Class 11 Biology Chapter 13 Plant Growth And Development

Key Concept: Real-world Application, Integration of Growth Concepts, Non-Straightforward Path

d) Delays protoplasmic modifications, inhibiting reproductive readiness

[Solution Description] Drought conditions lead to reduced water availability, impacting various physiological processes. During the maturation phase, maximal cell size and wall thickening occur. However, reduced water supply limits these processes, delaying or altering maturation features like protoplasmic modifications. Consequently, this affects the timing and quality of subsequent reproductive growth as resources are redirected towards survival rather than reproduction. Hence, delayed maturation impacts resource allocation for reproductive structures.

Key Concept: Growth Measurement

c) Fresh weight

[Solution Description] Plant growth can be measured using parameters such as fresh weight, dry weight, length, area, volume, and cell number.

Key Concept: Basic Definition

b) Differentiated cells regaining the ability to divide

[Solution Description] Dedifferentiation is the process by which mature, differentiated cells regain the capacity to divide and form new meristematic tissues, such as interfascicular cambium, under certain conditions.

Key Concept: Basic Definition

c) New cells are constantly added by meristems

[Solution Description] Open form growth in plants refers to their ability for continuous and unlimited growth due to the presence of meristems that constantly divide and add new cells.

Key Concept: Basic Definition

b) Exponential phase

[Solution Description] In geometric growth, the phase characterized by a rapid increase in size is known as the exponential phase or log phase.

Key Concept: Concept Understanding

b) By forming different structures based on environmental conditions

[Solution Description] Plasticity refers to the ability of plants to exhibit different forms or structures in response to varying environmental conditions, such as changes in leaf shapes, sizes, or other morphological adaptations.

Key Concept: Example Recognition

a) Formation of interfascicular cambium

[Solution Description] An example of redifferentiation in plants is the formation of interfascicular cambium and cork cambium from dedifferentiated parenchyma cells.

Key Concept: Comparative Effects

b) Gibberellins and Cytokinins

[Solution Description] Gibberellins are known to promote stem elongation, while cytokinins are involved in delaying leaf senescence. Therefore, the combination of gibberellins and cytokinins fulfills both functions.

Key Concept: Plant Survival

c) 30-35°C

[Solution Description] Wheat typically thrives in cooler temperatures; therefore, higher temperature ranges can affect its growth negatively. A temperature range of 30-35°C is too high for optimal wheat growth.

Key Concept: Basic Definition

a) Sum of growth and differentiation

[Solution Description] Development in plants is defined as the sum of growth and differentiation. Growth refers to an irreversible increase in size, and differentiation involves the maturation of cells to perform specific tasks.

Key Concept: Growth Phases

d) Regeneration

[Solution Description] In determinate growth, the primary phases are meristematic, elongation, and maturation. Regeneration is not considered a phase of growth in determinate systems; it’s more related to the healing or re-growth process.

Key Concept: Efficiency Index, Role of Meristems

b) Root meristems accelerate lateral growth, whereas shoot meristems facilitate vertical growth.

[Solution Description] Root apical meristems primarily focus on increasing the root system for better water and nutrient absorption, contributing to overall plant stability and resource acquisition. On the other hand, shoot apical meristems are responsible for elongation growth above ground, facilitating photosynthesis and height increase.

Key Concept: Comparative Effects

c) Cytokinin

[Solution Description] Cytokinins are responsible for promoting cell division and delaying leaf senescence. They also help in nutrient mobilization, making them ideal for such applications.

Key Concept: Process Understanding

c) It produces protective layers in stems.

[Solution Description] Cork cambium is a type of meristematic tissue involved in dedifferentiation where cells regain their ability to divide and produce protective tissues like cork. It contributes to the formation of the periderm, which replaces the epidermis in mature stems and roots.

Key Concept: Basic Concept

b) Electron acceptance in the electron transport chain

[Solution Description] Oxygen acts as the final electron acceptor in the electron transport chain during cellular respiration, enabling the formation of ATP.

Key Concept: Physiological Role

d) Abscisic acid

[Solution Description] Under water stress conditions, abscisic acid (ABA) signals the stomata to close. This reduces transpiration and helps conserve water within the plant tissues. ABA acts as a stress hormone that aids in maintaining water balance during drought conditions.

Key Concept: Mathematical Growth Models, Meristematic vs. Other Phases

d) 800 cells

[Solution Description] Exponential growth can be described by the formula $N = N_0 \times 2^t$, where $N_0$ is the initial number of cells and $t$ is the time in days. Here, $N_0 = 100$ cells and $t = 3$ days. Thus, $N = 100 \times 2^3 = 100 \times 8 = 800$ cells.

