/yeast cells

  1. Oxidation of glucose

  2. Incomplete oxidation

  3. Low energy transferred

  4. Ethanol and CO2 produced