Plant Hormones

• What hormone does the plant produce to coordinate and control growth ?

  • Auxin
• What does an unequal distribution of auxin lead to?

  • Unequal growth rates
  • In plant shoots + roots
• Plant shoots grow towards the light is known as?

  • Phototropism
• Why does phototropism in a plant take place?

  • Grow towards the light
  • Allows shoot to absorb more light
  • more photosynthesis
  • produces more glucose
• How does phototropism take place in the shoots?

  • Auxins promote growth
  • Auxins accumulate in the side of the shoot furthest away from the light source
  • Cells grow + elongate more on the shady side
  • Causes the shoot to bend towards the light

  A) Auxins

  B) Light

  C) Shoot

  D) Auxins

  E) Light

  F) Shoot

  
• Geotropism


  • Roots grow in direction of gravity
• Why is geotropism of the roots helpful to a plant ?

  • Absorb water + mineral ions(nutrients) from the soil
  • Anchor the plant into the ground
• How does geotropism occur in the roots?

  • Auxins inhibit growth
  • If a root is growing sideways, auxins will accumulate in the lower side of the root tip due to gravity.
  • Cells grow + elongate less than the cells on the upper side
  • causes the shoot to bend downwards, in direction of gravity

  A) Gravity

  B) Auxins

  C) Gravity

  D) Auxins

  
• What part of the plant experiences phototropism?


  • Shoots
• What part of the plant experiences geotropism?

  • Root
• Control variables : investigate the effect of light or gravity on the growth of newly germinated seedlings.


  • Number / Type of seed used
  • Light intensity
  • Keep temperature the same for all dishes
  • Give all dishes the same volume of water
• Use of control


  • To compare to other areas
  • To check other factors are not affecting the results
• A rotating plant : 


  • Gravity acts evenly in all directions
• How to increase the validity of this investigation?

  • Repeat investigation + discard anomalies + calculate a mean
• Dependent variable 


  • Height of the seedlings
• How to measure the length of a curved shoot?

  • Straighten seedling / shoot
  • Measure with ruler
• Independent variable 


  • Conditions the seeds are kept in
• 6 marker

  Describe how different environmental factors affect:

  • the direction of growth of roots

  • the direction of growth of shoots


  Environmental factors

  • light
  • direction of gravity

  Effects on direction of growth

  • shoots grow upwards
  • shoot grows towards the light
  • roots grow downwards towards the force of gravity

  Hormone :

  • auxin promote growth
  • unequal distribution of hormone causes unequal growth rates
• Gibberellin 


  • Ending seed dormancy - Initiates seed germination
  • Increase fruit size
  • Promote flower production
• Ethene

  • Controls cell division
  • Ripening of fruits
• PRACTICAL : Investigating the affect of light on the growth of seedlings.- 1st PART


  1. Set up 3 petri dishes with cotton wool soaked in equal amounts of water.
  2. Place 10 mustard seeds in each petri dish
  3. Place petri dish in warm places, undisturbed + unmoved
  4. Allow mustard seeds to germinate.
  5. Water daily with equal amounts of water in each dish
  6. Ensure each dish have same no. of seedlings. Remove excess seedlings from any dish that has too many.
• Different conditions to investigate phototropism 


  • 1st - placed in Windowsill in full sunlight
  • 2nd - placed in a dark cupboard
  • 3rd - in partial light
• PRACTICAL : Investigating the affect of light on the growth of seedlings.- 2nd PART



  • Measure the height of each of seedling in mm
  • Move the petri dishes into position ; one in windowsill in full sunlight, one in partial light, third one in a dark cupboard
  • Measure height of each seedling every day, for at least 7 consecutive days
  • Record the heights in table
• Calculate mean 


  • Calculate mean height of the seedlings each day
  • Compare mean heights in full sunlight, partial light + darkness
• Use of auxins


  • Weed killers
  • Rooting powders
  • Promoting growth in a tissue culture
• Weed killers 


  • Initiate rapid growth that the weed exhausts all of their resources and die
• Problem with weed killers

  • Removing weed reduces biodiversity
• Rooting powders


  • Grow full new plants from plant cuttings
  • Quick to produce clones of the same plant
• Tissue culture 


  • Scientists add auxins + nutrients to help cell divide to grow a full plant from a few cells in petri dish in lab
• End seed dormancy 


  • Adding gibberellins can cause these seeds to germinate at a time it wouldn’t usually and all at the same time.
• Flowering


  adding gibberellins can cause plants to flower regardless of the weather and can make flowers grow bigger.
• Large fruit 


  •  gibberellins can make fruits grow larger
• Ethene use in food industry

  • Ethene is used in the food industry to control the ripening of fruit during storage and transport.