MCQ (Practice) - Practice Growth Hormone And Plant Movement (Level 1) - Class 11 MCQ

F. W. Went in 1928 used tip of Avena coleoptile. He removed the tip of Avena coleoptile and placed in on the agar block for the definite measured amount of time. Then this agar block was placed asymmetrically on the stump, this showed a positive curvature. 

When this agar block was placed centrally on the stump then the growth of the coleoptile was found to be renewed. He named this growth promoting substance or hormone as auxin. 

He also noticed that curvature in Avena coleoptile is proportional, to the amount of auxin in agar block. Hence, option A is correct. 

Primary precursor of I.A.A:
- Phenyl alanine: Phenylalanine is an essential amino acid that is converted into tyrosine in the body. It is not the primary precursor of I.A.A.
- Tyrosine: Tyrosine is an amino acid that is synthesized from phenylalanine. It is further converted into L-DOPA, which serves as a precursor for the synthesis of dopamine, norepinephrine, and epinephrine. However, tyrosine is not the primary precursor of I.A.A.
- Tryptophan: Tryptophan is an essential amino acid that serves as the primary precursor of I.A.A. It is converted into 5-hydroxytryptophan (5-HTP) and then into serotonin, which acts as a neurotransmitter in the central nervous system.
- Leucine: Leucine is an essential amino acid that plays a key role in protein synthesis and muscle growth. However, it is not the primary precursor of I.A.A.
Conclusion: The primary precursor of I.A.A is tryptophan. It is converted into serotonin, which is an important neurotransmitter in the brain.

The biological activity of Indole-3-Acetic Acid (I.A.A.) can be tested using various methods. Among the options provided, the most suitable test is the Avena curvature test. Here is a detailed explanation of the test and why it is used:
Avena Curvature Test:
The Avena curvature test is a widely used bioassay to evaluate the biological activity of plant hormones, particularly auxins like I.A.A. It involves observing the growth response of oat (Avena sativa) coleoptile segments in the presence of the hormone.
Procedure:
1. Oat seeds are germinated, and the coleoptiles (the protective sheath covering the emerging shoot) are cut into equal-sized segments.
2. These segments are then placed in a horizontal position on a solid medium, such as agar gel, containing different concentrations of I.A.A.
3. After a specific period of incubation, the curvature of the coleoptile segments is measured and compared to a control group.
4. The degree of curvature indicates the stimulatory or inhibitory effect of I.A.A. on the growth of the oat coleoptiles.
Reasons for using Avena Curvature Test:
- The Avena curvature test is highly sensitive to auxin activity, making it suitable for testing the biological activity of I.A.A.
- The test allows for the evaluation of different concentrations of I.A.A., providing a dose-response relationship.
- The growth response of oat coleoptiles is easily observable and measurable, providing quantitative data.
- The test is relatively simple and cost-effective, making it a preferred choice for bioassays.
Therefore, the correct answer is B: Avena curvature test.

Explanation:
The correct answer is A: Human urine. Here is a detailed explanation:
Indole-3-acetic acid (IAA) or auxin:
- Indole-3-acetic acid (IAA) is a type of plant hormone known as auxin.
- Auxins play a crucial role in plant growth and development, including cell elongation, root initiation, and fruit development.
- IAA is the most common naturally occurring auxin in plants.
Isolation of Indole-3-acetic acid:
- IAA was first isolated from human urine in 1930 by the Dutch plant physiologist Frits Warmolt Went.
- Went discovered that IAA is responsible for the phototropism (bending towards light) in plants.
- He extracted IAA from human urine and demonstrated its role in plant growth.
Other options:
B: Corn germ oil: Corn germ oil is not related to the isolation of IAA. It is extracted from the germ of corn and is used in cooking and as a source of vitamin E.
C: Fusarium: Fusarium is a type of fungus that can infect plants and cause diseases. It is not directly related to the isolation of IAA.
D: Rhizopus: Rhizopus is a genus of fungi that includes species commonly known as bread mold. It is not related to the isolation of IAA.
In conclusion, IAA or auxin was first isolated from human urine by Frits Warmolt Went.

Effects of Auxins:
There are various effects of auxins, but the one that is of wide application is:
Induction of root initiation:
- Auxins play a crucial role in promoting the formation of roots from plant cuttings and explants.
- They stimulate cell division and elongation, leading to the development of roots.
- This effect is widely used in horticulture and agriculture for vegetative propagation and the production of new plants.
Other effects of auxins include:
Induction of fruit development:
- Auxins promote fruit growth and development by stimulating cell division and enlargement in the fruit tissues.
- They also influence fruit ripening processes, such as color change, softening, and flavor development.
Prevention of abscission:
- Auxins inhibit the abscission or shedding of leaves, flowers, and fruits.
- They maintain the attachment of these plant parts to the parent plant by promoting the development of abscission zones.
All of the above:
- The correct answer is option D, as all of the mentioned effects of auxins (root initiation, fruit development, and prevention of abscission) have wide applications in various fields, including agriculture, horticulture, and plant propagation.
In summary, while auxins have various effects on plant growth and development, the induction of root initiation is particularly of wide application. However, the other effects of auxins, such as fruit development and prevention of abscission, also have significant practical applications.

