Interdependence and Interaction among Organisms, and between Organisms and the Environment



Interdependence and Interaction among Organisms, and between Organisms and the Environment

  • Habitat
    • The natural surroundings or home of an organism.
  • Species
    • A group of organisms that have common  characteristics and can reproduce to breed offsprings
  • Population
    • A group of organisms of the same species that live in the same habitat.
  • Community
    • ​​​​​​​A few populations of different organisms live together in one habitat and have mutual interaction with one another.
  • Ecosystem
    • ​​​​​​​​​​​​​​A few communities that live together in one habitat and have mutual interaction with one another,  including all the non-living components such as water, air and soil.
  • An ecosystem is said to be balanced if the living organisms and non-living components in the environment are in a state of harmony without any external interference.


Interaction between Organisms
Interaction between organisms comprises symbiosis, prey-predator and competition.



  • Symbiosis happens when two or more organisms of different species live closely together and interact with one another. 
  • Symbiosis includes mutualism, commensalism and parasitism.



An interaction that benefits both organisms

Example: Lichens are algae and fungi that live together


The interaction between two organisms which only benefits one organism without harming or benefitting the other

Example: The remora fish (commensal)  latches on the shark (host)


An interaction that benefits one organism and only and harms the other. The parasite gets benefit and host is harmed.

Example: Tapeworm(parasite) that lives in the human intestine(host)



  • Involves one organism that eats another organism
  • Prey is the organism that is eaten by the predator
  • Predator is the organism that hunts another organism for food
  • Example : Lion(predator) and deer(prey)



  • Competition happens when organisms in one habitat compete for a limited supply of basic needs such as light, space, water, food and mates


Biological Control

  • Biological control is a method that uses organisms that are natural predators or parasites to reduce the number of pests in an area.
  • Example: Owls are kept in palm oil plantations to control the population of rats


Factors that Influence Population Size in an Ecosystem
\(\downarrow\) \(\downarrow\) \(\downarrow\) \(\downarrow\)
Disease Presence of predators Source of food Change of weather


Changes in the Ecosystem

  • Limited water supply
    • Example: Drought season that will upset the paddy field ecosystem
  • Migration
    • Example: The cattle egret migrates to Kuala Gula from September to April every year.
    • As a result, the number of insects decreases as they are eaten by the egrets
  •  Change in population size
    •  Example: The increase of pests causes the population of plants to decrease