Plant physiology is a branch of study in Botany dealing with the physiological processes or functions of plants. Specifically, it is a descriptive study of structure and variation of plants at the cellular and molecular level leading to ecological, physiological and biochemistry related aspects of plants exploration.
As plants evolved on land they required methods to survive with the separation of carbon dioxide and water.
Plant physiology gives an account of the different parts of the plant and their functioning. It helps us analyze plant processes such as mineral nutrition, photosynthesis, transportation, respiration and finally plant development and growth which are characteristics exhibited by living entities.
The description is in the context of cellular activities in molecular parameters. It also gives a brief idea of the role of physiological processes in the environment.
Physiology of Plant Parts
Leaves are an important organ of the plant. They can grow in a variety of shapes and sizes. They are the primary centre of photosynthesis.
The stem provides support and structure to the plant. They perform many important functions such as plant growth, compete and survive in different environments, etc. The structure of the stem differs in different species.
The roots are an underground part of the plant that absorbs water and nutrients from the soil. That is why they are an important part of the plant.
Xylem and Phloem
These form the vascular tissues of the plant. These are also known as sap. They transport water, sugars and other important substances between the roots, stem and leaves.
Functions of Plant
Transport In Plants
Plants have a distinct vascular system (xylem and phloem) which helps in transporting nutrients and water from roots to all the parts of the plant through translocation.
Transport of water and nutrients in rooted plants is unidirectional or multidirectional. Modes of transportation can either be passive which occurs through diffusion, facilitated diffusion to be precise or can be through active mode carried out by specific membrane proteins which are called pumps.
Water plays a pivotal role in carrying out physiological activities hence understanding the importance of plant-water relations is essential.
The concept of water potential helps in comprehending the water movement through terms such as- Solute potential and pressure potential.
At the cellular level, osmosis takes place in plants which allows movement of molecules in and out of the cells.
Transpiration is another aspect crucial in the life cycle of plants.
Plant nutrition is an important aspect instrumental in the growth of plants. It gives an insight into the methods used to identify essential elements for the development of plants, the role of these elements, criteria to identify their essentiality, deficiency symptoms and mechanism of absorption of these elements. It also conveys the importance of nitrogen fixation.
Macro and micronutrients present in plants carry out essential processes such as cell-membrane permeability, osmotic concentration of cell sap and its maintenance, enzyme activity and so on.
Inadequate supply of essential elements can lead to critical concentration in plants. Elements are absorbed through a mechanism which involves isolated cells, tissues and organs.
Apart from other essential elements, nitrogen fixation also takes place in plants.
Photosynthesis In Higher Plants
Plants synthesize their own food through photosynthesis and hence are called autotrophs.
Photosynthesis is important since it is the primary source of food for all living entities on earth and it releases oxygen in the atmosphere which we inhale to breathe.
It takes place in chloroplasts through light and dark reactions using 4 pigments- Chlorophyll a, chlorophyll b, Xanthophyll, carotenoids. Extracting energy from oxidizable substances and storing in the form of bond energy is phosphorylation.
In plants, cyclic and non-cyclic photo-phosphorylations take place. During photosynthesis, the Calvin cycle takes place through a set of 4 chemical reactions.
Respiration In Plants
Food that is required for life processes comes from photosynthesis. Cellular respiration results in the release of energy which is used for the synthesis of ATP which involves glycolysis.
Aerobic respiration leads to complete oxidation of organic substances in the presence of oxygen which is common in higher organisms.
To release and utilize the energy stored in molecules, they undergo the following steps: electron transport system and oxidative phosphorylation.
Another important aspect of respiration is the respiratory quotient. The ratio of the volume of carbon dioxide released to the volume of oxygen consumed gives the respiratory quotient.
Plant Growth And Development
The process of plant development starts right from germination under favourable environmental conditions.
Generally, plant growth is indeterminate as they retain their capacity to grow throughout their lives because of the presence of meristems. The growth of plants is however measurable through parameters such as – dry weight, increase in fresh weight, length, area, volume, cell number etc.
The period of plant growth is categorized into three phases – meristematic, elongation and maturation.
Growth rate can be determined quantitatively in 2 ways – absolute growth rate and relative growth rate.
The growth of plants is controlled by plant growth regulators.
Plants also produce compounds such as phytochromes that are light sensitive and stimulate the growth of the plant in response to environmental signals.
Plant physiology is also an important topic related to fruits, vegetables and other edible parts of the plants. The production of food crops including the harvest and post-harvest storage of plant products also hinges on the plant physiology studies.
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