Carbohydrate Metabolism in Plants | Agriculture Optional Notes for UPSC PDF Download

Metabolism of Carbohydrates

Carbohydrates represent a primary source of energy for both animals and plants. Plants utilize sunlight to create carbohydrates through photosynthesis, whereas animals acquire carbohydrates by consuming plants or other animals. In plants, carbohydrates are stored as starch in lengthy polysaccharide chains, while animals store carbohydrates in the form of glycogen molecules. These extensive polysaccharides contain numerous chemical bonds, effectively storing a substantial amount of chemical energy. When these molecules undergo metabolic processes, the energy within these chemical bonds is released and can be utilized for various cellular functions.

Energy Production from Carbohydrates (Cellular Respiration)

The metabolism of any monosaccharide, a simple sugar, is a source of energy for the cell. Excess carbohydrates are stored in the form of starch in plants and glycogen in animals, ready for utilization in case the organism's energy needs suddenly increase. When such demands arise, carbohydrates are broken down into their individual monosaccharide components, which are then distributed to all living cells within an organism. Glucose (C₆H₁₂O₆) is a common example of a monosaccharide used for energy production.

Inside the cell, each sugar molecule undergoes a complex series of chemical reactions for breakdown. The energy released from the bonds within the monosaccharide is harnessed to produce high-energy molecules known as adenosine triphosphate (ATP). ATP serves as the primary energy currency for all cells. Similar to how the dollar is used as currency to purchase goods, cells employ ATP molecules to perform immediate tasks and drive chemical reactions.

The process of breaking down glucose during metabolism, referred to as cellular respiration, can be described by the following equation:

Producing Carbohydrates (Photosynthesis)

Plants and certain other organisms engage in photosynthesis to create carbohydrates. In this process, light energy is transformed into chemical energy as plants combine carbon dioxide gas molecules (CO₂) to form sugar molecules like glucose. Since this process involves the formation of chemical bonds to create a larger molecule, it necessitates an energy input (light) to advance.
The synthesis of glucose through photosynthesis can be represented by the following equation, noting that it is the reverse of the previous equation:

As part of plants’ chemical processes, glucose molecules can be combined with and converted into other types of sugars. In plants, glucose is stored in the form of starch, which can be broken down back into glucose via cellular respiration in order to supply ATP.

Key Points

• The breakdown of glucose living organisms utilize to produce energy is described by the equation:
• The photosynthetic process plants utilize to synthesize glucose is described by the equation:
  
• Glucose that is consumed is used to make energy in the form of ATP, which is used to perform work and power chemical reactions in the cell.
• During photosynthesis, plants convert light energy into chemical energy that is used to build molecules of glucose.

Key Terms

• Adenosine triphosphate (ATP): A versatile nucleoside triphosphate employed as a coenzyme within cells, often referred to as the "molecular unit of energy currency" for intracellular energy transfer.
• Glucose: A basic monosaccharide (sugar) with the chemical formula C₆H₁₂O₆, serving as a primary source of energy for cellular metabolic processes.