Autotrophic Nutrition: Definition, Type, Examples

Autotrophic Nutrition: Definition, Type, Examples

Autotrophic Nutrition Definition

Autotrophic nutrition is composed of two words. One is ‘auto’ which means self and the other part which is ‘tropic’ means nutrition. Combining both, we will get self-nutrition. Hence Autotrophic Nutrition is the nutrition process adopted by plants and blue-green algae, by using simple inorganic compounds like water and carbon dioxide. Thus the organism which is self-reliant in their nutrition is called autotrophs.

The major tool for autotrophic organisms is the green-coloured pigment called chlorophyll. The plant captures the sun’s energy to proceed with the process of photosynthesis. Autotrophic nutrition is a feature of all green plants. With the help of solar energy, water, and carbon dioxide, green plants make their own food with the help of photosynthesis. The process leads to the formation of glucose.

Autotrophic Nutrition examples

Following are the important examples of autotrophs:

  • Plants
  • Algae- Green algae and red algae
  • Bacteria such as cyanobacteria

Necessary Conditions for Autotrophic Nutrition

Autotrophic nutrition is dependent on photosynthesis for the production of food. Here is some necessary condition for Autotrophic Nutrition:

  • Carbon dioxide
  • Water
  • Chlorophyll Pigment
  • Sunlight
Chlorophyll Facts

  • Chlorophyll is the primary tool for photosynthesis, which enables plants to absorb energy from sunlight.
  • Chlorophyll molecules are distributed around the membranes of chloroplastids, the cell organelles.
  • The Chlorophyll pigments are separated through paper chromatography experiment for research purpose.
  • Chlorophyll is a chlorin pigment.
  • Magnesium ion Mg2+ is found at the centre of the chlorin ring.
  • Types of Chlorophyll: Chlorophyll a, Chlorophyll b, Chlorophyll c1, Chlorophyll c2, Chlorophyll d, Chlorophyll f

Nutrition in plants

Nutrition in any organism is the building block of the proper functioning of their organs or parts whether it is plant or animals. Nutrition is a very critical part for proper plant growth and metabolism. There are two types of nutrients, plants usually absorb during its nutrition

(i) Macronutrients
(ii) Micronutrients

Macronutrients: These nutrients can be termed as nutrients that are used in large quantity usually in around 10mmole kg-1 of dry matter. Carbon, oxygen, hydrogen, phosphorous, sulphur, magnesium and calcium.CO2 and H2O are the primary sources of carbon, oxygen as well as hydrogen. Other nutrients that are mentioned can be easily found in soil and plants can absorb them through roots.

Micronutrients: Micronutrients are needed in very micro quality usually less than 10mmole kg of dry matter. Molybdenum, manganese, zinc, chlorine, nickel, iron and chlorine. There are some extremely important elements from the above list such as silicon, sodium, cobalt and selenium. Usually higher plants consume them.

There are basically two types of Nutrition on plants depending on the process.

(i) Autotrophic Nutrition

(ii) Heterotrophic Nutrition

Types of Plant Nutrition
Types of Plant Nutrition


Soil is a reservoir of thousands of necessary mineral nutrition which have been there in soil due to the process of weathering and breakdown of stones. Due to weathering, the soil gets loaded with tons of ions and inorganic salts. The ultimate source of this nutrition are rocks therefore it can be also termed as mineral nutrition. Soil is a more important place to get a rich substance. Soil also hosts nitrogen-fixing bacteria as well as other microbes. Soil holds water and also provide air to the roots. Soil also provides a place to give the plant some hold so that it doesn’t leave its place. Deficiency of 1 mineral can affect seriously the crop yield. The deficiency of nutrition can be fulfilled with the help of fertilizers. Fertilizers contain macro-nutrients and micro-nutrients and can be given to the plant as per needs.

What are Chemoautotrophs ?

Chemoautotrophs are those organisms that are depended on inorganic chemicals for their nutrition. In chemoautotrophs, chemo means chemicals, auto means self and tropism means nutrition. This type of nutrition is generally seen in single-cell organisms that can tolerate hard environments such as hot springs and cold shivering conditions. As these organisms can make food from chemicals, these organisms can easily survive in rude conditions such as very acidic areas and sulphur containing pools. The world is full of symbiotic biological natural nitrogen fixation associations. Legum-bacteria relationship is one of the striking relationships. There is a good relationship of roots of plants of legumes category and with rod-shaped Rhizobium. Legume category plants include sweet pea, lentils, clover beans etc.

