ICSE – Grade 10 – Biology – Ch 07 – QA

Questions & Answers

ICSE - Grade - 10

Subject: Biology

Chapter - 07 - Chemical Coordination in Plants

Types of Questions

MCQ

  1. Which of the following is a plant hormone that promotes cell elongation?
    A) Ethylene
    B) Auxin
     C) Cytokinin
     D) Abscisic acid
     Answer: B) Auxin

 

  1. Gibberellins are mainly responsible for:
    A) Closing stomata
    B) Fruit ripening
     C) Stem elongation
     D) Inhibiting growth
     Answer: C) Stem elongation

 

  1. The natural auxin found in plants is:
    A) IBA
    B) NAA
     C) IAA
     D) 2,4-D
     Answer: C) IAA

 

  1. Which hormone promotes fruit ripening?
    A) Gibberellin
    B) Cytokinin
     C) Ethylene
     D) Auxin
     Answer: C) Ethylene

 

  1. Which plant hormone is known as the ‘stress hormone’?
    A) Auxin
    B) Cytokinin
     C) Ethylene
     D) Abscisic acid
     Answer: D) Abscisic acid

 

  1. Which of the following promotes apical dominance?
    A) Cytokinin
    B) Gibberellin
     C) Ethylene
     D) Auxin
     Answer: D) Auxin

 

  1. The hormone used in tissue culture to promote cell division is:
    A) Ethylene
    B) Auxin
     C) Cytokinin
     D) ABA
     Answer: C) Cytokinin

 

  1. Which hormone is gaseous in nature?
    A) Cytokinin
    B) Auxin
     C) Ethylene
     D) Gibberellin
     Answer: C) Ethylene

 

  1. Which hormone helps in breaking dormancy in seeds?
    A) ABA
    B) Cytokinin
     C) Ethylene
     D) Gibberellin
     Answer: D) Gibberellin

 

  1. Heliotropism is a type of:
    A) Geotropism
    B) Chemotropism
     C) Phototropism
     D) Thigmotropism
     Answer: C) Phototropism

 

  1. Pollen tube growth towards the ovule is an example of:
    A) Hydrotropism
    B) Chemotropism
     C) Geotropism
     D) Phototropism
     Answer: B) Chemotropism

 

  1. Which hormone delays aging in leaves?
    A) Cytokinin
    B) Auxin
     C) ABA
     D) Ethylene
     Answer: A) Cytokinin

 

  1. Thigmotropism is seen in:
    A) Roots
    B) Sunflower
     C) Tendrils
     D) Fruits
     Answer: C) Tendrils

 

  1. Which hormone promotes abscission of leaves and fruits?
    A) Auxin
    B) Cytokinin
     C) Ethylene
     D) Gibberellin
     Answer: C) Ethylene

 

  1. Positive geotropism is shown by:
    A) Shoots
    B) Leaves
     C) Flowers
     D) Roots
     Answer: D) Roots

 

  1. Which of the following promotes parthenocarpy?
    A) ABA
    B) Cytokinin
     C) Auxin
     D) Gibberellin
     Answer: C) Auxin

 

  1. Phototropism occurs due to uneven distribution of:
    A) Gibberellin
    B) Ethylene
     C) Cytokinin
     D) Auxin
     Answer: D) Auxin

 

  1. Which hormone causes stomatal closure during drought?
    A) ABA
    B) Cytokinin
     C) Gibberellin
     D) Auxin
     Answer: A) ABA

 

  1. The first plant hormone discovered was:
    A) Gibberellin
    B) Auxin
     C) Cytokinin
     D) ABA
     Answer: B) Auxin

 

  1. Which hormone promotes bolting in plants like cabbage?
    A) ABA
    B) Cytokinin
     C) Gibberellin
     D) Auxin
     Answer: C) Gibberellin

 

  1. Hydrotropism is the response of a plant towards:
    A) Light
    B) Water
     C) Gravity
     D) Chemicals
     Answer: B) Water

 

  1. Which hormone is used in artificial rooting powders?
    A) ABA
    B) Gibberellin
     C) Cytokinin
     D) Auxin
     Answer: D) Auxin

 

  1. Which plant movement is independent of direction?
    A) Tropic movement
    B) Turgor movement
     C) Nastic movement
     D) Phototropism
     Answer: C) Nastic movement

 

  1. Which hormone induces seed dormancy?
    A) Cytokinin
    B) ABA
     C) Gibberellin
     D) Auxin
     Answer: B) ABA

 

  1. Which of the following is not a function of auxin?
    A) Apical dominance
    B) Fruit ripening
     C) Root growth
     D) Cell elongation
     Answer: B) Fruit ripening

 

  1. Ethylene promotes:
    A) Seed germination
    B) Cell division
     C) Fruit ripening
     D) Stomatal opening
     Answer: C) Fruit ripening

 

  1. Which hormone is involved in leaf fall?
    A) Auxin
    B) ABA
     C) Gibberellin
     D) Cytokinin
     Answer: B) ABA

 

  1. Which hormone is mainly responsible for increasing plant height?
    A) Cytokinin
    B) Ethylene
     C) Gibberellin
     D) Auxin
     Answer: C) Gibberellin

 

  1. Which movement occurs in sunflower tracking sunlight?
    A) Geotropism
    B) Chemotropism
     C) Heliotropism
     D) Hydrotropism
     Answer: C) Heliotropism

 

  1. ABA is antagonistic to:
    A) Cytokinin
    B) Gibberellin
     C) Auxin
     D) All of the above
     Answer: D) All of the above

 

  1. Chemotropism is essential for:
    A) Pollination
    B) Germination
     C) Fertilisation
     D) Photoperiodism
     Answer: C) Fertilisation

 

  1. What causes the tendrils of a pea plant to curl around a support?
    A) Phototropism
    B) Geotropism
     C) Thigmotropism
     D) Hydrotropism
     Answer: C) Thigmotropism

 

  1. Which hormone is found in high concentration in mature fruits?
    A) Cytokinin
    B) Ethylene
     C) Auxin
     D) Gibberellin
     Answer: B) Ethylene

 

  1. Tropic movements are:
    A) Non-directional
    B) Growth movements
     C) Movement in animals
     D) Seasonal responses
     Answer: B) Growth movements

 

  1. Which hormone increases resistance to drought?
    A) Cytokinin
    B) Auxin
     C) ABA
     D) Gibberellin
     Answer: C) ABA

 

  1. Seed germination is promoted by:
    A) ABA
    B) Cytokinin
     C) Ethylene
     D) Gibberellin
     Answer: D) Gibberellin

 

  1. Apical dominance is the inhibition of:
    A) Root growth
    B) Shoot tip growth
     C) Lateral bud growth
     D) Leaf formation
     Answer: C) Lateral bud growth

 

  1. Which hormone inhibits growth?
    A) Cytokinin
    B) Auxin
     C) Gibberellin
     D) Abscisic acid
     Answer: D) Abscisic acid

 

  1. A hormone used to induce flowering in pineapple is:
    A) Cytokinin
    B) Ethylene
     C) Auxin
     D) ABA
     Answer: B) Ethylene

 

  1. Gibberellin was first isolated from:
    A) Plants
    B) Bacteria
     C) Fungus
     D) Algae
     Answer: C) Fungus

 

  1. Lateral buds grow when apical dominance is removed by:
    A) Gibberellin
    B) Ethylene
     C) Cytokinin
     D) ABA
     Answer: C) Cytokinin

 

  1. The hormone responsible for opening of flower buds in some plants is:
    A) Cytokinin
    B) Ethylene
     C) ABA
     D) Gibberellin
     Answer: B) Ethylene

 

  1. Which of these is a synthetic auxin?
    A) NAA
    B) ABA
     C) IAA
     D) Cytokinin
     Answer: A) NAA

 

  1. Which of these causes epinasty in leaves?
    A) Gibberellin
    B) ABA
     C) Ethylene
     D) Cytokinin
     Answer: C) Ethylene

 

  1. What promotes development of parthenocarpic fruits?
    A) ABA
    B) Gibberellin
     C) Ethylene
     D) Auxin
     Answer: D) Auxin

 

  1. The main site of cytokinin synthesis is:
    A) Shoot tip
    B) Leaf
     C) Fruit
     D) Root tip
     Answer: D) Root tip

 

  1. Which hormone inhibits seed germination?
    A) ABA
    B) Gibberellin
     C) Cytokinin
     D) Ethylene
     Answer: A) ABA

 

  1. Movement of roots towards gravity is called:
    A) Positive phototropism
    B) Negative geotropism
     C) Positive geotropism
     D) Chemotropism
     Answer: C) Positive geotropism

 

  1. Cytokinins act in opposition to:
    A) Gibberellins
    B) Ethylene
     C) Auxins
     D) ABA
     Answer: C) Auxins

 

  1. Which hormone increases sugar content in sugarcane?
    A) Cytokinin
    B) Auxin
     C) Gibberellin
     D) Ethylene
     Answer: C) Gibberellin

