Biology

All organisms are classified into a number of different groups, starting with their kingdom and finishing with their species.

The group are; kingdom, class, order, family, genus and species.

As you move down towards 'species', there are fewer organisms within each group and they share more imilarities.

Organisms can be classified in two ways;

- an artificial system is based on one or two characteristics that make indentification easier, for example birds that always live by or on the sea can be called sea birds. & -a natural system is based on evolitionary 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 scientists to know much more about how closely related organisms are, and has often meant that organisms can be re-classified.

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

all organisms are named by the binomial system. The sytem works like this;

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

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

Living things are at different stages of evolution, and new ones are being discovered all the time. This makes it difficult to place organisms into distinct groups. An example of this is Archaeopteryx. This creature had characteristics that would put it into two different groups;

-it had 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, they reproduce asexually, so they cannot be classified into different secies using the 'fertile offspring' idea.

Mules are hybrids, produced when members of two species (a donkey and a horse) interbreed. Hybrids are infertile, so mules cannot be classed as a species.

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.

Pyramids of biomass can both be used to represent feeding relationships

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 mammal

Although pyrmids of biomass are a better way of representing trophic levels they are difficlut to construct. This is because;

-some organisms feed on organisms from different trophic levels

-measuring dry mass is difficult as it involves removing all the water from an organism, which willl kill it.

As energy flows along a food chain some is used in growth. However, at each trophic level much of the energy is transferred into other, less useful 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 used by decomposers that can then start another food chain.

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

The effiiciency of energy transfer can be calculated between trophic levels;

energy used for growth ,divided by, energy input

Carbon is one of a number of elements that are 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 or 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.

Plants take in nitrogen as nitrates from the soil to make protein for growth. Feeding passes nitrogen compounds along a food chain or web. The nitrogen compounds in dead plants and animals are broken down by decomposers and returned to the soil

A number of microorganisms are responsible for the recycling of nitrogen;

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

-nitrifying bacteria convert the ammonia to nitrates

-denitrifying bacteria convert nitrates to nitrogen gas

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

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

-decay will therefore be slower in waterlooged soils as there will be less oxygen

-acidic conditions will also slow down decay

Similar animals living in the same habitat compete with eachother for resources (e.g food).

If they are members of the same species they will also compete with each other for mates so they can breed.

An ecological niche describes the habitat that an organism lives in and also its role in the habitat. For example, ladybirds live on trees such as sycamore and eat greenfly.

Organisms that share similar niches are more likely to compete, as they require similar resources. The harlequin ladybird arrived in Britain in 2004 and competes strongly with native ladybirds.

Competition can be interspecific and 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.

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

-when their 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 occur soon after the peaks 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.

As well as competing with each other or eating each other, organisms of different species can also be dependent 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 systems of various animals.

Sometimes both organisms benefit as a result of their relationship, this is called mutualism. -insects visit flowers and so transfer pollen, allowing pollination to happen, they are 'rewarded' by sugary nectar from the flower. - on some coral reefs 'cleaner' fish are regularly visited by larger fish,the large fish benefit by having their parasites removed by the cleaner fish and the cleaner fish gain food, --- Pea plants and certain types of bacteria also benefit from mutualism, pea plants are legumes with structures on the roots called nodules, in these nodules live nitrogen-fixing bacteria. - the bacteria turn nitrogen into nitrogen-containing chemicals and give some to the pea.-the pea plant gives the bacteria some sugars that have been produced by photosynythesis

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. The arctic fox has thick fur that traps plents of air for insulation. Seals have thin fur but a thick layer of fat (blubba) under the skin.

These animals are usually quite large, with small ears, this helps to decrease heat loss by decreasing the surface area to volume ratio,

Animals may try to avoid the cold by changing their behaviour, 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.

To increase heat loss, animals adapt in a variety of ways;- some are anatomical adaptions, for example camels increase the loss of heat having very little hair on the underside of their bodies. Animals that live in hot areas are usually smalled and have larger ears than similar animas that live in cold areas. these factors give them a larger surface area to volume ratio,so that they can loose more heat. - other adaptions to lose more heat are behavioral, such as panting or licking their fur.

To reduce heat gain, animals may change their behaviour, for example they seek shade during th hotter hours around the middle of the day. - To cope with dry conditions,organisms have behavioural, anatomical and physiological adaptions for example; - camels can survive with little water because they can produce very concentrated urine, - cacti reduce water loss because their leaves have been reduced to spines, they also have deep roots and can store more water in the stem.

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

Some organisms, like polar bears, are called specialists, as they are very well adapted to living in specific habitats. They would struggle to live else where,

Others , for example rats, can live in several habitats.

-these organisms are called generalists

-they will lose to the specialists in certain habitats.

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 enviroment , they and the following generations are more likely to survive. He did not know exactly how adaptations were passed on. We now know that when organisms reproduce, their genes are passed on to the next generation.

The modern version of natural selection can be summarised like this, -within any species there is variation, -organisms produce far more young than will surive, so there is competition for limited resources such as food, -only those best adapted will survive, which is called survival of the fittest., -those that survive pass on successful adaptations to the next generation in their genes.

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.This is geographical isolation.They might be prevented from mating because of behavioural isolation,- if each group evolves differently they might over time become different enough to be classified as seperate species.

Natural selection is difficult to study because 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,