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Q1. Gibberellins promote

• 1) Seed germination
• 2) Root elongation
• 3) Leaf fall
• 4) Seed dormancy

Solution

Gibberellin increases the length of hypocotyls and cotyledonary leaf area during germination. GA induces synthesis of α-amylase and other hydrolytic enzymes in seeds of monocots and dicots.

Q2. Define development.

Solution

Development can be defined as all the changes which an organism goes through during its life cycle.

Q3. Mowing the grass lawn facilitates better maintenance because

• 1) Wounding stimulates regeneration
• 2) Removal of apical dominance
• 3) Removal of apical dominance and promotion of the lateral meristem
• 4) Removal of apical dominance and stimulation of intercalary meristem

Solution

According to Thimann and Skoog, the removal of the apical bud causes the sprouting of lateral buds with stimulation of the intercalary meristem and this is the reason that mowing a grass lawn facilitates better maintenance.

Q4. Plasticity in plant growth means that  

• 1) Plant growth is dependent on the environment.  
• 2) None of the above.  
• 3) Stems can extend.  
• 4) Plant roots are extensible.  

Solution

Plant organs change their structures to cope with the change in the environment; this is called the property of plasticity.  

Q5. A mass of undifferentiated cells is called

• 1) Callus
• 2) Meristem
• 3) Culture
• 4) Both C and D

Solution

The dividing cells form a mass of undifferentiated cells called callus.

Q6. Leaves of many grasses are capable of folding and unfolding because they

• 1) Are isobilateral
• 2) Are very thin
• 3) Have parallel vascular bundles
• 4) Have specialised bulliform cells

Solution

Leaves of monocots are characterised as isobilateral with dumb bell-shaped guard cells. The upper epidermis possesses groups of large-sized, thin-walled, vacuolated cells called bulliform or motor cells. Bulliform cells help in the rolling of leaves during water stress or drought.  

Q7. What is dedifferentiation? State one example.

Solution

As the cells grow and mature, they lose their capacity to differentiate. However, under certain conditions, such cells regain the capacity of division which is called dedifferentiation. Differentiated parenchymatous cells dedifferentiate to form interfascicular cambium and cork cambium.

Q8. Gibberellin was discovered from 

• 1) Algae
• 2) Bacteria
• 3) Roots of higher plants
• 4) Fungi

Solution

GA was first isolated by Kurasawa in 1926 from the fungus Gibberella fujikuroi, the causal organism of foolish seedling disease of rice plants in Japan.

Q9. Maturation of dedifferentiated tissues is called

• 1) Development
• 2) Redifferentiation
• 3) Differentiation
• 4) Dedifferentiation

Solution

Redifferentiation is the maturation or differentiation of dedifferentiated tissues.

Q10. Phytohormones are

• 1) Hormones regulating growth from seed to adulthood
• 2) Chemicals regulating secondary growth
• 3) Chemicals regulating flowering
• 4) Regulators synthesised by plants and influencing physiological processes

Solution

Phytohormones are plant hormones, i.e. organic substances which are naturally produced in plants and control the growth or other physiological functions at a site away from their place of synthesis and are active in extremely minute quantities.

Q11. A plant hormone used for inducing morphogenesis in plant tissue culture is

• 1) Gibberellin
• 2) Abscisic acid
• 3) Ethylene
• 4) Cytokinin

Solution

The ratio of cytokinin to auxin controls cell differentiation. If there is more cytokinin than auxin, then shoot buds develop. Relatively more auxin than cytokinin leads to the development of roots. Abscisic acid is known as a natural plant growth inhibitor. Gibberellin stimulates stem elongation, leaf expansion, bolting, flowering etc. Ethylene is a fruit-ripening hormone.

Q12. All are extrinsic factors responsible for the development of an organism except

• 1) Temperature
• 2) Light
• 3) Amount of oxygen
• 4) Hormones

Solution

Factors responsible for development are intrinsic and extrinsic. The intrinsic factors include genetic factors and hormonal factors, and the extrinsic factors include light, temperature etc.

Q13. Name the fungus which causes the bakanae disease in rice seedlings.

Solution

Gibberella fujikuroi

Q14. Differentiation of the shoot is controlled by  

• 1) High gibberellin-cytokinin ratio  
• 2) High gibberellin-auxin ratio  
• 3) High auxin-cytokinin ratio  
• 4) High cytokinin-auxin ratio  

Solution

The ratio of cytokinins to auxins controls differentiation. If both of these are present in equal quantities, the cells divide but fail to differentiate. If there is more cytokinin than auxin, shoot buds develop. If there is more auxin than cytokinin, roots develop.  