Fill in the Blanks

  1. The plant hormones are also known as ___ substances.
     Answer: chemical


  2. Auxins promote ___ in stem cells.
     Answer: cell elongation


  3. Gibberellins help in breaking the ___ of seeds.
     Answer: dormancy


  4. Cytokinins promote ___ division.
     Answer: cell


  5. Ethylene is the only plant hormone which exists in the ___ state.
     Answer: gaseous


  6. Abscisic acid helps in closing the ___ during water stress.
     Answer: stomata


  7. Phototropism is the movement of plant parts in response to ___.
     Answer: light


  8. Geotropism is the growth response to ___.
     Answer: gravity


  9. Hydrotropism occurs in response to ___.
     Answer: water


  10. Thigmotropism is the response of plants to ___.
     Answer: touch


  11. The natural auxin found in plants is ___.
     Answer: IAA (Indole-3-acetic acid)


  12. Auxins are produced at the ___ of shoots.
     Answer: tip


  13. ___ shows positive geotropism.
     Answer: Root


  14. ___ shows negative phototropism.
     Answer: Root


  15. Tendrils wrap around a support due to ___.
     Answer: thigmotropism


  16. The bending of sunflower towards the sun is called ___.
     Answer: heliotropism


  17. Cytokinins are mainly produced in the ___ regions of plants.
     Answer: root


  18. Abscisic acid is also called a ___ hormone.
     Answer: stress


  19. Fruit ripening is accelerated by ___.
     Answer: ethylene


  20. The hormone responsible for bolting is ___.
     Answer: gibberellin


  21. Apical dominance is caused by the hormone ___.
     Answer: auxin


  22. The first plant hormone discovered was ___.
     Answer: auxin


  23. ___ promotes growth in dwarf plants.
     Answer: Gibberellin


  24. The growth of pollen tube towards the ovule is an example of ___.
     Answer: chemotropism


  25. Leaf fall is promoted by the hormone ___.
     Answer: abscisic acid


  26. ___ hormones can be both natural and synthetic.
     Answer: Auxin


  27. ___ is used in tissue culture to promote cell division.
     Answer: Cytokinin


  28. The growth movement of plant parts towards a stimulus is called ___.
     Answer: tropism


  29. The hormone responsible for root initiation in stem cuttings is ___.
     Answer: auxin


  30. The hormone that delays leaf senescence is ___.
     Answer: cytokinin


  31. Artificial auxins like NAA are used for ___ of fruits.
     Answer: thinning


  32. ABA plays a major role in inducing ___ in seeds.
     Answer: dormancy


  33. Cytokinins promote growth of ___ buds.
     Answer: lateral


  34. The movement of tendrils is a response to ___ stimuli.
     Answer: mechanical


  35. Gibberellin causes elongation of the ___ in rosette plants.
     Answer: internodes


  36. ___ tropism is involved in the growth of roots towards moisture.
     Answer: Hydro


  37. ___ hormone is used to induce flowering in pineapples.
     Answer: Ethylene


  38. ___ prevents premature germination of seeds.
     Answer: ABA (Abscisic acid)


  39. The part of the plant that grows towards the light is the ___.
     Answer: shoot


  40. Cytokinins work in opposition to ___.
     Answer: auxins


  41. Movement of plants that do not depend on the direction of stimulus is called ___.
     Answer: nastic


  42. ___ acid helps plants to survive under drought conditions.
     Answer: Abscisic


  43. The growth movement of roots in response to gravity is called ___.
     Answer: positive geotropism


  44. ___ is the directional growth movement due to chemicals.
     Answer: Chemotropism


  45. A hormone that helps in increasing the size of grapes is ___.
     Answer: gibberellin


  46. The curling of tendrils around a support is due to unequal growth caused by ___.
     Answer: auxin


  47. The hormone responsible for regulating various plant stresses is ___.
     Answer: abscisic acid


  48. Synthetic auxins like 2,4-D are used as ___.
     Answer: weed killers


  49. ___ is responsible for the premature yellowing of leaves.
     Answer: ABA


  50. The elongation of cells on the shaded side of a plant is due to the accumulation of ___.
     Answer: auxin

Name the Following

  1. Name the natural auxin found in plants.
     Answer: Indole-3-acetic acid (IAA)


  2. Name the gaseous plant hormone.
     Answer: Ethylene


  3. Name the hormone that promotes cell elongation.
     Answer: Auxin


  4. Name the hormone that promotes fruit ripening.
     Answer: Ethylene


  5. Name the hormone responsible for bolting.
     Answer: Gibberellin


  6. Name the hormone that promotes seed dormancy.
     Answer: Abscisic acid (ABA)


  7. Name the hormone used in artificial rooting powders.
     Answer: Auxin


  8. Name the hormone that inhibits lateral bud growth.
     Answer: Auxin


  9. Name the hormone that promotes cell division.
     Answer: Cytokinin


  10. Name the hormone that delays senescence in leaves.
     Answer: Cytokinin


  11. Name the hormone that closes stomata during drought.
     Answer: Abscisic acid (ABA)


  12. Name the hormone responsible for apical dominance.
     Answer: Auxin


  13. Name the movement of roots towards gravity.
     Answer: Positive geotropism


  14. Name the movement of stem away from gravity.
     Answer: Negative geotropism


  15. Name the movement of shoots towards light.
     Answer: Positive phototropism


  16. Name the movement of pollen tubes towards ovule.
     Answer: Chemotropism


  17. Name the movement shown by tendrils in response to touch.
     Answer: Thigmotropism


  18. Name the plant hormone that increases the size of grapes.
     Answer: Gibberellin


  19. Name the movement shown by sunflower turning towards the sun.
     Answer: Heliotropism


  20. Name the hormone used to induce flowering in pineapple.
     Answer: Ethylene


  21. Name the hormone that promotes parthenocarpic fruit formation.
     Answer: Auxin


  22. Name the synthetic auxin commonly used in agriculture.
     Answer: NAA (Naphthalene Acetic Acid)


  23. Name the hormone that prevents premature germination.
     Answer: Abscisic acid (ABA)


  24. Name the hormone that promotes growth in dwarf plants.
     Answer: Gibberellin


  25. Name the hormone that promotes fruit setting.
     Answer: Auxin


  26. Name the hormone found in high concentration in mature fruits.
     Answer: Ethylene


  27. Name the hormone that promotes abscission of leaves.
     Answer: Ethylene


  28. Name the hormone that acts opposite to auxin.
     Answer: Cytokinin


  29. Name the plant hormone responsible for stress responses.
     Answer: Abscisic acid (ABA)


  30. Name the plant movement that depends on the direction of stimulus.
     Answer: Tropic movement


  31. Name the hormone that promotes elongation of internodes.
     Answer: Gibberellin


  32. Name the hormone that causes early germination in barley seeds.
     Answer: Gibberellin


  33. Name the hormone that helps in overcoming seed dormancy.
     Answer: Gibberellin


  34. Name the first plant hormone discovered.
     Answer: Auxin


  35. Name the fungus from which gibberellin was first isolated.
     Answer: Gibberella fujikuroi


  36. Name the hormone that increases resistance to drought.
     Answer: Abscisic acid (ABA)


  37. Name the hormone that increases sugar content in sugarcane.
     Answer: Gibberellin


  38. Name the hormone that regulates various stresses in plants.
     Answer: Abscisic acid (ABA)


  39. Name the hormone that promotes the opening of flower buds.
     Answer: Ethylene


  40. Name the organ of the plant where cytokinins are mainly produced.
     Answer: Root tip


  41. Name the hormone that promotes lateral bud growth.
     Answer: Cytokinin


  42. Name the growth movement in plants in response to a stimulus.
     Answer: Tropism


  43. Name the movement of plant roots towards water.
     Answer: Hydrotropism


  44. Name the synthetic auxin used as a weed killer.
     Answer: 2,4-D (2,4-Dichlorophenoxyacetic acid)


  45. Name the hormone that stimulates vascular tissue differentiation.
     Answer: Auxin


  46. Name the hormone that promotes flowering in mango.
     Answer: Gibberellin


  47. Name the hormone involved in senescence and abscission.
     Answer: Abscisic acid (ABA)


  48. Name the hormone that promotes chloroplast development.
     Answer: Cytokinin


  49. Name the plant response which is independent of the direction of stimulus.
     Answer: Nastic movement


  50. Name the hormone that causes swelling of cells during ripening.
     Answer: Ethylene

Answer in One Word

  1. Name the hormone that promotes cell elongation.
     Answer: Auxin


  2. Which hormone helps in fruit ripening?
     Answer: Ethylene


  3. Which hormone causes seed dormancy?
     Answer: Abscisic


  4. Name the gaseous plant hormone.
     Answer: Ethylene


  5. Which hormone promotes bolting?
     Answer: Gibberellin


  6. What is the natural auxin in plants?
     Answer: IAA


  7. Which hormone delays leaf senescence?
     Answer: Cytokinin


  8. Which hormone promotes apical dominance?
     Answer: Auxin


  9. Which hormone is used as a weed killer?
     Answer: 2,4-D


  10. Which hormone promotes cell division?
     Answer: Cytokinin


  11. Which plant hormone is produced in root tips?
     Answer: Cytokinin


  12. Name the hormone that promotes flowering in pineapples.
     Answer: Ethylene


  13. Which hormone closes stomata during drought?
     Answer: Abscisic


  14. What is the movement of roots towards gravity called?
     Answer: Geotropism


  15. What is the response of shoots to light called?
     Answer: Phototropism


  16. Which hormone promotes parthenocarpy?
     Answer: Auxin


  17. Name the hormone used in tissue culture.
     Answer: Cytokinin


  18. Which hormone helps overcome seed dormancy?
     Answer: Gibberellin


  19. Which hormone increases the size of fruits?
     Answer: Gibberellin


  20. What is the movement in response to water called?
     Answer: Hydrotropism


  21. Which hormone causes fruit fall?
     Answer: Ethylene


  22. Which hormone is responsible for abscission of leaves?
     Answer: Abscisic


  23. Which hormone works opposite to auxin?
     Answer: Cytokinin


  24. Which hormone is involved in stress regulation?
     Answer: Abscisic


  25. What type of movement is thigmotropism?
     Answer: Tropic


  26. What is the stimulus for thigmotropism?
     Answer: Touch


  27. Name the movement of pollen tube towards ovule.
     Answer: Chemotropism


  28. What is the movement of sunflower towards sun called?
     Answer: Heliotropism


  29. Which hormone promotes lateral bud growth?
     Answer: Cytokinin


  30. Which hormone is responsible for apical bud growth?
     Answer: Auxin


  31. Which part of the plant is rich in auxin?
     Answer: Shoot


  32. Name the movement in response to chemicals.
     Answer: Chemotropism


  33. Which hormone is used to increase sugarcane yield?
     Answer: Gibberellin


  34. Which hormone is used for artificial fruit setting?
     Answer: Auxin


  35. Which movement is not dependent on direction of stimulus?
     Answer: Nastic


  36. Name the hormone that delays aging in leaves.
     Answer: Cytokinin


  37. Which hormone controls transpiration under stress?
     Answer: Abscisic


  38. Which hormone breaks dormancy in barley seeds?
     Answer: Gibberellin


  39. Which fungus was gibberellin first extracted from?
     Answer: Gibberella


  40. Which hormone causes swelling of cells during ripening?
     Answer: Ethylene


  41. What is the scientific name of natural auxin?
     Answer: IAA


  42. Name the hormone that causes yellowing of leaves.
     Answer: Abscisic


  43. What is the function of cytokinins in senescence?
     Answer: Delay


  44. Which hormone promotes cell division in meristem?
     Answer: Cytokinin


  45. What kind of movement is shown by tendrils?
     Answer: Thigmotropism


  46. Which hormone is used for root initiation?
     Answer: Auxin


  47. Name the only gaseous phytohormone.
     Answer: Ethylene


  48. Which hormone regulates plant responses to drought?
     Answer: Abscisic


  49. What is the movement in response to light called?
     Answer: Phototropism


  50. What is the movement of roots towards moisture called?
     Answer: Hydrotropism

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Find the Odd Man Out

  1. Auxin, Cytokinin, Gibberellin, DNA
     Answer: DNA
     Explanation: Others are plant hormones; DNA is genetic material.


