environment, competition for resources, our influence on the environment,chains webs and pyramids, wheat vs meat,natural selection and evolution, variation.



competition for resources

animals compete with each other for for resources like food. animals can compete between species and within a species. the strongest, best adapted animals get to eat most of the food, so they survive and breed at the expense of less well adapted animals. predators kill and eat other animals. scavengers are animals that eat what is left after predators have eaten what they need of their prey; they also eat other dead animals. plants and animals are interdependent, one cannot live without the other. changes in the numbers of one organism affect the numbers of the other organisms. population changes in predators lag behind changes in the population of their prey.


interdependent: a change in one organism causes a change in another.

population:the total number of a single species living in an area.

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our influence on the enviroment

the population of humans has increased. the increase in population puts pressure on the resources. every person needs water, food and somewhere to live. forest is burned and cleared to make more room for farming. burning fuel for electricity generation and transport produces carbon dioxide. carbon dioxide i a greenhouse gas and contributes to global warming. over using land can make it less fertile, which can result in in desertification. cutting down rainforest is an example of deforestation.


environment: the place where an organism lives e.g. air, water, soil and other living things.

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chains, webs and pyramids.

green plants use photosynthesis to make their own food. green plants are producers. the arrows in a food chain show the flow of energy through the food chain. several food chains link together to make a food web. a food pyramid shows the numbers of organisms in a food chain. pyramids of number show how many of each organism are found at each level of the food chain. pyramids of biomass show the dry mass of living matter in the food chain.


biomass: mass of an organism (or population) after water is removed.

ecosystem: interacting group of plants an animals

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wheat vs meat

food chains are made up of only three or four links. only about 1% of the energy falling on a wheat field is used for photosynthesis. the rest is lost through reflection and evaporation of water from plants. only about 10% of the energy captured by a plant is transferred to primary consumers. only about 10% of the energy eaten by a by a primary consumer is transferred to secondary consumers. feeding cereals to animals that we can then eat is a very efficient way of making protein. organic farming is a more natural way of producing food by avoiding the use of chemicals when growing crops.


organic farming: uses natural ways to control pests and keep soil fertile.

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natural selection and evolution

the theory of evolution was developed by Charles Darwin. fossils are important evidence for evolution. an important part of evolution and natural selection. all organisms produce many young, so the population should increase, but it doesn't so some offspring must die. organisms which have the variations which give them better adaptations to their environment are more likely to survive and breed. some characteristics are inherited, so useful characteristics may be passed on to future generations. eventually this may give rise to a new species. natural selection takes place over very long periods of time. if there is a big change to the environment, some groups of organisms cannot adapt and become extinct.


reproduction: propagation of the next generation

adaptation: how organisms change to suit their environment better.

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there are million of different species of organisms in the world. scientists record these and put then into groups. this makes it easier to identify new species when they are discovered. the groups contain related organisms to try and show how they evolved. humans and apes are in a group together called primates. the animal kingdom is divided into animals with backbones and those without backbones. some organisms are difficult to classify: euglena is an animal but it can photosynthesise like plants. the smallest classification of organisms is called a species, and even then there is variation amongst the individuals.


classification: a way to group things systematically

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