Plant Growth and Development - Class 11 Biology - Chapter 12 - Notes, NCERT Solutions & Extra Questions
Renews every month. Cancel anytime
Your personal doubt-solving assistant
Chatterbot AI gives you 100% accurate answers to your questions in an instant.
Extra Questions - Plant Growth and Development | NCERT | Biology | Class 11
How does secondary growth take place in a dicot stem?
Secondary growth occurs in dicotyledonous (dicot) plants, specifically those that have a cambium present between the xylem and phloem. Within any single vascular bundle of a dicot stem, you would observe primary xylem oriented towards the plant's inner core or pith, primary phloem facing the outer cortex, and between both, the vascular cambium also known as intrafascicular cambium.
The tissues located between these vascular bundles are called medullary rays. These cells differentiate to form the interfascicular cambium. During the process of secondary growth, both the interfascicular and intrafascicular cambium merge to construct a continuous ring known as the cambium ring.
Once formed, the cambium ring becomes metabolically active and begins generating new cells both towards the stem's outer and inner sides, producing secondary phloem outward and secondary xylem inward. There is a greater production of secondary xylem compared to secondary phloem, which leads to compression and eventual crushing of the primary and secondary phloem due to the accumulation of the xylem.
As division continues in the vascular cambium cells, the stem's outer tissues also expand. This expansion helps accommodate the increasing internal width while maintaining essential functions such as nutrient and water transport along the stem.
To aid this adjustment, another lateral meristem called the cork cambium or phellogen develops in the cortex area. It produces cells inwardly forming the phelloderm or secondary cortex, and cells outwardly forming the phellem or cork. Together, phellem, phellogen, and phelloderm are referred to as the periderm. Externally, the dead tissues beyond the vascular cambium constitute what is known as bark.
This comprehensive activity of cambium and cork cambium essentially explains the mechanism behind secondary growth in dicot stems.
Petioles of leaves are weakened by which hormone(s)?
A) Auxin
B) Gibberellin
C) Cytokinin
D) Abscisic acid
The correct options are:
A) Auxin
D) Abscisic acid
Abscisic acid (ABA) originally received its name due to its believed role in abscission, which is the process through which leaves and fruits detach from plants. Despite later findings, ABA is recognized for inhibiting growth, thereby acting in opposition to hormones like auxins and gibberellins. Specifically, in leaves, ABA contributes to the weakening of the petiole, leading to the shedding of the leaves. Additionally, ethylene in excessive quantities can also significantly induce abscission.
Is commercially used to increase the length of plants?
A. Gibberellin
B. Auxin
C. Cytokinin
D. Ethylene
The correct option is A. Gibberellin
Gibberellin is a plant hormone that primarily promotes cell elongation, contributing to the increased length of plant internodes. This hormone is key in several vital developmental processes in plants including fruit growth, breaking seed dormancy, and initiating seed germination. For commercial applications, it is especially significant in enhancing the longitudinal growth of internodes in dwarf plants and is utilized in agriculture for increasing the length of crops like sugarcane.
Transgenic plants take longer to develop when compared to plants being improved using traditional breeding.
A) True
B) False
The correct option is B) False.
Transgenic plants are developed through the direct transfer of desirable genes from one species to another. This method is generally faster than traditional breeding methods, such as cross-pollination and selective breeding, which often involve multiple generations to achieve the desired traits.
Identify the gland in the picture and select the correct pair accordingly:
A) Dwarfism
B) Goiter
C) Sterility
D) Gigantism
The correct option is D) Gigantism
The image depicts the pituitary gland, which consists of two main lobes: the anterior and the posterior pituitary lobes. The hormone somatotropin, also known as growth hormone, is secreted by the anterior lobe. When there is an increase in the production of this hormone during the growth phase of an individual, it can cause excessive body growth, a condition known as gigantism. Conversely, if there is a deficiency in this hormone's production during the growth phase, it results in a condition known as dwarfism.
The posterior lobe of the pituitary gland is important for the storage and release of hormones produced by the neurosecretory cells of the hypothalamus, although it does not produce hormones itself.
"What is meant by parametabolous development?"
Paurometabolous development, often known as gradual metamorphosis, is characterized by juvenile stages, called nymphs, that closely resemble adults but feature external wing buds. These nymphs share the same habitat and diet as the adults. A notable example of organisms undergoing this type of development is the Hemiptera, or true bugs and their allies. This developmental process stands out because it doesn't involve a distinctively different larval stage, but rather a series of progressively mature stages culminating in the adult form.
True or false: The development of monocot and dicot embryos is similar until the globular stage.
A) True
B) False
The correct answer is A) True.
Embryogenesis in both monocot and dicot embryos progresses similarly from the zygote up to the globular stage.