Q15. 'Foolish seedling' disease of rice led to the discovery of   

• 1) 2-4 D  
• 2) ABA  
• 3) GA  
• 4) IAA  

Solution

Gibberellins (GA) were first isolated from the fungus Gibberella fujikuroi, the causal organism of foolish seedling disease of rice plants, by Kurasawa in Japan in 1926.

Q16. The phytohormone which induces triple response is

• 1) IAA
• 2) GA
• 3) C₂H₄
• 4) ABA

Solution

Ethylene is a gaseous hormone which stimulates shoot growth, root growth and differentiation which is otherwise called triple response.

Q17. What is open form growth?

Solution

Open form growth is the growth in which new cells are always added to the plant body by the activity of meristems.

Q18. What are plant growth regulators? Name the six compounds which fall under the category of plant growth regulators.

Solution

Plant growth regulators are small diverse molecules which act as either phytohormones or plant growth substances.

Q19. Growth can be measured in various ways. Which of these can be used as parameters to measure growth?

• 1) Increase in length and weight
• 2) All of the above
• 3) Increase in cell size
• 4) Increase in cell number

Solution

Growth can be measured when there is an increase in cell number, cell size, length and fresh or dry weight.

Q20. Which of the following is an intrinsic factor which controls the development of an organism?

• 1) Hormonal
• 2) Both A and C
• 3) Temperature
• 4) Genetic

Solution

The process of development is controlled by intrinsic factors such as genetic and hormonal factors. Extrinsic factors include light, temperature, water and oxygen.

Q21. If a plant contains more nitrogenous compounds, then it produces

• 1) Vigorous vegetative growth
• 2) More cytoplasm
• 3) Both A and C
• 4) Less cytoplasm

Solution

If a plant contains more nitrogenous compounds, then it produces more cytoplasm, less mechanical tissues and vigorous vegetative growth.

Q22. Which of the following movements in plants is related to the changes in the auxin level?

• 1) Movement of the shoot towards a source of light
• 2) Movement of sunflower towards the Sun
• 3) Nyctinasty
• 4) All of the above

Solution

The movement in plants is related to the movement of shoots towards a source of light due to changes in the auxin level.

Q23. Give one example of cells of plants which have undergone Dedifferentiation Redifferentiation

Solution

Dedifferentiation - Cells forming cork cambium and interfascicular cambium Redifferentiation - Secondary cortex cells and phellem cells

Q24. Name the PGR which is a modified form of adenine.  

Solution

Kinetin  

Q25. The xylem which differentiates has a thick secondary wall made of

• 1) Lignin
• 2) Suberin
• 3) Pectin
• 4) Cellulose

Solution

The development of a thick secondary wall is made of lignin, and it becomes living permanent cells of the parenchyma.

Q26. From where was auxin first isolated?

Solution

Human urine

Q27. Which amino acid is responsible for indole acetic acid formation?  

• 1) Phenylalanine  
• 2) None of the above  
• 3) Tryptophan  
• 4) Tyrosine  

Solution

IAA is synthesised in shoot apices, leaf primordia and developing seeds from the amino acid tryptophan.  

Q28. State the parameters which are considered while measuring the growth of plants.

Solution

Parameters which are considered while measuring the growth of plants are as follows: Increase in fresh weight Increase in dry weight Increase in length of plants Increase in area and volume of plants Increase in cell number

Q29. How is the quantitative comparison between the growth of living beings done?  

Solution

The quantitative comparison between the growth of living beings can be done in two ways:     Absolute growth rate: Measurement and comparison of the total growth per unit time.   Relative growth rate: Growth of the given system per unit time expressed on a common basis.  

Q30. The time interval between the formative phase and the maturation phase of plant growth is known as  

• 1) Grand period of growth  
• 2) Phase of elongation  
• 3) Stationary phase  
• 4) Lag phase  

Solution

The formative phase is also called the phase of cell division. New cells are produced by mitotic divisions having meristematic tissue.           Phase of maturation or differentiation is the development of special types of cells by undergoing structural and physiological differentiation.           The intermediate phase between the formative phase and the maturation phase is the phase of elongation.  

Q31. From where was auxin isolated first? Name one natural auxin and one synthetic auxin.  

