Plant nutrition is the study of the chemical elements and compounds necessary for plant growth, plant metabolism and their external supply. In 1972, Emanuel Epstein defined two criteria for an element to be essential for plant growth:
- In its absence the plant is unable to complete a normal life cycle.
- or that the element is part of some essential plant constituent or metabolite.
All living organisms such as plants and animals require food. So food is essential for all living organisms.
- Plants are capable of making their food themselves but humans and animals cannot.
- Carbohydrates, proteins, fats, vitamins and minerals are essential components of food, these components are called nutrients.
Every living organism needs some kind of energy and nutrient materials to ensure that the life processes go on smoothly. Moreover, this energy requirement is got from the food. You can understand this better in animals and human beings as you see it on a daily basis. You very well know what happens if you skip breakfast or lunch! But what about plants? Do they require any nutrition at all?
Plants and their nutrition requirements
Plants are also living things that need some form of energy. They have cells and tissues. They also grow in size and girth. And they are the producers of the ecosystem. So, in order to synthesize food, they do have nutrient requirements. Of course, the kind of nutrient requirements varies.
This kind of nutrition in plants is called the autotrophic mode of nutrition. What does this actually mean? It means that plants have the special capability to make their own food, by using simple inorganic substances to produce organic molecules/substances. They get the energy sources from non-living things such as sun and carbon dioxide.
Plants also have chlorophyll in them, the green colour pigment. With the help of all these above factors, plants can produce simple carbohydrates. The carbohydrates thus produced are utilized by the plant and gives it energy. When there is an excess of carbohydrates in the plants, then it is stored as a reserve for later use.
Modes of Nutrition
Every moment you’re alive, your body is using energy, even if you’re just sitting here reading this lesson. Where does that energy come from? Our energy is acquired through eating food, like pizza for lunch. Organisms that depend on other organisms for food, and thus energy, like us, are called heterotrophs.
Although eating might seem like the only way to get food, think for a minute about how plants get their food. They don’t eat, but rather they create their own food from sunlight or chemicals that are then used to generate the energy they need to grow and reproduce. Organisms that make their own food are called autotrophs. Today, we’re going to look in more detail about each of these modes of nutrition and examine how they impact agriculture and our food supply.
This is a type of nutrition in which organisms synthesize the organic materials they require from inorganic sources. Chief sources of carbon and nitrogen are carbon dioxide and nitrates, respectively. All green plants are autotrophic and use light as a source of energy for the synthesis, i.e. they are photoautotrophic. Some bacteria are also photoautotrophic; others are chemoautotrophic, using energy derived from chemical processes.
Autotrophs make their own food. Typically, we think of plants as autotrophs, and this is true, but there are other kinds as well. Plants, algae, phytoplankton, and some bacteria are photosynthetic, meaning they use sunlight to make sugar, which they then use to make energy. Photosynthetic organisms are green because they contain a pigment called chlorophyll that does photosynthesis. Some other types of bacteria are also autotrophic, but they are chemosynthetic. They use the energy stored in chemicals, usually released from deep sea vents, to make their food, and then energy.
THIS VIDEO SHOWS AUTOTROPHIC NUTRITION
Autotrophs form the basis of all food webs. They gather energy from inorganic sources, like chemicals or the sun, and convert it into a form that other animals can use. Energy is transferred from the autotrophs to consumers that eat them, and then to carnivores that eat those animals. Without autotrophs, all of our food webs would collapse.
Since there is so much energy available to this layer of the food web, autotrophs have the greatest number of organisms in an ecosystem. Think of how many blades of grass there are in a field compared to how many bears you typically see. Autotrophs also have an easier time finding a suitable environment. All they need are the right conditions and plenty of sunlight or chemicals to survive and flourish.
This is the mode of nutrition in which organisms depend upon other organisms to survive. All animals and non-green plants are heterotrophic.