Stem elongation is affected by:
Auxin and gibberellin:
- Auxin is a plant hormone that promotes stem elongation by stimulating cell division and elongation in the stem.
- Gibberellin is another plant hormone that also promotes stem elongation by stimulating cell division and elongation in the stem.
Therefore, the correct answer is B: Auxin and gibberellin. These hormones work together to regulate and promote stem elongation in plants.
Note: Florigen and kinin are not directly involved in stem elongation. Florigen is a hormone that promotes flowering in plants, while kinin is involved in cell division and differentiation in plants.

Apical dominance means:
Apical dominance refers to the phenomenon where the growth of the apical bud inhibits the growth of axillary buds.
Explanation:
The apical bud is located at the top of the plant stem and is responsible for the vertical growth of the plant. It produces a hormone called auxin, which suppresses the growth of axillary buds located in the leaf axils (the angle between the upper side of the leaf and the stem).
The process of apical dominance:
1. Suppression of growth: The apical bud produces auxin, which inhibits the growth of axillary buds by preventing their elongation and branching.
2. Resource allocation: The apical bud receives most of the nutrients and resources from the plant, diverting them away from the axillary buds.
3. Inhibition of lateral branches: The apical bud's dominance leads to the formation of a single, dominant main stem, while the axillary buds remain dormant or grow at a slower rate.
Importance of apical dominance:
1. Vertical growth: Apical dominance allows the plant to grow vertically, ensuring that it reaches sunlight and maximizes its exposure to light for photosynthesis.
2. Preventing competition: By suppressing the growth of axillary buds, the plant ensures that resources are allocated primarily to the main stem, preventing competition for resources among multiple branches.
3. Shaping the plant: Apical dominance helps in shaping the plant's overall structure by controlling the number and positioning of lateral branches.
In conclusion, apical dominance refers to the suppression of growth in axillary buds by the presence of the apical bud. This phenomenon is crucial for the vertical growth and overall structure of the plant.

Auxin inhibits the growth of:
- Apical bud: Auxin promotes the growth of the apical bud, rather than inhibiting it.
- Lateral axillary buds: Auxin inhibits the growth of lateral axillary buds, preventing them from developing into branches. This phenomenon is known as apical dominance.
- Roots on stem cutting: Auxin promotes the formation of roots on stem cuttings, rather than inhibiting their growth.
- Parthenocarpic development of fruits: Auxin can promote the development of fruit without fertilization (parthenocarpy), rather than inhibiting it.
Therefore, the correct answer is B: Lateral axillary buds. Auxin inhibits the growth of lateral axillary buds, directing the plant's energy towards the growth of the main apical bud.

Introduction:
The induction of rooting in stem cuttings by auxin treatment is a common technique used in horticulture and plant propagation. Auxins are plant hormones that promote root development, and their application can enhance the success rate of root formation in stem cuttings. In this case, the question is asking which of the given plant species would benefit from auxin treatment to induce rooting in stem cuttings.
Detailed
The correct answer is D: Bougainvillea. Here's why:
Bougainvillea:
- Bougainvillea is a popular ornamental plant with vibrant and colorful flowers.
- It can be propagated through stem cuttings, and auxin treatment can significantly enhance root formation in these cuttings.
- Auxin treatment stimulates the development of adventitious roots, which are roots that form from non-root tissues.
- The use of auxin in Bougainvillea cuttings can increase the success rate of rooting and ensure the establishment of healthy plants.
The other options A, B, and C are not suitable candidates for auxin treatment-induced rooting in stem cuttings:

Marchantia:
- Marchantia is a liverwort, a type of non-vascular plant.
- Unlike seed plants, liverworts reproduce through spores or gemmae cups, not stem cuttings.
- Auxin treatment would not be beneficial for inducing rooting in Marchantia.
Wheat:
- Wheat is a cereal crop that is primarily propagated through seeds.
- While it is possible to propagate wheat through stem cuttings, the success rate is low, and auxin treatment is not commonly used.
- Other methods, such as tissue culture or seed propagation, are more effective for wheat propagation.
Cuscuta:
- Cuscuta, commonly known as dodder, is a parasitic plant that lacks chlorophyll.
- It obtains nutrients from its host plants by attaching itself to their stems.
- Since Cuscuta does not rely on root development for survival, auxin treatment to induce rooting in stem cuttings would not be beneficial.
Conclusion:
Auxin treatment for inducing rooting in stem cuttings is beneficial for Bougainvillea, a popular ornamental plant. However, it is not suitable for Marchantia, wheat, or Cuscuta. Understanding the specific requirements and propagation methods of different plant species is crucial for successful plant propagation.

