HideShow resource information

Species, adaptation and extinction

A species is a group of organisms that can breed together to produce fertile offspring.

Species are adapted to the environment they live in so that they can survive and reproduce successfully. Within a habitat, organisms rely on other species for food and compete with each other for resorurces. Animals compete with each other for food, a mate, living space and territories. Plants compete for light, water, nutrients and space.

Interdependence=the relationship between several oragnisms that depend on each other.

A species becomes extinct if it is unable to adapt rapidly to a change in its environment eg. climate change. A species' extinction can lead to the extinction of other animals within the same food web.

Removal of habitats due to human activity threatens species such as the Siberian tiger and the mountain gorilla.

1 of 9

Energy transfer

Nearly all organisms on earth are dependent on energy from the sun. Plants absorb a small percentage of the energy from sunlight to produce their own food by photosynthesis. Other organisms get their energy by eating plants.

Energy is transferred from one organism to the next along a food chain. Only a small percentage of the energy transferred remains in the organism's body. Energy is lost at each level of the food chain so a food chain's length is limited to 4 or 5 organisms. In transfer from a plant to an animal, some energy is lost because:

  • Some parts of the plant aren't eaten or cannot be digested by the animal
  • The animal uses some of the plant's energy for respiration when some energy is lost as heat
  • The waste products of the animal contains some energy

You can calculate the efficiency of energy transfer at any level using the equation: Percentage efficiency = ( Energy in tissues / Energy in food eaten ) x 100%

Energy transfer continues after an organism has died. Microorganisms called decomposers such as bacteria feed on the decaying or dead organisms. Detrivores such as earthworms and woodlice, feed on detritus and break it down further.

2 of 9

The carbon & nitrogen cycles

The Carbon Cycle: Carbon is a key element that makes up all living things. It is continually recycled through the carbon cycle. Carbon enters the carbon cycle as carbon dioxide in the air. Plants fix this carbon, so that it can be used and stored by organsisms by photosynthesis. Carbon is then returned to the air either as a product of respiration; through the decomposition of dead organisms by soil microorganisms such as bacteria and fungi; or by the combustion of organic materials.

The Nitrogen Cycle: Nitrogen is an essential component of living things. It is recycled through the nitrogen cycle. Nitrogen enters the cycle in two ways: Nitrogen molecules in the air are split by lightning. Nitrogen atoms then combine with the oxygen in the air to form nitrates, which are washed into the soil by rain. The other mathod is using nitrogen-fixing bacteria, found in the soil and in the roots of leguminous plants such as beans and peas, convert nitrogen in the air into nitrates. Plants then take up these nitrates and convert them into proteins (an important nutrient in animals' diets). Nitrogen leaves the cycle in a process called denitrification when denitrifying baceria convert nitrates in the soil back into nitrogen gas. Nitrates are released back into the soil as animals excrete waste, and as plants and animals die and are decomposed by microorganisms.

3 of 9

Environmental change & Life on earth

Indicators of environmental change:

Environmental change can be measured using:

  • Non-living indicators such as temperature, nitrate levels or carbon dioxide levels.
  • Living indicators such as phytoplankton, lichens and aquatic organisms such as mayfly larvae.

Observations of some living indicators can give us very precise information about levels of pollution and environmental change. This is called biotic index. For example, mayfly larvae need high levels of oxygen in the water, so will indicate very low levels of pollution.

Life on Earth:

Life on earth began around 3500 million years ago with very simple life forms. Over time, life evolved, giving us the species we have today. The changes involved in evolution began with variation in individuals which has either genetic or environmental causes. Fossils provide evidence for how organisms have changed over time. Scientists can date fossils from the layer of rock they are found in.

4 of 9

Variation, Natural Selection & Selective Breeding

A mutation is the change in genetic information in a cell. A mutation will result in a change in the characteristics of an organism. Mutations occur as DNA is copied during the production of new cells. If a mutation occurs as sex cells are produced, the mutation is passed on to the offspring. Most mutations are harmful but sometimes, useful, new characteristics are produced which can then be passed on through the poopulation.

In a population of organisms, the alleles of genes that occur in that population-the gene pool-will change because of mutations and other causes of genetic variation.

Because of genetic variation, some organisms will have characteristics which will give them a better chance of survival than others. These individuals with advantageous genes will survive to reproduce and pass on their characteristics to their offspring. This is natural selection as nature is selecting the best genes to be passed on.

Selective breeding is when humans choose individuals with desirable characteristics breed these, repeating the process over several generations. Here, humans are choosing the desirable characteristics whilst in natural selection, humans have no control over this and nature decides.

5 of 9

Natural selection and evolution

A number of factors influence the rate at which evolution takes place:

  • When the environment changes, only those that are best adapted or are able to re-adapt will survive.
  • If organisms, become isolated, for instance on an island, natural selection will act indpendently on the different populations. Over time, the populations will become distinct and no longer able to reproduce with each other. They will be a new species.

In the search for evidence of evolution, scientists have investigated the relationships between organisms by:

  • examining the fossil record
  • observing similarities and differences in physical features eg. skeletons and flowers
  • analysing DNA sequences
6 of 9

Evidence for evolution

Organisms are classified by putting them into groups. This helps us to understand the enormous diversity of organisms on earth and how they evolved. Classification is based on grouping organisms with similar features and, more recently, by analysing DNA sequences.

There is evidence to support the theory of evolution: the simplest organisms are found in the earliest rocks. More complex ones appear in younger rocks.

The theory of evolution was proposed by Charles Darwin and Alfred Russel Wallace in 1859. The theory was based on Darwin's observations on the Galapagos Islands. The islands are volcanic so the organisms must have arrived at some point from the mainland. Darwin noticed variations between the organisms from island to island, indicating they must have evolved.

By contrast, Lamarck's theory suggested that animals gained characteristics during their lifetime and then passed them on to their offpsring but there was no evidence for this.

7 of 9

Conserving biodiversity

Biodiversity: the variety in terms of number and range of different life forms in an ecosystem.

Habitats such as tropical rainforests have a very high biodiversity and many of these species could be useful to us as food or medicines.

Species are now becoming extinct more than ever before (except mass extinction periods). It is thought that this is connected with human activity as organisms are hunted and their habitats are destroyed. Climate change will also accelerate this rate of extinction.

Organisms are classfied in the following way:

  • A kingdom is a large group with many organisms but fewer characteristics in common
  • Moving down from the kingdom, the groups get smaller and have fewer organisms with more characterisitics in common.
  • The level identifying the individual type of organism is the species.
8 of 9


Sustainability means: limiting our impact on wildlife, habitats and the environment; actively supporting ecosystems and populations of living organisms. To ensure sustainability, we need to maintain biodiversity. The loss of a single species removes and food supply and can have a huge impact on the whole ecosystem. Intensive monoculture crop production maximises crop yileds but is not sustainable. It reduces the biodiversity of the field by: growing just one crop species; removing hedgerows to create huge fields for planting; spraying cops with herbicides and pesticides.

We can improve sustainability in product manufacture by:

  • using as little energy as possible and minimal packaging
  • using locally available materials and limiting transport of the product
  • creating as little pollution as possible

The Life Cycle Assessment tracks the environmental impact of a product from:

Sourcing of raw materials--> Manufacture--> Transport--> Use--> Disposal

9 of 9


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Life on Earth resources »