Growth is defined as an irreversible constant increase in the size of an organ or even an individual cell. Put differently, growth is the most fundamental characteristics of living bodies accompanied by various metabolic processes that take place at the cost of energy. The processes can be anabolic or catabolic. When it comes to plants, the seeds germinate, develop into a seedling and acquires a shape of an adult plant are discrete stages of growth and the growth of Plants is indefinite.
In the Biological term, there’s a minute difference between the terms growth and development. These words describe a separate set of events in an organism or plant.
Growth refers to the increase in mass and size of a body.
Development is the process where a particular organism not only grows physically but acquires mental and physiological growth as well.
Growth and Development
Growth occurs throughout the lifespan but not uniformly. It occurs at a faster rate until a plant or animal attains maturity. After this stage, gradually growth slows down and stops after a particular time.
This entire process and phenomena, where an organism, grows physically, evolves physiologically, attains mental growth and maturity. This is collectively known as Development. The process of development of shape and structure of a living organism is known as Morphogenesis, whereas Differentiation is the process of change in cells, tissues and internal & external organs.
Types of Growth
- Primary and Secondary Growth: The mitotic divisions in meristematic cells at the root and shoot apex hikes the length of the plant. This is called as Primary Growth while Secondary meristem which results in an increased diameter of the plant known as Secondary Growth.
- Vegetative Growth: The growth in plants before flowering is known as vegetative growth and includes the formation of leaves, branches, and stems.
- Reproductive Growth: In this stage, the plants begin to flower which is a reproductive member of the plant.
Characteristics of Growth
Plants exhibit the ability of growth throughout their life. It is because of the presence of meristems at particular locations on the body and meristems have the capability to divide and self-perpetuate.
Growth is measurable. Growth is the consequence of the increase in protoplasm and this rise is not easy to measure. Growth is measured by different methods such as the rise in dry weight, the number of cells, volume, hike in fresh weight or volume.
The figure below shows the position of root apical meristem, vascular cambium and shoot apical meristem. The arrows show the growth direction of organs and cells.
The growth of plants are classified into three phases:
Formative Phase: The division of cells in the growth of plants is the most basic event. Every cell result in the division of cells that existed before. Mitosis is a kind of cell division that occurs during growth and involves both qualitative and quantitative division of the cells.
This division takes place in two steps:
First, the division of the nucleus which is called as karyokinesis and division of cytoplasm known as cytokinesis. An increased number of cells is carried out in higher plants in meristematic location and some daughter cells retain this meristematic occurrence while some enter in the next phase of the growth, called as the phase of cell enlargement.
Cell Differentiation and Cell Enlargement: At this stage, the size of organs and tissues increases and this occurs by the formation of Protoplasm, developing vacuoles, Hydration and then integrating new cell wall to make it thicker and permanent.
Cell Maturation: The enlarged cells at this stage acquire specific forms and size based on their role and location. Hence, various cells are differentiated from complex and simple tissues that perform different functions.
Factors Affecting Growth
Hormones in animals and Growth regulators help plants to grow steadily. Let’s discuss some of the factors affecting growth in various living beings. It would be convenient if we divide these factors into two broad categories namely – Internal and External Factors.
External Growth Factors
- Light – Light is one of the most crucial components of photosynthesis in plants.
- Temperature – Every organism needs a suitable temperature to survive, to grow, to develop various tissues & organs, to reproduce.
- Water – Plants absorbs water through their roots and use it for photosynthesis and other biochemical processes.
- Mineral Nutrients – Other than light, water, and a perfect temperature, organisms need special nutrients to support their food making process and metabolism, which ultimately boosts growth in them.
Internal Growth Factors
In humans, the Growth Hormone is known as Somatotropin. Plants also contain such hormones called – Auxins, Gibberellins, Cytokinins, Ethylene, Abscisic acid. These are also called Plant Growth Regulators.
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