Plants obtain their nutrition by various modes. The mode of nutrition can be divided into four distinct types. Broadly speaking, plants can be divided into autotrophs and heterotrophs.
Heterotrophic plants can be further divided into parasites, saprophytes and symbiotic plants.
In plants, the green pigments called chlorophyll collect simple substances like water and salts from the soil and CO2 from the air, and using sunlight as a source of energy, convert the simple substances into complex food for the plant. This process is called photosynthesis.
Leaves are the food factories of a plant. However, other parts of the plant play important roles, too. The roots absorb water and minerals from the soil.
- Photosynthesis takes place in the leaves.
- The lower epidermis has openings called the stomata.
- The stomata take in carbon dioxide from the air.
- Chlorophyll captures energy from sunlight, and uses it to prepare food from carbon dioxide and water.
The by-products are oxygen and water, which are released through the stomata during daytime. The food that has been made is sent to the other parts of the plant through the veins.
All chlorophyll-containing plants, including algae, and some plants with red, brown or other dominant pigment, make food using this process. Thus, both sunlight and trees are essential to sustain life on Earth. As we saw, during photosynthesis, plants produce food in the form of glucose.
This is then converted into complex compounds called carbohydrates, like starch and cellulose. Plants also prepare proteins with the help of nitrogen, which is obtained from the soil. Thus, the minerals dissolved in water are used to convert sugar into carbohydrates, proteins and fats. These food components form the source of energy for other heterotrophic plants and animals.
The insectivorous mode of nutrition is observed in plants such as the pitcher plant and the Venus fly trap.
- Heterotrophic plants don’t have chlorophyll, and are, therefore, unable to produce food using the process of photosynthesis.
- They obtain food from other plants by following either a parasitic, saprophytic or some other form of symbiotic relation with them for food.
Some plants, like the cuscuta, snatch food from other plants by climbing onto them. The plants on which they climb are called hosts. Since they deprive the host plant of valuable nutrients, the plant itself is called parasitic. Some plants obtain their nutrition from decaying organic matter. They secrete digestive juices onto dead and decaying matter, and then absorb the nutrients from it.
This mode of nutrition is called saprtorophic nutrition. Plants that use the saprotrophic mode of nutrition are called saprotrophs.
Plants get nitrogen from the soil by a mechanism of symbiosis.
- A bacterium called rhozobium plays an important role in symbiotic nitrogen fixation.
- This type of nitrogen fixation is observed in plants like peas, moong beans and other legumes.
- By this process, both bacteria and plants get benefited mutually.