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All questions of November Week 2 for NEET Exam

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The natural plant hormones were first isolated from
  • a)
    Cotton fruits, spinach leaves and rice plant
  • b)
    Avena coleoptiles, spinach leaves and fungus Gibberella
  • c)
    Human urine and corn germ oil
  • d)
    Human urine and rice plant
Correct answer is option 'C'. Can you explain this answer?

Preeti Iyer answered
Auxins were first isolated from human urine. The term auxin is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.
Cytokinins have specific effects on cytokinesis and were discovered as kinetin from the autoclaved herring sperm DNA.
Kinetin does not occur naturally in plants. Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn kernels (corn germ oil) and coconut milk.
Hence option C is correct.

Seedless fruits can be obtained by treating the unpollinated ovaries with :-
  • a)
    Colchicine
  • b)
    Sucrose solution
  • c)
    Hormones
  • d)
    Pure lanolin
Correct answer is option 'C'. Can you explain this answer?

Stepway Academy answered
Seedless fruits like grapes and papaya are called Parthenocarpic fruits. These fruits are developed from unfertilized ovaries.
Plant hormones like auxins induce parthenocarpy.
Example: Tomatoes.

Leaf fall occurs when the content of :-
  • a)
    Auxin increases
  • b)
    Auxin decreases
  • c)
    Abscisic acid decreases
  • d)
    Gibberellic acid decreases
Correct answer is option 'B'. Can you explain this answer?

Rajeev Saxena answered
Due to a reduction in photosynthesis, this may trigger the abscission of leaves (separation of leaves) and this abscission layer is produced when auxin content falls below a minimum causing leaf or other plant part to fall off.CORRECT OPTION IS B.

Apical dominance means :-
  • a)
    Suppression of growth of apical bud by axillary buds
  • b)
    Suppression of growth of axillary buds by the presence of apical bud.
  • c)
    Stimulation of growth of axillary buds by removal of apical bud
  • d)
    Inhibition of growth of axillary buds by removal of apical bud.
Correct answer is option 'B'. Can you explain this answer?

Lalit Yadav answered
Auxins are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.

Stem elongation is affected by :-
  • a)
    Gibberellin and florigen
  • b)
    Auxin and gibberellin
  • c)
    Florigen and kinin
  • d)
    Kinin and auxin
Correct answer is option 'B'. Can you explain this answer?

Pooja Mehta answered
Auxins promote stem elongation, inhibit growth of lateral buds (maintains apical dominance). They are produced in the stem, buds, and root tips. Example: Indole Acetic Acid (IA). Auxin is a plant hormone produced in the stem tip that promotes cell elongation. 

Gibberellic acid is a simple gibberellin, a pentacyclic diterpene acid promoting growth and elongation of cells. .Gibberellins have a number of effects on plant development. They can stimulate rapid stem and root growth, induce mitotic division in the leaves of some plants, and increase seed germination rate.

Auxanometer is meant for measuring -
  • a)
    Respiratory activity
  • b)
    Photosynthetic activity
  • c)
    Growth activity
  • d)
    Osmotic pressure
Correct answer is option 'C'. Can you explain this answer?

Hansa Sharma answered
Auxanometer is a simple instrument to measure growth of a plant. Most common type of auxanometer is arc auxanometer, which measures growth as the increase in length of axis. This increase can be caused due to increase in mass of protoplasm (cell division) or simply by absorption of water (increase in length or surface of existing cells).

Auxin inhibits the growth of -
  • a)
    Apical bud
  • b)
    Lateral axillary buds
  • c)
    Roots on stem cutting
  • d)
    Parthenocarpic development of fruits
Correct answer is option 'B'. Can you explain this answer?

Pooja Shah answered
The apical bud produces an auxin hormone that inhibits the growth of the lateral buds further down on the stem towards the axillary bud.

In a growing plant, the first phase during the process of growth is -
  • a)
    Cell division
  • b)
    Cell enlargement
  • c)
    Cell differentiation
  • d)
    Cell maturation
Correct answer is option 'A'. Can you explain this answer?

Pooja Mehta answered
Phases Of Plant Growth
Meristematic Phase
The cells in the root and shoot apex of a plant are constantly dividing. They represent the meristematic phase of growth. The cells in these regions have large nuclei and are rich in protoplasm and their cell walls are thin and contain cellulose.

Elongation Phase
The cells in the zone just after the meristematic region represent the phase of elongation. The characteristics of cells in this zone are cell enlargement, increased vacuole formation and new cell wall deposition.

