Food relationships among living organisms ( Predation , Symbiosis & Saprophytism )

Food is the main source of energy for all living organisms , where green plants make their own food during photosynthesis process from simple substances which are carbon dioxide gas and water , Sunlight as a source of energy , So , green plants are called producers ( autotrophic organisms ) . 

Some animals depend on plants directly , so , these animals are called herbivorous such as rabbit , sheep ….etc. , Some other animals depend on plants indirectly , so , these animals are called carnivorous such as lion , snake …..etc. , so, there are many food relationships among living organisms .

Types of food relationships

The types of food relationships are Predation , Symbiosis and Saprophytism .


Predation is a food relationship among living organisms , where one living organism devours another one , Predation occurs between two living organisms , The predator which devours the other living organisms , The prey which is the devoured living organisms .

Predation is a temporary relationship , because it ends by devouring the prey or a part of it , where the predator attacks , kills or devours the prey , Predation occurs in plant world and animal world .

Predation in plants

Predation is less common in plant world than that in animal world because plants can make their own food ( carbohydrates and protein ) by photosynthesis process , Some plants can not make protein , because they can not absorb some components from the soil .

So , they prey some tiny animals as insects to get their required elements for making protein and these plants are known as insect-eaters ( insectivorous ) plants , such as Drosera and Dionaea , Drosera is an insectivorous plant because it preys some insects to get the required elements for making protein .



Predation in animals

Predation in animals such as a lion preys a deer , a wolf preys a rabbit , a cat preys a rat , Spiders , where they make woven to catch insects , So , Lions , tigers , spiders , wolves , cats , snakes and sharks are considered as predator animals .

Some ways of self-defence against predation in living organisms

Many living organisms have ( appeal to ) different ways of defending themselves against enemies such as camouflage and mimicry .


Camouflage is a phenomenon in which living organisms protects itself ( hides ) from enemies by changing its colour to simulate the colours of its surrounding environment , This phenomenon is found in fish , frogs , birds , chameleon and most insects as butterflies .

Examples of Camouflage
  1. A butterfly stands on a tree with the similar colours .
  2. A frog changes its colour to hide from its enemies .
  3. A chameleon simulates the colour of the surrounding environment to protect itself ( hide ) from its enemies .
  4. A cuttlefish ( sepia ) ejects a black fluid in the surrounding water to hide when attacked by enemies .

Mimicry is a phenomenon in which the harmless living organisms imitate other harmful or poisonous living organisms to frighten their enemies and escape from them , such as some bees look like wasps in forming lines ( stripes ) on their bodies to frighten their enemies .

Some bees look like wasps in forming lines ( stripes ) on their bodies to frighten their enemies which get afraid of wasps and escape from them .


Symbiosis is a common food relationship between two different types of living organisms , Types of symbiosis are mutualism , commensalism & parasitism .


Mutualism is a food relationship in which each organism gets benefit ( in the form of food ) from the other , Such as the relationship between nodular bacteria and leguminous plants ( as beans ) , Each of them gets benefit from the other in the form of food , where :

  1. Nodular bacteria fix nitrogen in an inorganic form to provide the plant with it .
  2. The plant provides bacteria with sugar made by the plant during photosynthesis process .
The benefits of mutualism in human body

There are several kinds of bacteria that coexist with man , where each of them benefits from the other as follows :

Human body benefits from bacteria as : Some types of bacteria live inside man’s intestine and change some food remains into vitamin ( B ) , Some live on his skin and work on increasing the immunity of skin against diseases infection , Bacteria benefit from man in the previous case as the human body provides bacteria with food and shelter .


Commensalism is a food relationship between two living organisms where , one of them benefits from the other , while the other neither gets benefit ( in the form of food ) nor is harmed .

Example : The relationship between sponge and tiny aquatic living organisms , Tiny aquatic living organisms get food and shelter from the canals and fissures that are found inside the sponge , while the sponge neither gets food ( benefit ) nor is harmed .


Parasitism is a food relationship between two different kinds of living organisms , where one benefits from the other and is known as the parasite , while the other is harmed and is known as the host , Parasitism causes weakness to the host but it does not kill it , The types of Parasitism are external parasitism and internal Parasitism .

External parasitism

In this type of parasitism : The parasite lives externally on the host’s body and feeds by sucking the blood of the host , A parasite conveys diseases to the host , such as mosquitoes , lice , fleas , bugs , ticks , jawless lamprey ( that sucks fish’s blood ) .

Internal Parasitism

In this type of parasitism : The parasite lives internally inside the host’s body and shares the host its digested food or feeds on its cells and tissues , Such as Bilharzia worms , ascaris worms , tape worms , filaria worms and liver worms .

Harms of parasitism

Parasites cause many diseases to man such as :

  1. Filaria worm causes elephantiasis disease .
  2. Mosquitoes cause malaria disease .
  3. Fleas can convey small pox disease to man .
  4. Bilharzia worms cause bilharziasis disease .
  5. Ascaris worms cause anaemia .

The death of the host is considered a loss to the parasite because the parasite will lose its source of food and shelter , Some dogs , cats and birds which we have at home can be hurt by worms and some of these worms can infect human , To protect man and these living organisms , follow the proper way of cleaning and visit the veterinaries regularly to check them .


Saprophytism is food relationship in which saprophytes ( decomposers ) get their food by decomposing food remains or bodies of dead organisms , such as mushroom fungus , Bread mold fungus and Penecillium fungus that decomposes orange fruits .

Saprophytic organisms as bread mold fungus get their food by decomposing the food remains ( as moist bread ) causing the dark green layer on bread .

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