  2. Ethylene, IAA, Cytokinin, ATP
     Answer: ATP
     Explanation: ATP is an energy molecule; others are hormones.


  3. Light, Gravity, Touch, Oxygen
     Answer: Oxygen
     Explanation: Others are directional stimuli causing tropism; oxygen is not.


  4. Shoot, Root, Flower, Tendril
     Answer: Flower
     Explanation: Others show directional movement; flower does not.


  5. Gibberellin, Abscisic acid, Auxin, Water
     Answer: Water
     Explanation: Water is not a hormone.


  6. Geotropism, Hydrotropism, Phototropism, Parthenocarpy
     Answer: Parthenocarpy
     Explanation: Others are types of tropic movement; parthenocarpy is fruit development.


  7. Cytokinin, ABA, Ethylene, CO₂
     Answer: CO₂
     Explanation: CO₂ is a gas used in photosynthesis; not a hormone.


  8. IAA, NAA, 2,4-D, DNA
     Answer: DNA
     Explanation: DNA is not an auxin.


  9. Stomata closure, Drought resistance, Seed dormancy, Flower formation
     Answer: Flower formation
     Explanation: Not a function of ABA; others are.


  10. Apical dominance, Root initiation, Lateral bud growth, Fruit setting
     Answer: Lateral bud growth
     Explanation: Promoted by cytokinin, not auxin.


  11. Root tip, Shoot apex, Xylem, Young leaves
     Answer: Xylem
     Explanation: Others are hormone production sites; xylem is conducting tissue.


  12. Positive phototropism, Negative geotropism, Thigmotropism, Photosynthesis
     Answer: Photosynthesis
     Explanation: Not a type of movement.


  13. Cytokinin, NAA, IAA, 2,4-D
     Answer: Cytokinin
     Explanation: Others are auxins; cytokinin is not.


  14. Gibberellin, Apical dominance, Bolting, Breaking dormancy
     Answer: Apical dominance
     Explanation: Caused by auxin; others by gibberellin.


  15. Auxin, Ethylene, Cytokinin, DNA
     Answer: DNA
     Explanation: DNA is genetic material, not a hormone.


  16. Thigmotropism, Chemotropism, Respiration, Hydrotropism
     Answer: Respiration
     Explanation: Not a movement type.


  17. Mango, Tomato, Banana, Cactus
     Answer: Cactus
     Explanation: Others show tropic movement clearly; cactus shows minimal.


  18. Cytokinin, ABA, Fruit fall, Lateral growth
     Answer: Lateral growth
     Explanation: Promoted by cytokinin; others are ABA functions.


  19. Ethylene, Heliotropism, ABA, Cytokinin
     Answer: Heliotropism
     Explanation: A movement type; others are hormones.


  20. Water, Light, Gravity, Leaf
     Answer: Leaf
     Explanation: Others are stimuli for tropism; leaf is a plant organ.


  21. Abscisic acid, Cytokinin, IAA, Hemoglobin
     Answer: Hemoglobin
     Explanation: A respiratory pigment; not a plant product.


  22. Gibberellin, DNA, RNA, ABA
     Answer: Gibberellin
     Explanation: Others are genetic materials.


  23. Shoot, Root, Stem, Flower
     Answer: Flower
     Explanation: Does not exhibit directional movement.


  24. Cytokinin, Gibberellin, Rooting hormone, Auxin
     Answer: Cytokinin
     Explanation: Does not promote rooting.


  25. Tendril, Pollen tube, Root hair, Leaf
     Answer: Leaf
     Explanation: Does not respond directionally to external stimuli.


  26. ABA, Water conservation, Stomatal closure, Lateral bud growth
     Answer: Lateral bud growth
     Explanation: Cytokinin function; others are ABA related.


  27. Hydrotropism, Chemotropism, Phototropism, Germination
     Answer: Germination
     Explanation: Others are plant movements.


  28. 2,4-D, IAA, Ethylene, NAA
     Answer: Ethylene
     Explanation: Not an auxin.


  29. Gibberellin, Bolting, Fruit ripening, Internode elongation
     Answer: Fruit ripening
     Explanation: Controlled by ethylene, not gibberellin.


  30. Touch, Light, Pressure, Respiration
     Answer: Respiration
     Explanation: Not a stimulus for tropism.


  31. Cell division, Leaf fall, Bud growth, Seed dormancy
     Answer: Cell division
     Explanation: Done by cytokinin; others by ABA.


  32. Seed germination, Dormancy, Leaf fall, Drought resistance
     Answer: Seed germination
     Explanation: Opposite of ABA action.


  33. Chemotropism, Hydrotropism, ABA, Geotropism
     Answer: ABA
     Explanation: Others are types of movements.


  34. Auxin, Apical dominance, Rooting, Leaf fall
     Answer: Leaf fall
     Explanation: Not caused by auxin.


  35. IAA, NAA, 2,4-D, RNA
     Answer: RNA
     Explanation: Not a plant hormone.


  36. Tropic, Nastic, Elastic, Heliotropic
     Answer: Elastic
     Explanation: Not a movement type.


  37. Xylem, Shoot apex, Root tip, Young leaves
     Answer: Xylem
     Explanation: Not a hormone-producing region.


  38. Cytokinin, Leaf senescence delay, Stomatal closure, Cell division
     Answer: Stomatal closure
     Explanation: Not a cytokinin function.


  39. Geotropism, Gravity, Hydrotropism, Touch
     Answer: Touch
     Explanation: Not related to root direction.


  40. Flower, Leaf, Tendril, Stem
     Answer: Flower
     Explanation: Least involved in tropic responses.


  41. Ethylene, Flowering, Fruit ripening, Internode elongation
     Answer: Internode elongation
     Explanation: Done by gibberellin.


  42. Water, Cytokinin, Light, Gravity
     Answer: Cytokinin
     Explanation: Not a stimulus.


  43. IAA, Ethylene, DNA, ABA
     Answer: DNA
     Explanation: Not a hormone.


  44. Seed dormancy, Water conservation, Bud growth, Stress hormone
     Answer: Bud growth
     Explanation: Not related to ABA.


  45. Cytokinin, Apical dominance, Cell division, Bud growth
     Answer: Apical dominance
     Explanation: Controlled by auxin.


  46. 2,4-D, Gibberellin, NAA, IAA
     Answer: Gibberellin
     Explanation: Not an auxin.


  47. Tropism, Phototropism, Geotropism, Cell wall
     Answer: Cell wall
     Explanation: Not a movement type.


  48. Bolting, Internode elongation, Cell elongation, Seed dormancy
     Answer: Seed dormancy
     Explanation: ABA function; others by gibberellin.


  49. Thigmotropism, Chemotropism, Respiration, Geotropism
     Answer: Respiration
     Explanation: Not a movement.


  50. Cytokinin, Gibberellin, ABA, DNA
     Answer: DNA
     Explanation: Not a hormone.

Match the Pair

Set 1:

Match the items in Column A with Column B.

Column A

  1. Auxins
  2. Gibberellins
  3. Cytokinins
  4. Ethylene
  5. Abscisic Acid (ABA)

Column B
 A. Fruit ripening hormone
 B. Promotes cell division in roots and shoots
 C. Causes seed dormancy
 D. Promotes stem elongation
 E. Delays leaf abscission

Answers:
 1-D, 2-B, 3-B, 4-A, 5-C

Set 2:

Match the items in Column A with Column B.

Column A

  1. Phototropism
  2. Geotropism
  3. Hydrotropism
  4. Thigmotropism
  5. Chemotropism

Column B
 A. Response to water
 B. Movement of tendrils to touch
 C. Directional growth towards chemicals
 D. Growth towards light
 E. Growth influenced by gravity

Answers:
 1-D, 2-E, 3-A, 4-B, 5-C

Set 3:

Match the items in Column A with Column B.

Column A

  1. Function of Cytokinins
  2. Function of Ethylene
  3. Function of Auxins
  4. Function of ABA
  5. Function of Gibberellins

Column B
 A. Induces dormancy
 B. Promotes cell elongation
 C. Delays aging of leaves
 D. Promotes fruit ripening
 E. Breaks seed dormancy

Answers:
 1-C, 2-D, 3-B, 4-A, 5-E

Set 4:

Match the items in Column A with Column B.

Column A

  1. Source of Auxins
  2. Source of Cytokinins
  3. Source of Ethylene
  4. Source of Gibberellins
  5. Source of ABA

Column B
 A. Root tips
 B. Senescing leaves and fruits
 C. Shoot apex
 D. Developing seeds
 E. Mature leaves during stress

Answers:
 1-C, 2-B, 3-B, 4-D, 5-E

Set 5:

Match the items in Column A with Column B.

