Science B2.

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Grouping organisms.

-All organisms are classified into a number of different groups:

Kingdom, Phylum, Class, Order, Family, Genus, and Species.

-As you move towards species there are fewer organisms within each group, they also share more similarities.

Organisms can be classified in two ways:

-An artificial system is based on one or two characteristics that make indentification easier.

E.g. Birds that alwasy live by the sea can be called seabirds.

-A natural system is based on evoltionary relationships and is much more detailed.  Animals that are more closely related are more likely to be in the same group.

Sequencing the bases in DNA has enabled sciencists to know much more about how closely related organisms are, and has meant that organisms can be reclassified.

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

All organisms are named by binomial systems. The systems work like this:

-There are two parts to the name, the first is the genus, and the second is the species.

-The genus part starts with a capital letter; the species starts with a lower case letter.

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Problems with classifying.

Difficulties when classifying:

-Living things are at different stages of evolution.

-New organisms are being discovered all the time.

Therefore it is difficult to place the organisms into distinct groups.

Some organsims have characteristics that would put it into two groups, e.g. a Aecheaopteryx:

-It has feathers, like a bird.

-It also had teeth and a long bony tail, like a reptile.

Some organisms present specific problems:

-Bacteria, do not interbreed, the reproduce asexually, so cannot be classified into different speciies using a ferile offspring idea.

-Mules are hybrid, produced when members of two species (a donkey and a horse) interbreed. Hybrids are fertile, so mules can be classified as a species.

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Classification and evolution.

Organisms that are grouped together are usually closely related and share a recent common ancestor.

However, they may have different features if they live in different habitats.

When classifying organisms, it is important to bear in mind that similarities and differences between organisms may have different explanations:

-Dolphins have similarities to fish because they live in the same habitat (ecologically related). However, they are classified differently - dolphins are mammals.

-Dolphins and bats have evolved to live in different habitats, but both are mammals- they are related through evolution.

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pyramids of biomass.

Pyramids of numbers and pyramids of biomass can both be used to represnt feeeding relationships between organisms in a food chain or web.

Pyramids of biomass show the dry mass of living material at each stage of a food chain.

They may look different to pyramids of numbers if:

-Producers are very large

-A small parasite lives on a large animal.

Although pyramids of biomass are a better way of representing trophic levels they are difficult to construct. Because:

-Some organisms feed on organisms from different trophic levels.

-Measuring dry mass is difficult as it invoves removing all the water from an organism, which will kill it.

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Energy flow.

As energy flows along a food chain some is used for growth. However at each trophic level much energy is transferred into other forms, such as: Heat from respiration, Egestion, Excretion. 

The material that is lost at each stage of the food chain is not wasted. Most of the waste is useful by decomposers that can then start another food chain.

Because each trophic level 'loses' up to 90% of the available energy, an animal at the end of a long food chain does not have much food available to it.

The efficiency of energy transfer can be calculated between trophic levels:

energy used for growth =

     energy input                    

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The carbon cycle.

Carbon is found in living organisms.

Carbon needs to be recycled so it can become available again to other living organisms.

Carbon dioxide is removed from the air by photosynthesis in plants.

Feeding passes carbon compounds along a food chain web.

Carbon dioxide is released into the air by:

-Plants and animals respiring, Soil bacteria and fungi acting as decomposers, The burning of fossil fuels (combustion).

Carbon dioxide is also absorbed from the air by oceans.

Marine organisms make shells made of carbonate, which become limestone rocks.

The carbon in limestone can return to the air as carbon dioxide during volcanic eruptions or weathering.

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The nitrogen cycle.

Plants take in nitrogen as nitrates from soil to make protein for growth.

Feeding passes nitrogen compounds along a food chain or web.

The nitrogen compounds in dead plants and aniamls are broken down by decomposers and returned to the soil.

A number of microorganisms are responsible for recycling nitrogen:

-Decomposers are soil bacteria and fungi and they convert proteins and urea into ammonia.

-Nitrifying bacteria converts the ammonia to nitrates.

-Denitrifying bacteria convert nitrates to nitrogen gas.

-Nitrogen- fixing bacteria living in root nodules (or in the soil) fix nitrogen gas - this also occurs by the action of lighting.

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Keeping decomposers working.

For decomposers to break down dead material in soil, they need oxygen and a suitable pH.

