exam questions

• Explain how IAA affects the growth of the coleoptile (4)

  -       IAA diffuses from the tip-down shaded side of plant 

  -       Therefore, can be taken up by cells in the zone of elongation 

  -       Which causes cells to elongate- 

  -       Leading to lowering of the PH in the cellulose cell wall, causing it to loosen, which means they take in more water via osmosis and elongate/expand.

  -       Therefore, causing the coleoptile to grow towards the light- positive phototropism
• Describe the role of IAA in the phototropic response of plants (4) 

  -       IAA is produced in the tip of the shoot (a diffusion gradient is established)

  -       IAA accumulates on the dark side of the shoot 

  -       IAA stimulates cell elongation 

  -       Causing the shoot to grow towards the light source
• Give three similarities between IAA and animal hormones (3)

  -       Both chemicals produced in cells 

  -       Long term effects 

  -       Both move away from the site of production 
• Suggest how auxin stimulate the weeds to grow rapidly but not the grass (2)

  -       Weeds are affected because they take up more auxin 

  -       And auxin causes cell elongation
• Describe how the effect of IAA on plant roots differ from plant shoots (2)

  -       Low IAA conc with increase root growth while having no effect on shoot growth 

  -       Medium IAA conc will inhibit root growth while increasing shoot growth