The phytohormone auxin was first isolated by:
A) C. Darwin
B) F. Darwin
C) F. W. Went
D) F. Skoog
Correct answer: C) F. W. Went
Explanation:
Although C. Darwin and F. Darwin were instrumental in documenting phototropic responses in canary grass coleoptiles, F. W. Went is credited with the pioneering discovery of auxin. He adeptly isolated auxin from the tips of oat seedling coleoptiles. Following his discovery, F. Skoog further explored auxin, focusing on its role in the nutrient medium.
Growth in plants:
A. Ceases organs formation
B. is not influenced by the environment
C. is of open form
D. is restricted to apices only
The correct answer is C. is of open form.
In plants, the growth occurs continuously due to the presence and activity of meristems, which constantly add new cells to their structure. This type of growth is referred to as an open form of growth.
Identify the phenotypic ratio of Filial 2 generation given that the parents are tall (TT) and dwarf (tt).
A. 3 Tall, 1 Dwarf
B. 2 Tall, 2 Dwarf
C. 1 Tall, 3 Dwarf
D. 4 Tall, 0 Dwarf
The correct answer is A) 3 Tall, 1 Dwarf.
The F1 generation results from crossing purebred tall (TT) and purebred dwarf (tt) plants. Since 'T' (tall) is dominant over 't' (dwarf), all offspring (F1) will be heterozygous tall (Tt).
When these F1 individuals are self-crossed (Tt x Tt), the F2 generation exhibits both tall and dwarf phenotypes. This crossing follows the Mendelian inheritance pattern for a single trait with a simple dominance relationship:
Genotypes obtained:
TT (tall): appears when both parents pass the dominant allele.
Tt (tall): appears when one parent passes the dominant allele and the other a recessive allele.
tt (dwarf): appears when both parents contribute the recessive allele.
Combining these possibilities for the F2 generation gives a phenotypic ratio of 3 tall to 1 dwarf:
Tall Homozygous (TT): 1
Tall Heterozygous (Tt): 2
Dwarf Homozygous (tt): 1
Hence, the offspring's phenotypic ratio in the F2 generation is 3:1 favoring tall plants.
What is the importance of intercalary meristematic tissue?
Intercalary meristematic tissues play a critical role in plant growth, particularly in monocotyledons such as grasses and horsetails. These tissues are strategically located either at the internodes (the spaces between nodes along the stem) or at the base of leaves.
The primary function of intercalary meristems is to facilitate rapid longitudinal growth. Unlike apical meristems, which focus on increasing the overall length at the tips of roots and shoots, intercalary meristems enable the elongation of internodes or bases of leaves, allowing plants to quickly recover from injuries and continue growing in height. This aspect is especially beneficial for plants in environments where being taller provides an advantage, such as in competing for sunlight.
Moreover, because intercalary meristems remain active in cell division, they are essential for not only initial growth but also regrowth after pruning or grazing. This capability makes monocots robust in handling environmental stress and physical damage, ensuring their survival and continual propagation.
Crescograph and auxanometer are:
A. Used to study the effect of sunlight on plants. B. Used to grow plants in a controlled environment. C. Growth-measuring instruments. D. Instruments to study the age of trees.
The correct answer is C. Growth-measuring instruments.
Growth in plants is assessed by measuring changes in parameters like length, volume, area, or diameter. A crescograph is specifically designed to measure the growth rates of plants, highlighting how these rates can vary under different conditions. An auxanometer, on the other hand, is utilized specifically for measuring the growth in length of plant organs.
Germplasm for a particular species includes:
A) Seeds
B) Plants or plant parts
C) Tissues or cells
D) Only A and B
The correct options are:
A) Seeds
B) Plants or plant parts
C) Tissues or cells
Germplasm is living tissue from which new plants can be grown. It can include a seed or another plant part such as a leaf, a stem piece, pollen, or even just a few cells that can develop into a whole plant. Germplasm houses the information for a species' genetic makeup, serving as a valuable natural resource for plant diversity.
Cells with abundant plasmodesmatal connections are found in:
A) Elongation zone
B) Meristematic zone
C) Maturation zone
D) Root hair zone
The correct answer is B) Meristematic zone.
Cells with abundant plasmodesmatal connections are typically found in the meristematic zone. This area of plants is crucial for growth as it contains cells that actively divide and often require substantial communication via plasmodesmata to coordinate their activities.
In plants, growth occurs due to
A. Accretion
B. Intussusception
C. Deposition
D. None of the above
The correct answer is B. Intussusception.
Intussusception refers to the growth process where cell walls expand, primarily by the incorporation and synthesis of new cellulose microfibrils into existing cell walls. This process allows cells to grow in both size and strength.