The correct answer is A: 2, 4-D. This is not a naturally occurring plant hormone. Here is a detailed explanation of each option:
A: 2, 4-D:
- 2, 4-D (2,4-Dichlorophenoxyacetic acid) is a synthetic herbicide and plant growth regulator.
- It is not naturally produced by plants.
B: GA₂:
- GA₂ refers to Gibberellin A₂.
- Gibberellins are a group of naturally occurring plant hormones.
- GA₂ is one of the many gibberellin compounds present in plants.
- It plays a role in various plant growth and development processes.
C: Gibberellin:
- Gibberellins are a group of naturally occurring plant hormones.
- They are involved in regulating various aspects of plant growth and development.
- Gibberellins are synthesized by plants and help in processes such as seed germination, stem elongation, and flowering.
D: I.A.A:
- I.A.A (Indole-3-acetic acid) is a naturally occurring plant hormone.
- It is a type of auxin, which is involved in regulating plant growth and development.
- I.A.A plays a key role in processes such as cell elongation, root development, and tropisms.
In conclusion, option A (2, 4-D) is not a naturally occurring plant hormone, while options B (GA₂), C (Gibberellin), and D (I.A.A) are all naturally occurring plant hormones.

Answer:
To obtain seedless fruits, the unpollinated ovaries can be treated with hormones. Here is a detailed explanation:
1. Introduction:
- Seedless fruits are preferred for various reasons, such as convenience, ease of consumption, and improved taste.
- Treating the unpollinated ovaries with hormones can result in the development of seedless fruits.
2. Hormones and Seedlessness:
- Hormones play a crucial role in the development and growth of plants.
- By treating the unpollinated ovaries with hormones, the natural process of seed development can be altered, leading to seedlessness.
- The specific hormones used for this purpose may vary depending on the fruit type, but commonly used hormones include auxins, gibberellins, and cytokinins.
3. Hormones and Fruit Development:
- Auxins: Auxins are responsible for cell elongation and fruit growth. By applying auxins, the development of seeds can be inhibited, resulting in seedless fruits.
- Gibberellins: Gibberellins promote fruit enlargement and cell division. When applied in specific concentrations, they can prevent seed development, leading to seedless fruits.
- Cytokinins: Cytokinins are involved in cell division and differentiation. By manipulating the levels of cytokinins, seed formation can be suppressed, resulting in seedless fruits.
4. Application and Process:
- The application of hormones to obtain seedless fruits can be done through different methods, such as spraying, dipping, or injecting the hormone solution into the unpollinated ovaries.
- The concentration and timing of hormone application need to be carefully controlled to achieve the desired result.
- After the treatment, the fruits develop without seeds, providing a seedless fruit variety.
Conclusion:
- Seedless fruits can be obtained by treating the unpollinated ovaries with hormones.
- Hormones like auxins, gibberellins, and cytokinins play a vital role in inhibiting seed development and promoting seedlessness in fruits.
- The application of hormones needs to be done carefully and at the right stage of fruit development to achieve the desired result.

Leaf fall occurs when the content of auxin decreases.
Leaf fall, also known as abscission, is a natural process that occurs in plants during the autumn season. It is triggered by a decrease in the content of auxin, a plant hormone that regulates various physiological processes. Here's a detailed explanation of why auxin decrease leads to leaf fall:
1. Role of auxin:
- Auxin is responsible for promoting cell elongation and growth in plants. It helps in maintaining the attachment between the leaf petiole and the stem.
- It inhibits the formation of the abscission zone, a layer of specialized cells that facilitate leaf detachment.
2. Formation of the abscission zone:
- As the days become shorter and temperatures drop during autumn, plants start preparing for winter dormancy.
- In response to these environmental cues, the production of auxin decreases.
- The decrease in auxin content triggers the formation of the abscission zone at the base of the leaf petiole.
- The abscission zone consists of a layer of cells that produce enzymes, such as cellulase, that break down the cell wall between the leaf and the stem.
3. Leaf detachment:
- As the abscission zone develops, the connection between the leaf and the stem weakens.
- Eventually, the cell wall between the leaf and the stem breaks down, leading to leaf detachment.
- The leaf falls to the ground, allowing the plant to conserve energy and resources during the winter months.
In conclusion, leaf fall occurs when the content of auxin decreases. This decrease in auxin triggers the formation of the abscission zone, leading to leaf detachment.

