Class 11 Plant Growth and Development

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plant growth and development

The 15th chapter of NCERT Biology class 11, Plant Growth and Development discusses that growth is a fundamental characteristic of a living being and thoroughly explains that growth is a permanent and irreversible increase in the size of an organ or any part in a living being. Considering the importance of this chapter in various competitive exams and basic concepts in Biology, it is essential to understand its key components. Through this blog, we have covered the chapter on Plant Growth and Development and have provided summary and study notes to assist you in grasping this topic in a simpler manner.

Plant Growth is Indeterminate

Plants have the unique ability to retain their growth throughout life. It is because meristems are present at various locations in their body. These meristem cells can self-perpetuate and divide. However, root and shoot apical meristem lead to primary growth in plants and contribute to the elongation of plants at the axis. In the chapter Anatomy of Plants, we have seen that cork cambium and vascular cambium lead to secondary growth in plants. 

Plant Growth is Measurable

In plants, cellular level growth happens because of protoplasm increase. However, protoplasm can not be measured. The cell number, cell size, and increase in the cell are measurable. The growth of plants is regulated by parameters like dry weight, area, length, fresh weight, volume, and cell number. 

Phases of Growth

The chapter Plant Growth and Development classifies plant growth in three phases, that are Formative, Enlargement and Maturation. Let’s elaborate on these three phases further:

Formative Phase (Phase 1)

It is the cell formation phase that occurs at the root and shoots apex. Cells go through mitosis division in the formative phase with a high respiration rate. 

Phase of Enlargement (Phase 2)

Cells that are produced informative phase become enlarged. These enlarged cells are high in volume because vacuoles are developed.

Phase of Maturation (Phase 3)

Cells attain their maximum size after physiological and structural differentiation.

Courtesy: NCERT

Growth Rate

As per the chapter plant growth and development, it is termed as an increase in growth per unit. Thus, the growth rate is expressed mathematically. To calculate the same, the growth rate is represented as arithmetic growth and geometric growth. 

Arithmetic Growth

It is defined as a constant rate of growth that occurs in arithmetic progression. Arithmetic growth is usually seen in root and shoot elongation. Mathematically, it is represented as:

Lt = L0 + rt

Where,
Lt = length at time ‘t’
L0 = length at time ‘zero’
r = growth rate / elongation per unit time.

Geometric Growth

Initially, the growth in plants is slow and increases at an exponential rate. The progeny cell retains the ability to divide, and so does the mitotic cell. However, it is common in unicellular organisms that grow in a nutrient-rich medium. The exponential growth is expressed mathematically as:

W1 = W0 ert

Where,
W1 = final size (weight, height, number, etc.)
W0 = initial size at beginning of period 
r= growth rate
t= time of growth 
e= base of natural logarithms

However, quantitative comparison can be made in two ways:

  • Absolute Growth Rate: It is the comparison and measurement of total growth per unit time
  • Relative Growth Rate: It is the growth of a given system per unit expressed regularly

Conditions Required for Growth

Plant growth requires a sufficient amount of essential elements like oxygen, water, and nutrients. Enlargement and development of plant cells require water. At the same time, oxygen leads to the release of metabolic energy that is essential for growth activities. Lastly, nutrients act as an energy source and help plants with protoplasm.

As stated in the chapter on plant growth and development, plants show various phenomena during their growth process like:

Phenomenon Meaning
Differentiation It is the maturation process where cells from the root and shoot apical meristem differentiate and mature to perform particular functions.
Dedifferentiation It is the process where cells that have lost their capacity to re-divide can regain their ability to divide under few conditions. 
Redifferentiated The process where dedifferentiated cells lose the capacity to divide but mature to perform certain functions. 

Plant Development

Now, let’s talk about plant development. In simple terms, development is stated as the changes that the organism goes through in its lifetime. Several intrinsic and extrinsic variables influence the development of a plant:

  • Intrinsic factors: Which include genetic and hormonal regulation.
  • Extrinsic Factors: Environmental variables like oxygen, temperature, water, nutrients, and so on are examples of extrinsic influences.

However, plants follow different ways to develop under environmental conditions during their life phases. This plant’s ability is termed plasticity. For example, in plants like cotton, coriander, and Larkspur, the juvenile and mature plant has different shapes of leaves. Another example of plasticity is leaves produced in water, and air represents the heterophyllous development of plants.