Column A

  1. Phototropism occurs due to
  2. Geotropism in roots is
  3. Hydrotropism is important for
  4. Thigmotropism is shown by
  5. Chemotropism assists in

Column B
 A. Growth towards water
 B. Pollen tube growth
 C. Unequal distribution of auxins
 D. Response of tendrils to touch
 E. Positive response to gravity

Answers:
 1-C, 2-E, 3-A, 4-D, 5-B

Set 6:

Match the items in Column A with Column B.

Column A

  1. Effect of Ethylene on fruits
  2. Effect of ABA during drought
  3. Effect of Cytokinins on senescence
  4. Effect of Gibberellins on stem
  5. Effect of Auxins on abscission

Column B
 A. Inhibits leaf fall
 B. Causes wilting by closing stomata
 C. Promotes stem elongation
 D. Causes fruit ripening
 E. Delays leaf and fruit drop

Answers:
 1-D, 2-B, 3-A, 4-C, 5-E

Set 7:

Match the items in Column A with Column B.

Column A

  1. Positive phototropism
  2. Negative geotropism
  3. Positive hydrotropism
  4. Positive thigmotropism
  5. Positive chemotropism

Column B
 A. Growth towards light
 B. Growth towards water
 C. Growth away from gravity
 D. Response to chemicals
 E. Growth of tendrils around support

Answers:
 1-A, 2-C, 3-B, 4-E, 5-D

Set 8:

Match the items in Column A with Column B.

Column A

  1. Hormone responsible for breaking seed dormancy
  2. Hormone responsible for fruit ripening
  3. Hormone responsible for cell division
  4. Hormone responsible for stem elongation
  5. Hormone responsible for closing stomata

Column B
 A. Gibberellins
 B. Cytokinins
 C. Ethylene
 D. ABA
 E. Auxins

Answers:
 1-A, 2-C, 3-B, 4-E, 5-D

Set 9:

Match the items in Column A with Column B.

Column A

  1. Heliotropism example
  2. Hormone that causes seed dormancy
  3. Hormone that promotes lateral bud growth
  4. Tropic movement in roots towards water
  5. Hormone used as a weedicide

Column B
 A. Sunflower
 B. Auxins
 C. ABA
 D. Cytokinins
 E. Hydrotropism

Answers:
 1-A, 2-C, 3-D, 4-E, 5-B

Set 10:

Match the items in Column A with Column B.

Column A

  1. Cause of bending in phototropism
  2. Site of synthesis of gibberellins
  3. Role of ABA in stomata
  4. Role of ethylene in senescence
  5. Cytokinins delay

Column B
 A. Shoot apex
 B. Wilting during drought
 C. Unequal auxin distribution
 D. Aging of leaves
 E. Senescence

Answers:
 1-C, 2-A, 3-B, 4-D, 5-E

Short Answer Questions  

  1. What are plant hormones?
     Plant hormones are chemical substances produced in plants that regulate growth and development.


  2. Name the main plant hormone responsible for cell elongation.
     Auxins


  3. Where are auxins mainly produced in a plant?
     In the shoot apex and young leaves.


  4. What is the primary function of gibberellins?
     To promote stem elongation and seed germination.


  5. How do cytokinins affect plant cells?
     They promote cell division and delay leaf senescence.


  6. Which hormone is responsible for fruit ripening?
     Ethylene


  7. What role does Abscisic Acid (ABA) play during drought?
     It closes stomata to reduce water loss.


  8. Define phototropism.
     Phototropism is the growth of a plant towards or away from light.


  9. What is geotropism?
     Growth response of plants to gravity.


  10. How do roots show positive geotropism?
     By growing downward into the soil.


  11. What is hydrotropism?
     Growth response of roots towards water.


  12. Which plant movement is a response to touch?
     Thigmotropism


  13. What is chemotropism?
     Growth movement in response to chemicals.


  14. Give an example of heliotropism.
     Sunflower turning towards the sun.


  15. How do auxins affect lateral buds?
     They inhibit lateral bud growth (apical dominance).


  16. What effect does ethylene have on leaves?
     It causes leaf abscission.


  17. Which hormone induces seed dormancy?
     Abscisic Acid (ABA)


  18. How do gibberellins break seed dormancy?
     By stimulating enzymes that promote germination.


  19. What is the role of cytokinins in plant growth?
     They promote cell division and stimulate shoot formation.


  20. Where is ethylene produced in plants?
     In ripening fruits, senescing leaves, and stressed tissues.


  21. What causes the bending of plants towards light?
     Unequal distribution of auxins.


  22. How does ABA help plants during stress?
     By inducing dormancy and closing stomata.


  23. What type of movement is phototropism?
     Tropic movement.


  24. How do tendrils respond to touch?
     By coiling around the support (thigmotropism).


  25. What is the effect of gibberellins on stem internodes?
     They cause elongation of internodes.


  26. Name a synthetic auxin used as a weedicide.
     2,4-Dichlorophenoxyacetic acid (2,4-D)


  27. How do cytokinins delay aging?
     By promoting nutrient mobilization and protein synthesis.


  28. What is the primary site of ABA synthesis?
     Mature leaves and seeds.


  29. What is the difference between positive and negative tropism?
     Positive tropism is growth towards stimulus; negative is growth away.


  30. What hormone controls the abscission of leaves?
     Ethylene


  31. Which hormone promotes lateral bud growth?
     Cytokinins


  32. How do auxins affect fruit development?
     They promote fruit formation and growth.


  33. What is the role of chemotropism in fertilization?
     Pollen tube grows towards ovule guided by chemical signals.


  34. How do gibberellins affect flowering?
     They promote flowering in some plants.


  35. What is the function of ethylene in seed germination?
     It has little or no effect on seed germination.


  36. How do auxins affect root formation in cuttings?
     They stimulate root initiation.


  37. What type of tropism is growth in response to water?
     Hydrotropism


  38. What hormone regulates stomatal closure?
     Abscisic Acid (ABA)


  39. Give an example of negative geotropism.
     Stem growing upwards against gravity.


  40. What is the role of ethylene in senescence?
     It accelerates aging and abscission.


  41. What causes bending in phototropism?
     Unequal auxin distribution on shaded and illuminated sides.


  42. Which hormone promotes seed germination?
     Gibberellins


  43. What is the main effect of ABA on seeds?
     Maintains dormancy.


  44. How do cytokinins affect nutrient mobilization?
     They stimulate mobilization to growing parts.


  45. Name the hormone that causes leaf drop.
     Ethylene


  46. What is apical dominance?
     Suppression of lateral buds by auxins from the shoot apex.


  47. Which plant hormone is gaseous?
     Ethylene


  48. How does hydrotropism benefit the plant?
     Helps roots find water.


  49. What is the effect of gibberellins on dwarf plants?
     They promote elongation to normal height.


  50. How do auxins promote cell elongation?
     By loosening cell walls to allow expansion.

Puzzles

  1. Puzzle: I am a plant hormone that promotes cell elongation and is mainly produced in the shoot tip. What am I?
     Answer: Auxin


  2. Puzzle: I am a hormone that breaks seed dormancy and causes stem elongation. Who am I?
     Answer: Gibberellin


  3. Puzzle: I am the hormone responsible for cell division and delay of leaf senescence. Name me.
     Answer: Cytokinin


  4. Puzzle: I am a gaseous hormone that promotes fruit ripening and leaf fall. What is my name?
     Answer: Ethylene


  5. Puzzle: I induce stomatal closure during water stress and maintain seed dormancy. Identify me.
     Answer: Abscisic Acid (ABA)


  6. Puzzle: Which tropic movement causes a plant shoot to bend towards light?
     Answer: Phototropism


  7. Puzzle: Roots grow downward into the soil because of which type of tropism?
     Answer: Geotropism (or Gravitropism)


  8. Puzzle: The curling of tendrils around a support is due to which tropic movement?
     Answer: Thigmotropism


  9. Puzzle: Roots grow towards water due to which tropic movement?
     Answer: Hydrotropism


  10. Puzzle: Sunflowers follow the sun during the day due to which movement?
     Answer: Heliotropism


  11. Puzzle: Which plant hormone is used commercially to ripen fruits faster?
     Answer: Ethylene


  12. Puzzle: Which hormone is known as the ‘growth hormone’ for plants?
     Answer: Gibberellin


  13. Puzzle: Name the hormone that prevents premature seed germination.
     Answer: Abscisic Acid (ABA)


  14. Puzzle: Which hormone is responsible for apical dominance in plants?
     Answer: Auxin


  15. Puzzle: What causes the bending of shoots towards light?
     Answer: Unequal distribution of auxin


  16. Puzzle: Name the hormone that stimulates cell division in plants.
     Answer: Cytokinin


  17. Puzzle: Which hormone promotes lateral bud growth by counteracting auxin?
     Answer: Cytokinin


  18. Puzzle: What hormone causes leaves to fall during autumn?
     Answer: Ethylene


  19. Puzzle: Which hormone helps plants survive drought by closing stomata?
     Answer: Abscisic Acid (ABA)


  20. Puzzle: Name the movement in which plant roots grow away from light.
     Answer: Negative Phototropism


  21. Puzzle: Which hormone increases in fruit during ripening?
     Answer: Ethylene


  22. Puzzle: What causes seed dormancy?
     Answer: Abscisic Acid (ABA)


  23. Puzzle: Which hormone helps in breaking seed dormancy and initiating germination?
     Answer: Gibberellin


  24. Puzzle: The coiling of tendrils when touched is an example of which tropism?
     Answer: Thigmotropism


  25. Puzzle: What type of movement causes roots to grow towards water?
     Answer: Hydrotropism


  26. Puzzle: Name the hormone that regulates vascular tissue differentiation.
     Answer: Auxin


  27. Puzzle: Which hormone delays aging in leaves?
     Answer: Cytokinin


  28. Puzzle: What causes the elongation of internodes in stems?
     Answer: Gibberellins


  29. Puzzle: Which hormone controls leaf abscission?
     Answer: Ethylene


  30. Puzzle: Which hormone is produced in the roots but affects the shoots?
     Answer: Cytokinin


  31. Puzzle: Which hormone is involved in mechanical stress responses?
     Answer: Ethylene


  32. Puzzle: Which hormone is responsible for seed dormancy during unfavorable conditions?
     Answer: Abscisic Acid (ABA)