Substance which originate at the tip of stem to control growth:
The substance that originates at the tip of the stem to control growth is called auxins. Here is a detailed explanation of auxins and their role in plant growth:
1. What are auxins?
- Auxins are a class of plant hormones that regulate various aspects of plant growth and development.
- They are primarily produced in the apical meristem, which is the growing tip of the stem.
2. Functions of auxins:
- Promote cell elongation: Auxins stimulate cell elongation, allowing the stem to grow longer.
- Apical dominance: They inhibit the growth of lateral buds, promoting the growth of the main stem.
- Phototropism: Auxins are responsible for the bending of plants towards a light source.
- Gravitropism: They help in the downward growth of roots and the upward growth of stems in response to gravity.
- Root initiation: Auxins promote the formation of new roots, enabling vegetative propagation.
3. Modes of auxin transport:
- Polar transport: Auxins move in a polar manner, from the apical meristem towards the base or downward in the stem.
- Lateral transport: Auxins can also move laterally from one part of the plant to another, influencing growth in different regions.
4. Synthetic auxins:
- Synthetic auxins, such as indole-3-acetic acid (IAA), are used in agriculture for various purposes like weed control, fruit thinning, and rooting of cuttings.
In conclusion, auxins are substances that originate at the tip of the stem and play a crucial role in regulating plant growth and development. They promote cell elongation, control apical dominance, and are involved in tropic responses and root initiation.

Answer:
Introduction:
During nodule formation in leguminous plants, certain growth substances act as stimulants. Among these growth substances, one of them is indole-3-acetic acid (IAA). In this solution, we will explain in detail how IAA acts as a stimulant during nodule formation in leguminous plants.
Explanation:
IAA is a type of auxin, which is a plant hormone responsible for various growth and developmental processes. When it comes to nodule formation in leguminous plants, IAA plays a crucial role in stimulating the process. Here is a detailed explanation of how IAA acts as a stimulant during nodule formation:
1. Induction of nodule primordia:
- IAA promotes the initiation and formation of nodule primordia, which are the initial structures that give rise to nodules.
- It induces the expression of specific genes involved in nodule development, leading to the formation of primordia.
2. Cell division and differentiation:
- IAA stimulates cell division and differentiation in the nodule primordia.
- It promotes the proliferation of cells in the primordia, leading to the growth and development of the nodule.
3. Rhizobial infection:
- IAA enhances the infection process by rhizobia, which are symbiotic bacteria that form a mutualistic relationship with leguminous plants.
- It promotes the formation of infection threads, which are structures through which rhizobia enter the root cells.
4. Nitrogen fixation:
- IAA stimulates the expression of genes involved in nitrogen fixation, a process carried out by rhizobia inside the nodules.
- It enhances the efficiency of nitrogen fixation, allowing leguminous plants to obtain a vital nutrient for their growth.
In conclusion, IAA acts as a stimulant during nodule formation in leguminous plants. It induces the formation of nodule primordia, stimulates cell division and differentiation, enhances rhizobial infection, and promotes nitrogen fixation. These processes are essential for the successful establishment of symbiotic nitrogen fixation in leguminous plants.

Auxanometer is meant for measuring growth activity.
Explanation:
Auxanometer is a device used to measure the growth activity of plants. It is based on the principle that as a plant grows, it exerts a force on a sensitive spring or lever, which can be measured to determine the rate of growth.
Here are the key points explaining why auxanometer is used for measuring growth activity:
1. Definition of auxanometer: An auxanometer is a scientific instrument used to measure the growth of plants. It consists of a sensitive lever or spring that records the force exerted by a growing plant.
2. Principle of measurement: The auxanometer works on the principle that as a plant grows, it exerts a force on the lever or spring of the instrument. This force is directly proportional to the rate of growth of the plant.
3. Measurement of growth: By measuring the force exerted by the plant, the auxanometer provides a quantitative measurement of the growth activity. The instrument can be calibrated to convert the force into growth rate or length increment of the plant.
4. Applications: Auxanometers are commonly used in plant physiology research to study the effects of various factors on plant growth. They help in understanding the growth patterns, response to environmental conditions, and the influence of hormones on plant development.
5. Advantages: Auxanometers provide a non-destructive and accurate method for measuring plant growth. They allow researchers to monitor the growth of plants over time without causing any damage.
In conclusion, an auxanometer is specifically designed to measure the growth activity of plants. It provides a valuable tool for researchers studying plant physiology and understanding the factors influencing plant growth.

