[III] Biology - B3

The term SPECIES is used to mean a group of organisms that can breed together to produce fertile offspring; that is, offspring that are able to produce offspring themselves. Species are adapted to ensure that they survive in the environment in which they are living. We call the environment where an organism lives its HABITAT.

Being adapted to a habitat means that an animal or plant has features that help it to survive in that ecosystem. These might be physical features (like a crocodile's muscular tail for strong swimming) or ways of behaving (such as desert kangaroo rats sleeping during the hottest part of the day to keep cool). Organisms are adapted to live in their habitat in a huge variety of ways. 

In hot and dry conditions, cactus' are adapted. They have a thick, waxy cuticle to prevent water loss and spines instead of leaves to reduce the water loss and to discourage animals from eating it. Many cactuses have a stumpy shape which gives a smaller surface area : volume radtio, which reduces the amount of water lost. Very shallow and wide root systems to gather the maximum water when it rains.

In the coral reef, fins help to keep the fish upright and steady when swimming. Gills are the gaseous exchange surface, water passes over them and oxygen and carbon dioxide are exchanged. Different fish have different mouth positions depending on how they feed and many bony fish have a swim bladder to help to maintain their position.

It is not just the environment that affects the chances of an individual surviving. Organisms are also dependent on other species for their survival. They may depend on other species for food or for their habitat. Many species of insect, for example have habitats within or on particular plants.

In a particular habitat there will be COMPETITION between species for resources. Animals may compete for breeding sites or territories, food, mates or living space. Plants may compete for space, light, nutrients and water.

A FOOD WEB shows the feeding interactions of some of the species within a habitat. Most species will have feeding links with several other animals and plants within the habitat.

Because species depend on each other in many ways, any impact on one species within a food web will have a knock-on effect on many of the other species that are part of the same food web. Food web are extremely useful because they give us a visual representation of how species in a habitat depend on each other for survival. We call this INTERDEPENDENCE.

Interdependence means that all species in a food web have an influence on one another. 

The Siberian tiger and the Mountain gorilla have both suffered from the loss of or damage to their habitat and are at grave risk of EXTINCTION. When environments or habitats change, species that were previously well adapted have to make rapid changes to the way they live or they may become extinct. 

Many species are able to cope with small changes in their environment, such as perhaps breeding earlier as the weather becomes warmer earlier in the season. Some species are not able to cope with such changes. A large number of species are currently at risk of extinction because they are not able to respond quickly enough to changes in their habitat.

Species may become under threat if another species that competes with them, preys on them or causes disease is introduced into their habitat. A good example of such a threat it the Signal crayfish. It is extimated that 95% of the UK native crayfish population has been lost due to the introduction of this species from North America.

Another example of a species that was introduced into a habitat and subsequently had a devestating effect on the NATIVE SPECIES already present is the Cane toad. This NON-NATIVE  SPECIES was introduced into Australia deliberately to try to control the cane beetles on sugar cane. Once in Australia, they competed with native frogs for breeding and egg-laying sites. The toads soon reproduces and spread, reducing the populations of their prey.

The extinction of one organism in a habitat will have effects on all the other organisms in the food web. This is the case whether it is an animal, a plant or a microorganism that becomes extinct.

For example, if squirrels became more extinct, this would have effects on mouse, rabbit and bird populations. Although there might be more plants available for food, these remaining small animals would be predated upon more heavily by the foxes, hawks and owls. 

In chalk grassland, the Large Blue butterfly had a very specialised life cycle that depended on ants. The larvae of the butterfly were taken into ants' nests during the winter because they secreted a sugar solution that the ants fed from. This kept the larvae alive over the winter.

When the habitat was not grazed sufficiently, the grass became too tall for the ants to live beneath as it shaded the ground and reduced the temperature. The ants disappeared from the habitat and so the Large Blue butterfly larvae were not able to survive over winter. The Large Blue butterfly became extinct from the UK, but conservationists are now trying to re-introduce them.