  33. Puzzle: The bending of shoots away from gravity is called?
     Answer: Negative Geotropism


  34. Puzzle: Which hormone is used in rooting powders to promote root growth?
     Answer: Auxin


  35. Puzzle: Name the tropic movement where plants grow towards chemicals.
     Answer: Chemotropism


  36. Puzzle: Which hormone promotes flowering in some plants?
     Answer: Gibberellin


  37. Puzzle: What is the effect of ethylene on flowers?
     Answer: Promotes senescence (aging and wilting)


  38. Puzzle: Which hormone controls stomatal closure?
     Answer: Abscisic Acid (ABA)


  39. Puzzle: Name the hormone that stimulates nutrient mobilization in plants.
     Answer: Cytokinin


  40. Puzzle: What is the term for plant movement towards touch?
     Answer: Thigmotropism


  41. Puzzle: What hormone concentration is higher on the shaded side during phototropism?
     Answer: Auxin


  42. Puzzle: Which hormone promotes seed germination by activating enzymes?
     Answer: Gibberellin


  43. Puzzle: Which hormone is responsible for cell elongation in stems?
     Answer: Auxin


  44. Puzzle: Which hormone delays leaf senescence?
     Answer: Cytokinin


  45. Puzzle: What hormone causes the fruit to soften and sweeten?
     Answer: Ethylene


  46. Puzzle: What is the hormone that inhibits growth and promotes dormancy?
     Answer: Abscisic Acid (ABA)


  47. Puzzle: Name the movement in which shoots bend towards sunlight.
     Answer: Phototropism


  48. Puzzle: Which hormone is synthesized in young leaves and roots?
     Answer: Cytokinin


  49. Puzzle: Which hormone causes the thickening of stems and leaves?
     Answer: Gibberellin (by promoting elongation and division)


  50. Puzzle: What hormone regulates fruit ripening and leaf fall?
     Answer: Ethylene

Difference Between:

  1. Difference between Auxins and Gibberellins:
  • Auxins promote cell elongation, especially in shoots and roots.
  • Gibberellins promote stem elongation, seed germination, and fruit development.
  • Auxins control apical dominance; gibberellins break seed dormancy.
  • Auxins are active in root initiation; gibberellins stimulate flowering in some plants.

 

  1. Difference between Cytokinins and Auxins:
  • Cytokinins promote cell division and delay senescence.
  • Auxins promote cell elongation and suppress lateral bud growth.
  • Cytokinins are synthesized in roots and travel upward.
  • Auxins are produced in shoot tips and travel downward.

 

  1. Difference between Ethylene and Abscisic Acid (ABA):
  • Ethylene is a gaseous hormone that promotes ripening and abscission.
  • ABA is a stress hormone that induces dormancy and stomatal closure.
  • Ethylene accelerates aging; ABA inhibits growth.
  • Ethylene is involved in fruit ripening; ABA helps in drought resistance.

 

  1. Difference between Phototropism and Geotropism:
  • Phototropism is the directional growth in response to light.
  • Geotropism is the directional growth in response to gravity.
  • Shoots show positive phototropism; roots show positive geotropism.
  • Controlled by unequal distribution of auxins in both cases.
  1. Difference between Hydrotropism and Chemotropism:
  • Hydrotropism is growth in response to water.
  • Chemotropism is growth in response to chemicals.
  • Roots grow towards moisture in hydrotropism.
  • Pollen tubes grow toward ovules in chemotropism.

 

  1. Difference between Thigmotropism and Heliotropism:
  • Thigmotropism is growth response to touch or contact.
  • Heliotropism is movement of plant parts towards sunlight.
  • Seen in tendrils winding around supports in thigmotropism.
  • Seen in sunflower tracking the sun in heliotropism.

 

  1. Difference between Positive and Negative Tropism:
  • Positive tropism is growth towards the stimulus.
  • Negative tropism is growth away from the stimulus.
  • Roots show positive hydrotropism.
  • Shoots show negative geotropism.

 

  1. Difference between Plant Hormones and Animal Hormones:
  • Plant hormones are simple organic substances like auxins and ABA.
  • Animal hormones are complex proteins or steroids like insulin.
  • Plant hormones control growth and movement.
  • Animal hormones regulate metabolism and body processes.

 

  1. Difference between Apical Dominance and Lateral Bud Growth:
  • Apical dominance is suppression of lateral buds by the apical bud.
  • Lateral bud growth occurs when apical dominance is removed.
  • Auxins from apical bud inhibit side branches.
  • Cytokinins promote lateral bud development.

 

  1. Difference between Seed Dormancy and Seed Germination:
  • Seed dormancy is a state of suspended growth.
  • Germination is active growth of seed into seedling.
  • Dormancy is maintained by ABA.
  • Germination is initiated by gibberellins.

 

  1. Difference between Stomatal Opening and Closing:
  • Stomatal opening allows gas exchange and transpiration.
  • Stomatal closing prevents water loss during drought.
  • Opening occurs in presence of water and light.
  • Closing is induced by ABA during stress.

 

  1. Difference between Natural and Synthetic Auxins:
  • Natural auxins are produced by plants (e.g., IAA).
  • Synthetic auxins are man-made (e.g., NAA, 2,4-D).
  • Natural auxins regulate natural growth processes.
  • Synthetic auxins are used in agriculture as herbicides and rooting agents.

 

  1. Difference between Leaf Senescence and Leaf Abscission:
  • Senescence is aging of leaf tissues.
  • Abscission is shedding of leaves.
  • Senescence is regulated by reduced cytokinins.
  • Abscission is promoted by ethylene and ABA.

 

  1. Difference between Photoperiodism and Phototropism:
  • Photoperiodism is response to length of day/night.
  • Phototropism is directional growth towards light.
  • Photoperiodism controls flowering.
  • Phototropism controls growth direction.

 

  1. Difference between Cytokinin and Gibberellin Effects:
  • Cytokinins stimulate cell division and delay aging.
  • Gibberellins stimulate elongation of stems and break dormancy.
  • Cytokinins promote shoot formation.
  • Gibberellins promote seed germination.

 

  1. Difference between Tropic and Nastic Movements:
  • Tropic movements are directional responses to stimuli.
  • Nastic movements are non-directional.
  • Tropic responses depend on the direction of stimulus.
  • Nastic movements depend on intensity of stimulus.
  1. Difference between Auxin and Ethylene in Plant Growth:
  • Auxin promotes elongation and root initiation.
  • Ethylene promotes ripening and abscission.
  • Auxin is growth-promoting.
  • Ethylene is growth-inhibiting under stress.

 

  1. Difference between ABA and Ethylene during Stress:
  • ABA helps conserve water by closing stomata.
  • Ethylene causes shedding of leaves and fruits.
  • ABA prevents growth.
  • Ethylene promotes senescence.

 

  1. Difference between Role of Gibberellin and Cytokinin in Germination:
  • Gibberellin breaks seed dormancy and activates enzymes.
  • Cytokinin promotes cell division after germination.
  • Gibberellin is active at the beginning of germination.
  • Cytokinin is active during shoot development.

 

  1. Difference between Positive and Negative Phototropism:
  • Positive phototropism is growth towards light (shoots).
  • Negative phototropism is growth away from light (roots).
  • Controlled by differential auxin distribution.
  • Ensures proper orientation for photosynthesis.

Assertion and Reason

Directions:
 For each question, choose the correct option:
 A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
 B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
 C. Assertion is true, but Reason is false.
 D. Assertion is false, but Reason is true.

  1.  

Assertion: Auxins promote elongation of stem cells.
 Reason: Auxins stimulate cell division in the apical meristem.
 Answer: C

  1.  

Assertion: Gibberellins promote bolting in rosette plants.
 Reason: Gibberellins increase internodal length rapidly.
 Answer: A

  1.  

Assertion: Ethylene is used commercially to ripen fruits.
 Reason: Ethylene retards the ripening process.
 Answer: C

  1.  

Assertion: Cytokinins delay senescence in leaves.
 Reason: Cytokinins promote synthesis of proteins and RNA.
 Answer: A

  1.  

Assertion: ABA helps in seed germination.
 Reason: ABA breaks seed dormancy.
 Answer: D

  1.  

Assertion: Tropic movements are growth movements.
 Reason: These movements occur in response to stimuli.
 Answer: A

  1.  

Assertion: Geotropism is seen in roots.
 Reason: Roots grow towards light.
 Answer: C

  1.  

Assertion: Phototropism is a directional movement.
 Reason: Plants bend away from the source of light.
 Answer: C

  1.  

Assertion: Hydrotropism is movement toward water.
 Reason: Roots show positive hydrotropism.
 Answer: A

  1.  

Assertion: Thigmotropism occurs in tendrils.
 Reason: Tendrils coil around support in response to touch.
 Answer: A

  1.  

Assertion: Auxins are produced in root tips.
 Reason: Root tips are the primary site of auxin synthesis.
 Answer: D

  1.  

Assertion: Cytokinins promote lateral bud growth.
 Reason: Cytokinins inhibit apical dominance.
 Answer: A

  1.  

Assertion: ABA closes stomata during water stress.
 Reason: ABA increases guard cell turgidity.
 Answer: C

  1.  

Assertion: Chemotropism helps in fertilisation.
 Reason: Pollen tubes grow toward ovules due to chemical stimuli.
 Answer: A

  1.  