Seed can germinate without the presence of soil.
A) True
B) False
The correct answer is A) True.
Hydroponics is a technique where plants are grown in a water-based, nutrient-rich solution, bypassing the need for soil. Instead of soil, the plant roots are supported by an inert medium such as perlite, rockwool, clay pellets, peat moss, or vermiculite. This demonstrates that seeds can indeed germinate without soil.
List some abiotic factors which are important for the growth of the plants.
Abiotic factors essential for plant growth include:
Air
Water
Light
Soil
Heat
These elements play crucial roles in supporting various physiological and biochemical processes in plants.
A plant requires magnesium for
A) Cell wall development
B) Holding cells together
C) Protein synthesis
D) Chlorophyll synthesis
The correct answer is D) Chlorophyll synthesis.
Chlorophyll, a critical component for photosynthesis, includes a magnesium ion enclosed within a structure called chlorin. This relationship highlights the essential role of magnesium in the synthesis of chlorophyll, which is pivotal for the plant's ability to absorb sunlight and convert it into usable energy.
Gametophyte is most developed in:
A. Fern
B. Moss
C. Pinus
D. Cycas
The correct answer is B. Moss.
In mosses, which belong to the group of plants known as bryophytes, the gametophyte stage is the most prominent and developed. This stage is dominant and carries out most of the plant's photosynthesis, differing significantly from other groups like ferns, pines, and cycads where the sporophyte is more developed.
Which statement is correct about the centre of origin of plants?
A. Wild or domesticated varieties developed their distinct characters.
B. Frequency of dominant genes is more.
C. Climatic conditions more favorable.
D. None of the above.
The correct statement about the center of origin of plants is:
A. Wild or domesticated varieties developed their distinct characters.
A center of origin, or geographical area where an organism originates, is crucial as it is where domesticated or wild varieties first developed their distinctive traits. This area is also recognized as a center of diversity, which means it's a region where maximum genetic variations within the species can be observed.
"Can growth be considered as a defining feature of all living things without an exception?"
Growth is a characteristic observed in all living organisms, typified by an increase in mass and a rise in the number of individuals. In multicellular organisms, growth occurs through cell division, and while plants exhibit this throughout their lives, animals generally grow only until a certain age. Post this period, cell division persists only in specific tissues for the purpose of replacing lost cells. Unicellular organisms grow by cell division as well, a phenomenon that can be observed under a microscope in in-vitro cultures.
In complex animals and plants, it's important to note that growth and reproduction are distinct and separate processes. Commonly, growth in living organisms is associated with internal increases in body mass, unlike non-living entities like mountains or boulders, where apparent growth is due to material accumulation on their surfaces.
Given this, it's clear that while growth is prevalent among living things, it's not completely definitive of life since non-living objects can also 'grow' under certain definitions. Additionally, growth ceases upon death, thus it is not inherently exclusive to life forms. Hence, growth alone should not be considered a definitive characteristic of all living organisms without exception. The conditions and nature of growth need to be clearly understood and delineated when discussing it as a characteristic of living systems.
"How do plants grow in different ways and in different parts?"
Plants grow and react to the changing seasons in various ways, a phenomenon primarily regulated by the photoperiod or the length of daylight they experience. Unlike humans, who might notice seasonal changes through temperature shifts, plants use daylight length as their primary environmental cue.
During different seasons, due to the Earth's tilt, the length of the day varies. In winter, the days are shorter, leading to earlier sunsets, while in summer, days are longer with late sunsets. Plants possess a light-sensitive chemical that detects these changes in day length.
This sensitivity to the duration of light and dark is called photoperiodism. For example, as days start to shorten in autumn, trees interpret this decrease in sunlight. Consequently, they initiate processes that cause their leaves to change color and eventually drop — an adaptation preparing them for winter.
Photoperiodism also influences when plants flower. Many flowering species use the length of night, or the dark period, as a signal to initiate blooming. Plants are often categorized as either long-day plants or short-day plants based on their photoperiodic flowering requirements. Long-day plants, like wheat and lettuce, require longer daylight periods to flower, whereas short-day plants, including rice and sugar cane, flower when daylight is less than a specific duration.
Understanding these adaptative traits of plants concerning photoperiods helps in explaining not only their growth patterns but also their survival strategies across different seasons.
What is the name of the process by which a seed grows into a baby plant?
A) Harvesting
B) Germination
C) Layering
D) Grafting
The correct answer is B) Germination.
Germination is the process where a seed develops into a new plant, also known as a seedling. This process occurs under suitable conditions of moisture, sunlight, and soil quality, enabling the seed to sprout and grow.
Which plant hormone helps in delaying senescence?
