B2 OCR

• Natrual Classification systems- based on evolutionary relationships and genetic similarities between organsims
• Artificial Classification Systems- based on appearance rather than genes, used to identify organisms
• Classification Systems adapt to fit new findings- 1.New species may not fit into any category 2.DNA sequencing allows us to see genetic differences between groups, as this information is collected we may find that two groups aren't as closely related as thought

• Species- A group of organisms which can interbreed to produce fertile offspring 
• Asexual reproduction- where there is no interbreeding with another organism so they don't fit the definition of a species, the organism makes a copy of itself e.g. bacteria 
• Hybrids- Interbreed a male from one species with a female from another species e.g. a mule. Hybrids are usually infertile. 
• Evoluation-organisms change and evolve over time, sometimes a group of organisms will change so much it will form a new species. 
• Binomial system- two part latin name, the first part refers to the genus the second to the speciese e.g. Humans= Homo sapiens
• Similar species often have recent common ancestors so they're closely related, they often look alike and live in a similar habitat. Closely related species may look different if they live in different habitats. You have to consider how species are related in evolutionary terms and the type of environment that they've adapted to.

• Each bar on a piramid of biomass shows the mass of living material. Biomass is lost at each stage in the food chain.
• To contstuct a piramid of biomass you use the 'dry mass' of the organisms. This is difficult as you need to kill the organisms. This would be okay for a plant but not for animals. 
• Sometimes organisms feed at more than on trphic level of the pyramid making them hard to construct.
• Pyramids of number show the number of organisms at each trophic level
• Pyramids of number may not be in the shape of a pyramid e.g. one plant/tree may feed many insects.

• Energy from the sun is the source of energy for all life on earth
• The energy lost at each stage of the food chain is used for staying alive. Most of the energy is lost to the suuroundings as heat. Energy is also lost as waste products e.g. egestion (when food cant be digested) and excretion (waste products of bodily processes)
• Waste products can become the start of another food chain e.g. houseflies eat faeces
• The loss of energy is why the biomass piramid gets smaller as it goes up
• Efficiency= energy available to next trophic level                     x100

            energy that was available to the previous trophic level

• Organisms must compete against eacother to surviv. Similar species in the same habitat will be in the closest competition
• A species' ecological niche is how it fits into its ecosystem, it depends on where they live and what they feed on
• Interspecific Competition- organisms compete for resources against individuals of another species
• Intraspecific Competition- organisms compete for resources against individuals of the same species
• If the population of a prey increases then the population of their predator will also increase and the same if the population decreases. Prey and predator cycles are out of phase with eachother as it takes a while for the other one to respond.
• Parasitic Relationships- parasites live off of a host, they take what they need to survive without giving anything back. This often harms the host. E.g. Tapeworms absorb nutrients from their host causing them to suffer malnutrition. Fleas are also parasites.
• Mutualistic relationships- Both organisms benefit. E.g. 'Cleaner species'- oxpeckers live on the backs of buffalo, they eat the pests but also alert them if a predator is near by hissing. Many plants are pollinated by insects allowing them to reproduce, in return the insects get to eat the plants necter

• Adaptations- features organisms have that make them better suited to their environment meaning they are better at competing for resources meaning they are more likely to survive.
• Specialists- organisms which are highly-adapted t survive in a specific habitat.
• Generalists- organisms whic are adapted to survive in a range of different habitats.
• If a habitat has stable conditions then specialists are more likely to survive as they have adapted to those excat conditions. However if a habitat has varying conditions then generalists are more likely to survive as they can adapt to many different conditions.
• Organisms that are adapted to live in extreme habitats, e.g. volcanoes, are called extremophiles.
• Extremophile bacteria that live in very hot conditions have enzymes that work best at high temperatures.
• Organism that live in very cold habitats sometimes have antifreeze protiens which interfere with the formation of ice crystals in the cells which stop the cells from being damaged by ice.

Anatomical adaptations to the cold include-

1.Having a thick coat or layer of blubber t insulate the body.

2.Having a large size and compact body shape giving a small surface area to volume ratio reducing heat loss as less body heat can be lost through the skins surface.

3.Having a countercurrent heat exchange system:

• Animals like penguins have to stand on cold ice all day
• Blood vessels going from te feet carry blood that flows in opposite directions 
• The vessels pass close to eachother allowing heat to transfer between them
• Warm blood flowing through arteries in the feet warms the cold blood returning to the heart 
• This means that the feet stay cold but it stops the blood from cooling down the rest of the body

4. Many species have behavioural adaptations to the cold e.g. migrating to warmer climates during winter, hibernating in the winter months or huddle together to keep warm e.g. penguins.

Anatomical adaptations to keep cool include-

• Having a large surface area t volume ratio (being small) which allows more heat to be lost.
• Large thin ears allow more blood flow near the surface of the skin so more heat is lost.
• Some animals store fat in just one part of the body so the rest isn't very insulated.

Behavioural adaptations to keep cool include-

• Spending time in the shadeto minimise the amount of heat their bodies gain.
• By being active at night when it is much cooler.
• By bathing in water, as the water evaporates it uses body heat which cools them down.

Adaptations to dry environments-

• Plants: round shapes to give them a small surface area to volume ratio, thick waxy layer (cuticle) and spines instead of leaves to reduce water loss, store water in stems for emergencies, have shallow but extensive roots to ensure water is absorbed quickly.
• Animals: specialised kidneys allowing them to produce concentrated urine with low water content, no sweat glands, spend lots of time underground where the air is moist.