Maturation Phase
Just close to the phase of elongation, but away from the apex lies the phase of maturation. The cells in this region reach their maximum size with respect to their protoplasm and cell wall thickening.

Apical dominance in higher plants is due to -
  • a)
    Phyto hormones
  • b)
    Enzymes
  • c)
    Carbohydrates
  • d)
    Photoperiodism
Correct answer is option 'A'. Can you explain this answer?

Anshul Nair answered
Apical Dominance in higher plants is due to Phytohormones. Phytohormones are naturally occurring organic substances that regulate plant growth and development. They are also known as plant hormones or growth regulators. Phytohormones are synthesized in one part of the plant and transported to other parts where they exert their effects.

Explanation:

1. Definition of Apical Dominance:

Apical dominance is the phenomenon in which the apical bud of a plant inhibits the growth of lateral buds below it. This ensures that the plant grows in a single, upward direction, with a dominant main stem.

2. Role of Phytohormones:

Phytohormones play a crucial role in apical dominance. The apical bud releases a hormone called auxin, which inhibits the growth of lateral buds. Auxin is produced in the apical meristem (the growing tip of the plant) and is transported downwards towards the base of the plant.

3. Mechanism of Phytohormones:

Auxin acts by inhibiting the growth of lateral buds by inducing the production of cytokinins in the roots. Cytokinins are another type of phytohormone that promote cell division and growth. When auxin is transported downwards towards the roots, it induces the production of cytokinins in the roots. These cytokinins are then transported upwards towards the lateral buds, where they promote cell division and growth. However, the concentration of cytokinins is not enough to overcome the inhibitory effect of auxin, so the lateral buds remain dormant.

4. Importance of Apical Dominance:

Apical dominance is an important mechanism for plants because it ensures that the plant grows in a single, upward direction, with a dominant main stem. This is important for plants that need to compete for light and space. By growing upwards, the plant can maximize its exposure to sunlight and outcompete other plants for resources.

Conclusion:

In conclusion, Apical Dominance in higher plants is due to Phytohormones. Auxin is the hormone responsible for inhibiting the growth of lateral buds, while cytokinins promote cell division and growth. The balance between these two hormones ensures that the plant grows in a single, upward direction, with a dominant main stem.

The oxidation half reaction for following reaction is
Fe2+(aq) + Cr2O72-(aq) → Fe3+ (aq) + Cr3+(aq)
  • a)
    Fe3+(aq) → Fe2+ (aq)
  • b)
    Cr2O72-(aq) → Cr3+(aq)
  • c)
    Cr3+(aq) → Cr2O72-(aq)
  • d)
    Fe2+ (aq) → Fe3+(aq)
Correct answer is option 'D'. Can you explain this answer?

Geetika Shah answered
Oxidation half reaction for a reaction is that reaction which gives us the reactant and product formed after the oxidation of the reactant. In this case Fe+2 oxidizes itself to Fe+3 and so the oxidation of Fe+2 is oxidation half reaction. Option d correct.

When water is heated from 0° C to 20° C its volume:
  • a)
    first decreases and then increases
  • b)
    goes on increasing
  • c)
    remains constant up to 15°C and then increases
  • d)
    goes on decreasing
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
When water is heated from 0°C, its volume decreases because its density increases and you can see this effect upto 4°C. Since the density of ice is maximum at 4°C, afterwards as the density decreases the volume increases. The main reason for this is hydrogen bond in ice gets cleaved due to the melting of ice.

Growth is primarily affected by two climatic factors which are ?
  • a)
    Light and temperature
  • b)
    Temperature and relative humidity
  • c)
    Light and wind
  • d)
    Rainfall and temperature
Correct answer is option 'A'. Can you explain this answer?

Rohan Singh answered
The climatic factors include rainfall and water, light, temperature, relative humidity, air, and wind. They are abiotic components, including topography and soil, of the environmental factors that influence plant growth and development.

Coconut milk contains a cytokinin called ____ which promotes plant growth.
  • a)
    Naphthalene acetic acid
  • b)
    Indole-3-acetic acid
  • c)
    Gelatin
  • d)
    Zeatin
Correct answer is option 'D'. Can you explain this answer?

Priya Menon answered
trans-zeatin riboside is the most abundant type of cytokinin found in coconut water (Table 2). trans-zeatin is normally used to induce plantlet regeneration from callus in plant tissue culture. Based on experimental data, trans-zeatin plays a key role in the G2-M transition of tobacco cells.