A) Ethylene
B) Auxin
C) Gibberellins
D) Abscisic acid
The correct answer is C) Gibberellins.
Senescence refers to the ageing of plant parts. Plant hormones significantly impact this process, with some promoting senescence and others delaying it. Gibberellins are known for their role in delaying senescence. Unlike Ethylene, which accelerates ageing, Gibberellins help extend the functional lifespan of plant parts. This hormone also plays roles in inducing parthenocarpy (development of fruit without fertilization) and breaking dormancy during seed germination.
Cells of the maturation zone attain their maximal size in terms of wall thickening and protoplasmic modifications.
A) True
B) False
The correct answer is A) True.
Cells in the maturation zone are located just beyond the elongation phase. In this stage, cells achieve their maximum size and undergo substantial changes including maximum thickening of the cell wall, allowing them to reach their final mature state.
Why do we consider pericycle an important layer of the root system?
A Cork and cambium arise from this layer.
B Play an important role in conducting water.
C Root branching occurs from these cells.
D Both A & C (E) Both B & C.
The correct answer is D) Both A & C.
The pericycle, located just below the endodermis, plays a crucial role in the root system for several reasons:
It is from the pericycle that cork cambium (a part of secondary growth) and root branches develop. This makes the pericycle vital for both the structural complexity and increased functionality of the root system.
The pericycle consists of a thin, yet crucial layer of cells that form a ring around the stele, supporting these developmental processes.
Thus, the key functions of the pericycle include the initiation of root branching and the formation of cork and cambium.
Identify the plant growth regulator, which is not a growth-promoting hormone from the options given below:
A) Auxins
B) Gibberellins
C) Ethylene
D) Cytokinins
The correct option is C) Ethylene
Plant growth regulators (PGRs) are classified based on their roles within the plant body into growth-promoting hormones and growth-inhibiting hormones.
Growth-promoting hormones are responsible for various physiological processes such as cell division, cell enlargement, tropic growth, as well as critical stages like flowering, fruiting, and seed formation. Examples include Auxins, Gibberellins, and Cytokinins.
Growth-inhibiting hormones, on the other hand, mainly induce dormancy and abscission (the shedding of leaves, flowers, and fruits). They are also vital in the plant’s response to wounds and stress from both biotic and abiotic sources. Abscisic acid is a well-known growth inhibitor.
Ethylene, a gaseous plant growth regulator, predominantly plays a role in inhibiting growth by accelerating abscission and promoting the ripening of fruits, which categorizes it as a growth-inhibiting hormone.
Assertion (A): ABA helps seeds to withstand desiccation and other factors unfavorable for growth. Reason (R): ABA induces seed dormancy.
A. Both $A$ & $R$ are true and $R$ explains $A$.
B. Both $A$ & $R$ are true and $R$ does not explain $A$.
C. $A$ is true and $R$ is false.
D. Both $A$ & $R$ are false.
The correct answer is A: Both $A$ & $R$ are true and $R$ explains $A$.
ABA (abscisic acid) is crucial for seed development, maturation, and dormancy. By inducing dormancy, ABA aids seeds in enduring desiccation and other adverse growth conditions. Thus, the induction of seed dormancy by ABA directly contributes to its ability to help seeds withstand unfavorable conditions, linking the reason (R) as an explanation for the assertion (A).
A pea plant shows the genetic makeup TtRr. How will the plant appear externally?
A. Dwarf with round seeds
B. Tall with round seeds
C. Dwarf with wrinkled seeds
D. Tall with wrinkled seeds
The correct answer is B. Tall with round seeds.
The pea plant's genotype is given as $TtRr$. This implies the presence of both tall trait ($T$) which is dominant over dwarf ($t$), and round seed shape ($R$) which is dominant over wrinkled ($r$). Consequently, since the plant carries at least one dominant allele for each trait (Tallness and Roundness), it will express these dominant phenotypes.
Thus, physically, the plant will be tall and will produce round seeds.
Which of the following plant tips has Quiescent center:
A. Stem
B. Root
C. Leaf
D. Sepal
The quiescent center is a region found within plant roots. It consists of a small number of cells, approximately 100, that are relatively less active in terms of cell division. This area is critical for the synthesis of growth hormones, which support the regulation of growth processes in plants.
These cells are present in a hemispherical form at the tip of the root, specifically known as the root tip. Surrounding the relatively dormant cells of the quiescent center, there are more actively dividing cells, which contribute to the growth and development of the root system.
From the understanding that the quiescent center is located at the root tip, the correct answer to the question is:
B. Root
This is because the quiescent center, with its role in hormone synthesis and maintaining the growth balance, is specifically found at the root tip of plants.
Which is Phytohormone?