Solution

Auxin was first isolated from human urine.     Natural auxin - Indole butyric acid     Synthetic auxin - Naphthalene acetic acid  

Q32. Seeds of some plants are unable to germinate even when conditions are favourable. This is called

• 1) Vivipary
• 2) Non-viability
• 3) Quiescence
• 4) Dormancy

Solution

Seed dormancy is the innate inhibition of germination of a viable seed placed in the most favourable environment for germination.

Q33. Abscisic acid is also known as stress hormone.

Solution

Abscisic acid inhibits seed germination. It also stimulates the closure of stomata and increases the tolerance level in plants against various stresses. Hence, abscisic acid is also known as a stress hormone.

Q34. Differentiate between arithmetic and exponential growth.

Solution

Arithmetic Growth Geometric Growth After mitotic division, only one daughter cell divides and the other daughter cell differentiates and matures. All the daughter cells continue to divide. On plotting the growth against time, a linear curve is obtained. On plotting the growth against time, a sigmoid curve is obtained.  

Q35. What will be the effect on phytochrome in a plant subjected to continuous red light?

• 1) Destruction and synthesis of phytochrome remain in equilibrium
• 2) Phytochrome synthesis increases
• 3) Phytochrome is destroyed
• 4) Level of phytochrome decreases

Solution

Continuous exposure to red light causes conversion of Pr to Pfr which is rapidly destroyed and the inhibition of synthesis of Pr. Thus, the total amount of phytochrome is decreased.

Q36. Cell elongation in the internodal regions of green plants occurs due to   

• 1) Cytokinins  
• 2) Gibberellins  
• 3) Indole acetic acid  
• 4) Ethylene  

Solution

Cells elongate due to the presence of the synthetic auxin indole acetic acid. Cell elongation occurs because the cell walls become plastic and due to endosmosis.  

Q37. Culturing of plant tissues is an example of

• 1) Dedifferentiation
• 2) Redifferentiation
• 3) Both B and C
• 4) Differentiation

Solution

Culturing of plant tissues is an example of dedifferentiation and redifferentiation. During this technique, a lump of permanent tissue from the portion of pith is dissected out and cultured on solid culture media. 

Q38. What are the important aspects of growth?

• 1) Maturation and differentiation
• 2) Cell division and plasmatic growth
• 3) Maturation and cell division
• 4) Cell division and differentiation

Solution

Cell division and differentiation are important aspects of growth, because cell division is an important phase which determines the birth of a cell and differentiation is required to become a permanent cell as morphological change occurs in a meristematic daughter cell.

Q39. What is the best example of commitment?  

• 1) Final structure at maturity of cells  
• 2) Interfascicular vascular cambium  
• 3) Vascular elements  
• 4) Wound meristem  

Solution

The final structure at maturity of cells appearing due to the same meristem is determined by location of cells. The root cap cells when pushed to the periphery produce the epidermis.  

Q40. Coconut milk (coconut water) is widely used in tissue culture because it contains  

• 1) Auxins  
• 2) Gibberellins  
• 3) Ethylene  
• 4) Cytokinin  

Solution

Skoog observed that coconut milk contained a substance which stimulated cell division. The substance was later on called cytokinin.   

Q41. Ripening of fruit is controlled by

• 1) Gibberellin
• 2) Cytokinin
• 3) Auxin
• 4) Ethylene

Solution

The ripening of fruits is controlled by ethylene. Ethylene is produced in plants from the amino acid methionine.

Q42. Which one of the following pairs is not correctly matched?   

• 1) Abscisic acid - Stomatal closure  
• 2) IAA - Cell wall elongation  
• 3) Cytokinin - Cell division  
• 4) Gibberellic acid - Leaf fall  

Solution

Gibberellic acid is a plant hormone, and it helps in cell growth of the stem, leaves and other aerial parts.  

Q43. A hormone delaying senescence is 

• 1) Auxin
• 2) Ethylene
• 3) Gibberellin
• 4) Cytokinin

Solution

Richmond and Lang proved that cytokinin delayed senescence. They observed that application of cytokinins increased the chlorophyll content which delays senescence for several days.

Q44. The ideal temperature for growth in plants is

• 1) None of the above
• 2) Day: 30°C, Night: 15°C
• 3) Day: 25°C, Night: 12°C
• 4) Day: 20°C, Night: 12°C

Solution

Growth in many plants is best when the day temperature is 25°C and the night temperature is 12°C.