Plant Growth Regulators 

According to the chapter on plant growth and development, regulators are defined as simple, small molecules with diverse chemical compositions. They are plant growth substances, phytohormones, or plant hormones. The plant growth regulators have some physiological effects, and those are classified as:

Courtesy: ResearchGate

Auxins

The term auxin applies to indole-3-acetic acid and various other substances with numerous growth-regulating properties. It is produced at the root apex and is used to promote flowering. The standard functions include apical dominance, cell enlargement, inhibition of abscission, and cell division.

Gibberellins

They encourage plant growth regulators. There are about 100 kinds of gibberellins, mostly found in fungi and higher plants. They are denoted as GA1, GA2, GA3,….GA100. The common gibberellin among these is GA3. The function includes the breaking of dormancy, seed germination, cell elongation, and early maturity.

Cytokinins

It is the primary plant growth hormone, and standard forms are zeatin, kinetin, etc. They are mainly found in the roots and help with cell division, promote nutrient mobilization, and are vital for tissue culture.

Ethylene

It helps with transverse and isodiametric growth. Primary functions include fruit ripening and inhibition of longitudinal growth.

Abscisic Acid

It is a stress hormone and is found in the roots of the plant. It helps with bud dormancy and leaf senescence.  

Brassinosteroids

They are found in the form of seeds, fruits, leaves, and flower buds. As an example, consider brassinolide. The effects of brassinosteroids include the following: 

  • Light-mediated gene expression
  • Cell division and cell elongation
  • Seed germination
  • Vascular development

Important Note: PGRs offer internal regulation, but they also impact plant growth and development through genetic and extrinsic or environmental variables, such as tropic movements (phototropism, geotropism), photoperiodism, vernalisation, seed dormancy and germination, and so on.

Photoperiodism

It is the effect of the duration of light hours on the growth and development of plants. As mentioned in the chapter plant growth. Based on their flowering pattern in response to light, flowering plants are categorised into the following categories:

  • Short day plants: Flowering begins when light is exposed for a shorter period of time.
  • Long day plants: Flowering begins when plants are exposed to light for an extended period of time.
  • Day-neutral plants: Flowering is unaffected by the length of light exposure.

Vernalisation

It’s a temperature-dependent occurrence. A spell of chilly temperatures promotes flowering. To hasten to bloom, seeds are chilled during germination. Food crops such as wheat, rye, and barley are produced twice a year. Spring varieties are sown in the spring and harvested at the end of the season. Winter varieties are sown in the fall and harvested in the middle of summer. If planted in the spring, winter cultivars will not blossom throughout the growing season. Biennial plants, such as cabbage, sugarbeets, and carrots, require a period of low temperature before flowering in the following months.

Seed Dormancy

Endogenous control is used to regulate seed dormancy. Even under favourable environmental circumstances, seeds do not germinate. Several factors contribute to seed dormancy:

  • The seed coat is tough and impenetrable
  • Chemical inhibitors such as ABA, para-ascorbic acids, phenolic acids, and others
  • The embryo in its infancy
Courtesy: Botany One

Natural abrasions, such as microbial activity and digestive tract enzymes in animals that consume seeds, break down the seed covering. Knives, forceful shaking, and sandpaper can also be used to cause this. Hormones can be neutralised by cold temperatures, nitrates, and gibberellic acids.

Important Topics for NEET Exam

For all those who are looking forward to qualifying for the NEET exam, here are some important topics of this chapter from the competitive exam point of view.

Plant Growth Regulators (PGRs)

PGRs are the chemical compounds that occur naturally in plants. They are very essential for agricultural purposes, hence, are synthesized and used commercially in such practices. Plant growth regulators are also known as plant hormones or phytohormones. Mentioned below are some important points related to them- 

  • Their concentration is very low and they act as a chemical signal between the cells 
  • They are the derivatives of Adenine (kinetin), Carotenoids (ABA), Indole compounds (auxins) and terpenes (GA3). 
  • When present in different concentrations at different stages, plant hormones show different effects 
  • the hormone production as well as gene expression is affected by the environmental influence 
  • Plant growth regulators aur plant hormones act as a signal transduction, i.e., an external signal is converted to internal signal which in turn causes multiple responses
  • Brassinosteroids are also being discovered to to function as a phytohormone 

