Nutrition in plants

Classification of plants on the basis of mode of nutrition:
Plants can be divided into two groups on the basis of their mode, The two groups are:
1. Autotrophic or autotrophs
2. Heterotrophic or heterotrophs
Heterotrophic nutrition is the type of nutrition obtained by digesting organic compounds. Animals, fungi, a lot of prokaryotes and protoctists which are incapable of synthesizing organic compounds for their food, feed heterotrophically. They are thus referred to as heterotrophs.
Holozoic nutrition is a form of heterotrophic nutrition which requires dependence.
Parasitic nutrition is a mode of heterotrophic nutrition where an organism lives on the body surface or inside the body of another type of organism

1. Autotrophic nutrition

Autotrophic nutrition is the type of nutrition in which organic compounds are manufactured from available inorganic raw material obtained from the environment. In autotrophic nutrition, the nutrients do not require to be broken down or digested before they are taken into the cells.
Two methods of autotrophic nutrition
On the basis of source of energy, autotrophic nutrition can be further divided into the sub-types listed below:
(I) Phototrophic nutrition
(II) Chemotrophic nutrition
I. Phototrophic nutrition:
Phototrophic nutrition is the form of autotrophic nutrition in which organic molecules are produced from uncomplicated inorganic molecules with the help of energy obtained from sunlight.
Example of phototrophic nutrition can be seen in:
a. Green Plants
b. Photosynthetic Bacteria
Phototrophic nutrition as obtained in green plants
Green plants are well-known example of phototrophic nutrition. Green plants manufacture their own food through the process of photosynthesis. The materials necessary for photosynthesis to occur are:
CO2 and H20
Carbon dioxide and water make available carbon, hydrogen and oxygen which are required for the synthesis of organic molecules.
The minerals such as Nitrogen, Phosphorus and Sulphur and Magnesium are also essential for photosynthesis to take place.
The Chlorophyll:
The green pigments known as Chlorophyll is as well necessary for photosynthesis to take place. It is essential to absorb the energy from the sun which is the universal source of light.
The sunlight :
In the presence of sun light, the above mentioned nutrients are used to synthesize the energy rich compound known as (CHO). This process is known as photosynthesis.
Photosynthesis can be represented through the following equation:
6CO2 + 12H2O -> C6H12O6 + 6O2 + 6H2O
Phototrophic nutrition in photosynthetic bacteria
Photosynthetic bacteria are inimitable due to the fact that they are the only organisms that have the capacity to synthesize carbohydrate food in the absence of chlorophyll.

Differences between photosynthetic bacteria and green plants

Photosynthesis in bacteria differs from that of green plants. Some differences between them are
Photosynthetic bacteria normally grow in sulphide spring which usually contains H2S.
The hydrogen used in the synthesis is obtained from H2S as opposed to water – H2O in green plants.
In bacteria photosynthesis, oxygen is not liberated to the surrounding as a byproduct.
The process of bacteria photosynthesis occurs with a little release of energy.

Two types of photosynthetic bacteria:

There are two types of photosynthetic bacteria. The first group releases sulphur “S” as a bye product. This type of bacteria gets the hydrogen for the synthesis from H2S. The energy from the light divides into hydrogen ion and sulphide ion. Hydrogen reacts with CO2 to form H2O as shown in the equation below:
2H2S + CO2 -> (CH2O)n + H2O + 2S
Example of such bacteria is the Purple Sulphur Bacteria which make use of bacterio chlorophil and caretenoid as the pigments for photosynthesis.
The second group of photosynthetic bacteria is those who do not release sulphur “S” as the by-product. These bacteria make use of H2S as the donor of hydrogen but sulphur is not released as a by-product.
Examples of this type of bacteria are the purple non-sulphur bacteria and the brown non-sulphur bacteria. Both of them have “bacterio chlorphyll” as their photosynthetic pigments.

Chemotrophic nutrition:

Chemotrophic autotrophic nutrition is the type of autotrophic nutrition where organic molecules are produced from simple inorganic molecules through the use of energy obtained from the oxidation of a few inorganic substances like ammonia, nitrates, nitrites, ferrous ions, H2S and so on.
This type of nutrition is known as chemotrophic nutrition and process of manufacturing food in this manner is referred to as chemosynthesis.
Example of organism that does chemosynthesis is the bacteria like ammonia using bacteria. They obtain their energy by oxidizing Ammonia as illustrated in the equation below:
NH4+ + O2 -> 2NO2 + 2H2O + 4H+ + energy
Another type of bacteria which converts nitrites to nitrate does it through the process of chemosynthesis as shown in the equation below:
2NO2 + O2 -> 2NO3- + energy
Importance of chemosynthetic bacteria:
The chemosynthetic bacteria that act on nitrogen compounds play a crucial role in nitrogen cycle and ensure that a balance of nitrogen is sustain in the life system.