Heterotrophic organisms have to acquire and take in all the organic substances they need to survive.
Heterotrophs depend on other organisms for food. Some heterotrophs, called herbivores, only eat plants. The herbivores only get 10% of the energy available from the autotrophs, because the producers used 90% of their energy to grow and reproduce. So, there are substantially fewer herbivores in an ecosystem compared to autotrophs since they get less energy. Consider our field. There are millions of blades of grass, but only one herd of about twenty deer.
THIS VIDEO SHOWS HETEROTROPHIC NUTRITION
Omnivores eat plants too, but they also can eat meat. These animals might consume the herbivores or plants. If the omnivores are eating the herbivores, they get even less energy. They only get 10% of the energy the herbivores get, so they end up with only 1% of the energy that was present in the autotrophs. Thus, there are going to be even fewer of these heterotrophs compared to the herbivores. Carnivores only eat meat. Carnivores are typically the smallest group in an ecosystem, since there is even less energy available as you move up the food chain. Carnivores need a steady diet of other heterotrophs, so they will only be able to live in locations that contain prey, unlike plants which only require sunlight and water.
Types of Heterotrophic Nutrition
1. Holozoic Nutrition:
The name of this nutrition originated from Greece where ‘holos’ means complete and ‘zoon’ stands for animal. This type of nutrition involves consumption of food portion through mouth (opening) .This process is called ingestion. Once consumed, the food particles are broken down into simpler forms and the process is termed as digestion.
Finally, the vital nutrients are absorbed by the body and the unwanted and undigested portions are eliminated. The process of expelling the waste material from the digestive tract via anus is defined as egestion. Holozoic nutrition involves all the processes including ingestion, digestion and egestion.
2. Saprophytic Nutrition:
Again ‘Saprophytic’ is a Greek term in which ‘sapro’ means rotten while ‘phyto’ is plants. This kind of nutrition involves processing or decomposing the rotten foliage and dead or decaying organic matter of organisms.
Saprophytes have a tendency to gorge on dead products like wood, rotten plants, stored food to name a few. Some organisms that follow saprophytic nutrition are a host of fungi like mushrooms, yeasts and moulds.
In this mode of nutrition, secretion of certain enzymes are released which break down the complex food into simpler forms. The processed leftover is then reabsorbed by the saprophytes.
This process of extracellular digestion is an integral part of saprophytic nutrition. It can be best observed on Neurospora, a common bread mould or even pin mould.
3. Parasitic Nutrition:
Parasitic is derived from the root word Parasite. ‘Para’ is a Greek term for feeding and ‘site’ denotes grains. Parasitic nutrition is a mode of heterotrophic nutrition where an organism (known as a parasite) lives on the body surface or inside the body of another type of organism (known as a host).
For instance, a hook-worm lives in the intestine of humans and feeds on it without going through the process of ingestion or egestion. This nutrition is viable for those organisms that do not possess properly developed organs and depend on their host’s body for deriving the nourishment. Some most common examples of organisms following this nutrition are cuscuta, tapeworms, leeches, plasmodium, and so on.
Ideally, parasitic nutrition involves dwelling of the parasites within the host’s body and feeding on their blood and intestines as their nutrition. However, sometimes the organisms position itself on the surface of the host’s body, probably the skin and derive the nutrition, such types are called ectoparasites.
Mosquitoes and leeches are the perfect examples of parasitic nutrition in which they suck out blood as nutrition from the host’s body surface.
On the basis of heterotrophic nutrition, animals and plants have been classified under the above mentioned groups; however these organisms can be further classified as herbivores, carnivores, omnivores and scavengers.
Heterotrophic nutrition essentially differs from autotrophic nutrition. Organisms following heterotrophic nutrition are ideally known as consumers of the ecosystem. Unlike autotrophs, heterotrophs are dependent on others for their survival and require ready-made complex food for nutrition, sourced to them by similar organisms in the form of other animals and plants.