How do plants digest their food? Is there any digestive system in plants?

The `food' for plants is sunlight, water and air (carbon dioxide and oxygen). Plants have the amazing ability to harvest energy from the sun using chlorophyll and convert it in to chemical energy. They then utilise it to produce carbohydrates such as sugars and starch (`photosynthesis'). These carbohydrates serve as chief energy source for almost all living beings in the world, including plants themselves. Nutrients such as nitrogen, phosphorus, potassium and other micronutrients are taken up by plants in very simple forms and used directly. So, plants do not need a digestive system.

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Plant cells oxidise the sugars to release carbon dioxide and energy and utilise the energy to drive reactions for normal functions of the cell.In addition, cells use carbohydrates and derived products as building blocks for proteins and lipids (fat). Carbohydrates, proteins and lipids are the chief components of several sub-cellular organelles (parts of a cell). Herbivorous animals derive energy and most of the components necessary for making proteins and fat by eating plants. The only time plants have to `digest' something is when the seed cotyledons breakdown complex molecules in order to provide energy to the germinating embryo. However, certain carnivorous plants do have a very primitive digestive system.

Carnivorous plants are often found in marshy landscapes where they do not get adequate nitrogen. Nitrogen is an essential component of proteins. These plants attract and trap primarily insects, but occasionally small frogs and rodents in specialised structures.They then digest the `catch', using proteolytic enzymes and absorb the released nutrients. Some plants establish an association with certain bacteria to help produce proteolytic enzymes to digest the insect and absorb the nutrients.