Life on Earth - How Species Depend on Each Other


There are similarities and differences between living things on Earth. Many species of animal and plant have become extinct while others have survived. Many different species are dependent on each other. 


Similarities and differences between living things on Earth are used to put them into groups. This process is called classification. You may have met the first big division of living things in the classification system called the five kingdoms in Key Stage 3.


A species is a group of organisms that can breed together to produce fertile offspring. The most common example to show this is with horses and donkeys. A horse and donkey can breed together: the offspring is called a mule. The mule is infertile, which shows that the horse and donkey are a different species. 


Adaptations are features that help an organism survive in the environment it lives in. Such adaptations increase the organism's chance of surviving. If the chances of survival are increased it also increases the chances that the organism will successfully reproduce.

Food Webs

A food web is simply a number of food chains joined together. It shows how the loss of one organism has an effect of other organisms in the food web. This is called the interdependence of living things. Slugs, rabbits and insects all eat grass. If there were fewer slugs there would be more grass for the rabbits and insects. With more food the populations of rabbits and insects would increase. However, the thrushes would have to eat more insects to maintain their population, so it is also possible that the population of insects could decrease. This is turn may reduce the populations of voles and frogs.


Living organisms are dependent on the environment and other species for their survival. When the environment changes, organisms are not as well adapted to it. Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its environment will become extinct. Here are some factors that can cause a species to become extinct: rapid changes to the environment (such as the climate), new diseases, new predators and new competitors. Because we are all part of a giant food web, changes in one part of the web can have a big impact on other parts of the web. When one food source disappears, a predator will have to find another food source in order to survive. The fossil record shows that since life on Earth began many species have become extinct. Extinction is still occurring, a lot of it because of human activity. We compete with other living things for space, food and


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