Assertion: Auxins delay the falling of leaves and fruits.
 Reason: They increase abscission layer activity.
 Answer: C

  1.  

Assertion: Gibberellins break seed dormancy.
 Reason: They stimulate hydrolytic enzymes.
 Answer: A

  1.  

Assertion: ABA is also called the stress hormone.
 Reason: ABA helps plants tolerate environmental stress.
 Answer: A

  1.  

Assertion: Ethylene is useful in agriculture.
 Reason: It inhibits fruit ripening.
 Answer: C

  1.  

Assertion: Phototropism occurs due to unequal distribution of auxins.
 Reason: Auxins accumulate on the darker side of the stem.
 Answer: A

  1.  

Assertion: Gibberellins promote leaf fall.
 Reason: Gibberellins delay senescence.
 Answer: D

  1.  

Assertion: ABA causes wilting in plants.
 Reason: ABA closes stomata reducing water loss.
 Answer: B

  1.  

Assertion: Light is the stimulus for phototropism.
 Reason: Gravity is the stimulus for phototropism.
 Answer: C

  1.  

Assertion: Gibberellins are involved in seed germination.
 Reason: They activate α-amylase enzyme in endosperm.
 Answer: A

  1.  

Assertion: ABA induces dormancy in buds.
 Reason: ABA inhibits metabolic processes in buds.
 Answer: A

  1.  

Assertion: Ethylene helps in fruit abscission.
 Reason: It weakens the abscission layer.
 Answer: A

  1.  

Assertion: Cytokinins promote apical dominance.
 Reason: Cytokinins are found in shoot tips.
 Answer: D

  1.  

Assertion: Ethylene is effective in senescence.
 Reason: Ethylene promotes aging in plants.
 Answer: A

  1.  

Assertion: Hydrotropism is slower than phototropism.
 Reason: Water stimulus reaches slower than light stimulus.
 Answer: B

  1.  

Assertion: Heliotropism is movement in response to light.
 Reason: Sunflower shows heliotropic movement.
 Answer: A

  1.  

Assertion: Thigmotropism is shown by all plant parts.
 Reason: All plant parts are sensitive to gravity.
 Answer: D

  1.  

Assertion: ABA is antagonistic to gibberellins.
 Reason: ABA promotes dormancy while gibberellins break it.
 Answer: A

  1.  

Assertion: Cytokinins initiate rooting in stem cuttings.
 Reason: Cytokinins increase root cell elongation.
 Answer: C

  1.  

Assertion: Gibberellins cause elongation of dwarf plants.
 Reason: They increase internodal length.
 Answer: A

  1.  

Assertion: ABA regulates stomatal opening.
 Reason: It increases osmotic potential of guard cells.
 Answer: C

  1.  

Assertion: Auxins are used as herbicides.
 Reason: In high concentrations, they kill broad-leaved weeds.
 Answer: A

  1.  

Assertion: Thigmotropism helps climbing plants.
 Reason: Tendrils respond to touch by coiling.
 Answer: A

  1.  

Assertion: Chemotropism is crucial for sexual reproduction.
 Reason: Pollen tubes grow towards ovary due to chemicals.
 Answer: A

  1.  

Assertion: Cytokinins are produced in shoot apex.
 Reason: Shoot apex inhibits cytokinin production.
 Answer: D

  1.  

Assertion: Phototropism is a non-directional movement.
 Reason: It depends on light direction.
 Answer: C

  1.  

Assertion: ABA increases water loss.
 Reason: It opens stomata under stress.
 Answer: D

  1.  

Assertion: Gibberellins are responsible for fruit setting.
 Reason: They promote ovary development after fertilisation.
 Answer: B

  1.  

Assertion: Auxins cause curvature in plants.
 Reason: They are uniformly distributed in plant tissues.
 Answer: C

  1.  

Assertion: Geotropism helps anchor plants.
 Reason: Roots grow toward gravity for fixation.
 Answer: A

  1.  

Assertion: Light causes roots to bend upward.
 Reason: Roots exhibit negative phototropism.
 Answer: A

  1.  

Assertion: ABA regulates closing of stomata.
 Reason: It increases solute concentration in guard cells.
 Answer: C

  1.  

Assertion: Tendrils are positively thigmotropic.
 Reason: They move away from solid support.
 Answer: C

  1.  

Assertion: Auxins play a major role in phototropism.
 Reason: They migrate to the illuminated side.
 Answer: C

  1.  

Assertion: ABA is present only in stressed plants.
 Reason: It is not found under normal conditions.
 Answer: D

  1.  

Assertion: Cytokinins promote chloroplast development.
 Reason: They regulate protein synthesis.
 Answer: B

  1.  

Assertion: Fruit ripening involves increased respiration.
 Reason: Ethylene enhances cellular respiration.
 Answer: A

True or False

  1. Gibberellins are responsible for seed dormancy. False
  2. Cytokinins promote cell division in plants. True
  3. Ethylene causes fruit ripening. True
  4. Abscisic Acid (ABA) promotes seed germination. False
  5. Phototropism is a plant’s response to gravity. False
  6. Geotropism helps roots grow downwards into the soil. True
  7. Hydrotropism is the growth of roots towards water. True
  8. Thigmotropism is the response of plants to touch. True
  9. Chemotropism is the movement of plants towards chemicals. True
  10. Auxins delay leaf abscission. True
  11. Ethylene is a gaseous hormone. True
  12. Cytokinins delay senescence (aging) of leaves. True
  13. Abscisic Acid helps plants survive drought by closing stomata. True
  14. Gibberellins promote stem elongation and flowering. True
  15. Phototropism causes plants to grow away from light. False
  16. Ethylene inhibits fruit ripening. False
  17. ABA induces dormancy in seeds. True
  18. Cytokinins are produced mainly in root tips. False
  19. Auxins are mainly produced in the shoot apex. True
  20. Heliotropism is the movement of plants in response to sunlight. True
  21. Thigmotropism is only seen in roots. False
  22. Chemotropism plays a role in pollen tube growth. True
  23. Gibberellins cause dwarfism in plants. False
  24. Auxins are used as weed killers. True
  25. Ethylene accelerates the aging of leaves. True
  26. ABA promotes seed germination under favorable conditions. False
  27. Cytokinins promote lateral bud growth. True
  28. Geotropism is also called gravitropism. True
  29. Hydrotropism is a negative response to water. False
  30. Phototropism is controlled by unequal distribution of auxins. True
  31. Ethylene is produced in ripening fruits and senescing leaves. True
  32. Auxins inhibit the growth of lateral buds (apical dominance). True
  33. Abscisic Acid promotes stomatal opening during drought. False
  34. Cytokinins are involved in delaying leaf senescence. True
  35. Gibberellins promote breaking of seed dormancy. True
  36. Heliotropism is best observed in sunflower plants. True
  37. Thigmotropism helps climbing plants like tendrils to coil around supports. True
  38. Chemotropism causes roots to grow away from chemicals. False
  39. Ethylene is responsible for leaf and fruit abscission. True
  40. Auxins promote root initiation in cuttings. True
  41. ABA levels increase during water stress. True
  42. Cytokinins inhibit cell division. False
  43. Phototropism results in bending of stems towards light. True
  44. Gibberellins are mainly produced in mature leaves. False
  45. Ethylene production decreases during fruit ripening. False
  46. Hydrotropism is important for plants to find water sources. True
  47. Thigmotropism is a non-directional movement. False
  48. Auxins are transported from shoot tip to root. True
  49. ABA is also called stress hormone in plants. True
  50. Auxins promote cell elongation in plants. True

Long Answer Questions

  1. What are plant hormones and why are they important?
     Plant hormones, or phytohormones, are chemical substances produced in small quantities in various parts of plants. They regulate growth, development, and responses to environmental stimuli. They coordinate processes like cell division, elongation, dormancy, flowering, fruit ripening, and abscission. Their precise control allows plants to adapt and survive in diverse conditions.


  2. Explain the role and functions of auxins in plants.
     Auxins are primarily produced in the shoot apex and young leaves. They promote cell elongation by loosening cell walls, thus allowing cells to expand. Auxins regulate apical dominance by inhibiting lateral bud growth, promote root initiation in cuttings, stimulate fruit development, delay leaf abscission, and mediate tropic responses such as phototropism and geotropism.


  3. Describe gibberellins and their functions in detail.
     Gibberellins are growth-promoting hormones synthesized mainly in young leaves, roots, and developing seeds. They promote stem elongation by stimulating cell division and elongation, break seed dormancy by activating enzymes that mobilize stored food, induce flowering in some plants, and enhance fruit growth and development. Gibberellins help dwarf plants grow taller and promote germination.


  4. What are cytokinins and how do they influence plant growth?
     Cytokinins are hormones produced mainly in root tips and developing fruits. They stimulate cell division (cytokinesis), promote shoot formation, and delay leaf senescence by mobilizing nutrients and enhancing protein synthesis. Cytokinins also work in coordination with auxins to regulate apical dominance and lateral bud growth.


  5. Explain the hormone ethylene and its effects on plants.
     Ethylene is a gaseous hormone produced in ripening fruits, aging leaves, and stressed tissues. It promotes fruit ripening by breaking down cell walls and converting starch into sugars. Ethylene also causes leaf and fruit abscission, accelerates senescence, and influences responses to mechanical stress. It helps synchronize fruit ripening and leaf fall.


  6. Discuss Abscisic Acid (ABA) and its importance in plants.
     ABA is a growth-inhibiting hormone produced in mature leaves and seeds. It induces seed dormancy by preventing premature germination, helps plants survive drought by causing stomatal closure to reduce water loss, and slows down growth during unfavorable conditions. ABA plays a vital role in stress responses and maintaining dormancy.


  7. What is phototropism? Explain the mechanism in detail.
     Phototropism is the directional growth of plants in response to light. When light falls on one side of the shoot, auxins redistribute to the shaded side, causing cells there to elongate more than on the lighted side. This differential growth causes the shoot to bend towards the light source, optimizing photosynthesis.