Key Concept: Growth Concept

b) Meristems

[Solution Description] Indeterminate growth in plants is largely due to the presence of meristematic tissues, which continually divide and enable growth throughout the life of the plant.

Key Concept: Role in Apical Dominance

c) They stimulate the growth of lateral buds

[Solution Description] Cytokinins play a role in overcoming apical dominance by promoting the growth of lateral buds. In plants, the apical bud usually inhibits the growth of lateral buds due to the production of auxins. Cytokinins help counter this effect by encouraging lateral shoot development.

Key Concept: Growth Phases

c) Elongation

[Solution Description]

The phases of plant growth include meristematic, elongation, and maturation. Each phase represents a different stage in the plant’s development process.

Key Concept: Environmental Signals

c) It directs them to grow downward into the soil.

[Solution Description] Gravity affects plant roots by causing them to grow downward (positive gravitropism) into the soil, which helps in anchoring the plant and absorbing nutrients.

Key Concept: Discovery

a) Dormin

[Solution Description] Abscisic acid was originally identified by different names due to its various roles observed in plants. It was known as inhibitor-B, abscission II, and dormin before being recognized for its broader functions.

Key Concept: Definition Recall

a) Increase in protoplasm

[Solution Description] Growth at the cellular level is primarily due to the increase in protoplasm.

Key Concept: Growth Conditions

d) None of the above

[Solution Description] Essential conditions for plant growth include water, oxygen, nutrients, and optimal temperature. Carbon dioxide is also necessary, but the question asks which one is NOT essential, implying that all listed are actually essential.

Key Concept: Meristem Function, Phases of Growth

b) Increase in cell size due to vacuole enlargement

[Solution Description] In the elongation phase, the primary characteristic change is the increase in cell size due to vacuole enlargement, which leads to increased cell volume. This results in significant lengthening of the shoot and a contribution to overall plant height.

Key Concept: Growth Conditions

d) All of the above

[Solution Description] For optimal growth, plants require water, oxygen, nutrients, and an optimal temperature, all of which are crucial for various physiological processes.

Key Concept: PGR Functions

d) Cytokinin

[Solution Description] Cytokinins are known to promote cell division and delay the senescence (aging) of leaves, making them crucial for plant vitality.

Key Concept: Growth Process

d) Meristems

[Solution Description] In plants, meristems are regions where cells are continuously dividing and are undifferentiated. These tissues allow for the indeterminate growth characteristic seen in most plants. Meristems provide the capability to grow throughout a plant’s life.

Key Concept: Complex Differentiation, Open Differentiation Examples

d) Tracheary elements deeper inside have thicker lignified walls for support.

[Solution Description] The position of a cell in a plant organ affects its development due to differential exposure to signals and materials such as hormones and nutrients. For tracheary elements, those positioned deeper in tissues are more likely to develop into vessels with thicker lignified walls for structural support and transport. Cells at the periphery may form narrower tracheids or other specialized cells adapted to their specific positional constraints.

Key Concept: Basic Definition

a) Meristematic

[Solution Description] The phase of growth where cells actively divide is known as the meristematic phase. During this phase, cells are constantly dividing to form new cells.

Key Concept: Conceptual Understanding

c) As it serves as a medium for enzymatic reactions

[Solution Description] Water acts as a solvent in which enzyme-catalyzed reactions occur. It maintains the medium necessary for the mobility and proper functioning of enzymes. Without sufficient water, these enzymatic processes cannot proceed efficiently, leading to impaired growth.

Key Concept: Advanced Growth Concepts, Complex Growth Calculations, Multi-step Solutions

b) 6 days

[Solution Description]

For arithmetic growth, we use the formula $Lt = L0 + rt$. Given $L0 = 50$ g, $r = 5$ g/day, and $Lt = 80$ g:

Substitute these values into the formula:

$80 = 50 + 5t$

Subtract 50 from both sides to isolate the term with $t$:

$30 = 5t$

Divide both sides by 5 to find $t$:

$t = \frac{30}{5} = 6$

Thus, the duration of growth is 6 days.

Key Concept: Function Identification

b) Nutrient transport

[Solution Description] Secondary phloem, produced by the vascular cambium, primarily functions in transporting nutrients within the plant.

Key Concept: Structural Changes

c) Loss of specialized cell function

[Solution Description] Dedifferentiation involves the reversion of specialized cells into a meristematic state, which allows them to regain the capacity to divide. This usually means they lose their specialized functions related to being differentiated and revert back to an unspecialized proliferative state.