Q45. The hormone responsible for apical dominance is

• 1) IAA
• 2) ABA
• 3) GA
• 4) Florigen

Solution

Apical dominance is the phenomenon in which the presence of an apical bud does not allow the nearby lateral buds to grow. This is characteristically caused by auxins.

Q46. What type of tissues synthesise ethylene? State any two functions of ethylene.

Solution

Ethylene is synthesised in tissues which undergo senescence and in ripening fruits. It accelerates abscission in flowers and fruits. It breaks seed and bud dormancy.

Q47. Name the three substances which were discovered and later collectively named abscisic acid (ABA).

Solution

Inhibitor B, abscission II and dormin.

Q48. The phenomenon exhibited by green plants when grown in darkness is called

• 1) Photoperiodicity
• 2) Thermoperiodicity
• 3) Photomorphogenesis
• 4) Etiolation

Solution

If a plant is allowed to grow in complete darkness, then it shows etiolation.

Q49. The maximum growth rate occurs in

• 1) Stationary phase
• 2) Senescent stage
• 3) Lag phase
• 4) Exponential phase

Solution

The maximum growth rate occurs in the exponential phase because each cell divides to form two cells. This phase has the greatest rate of increase in population size. The rate is influenced by environmental conditions such as temperature, aeration and composition of medium. 

Q50. Intercalary meristem results in 

• 1) Primary growth
• 2) Apical growth
• 3) Secondary growth
• 4) Lateral growth

Solution

Cells of the meristematic region have the capacity to divide. Root apical meristem and shoot apical meristem contribute to cell elongation of plants which is called primary growth.

Q51. State the term which explains the ability of plants to respond to the environment or phases of life by following different pathways.  

Solution

Plasticity  

Q52. When the rate of growth is proportional to the size of the tuber, it is called  

• 1) Law of mass growth  
• 2) Formative growth  
• 3) Geometric growth  
• 4) Absolute growth  

Solution

The law of mass growth is the rate of growth which is proportional to the size of the tuber.  

Q53. Define growth. Give an example of growth in plants.

Solution

Growth is an irreversible permanent increase in the size of an organ or part or the individual cell. Expansion of leaves is an example of growth in plants.

Q54. Which one of the following plant is LDP?  

• 1) Soybean  
• 2) Wheat  
• 3) Xanthium  
• 4) Tobacco  

Solution

LDPs (i.e. long-day plants) require long days of summer which provide the plants perfect photoperiods to permit flowering.  

Q55. Name the phenomenon which explains the importance of low temperature and flowering in plants.

Solution

Vernalisation 

Q56. Which one increases in the absence of light?

• 1) Ascent of sap
• 2) Elongation of internodes
• 3) Uptake of water
• 4) Uptake of minerals

Solution

The absence of light reduces overall growth, photosynthesis, uptake of minerals and ascent of sap. However, the elongation of internodes is seen to occur in the absence of light.

Q57. Phytochrome is involved in

• 1) Phototropism
• 2) Geotropism
• 3) Photorespiration
• 4) Photoperiodism

Solution

Phytochrome is involved in photomorphogenetic responses, seed germination, bud dormancy, synthesis of gibberellins and photoperiodism.

Q58. Twining of tendrils is due to

• 1) Diageotropism
• 2) Thigmotropism
• 3) Heliotropism
• 4) Seismonasty

Solution

Thigmotropism is the curvature movement of a plant in response to a unilateral stimulus of touch and can be observed in many climbers. In tendril climbers, the tendrils first show mutation and as soon as their apices touch a support, they move thigmotropically to turn around it.

Q59. The increase in total growth of two organisms and their comparison is known as

• 1) Both A and B
• 2) Relative growth rate
• 3) Absolute growth rate
• 4) Sigmoid growth curve

Solution

The increase in total growth of two organs or organisms is measured and the comparison of total growth per unit time is called absolute growth rate.

Q60. What is the last stage of a plant called?

• 1) Dormancy
• 2) Senescence
• 3) Vernalisation
• 4) Scarification

Solution

The last phase of development is senescence. Senescence or old age leads to death.

Q61. Geocarpic fruits are produced by  

• 1) Onion  
• 2) Watermelon  
• 3) Groundnut  
• 4) Carrot  

Solution

Geocarpy refers to the ripening of fruits underground. For groundnut, the young fruits are pushed into the soil as a result of the post-fertilisation curvature of the stalk.  

Q62. Vernalisation is done at  

• 1) High light intensity  
• 2) Higher temperature  
• 3) Low light intensity  
• 4) Lower temperature  

Solution

Vernalisation is the promotion of flowering in plants at a low temperature. Plants grow vegetatively during the warm season, receive low temperature treatment during the winter and grow further to bear flowers and fruits in the warm season.  

