B3

• a species is a group of organisms that can breed together to produce fertile offspring
• species are adapted to live in their environment 
• adaptation of organisms to their environment means they are able to survive and reproduce successfully
• organisms that live in a habitat are dependent on their environment and other species living there. they compete with eachother for resources
• animals compete with eachother for food, a mate, living space, and territories, plants compete for sunlight, water, and space
• a food web shows feeding relationships between organisms
• interdependence is when organisms in a habitat depend on eachother in more ways than just food
• any change affecting one species in a food web is likely to affect all species in that food web

• a species can become extinct if it is unable to adapt rapidly to a change in the environment
• removal of habitats due to human activity threatens species
• the introduction of a new species can lead to extinction if the species is a competitior, predator, or causes disease
• the extinction of a species in a habitat will affect other organisms in the food web and may also cause them to become extinct

• 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
• almost every food chain begins with a plant
• energy is transferred from one organism to another through a food chain
• only a small percentage of the energy transferred remains in the organisms body, this is because some parts cant be eaten/digested, the animal uses some energy during respiration, the waste products of the animal uses energy
• the length of food chains is limited because energy is lost
• you can calculate efficiency of energy transfer using energy in tissues/energy in food eatenX100

• enters the carbon cycle as carbon dioxide from the air
• plants fix this carbon, so that it can be used and stored by organisms e.g. photosynthesis
• carbon is returned to the air as a product of respiration, decomposition of dead organisms, and combustion 

• plants take up nitrogen from the soil through their roots in the form of nitrates
• these are converted into proteins
• these proteins pass along the food chain
• nitrates are released back into the soil as animals excrete waste, and as plants and animals die and are decomposed by microorganisms
• nitrogen enters the nitrogen cycle by being split by lightning, and combining with oxygen in the air to form nitrates, or through nitrogen fixing bacteria which are found in the oil and roots of leguminous plants such as beans, which convert nitrogen in the air into nitrates
• nitrogen leaves the nitrogen cycle when denitrifying bacteria convert nitrates in the soil into nitrogen gas

• non-living indicators- carbon dioxide levels, temperature, and nitrate levels
• living indicators- phytoplankton lichens and mayfly larvae
• mayfly larvae need high levels of oxygen in water so will indicate low levels of pollution
• lichens are sensitive to sulfur dioxide in the air 
• phytoplankton grow in places of high carbon dioxide levels

• began around 3500 million years ago
• over millions of years simple organisms became more complex which is evolution
• variation has genetic and environmental causes
• evidence of how organisms changed over time is in fossils
• fossils are the remains of organisms which have turned into rock

• a mutation is the change in the genetic information in a cell
• mutations can be harmful however sometimes new useful characteristics are formed and passed down
• over thousands of millions of years, with changes in the frequency of different genes, new species emerge

Charles Darwin

The basic idea behind the theory of evolution is that all the different species have evolved from simple life forms. These simple life forms first developed more than 3 billion years ago (the Earth is about 4.5 billion years old).

Darwin was not the only person to develop a theory of evolution. Jean-Baptiste Lamarck was a French scientist who developed an alternative theory at the beginning of the 19th century. His theory involved two ideas. His theory stated that a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears. Any feature of an organism that is improved through use is passed to its offspring.

• because of genetic variation, some individuals will have characteristics that give them a better chance of survival than others
• individuals with advantageous genes will survive to reproduce and pass these to their offspring, this is natural selection
• selective breeding is also used in animals and plants; this involves choosing individuals with the best fenes, breeding them and repeating over several generations
• natural selection is important because it results in an organism that is better able to survive in terms of reproduction, and competition with other animals
• over time, advantageous genes through natural selection are likely to become the norm in the population
• factors that influence the rate of evolution; environmental change, isolation

• organisms are classified by putting them into groups
• classification is based on analysing DNA sequences and groups with similar features
• a common ancestor is the most recent organism from which the species in a group descended
• evidence to support evolution; simple organisms are found in the earliest rocks, more complex ones appear in younger rocks. more recent fossils have features that look like adaptations or developments of those of older organisms. DNA analysis
• the theory of evolution was based on Darwins observations that species were not fixed and could change over time. Lamarcks theory was that animals acquired characteristics during their lifetime that were passed on to their offspring

• the variety of life on Earth and in different habitats. the number of species, and range of different organisms
• species are now rapidly becoming extinct, it is thought that this is linked to human activity as organisms are hunted and their habitats are destroyed
• climate change accelerates the rate of extinction
• organisms are classified into kingdoms, then smaller groups, then identified individually as a species.

Sustainability

• meeting todays needs without stopping future generations from meeting theirs
• 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 a food supply and impacts an ecosystem
• monoculture crop production maximises crop yields but is not sustainable, it reduces biodiversity by growing just one crop
• we can improve sustainability in product manufacture
• the life cycle assessment: sourcing of raw materials*manufacture*transport*use*disposal