You may think that you could live without the Sun's light. But it is not just the convenience of daylight we have to thank the Sun for. The energy it radiates powers the most important process on Earth - PHOTOSYNTHESIS.

The Sun is important to all of us. Nearly all organisms on Earth are dependent on the energy from the Sun for their survival. Without the Sun, there would be very little of life as we know it on Earth. We are all able to benefit from the energy of the Sun because of plants. Plants are able to absorb some of the energy in sunlight by the process of PHOTOSYNTHESIS.

Plants then store this energy in the carbon-based chemicals that make up their cells and tissues. Other organisms can get energy by eating plants. Almost every food chain begins with a plant absorbing energy from the Sun.

The energy plants absorb is used to power the process of photosynthesis; the reaction that uses water and carbon dioxide to make oxygen and glucose. The oxygen is released into the atmosphere, but the sugars can be stored by the plant as starch, a molecule made of many joined glucose molecules. When animals eat plants, this energy that has been absorbed by the plant and used to create glucose passes to the animal.

Not all the enrgy that plants absorb from the Sun can be stored. The plant needs to use some of the energy to reproduce and respire. Of the energy that is stored by the plant, not all is passed on to the animal that eats it. For example, there are parts of the plant that cannot be digested.

At each stage of a food chain, as energy is transferred from one organism to the next, some of that energy passes out of the food chain through: 

- heat as organisms use energy to respire, move and keep themselves war.

- waste products from excretion.

- uneaten parts such as stalks in plants and hair and claws in animals.

This energy cannot be used by the next organism in the food chain. The efficiency of the transfer of energy at each level of a food chain is the ration of the energy available in the organisms tissues (as food) to the total amount of energy the organism has ingested (eaten). 

PERCENTAGE EFFICIENCY = ENERGY IN TISSUES / ENERGY IN FOOD EATEN X 100%

Another important transfer of energy goes on after organisms have died. There are a very large number of organisms and microorganisms that feed on dead and decaying matter. Most of these DECOMPOSERS are bacteria and fungi, which release enzymes to break down organic matter before they digest it. Decomposers play an important role in recycling the nutrients in the ecosystem. Organisms called DETRITIVORES begin the decay process by breaking dead matter into smaller pieces and feeding on it (eg: earthworms and woodlice).

Carbon is the basis of the molecules we are made up of. It is continually recycled in the environment, in the CARBON CYCLE.

Carbon enters the carbon cycle as CARBON DIOXIDE in different ways:

- through COMBUSTION (burning)

- through RESPIRATION (when living things release the energy from food)

- through DECOMPOSITION (where dead animals and plants are broken down by microorganisms. Their carbon molecules can then become part of the cycle again).

Carbon is removed from the atmosphere when plants photosynthesise. They are able to "fix" the carbon from carbon dioxide so that it stored in their tissues.

In the past, the amount of carbon dioxide in the atmosphere was kept in balance by this natural cycle. Since industrialisation began in the western world, the amount of carbon dioxide in the atmosphere has been increasing. This contributes to global warming because carbon dioxide is a greenhouse gas.

As well as carbon, nitrogen is an essential component of living things, and this too is recycled in a process called the NITROGEN CYCLE.

Nitrogen is an important nutrient in animals' diets, in the form of nitrogen compounds in PROTEINS. Plants use NITRATES, which they absorb through their roots, to make proteins. The nitrogen compounds are passed along food chains when animals eat the proteins in the plants, and the animals eat other animals.

When animals excrete waste, nitrogen compounds are returned to the soil. When animals and plants die, the nitrates in their bodies are released in the process of decomposition, and pass back into the soil. Plants are then able to absorb these nitrates into their roots to make more proteins, and the cycle then begins again.

Plants absorb nitrates from soil through roots > Plants use nitrates to make proteins > Animals feed on proteins > Animals excrete waste > Nitrates are returned to soil > Plants absorb nitrates from soil through roots > Plants use nitrates to make proteins > Animals feed on proteins > Animals and plants die and decay > Nitrates are returned to the soil > Plants absorb nitrates from soil through roots.