Q63. State the three phases of the period of growth in plants, and describe the characteristic features of the cells of each phase.

Solution

The period of growth in plants has the following three phases: Meristematic phase: This phase is represented by the root and shoot apices. The cells of the meristematic region are rich in protoplasm and possess large conspicuous nuclei. The cell walls are thin, cellulosic, primary and show more plasmodesmata connections. Elongation phase: The zone of elongation is proximal to the meristematic zone. The cells show more number of vacuoles. Enlargement of cells and new cell wall deposition occur during this phase. Maturation: It lies proximal to the zone of elongation. The cells of this phase show more protoplasmic modifications and thickened cell walls.

Q64. Describe arithmetic growth.  

Solution

In arithmetic growth following mitotic cell division, only one daughter cell continues to divide while the other daughter cell differentiates and matures.     When arithmetic growth is plotted against time, it gives a linear growth curve.           The mathematical expression of arithmetic growth is     L_t = L₀ + rt,      where L_t = length at time ‘t’      L₀ = length at time zero      r = growth rate  

Q65. Cholodny-Went theory is concerned with which of the following processes:  

• 1) Photomorphogenesis  
• 2) Photoperiodism  
• 3) Photorespiration  
• 4) Phototropism  

Solution

The Cholodny-Went model which was proposed in 1927 showed a tendency for the shoot to grow towards light and for the roots to grow downwards.  

Q66. Which method out of the following renders the seed coat permeable to water so that embryo expansion is not physically retarded?  

• 1) Scarification  
• 2) Denudation  
• 3) Vernalisation  
• 4) Stratification  

Solution

In many plants, the seed coat is quite tough and provides mechanical resistance to the growth of the embryos. Scarification by abrasion through machine, threshing, filling etc., ruptures or weakens the seed coat and promotes germination.   

Q67. How many cells can a single maize root apical meristem produce in one hour?

Solution

17,500

Q68. Draw a chart indicating the sequence of development in plants.  

Solution

   

Q69. The increase of growth per unit time is defined as

• 1) Absolute growth rate
• 2) Growth rate
• 3) Exponential growth
• 4) Geometric growth

Solution

Growth of an organism is expressed in the form of growth rate which is defined as the increase of growth per unit time.

Q70. Name the plant growth regulator used in the brewing industry for the malting process.

Solution

Gibberellic acid

Q71. Crescograph and auxanometer are

• 1) Used to grow plants in a controlled environment
• 2) Growth-measuring instruments
• 3) Instruments to study the age of tree
• 4) Used to study the effect of sunlight on plants

Solution

Growth is measured by measuring an increase in length, volume, area, diameter etc. A crescograph is a device to measure the growth in plants which showed how the rate of growth varies under varying stimuli. So, an auxanometer is used to measure the growth in length of a plant organ. 

Q72. Name any two parts of the plant which synthesise natural cytokinins.

Solution

Young fruits, root apices

Q73. Name the meristems which cause secondary growth in plants.

Solution

Lateral meristems, vascular cambium and cork cambium.

Q74. Write the mathematical expression for exponential growth.

Solution

W₁ = W₀e^rt

Q75. State any two extrinsic factors important in the development of a plant.

Solution

Light and oxygen

Q76. How do gibberellins help in increasing the sugar yield?  

Solution

Gibberellins help in stem elongation in plants. In sugarcane, sugar is stored in stems. Use of gibberellin ensures an increase in the stem length of sugarcane; hence, the yield increases.  

Q77. Which is a stress hormone?  

• 1) Ethylene  
• 2) Dichlorophenoxy acetic acid  
• 3) Benzyl aminopurine  
• 4) Abscisic acid  

Solution

Abscisic acid is called a stress hormone because the production of this hormone is stimulated by drought, water logging and other adverse environmental conditions.  

Q78. An auxanometer is used to measure

• 1) The growth of leaves
• 2) The growth in breadth of a plant organ
• 3) Population of the pests attacking a plant
• 4) The growth in length of a plant organ

Solution

Growth is measured by measuring an increase in length, volume, area, diameter etc. So, an auxanometer is used to measure the growth in length of a plant organ.

Q79. Represent diagrammatically the locations of root and shoot apical meristems and the direction of the growth of cells in meristems.  

Solution

   

Q80. Name the component which a plant cell loses in order to form a tracheary element.

