Plant Growth: Plants are a vital component of the ecosystem. They are the source of many essential substances, which are utilised by many living organisms to survive. Just like any other living organism, plants also show growth in height and size. Have you ever thought, about how seeds or seedlings grow into a tree in a particular time period? Through this article, we will learn how plant growth occurs, characteristics of plant growth, different stages in plant growth, and factors that affect plant growth.

What is Plant Growth?

Growth is the fundamental and salient characteristic feature of all living organisms, including plants. It is the irreversible, permanent increase in size, mass, volume, organ, or part of an organism accomplished as a result of various metabolic reactions of the body.

Fig: Plant Growth

Types of Plant Growth

The types of growth in plants can be based on different criteria. These are:

A. Based on the Sequence of Growth

1. Primary Growth – The division is at the root and shoots apex.
2. Secondary Growth – The lateral meristem or cambium helps increase the girth or diameter of the plant.

Fig: Primary and Secondary Growth in Plants

B. Based on the Continuity of Growth

1. Unlimited Growth – The growth of root and stem apex in plants.
2. Limited Growth – The growth of leaves, flowers, and fruits after obtaining a certain size.

C. Based on Growing Plant Organ (Morphogenesis)

1. Vegetative Growth – The growth of vegetative parts like leaves, stems, and roots.
2. Reproductive Growth – The growth of flowers and other reproductive parts of plants.

Characteristics of Growth in Plants

The following are the characteristic features of plant growth:

1. It is indeterminate (occurs throughout life).
2. It is localised.
3. It is measurable.
4. Meristems are involved in plant growth.
5. At the cellular level, growth can be measured as the increase in the mass of protoplasm.

Stages of Plant Growth

The different phases of growth are mentioned below:
i) Meristematic phase of cell division is when active cell division increases the numbers.
ii) Elongation phase is when the cells elongate by changing their size of vacuoles, the mass of protoplasm, etc.
iii) Maturation or differentiation is the phase in which there is the distribution of functionality to the newly formed cells.

Fig: Phases of Growth in Plants

Growth Rate

The growth rate is the increase in number per unit time (growth/time). There are two major growth rates:

1. Arithmetic rate is followed in mitosis division in certain organs, where one of the two cells formed differentiate and the other continues division.
2. Geometric rate is shown by various organisms, where both the daughter cells of cell division undergo repeated cell division. The development of an embryo from a zygote is an example of such growth.

Measurement of Growth in Plants

The rate of growth can be measured in various ways:

(i) The growth can be measured by a horizontal microscope and an auxanometer instrument. An auxanometer is an instrument used for measuring the increase of growth in plants.
(ii) Bose developed an instrument called a crescograph for measuring growth. It magnifies growth up to \(10000\) times. In the early \({20^{{\text{th}}}}\) century, Sir Jagadish Chandra Bose invented a device for measuring growth in plants known as a crescograph.
(iii) The growth can also be measured by calculating an increase in cell number, weight, volume, and diameter.

Fig: Auxanometer

Factors Affecting Growth in Plants

The external and internal factors influence the growth of plants. They are mentioned below:

1. External factors needed for growth
a) Light – It is required for the synthesis of food. It also determines the root and shoots growth. Variations in the intensity, quality, and duration of light affect seed germination and flowering in different plants.
b) Temperature – A optimum temperature of \(25 – 30^\circ C\) is required for plants’ normal and appropriate growth. The temperature above \(45^\circ C\) hinders plant growth due to excessive transpiration, denaturation of enzymes, and coagulation of protoplasm.
c) Water – It is the most important medium for all chemical reactions and physiological processes. It is essential for photosynthesis, cell elongation, and maintenance of turgidity of growing cells. Under conditions of water stress, plant growth completely stops.
d) Oxygen – It is required for cellular respiration in plants. This energy is used for various activities of the cell and directly takes part in the growth processes.
e) Nutrients – The macro and micronutrients are essential raw materials for protoplasmic synthesis and act as a source of energy. Growth stops when the nutrient supply becomes limited.
f) Soil – Soil is a substrate in which plants grow. Soil provides support, nutrients, and a network of water and air to the plant’s roots. 

2. Internal factors needed for growth
a) Genetic Factors– These are internal factors. These are involved in the overall maintenance of a plant.
b) Plant Growth Hormones or Regulators – The plant’s growth is controlled by some organic compounds, which are present in minimal quantities. These compounds are called phytohormones or plant growth regulators. Auxins, gibberellins and cytokinins are involved in growth-promoting activities and thus are known as growth promoters. Abscisic acid is responsible for growth-inhibiting activities and thus is known as a growth inhibitor. Ethylene has mixed effects, i.e. it shows both promoting and inhibitory effects.

Fig: Factors Affecting Plant Growth

Summary

Growth is the fundamental and salient characteristic feature of all living organisms, including plants. It is the irreversible, permanent increase in size, mass, length, height, volume, area, cell number, etc. Growth is indeterminate in higher plants. The three phases of cellular growth are cell division, cell enlargement, and cell differentiation. Growth is associated with development. Plant growth and development are affected by both internal and external factors. Light, temperature, water, nutrients, oxygen, soil, etc., are external factors of growth, and genetic factors and plant growth regulators are internal features of growth.

Frequently Asked Questions (FAQS) on Plant Growth

Q.1: What is plant growth?
Ans: Growth is the fundamental and salient characteristic feature of all living organisms, including plants. It is the irreversible, permanent increase in size, mass, volume, organ, or part of an organism accomplished as a result of various metabolic reactions of the body.

Q.2: What are the two types of plant growth based on the sequence of growth?
Ans: 1. Primary Growth: The division is at the root and shoots apex.
2. Secondary growth: The lateral meristem or cambium helps increase the girth or diameter of the plant.

Q.3: What are the two characteristics of growth in plants or plant growth?
Ans: 1. It is indeterminate (occurs throughout life).
2. It is localised and measurable.

Q.4: Name two processes that are common to both plants and animals during growth and development.
Ans: Cell differentiation and cell division are two processes common to both plants and animals.

Q.5: Name the instrument used to measure growth in plants.
Ans: Auxanometer is used to measure growth in plants.

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