Apical dominance in higher plants is due to phytohormones.
Apical dominance is the phenomenon where the terminal bud of a plant inhibits the growth of lateral buds. This allows the plant to allocate resources to the growth of the main stem and apical bud. The main factor responsible for apical dominance is the presence of phytohormones, specifically auxins.
Here is a detailed explanation:
1. Phytohormones:
- Phytohormones are chemical substances produced by plants that regulate various physiological processes.
- The hormone responsible for apical dominance is auxin.
- Auxin is primarily produced in the apical bud and is transported downwards, inhibiting the growth of lateral buds.
- It prevents the lateral buds from developing into branches, allowing the apical bud to grow and dominate the plant's growth.
2. Inhibition of Lateral Bud Growth:
- Auxin inhibits the growth of lateral buds by suppressing their development and elongation.
- It restricts the cell division and elongation in the lateral buds, preventing them from growing into branches.
- This inhibition allows the apical bud to receive more resources and grow vigorously.
3. Transport of Auxin:
- Auxin is transported in a polar manner, moving from the apical bud towards the base of the plant.
- This transport is facilitated by the phloem, which allows the movement of auxin from the apical bud to the lower parts of the plant.
4. Release from Apical Dominance:
- When the apical bud is removed or damaged, the inhibition of lateral bud growth is released.
- The removal of the apical dominance allows the lateral buds to grow and develop into branches.
- This is why pruning is often used to promote branching and bushier growth in plants.
In conclusion, apical dominance in higher plants is primarily due to the presence of phytohormones, with auxin being the main hormone responsible for inhibiting the growth of lateral buds.

Parthenocarpy is the production of fruits without fertilization.
Parthenocarpy is a phenomenon in plants where fruits develop without the need for fertilization or pollination. This process occurs naturally in some plant species and can also be induced artificially in others. Here's a detailed explanation of parthenocarpy and why it results in the production of fruits without fertilization:
1. Definition:
- Parthenocarpy refers to the development of fruits without the fusion of male and female gametes, which typically occurs during fertilization.
- Parthenocarpic fruits are seedless or contain underdeveloped seeds due to the absence of fertilization.
2. Natural occurrence:
- Some plant species naturally exhibit parthenocarpy, producing fruits without the need for pollination or fertilization.
- Examples include bananas, grapes, oranges, and certain varieties of tomatoes and cucumbers.
- In these cases, the fruits develop from unfertilized eggs present in the ovule.
3. Artificial induction:
- Parthenocarpy can also be induced artificially in plants that do not naturally exhibit this trait.
- This is often done by applying plant hormones, such as auxins or gibberellins, to stimulate fruit development without fertilization.
- Artificial parthenocarpy is commonly used in horticulture to produce seedless fruits, which are often preferred by consumers.
4. Advantages and uses:
- Parthenocarpy has several advantages, including the production of seedless fruits that are generally larger, sweeter, and more appealing to consumers.
- Seedless fruits are also convenient for culinary purposes as they eliminate the need for seed removal.
- Additionally, parthenocarpy allows the production of fruits in the absence of pollinators or in unfavorable environmental conditions.
- This trait is particularly beneficial for greenhouse cultivation and in regions where pollinators are scarce.
In conclusion, parthenocarpy is the process through which fruits develop without the need for fertilization. This can occur naturally in some plant species or be induced artificially through the application of plant hormones. Parthenocarpic fruits are seedless or contain underdeveloped seeds, making them desirable for culinary purposes and convenient for growers.

Auxin production in plants
Introduction:
Auxin is a plant hormone that plays a crucial role in various physiological processes such as cell elongation, root development, and fruit ripening. It is mainly produced in specific regions of the plant.
Answer:
The correct option is C: Apical shoot meristem as it is the primary site of auxin production in plants. Here are some key points explaining why:
- Apical shoot meristem: This is the actively growing region located at the tip of the shoot. It consists of undifferentiated cells that continuously divide and differentiate into various tissues of the plant.
- Meristematic cells: Within the apical shoot meristem, there are specialized cells called meristematic cells that have the ability to produce auxin.
- Auxin synthesis: These meristematic cells synthesize auxin through a series of enzymatic reactions. The main auxin produced in plants is indole-3-acetic acid (IAA).
- Transport: Once synthesized, auxin is transported from the apical shoot meristem to other parts of the plant through the phloem and xylem tissues. This allows auxin to exert its effects on various plant tissues and organs.
- Other sources: While the apical shoot meristem is the primary site of auxin production, other plant tissues such as young leaves, developing fruits, and root tips can also contribute to auxin production to a lesser extent.
It is important to note that while the apical shoot meristem is the main site of auxin production, other parts of the plant also play a role in auxin synthesis. However, the apical shoot meristem remains the primary source of auxin in plants.

