Plant Hormones

• What is phototropism?

  It is the growth of plant shoots towards light
• What hormone is suggested to be produced by shoot tips that affects phototropism?

  Auxin
• What happened when scientists removed the tips of the shoots in their experiments?

  The shoots did not grow towards the light
• What does covering the tips of the shoots with foil indicate about their sensitivity to light?

  It shows that the tips are sensitive to light
• What was the result when the lower parts of the shoots were covered with foil?

  The shoots grew towards the light as normal
• How do shoots use auxin to grow towards light?

  • Auxin is produced at the tip of the shoot
  • Light causes auxin to concentrate on the darker side
  • Auxin spreads down the shoot
  • Cells on the darker side grow faster than those on the lighter side
  • This causes the shoot to bend towards the light
• What is gravitropism or geotropism in plants?

  It is the growth of plant roots towards the force of gravity
• How does auxin behave in roots compared to shoots?

  In roots, auxin inhibits cell growth
• What effect does gravity have on auxin concentration in roots?

  Gravity causes auxin to concentrate on the lower side of the root
• What are the roles of gibberellins and ethylene in plants?

  • Gibberellins: Important for starting the germination of seeds
  • Ethylene: Controls cell division and the ripening of fruits
• What is the independent variable in the investigation of light intensity on seedlings?

  • Light intensity
• What is the dependent variable in the investigation of light intensity on seedlings?

  • Height of the seedlings
• What is a control variable in the experiment?

  The volume of water used for soaking the cotton wool
• How many mustard seeds are placed in each petri dish?

  10 mustard seeds
• Why is it important to have the same number of seedlings in each dish?

  To ensure that the number of seedlings is a control variable
• What should be done if one dish has more seedlings than the others?

  Remove seedlings from the dishes with more to match the lowest number
• How should the height of each seedling be measured?

  Using a ruler while holding the stems straight
• What are the conditions for placing the petri dishes during the experiment?

  1. One dish in full sunlight
  2. One dish in partial light
  3. One dish in darkness
• How long should the height of the seedlings be measured for?

  At least five consecutive days
• What should be done with the results after the experiment?

  Calculate the mean seedling height for each day and record it
• Why do seedlings grow towards the light source?

  Due to phototropism caused by auxin concentration
• What is the main focus of the video on plant hormones?

  To describe the uses of plant hormones
• What happens to auxin in seedlings when they are exposed to light?

  Auxin concentrates on the side of the seedling furthest from the light
• Who is the target audience for the video on plant hormones?

  Triple biology higher-tier students
• What is the effect of keeping seedlings in the dark?

  They grow rapidly trying to reach the light but have small yellow leaves
• What are the main plant hormones discussed in the video?

  • Auxins
  • Gibberellins
  • Ethylene
• Why do seedlings have small yellow leaves when kept in the dark?

  They cannot carry out photosynthesis without light
• What role do gibberellins play in seed germination?

  They are important in initiating seed germination
• How does gravity affect the growth of seedlings?

  • Chutes grow upwards against gravity
  • Roots grow downwards towards gravity
• What is phototropism?

  It is the growth of plants towards light
• What happens to auxin in roots due to gravity?

  Auxin builds up on the lower side of the root, inhibiting growth
• What is gravitropism?

  It is the growth of plants in response to gravity
• What are the three main uses of auxins in agriculture and horticulture?

  1. Used as weed killers
  2. Used as rooting powders
  3. Used for promoting growth in tissue culture
• How are auxins used as weed killers?

  They kill unwanted plants in gardens
• How does auxin affect the growth direction of roots?

  It causes the lower side to grow more slowly, directing growth downwards
• How do auxins function as rooting powders?

  They help in the rooting of plant cuttings
• Where can students find additional questions on this required practical?

  • In the vision workbook linked in the video
• What is the role of auxins in tissue culture?

  They promote growth in tissue culture
• What are the uses of gibberellins in agriculture?

  1. To end seed dormancy
  2. To encourage plants to flower
  3. To make food grow larger
• What effect do gibberellins have on seed dormancy?

  They can force a seed to germinate earlier