Charles Darwin- Theory of natrual selection-

• Organisms in a species show wide variation and organisms compete for limited resources
• The organisms that are best adapted would be more successful competitors and would be more likely to survive
• Organisms that survive reproduce and pass on their adaptations to offspring, organisms that are less likely to survive wont pass on their genes
• Over time more successful adaptations become more common and the specie changes

Speciations- Over a long period of time a species may change so much that a new species is formed. This happens when populations of as species change enough to be reproductively isolated- they cant interbreed. Reproductive isolation is caused by geographic isolation:

• A physical barrier divides a population of species e.g. rivers
• Different mutations create new features in the two groups of organisms
• If the new features benefit they spread through each population
• Conditions on each side of the barrier will be slightly different, so the features that are beneficial will be different for each population
• Individuals from each population will have such different features that they will not be able to interbreed to make fertile offspring and so will be two seperate species.

Opposition-

• It was the first plausable explanation for how the earth developed that went against religious beliefs
• Darwin had no explanation for how this worked
• There wasn't enough evidence to convince many scientists

Lamark-

• If a characteristic was used a lot then it would become more developed. Lamark though these could be passes on to the offspring.
• People eventaully concluded that acquired characteristics could not be passed on as they dont have a genetic basis.

Most people accept Darwins theory as-

• No one can prove that this theory is wrong
• This theory offers a plausible explanation for many observations of plants and animals.

The carbon cycle-

• The whole thing is powered by photosynthesis
• Plants convert the carbon from CO2 into sugars, it is then changed to carbohydrates
• Eating passes carbon compounds in the plant to animals shown in the foodchain
• Plant and animal respiration release CO2 back into the air
• Plants and animals die and decay into bacteria and fungi in the soil producing CO2 from the respiration of decomposers
• Plants and animals are burnt at fossil fuels producing CO2

Recycling of Carbon-

• This takes longer in waterlogged soils as they dont have much oxygen and bacteria and fungi that decompose organic material need oxygen to work quickly. It also takes longer in highly acidic soil as the high pH slows the process down
• Many marine organisms have shells made of carbonates, when they die the shells create limestone rocks. The carbon in the rocks returns to the atmosphere during volcanic eruptions or when rocks are weathered down. The sea contains lots of CO2.

• The atmosphere contains 78% of nitrogen, this is very unreactive so can't be directly used by plants or animals.
• Nitrogen is needed for protiens for growth, organisms need it.
• Nitrogen in the air is turned to nitrates in the soil for use of plants.
• Decomposers break down protiens and urea into ammonia, this returns the nitrogen compounds to the soil
• Nitrogen fixation- turns N2 from the air into nitrogen compounds plants can use, there are two main methods- 1) The energy in lightning means teh nitrogen can react with oxygen to give nitrates. 2) Nitrogen fixing bacteria in roots and soil.
• There are 4 types of bacteria involved in the nitrogen cycle- Decomposers (decompose protiens and urea into ammonia), Nitrifying Bacteria (turns ammonia into nitrates), Nitrogen-Fixing Bacteria (turns atmospheric N2 into nitrogen compounds plants can use) and Denitrifying Bacteria (Turns nitrates back into N2 gas with no benefit to living organisms)

• The worlds human population is rising exponentially, this is putting pressure on the environment
• Global Warming- when fossil fuels, coal, oil and natrual gases are burned they release lots of CO2 which is a greenhouse gas which trap heat in the atmosphere causing the worlds temperature to rise. Scientists predict that if global warming continues the sea levels will rise, weather systems will become unpredictable and agricultural output will fall.
• Acid Rain- burning fossil fuels waste materials releases sulfur dioxide which reacts with water in the atmosphere to form sulfuric acid which falls as acid rain, this damages soil and kill trees. Acid rain causes lakes to become more acidic, many organisms are sensitive to changes in the pH meaning they die. Acid rain damages limestone buildings and statues.
• Ozone Depletion- CFC's break down ozone in the atmosphere allowing UV rays to reach the earth. Being exposed to UV increases the risk of skin cancer and kills plankton in the sea.

• Counting the amount off indicator species in an environnment can tell you if it is polluted or not. If a species that dies in polluted environments is present the environment muct be clean. Advantages of this- relatively cheap, quick and easy. Disadvantages- factors other than polluation can influence the survival of the species.
• The more lichen present the better the air quality as they are damaged by pollution
• The more mayfly lavae the better the water quality as they can't survive in polluted water
• The more sludgeworms present the more polluted the water.
• sensitive instruments are used to measure concentrations of chemical pollutants
• Satellite data can be used to indicate pollution levels e.g. CFC's depleting the ozone layer
• Non-living methods: Advantages- reliable, numerical data which is easy to compare. The exact pollutants can be identified. Disadvatages- more expensive equipment and expert knowledge.

If the following factors are below a critical level an animal is at risk of extinction-

• Number of habitats
• Number of individuals
• Genetic variation

Evaluating conservation programmes-

• Genetic Variation- the animal should have enough genetic variation to survive new diseases and cope with environmental change
• Viability of Populations- populations should be able to reproduce
• Available Habitats- plenty of suitable habitats
• Interactions Between Species- important for them to react as they would natrually

Conservation programmes- protect the human food supplies, ensure minimal change to food chains, provide future medicines (saving plants), cultural aspects (individual species may be important to a specific cultures heritage.