Principles of Plant Physiology | Agriculture Optional Notes for UPSC PDF Download

Plant Physiology

Plant physiology is a subfield within Botany that focuses on understanding the various physiological processes and functions of plants. Essentially, it involves the in-depth examination of the structure and variations in plants at the molecular and cellular levels, leading to insights into ecological, physiological, and biochemical aspects of plant life.

As terrestrial plants evolved, they developed specific techniques and mechanisms to ensure their survival, particularly in managing the uptake of water and carbon dioxide.

Plant physiology encompasses the study of different plant structures and how they operate. This field allows us to investigate critical processes in plants, including photosynthesis, mineral uptake, respiration, transport, as well as the overall growth and development of plants, which are characteristics exhibited by all living organisms.

This study focuses on the cellular activities at the molecular level and also highlights the significance of physiological processes within the broader environmental context. For a more comprehensive grasp of this topic, let's delve into detailed plant physiology notes.

Physiology of Plant Parts

• Leaves: Leaves represent a vital component of plants and can exhibit diverse shapes and sizes. They serve as the central hub for the process of photosynthesis.
• Stem: The stem plays a crucial role in providing structural support to the plant. It serves various essential functions, including facilitating plant growth and enabling plants to thrive in different environmental conditions. The specific structure of the stem can vary among different plant species.
• Roots: Roots are located underground and are responsible for absorbing water and nutrients from the soil. Their role in this regard is of utmost significance, making them a fundamental component of the plant.
• Xylem and Phloem: These constitute the plant's vascular tissues, also known as sap. They are responsible for the transportation of water, sugars, and other essential substances between the roots, stem, and leaves.

Functions of Plant

Plant Transport

• Plants possess a unique vascular system (xylem and phloem) that facilitates the transport of nutrients and water from the roots to all parts of the plant through a process known as translocation.
• The movement of water and nutrients in rooted plants can occur in one direction or multiple directions. Transport can be passive, achieved through processes like diffusion, especially facilitated diffusion, or active, carried out by specific membrane proteins known as pumps.
• Water plays a critical role in various physiological activities, and understanding plant-water relationships is crucial.
• The concept of water potential helps us understand the movement of water, involving terms such as solute potential and pressure potential.
• At the cellular level, plants undergo osmosis, which permits the movement of molecules in and out of cells.
• Transpiration is another essential aspect of a plant's life cycle.

Mineral Nutrition

• Plant nutrition is a vital factor influencing plant growth. It encompasses the identification of essential elements required for plant development, the roles of these elements, criteria for determining their essentiality, symptoms of deficiency, and the mechanisms of element absorption. This field also underscores the importance of nitrogen fixation.
• Both macro and micronutrients in plants are involved in critical processes like maintaining cell-membrane permeability, regulating the osmotic concentration of cell sap, and facilitating enzyme activity, among other functions.
• The supply of essential elements is achieved through a mechanism involving isolated cells, tissues, and organs.
• In addition to other essential elements, nitrogen fixation is an essential process in plants.

Photosynthesis in Higher Plants

• Plants produce their own food through photosynthesis, earning them the label of autotrophs.
• Photosynthesis is of paramount importance as it serves as the primary source of sustenance for all life on Earth and releases oxygen into the atmosphere, which we require for respiration.
• This process occurs in chloroplasts through both light and dark reactions, involving four pigments: Chlorophyll a, chlorophyll b, Xanthophyll, and carotenoids. It entails extracting energy from oxidizable substances and storing it in the form of bond energy via phosphorylation.
• Within plants, cyclic and non-cyclic photo-phosphorylations take place, and during photosynthesis, the Calvin cycle occurs through a series of four chemical reactions.

Respiration in Plants

• Food required for vital life processes is generated through photosynthesis. Cellular respiration is responsible for releasing energy used in the synthesis of ATP and involves glycolysis.
• Aerobic respiration leads to the complete oxidation of organic substances in the presence of oxygen, which is typical in higher organisms.
• To release and utilize the stored energy in molecules, several steps are involved, including the electron transport system and oxidative phosphorylation.
• Respiration also involves the concept of the respiratory quotient, which represents the ratio of the volume of carbon dioxide released to the volume of oxygen consumed.

Plant Growth and Development

• The process of plant development initiates with germination under favorable environmental conditions.
• Plant growth is typically indeterminate due to the presence of meristems, allowing plants to continue growing throughout their lives. Plant growth can be quantified through various parameters, such as dry weight, fresh weight increase, length, area, volume, and cell number.
• Plant growth is categorized into three phases: meristematic, elongation, and maturation.
• The rate of growth can be quantitatively determined in two ways: absolute growth rate and relative growth rate.
• Plant growth is regulated by plant growth regulators.
• Plants also produce light-sensitive compounds like phytochromes, which stimulate growth in response to environmental signals.
• Plant physiology is a crucial field, not only for understanding fruits, vegetables, and other edible plant parts but also for the production, harvest, and post-harvest storage of plant products.