Indole acetic acid generally inhibits the growth of roots.
Explanation:
- Indole acetic acid (IAA) is a naturally occurring plant hormone that plays a crucial role in regulating various aspects of plant growth and development.
- IAA is primarily produced in the apical meristems of plants and is transported downwards through the vascular tissues to the roots.
- While IAA has diverse effects on different plant tissues, it generally inhibits the growth of roots.
- Here's why IAA inhibits root growth:
1. IAA reduces cell division in the root meristem: The meristem is the region of actively dividing cells in the root tip. IAA suppresses cell division in this region, leading to a decrease in root growth.
2. IAA promotes root elongation: While IAA inhibits cell division, it promotes cell elongation in the root. This results in the elongation of existing cells rather than the formation of new cells, leading to a decrease in overall root growth.
3. IAA induces lateral root formation: IAA stimulates the initiation and development of lateral roots. These lateral roots compete with the main root for resources, resulting in reduced growth of the primary root.
- Overall, the inhibitory effect of IAA on root growth is essential for maintaining the balance between root and shoot growth and for adapting to changing environmental conditions.
In conclusion, indole acetic acid generally inhibits the growth of roots in plants.

Explanation:

Fruit drop is caused by:

A: From the shoot tip in the downward direction:

• Fruit drop can occur when the fruit is not properly supported by the shoot tip, causing it to detach and fall downwards.


• This can happen due to weak attachment or damage to the fruit stem.

B: From the root tip in the upward direction:

• Fruit drop does not occur from the root tip in the upward direction.


• The root tip is responsible for absorbing water and nutrients from the soil, but it does not have a direct effect on fruit drop.

C: Through vascular systems in plants:

• The vascular systems in plants, such as the xylem and phloem, play a role in transporting water, nutrients, and sugars.


• However, fruit drop is not directly caused by the vascular systems.

D: By a special transport system in the root:

• There is no special transport system in the root that causes fruit drop.


• The root system primarily functions to absorb water and nutrients.

Therefore, the correct answer is:

a. From the shoot tip in the downward direction.

Fruit drop can occur due to various factors such as hormonal imbalance, environmental stress, insufficient pollination, disease, or insect damage. It is important to identify and address the underlying cause of fruit drop in order to prevent it and ensure a healthy crop yield.

Explanation:
The phenomenon of fruit drop, where fruits prematurely fall off the plant before reaching maturity, is caused by several factors. One of the main factors is the difference in auxin levels between the fruit and the stem. Auxin is a plant hormone that plays a crucial role in fruit development and growth.
Reasons for fruit drop:
1. Less auxin in fruit than in stem: When the fruit has lower levels of auxin compared to the stem, it disrupts the hormonal balance and leads to fruit drop. This can happen due to various reasons such as poor nutrient supply, hormonal imbalances, or environmental stress.
2. More auxin in fruit than in stem: Conversely, if the fruit has higher levels of auxin compared to the stem, it can also result in fruit drop. This imbalance in auxin distribution can occur due to genetic factors or hormonal abnormalities.
3. Equal distribution of auxin in stem and fruit: If there is an equal distribution of auxin between the stem and the fruit, it promotes proper fruit development and prevents premature fruit drop.
4. Absence of auxin in stem and fruit: The absence of auxin in both the stem and the fruit can also lead to fruit drop. Auxin is essential for the growth and development of plant tissues, and its absence can disrupt normal physiological processes.
In conclusion, fruit drop is primarily caused by a difference in auxin levels between the fruit and the stem. When there is less auxin in the fruit compared to the stem, it can result in premature fruit drop.

In plants growth is -


A: Restricted to certain regions or structure
- Plants have specific regions or structures where growth is concentrated, such as the apical meristem at the tips of roots and shoots.
- Growth is regulated by hormones and genetic factors that determine the regions where cells divide and elongate.
B: Irreversible
- Once plant cells undergo growth, it is usually irreversible. The cells increase in size and volume, and their walls expand to accommodate the growth.
- However, some plants have the ability to undergo secondary growth, where new cells are produced in specific regions, leading to an increase in girth.
C: Change in size
- Growth in plants involves an increase in size, both in terms of cell expansion and cell division.
- The increase in size is a result of the accumulation of new cells and the expansion of existing cells.
D: All the above
- All of the above options are correct.
- Plant growth is restricted to certain regions or structures, it is usually irreversible, and it involves a change in size.
In summary, plant growth is regulated and occurs in specific regions or structures, it is typically irreversible, and involves an increase in size through cell division and expansion.

