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Cell Metabolism

There are many activities, which a cell has to perform from the time of birth till the  death of a single individual. These activities include physical, chemical and biological reactions. All types of reaction occur within the cell.

What is cell metabolism and its importance?

Cell metabolism can be defined as a set of chemical process that helps an individual or an organism to respond to their surroundings. The cell metabolism is mainly involved in the extraction of energy that is used for many activities like cell growth, cells and tissue repair, etc. The cell extracts energy from breaking down the excess amount of carbohydrates, amino acids and lipids. This biological process is  very much important for an organism, which is involved in obtaining chemical energy, synthesizing complex molecules and converting nutrient molecules into usable forms for further use . Without this process, a cell dies with lack of energy to carry out biological reactions. If a cell starts to die, finally an organism ends.


Types of Cell Metabolism

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Cell metabolism can be generally classified into two major categories.

Types of Cell Metabolism

Catabolism: In this reaction of metabolism, energy is obtained by the breakdown of the larger molecules into smaller ones. In this process the energy is released. Hydrolysis is an example of catabolism reaction.

Hydrolysis- catabolism reaction.
Hydrolysis Catabolism Reaction
In the above reaction of hydrolysis, a water molecule is used.

Anabolism: In this reaction of metabolism, cell synthesis all necessary compounds, which are required for cellular growth and repair. This necessary compound includes- DNA, RNA and proteins. This process requires energy to build larger molecules. Dehydration synthesis is an example of anabolism reaction.

Dehydration synthesis -anabolism reaction.
Dehydration Synthesis Anabolism Reaction
In the above reaction of dehydration synthesis, a water molecule is produced as a bi-product.

Plant Metabolism

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Plant metabolism is the set of chemical reactions, which helps a plant to perform its own activities. Plants are the primary source of essential nutrients for billions of individuals globally. Plant metabolism is of two types.

Plant Metabolism

Types of Plant Metabolism

Types of Plant Metabolism

Primary Plant Metabolites

Primary metabolites are the compounds, which are commonly produced by all plants and are directly used by them for their growth and their development. Carbohydrates, proteins, nucleic acids and lipids are considered as the main primary metabolites.
  • Functions of primary metabolic compounds.
  • Polysaccharides are mainly used in providing support for plants and also stores energy for their later use.
  • A protein builds the remaining biomass of living plant cells.
  • A protein consists of polypeptides, which are made up of amino acids. 
  • Plants synthesize amino acids from the products of photosynthesis by using large amounts of energy in the form of   ATP and NADPH.
  • A protein stores energy in seeds and are used as a source of nutrition in the early development of seedlings. For example: Corn produces a storage protein called ZEIN.  

Secondary Plant Metabolism

Secondary metabolites are the compounds, which are not required for normal growth and for the development of plant cells. The products of secondary metabolism are morphine, caffeine, nicotine, menthol and rubber.  The products of secondary metabolism are the metabolism of chemicals, which are very rarely found in plants and do not have any specific role in plants functioning.

Functions of secondary metabolic compounds.
  • The product of secondary metabolism plays a vital role in interactions between plants and other organisms.
  • They also play an ecological role in governing interactions between plants and other organisms.
  • The product of secondary metabolism also helps in attracting pollinators, fruit and seed dispersers. These are because of their bright coloured pigments of flowers.
  • Few toxic compounds, which are produced from secondary metabolism like nicotine, which helps the plant in protecting them from plant eating animals (herbivores) and also from the microbes.

A plant cell receives their energy from photosynthesis.


Plants depend on photosynthesis to obtain their energy. In plant cells, the presence of chlorophyll pigment helps to carry out the photosynthetic reaction. Photosynthesis is the process, which occurs in all green plants. The main role of photosynthesis is to trap solar energy and use this energy to drive the synthesis of carbohydrates from carbon dioxide. An equation for photosynthetic reaction is

6CO2 + 6H2O + sunlight à C6H12O6 + 6O2 

Photosynthesis is a biological process, which is carried out in two steps.

Light-dependent reaction (or) Light reaction
  • In this biochemical process, light energy is converted into chemical energy and ATP molecules are produced. 
  • This process requires light and occurs in thylakoids in chloroplast cells.
  • There is a loss of energy along the electron transport chain to recharge ATP from ADP.

Light-independent reaction (or) Dark reaction
  • In this biochemical process, produced ATP molecules are used to convert them into simple sugars.
  • This process does not require light and occurs in the stroma of chloroplast cells.
  • In this process, ATP and NADPH are used to produce energy.
  • Prepares glucose sugar from carbon dioxide and Hydrogen.

Calvin Cycle

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The second step of photosynthesis, which takes place in the stroma of chloroplast cells and in the absence sunlight. In this biochemical process the carbon molecules from carbon dioxide (CO2) are fixed into glucose (C6H12O2). 

Calvin Cycle Reaction

Calvin Cycle Reaction

Animal Metabolism

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The chemical reactions, which occur in the cells of an animal body, are called as an animal's metabolism. In animal cells, mitochondria and the nucleus are the sites where an energy production reaction takes place. Cellular respiration is the type of metabolism that takes place in all animal cells.

Cellular Respiration

It is the process of respiration; energy is released by breaking down of food molecules in the presence of oxygen. An equation for cellular respiration is

6O2 + C6H12O6 → 6CO2 + 6H2O + Energy

Cellular respiration is carried out in 3 stages

Glycolysis – the first stage in cellular respiration.
  • In this stage of cellular respiration, a series of enzyme catalyzes the reactions.
  • In this process, glucose gets converted to pyruvic acid.
  • Small numbers of ATPs molecules are formed.
  • This process does not require oxygen and takes place in the cytoplasm of a cell.
  • All living organisms use glycolysis.
  •  An equation for cellular respiration is  
Glucose + 2ADP + 2Pi + 2 NAD+à  2 Pyruvic acid + 2 NADH + 2ATP

  • It harvests electrons and uses their energy to power ATP production. 
  • This process is a more powerful reaction and takes place only in the mitochondria of a cell. 
  • An atom that loses an electron gets oxidized. Oxygen is a common electron acceptor.
Anaerobic Respiration
  • This process does not require oxygen and glucose is completely oxidized.
  • Different types of electron acceptors are used  in this process instead of oxygen (sulfur, or nitrate).
Comparing Photosynthesis (Plant metabolism) and Respiration (Animal metabolism).

   Photosynthesis (Plant metabolism)   Cellular Respiration (Animal metabolism)
 Function   Energy Storage  Energy Release
 Location  Chloroplasts  Mitochondria
 Reactants   CO2 and H2O  C6H12O6 and O2
 Products C6H12O6 and O2  CO2 and H2O
 Equation  6CO2 + 6H2O → C6H12O6 + 6O2  C6H12O6 + 6O2 → 6CO2 + 6H2O
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