Plant hormones

விளையாடிக் கற்றுக்கொள்ளுங்கள்

ஆற்றல் சம்பாதிக்க இந்த கேள்விகளுக்குப் பதிலளியுங்கள், பின்னர் மீன் பிடித்து ஆராயுங்கள். கணக்கு தேவையில்லை.

கல்வியாளர்களுக்கு: Plant hormones (Science, Biology)-க்கான தயாரான பாட ஸ்லைடுகள், திருப்புதல் குறிப்புகள் — உங்கள் பாடத்தில் அவற்றைப் பயன்படுத்தவும், அல்லது கற்பவர்கள் நேரலை விளையாட்டாக விளையாடும் ஊடாடும் வகுப்பு செயல்பாடாக தலைப்பை இயக்கவும்.

பாட குறிப்புகள்

Tropisms: Growth Responses in Plants

  • Plants need to grow in response to light so leaves can absorb light for photosynthesis.
  • Plants need to grow in response to gravity so shoots grow upwards and roots grow downwards.
  • A directional growth response to light is called phototropism.
  • A directional growth response to gravity is called gravitropism or geotropism.
  • Growth towards a stimulus is a positive tropism; growth away from a stimulus is a negative tropism.
  • Shoots show positive phototropism (grow towards light) and negative gravitropism (grow away from gravity).
  • Roots show negative phototropism (grow away from light) and positive gravitropism (grow towards gravity).

Auxins: The Growth Hormone

  • Auxins are plant hormones that coordinate and control growth responses such as phototropism and gravitropism.
  • Auxins are produced in the tips of shoots and roots and diffuse to cells behind the tips.
  • In shoots, auxin promotes cell elongation; more auxin means more elongation and more growth.
  • In roots, auxin inhibits cell elongation; more auxin means less elongation and less growth.
  • Unequal distributions of auxin cause unequal growth rates in roots and shoots.
  • Auxin distribution in shoots is affected by both light and gravity; in roots it is mainly affected by gravity.

Phototropism: How Shoots Bend Towards Light

  • When light comes from all directions, auxin is distributed evenly and cells grow at the same rate.
  • When light comes mainly from one side, auxin concentrates on the shaded side of the shoot.
  • Auxin on the shaded side makes cells elongate faster than cells on the lit side.
  • This unequal growth causes the shoot to bend and grow towards the light.
  • Positive phototropism in shoots is the result of auxin accumulating on the shaded side.

Gravitropism: How Shoots and Roots Respond to Gravity

  • If a shoot or root is placed on its side, auxin accumulates on the lower side due to gravity.
  • In shoots, the lower side grows faster than the upper side, so the shoot grows upwards.
  • In roots, the lower side grows slower than the upper side, so the root grows downwards.
  • This shows that the same hormone can have opposite effects in shoots and roots.

Other Plant Hormones (Higher Tier)

  • Gibberellins are important in initiating seed germination.
  • Gibberellins also have a role in inducing flowering and the growth of fruit.
  • Ethene is a gas released by plants that controls cell division and ripening of fruits.
  • The mechanisms of how gibberellins and ethene work are not required.

Required Practical: Investigating Light or Gravity

  • Aim: to investigate the effect of light or gravity on the growth of newly germinated seedlings.
  • Set up two petri dishes with damp cotton wool and seedlings; place one on a clinostat and the other on its side.
  • A clinostat rotates slowly and cancels out the effect of gravity.
  • Place both dishes in a light-proof box so seedlings are in complete darkness; this controls the effect of light.
  • Record the direction of growth of shoots and roots, and measure length as well as making labelled drawings.
  • Expected results: on the support, roots grow downwards and shoots grow upwards; on the clinostat, roots and shoots grow straight outwards with no gravitropic response.

Commercial Uses of Auxins

  • Auxins can be used as selective weed killers that affect broad-leaved weeds but not narrow-leaved grasses and cereals.
  • Selective weedkillers disrupt the growth of weeds, causing them to die, reducing competition for space and nutrients.
  • However, once applied, their spread cannot be controlled and they could affect other plant species negatively.
  • Auxins are sold as rooting powders; dipping cuttings in them encourages rapid root development.
  • Auxins are also used in tissue culture to promote growth and produce clones of desirable plants.

Commercial Uses of Ethene and Gibberellins

  • Ethene is used in the food industry to control ripening of fruit during storage and transport.
  • Transporting unripe fruit is better because ripe fruit is softer and more easily damaged.
  • Ethene production can be inhibited to delay ripening, or ethene gas can be released to speed up ripening.
  • Gibberellins can be used to end seed dormancy and promote seed germination.
  • Gibberellins can promote flowering regardless of weather conditions.
  • Gibberellins can increase fruit size and produce seedless fruit when applied to unpollinated flowers.

Environmental Impact of Plant Hormone Use

  • Using hormones as weed killers can have a negative effect on biodiversity.
  • Many plants classed as weeds are a food source and habitat for other organisms.
  • Destroying weeds can therefore have negative effects on other organisms in the ecosystem.

ஸ்லைடுகள்

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பயிற்சி கேள்விகள்

இலவச முன்னோட்டம் — 56-இல் 8 கேள்விகள். அனைத்தையும் பார்க்க பதிவு செய்யவும்.
  1. 1.Which plant hormone is responsible for controlling phototropism and gravitropism?

    Easy
    • AAuxin
    • BGibberellin
    • CEthene
    • DOestrogen
  2. 2.What is phototropism in plants?

    Easy
    • AGrowth stimulated by light
    • BGrowth due to photosynthesis
    • CGrowth inhibited by light
    • DGrowth stimulated by temperature
  3. 3.Plant roots respond to gravity by growing downwards. What is this response called?

    Easy
    • APositive gravitropism
    • BNegative geotropism
    • CPositive phototropism
    • DNegative gravitropism
  4. 4.What effect would positive gravitropism have on a plant?

    Easy
    • ARoots would grow towards gravity
    • BRoots would grow away from gravity
    • CShoots would grow away from gravity
    • DShoots would grow sideways
  5. 5.What happens to the cells in plant shoots in response to auxins?

    Easy
    • AElongate
    • BThe cell cycle is stopped
    • CMitosis is increased
    • DShorten
  6. 6.Which gas acts as a plant hormone?

    Easy
    • AEthene
    • BEthane
    • CMethane
    • DCarbon dioxide
  7. 7.A gardener wishes to remove all the dandelions (a type of weed) from their lawn without damaging the grass. They purchased a selective weedkiller which contained a synthetic plant hormone. Which hormone would most likely be in the weedkiller?

    Medium
    • AAuxin
    • BOestrogen
    • CGibberellin
    • DEthene
  8. 8.A plant is grown near a fixed light source. The plant is then rotated by 180°. Predict the direction of growth of the plant shoots over the next 48 hours.

    Medium
    • AThe shoots will bend towards the new light direction
    • BThe shoots will continue growing in the original direction
    • CThe shoots will grow straight upwards
    • DThe shoots will grow away from the light

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