-Decay will therefore be slower in waterlogged soils as there will be less oxgyen.

-Acidic conditions will also slow down decay.

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Similar animals living in the same habitat compete with each other for resources.

If they are memebr of the same species they will also compete with eachother for mates, so they can breed.

An ecological niche describes the habitat that an organism lives in and also its role in the habitat. 

Organisms that share similar niches are more likely to compete, as they require similar resources.

Competition can be interspecific or intraspecific:

-Interspecific is between organisms of different species.

-Intraspecific is between organisms of the same species and is likely to be more significant as the organisms share more similarities and so need the same resources.

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Predator- prey relationships.

Both predator and prey show cyclical (ups and downs) in their numbers. This is because:

-When there are lots of prey, more predators survive and so their numbers increase.

-This means that the increased number of predators eat more prey, so prey numbers drop.

-More predators starve and so their numbers drop.

The predator peaks occurs soon after the peak of the prey. This is because it takes a little while for the increased supply of food to allow more predators to survive and reproduce.

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Parasitism and mutualsim.

As well as competing with each other or eating each other, organisms of different species can also be dependant on each other in other ways.

Parasites feed on or in another living organism called the host.

-The host suffers as a result of the relationship.

-Fleas are parasites living on a host (which may be human).

-Tapeworms are also parasites feeding in the digestive system of various animals.

Sometimes both organisms benefit as a result of their relationship. This is called mutualism.

-Insects visit flowers and transfer pollen, allowing pollination to happen. They are rewarded by sugary nectar from the flower.

-On some coral reefs 'cleaner' fish regularly visited by larger fish. The larger fish benefit by having their parasites removed by the cleaner fish and the cleaner fish gain food.

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Parasites and mutualism 2.

Pea plants and certain types of bacteria also benefit from mutualism. Pea plants are legumes with structures on the roots called nodules.

In the nodules lives nitrogen-fixign bacteria.

-The bacteria turn nitrogen into nitrogen-containing chemicals and give some ot the peas.

-The pea plant gives the bacteria some sugars that have been produced by photosynthesis.

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Adapting to the cold.

Some animals are adapted to living in very cold conditions.

They keep warm by reducing heat loss. Some have anatomical adaptations to help reduce heat loss, so : They have excellent insulation to cut down heat loss. They arctic fox has thick fur that traps plenty of air for insulation. 

-These animals are usually quite large, with small ears. This helps to reduce heat loss by decreasing the surface area to volume ratio.

Animals may try to avoid the cold by changing their behavior. Some Migrate long distances to warmer areas. Others slow down all their body processes and hibernate.

Penguins have a counter current heat exchange mechanism to help reduce heat loss. The warm blood entering the flippers warms up the cold blood leaving, to stop it cooling the body.

Other organisms that live in cold climates may have biochemical adaptations, such as antifreeze proteins in their cells.

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Adapting to hot, dry conditions 1.

To increase heat loss, animals adapt a variety of ways.

-Some are anatomical adaptations, for example camels increase the loss of heat by having very little hair. 

-Animals that live in hot areas are usually smaller and have larger ears than similar animals that live in cold areas.

-These factors give them a larger surface area to volume ratio, so they can lose more heat.

-Other adaptations to lose more heat are behavioural, for example they seek shade during the hotter hours around the middle of the day.

To cope with dry conditions, organisms have behavioural, anatomical, and physiological adaptations. For example:

-Camels can survive with little water as they produce very concerntrated urine.

-Cacti reduce water loss, as they have very long roots, and ca store water in the roots.

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Adapting to hot, dry conditions 2.

Organisms that can survive in hot conditions are called exremephiles. Some bacteria can live in hot springs as they have enzymes that do not denature at temperatures as high as 100 degrees C.

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Specialists and generalists.

Some organisms, like polar bears, are called specialists, as they are very well adapted to living in specific habitats.

Others for example rats, can live in several habitats.

-These organisms are called generalists.

-They will lose to specialists in certin habitats.

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Charles darwin and natural selection.

Over 150 years ago Charles darwin wrote his theory of natural selection, to explain how evolution might happen.

It says that if animals and plants are better adapted to their environmnet, they and the follwong generations are more likely to survive.

Although he was unsure of how adaptations were passed on, we now know that when organisms reproduce, their genes are passed on ot the next generation.