Bacteria are a key part of the nitrogen cycle. Leguminous plants (peas and beans) have NITROGEN-FIXING BACTERIA in nodules on their roots. These bacteria, which are also present in the soil, are able to convert nitrogen gas, abundant in the air, which the plants can use to make proteins.

In waterlogged conditions, DENITRIFYING BACTERIA convert nitrates in the soil back into nitrogen gas, which enters the atmosphere. 

An important part of the work of scientists is to monitor environments to see whether they are changing. There are a variety of ways to check whether an environment has been changed, been damaged or improved over time. Both living and non-living indicators can be used to keep track of the changes in the environment.

NON-LIVING INDICATORS that scientists might monitor are the levels of carbon dioxide, the temperature, or the levels of nitrates in the water. Nitrates are found in fertiliser and are a common cause of pollution in waterways.

LIVING INDICATORS include organisms such as PHYTOPLANKTON (microscopic plankton that can photosynthesise), mayflies and LICHENS, which are very sensitive to the environment they live in.

Environmental change takes place on many scales, from chemical changes in local habitats like streams and rivers to global-scale changes such as the global increase in carbon dioxide in the atmosphere. Scientists monitor environmental change on all scales.

Non-living indicators can give scientists a good idea of the changes taking place in our environment. Measurements of carbon dioxide in the air, for example, have been rising over reacing years, leading to concerns about GLOBAL WARMING.

Living indicatiors give us very precise information on how a habitat is being degraded or whether the habitat is improving. Phytoplankton photosynthesise and are at the start of aquatic food chains, so any effect on the will have knock-on effects on the whole food chain.

Mayflies are insects that spend nearly all their lives in the water, only coming out briefly to mate and lay eggs. Mayflies need a high level of oxygen in the water and little pollution to survive.

Lichens absorb water and minerals directly from the air over their whole surface area, and so are very sensitive to levels of pollution in the air. Different lichens are sensitive to different types and levels of pollution. Air quality can be monitored by observing the communities of lichens that are able to grow.

Data from both living and non living indicators can be used to provide information about a habitat. Living indicators are particularly useful as they give us a view of what the environmental conditions have been like in a habitat over time.

Some organisms are very tolerant of some types of pollution, whereas other organisms may be very sensitive. The different sensitivites can be used to gauge the health of an aquatic environment. The organisms most sensitive to pollution are given a higher "score" than those less sensitive. A survey of the organisms present can then give a good indication of the health of a stream, river or pond. 

A site where a number of organisms are found that are very sensitive to pollution, for example, is likely to get a high score on the survey, indicating that it is un-polluted.

Long term studies of non-living indicators such as carbon dioxide levels or concentrations of chemicals can help us to see whether there are trends over time. If there are, action might be needed to protect the environment. 

Testing the nitrate or phosphate levels only gives a snapshot of the conditions at the time the sample is taken. However, using non-living indicators like this is cheaper and quicker.

Evidence shows that life on Earth began around 3500 million years ago. Most scientists agree that the first life forms were very simple. Over an immensey long period of time, these simple living thing changed to become all the species we see on Earth today. Many, many millions of species will also have become EXTINCT in that time.

FOSSILS are found in rocks. They are made from the dead bodies of plants and animals, or traces such as footprints, which became buried. Over millions of years, these remains turned to rock. It is possible to date fossils accurately because of the rock they are found in. Most of the animals and plants now found as fossils are extinct, but they give us very important information about how organisms changed over time, or evolved.

EVOLUTION has come about because of variation. Individuals within the same species are different. Some of these differences between individuals are due to the environment but some are due to the genes they carry. Variation that is caused by an individual's genes can be passed on to their offspring. 

Because of the shuffling of chromosomes, when eggs and sperm are produced, offspring of the same parents can be very different.