What are Photoautotrophs ?

Photoautotrophs are dependent on light for their process of food making to start. Their primary source of energy is light. Light is the most important condition for them and they cannot proceed without sunlight. For example, green plants some bacteria and algae. Autotrophs are very important constituents on the planet as they serve the food source for everyone. Heterotrophs are directly dependent on photoautotrophs which help them to gain energy and reproduce. Autotrophs are the only organisms on the whole planet that can fix CO2 and covert to O2. The CO2 that heterotrophs release get consumed by photoautotrophs which help in controlling global warming.


Heterotrophs are incapable of making their own food and their main food source is provided by producers or green plants and carnivores get food from other animals. This nutritional mode is called the heterotrophic mode of nutrition.

Heterotrophs are completely depended on autotrophs directly or indirectly from where they receive their nutrition. The title of consumers in the food chain has been given to heterotrophs and located at secondary or tertiary level.

The example of heterotrophs are animals and non-green plants and humans are also heterotrophs.

How heterotrophs are dependent on photosynthesis:

  • Heterotrophs feed by consuming plants or herbivores.
  • They hunt or attack herbivores animals or carnivores or sometimes both which directly dependent on plants
  • Use of oxygen by respiration process

Difference between Autotrophic and Heterotrophic nutrition

1.Autotrophs make their own food whereas heterotrophic organisms are dependent on autotrophs directly and indirectly.

2.Autotrophs are equipped with chloroplasts whereas there is no concept heterotrophic nutrition.

3.Autotrophs can make their own food with the help of chloroplast and in heterotrophs, since there is no chloroplast they cant make their own food.

4.They main source of energy for autotrophs is sunlight but heterotrophs are dependent on other organisms for their energy.

5.Autotrophes are generally unmovable whereas heterotrophs have the power to move from 1 place to another.

6.Autotrophes have to power to store energy in form of starch whereas heterotrophs cannot store energy.


Autotrophic Nutrition (Photoautotrophic) is a process is carried through Photosynthesis. The chemical energy is formed from solar energy through the process of photosynthesis. Each part of the plant has a separate function in photosynthesis and gives its contribution in its own way. Such as leaves have chlorophyll pigments in them which help in capturing the sun’s energy. Stomata are mostly found in the bottom region of the leaf and contain chlorophyll. The minerals that are required in this process are supplied through the roots and through plant vessels, it gets transported to different parts of the plant.

Leaves are equipped with chloroplast that have chlorophyll in them. With the use of carbon dioxide and water along with sunlight plants synthesize glucose. Oxygen is the resultant material in this process during the daytime. The plant store this synthesized food in different parts. The protein synthesis is done by nitrogen which can be taken up through the soil.

Whatever mineral is found in water are later used to process sugar into proteins, fats, and carbohydrate which later become the energy source for heterotrophic animals and plants. For storing purpose, glucose is converted into cellulose and starch and are kept in different units of the plant.


The leaf

The leaf is the centre of photosynthesis. Different layers are present in the leaf. The mesophyll layer of the leaf is the layer in which photosynthesis happens. Palisade parenchyma is the middle layer of the leaf. Chlorophyll lies in the mesophyll cells of the leaf in which photosynthesis occurs.

Leaves contain small openings known as “stomata”.Through this pore, CO2 enters the leaf and gaseous exchange occurs.

The chloroplast

The chloroplast is the main centre of photosynthesis. The chloroplast is the double membrane structure. Disc-shaped Thylakoids are present in the chloroplast that are arranged together called grana.

Pigments required in photosynthesis

There are mainly 4 types of pigments that are found in photosynthesis that are found in the leaves of the plant. The role of this pigment is to absorb light of different wavelengths:-

  • Carotenoids (yellow to yellow-orange)
  • Chlorophyll a (bright or blue-green in the chromatogram)
  • Chlorophyll b (yellow-green)
  • Xanthophylls (yellow)

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Photosynthesis Process

Photosynthesis happens in 2 different stages:

Light reaction

The main purpose of the light reaction is the formation of energy molecules such as ATP and NADPH. The reaction depends on light for its processing. In chloroplast, there is a thylakoid membrane and in this place, this light reaction happens. This reaction turns on the chlorophyll pigment which initiates the capturing of sunlight.