In plants growth is -
  • a)
    Restricted to certain regions or structure
  • b)
    Irreversible
  • c)
    Change in size
  • d)
    All the above
Correct answer is option 'D'. Can you explain this answer?

Rajat Kapoor answered
The key to plant growth is meristem, a type of plant tissue consisting of undifferentiated cells that can continue to divide and differentiate. Meristem allows plant stems and roots to grow longer (primary growth) and wider (secondary growth).

Water contract on heating between the temperatures
  • a)
    0°C to 4°C
  • b)
    0°K to 4°K
  • c)
    0o K to 273 K
  • d)
    0°F to 4°F
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
When water is heated from 0oC, its volume decreases because its density increases and you can see this effect upto 4oC. Since the density of ice is maximum at 4oC, afterwards as the density decreases the volume increases. The main reason for this is hydrogen bond in ice gets cleaved due to the melting of ice.

The temperature for which the reading on Celsius and Fahrenheit scales are identical is
  • a)
    -273°C, -273 °F
  • b)
    -30°C, -30 °F
  • c)
    0 °C, 0 °F
  • d)
    -40 °C, -40 °F
Correct answer is option 'D'. Can you explain this answer?

Preeti Iyer answered
The Celsius and Fahrenheit are two important temperature scales. The Fahrenheit scale is used primarily in the United States, while Celsius is used throughout the world. The two scales have different zero points and the Celsius degree is bigger than the Fahrenheit one. There is one point on the Fahrenheit and Celsius scales where the temperatures in degrees are equal. This is -40 degree C and -40 degree F.

Can you explain the answer of this question below:

Two identical rectangular strips, one of copper and the other of steel, are riveted as shown to form a bi-metal strip. On heating, the bi-metal strip will

72601_ra1 (1)

  • A:

    bend with steel on the concave side

  • B:

    get twisted

  • C:

    remain straight

  • D:

    bend with steel on the convex side

The answer is a.

Nandini Patel answered
On heating, the copper strip will suffer greater elongation and hence the bimetal strip will bend with the steel strip on the concave side. 
[Bimetal strips are widely used in thermal switching applications such as automatic electric iron].

Which of the following instrument can be used to record plant growth by seconds ?
  • a)
    Arc auxanometer
  • b)
    Arc indicator
  • c)
    Space marker disc
  • d)
    Crescograph
Correct answer is option 'D'. Can you explain this answer?

Pooja Mehta answered
Crescograph is a sensitive devise, devised by J.C. Bose. It records primary growth very accurately. It magnifies growth upto 10,000 times giving information of growth per second.

 In this method, the two half equations are balanced separately and then added together to give balanced equation
  • a)
    Reluctant method
  • b)
    Oxidizing agent method
  • c)
    Reducing agent method
  • d)
    Half reaction method
Correct answer is option 'D'. Can you explain this answer?

Kavita Joshi answered
In the ion-electron method (also called the half-reaction method), the redox equation is separated into two half-equations - one for oxidation and one for reduction. Each of these half-reactions is balanced separately and then combined to give the balanced redox equation.

The relation between coefficient of volume expansion  and coefficient of linear expansion  is
  • a)
    αv = 2α1
  • b)
    α1 = 3αv
  • c)
    αv = 3α1
  • d)
    α1 = 2αv
Correct answer is option 'C'. Can you explain this answer?

The Amazing Spider Fan answered
This is simple,because the coefficients of linear expansion A,areal expansion B,and volume expansion G,are in the ratio of 1:2:3 i.e; A:B:G::1:2:3 Hence,G=3A

Gibberellic acid is a/an:
  • a)
    lndole compound
  • b)
    Terpene
  • c)
    Adenine derivative
  • d)
    Carotenoid
Correct answer is option 'B'. Can you explain this answer?

Ashutosh Rane answered
Terpene
Gibberellic acid is a type of plant hormone known as a terpene. Terpenes are a large and diverse class of organic compounds produced by a variety of plants, particularly conifers and flowering plants. They are often responsible for the characteristic scents of plants and have a wide range of biological functions.

Role of Gibberellic Acid
Gibberellic acid plays a crucial role in plant growth and development. It is involved in various processes such as seed germination, stem elongation, leaf expansion, and flowering. This hormone promotes cell division and cell elongation, leading to overall plant growth and development.