Motivation Force for Growth:
There are various factors that contribute to the growth of plants. Among them, the motivation force for growth can be attributed to turgor pressure. Here is a detailed explanation:
Turgor Pressure:
Turgor pressure is the force exerted by the fluid within the cell against the cell wall. It is responsible for maintaining the shape and rigidity of plant cells. Turgor pressure is generated when water enters the cell vacuole through osmosis, causing the cell to swell and exert pressure on the cell wall. This pressure is crucial for various growth processes in plants, such as:
1. Cell Expansion: Turgor pressure pushes against the cell wall, allowing the cell to elongate and expand. This is essential for plant growth and development.
2. Stomatal Opening: Turgor pressure plays a role in the opening and closing of stomata, which are tiny pores on the leaf surface. When the guard cells surrounding the stomata fill with water, they become turgid and the stomata open, facilitating gas exchange and transpiration.
3. Lifting of Plant Parts: Turgor pressure enables the lifting of plant parts, such as leaves and stems. When turgor pressure is high in the cells at the base of a leaf or stem, it causes the plant part to rise.
4. Support and Structure: Turgor pressure provides structural support to plants. It helps them maintain an upright posture and prevents wilting.
In conclusion, turgor pressure serves as the motivation force for growth in plants. It drives various physiological processes that are essential for plant development and survival.

Factors affecting growth
There are two primary climatic factors that affect the growth of plants:
1. Light
- Light is essential for photosynthesis, the process by which plants convert sunlight into energy.
- Adequate sunlight is necessary for the production of chlorophyll, which enables plants to absorb and use light energy.
- Different plants have different light requirements, with some species thriving in full sun while others prefer shade or indirect light.
2. Temperature
- Temperature plays a crucial role in plant growth and development.
- Each plant species has its own temperature requirements for optimal growth.
- Extreme temperatures, whether too hot or too cold, can limit or even halt plant growth.
- Temperature affects various plant processes, such as seed germination, photosynthesis, and enzyme activity.
Conclusion
In summary, the two primary climatic factors that affect plant growth are light and temperature. While light is essential for photosynthesis, temperature influences various physiological processes. Understanding the specific light and temperature requirements of different plants is crucial for successful growth and cultivation.

Instrument to Record Plant Growth by Seconds:
Detailed
The correct instrument that can be used to record plant growth by seconds is the Crescorgraph. Here is a detailed explanation:
1. Crescorgraph:
- The Crescorgraph is a specialized instrument used to measure plant growth by recording the growth rate in seconds.
- It consists of a clock mechanism and a revolving drum covered with a sheet of graph paper.
- The plant is attached to a marker, which is connected to the clock mechanism.
- As the plant grows, the marker moves and leaves a trace on the graph paper, recording the growth rate over time.
- The graph paper allows for precise measurements and analysis of the growth patterns.
2. Arc Auxanometer:
- The Arc Auxanometer is not suitable for recording plant growth by seconds.
- It is an instrument used to measure the rate of elongation or growth of a plant stem over a longer period of time.
- It uses a calibrated arc that measures the displacement of a weighted wire or thread as the stem grows.
3. Arc Indicator:
- The Arc Indicator is also not designed for recording plant growth by seconds.
- It is an instrument used to measure the angle of leaf inclination or leaf movement in response to environmental stimuli such as light or gravity.
4. Space Marker Disc:
- The Space Marker Disc is not specifically used for recording plant growth by seconds.
- It is a tool used to measure the spacing between plants or to mark the location of individual plants in a field or garden.
In conclusion, the correct instrument for recording plant growth by seconds is the Crescorgraph. It provides precise measurements and allows for detailed analysis of growth patterns over time.

The first phase during the process of growth in a growing plant is cell division. Here is a detailed explanation:
Cell Division:
- Cell division is the process by which a parent cell divides into two or more daughter cells.
- It is the basis of growth in multicellular organisms, including plants.
- During cell division, the genetic material of the parent cell is evenly distributed to the daughter cells, ensuring that each new cell receives a complete set of genetic instructions.
- Cell division allows for the increase in the number of cells in a growing plant, leading to overall plant growth and development.
Other Phases:
- Cell enlargement: After cell division, the newly formed daughter cells undergo cell enlargement. This process involves an increase in cell size and volume, as well as the accumulation of cell contents.
- Cell differentiation: Once the cells have enlarged, they undergo cell differentiation. Cell differentiation is the process by which cells become specialized and acquire specific structures and functions.
- Cell maturation: Finally, the differentiated cells undergo cell maturation, where they fully develop and acquire their characteristic features.
Importance of Cell Division:
- Cell division is crucial for the growth and development of a plant.
- It allows for the formation of new tissues and organs, as well as the repair of damaged or injured tissues.
- It also plays a vital role in processes like reproduction and regeneration in plants.
In conclusion, the first phase during the process of growth in a growing plant is cell division. This process is essential for increasing the number of cells, leading to overall plant growth and development.

