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, the 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 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.

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 phenomenon 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 their lifetime. However, plants follow different ways to develop under the environmental conditions during their life phases. This plant’s ability is termed as 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 composition. They are plant growth substances, phytohormones, or plant hormones. The plant growth regulators have some physiological effects, and those are classified as:

Auxins

The term auxin applies to indole-3-acetic acid and various other substances with numerous growth-regulating properties. It is produced at 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.  

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 and based on their response to light, these flowering plants are classified as short-day plants, long-day plants, and day-neutral plants.

Vernalisation

In cold treatment, when juveniles of flowering plants are shortened. This process applies to wheat, millets, rice, etc.

Important Topics for NEET Exam

For all those who are looking forward to qualifying 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

Important Questions

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

  • What are plant growth regulators?
  • What functions does auxin perform in plant growth?
  • Explain differentiation, dedifferentiation, and redifferentiation.
  • Which factors affect plant growth?
  • Which three physiological processes in plants are affected by light?
  • What do you mean by cell enlargement?

Thus, we hope that these study notes on plant growth and development have helped you brush up your concepts on this topic. Confused about finding the right course after 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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