A. Auxin
B. Gibberellin
C. Cytokinin
D. All of the above
Phytohormones, also known as plant hormones, are chemical messengers that play critical roles in the growth and development of plants. They help in various physiological processes, ensuring proper growth in plants.
When we look at the options provided:
Auxin is a phytohormone that is essential for the growth and development of plants. It assists in cellular processes and growth direction.
Gibberellins are another class of phytohormones that affect aspects like plant height and other growth characteristics. They assist in the elongation of cells.
Cytokinins influence cell division and are accountable for numerous growth functions within the plant's development stages.
Considering the definition of phytohormones and the roles mentioned for each option, all the options listed (Auxin, Gibberellins, Cytokinins) are phytohormones. Thus, the correct answer to the question "Which is Phytohormone?" would be:
D. All of the above.
These are among the five major types of phytohormones, with others including Abscisic Acid (ABA), which is also significant in plant hormone regulation but was not listed as an option here.
Intercalary meristem is present in:
A. at the base of the leaves and both the sides of the node.
B. in the roots.
C. at the tip of the leaves.
D. at the shoot apex.
Intercalary meristem is a type of meristem involved in the growth and development of plants, particularly responsible for their increase in length and in some cases, branching and diameter growth.
Key Characteristics of Intercalary Meristem:
Presence in Plants: These are special cells known as meristematic cells which are responsible for generating different types of plant cells. These cells possess a special ability to create various types of cells needed for plant growth.
Location: It is specifically located at the base of the leaves and on both sides of the node. This placement facilitates the plant’s ability to regenerate parts like leaves swiftly after injury.
Function: The primary role of intercalary meristem is to contribute to the growth in length of the plant at these specific areas. Additionally, it plays a role in branching and increasing the diameter of the plant in certain scenarios.
The correct answer is thus: A. at the base of the leaves and both the sides of the node.
This location enables the intercalary meristem to effectively participate in the rapid growth and regeneration of these plant parts, crucial for sustained growth and survival.
Which of the following plant hormones causes wilting of leaves?
A. Abscisic acid
B. Gibberellin
C. Cytokinin
D. Auxin
The correct answer to the question regarding which plant hormone causes wilting of leaves is A. Abscisic acid.
Abscisic acid is often referred to as the stress hormone in plants because it plays a crucial role during times of environmental stress. It prompts various responses that help the plant cope with unfavorable conditions. One of the key functions of abscisic acid is its regulatory effect on the closing of stomata, which are small openings on the surface of leaves.
When a plant is stressed, especially due to lack of water, abscisic acid levels increase, triggering the stomata to close. This closure helps in reducing water loss from the leaves through transpiration. While this mechanism conserves water, it also restricts gas exchange, necessary for photosynthesis. Consequently, the limited availability of gases and the slowdown of photosynthesis inhibit plant growth, leading ultimately to the wilting of leaves.
Hence, the increase in abscisic acid, particularly under stress conditions, such as drought, is primarily responsible for the wilting observed in plants.
In the figure given alongside, the parts marked A, B, and C are sequentially:
(a) cotyledon, plumule, and radicle. (b) plumule, radicle, and cotyledon. (c) plumule, cotyledon, and radicle. (d) radicle, cotyledon, and plumule.
The correct answer is (c) plumule, cotyledon, and radicle.
A represents the plumule, which will eventually develop into the shoot.
B represents the cotyledon, which serves as the seed leaf.
C represents the radicle, which will grow into the roots.
Thus, the parts marked A, B, and C in the figure are plumule, cotyledon, and radicle, respectively.
The hormone involved in the mobilization of food material in cereal grain during germination is:
A. Auxin
B. Gibberellin
C. Kinetin
D. ABA
The correct option is B: Gibberellin.
During the germination of cereal grains, Gibberellin (GA) plays a crucial role in mobilizing food materials for the growing embryo.
Which breaks dormancy of potato tuber?
Option 1: Gibberellin
Option 2: IAA
Option 3: ABA
Option 4: Zeatin
The correct option is Option 1: Gibberellin.
Gibberellin breaks the dormancy of potato tubers.
Which of these is not a plant growth promoter?
Auxin
Cytokinins
Ethylene
Gibberellins
Correct Option: C Ethylene
Plants produce hormones known as phytohormones which regulate their growth and development. These hormones are broadly categorized into plant growth promoters and plant growth inhibitors.
Plant Growth Promoters:
Auxins
Gibberellins
Cytokinins
Plant Growth Inhibitors:
Abscisic acid
Ethylene
Therefore, among the given options, Ethylene is not a plant growth promoter. Instead, it is recognized as a plant growth inhibitor.
💡 Have more questions?