The classical experiments on growth were performed by Boysen Jensen & Darwin

Explanation:

• Step 1: State the question and the correct answer.




• The question asks about the scientists who performed the classical experiments on growth.


• The correct answer is B - Boysen Jensen & Darwin.




• Step 2: Provide a brief explanation of the experiments on growth.




• The classical experiments on growth focused on studying the factors that influence the growth and development of organisms.


• These experiments aimed to understand how external factors such as light, temperature, and gravity affect plant growth.


• Scientists conducted various experiments to observe the responses of plants to different growth conditions.




• Step 3: Explain the role of Boysen Jensen in the experiments.




• Boysen Jensen, a Danish botanist, conducted experiments in the early 20th century to investigate phototropism in plants.


• He demonstrated that the growth of plants is influenced by the distribution of auxin, a plant hormone, in response to light.


• His experiments provided evidence for the role of auxin in plant growth and phototropic responses.




• Step 4: Explain the role of Darwin in the experiments.




• Charles Darwin, an English naturalist, conducted experiments and made observations on plant growth and movement.


• He studied the effects of light, gravity, and other factors on plant growth and tropisms.


• Darwin's experiments and observations contributed to the understanding of how plants respond to their environment and adapt to different conditions.




• Step 5: Summarize the answer.




• The classical experiments on growth were performed by Boysen Jensen and Darwin.


• Boysen Jensen investigated phototropism and the role of auxin in plant growth.


• Darwin studied plant growth and tropisms, contributing to the understanding of plant responses to the environment.

Therefore, the correct answer is B - Boysen Jensen & Darwin.

The natural plant hormones were first isolated from:
A: Cotton fruits, spinach leaves, and rice plant
- Cotton fruits, spinach leaves, and rice plant are not the correct sources of natural plant hormones.
B: Avena coleoptiles, spinach leaves, and fungus Gibberella
- Avena coleoptiles, spinach leaves, and fungus Gibberella are not the correct sources of natural plant hormones.
C: Human urine and corn germ oil
- Human urine and corn germ oil are the correct sources of natural plant hormones.
D: Human urine and rice plant
- Human urine is one of the correct sources of natural plant hormones, but rice plant is not.
Answer: C. Human urine and corn germ oil
The correct answer is C because the first isolated natural plant hormones were obtained from human urine and corn germ oil. These hormones are known as auxins and were first discovered by scientist Fritz Went in the 1920s. Went conducted experiments in which he extracted substances from human urine and corn germ oil and found that they had a significant effect on plant growth and development. This discovery paved the way for further research into plant hormones and their role in various physiological processes in plants.

Answer:

The nutrient concerned with the growth of plants in view of their role in the synthesis of auxin is Zinc (Zn).

• Zinc (Zn): Zinc is an essential micronutrient that plays a crucial role in plant growth and development. It is involved in various physiological processes, including the synthesis of auxin, a plant hormone responsible for cell elongation and growth.


• When plants have a deficiency of zinc, they may exhibit stunted growth, delayed maturity, and reduced leaf size.


• Zinc also plays a role in the activation of enzymes involved in auxin synthesis, such as tryptophan synthase.


• Without sufficient zinc, plants may have impaired auxin synthesis, leading to abnormal growth patterns and reduced overall growth.

Therefore, zinc is the nutrient that is concerned with the growth of plants in view of its role in the synthesis of auxin.

Why do plants bend toward the light?
Plants bend toward the light due to a process called phototropism. This is a growth response that allows plants to optimize their exposure to light for photosynthesis. The following factors contribute to this phenomenon:
1. Phototropism:
- Phototropism is a directional growth movement in response to light.
- It allows plants to position their leaves and stems in a way that maximizes light absorption.
2. Photoreceptors:
- Plants possess photoreceptors, such as phototropins, that detect the direction and intensity of light.
- These photoreceptors trigger growth responses in plants.
3. Differential cell elongation:
- Cells on the shaded side of a plant stem elongate more rapidly than those on the side exposed to light.
- This differential growth causes the stem to bend toward the light source.
4. Auxin distribution:
- Auxin is a plant hormone that plays a crucial role in phototropism.
- When light is detected, auxin moves from the illuminated side of the stem to the shaded side.
- This redistribution of auxin promotes elongation of cells on the shaded side, causing the plant to bend toward the light.
5. Photosynthesis:
- Light is essential for photosynthesis, the process by which plants convert light energy into chemical energy.
- By bending toward the light, plants can optimize their photosynthetic activity and enhance their overall growth and development.
In conclusion, plants bend toward the light because of phototropism, which is driven by photoreceptors, differential cell elongation, auxin distribution, and the need for light for photosynthesis. This adaptive response allows plants to maximize their exposure to light and ensure their survival and growth.