Plant Growth

Plant Growth Overview

• Plant growth refers to the process that results in the increase in size and number of cells in plants. This process occurs continuously over their life cycle.
• Plants exhibit indeterminate growth unlike animals. This means plant growth is not limited to a certain size but rather continuous throughout their lifespan.

Primary and Secondary Growth

• Plant growth is generally classified into two types: Primary and Secondary growth.
• Primary growth occurs at the tips of roots and shoots, known as apical meristems, and is responsible for the increase in length or height.
• Secondary growth occurs in the lateral meristems, such as vascular cambium and cork cambium, leading to an increase in thickness or girth of the plants.

Role of Plant Growth Regulators

• Plants contain five important types of chemical regulators or hormones that influence plant growth: Auxins, Cytokinins, Gibberellins, Ethylene, and Abscisic Acid.
• Auxins are primarily involved in cell elongation and are responsible for the phototropic (light-directed) and gravitropic (gravity-directed) responses of plants.
• Cytokinins promote cell division and differentiation, and work in conjunction with auxins to control the growth and development of plant tissues.
• Gibberellins have a variety of functions, such as promoting stem elongation, seed germination, flowering, and fruit development.
• Ethylene plays a crucial role in the ripening of fruits.
• Abscisic Acid inhibits growth and helps plants withstand stressful conditions.

Growth conditions and Tropism

• Tropism refers to the ability of plants to grow in response to environmental stimuli, such as light (phototropism), gravity (gravitropism), touch (thigmotropism), and chemicals (chemotropism).
• These responses are primarily controlled by plant hormones like Auxins, helping in optimising the plant’s orientation to environmental conditions for better growth.

The Importance of Light

• Light, particularly sun light, is essential for plant growth as it provides energy for photosynthesis, a process by which plants convert energy from sunlight into chemical energy (glucose).
• The quality, direction, duration and intensity of light all have a significant effect on plant growth. For example, lack of adequate light can result in a plant becoming “leggy” — growing tall and thin with fewer leaves.

Nutrients and Water

• Nutrients derived from the soil, like nitrogen, phosphorus, and potassium (NPK), are critical triggers for plant growth. Fertilisers often contain these key elements.
• Water, obtained mainly through roots, is crucial as it helps in nutrient transport, photosynthesis, and maintaining cell turgidity for structural support. Too much or too little water can be harmful to a plant’s growth.

Preparation and detailed understanding of these key areas on plant growth will provide a comprehensive insight into one of the most fundamental aspects of biology: How our green world grows!