The water gets splits into its constituents when they gain an excited electron from this activated chlorophyll. After this, a redox reaction happens which results in the formation of energy pigments such as ATP and NADPH. These molecules are the important constituents of dark reaction. The light-harvesting complex areas in the plant are made up of hundreds of pigment molecules bound to proteins. The photosystem consists of many pigments apart from chlorophyll that later forms the light-harvesting system which is known as antennae. The rate of photosynthesis increases due to these pigments as these pigments absorb a variety of wavelengths of lights. Reaction centre is composed of single chlorophyll a.

Dark reaction

People get confused that dark reactions happen at night. Dark reaction is not dependent on light that’s why it is called dark reaction. This reaction is independent of sunrays therefore it can happen with and without the sun.

Scientists such as Calvin and Benson have been studying this dark reaction therefore it is called the Calvin-Benson-Bassham cycle.

Stroma in the chloroplast is the place where this reaction happens. Using the energy from the light reaction, glucose is formed through CO2.

How Plants Obtain Water for Photosynthesis?

Soil is an important source of nutrition for photosynthesis. Xylem vessels are used to deliver nutrients from root to plants and later it is used for photosynthesis. Phloem is used to carry food material throughout the plant. Carbon dioxide and water use photosynthesis as raw material. These materials are later processed into carbohydrates. Phosphorus, nitrogen, magnesium and nitrogen are one of the most important nutrients which are provided by soils.

Factors that affect photosynthesis

1.Light-In order to take light as a factor in affecting photosynthesis, we need to consider the quality of light, the intensity of light and the duration of light. At low intensities, incident light has a direct impact on CO2 fixation rates. Due to other factors become limited, the rate doesn’t increase more if the light intensities increases. The saturation point is around 10% of sunlight which is very astonishing. Light doesn’t count too much is nature. If only affects plants that grow in shade or dense forest. If the light is in excess it can rupture the chlorophyll and decreases the rate of photosynthesis.

Carbon dioxide is another agent that affect photosynthesis.CO2 is in very. Less amount in the atmosphere which is somewhere in between 0.04-0.05%. The situation becomes critical if the concentration exceeds 0.05 per cent in terms of CO2 fixation rates. If the concentration stays high for a longer time, the situation can be detrimental. The CO2 dependency of C3 and C4 plants is different as compared to other plants. There is no reaction with CO2 conditions if the light conditions are low. There is an increased rate of photosynthesis for C3 and C4 plants when the light intensities increases.360 µlL-1 is the saturation limit for C4 plants whereas 450 µlL-1 is the CO2 concentration limit for C3 plants. The current situation of CO2 concentration is limiting for C3 plants.C3 are linked to higher production when there is increase volume of CO2 which increases rates of photosynthesis. This thing can be seen in crops such as tomatoes and bell pepper. More amount of CO2 has been provided to these crops for more production.

Temperature-Temperature is one factor that controls dark reactions. The effect of temperature is much less in light reaction. C4 plants are more sensitive to a higher temperature which result in increased photosynthesis.C3 have much less dependency on temperature. Habitat too plays an important rule while deciding the dependency of photosynthesis on temperature. Plants from temperate climates have low temperature optimum as compared to plants from tropics.

Water-Photosynthesis directly don’t depend up to water but has more effect on plants. The light reaction is also dependent on water as it is one of their reactants. The CO2 couldn’t enter the leaf as due to water lacking the stomata closes. Water lacking also causes leaves wilt. Therefore, the metabolic activity of leaves also affects due to reduced of surface area.