  8. Define geotropism and differentiate between positive and negative geotropism.
     Geotropism is the growth response to gravity. Positive geotropism refers to growth towards gravity, as seen in roots growing downward. Negative geotropism refers to growth away from gravity, as in shoots growing upwards. These responses help plants orient themselves correctly for nutrient absorption and light capture.


  9. Explain hydrotropism and its significance in plants.
     Hydrotropism is the growth of plant roots towards water. Roots sense moisture gradients in the soil and grow toward higher water concentrations, ensuring the plant’s access to essential water for survival, metabolism, and growth.


  10. What is thigmotropism? Give examples and explain its mechanism.
     Thigmotropism is the growth response of plants to touch or mechanical stimuli. Climbing plants like tendrils exhibit positive thigmotropism by coiling around supports upon contact. This is caused by unequal growth rates on opposite sides of the tendril, triggered by mechanical stimulation.


  11. Describe chemotropism and its role in plant reproduction.
     Chemotropism is the growth response towards or away from chemical stimuli. It is crucial during fertilization, where the pollen tube grows toward the ovule guided by chemical attractants secreted by the ovule, ensuring successful fertilization.


  12. Explain heliotropism with reference to the sunflower plant.
     Heliotropism is the movement or growth of plants in response to the sun’s direction. Sunflowers exhibit heliotropism by their flower heads tracking the sun’s movement from east to west during the day to maximize photosynthesis and warmth, then returning to the east at night.


  13. How do auxins control apical dominance?
     Auxins produced by the apical bud inhibit the growth of lateral buds by suppressing their development. This phenomenon, called apical dominance, ensures that the main shoot grows upward and is prioritized over side branches, optimizing light capture and resource allocation.


  14. Discuss the role of gibberellins in breaking seed dormancy.
     Gibberellins activate enzymes like amylase in seeds that convert stored starch into sugars, providing energy for the embryo to germinate. By overcoming the inhibitory effects of ABA, gibberellins initiate seed germination when conditions are favorable.


  15. How do cytokinins delay leaf senescence?
     Cytokinins delay aging by promoting nutrient mobilization, enhancing protein synthesis, and maintaining chlorophyll content in leaves. This keeps leaves green and functional longer, supporting photosynthesis and plant vitality.


  16. What is the significance of ethylene in fruit ripening?
     Ethylene triggers enzymatic processes that soften fruit tissues, convert starches to sugars, and change color, aroma, and taste, making fruits palatable and ready for seed dispersal.


  17. Describe the role of Abscisic Acid in stomatal closure during drought.
     ABA accumulates in guard cells during water stress, causing them to lose potassium ions and water, leading to stomatal closure. This reduces transpiration and water loss, helping the plant conserve water.


  18. Explain how phototropism helps plants survive.
     By bending towards light, phototropism enables plants to maximize light absorption for photosynthesis, which is essential for energy production, growth, and survival.


  19. What is the difference between tropic and nastic movements?
     Tropic movements are directional responses to stimuli (e.g., phototropism), while nastic movements are non-directional and independent of stimulus direction (e.g., closing of mimosa leaves).


  20. Explain the role of auxins in rooting of cuttings.
     Auxins promote root initiation by stimulating cell division and elongation at the cutting base, encouraging root formation and successful propagation.


  21. How do gibberellins influence flowering in plants?
     In some plants, gibberellins promote flowering by stimulating floral bud development and flowering even under non-inductive conditions.


  22. What causes the bending of a shoot in phototropism?
     Unequal distribution of auxins, accumulating on the shaded side, causes more cell elongation there, resulting in bending toward the light.


  23. Describe the function of cytokinins in tissue culture.
     Cytokinins stimulate cell division and shoot formation in tissue culture, aiding plant propagation and genetic engineering.


  24. How does ethylene affect leaf and flower abscission?
     Ethylene promotes the formation of an abscission layer at the base of leaves and flowers, facilitating their controlled shedding.


  25. What is the role of ABA in seed dormancy and germination?
     ABA maintains seed dormancy by inhibiting germination enzymes; its reduction allows gibberellins to break dormancy.


  26. Explain hydrotropism with a practical example.
     Roots growing towards moist soil patches show hydrotropism, enabling plants to access water critical for survival.


  27. Discuss the importance of thigmotropism in climbing plants.
     Thigmotropism enables tendrils to coil around supports, helping climbing plants gain better access to sunlight by growing vertically.


  28. How does chemotropism assist in fertilization?
     Chemical signals from the ovule guide the pollen tube growth towards the ovule, ensuring efficient fertilization.


  29. Explain the mechanism of heliotropism in sunflowers.
     Sunflower stems elongate on the shaded side due to auxin redistribution, causing flower heads to track the sun’s movement.


  30. What is apical dominance and why is it beneficial?
     Apical dominance prevents lateral bud growth, allowing the plant to grow taller and compete effectively for light.


  31. Describe the effects of gibberellins on dwarf plants.
     Gibberellins stimulate cell elongation, causing dwarf plants to grow taller and achieve normal height.


  32. How does ABA help plants survive adverse environmental conditions?
     By inducing dormancy, closing stomata, and slowing growth, ABA helps plants conserve resources during stress.


  33. Explain how cytokinins influence shoot and root growth.
     Cytokinins promote shoot formation and cell division but inhibit root growth when present in high concentrations.


  34. Describe the interplay between auxins and cytokinins in plant growth regulation.
     Auxins promote root formation; cytokinins promote shoot formation. Their relative concentrations regulate organ development.


  35. What are the physiological effects of ethylene on plants under mechanical stress?
     Ethylene mediates responses like the thickening of stems and leaf epinasty to adapt to mechanical injury.


  36. Explain the role of auxins in vascular tissue differentiation.
     Auxins stimulate the differentiation of vascular tissues like xylem and phloem during plant growth.


  37. What is the significance of leaf abscission in plants?
     Leaf abscission helps conserve water and nutrients, removes damaged leaves, and prepares plants for dormancy.


  38. How do gibberellins affect seedling growth in the dark?
     They promote elongation of the hypocotyl to help seedlings reach light.


  39. Explain the role of ABA in seed maturation.
     ABA promotes storage protein accumulation and desiccation tolerance during seed development.


  40. What is the role of cytokinins in delaying senescence?
     They maintain chlorophyll content and protein synthesis, prolonging leaf life.


  41. Describe the effect of ethylene on fruit shelf life.
     Ethylene shortens fruit shelf life by accelerating ripening and senescence.


  42. Explain the role of phototropism in agriculture.
     Understanding phototropism helps in optimizing plant spacing and light exposure for better crop yield.


  43. How do plants perceive and respond to gravity?
     Statoliths in root cap cells settle due to gravity, triggering auxin redistribution and root bending.


  44. What are the practical applications of auxins in horticulture?
     Auxins are used for rooting cuttings, tissue culture, and as herbicides.


  45. Describe the chemical nature of cytokinins.
     Cytokinins are adenine derivatives that promote cell division.


  46. How does ethylene influence flower senescence?
     Ethylene accelerates flower aging and petal drop.


  47. Explain the role of ABA in regulating seed germination under unfavorable conditions.
     ABA inhibits germination until conditions improve.


  48. What are the key differences between gibberellins and auxins?
     Gibberellins mainly promote stem elongation and seed germination, while auxins control cell elongation, apical dominance, and rooting.


  49. Describe how thigmotropism benefits plants in dense vegetation.
     By climbing or coiling, plants avoid shading and compete for light.


  50. Summarize the coordinated action of plant hormones during seed germination.
     ABA maintains dormancy, gibberellins break dormancy by activating enzymes, and auxins and cytokinins support embryo growth.

Give Reasons

  1. Give reason why plant hormones are called chemical messengers.
     Because they transmit signals from one part of the plant to another, regulating growth and responses.


  2. Give reason why auxins promote cell elongation.
     Auxins loosen the cell wall by increasing its plasticity, allowing cells to expand.


  3. Give reason why apical dominance occurs in plants.
     Auxins produced at the shoot apex inhibit the growth of lateral buds, causing apical dominance.


  4. Give reason why gibberellins break seed dormancy.
     Gibberellins activate enzymes that convert stored food into energy for the embryo to germinate.


  5. Give reason why cytokinins delay leaf senescence.
     Cytokinins maintain chlorophyll and promote protein synthesis, preventing premature aging.


  6. Give reason why ethylene is called a gaseous hormone.
     Because ethylene is a hydrocarbon gas that diffuses easily through plant tissues.


  7. Give reason why abscisic acid induces stomatal closure.
     ABA causes guard cells to lose potassium ions and water, leading to stomatal closure to conserve water.


  8. Give reason why phototropism helps plants survive.
     It allows shoots to grow towards light, maximizing photosynthesis.


  9. Give reason why roots show positive geotropism.
     Roots grow downward to anchor the plant and absorb water and minerals from the soil.


  10. Give reason why tendrils coil around supports in climbing plants.
     Due to thigmotropism, tendrils respond to touch by growing unevenly and coiling for support.


  11. Give reason why ethylene promotes fruit ripening.
     Ethylene activates enzymes that soften fruit and convert starch into sugars.


  12. Give reason why auxins are used in rooting powders.
     They stimulate root initiation by promoting cell division and elongation at cuttings.


  13. Give reason why gibberellins cause stem elongation.
     They stimulate both cell division and elongation in the internodes.


  14. Give reason why cytokinins promote shoot formation in tissue culture.
     Cytokinins encourage cell division and differentiation into shoots.


  15. Give reason why ABA maintains seed dormancy.
     It inhibits growth-promoting hormones, preventing germination under unfavorable conditions.


  16. Give reason why hydrotropism is vital for plants.
     It directs roots towards moisture, essential for water uptake.


  17. Give reason why heliotropism is observed in sunflowers.
     Sunflower heads track the sun to maximize light absorption for photosynthesis.