Solution

Protoplasm

Q81. Phytochrome is involved in  

• 1) Geotropism  
• 2) Phototropism  
• 3) Photoperiodism  
• 4) Photorespiration  

Solution

Phytochrome is a photosensitive pigment which exists in two states. It is involved in photomorphogenetic responses, seed germination, bud dormancy, synthesis of gibberellin and ethylene and photoperiodism.  

Q82. A short-day plant is 

• 1) Cucumis
• 2) Xanthium
• 3) Pisum
• 4) Avena

Solution

In short-day plants, the length of night is critical. Xanthium strumarium is a short-day plant which flowers after 9 hours of dark period irrespective of the day length. Even if a brief flash of light is interrupted by a dark period, the flowering is inhibited.

Q83. How does ethylene help plants to absorb more water and minerals?  

Solution

Ethylene promotes root growth and root hair formation, thus increasing the surface area of absorption which helps plants to absorb more water and minerals.  

Q84. Define plasticity and give one example. Or How can heterophylly be an example of plasticity?

Solution

Plasticity is the ability of plants to respond to the environment or phases of life or to form different structures by following different pathways. Terrestrial plants have different shapes of leaves, and the leaves of aquatic plants also show different shapes in their life cycle.   A coriander leaf in the juvenile stage looks different from the mature leaf.

Q85. Name the plant and its part from which auxin was isolated by F. W. Went.

Solution

Tips of coleoptiles of oat seedlings.

Q86. State the term used for the phenomenon in which the shape of leaves of the same plant changes during its development.  

Solution

Heterophylly  

Q87. Name the auxin which is used as a weedicide.

Solution

2,4-dichlorophenoxyacetic acid

Q88. Name the phenomenon in which a growing apical bud inhibits the growth of the lateral bud.

Solution

Apical dominance

Q89. Name the compound which is used in agriculture as a source of ethylene.

Solution

Ethephon 

Q90. Define growth rate.

Solution

The growth rate is the increased growth per unit time.

Q91. Describe relative growth. Also, plot a graph indicating relative growth.

Solution

In geometric growth, the progeny cells continue to divide mitotically. The initial phase, i.e. the lag phase, is very slow. After the lag phase, the growth takes place very rapidly at an exponential rate, which is called the log phase. Due to limited nutrient supply, the growth slows down leading to the stationary phase. When a graph is plotted of the growth rate against time, we get a sigmoid or S curve.   The geometric growth rate is expressed as W₁ = W₀e^rt,  where W₁ = final size (weight, height, number etc.)  W₀ = initial size at the beginning of the period  r = growth rate   t = time of growth  e = base of natural logarithm

Q92. Light grown seedlings are

• 1) Sturdy
• 2) Green with shorter internodes
• 3) Expanded leaves
• 4) All of the above

Solution

Light grown seedlings are sturdy, green with shorter internodes, expanded leaves and upright apex.

Q93. Who identified kinetin first?

Solution

Skoog and Miller

Q94. State the characteristics of cells in the elongation phase of the growth of a plant.  

Solution

Cells in the elongation phase of the growth of a plant show the following characteristics:     They show increased vacuolation, i.e. more number of vacuoles.   Cells are enlarged.   There is new cell wall deposition.  

Q95. State the intrinsic factors important in the development of plants.

Solution

Genetic factors and growth regulators

Q96. From where was kinetin isolated for the first time? Where are the natural cytokinins synthesised in plants?

Solution

Kinetin was first isolated from herring sperm. Natural cytokinins are synthesised in areas of rapid cell division.

Q97. State the name of the plant growth regulator which you will use in the following cases: To promote flowering in pineapples To stimulate early seed production in conifers To sprout potato tubers To prevent leaf drop at an early age To prepare weed-free lawns To delay leaf senescence

Solution

To promote flowering in pineapples - Auxins To stimulate early seed production in conifers - Gibberellins To sprout potato tubers - Ethylene To prevent leaf drop at an early age - Auxins To prepare weed-free lawns - Auxins To delay leaf senescence - Cytokinins

Q98. What does a sigmoid growth curve indicate?  

Solution

A sigmoid growth curve indicates that the living organism is growing in a natural environment.  

Q99. Name the PGR which hastens the ripening of oranges.

Solution

Ethylene

Q100. State the functions of cytokinins.

Solution

Functions of cytokinins: They help to overcome apical dominance. They also promote nutrient mobilisation which results in the delay of leaf senescence.