Important Discoveries of PGRs / Phytohormones 

  • Auxin was first isolated from human urine. 
  • Charles Darwin along with his son Francis, for the very first time, showed that there were a few substances present at the tip of the coleoptile of the canary grass and were transmittable and was responsible for the phenomena of phototropism. 
  • E Kurosawa discovered that the ‘bakanae’ disease of rice seedling or foolish seedling happened due to the presence of gibberellic acid in the fungus Gibberella fujikuroi 
  • Skoog found that the callus for liberation in the internodal region occurs only if the oxygen was supplemented with DNA or coconut milk that is extracted by yeast for vascular tissue. 
  • F.W. Went isolated auxin from the coleoptiles of oat
  • H. H. Cousins jury found out that the presence of any gaseous substance in ripened oranges fastens the ripening of bananas

Plant Growth and Development NCERT PDF

Plant Growth and Development PPT

Credits: Dr Uma Prasanna Pani

Important Questions and Answers 

Here are a few critical questions on Plant Growth and Development which you must prepare for your class 11 Biology exam.

Define the following terms: 
Growth
Differentiation
Development
Dedifferentiation
Development
Redifferentiation
Determinate growth 
Meristem
growth rate

Growth: It is defined as an irreversible, permanent increase in the size of an organ, its components, or even a single cell. Growth is aided by metabolic processes that occur as a result of energy.
Differentiation: It occurs when cells produced from the root apical and shoot-apical meristems, as well as the cambium, develop and mature to fulfil particular tasks. Differentiation is the act that leads to maturation.
Development: It refers to all of the changes that an organism goes through over its existence.
Dedifferentiation: Under certain conditions, plants that have lost their ability to divide can recover it. This is referred to as dedifferentiation.
Redifferentiation: Cells that have lost their ability to divide but have matured to execute particular tasks are said to be redifferentiated.
Determinate growth: It refers to a cell, tissue, or organism’s ability to expand for an extended period of time. Most plants grow indefinitely, with some plants reaching a plateau and then ceasing to develop.
Meristem: Meristem is plant tissue that contains undifferentiated cells (meristematic cells).
Growth rate: The pace at which growth increases per unit time is referred to as the growth rate.

Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?

Growth is caused by a rise in the amount of protoplasm. Measuring protoplasmic growth covers various parameters, such as height, weight, number of cells, fresh tissue sample, length, area, volume, and so on. As a result, demonstrating any one growth metric throughout the life of a blooming plant is challenging.

List five main groups of natural plant growth regulators. 

Plant growth regulators are intercellular intrinsic factors (chemical compounds) that control plant growth and development. The following are the five major categories of natural plant growth regulators (PGR):
-Auxins
-Gibberellins
-Cytokinins
-Abscisic acid
-Ethylene
These PGRs are produced in diverse plant sections and regulate various differentiation and developmental events that occur during a plant’s life cycle.

What do you understand by photoperiodism and vernalisation? Describe their significance.

Plants’ responses to day/night cycles are referred to as photoperiodism. It is thought that the hormonal component responsible for blooming is produced in the leaves and then migrates to the shoot apices, transforming them into flowering apices. When the length of light exposure is examined, this photoperiodism process aids in the research of blooming responses in various agricultural plants. 

Vernalisation is a phenomenon in which the blooming process of some plants is quantitatively or qualitatively reliant on exposure to lower temperatures. It specifically refers to accelerating the blooming process during a time of lower temperatures. The technique inhibits premature reproductive growth late in the growing season, allowing the plant to mature in its own time.

Why is abscisic acid also known as stress hormone?

Abscisic acid is responsible for stimulating the closing of stomata in the epidermis and increasing plant tolerance to many forms of stressors; hence, it is also known as a stress hormone. Abscisic acid is important for promoting seed dormancy, which ensures seed germination under favourable conditions. This allows the seeds to resist desiccation and induce dormancy in plants at the conclusion of the growing season, encouraging abscission of the fruits, leaves, and flowers.

Thus, we hope that these study notes on plant growth and development have helped you brush up on your concepts on this topic. Confused about finding the right course after the 12th? Connect with our experts at Leverage Edu and we will guide you in making an informed decision towards a rewarding career! Sign up for a free career counselling session with us today!

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