  18. Give reason why ethylene accelerates leaf abscission.
     It induces the formation of an abscission layer leading to leaf fall.


  19. Give reason why gibberellins are important in agriculture.
     They improve crop yield by promoting flowering and fruit growth.


  20. Give reason why auxins inhibit lateral bud growth.
     Auxins suppress lateral buds to maintain apical dominance.


  21. Give reason why phototropism occurs only in shoots and not in roots.
     Shoots grow towards light to photosynthesize, while roots grow away from light to seek nutrients.


  22. Give reason why cytokinins are called cell division hormones.
     Because they stimulate cytokinesis during cell division.


  23. Give reason why ethylene causes flower senescence.
     Ethylene triggers enzymatic degradation leading to petal wilting and drop.


  24. Give reason why ABA helps plants survive drought conditions.
     ABA induces stomatal closure to reduce water loss.


  25. Give reason why gibberellins break seed dormancy during germination.
     They stimulate production of amylase to convert starch into sugars for energy.


  26. Give reason why thigmotropism benefits climbing plants.
     It helps them attach to supports and grow upwards for better light exposure.


  27. Give reason why auxins are produced mainly in shoot tips.
     Because young growing regions need auxins to regulate elongation and development.


  28. Give reason why ethylene is involved in mechanical stress responses.
     It regulates growth adjustments to strengthen plant tissues under stress.


  29. Give reason why cytokinins delay aging in leaves.
     They enhance nutrient mobilization and chlorophyll retention.


  30. Give reason why roots show positive hydrotropism.
     To grow towards water sources ensuring plant hydration.


  31. Give reason why gibberellins promote flowering in some plants.
     They stimulate flower bud differentiation and development.


  32. Give reason why abscisic acid inhibits seed germination.
     ABA suppresses enzymes necessary for germination until conditions improve.


  33. Give reason why auxins promote vascular tissue differentiation.
     They regulate the development of xylem and phloem during growth.


  34. Give reason why ethylene is used commercially to ripen fruits.
     Because it uniformly accelerates ripening, making fruits market-ready.


  35. Give reason why phototropism results in bending of the shoot towards light.
     Unequal auxin distribution causes faster cell elongation on the shaded side.


  36. Give reason why cytokinins and auxins together regulate organ formation.
     Their balance controls whether shoots or roots develop from plant tissues.


  37. Give reason why ABA causes seed dormancy to ensure survival.
     Dormancy prevents germination under adverse environmental conditions.


  38. Give reason why tendrils exhibit thigmotropic movement.
     Contact with objects triggers differential growth, causing coiling.


  39. Give reason why gibberellins affect internode elongation.
     They promote cell division and elongation in stem internodes.


  40. Give reason why ethylene induces leaf and fruit abscission.
     It activates enzymes that degrade cell walls at the abscission zone.


  41. Give reason why auxins delay leaf abscission.
     Auxins maintain cell wall integrity, preventing premature leaf fall.


  42. Give reason why hydrotropism is more prominent in roots than shoots.
     Roots need to locate water for absorption; shoots do not.


  43. Give reason why ABA causes stomatal closure quickly during water stress.
     ABA triggers ion efflux in guard cells, leading to water loss and stomatal closing.


  44. Give reason why gibberellins are essential for seedling growth in darkness.
     They promote hypocotyl elongation to reach light.


  45. Give reason why ethylene is produced more in aging or stressed tissues.
     It signals the plant to initiate ripening or senescence processes.


  46. Give reason why auxins are unevenly distributed during phototropism.
     Light destroys auxins on the illuminated side, concentrating them on the shaded side.


  47. Give reason why cytokinins stimulate nutrient mobilization in plants.
     They promote protein synthesis and delay senescence by nutrient redistribution.


  48. Give reason why ABA levels increase during drought.
     To reduce water loss by closing stomata and slowing growth.


  49. Give reason why ethylene can act as a ripening hormone in climacteric fruits.
     Because its production increases rapidly, triggering ripening enzymes.


  50. Give reason why phototropism enhances plant productivity.
     By growing towards light, plants maximize photosynthesis and energy production.

Arrange the Words 

Case Studies

Case Study 1:
 A gardener noticed that the shoots of certain plants in his garden always bend toward the light source, while the roots grow downward into the soil. Explain the plant hormones or processes involved in this observation.

Answer:
 The bending of shoots toward light is due to phototropism, regulated by the hormone auxin, which accumulates on the shaded side, causing cell elongation. The roots growing downward is due to geotropism (gravitropism), where roots respond positively to gravity, growing downward, while shoots show negative geotropism (grow upward).

 

Case Study 2:
 In a greenhouse experiment, scientists applied auxins to the lower side of a horizontally placed stem. The stem bent upward. Explain the mechanism and significance.

Answer:
 Auxins promote cell elongation. When applied to the lower side, auxin concentration increases there, causing cells to elongate more on that side. This results in the stem bending upward, demonstrating positive phototropism or negative geotropism. This mechanism helps plants grow upright and toward light.

 

Case Study 3:
 A farmer observed premature leaf fall in some fruit trees. The fruits also ripened quickly. Which plant hormone is responsible, and what other effects does it have?

Answer:
 Ethylene is responsible for fruit ripening and leaf abscission (premature leaf fall). It is a gaseous hormone that promotes ripening by breaking down cell walls and converting starches to sugars. It also promotes abscission by weakening the cells at the leaf base.

 

Case Study 4:
 Seeds of a certain plant remained dormant despite being planted in favorable conditions. Scientists applied a hormone, and the seeds germinated rapidly. Identify the hormone and explain its function.

Answer:
 The hormone is gibberellin. It breaks seed dormancy by stimulating enzyme production that converts stored food into energy, promoting seed germination and rapid stem elongation.

 

Case Study 5:
 During drought conditions, a plant’s stomata close to conserve water. Name the hormone responsible and explain its mode of action.

Answer:
 Abscisic Acid (ABA) is responsible. It signals guard cells to lose turgidity, causing stomatal closure, which reduces transpiration and water loss during drought.

 

Case Study 6:
 A climbing plant twines around a support when touched. What type of movement is this? Which hormone is likely involved?

Answer:
 This is thigmotropism, a movement in response to touch stimulus. Auxins are involved by promoting cell elongation on the side opposite to the touch, causing the plant to coil around the support.

 

Case Study 7:
 In an experiment, cytokinins were applied to the leaves of a plant. The leaves showed delayed aging. Explain the role of cytokinins.

Answer:
 Cytokinins promote cell division and delay senescence (aging) in leaves by stimulating protein synthesis and nutrient mobilization, thus prolonging leaf lifespan.

 

Case Study 8:
 A sunflower’s flower head follows the sun’s movement throughout the day. What is this movement called, and which hormone regulates it?

Answer:
 This movement is called heliotropism. It involves differential growth regulated by auxins, which cause elongation of cells on the shaded side of the stem, enabling the flower to track the sun.

 

Case Study 9:
 Roots of a plant grown in dry soil bend towards moist areas. What is this response called? Which hormone might mediate this?

Answer:
 This is hydrotropism, movement of roots toward water. While auxins are generally involved in tropisms, the exact hormone signaling hydrotropism is less defined, but auxin redistribution may play a role.

 

Case Study 10:
 A plant exhibits shedding of older leaves as winter approaches. Identify the hormone responsible and explain how it causes leaf fall.

Answer:
 Abscisic acid (ABA) promotes leaf fall by inducing abscission, which involves weakening of the cells at the abscission zone, leading to leaf detachment.

 

Case Study 11:
 Gibberellins cause excessive elongation in some plants, making them weak. How can this effect be controlled agriculturally?

Answer:
 Agricultural practices can limit gibberellin effects by using growth retardants or by selective breeding to produce dwarf varieties with reduced gibberellin sensitivity.

 

Case Study 12:
 A researcher wants to delay fruit ripening to increase shelf life. Which hormone should be inhibited and how?

Answer:
 Inhibit ethylene production or action, possibly by using chemicals like silver thiosulfate which block ethylene receptors, delaying ripening and extending shelf life.

 

Case Study 13:
 A plant’s shoot apex was removed, and lateral buds started growing vigorously. Explain the hormonal reason behind this.

Answer:
 Removal of shoot apex removes the source of auxin, which suppresses lateral bud growth (apical dominance). Without auxin, cytokinins promote lateral bud growth, causing branching.

 

Case Study 14:
 How do auxins help in the process of vascular tissue differentiation?

Answer:
 Auxins promote differentiation of vascular tissues (xylem and phloem) by stimulating cell elongation and division in cambium, essential for transport of water and nutrients.

 

Case Study 15:
 Why do some fruits ripen quickly after being stored together with ripe bananas?

Answer:
 Ripe bananas release ethylene gas, which acts as a ripening hormone and accelerates ripening in nearby fruits.

 

Case Study 16:
 Explain how cytokinins and auxins interact to regulate plant growth.

Answer:
 Auxins promote cell elongation and apical dominance; cytokinins promote cell division and lateral bud growth. Their balance controls organ development and branching.

 

Case Study 17:
 A plant shows growth towards a chemical stimulus during fertilization. What is this movement called?

Answer:
 This is chemotropism, where pollen tubes grow toward the ovule guided by chemical signals.

 

Case Study 18:
 A farmer sprayed a hormone that caused his crops to grow taller and produce larger fruits. Which hormone was likely used?

Answer:
 Gibberellins promote stem elongation and can increase fruit size.

 

Case Study 19:
 Explain why auxin application is used in agriculture for weed control.

Answer:
 Synthetic auxins in high concentration cause uncontrolled growth in broadleaf weeds, leading to their death, making them effective herbicides.

 

Case Study 20:
 Why does a plant’s stem bend away from the direction of gravity?

Answer:
 This is negative geotropism where auxin accumulates on the lower side of the stem, promoting cell elongation, causing the stem to bend upward, away from gravity.

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