Life Processes in Plants

Life process has four components:

  • Nutrition
  • Respiration
  • Transportation
  • Excretion

The processes which perform maintenance job to prevent damage and break-down in the body are called life processes.

  1. A process to transfer a source of energy from outside the body of the organism, to the inside, is called nutrition. Depending on the complexity of these carbon food sources, different organisms use different kinds of nutritional processes.
  2. Oxidising-reducing reactions are the most common chemical means to break-down food molecules. The process of acquiring oxygen from outside the body, and to use it in the process of breakdown of food sources for cellular needs, is called respiration. In a single-celled organism, exchange of gases or removal of wastes takes place on the surface of the organism is in contact with the environment. In multi-cellular organisms, various body parts carry out functions.
  3. Food and oxygen are required to be supplied to all parts of the body. Therefore, a transportation system for carrying food and oxygen from one place to another in the body is required.
  4. Chemical reactions in the body use the carbon source and oxygen for energy generation. The harmful and useless biological waste products formed during the chemical reaction of food and oxygen is removed by excretion.

We examine these four processes in Plants.



  1. Food is the source of energy. Some organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water. These organisms are called autotrophs, include green plants and some bacteria and their mode of nutrition is called Autotrophic Nutrition.


Green Plants – Autotrophic Nutrition

  1. Autotrophic Nutrition – Autotrophic nutrition is that mode of nutrition in which an organism makes (or synthesizes) its own food from the simple inorganic materials like carbon dioxide and water present in the surroundings (with the help of sunlight energy).
  2. Photosynthesis – It is the process by which autotrophs take in carbon dioxide and water from the outside and convert them into stored forms of carbohydrates (energy) in the presence of sunlight and chlorophyll. Carbohydrates are utilized for providing energy to the plant.
  3. The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant.
  4. The following events occur during photosynthesis –
  • Absorption of light energy by chlorophyll.
  • Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
  • Reduction of carbon dioxide to carbohydrates.
  1. Some cells contain green dots which are cell organelles called chloroplasts which contain chlorophyll. Stomata are tiny pores present on the surface of the leaves. Massive amounts of gaseous exchange take through stomata for photosynthesis.103017_0250_ClassXScien3.jpg
  2.  The opening and closing of the stomata is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly, the pore closes if the guard cells shrink.103017_0250_ClassXScien4.png
  3. Autotrophs also need other raw materials for building their body. Water used in photosynthesis is taken up from the soil by the roots of terrestrial plants. Other materials like nitrogen, phosphorus, iron, and magnesium are taken up from the soil. Nitrogen is an essential element used in the synthesis of proteins and other compounds. This is taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.


  1. The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. The first step is the breakdown of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm.  The breakdown of glucose or a six-carbon molecule, into a three-carbon molecule called pyruvate in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than in the anaerobic process.103017_0250_ClassXScien5.jpg103017_0250_ClassXScien6.png
  2. The energy released during cellular respiration is immediately used to synthesize a molecule called ATP (Adenosine Triphosphate) which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.
  1. At night, when there is no photosynthesis occurring, CO2 elimination is the major exchange activity going on. During the day, CO2 generated during respiration is used up for photosynthesis, hence there is no CO2 Instead, oxygen release is the major event during the day.


  1. When the distances between soil-contacting organs and chlorophyll containing organs are small, energy and raw materials move through diffusion to all parts of the plant body. But when distances become a proper system of transportation is essential.
  1. Plants do not move, and plant bodies have a large proportion of dead cells in many tissues. As a result, plants have low energy needs and can use relatively slow transport systems.
  1. Plant transport systems will move energy stores from leaves and raw materials from roots. These two pathways are constructed as independently organized conducting tubes.
  1. Xylem moves water and minerals obtained from the soil. Phloem transports products of photosynthesis from the leaves where they are synthesized to other parts of the plant.
  1. In xylem tissue, vessels and tracheid of the roots, stems, and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant. At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil. Water, therefore, moves into the root from the soil to eliminate this difference. This means that there is a steady movement of water into root xylem, creating a column of water that is steadily pushed upwards. Evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration. Transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation. The effect of root pressure in the transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.


6.  The transport of soluble products of photosynthesis is called translocation.  Translocation occurs in the part of the vascular tissue known as phloem. Phloem transports amino acids and other substances. These substances are specially delivered to the storage organs of roots, fruits, and seeds and to growing organs. The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.

xylem and phloem2

  1. Unlike transport in xylem which can be largely explained by simple physical forces, the translocation in phloem is achieved by utilizing energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need the energy to grow.


  1. Plants can get rid of excess water by transpiration.
  2. Oxygen itself can be thought of as a waste product generated during photosynthesis.


  1. In many plant waste products are stored in cellular vacuoles. Waste products may be stored in leaves that fall off. Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them.


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