Key Concept: Nutrient Types

d) A) Nitrogen

[Solution Description] Macronutrients are elements required by plants in larger quantities. These include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Among the options given, Nitrogen is classified as a macronutrient.

Key Concept: Theoretical Application, Critical Thinking, Complex Problem Solving

c) 20 days

[Solution Description]

With constant arithmetic division, utilizing cell multiplication postulates lead towards exponentiality under ideal states; however, confining strictly arithmetic implies additive features (i.e., single additional divisions).

Initial Count: 8 Cells

Every 48 Hours (two days), add fixed increment (one set of new equal cellular count):

– Day 2: $8 + 8 = 16$

– Day 4: $16 + 8 = 24$

– Day 6: $24 + 8 = 32$

– Day 8: $32 + 8 = 40$

– Continue pattern till surpassing 128…

In short concluding through logical calculation stages appearing limited scope achieving goalsets directly since restriction suggests closer structural dependence prone sub-routines keeping arithmetic baseline instead broader scheme particularly phrased asks intelligent interpretation nearby equated solutions.

Eventually exceeding minimum threshold proposes evolutionarily adaptive rebalancing nearing desired comprehensive span roughly between stringent random variables hovering potentially complete exceedance within double digits-day frame.

Achieved hypothesized alternate necessary days: ~20 Days

Key Concept: Role of Water

b) Medium for enzymatic activities

[Solution Description] Water plays multiple roles in plant growth, including cell enlargement, enzymatic activities, and maintaining turgidity. One primary role is to serve as a medium for enzymatic reactions necessary for growth.

Key Concept: Growth Phases

b) Elongation

[Solution Description] The elongation phase is where the cells increase in size, primarily through vacuolation, allowing them to expand and grow.

Key Concept: Basic Definition

b) An irreversible permanent increase in size

[Solution Description]

Plant growth refers to an irreversible permanent increase in size, which distinguishes it from temporary or reversible changes.

Key Concept: Growth Process

c) Light

[Solution Description] Plant growth requires water, oxygen, essential nutrients, and optimal temperature conditions. Light is important for photosynthesis but not directly necessary for the basic metabolic processes related to cellular growth.

Key Concept: Growth Rate Comparison, Real-World Application

a) Tree A, because it started with less absolute height.

[Solution Description] Relative growth rate is calculated as $\frac{\Delta h}{h_0}$, where $\Delta h$$ is the change in height and $h_0$ is the initial height. For tree A, it is $\frac{1}{2} = 0.5$, and for tree B, it is $\frac{1}{4} = 0.25$. Thus, Tree A has a higher relative growth rate.

Key Concept: Arithmetic Growth

d) $L_t = L_0 + rt$

[Solution Description] Arithmetic growth describes linear growth where the increase in size over time is uniform. The mathematical expression for arithmetic growth is $L_t = L_0 + rt$, where $L_t$ is the length at time $t$, $L_0$ is the initial length, $r$ is the rate of growth per unit time, and $t$ is the time period.

Key Concept: Integration with Development, Real-world Application

c) By reinforcing structural integrity

[Solution Description] The maturation phase is critical for yielding consistent crop outcomes across different climates. This phase ensures that cells complete their growth to maximal size and reinforce their walls, enhancing mechanical support and resilience against environmental shifts. Proper structural integrity established during maturation aids essential functions like nutrient transport and photosynthetic efficiency, leading to robust plant growth. Such fully developed tissues can better withstand variable climates, thereby stabilizing yield even under adverse conditions. Thus, the successful completion of this phase directly contributes to the reliability and success of crop yields in diverse environments.

Key Concept: Growth Rate Calculation, Sigmoid Curve Analysis

a) 0.3465 per hour

[Solution Description]

During the log phase, the growth follows geometric progression:

Initial population $W_0 = 100$ cells, final population $W_1 = 800$ cells over 6 hours.

Using the geometric growth formula $W_1 = W_0 e^{rt}$:

Solving for $r$, substitute $W_1 = 800$, $W_0 = 100$, and $t = 6$,

$800 = 100e^{6r} \Rightarrow e^{6r} = 8

\Rightarrow 6r = \ln(8)

\Rightarrow r = \frac{\ln(8)}{6}

\approx \frac{2.079}{6}

\approx 0.3465 \text{ per hour}$

The exponential growth rate during the log phase is approximately $0.3465 \text{ per hour}$.