A mutation is a change in the genetic information in a cell, and can occur at random, sometimes during the process of copying the DNA for a new cell. Some mutations result in a change in the physical appearance or characteristics of an organism. If there is a mutation in a sex cell (an egg or sperm), this mutation can be passed on to the next generation. Such a mutation can cause variation between individuals. 

Sometimes this variation is an obvious difference in appearance. On other occasions a mutation may affect patterns of behaviour. Sometimes the outcome of a mutation has a useful effect for an organism that gives it a competitive advantage. For example, if a mutation occured that made an organism faster at running away fro predators, that organism might be more likely to survive to reproduce. This would increase the frequency of the gene for faster running in that population.

Scientists believe that the enormous variety of organisms we see around us came about because of EVOLUTION. Evolution is the change in the frequency of genes in a population over enormously long periods of time. Sometimes, genes change because of mutations. Some of these mutations are beneficial to the organism, but some are not. Some genes become more common over time, and some become less common. Some genes disappear from the GENE POOL altogether. As the frequencies of different genes varied over time and differently in different habitats, different species gradually emerged.

The theory of evolution is a good example of a scientific theory. It is based on data and observations, but scientists also need creative thought and a vision of how everything might fit together. The theory of evolution is based on the things we can observe around us, and what we have in the FOSSIL RECORD, which is the information from all fossils collected and recorded. Although the fossil record contains thousands of pieces of evidence that support the theory of evolution, not all parts of animals and plants from fossils, for example soft animals like jellyfish do not form good fossils. This means that scientists have had to accept that they are unlikely to find examples of certain species, but instead, draw conclusions about what they might have been like using their knowledge of other similar species. When new fossils are found, they fill in the gaps in our understanding of how life changed over time to become the animals and plants we see around us today.

Individuals of a species have variations that affect their physical appearance and behaviour. A differece in an individual can give it an advantage compared to others of the same species. This advantage may allow the individual to be more successful at reproducing, or more likely to survive to reproduce. If this advantage is due to a genetic difference, the individual will pass the advantageous genes on to the next generation. Less successful individuals are less likely to breed and pass their genes on. This means that in the next generation, more individuals will have this gene and thus more useful characteristics. This is NATURAL SELECTION

Humans have found ways to exploit the process shown by natural selection to their own advantage. If we want an animal with particular characteristics, we can choose two animals with characteristics nearer to these than is normal in the population and breed them together. The result will be an animal or plant with characteristics closer to those we want than in the previous generation. This is then repeated until the required characteristic is suffieiciently exaggerated. A good example is the way SELECTIVE BREEDING has been used is in the production of cattle. Different breeds of cattle have been selectively bred to have the "perfect" characteristics.

Natural selection is an important part of the evolutionary process. Evolution is the change in the frequency of genes in a population over enormously long periods of time. For example, a better camouflages animal might not be preyed upon as the predator would find it harder to see, and it would also have to spend less energy escaping from predators. The better camouflaged lizard might also find it easier to find food, as its own prey would be less likely to see it coming. These advantages make the lizard more likely to survive to reproduce, and it might therefore produce more offspring than other lizards. Thus its genes will occur slightly more often in the next generation than the genes of other lizards of the same species. The next generation will have more individuals with the genes for "better camouflage". If this is repeated for many thousands of generations, providing the genes continue to be advantageous, nearly all the members of the species will end up with the gene for better camouflage, and that will become "normal" for them.

Individuals of a species can vary due to MUTATIONS. These are changes in genes that affect the physical features or behaviour of an organism. The process of natural selection favours individuals who have the most useful traits, as these individuals are more likely to survive and pass their genes on to the next generation. Over a very long time, these genes are likely to become the norm in the population. This is how evolutionary change takes place.

The fossil record provides evidence for evolutionary change over very long periods of time. If there is enough pressure on a species, and the species reproduces very quickly, then evolution can also take place quickly. 

A number of factors influence the rate at which evolution takes place. If organisms are ISOLATED in their habitats, then natural selection will act independently on the two populations. Different genes are likely to become more frequent in different populations. 