Ask Chatterbot AINCERT Solutions - Plant Growth and Development | NCERT | Biology | Class 11
Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
Growth
Growth is defined as an irreversible permanent increase in size of an organ or its parts or even of an individual cell, generally accompanied by metabolic processes.
Differentiation
Differentiation is the process through which cells derived from root apical, shoot apical meristems, and cambium mature to perform specific functions by undergoing structural changes both in their cell walls and protoplasm.
Development
Development encompasses all changes an organism goes through during its life cycle, from germination of the seed to senescence. It is the sum of both growth and differentiation processes.
Dedifferentiation
Dedifferentiation is the phenomenon where living differentiated cells that have lost the capacity to divide regain it under certain conditions.
Redifferentiation
Redifferentiation is the process where cells produced by dedifferentiated meristems/tissues lose the capacity to divide again but mature to perform specific functions.
Determinate Growth
Determinate growth refers to growth that ceases after a certain period due to the cessation of meristem activity.
Meristem
A meristem is a type of plant tissue consisting of cells that retain the capacity to divide and self-perpetuate, leading to the formation of new cells that make up the plant body.
Growth Rate
Growth rate is the increased growth per unit time, which can be expressed mathematically. It can be either arithmetic or geometric in nature.
These definitions are based on the information provided in the chapter.
Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
No single parameter is sufficient to demonstrate growth throughout the life of a flowering plant because growth involves multiple aspects such as increase in fresh weight, dry weight, length, area, volume, and cell number. Different parameters capture different dimensions of growth. For example, increase in length may be significant in one growth phase while increase in area or volume may be more relevant in another. Hence, evaluating multiple parameters provides a more comprehensive understanding of the growth process.
Describe briefly:
(a) Arithmetic growth
(b) Geometric growth
(c) Sigmoid growth curve
(d) Absolute and relative growth rates
(a) Arithmetic Growth
Arithmetic growth occurs when, after cell division, only one daughter cell continues to divide while the other differentiates and matures. This results in linear growth. The growth formula for arithmetic growth is:
$$ L_t = L_0 + rt $$
where:
$ L_t $ = length at time 't'
$ L_0 $ = initial length at time 'zero'
$ r $ = growth rate/elongation per unit time
(b) Geometric Growth
Geometric growth involves both daughter cells retaining the ability to divide after every mitotic cell division. Initially, growth is slow (lag phase), then increases exponentially (log phase), and eventually slows down as resources deplete (stationary phase). This type of growth is represented by an exponential curve when plotted. The formula for geometric growth is:
$$W_1 = W_0 e^{rt} $$
where:
$W_1$ = final size (weight, height, number, etc.)
$ W_0$ = initial size
$ r$ = growth rate
$ t $ = time
$e$ = base of natural logarithms
(c) Sigmoid Growth Curve
The sigmoid growth curve is a characteristic S-shaped curve typical of growth in natural environments, particularly for cells, tissues, and organs in plants. It includes three phases:
Lag phase - Slow initial growth.
Log (exponential) phase - Rapid growth.
Stationary phase - Growth rate slows and stabilizes due to limited resources.
(d) Absolute and Relative Growth Rates
Absolute Growth Rate: It is the total growth per unit time. It compares the total increase in growth parameters (e.g., size, mass) over a period.
Relative Growth Rate: It expresses the growth per unit time relative to the initial size of the parameter being measured. This provides insight into the efficiency of growth relative to the starting condition. In Figure 13.7, leaf B shows a higher relative growth rate because its initial smaller size compared to leaf A results in a proportionally larger growth increment.
List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applications of any one of them.
The five main groups of natural plant growth regulators (PGRs) are:
Auxins
Gibberellins
Cytokinins
Abscisic acid
Ethylene
Note on Auxins
Discovery:
Auxins were first observed by Charles Darwin and his son Francis Darwin, who noted that the coleoptiles of canary grass bent towards light (phototropism). They concluded that the tip of the coleoptile was the site of a transmittable influence that caused the bending. Later, F.W. Went isolated auxin from the tips of oat coleoptiles.
Physiological Functions:
Cell Elongation: Auxins promote cell elongation by increasing cell wall plasticity.
Root Initiation: They help in the initiation of roots in stem cuttings.
Apical Dominance: Auxins maintain apical dominance by inhibiting the growth of lateral buds.
Fruit Development: Auxins can induce parthenocarpy in fruits like tomatoes.
Leaf Abscission: They help prevent leaf and fruit drop at early stages but promote abscission at later stages.
Agricultural/Horticultural Applications:
Rooting Agents: Used to promote rooting in stem cuttings, widely utilized in plant propagation.
Weed Control: Synthetic auxins like 2, 4-D are used as herbicides to control dicotyledonous weeds without affecting monocotyledonous plants.