Natural selection is now summarised like this:

-Within any species there is variation.

-Organisms produce more young than will survive, so there is competition for resources.

-Only the best adapted will survive (survival of the fittest).

-Those that survive pass on successful adaptations to the next generation.

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Charles Darwin and natural selection 2.

Over time, the changes produced by natural selection may result in new species.

-This only happens if different groups of organisms cannot mate for a long time.

-The organisms might be prevented from mating because they live in different areas (geographical isolation). They might be prevented from mating because of behavioural isolation. 

-If each group evolves differently they might over time become differet enough to be classified as seperate species.

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Modern example of natural selection.

Natural selection is difficult to study as it usually takes thousands of years to see the effect. Some examples have been studied over shorter time spans:

-More and more bacteria are developing resistance to antibiotics.

-Peppered moths are dark or pale in colour. Dark moths are better camouflaged in polluted areas, so more of them survive.

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Arguments over natural selection.

At first many people disagreed with darwins ideas:

-Some people thought he didnt have enough evidence to back up his theory.

-Many people disagreed because they thought God had created all species.

Now darwins theory is more widely accepted, because:

-It explains lots of observations.

-It has been discussed and tested by a wide range of scientists.

There have been many attempts to explain evolution. Before Darwin Jean Baptiste de Lamarck had a theory that, for example, giraffes acquired long necks to feed, and this characteristic was passed on. This was called the law of acquired characteristics.

As we have discovered more about genes and how they are passed on, therories like Lemarcks have been proven incorrect and Darwins more widely accepted.

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There are many different types of pollution. Three that have caused much concern are:

-Carbon dioxide, from increased burning fossil fuels, which may increase the greenhouse effect and global warming.

-CFC's, from aerosols, which destroy the ozone layer.

-Sulfur dioxide, from burning fossil fuels, which cause acid rain.

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Pollution and population.

The human population of the world is growing at an ever-increasing rate (exponential growth).

This growth in population is happening becasue the birth rate is exceeding the death rate.

The greatest rise in the worlds population figures is occuring in under-developed land masses (Africa and India). 

However the developed world uses the most fossil fuels (USA and Europe).

The amount of pollution is caused per person or organisation is called the 'carbon footprint'. This measures the total greenhouse gas given off by a person or organisation within a certain time.

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Measuring pollution.

Pollution in water or air can be measured using direct methods or by indicator organisms.

Direct methods include oxygen probes attached to computers that can measure the exact levels of oxygen in a pond. Special chemicals can be used to indicate levels of nitrate pollution from fertilisers.

The presence or absence of an indicator species is used to estimate levels of pollution. For example:

-The mayfly larva is an insect that can only live near water.

-The water louse, bloodworm and mussels can live in polluted water.

-Lichen grows on trees and rocks but only when teh air is clean. It is unusual to find licehn growing in cities, because it is killed by the pollution from motor engines.

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Measuring pollution 2.

There are advantages to the different methods of measuring pollution:

-Using indicator organisms is cheaper, does not need equipment that can go wrong and monitors pollution levels over long periods of time.

-Using direct methods can give more accurate results at any specific time.

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Conservation: trying to preserve the variey of plants and animals and the habitats that they live in. This is important because: -Protects food supplies.

-Prevents any damage to food chains, which are difficult to predict.

-Protects plants and animals that might be useful for medical uses.

-Protects organisms and habitats that people enjoy to visit and study.

Species are at risk of extinction if the number of individuals or habitats falls below critical levels. 

When trying to conserve species the important factors are:

-The size of the population (if the population is below a critical level there is unlikely to be enough genetic variation in the population to enable it to survive).

-The number of suitable habitats that are available for the organism to live in.

-How much competition there is from other species.

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Sustainable development.

Sustainable development means taking enough resources from the environment for current needs, while leaving enough for the future and preventing permanent damage. For example:

-Fishing Quotas are set, so that there are enough fish to breed.

-Woods are replanted to keep up the supply of trees.

As the world population increses it is crucial to carry out sustainable development.

-Fossil fuels will run out. As there is an increase in demand for energy, we must manage alternative fuels, such as wood.

-We need to supply increasing amounts of food for growing populations without destroying large areas of natural habitats.

-Large amounts of waste products must be disposed of to prevent or minimise pollution.

If all of this is acheived it should help to save endangered species.

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