Chemical Structure
Gibberellic acid is a diterpenoid compound with a complex structure. It is derived from the terpene precursor geranylgeranyl pyrophosphate. The unique structure of gibberellic acid allows it to interact with specific receptors in plant cells, triggering various physiological responses.

Applications
Due to its role in promoting plant growth, gibberellic acid is widely used in agriculture. It is used to increase crop yields, improve fruit quality, and promote flowering in ornamental plants. Additionally, gibberellic acid can be applied to induce seed germination and break seed dormancy in certain plant species.
In conclusion, gibberellic acid is a terpene compound that plays a crucial role in regulating plant growth and development. Its unique chemical structure and biological functions make it an important plant hormone with various applications in agriculture and horticulture.

The process in which the strength of an unknown solution is calculated using a known standard solution.
  • a)
    Titration
  • b)
    Oxidation
  • c)
    Reduction
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Nandini Iyer answered
A titration is a technique used to work out the concentration of an unknown solution based on its chemical reaction with a solution of known concentration. The process usually involves adding the known solution (the titrant) to a known quantity of the unknown solution (the analyte) until the reaction is complete.

Four cylindrical rods of different radii and lengths are used to connect two heat reservoirs at fixed temperatures t1 and t2 respectively. From the following pick out the rod which will conduct the maximum quantity of heat:
  • a)
    Radius 1 cm, length 2 m
  • b)
    Radius 1 cm, length 1 m
  • c)
    Radius 2 cm, length 4 m
  • d)
    Radius 3 cm, length 8 m
Correct answer is option 'D'. Can you explain this answer?

Neha Sharma answered
The rate of heat transfer is directly proportional to the bisectional surface area of the solid and inversely proportional to its parallel length. 
That is heat conduction rate say H ∝ r2
∝ 1/L
I.e ∝ r2/L
Hence the conduction would be
maximum in case in which  r2/L ratio is largest.

Cytokinin does not help in:
  • a)
    Lateral shoot growth
  • b)
    Promoting leaf senescence
  • c)
    Adventitious shoot formation
  • d)
    Overcoming apical dominance
Correct answer is option 'B'. Can you explain this answer?

Bs Academy answered
  • Cytokinin does not help in promoting leaf senescence.
  • Cytokinin production slows down the process of senescence. However, the accumulation of sugars during senescence, due to the breakdown of accumulated starch or the preferential export of N2 from the leaf, can block the effect of cytokinin, especially in low light.
  • Ethylene is regarded as a multifunctional phytohormone that regulates both growth, and senescence.
  • It promotes or inhibits growth and senescence processes depending on its concentration, timing of application, and the plant species.

Auxin does not:
  • a)
    Help to initiate rooting in stem cuttings
  • b)
    Promote female flowers in cucumbers
  • c)
    Prevent fruit and leaf drop in early stages
  • d)
    Promote abscission of older mature leaves and fruits
Correct answer is option 'B'. Can you explain this answer?

Nipuns Institute answered
They help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits

Which of the following is essential for fruit ripening?
  • a)
    Ethylene
  • b)
    Cytokinin
  • c)
    Auxin
  • d)
    Abscisic acid
Correct answer is option 'A'. Can you explain this answer?

Lead Academy answered
The following are plant growth regulators or phytohormones that control various developmental as well as physiological functions of a plant:
Auxin:
  • It helps in cell elongation, growth, and differentiation.
  • It is present mainly at the root and shoots apices.
  • It is responsible for the phenomenon of apical dominance, where the apical buds inhibit the growth of lateral buds.
  • It results in increasing the height of a plant due to apical dominance.
  • It can also initiate root growth in stem cuttings.
  • It may also promote flowering and prevent early fruit drop.
Cytokinin:
  • It is mainly associated with cell division and is present in regions of rapid cell division.
  • It helps to overcome apical dominance and promotes lateral shoot growth.
Ethylene:
  • It is a gaseous phytohormone produced in the tissues undergoing senescence.
  • It helps in fruit ripening and other senescence-related activities.
  • It breaks seed and bud dormancy to initiate germination in some species.
  • It also induces leaf epinasty under stress conditions.
  • The triple response of ethylene includes reducing the rate of elongation, increasing lateral expansion, and swelling of the region below the hook in seedlings.
Abscisic acid:
  • As the name suggests, it helps in abscission and dormancy.
  • It inhibits plant growth, metabolism, and seed germination.
  • It also plays an important role in the closure of stomata under stress conditions.

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