Demonstration that proves sunlight is a key element of photosynthesis

  • Go to a dark room and place a potted plant for 3 days thereafter. The remaining starch from the plant will be utilized from the plant.
  • Wrap the leaf in the middle portion of the leaf and make sure it’s not fully covered and some part of the leaf is open to sunlight. Make sure aluminium foil is stick to its place using thread so that sunlight doesn’t enter inside.
  • Now, take the plant out and keep in sunlight for 3-4 days.
  • Now take off the covered leaf from the plant and take the aluminium foil off. Now you have to break the cell membrane of the leaf by boiling the leaf. The iodine solution can easily go if the membrane is broken.
  • Before testing for starch make sure you remove chlorophyll. Chlorophyll become a hindrance in the testing of starch
  • Take a beaker and fill the alcohol and place the leaf and put the beaker in a water bath.
  • Now heat the alcohol in small beaker indirectly after heating the water bath. Make sure the alcohol is boiling. Chlorophyll gets removed by the boiling alcohol from the green leaf.
  • After the chlorophyll is removed the leaf and it will come colourless.
  • Put hot water on the left after removing it from alcohol.
  • There will colour change as soon as you will put iodine after placing the leaf in petri-dish.
  • On adding iodine solution will not turn blue-black when poured on the centre part of the leaf. There is no presence of starch on this middle part of the leaf this is because there is no processing of starch as sunlight couldn’t able to reach that part hence no photosynthesis occurs.
  • The part which is not covered by foil was receiving sunlight hence it was able to produce starch due to the process of photosynthesis hence this area turns blue-black on adding iodine.
  • Therefore, starch is processed only after the process of photosynthesis and which happens after receiving sunlight.

Demonstration that proves chlorophyll is a key element of photosynthesis

  • Take a plant with leaven partially white and partially green for example croton.
  • Go to a dark room and place a potted plant for 3 days thereafter. The remaining starch from the plant will be utilized from the plant.
  • Now take the plant and place in the sunshine for 3-4 days.
  • Now place the leaf in boiling water for a few minutes. In order to remove the green colour, place the leaf in boiling water.
  • Now flush the leaf with hot water to clean it.
  • The area which doesn’t have any colour put iodine solution on it and see the colour change.
  • The leaf which has white colour will change its colour from white to blue-black which is an indicator of no starch present on the portion. It also shows that chlorophyll is an important pigment for photosynthesis.
  • The part of the leaf which is green turns blue-black when iodine is poured.
  • Which shows that this part had starch. Therefore, chlorophyll is necessary for photosynthesis to make starch.
  • Therefore, in photosynthesis chlorophyll is a major component.

Demonstration that proves carbon dioxide is a key element of photosynthesis

  • Go to a dark room and place a potted plant for 3 days thereafter. The remaining starch from the plant will be utilized from the plant.
  • Place potassium hydroxide solution inside the bottle with wide-open mouth. This solution will take CO2 gas from around it that is present around it.
  • Put a rubber cork and place it over the mouth of the bottle and put a small cut into it
  • You have to place cork is such a position that leaf hangs outside the bottle. Tighten the cork inside the bottle.
  • One part of the leaf is inside and one is outside.
  • Take the bottle in bright sunlight for 3-4 days.
  • The part of the leaf which is inside the bottle will not receive oxygen and another part which is outside will get the carbon dioxide.
  •  Cut off the leaf from the plant and keep it away from a glass bottle. Place the leaf in alcohol which is boiling.
  • Place the decolourised leaf under water and wash it.
  • On the colourless lead put the iodine solution. The colour of the leaf will turn to a different colour.
  • The leaf part which is outside class will not turn blue-black which shows the presence of no starch in this particular part. Now we can conclude that carbon dioxide is an essential thing for starch preparation in process of photosynthesis.
  • The part present outside away from the bottle will turn to blue-black which is the indicator of starch present in it. Now we can conclude that carbon dioxide is an essential thing for starch preparation in process of photosynthesis.

Role of photosynthesis

1)The main function of photosynthesis to glucose which later produces energy that can be used to perform many functions such as transportation of water and minerals around the plant and for respiration. Biochemical and biological methods happen with the help of energies produced in the plant. Plant act as food for other organisms.

2)Photosynthesis is the basis of all the live cycles happening in the world. With the help of it, all the living creature sustain and the cycle ends. Without photosynthesis, the food chain cannot start as producers won’t be able to survive.

3)Every organism of this plant is dependent on photosynthesis in some way or the other. Heterotrophs can depend on autotrophs directly as well as indirectly. Herbivores are directly dependent on autotrophs as they directly consume plants whereas carnivores indirectly depend on autotrophs as they consume herbivores that are directly dependent on autotrophs. There is a group of animals called omnivores which can both directly as well as indirectly depend on producers. These organisms can consume the direct product of photosynthesis as well as an indirect product such as meat, insect etc.

4)Photosynthesis helps in getting stored food such as starch from plants. Potato is an example of it.


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