Parthenocarpy: Induction of seedless fruit formation in crops like tomatoes and cucumbers.
Flowering Stimulation: For example, auxins are used to promote flowering in pineapples.
Crop Yield Management: They are used in tea plantations and hedge-making to control plant growth and shape.
Why is abscisic acid also known as stress hormone?
Abscisic acid (ABA) is known as the stress hormone because it plays a crucial role in helping plants respond to various kinds of stresses. Here are the key reasons:
Stimulates the Closure of Stomata: ABA helps in reducing water loss by stimulating the closure of stomata during water stress conditions.
Increases Tolerance to Stress: ABA enhances the plant's tolerance to adverse environmental conditions such as drought, salinity, and temperature extremes.
Inhibits Seed Germination: By preventing seed germination under unfavorable conditions, ABA ensures that the seeds remain dormant until conditions become suitable for growth.
Induces Dormancy: ABA helps seeds and buds enter a state of dormancy, aiding in their survival during periods of environmental stress.
Thus, ABA helps plants adapt to and survive under stress conditions, reflecting its designation as a "stress hormone."
'Both growth and differentiation in higher plants are open'. Comment.
Both growth and differentiation in higher plants are referred to as open processes due to the following reasons:
Growth
Growth is Indeterminate: Plants can potentially grow indefinitely due to the continuous activity of meristems.
Meristematic Activity: The root apical meristem and shoot apical meristem contribute to primary growth, elongating the plant body, while lateral meristems like the vascular cambium and cork cambium contribute to secondary growth, increasing girth.
Differentiation
Open Differentiation: The cells in plants retain the ability to change their roles and specializations depending on their position and environmental conditions.
Flexibility: Differentiated cells can undergo dedifferentiation and redifferentiation to perform new roles as needed. For example, fully differentiated parenchyma cells can become meristematic again to form cork cambium.
In essence, both processes exhibit a high degree of adaptability, allowing plants to respond effectively to their environments throughout their lifecycle.
'Both a short day plant and a long day plant can produce can flower simultaneously in a given place'. Explain.
Both short day plants (SDP) and long day plants (LDP) can flower simultaneously in a given place due to plant growth regulators (PGRs) and environmental factors. Here's how:
Photoperiodism:
Short day plants flower when the duration of daylight is less than a critical length.
Long day plants flower when the daylight duration exceeds a critical length.
Manipulation with PGRs:
Gibberellins and cytokinins can induce flowering irrespective of photoperiod. For example, gibberellins can induce flowering in some LDP even under short day conditions.
Artificial Conditions:
Controlled Environments: Utilizing greenhouses or growth chambers with adjustable light cycles, both types of plants can be manipulated to initiate flowering simultaneously.
Geographical and Seasonal Variability:
Natural Day Length Variations: Regions at higher latitudes experience longer or shorter days depending on the season, making it possible to naturally achieve optimal conditions for both plant types at different times of the year.
By combining these factors, it is possible to synchronize the flowering of both SDP and LDP in the same place.
Which one of the plant growth regulators would you use if you are asked to:
(a) induce rooting in a twig
(b) quickly ripen a fruit
(c) delay leaf senescence
(d) induce growth in axillary buds
(e) 'bolt' a rosette plant
(f) induce immediate stomatal closure in leaves.
The appropriate plant growth regulators (PGRs) for each scenario:
(a) Induce rooting in a twig: Auxins (e.g., Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA))
(b) Quickly ripen a fruit: Ethylene
(c) Delay leaf senescence: Cytokinins
(d) Induce growth in axillary buds: Cytokinins
(e) 'Bolt' a rosette plant: Gibberellins
(f) Induce immediate stomatal closure in leaves: Abscisic acid (ABA)
Would a defoliated plant respond to photoperiodic cycle? Why?
A defoliated plant would not respond to photoperiodic cycles effectively. This is because the leaves are the primary sites for perceiving light and detecting photoperiods. Photoreceptors such as phytochromes are located in leaves, and these are essential for photoperiodic responses which control processes like flowering. Without leaves, the plant lacks the ability to sense the duration of light and dark periods, thereby disrupting its photoperiodic response.
What would be expected to happen if:
(a) $\mathrm{GA}_{3}$ is applied to rice seedlings
(b) dividing cells stop differentiating
(c) a rotten fruit gets mixed with unripe fruits
(d) you forget to add cytokinin to the culture medium.
(a) $\mathrm{GA}_{3}$ is applied to rice seedlings
Applying Gibberellic acid ($\mathrm{GA}_3$) to rice seedlings would likely induce elongation of the stems. This is because gibberellins are known to cause an increase in the length of the axis by promoting cell elongation and division.
