Autotrophic mode of Nutrition

Olawunmi Omosanya - Sat, 25th May, 2019 @ 19:11: PM

Topics in Biology

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Academic Questions in Biology

Please check out our Test Your Knowledge page to see all Questions and Answers

Organisms that manufacture their own food through the help of sunlight or chemicals are best referred to as _____.

  • A. autotrophs
  • B. chemosynthetic
  • C. photosynthentic
  • D. chemoautotrophs
  • E. photoautotrophs
  • F. chemoautotrophs

Organisms that begins a food chain and also manufacture their food through photosynthesis are best referred to as _____.

  • A. heterotrophs
  • B. autotrophs
  • C. homotrophs
  • D. producers
  • E. photosynthetic
  • F. chemosynthetic

_____ bones make up the skull.

  1. 10
  2. 12
  3. 15
  4. 20
  5. 22
  6. 25
  7. 30

Chemical digestion of carbohydrate (cooked starch) begins in the _____.

  1. mouth
  2. oesophagus
  3. stomach
  4. small Intestine
  5. large Intestine

Autotrophic Nutrition:

Every living organism must be able to feed. In fact, nutrition is one of the basic characteristics of living organisms. Please read our article on the introduction to biology.

Nutrition can be defined as the intake of food or nutrients by an organism; to be used for growth, repair and every other necessary requirement for the orgnism's survival

Regarding nutrition, an organism will either manufacture its own food or depend on readymade food. For this reason, the mode of nutrition can be grouped into two major classes. These are

  1. Autotrophic Nutrition
  2. Heterotrophic Nutrition

In this article, we will read about the autotrophic mode of nutrition.


Autotrophic mode of Nutrition

In autotrophic nutrition, organisms are able to manufacture or produce their own food. Such organisms are referred to as autotrophs.

Autotrophic nutrition can be put into two groups; these are:


a. Photosynthetic nutrition

Photosynthetic nutrition requires that organisms are able to manufacture their own food by utilizing carbon(IV)oxide (CO2) and water (H2O) in the presence of sunlight. This process is known as photosynthesis and is utilized by green plants.

Photosynthesis can be defined as the process whereby green plants manufacture sugars (food) by utilizing carbon(IV)oxide (CO2) and water (H2O) in the presence of light energy (sunlight) while giving off oxygen (O2) as a bye product. The equation below expresses the definition of photosynthesis.

6CO2 + 6H2O -> C6H12O6 + 6O2
  • CO2 = Carbon(IV)oxide
  • H2O = Water
  • C6H12O6 = Sugar
  • O2 = Oxygen

Please read on sugars here

Although not seen on the equation, light energy and chlorophyll are also involved (necessary) in the photosynthetic reaction.

Photosynthesis occurs in a plant’s leaf. The leaves of plant contain an organelle called chloroplast. The chloroplast houses the chlorophyll which gives the plant’s leaf its green coloration. Also, it is the chlorophyll that traps sunlight energy.


How Photosynthesis works

An endothermic reaction is a reaction that takes in heat from its surroundings. Photosynthesis is therefore an endothermic reaction since it requires sunlight energy. Not every stage in the process of photosynthesis requires sunlight. As a matter of fact, the photosynthetic reaction is put into two stages or reaction. These are;

  1. Light Stage or Light Reaction
  2. Dark Stage or Dark Reaction


  • Light Reaction

This stage of photosynthesis occurs in the presence of sunlight (during the day). The chlorophyll (present inside the chloroplast in the plant’s leaf) traps the light or solar energy. This trapped light energy is used to breakdown or split water into hydrogen ion (H+) and hydroxyl ion (OH-).

The process of splitting water into hydrogen ion (H+) and hydroxyl ion (OH-) is referred to as the photolysis of water. The equation below shows this process:

4H2O -> 4H+ + 4OH-

Note: A co-enzyme called NADH is reduced to NADPH. ATP is formed during this process.

  • NADH means Nicotinamide Adenine Dinucleotide
  • NADPH means Nicotinamide Adenine Dinucleotide Phosphate
  • ATP means Adenosine TriPhosphate

The formed hydroxyl ion is further converted into water as shown in the equation below.

4OH- -> 2H2O + O2

Although not seen on the equation, light energy and chlorophyll are also involved (necessary) in the photosynthetic reaction.

Note: The oxygen given off as a bye produce of photosynthesis comes from the light stage of photosynthesis.

One of the reasons why the sun is regarded as the ultimate source of energy is simply because of the process of photosynthesis. Without the sun, there will be no green plants on earth and without green plants, there will be no animals. Remember that human beings are higher animals.


  • Dark Reaction

This stage of photosynthesis occurs in the absence of light (at night). The ATP (which is energy itself) is utilized; as carbon(IV)oxide is taken in (by the stomata of the plant’s leaf) to react with the hydrogen ion (4H+) from the light reaction. After a series of step by step reaction (with each step being controlled by a specific enzyme), sugar (food) is formed. The dark reaction is shown in the equation below:

4H+ + CO2 -> C6H12O6 + H2O

Note: The sugar produced in photosynthesis occurs in the dark stage or reaction. Also, think of stomata as an opening in the plants leaf where gases enters and exits.

All green plants, blue-green algae, spirogyra and some protists carry out photosynthesis. Please read on protists here.


b. Chemosynthetic Nutrition

Organisms that manufacture food in a chemosynthetic manner do not require sunlight energy, rather chemicals are utilized here.  They synthesize their food from the oxidation of simple inorganic substances (chemicals) like carbon(IV)oxide (CO2), Ammonia (NH3) Nitrite (NO2) and water (H2O).

Note: Consider oxidation to be a chemical reaction that involves oxygen (O2)

Some bacteria like Nitrosomonas and Nitrobacter make use of chemosynthesis in the manufacture of food. This is shown in the equation below:

i. Nitrosomonas will convert ammonia (NH3) to Nitrite

2NH3 + 3O2 -> 2HNO3 + H2O + Energy


ii. Nitrobacter will convert nitrite (NO2) to nitrate (NO3)

HNO2 + O2 -> HNO3 + Energy

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Note: Habitat is a place where an organism live. It is of three types:

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  • Bios: means life. 
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Biology can therefore be defined is the study of life

Anything that has life is generally considered as a living organism (or organism) 🌱🐐🐓. All living organisms must be able to carry the following activities:

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  5. Growth
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  8. Death
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