2. Hetertrophic Nutrition in Plants

Plants which are not able to manufacture their own food completely or partially and are dependent on other in order to get their organic molecules are referred to as heterotrophic plants.
Classification of heterotrophic plants
On the basis of type of organisms on which heterotrophic plants depend on for the synthesis of their organic molecules, they can be divided into the two classes below:
•Parasitc Plants Or Parasites
•Saprophytic Plants Or Saprophytes


These are heterotrophic plants that depend on living plants and animals for their nutritional requirements.
Types of parasites
Parasitic plants can be further divided into the following types.
•Obligate or total parasites.
•Facultative or partial parasites.
Total parasites are those parasites which depend on other organism entirely for their food or organic materials.
Total parasites are further classified into two:
1. Total stem parasite
2. Total root parasite
1. Total stem parasites are the category of parasitic plants that depend entirely on the stem of other plants for their food. These plants propel a structure called haustoria which is a special structure used in the absorption of nutrients in parasitic plants inside the tissue of host.
The xylem of the parasite comes in contact with the xylem of host and the phloem of the parasite to the phloem of the host. Through the xylem it draws up the water and nutrients and through the phloem, it draws up prepared organic material.
This eventually leads to the death of the host plant as a result of exhaustion. Example of such parasite is the cuscuta (amer-bail)
2. Total root parasites:
These are parasitic plants which draw up their nutritional requirements from the roots of host. Examples are:
1. Orobanche- This normally attacks the roots of the plants that belonged to the families -Cruciferae and Solanaceae.
2. Cistanche – These Parasitizes attacks the roots of Calatropis.
3. Striga – These parasites are found on the roots of sugar cane
Partial parasites
These are those parasitic plants which depend partially on other organism for their nutritional value.
Classes of partial parasitic angiosperms:
Partial parasitic angiosperms can be generally classified into
1. Partial stem parasite
2. Partial root parasite
1. Partial stem parasites
Partial stem parasites are those parasites whose their haustoria penetrate into the stem of the host and to suck their nutrition from vascular tissues of stem.
2. Partial root parasites
The example of this category of parasite although uncommon is the sandle wood tree


Saprophytes are plants that depend on dead or rotten organic remains of plants or animals for their food or nutritional intake. Also plants which decompose composite dead food material into simple compounds and make use of them for their nutrition, growth and development are referred to as saprophytes.
Types of Saprophytes
Saprophytes can be sub divided into two namely:
1. Total Saprophytes
2. Partial Saprophytes
Total saprophytes
This group of saprophytes depends totally on dead organic material for their nutritional value.
Partial saprophytes
These are type of saprophytes which depend partly on dead organic matter for their nutritional value.
Examples of saprophytes
There are a few examples of Saprophytes amongst flowering plants.
1. Neothia -bird’s net or orchid
2. Monotrapa- Indian Pipe
In these two cases, the roots of plant form a Mycorhizzal Association with fungal mycelium to assist them in the absorption process.
Special mode of nutrition
Carnivorous or insectivorous plants
Carnivorous or insectivorous plants are plants which have as their prey, insects and small birds. This is a special mode of nutrition in partially autotrophic and partially heterotrophic plants.
Partially autotrophic and partially heterotrophic plants are carnivorous plants which has the green pigments and can produce CHO but are not able to synthesize nitrogenous compounds and proteins.
In order to get their nitrogen requirement, carnivorous plants depend on insects, which they trap and digest through particular devices developed in them.

Cellular respiration

This is the set of the metabolic reactions and processes that occur in the cells of organisms to transform the biochemical energy from nutrients into adenosine triphosphate (ATP), and after that releases waste products.
The reactions that are required in respiration are catabolic reactions, which split large molecules into smaller ones, with the release of energy in the process where the weak “high-energy” bonds are replaced by stronger bonds in the products.
Respiration is among the main ways a cell gains helpful energy to fuel cellular activity. Cellular respiration is taken as an exothermic redox reaction. The general reaction is converted into a lot of smaller reactions when it takes place in the body, the majority of which are redox reactions themselves.
Even though in principle, cellular respiration is a combustion reaction, it obviously does not bear a resemblance to one when it takes in a living cell. This variation is due to the fact that it takes place occurs in a lot of detached steps.
While on the whole, the reaction is a combustion reaction, no particular reaction that it is composed of is a combustion reaction.

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