(b) Dividing cells stop differentiating
If dividing cells stop differentiating, it would disrupt the development of specialized tissues and organs. Differentiation is essential for cells to take on specific roles and mature properly. Without differentiation, the plant would fail to develop functionally diverse structures.
(c) A rotten fruit gets mixed with unripe fruits
A rotten fruit mixed with unripe fruits would probably lead to the unripe fruits ripening faster. This is due to the release of the gaseous Plant Growth Regulator (PGR) ethylene from the rotten fruit, which promotes fruit ripening.
(d) You forget to add cytokinin to the culture medium
Forgetting to add cytokinin to the culture medium would likely hinder cell division and the formation of new leaves and shoots. Cytokinins are crucial for promoting cytokinesis and the development of shoots. This would result in poor or stunted growth in the cultured plant tissues.
In summary:
(a) Rice seedlings would undergo increased stem elongation.
(b) Plant development would be disrupted due to lack of specialized tissues.
(c) Unripe fruits would ripen more quickly.
(d) Plant tissue culture would exhibit poor growth and shoot formation.
💡 Have more questions?
Ask Chatterbot AINotes - Plant Growth and Development | Class 11 NCERT | Biology
Comprehensive Class 11 Notes on Plant Growth and Development
Plant growth and development encompass a wide range of processes integral to the lifecycle of plants. This article dives into the crucial aspects, phases, and factors affecting plant growth, making it a valuable resource for Class 11 students.
Overview of Plant Growth and Development
Plant growth refers to the irreversible increase in size and mass of a plant, while development includes all the changes that occur throughout a plant's lifecycle, from germination to senescence.
Seed Germination and Growth Phases
Seed Germination Process
Seed germination is the initial step in the plant growth process when seeds encounter favourable conditions. It begins with the uptake of water, leading to the resumption of metabolic activities and the growth of the embryonic plant.
Phases of Growth
Growth in plants can be divided into three distinct phases:
Meristematic Phase
This is characterised by active cell division in the root and shoot meristems.
Elongation Phase
Cells in this phase grow in size and volume, primarily due to water uptake and vacuole formation.
Maturation Phase
Cells attain their final form and functionality during this phase.
Measuring Growth in Plants
Parameters for Growth Measurement
Growth can be quantified using various parameters:
- Fresh weight
- Dry weight
- Length
- Area
- Volume
- Cell number
Growth Rates
Growth rates can be arithmetic or geometric:
- Arithmetic Growth: Linear, where one daughter cell continues to divide.
- Geometric Growth: Exponential, characterised by both progeny cells dividing.
Factors Affecting Plant Growth
Intrinsic Factors
These include genetic factors and plant growth regulators.
Extrinsic Factors
External conditions impacting growth consist of light, temperature, water, oxygen, and nutrients.
Plant Growth Regulators
Characteristics of Plant Growth Regulators
Plant Growth Regulators (PGRs) are small molecules that can be broadly classified based on their role in growth processes.
Types of Plant Growth Regulators
Auxins
Auxins such as IAA and IBA promote root initiation, floral development, and apical dominance.
Gibberellins
Gibberellins play a role in elongating stems, breaking dormancy, and promoting flowering.
Cytokinins
Cytokinins are vital for cell division, chloroplast formation, and delaying leaf senescence.
Ethylene
This gaseous hormone promotes fruit ripening and stress responses.
Abscisic Acid
Abscisic acid is crucial for seed dormancy and stress responses, such as stomatal closure during drought.
Differentiation, Dedifferentiation, and Redifferentiation
Differentiation in Plants
Differentiation is the process where cells become specialised for specific functions.
Dedifferentiation and Redifferentiation
Dedifferentiation occurs when specialised cells regain the ability to divide. Redifferentiation is when these cells become specialised again.
Developmental Plasticity in Plants
Plasticity refers to the plant's ability to modify its development in response to environmental conditions, such as heterophylly in some aquatic plants.
Impact of Light and Temperature
Light influences photosynthesis and flowering, while temperature affects metabolic rates and enzyme activities, thereby impacting plant development.
graph TD;
A[Seed] --> B[Seedling]
B --> C[Mature Plant]
C --> D[Flowering]
D --> E[Fruiting]
E --> F[Senescence]
Summary
In conclusion, plant growth and development are complex processes influenced by both internal and external factors. Understanding these processes provides insights into how plants grow, develop, and respond to their environment.
By mastering these concepts, students will be well-prepared for their Class 11 exams and further studies in botany and plant sciences.
This comprehensive guide on plant growth and development covers everything a Class 11 student needs to know, from seed germination to the roles of crucial hormones. By studying these notes, students will gain a solid understanding of how plants grow and thrive.
🚀 Learn more about Notes with Chatterbot AI