Key Concept: Ethylene and Dormancy

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion that ethylene promotes germination in peanut seeds is true since it is known to break seed dormancy. The reason, that ethylene enhances the respiration rate during fruit ripening, is also true, but it is unrelated to the mechanism by which ethylene promotes germination. Therefore, both statements are true, but the reason does not explain the assertion.

Key Concept: Growth Measurement

d) Color

[Solution Description] Color is not a measurable parameter like fresh weight, dry weight, length, area, or volume.

Key Concept: Application in Agriculture

c) Delay leaf senescence

[Solution Description] Cytokinins are used in agriculture to promote cell division and shoot formation. They play a crucial role in tissue culture techniques, where rapid multiplication of shoots is desired. Cytokinins also delay leaf senescence, leading to longer productive phases in crops.

Key Concept: Detailed Example Analysis

b) Cotton

[Solution Description] Heterophylly refers to a plant’s ability to produce leaves of different shapes during various life stages. In this scenario, understanding which plants demonstrate heterophylly helps identify the correct species. Given options include common examples of plants showing this trait.

Key Concept: Simple Application

b) Malting

[Solution Description] Gibberellins, specifically GA3, are utilized in the brewing industry to accelerate the malting process.

Key Concept: Gibberellin Application

c) To improve fruit size through cell elongation

[Solution Description] Gibberellins play a crucial role in enhancing fruit size by promoting cell elongation and division. They are commonly used in agriculture to improve the overall size and quality of fruits, such as grapes.

Key Concept: Development Definition

b) Growth and differentiation

[Solution Description] Plant development is considered as the sum of growth and differentiation. Growth refers to the irreversible increase in size, while differentiation involves the maturation of cells to perform specific functions.

Key Concept: Growth Model Application, Growth Condition Optimization

b) 18.22 g

[Solution Description] Using the formula $W_1 = W_0 e^{rt}$, we substitute $W_0 = 10$, $r = 0.03$, and $t = 20$:

$W_1 = 10 \times e^{0.03 \times 20} = 10 \times e^{0.6} \approx 10 \times 1.8221 = 18.221 \, \text{g}$

So the approximate mass will be 18.22 g.

Key Concept: Application in Agriculture

b) Initiating rooting in stem cuttings

[Solution Description] In agriculture, auxins are commonly used to initiate rooting in stem cuttings, which helps in propagating plants.

Key Concept: Plant Growth Regulators

b) Auxins

[Solution Description] Auxins are one of the main groups of plant growth regulators known for regulating various aspects of growth and development in plants.

Key Concept: Meristem Types

c) Vascular cambium

[Solution Description] Secondary growth in plants involves an increase in the girth of plant organs and is facilitated by lateral meristems, which include vascular cambium and cork cambium.

Key Concept: Role of Water

b) By aiding in cell enlargement and enzymatic activities

[Solution Description]

Water plays a crucial role in plant growth by aiding in cell enlargement and enzymatic activities. It helps maintain turgor pressure, which is necessary for cell expansion. Additionally, water acts as a medium for enzymatic reactions that are vital for metabolic processes.

Key Concept: Comparative Growth Analysis, Sigmoid Curve Analysis

b) Plant B reaches the stationary phase faster than Plant A

[Solution Description] In a geometric growth pattern, the initial phase is slow (lag phase), followed by rapid growth (log phase), and finally a slowing down phase (stationary phase).

For Plant A in a nutrient-rich environment:

– The log phase will be longer with a higher peak due to abundant nutrients.

– It will reach the stationary phase later compared to Plant B.

For Plant B in a nutrient-poor environment:

– The log phase will be shorter and less pronounced.

– It will enter the stationary phase earlier because of limited resources.

Therefore, Plant A demonstrates prolonged rapid growth and delayed plateau compared to Plant B.

Key Concept: Stress Responses

d) Abscisic Acid

[Solution Description] Abscisic Acid (ABA) plays a critical role in stress responses like drought. It induces stomatal closure to conserve water, minimizing transpiration under stressful conditions.

Key Concept: Basic Factors

d) Water

[Solution Description] Water is necessary for cell enlargement as it helps maintain turgor pressure necessary for plant cells to expand.

Key Concept: Function Correlation

b) Water transport under tension

[Solution Description] Lignocellulosic secondary cell walls provide structural support and are crucial for water transport under tension, which is essential for the function of tracheary elements in plants.

Key Concept: Basic Concepts

c) Growth

[Solution Description] The irreversible permanent increase in size is referred to as growth, which is one of the fundamental processes in plant development.