B6

• 6.1 Describe photosynthetic organisms


  the main producers of food and therefore biomass - all organisms need energy and when plants produce this they get it (the materials is an organism are its biomass)
• 6.2 Describe photosynthesis in plants and algae

  an endothermic reaction (a chemical reaction where the products have more energy than the reactants - this is because energy enters from the surroundings)

  
  

  it uses light energy to react carbon dioxide and water (reactants) to produce glucose and oxygen (products)
• 6.3 Explain the effect of temperature, light intensity and carbon dioxide concentration as limiting factors on the rate of photosynthesis

  there can be areas with fewer molecules in each cubic centimetre of air. this reduced concentration of carbon dioxide molecules causes a lower rate (speed) of photosynthesis

  
  

  the reactions in photosynthesis are catalysed by enzymes that work better at warmer temperatures. colder areas will experience a lower rate of photosynthesis

  
  

  if the light intensity at an area is limited, the rate of photosynthesis will be lower than if the light intensity was increased
• 6.4 Explain the interactions of temperature, light intensity and carbon dioxide concentration in limiting the rate of photosynthesis


  these are limiting factors, because they are factors that prevent a rate increasing. the maximum rate of photosynthesis is controlled by the factor in the shortest supply. once a factor is limiting, changing its supply changes the rate of photosynthesis
• 6.5 Core Practical: Investigate the effect of light intensity on the rate of photosynthesis


  A - decide on the different distances between the algae and the lamp you are going to use

  
  

  B - each distance needs one clear glass bottle and one extra one

  
  

  C - add 20 of the algal balls to each bottle

  
  

  D - add the same amount of indicator solution to each bottle (hydrogen carbonate indicator), and put on the bottle caps

  
  

  E - you will have a range of bottles showing the colours of the indicator at different pHs. compare the colour in your tubes with the pH rage to work out the start pH

  
  

  F - set up a tank of water between the lamp and the area where you will place your tubes

  
  

  G - cover one bottle in kitchen foil so that it is in the dark

  
  

  H - measure the different distances from the lamp and place bottles at the distances. put the bottle covered in foil next to the bottle closest to the lamp

  
  

  I - turn on the lamp and wait until you can see obvious colour changes in the bottles (longer you wait, more obvious results)

  
  

  J - compare the colours of all your bottles with the pH range bottles and write down the pHs

  
  

  (rate - change in pH / time)
• improvements of this experiment

  an LED bulb is best as this will not raise the temperature of the water

  
  

  have the distance between the lamp and bottles to be large so that there is a clear difference between light intensities
• what are potential hazards of this experiment and what should you do to prevent them

  
  

  why does pH change with photosynthesis

  take extreme care not to spill water near electrical apparatus (such as the lamp) and ensure your hands are dry when holding the lamp

  
  

  Carbon dioxide will lower the pH, making it more acidic. Therefore, when plants absorb carbon dioxide, thus removing it , the pH will rise (become more alkaline)
• graphs


  a straight line on a graph shows a linear relationship between two variables

  
  

  if the line goes through the origin, it shows the two variables are in direct proportion
• 6.7 Explain how the structure of the root hair cells is adapted to absorb water and mineral ions

  the outer surfaces of many roots are covered with root hair cells. the 'hairs' are extensions of the cell that provide a large surface area so that water and mineral ions can be quickly absorbed

  
  

  the 'hairs' also have thin cell walls so that the flow of water into the cells is not slowed down

  
  

  particles go down a concentration gradient through a semipermeable membrane, from a high to low concentration. inside plant roots, the cell walls have an open cell structure allowing water particles to diffuse towards the middle of the root (from where there are more of them to where there are fewer)
• 6.8 Explain how the structures of the xylem and phloem are adapted to their function in the plant

  xylem - the dead cells have no cytoplasm or end walls and so form an empty tube for water to flow through. thick side walls and rings of lignin form rigid tubes that will not burst or collapse and that provide support (they become strengthened by lignin). tiny pores allow water and mineral ions to enter and leave the xylem vessels

  
  

  phloem - holes in the ends of the cell walls allow liquids to flow from one sieve cell to the next. companion cells in sieve tubes use energy to actively (are living) pump/ transport sucrose into or out of the sieve cells and around the plant, which they can do because of pores. there is a very small amount of cytoplasm (and no nucleus) therefore there is more room for the central channel
• 6.9 Explain how water and mineral ions are transported through the plant by transpiration, including the structure and function of the stomata

  mineral ions in the earth dissolve in water

  transpiration is the flow of water (and mineral ions) into the root, up the stem and out of the leaves

  
  

  xylem vessels form a tiny continuous pipe from plant roots to leaves. Inside the xylem vessels is an unbroken chain of water, due to the forces of attraction between water molecules. water is pulled up the xylem vessels in the stem as water evaporates from the xylem vessels in the leaves. as the water vapour diffuses out of a leaf, more water evaporates from the xylem inside of the leaf

  
  

  stomata are microscopic pores in a leaf which allow carbon dioxide to diffuse into a leaf and water vapour to diffuse out. they are opened and closed by guard cells - In light, water flows into guard cells making them rigid - this opens the stoma. At night, water flows out of the guard cells, making the stoma shut
• 6.10 Describe how sucrose is transported around the plant by translocation

  sucrose is translocated (transported) in the sieve tubes in the phloem tissue. the large central channel in each sieve cell is connected to its neighbours by holes, through which sucrose solution flows. companion cells actively pump sucrose into or out of the sieve cells that form the sieve tubes. as sucrose is pumped into sieve tubes, the increased pressure causes the sucrose solution to flow up to growing shoots or down to storage organs
• 6.12 Explain the effect of environmental factors on the rate of water uptake by a plant, to include light intensity, air movement and temperature

  a factor that reduces the concentration of water molecules outside the stomata will increase transpiration

  
  

  light intensity - greater light intensity makes the stomata wider, increasing transpiration

  
  

  air movement - wind moves molecules away from the stomata, reducing the rate of transpiration

  
  

  temperature - higher temperature makes particles move faster and so diffuse faster, increasing transpiration
• 6.13 Demonstrate an understanding of rate calculations for transpiration


  The rate of transpiration can be calculated by measuring the distance travelled by an air bubble in a capillary tube over a given time. The faster the bubble moves, the greater the rate of water uptake - and so the greater the assumed rate of transpiration