Biology Unit 5 Ecology and Evolution Bitesize


What is a food chain?

A food chain describes the feeding relationships between species in a community

The arrows represent the molecules and energy as one organism is eaten by another. The first organism is a producer, the second is a primary consumer ...etc. 


Phytoplankton --> Krill --> Jellyfish --> Sea turtle

Wheat --> Locust --> Frog --> Snake

Oak Tree --> Woodmouse --> Viper --> Kestrel 

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What is a food web?

Few animals feed on only one kind of organism and have only one predator. 

A food chain shows a section of feed relationships, while a Food web will include more of these relationships, and shows a more accurate representation of the complex interactions between species. 

- There is more than one producer supporting the community

- each producer is a food source for a number of primary consumers

- A consumer may have a number of different food sources on the same or different trophic levels

- A consumer can be an omnivore, feeding as a primary consumer and as a consumer on higher trophic levels.

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The precautionary principle

Someone wishing to take a certain kind of action should prove that the action does not cause serious or irreversible harm to the public if there is no scientific consensus about the outcome of the action. 


We are not certain what the results of a change in our behaviour will be, the people wanting this change should prove that it is not harmful. 

Application of prec. principle: legalisation of new medication, EU and UN adopted the PP as a foundation for some policies. 

For environmental policies: alternatives do not exist. 

Wind turbines (noise pollution, wind polution, death of birds) vs using coal, oil or other fossil fuels....PP is hard to apply. 

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Consequences of a global temp. rise on arctic ecos

The average temp. in the arctic region is rising at twice the speed compared to the rest of the world. The Polar cap is shrinking. The fresh water lake on Ward Hunt Shelf dissapeared because the shelf melt, broke and drained into the ocean. 

The snow/ice reflects a lot of the Sun's radiation. When the snow and ice melts, the arctic absorbs more heat and warms up faster. 

Species (caribou, seals, polar bears)  are changing migration patterns affective native people who hunt them. 

Polar bear dens are melting, shortening hibernation. They have to swim to reach destination/prey. The process is slow and takes up energy. 

Reduced biodiversity can occur: species in the arctic survive with limited competition but a milder climate might bring more species creating competition and causing original species to die out.

Advantage: melting of arctic ice gives access to more oil and gas reserves but could lead to positive feedback (undesirable consequences)  

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Population size

There are four factors that influece the size of a populations

Natality (birth rate) - recruitment to a population through reproduction

mortality (death rate) - death rate from any source e.g predation

immigration ("moving in") - from external populations. eg. Bird migration 

Emigration ("moving out") - individuals leave population for another habitat.

immigration +


natality  + ________ population abudance __________ - mortality 


Emigration - 

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Evidence for evolution

Fossil record - all fossils, disovered and undisovered that exist. Fossils are mineralised remains of organisms. 

Fossilisation - dead organisms normally decompose quickly, without a trace. If they are covered in sediment soon after they die they may become fossils in part or whole. 
The most complete fossil record shows evolution of horse. The skeletons allow inferences about form and function and clearly show a gradual change over time.

Selective breeding of domesticated animals - humans and gods = long history. Dogs originally must have looke like wolves and used for hunting/pulling sledges. As breeding started, selection took place. Hhumans selected best hunters, and strongest dogs. And Humans made the start to different breeds of dogs. 

Homologous structure - Different species originated from a common ancestor, therefore they should have structures in common.

Human arms are similar to the front paws of a dog, the wings of a bat and flipper of dolphin. The structure of the pentadactyl limb is common to all tetrapods. Sam bones different size. 

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Seven levels of hierarchy of taxa-

Classifications of a dandelion and of a human below. 

Kingdom:  Plantae Animalia

Phylum: Tracheophyta Chordata

Class:  Angiospermae Mammalia

Order: Asterales Prima

Family: Asteraceae Hominidae

Genus:  Taraxacum Homo

Species:  Taraxacum officinale   Homo Sapiens

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Limits to Population Increase

Limiting Factors control population growth. 

For animal populations: 

- amount of food

- presence of parasites/disease

- amount of predation

- available nesting sites

For plant populations: 

amount of light available


amount of water available

amount of carbon dioxide

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