Over time, this will lead to different species evolving in each location, no longer able to reproduce with each other. 

Environmental change can have huge effects on evolution. When the climate or habitat changes, species must adapt or die.

It is thought that all life on Earth evolved from simple forms of life that existed 3500 million years ago. From these simple life forms, an immense variety of new species evolved, suited to different ways of life and different habitats. As the environment changed, so did the species, and many also became extinct.

Scientists are able to determine how closely related organisms are to each other in evolutionary terms by analysing their DNA. More closely related organisms will have more genes in common. The relationship between all organisms can be shown in a diagram often called the "tree of life", as it is a tree-shaped diagram and has branching paths. 

The tree of life shows the relationship between all organisms, with those on the same branches being more closely genetically related than those further away. Such DNA analysis has allowed scientists to quite precisely pinpoint when different branching events took place.

These ideas about how life evolved allows scientists to explain all the observations that are seen in the fossil record. They also allow scientists to predict what intermediate forms of animals or plant might look like, which can then be checked when further fossils are found.

Organisms can be classified in many different ways. In the past, organisms were classified mainly by their appearance: scientists grouped organisms that looked similar together. Today we have a much more accurate way of classifying organisms, based on their DNA sequences.

Organisms with more similar DNA are likely to be more similar species. Classifying organisms in this way helps us to see how they evolved. A common ancestor is the most recent individual from which all organisms in a group are descended. Organisms with the most similar DNA have more recent common ancestors than those with less similar DNA.

The fossil record has given scientists a huge amount of evidence for evolution, and has also provided information about how species have evolved. The theory of evolution predicts a very clear pattern in the fossil record. We would expect simpler organisms to appear earliest and become grafually more complex. We would also expect the features of newer organiss to look like adaptations or developments of those of earlier organisms. This is exactly what we do see in the fossil record.

DNA analysis of organisms that exist today has confirmed predictions made based on the fossil record, for example predictions about when animals split off from each other to form different groups of species, and how long ago common ancestors were shared. Both the fossil record and DNA analysis of species give us strong evidence for evolution.

The theory of the origin of species by natural selection was originally proposed by Charles Darwin in 1859. He had taken a five-year voyage on a ship called The Beagle and it was on this expedition that he observed the animals and plants on a group of islands off South America called the Galapogos Islands. He noticed that the animals and plants were similar to those on the South American mainland, but had slight differences. One group proved very useful in developing his theory was the mockingbirds. He observed these and noticed that the birds were slightly different on each island. He collected specimens of the mockingbirds from different islands, which are not at the Natural History Museum in London. Darwin deduced that a species could change according to the conditions where it lived. He used his creativity to come up with an explanation for his observations, and he proposed the theory of evolution by natural selection. Other scientists later found that the finches on the Galapogos Islands also showed variation that gave good evidence for Darwin's theory.

A previous theory for evolution, proposed by a scientist named Jean Lamarck around 50 years earlier, was quite different. Lamarck suggested that the characteristics that organisms acquire in their lifetime, through use or development, could be passed on to offspring. This would mean that a giraffe, constantly stretching its neck to reach tall branches might develop a slightly longer or more flexible neck, and that this "long neck" characteristic might be passed on, and there was no good evidence for his ideas. It was plain that human parents who had developed particular characteristics during their lifetime did not pass these onto their offspring.

Darwin's theory could be explained using ideas about genetics that were only just beginning to be understood in Darwin's time, and current understanding of the way genes are passed on confirms that his theory makes scientific sense.

Tropical rainforests are being destroyed or damaged at a very fast rate. These habitats and others like them are very important for large numbers of species. Some of these species may be ones we have not yet discovered, but they could be very important for us as they may be useful for medicines or for food. 

Biodiversity is the word used to describe the variety of living things in the world. It includes the variety of different species (across all species of animals, plants, bacteria and fungi). Bacteria also refers to the GENETIC DIVERSITY (variation) within each species. Habitats such as tropical rainforests have high biodiversity - they contain a lot of species. It is important that the rainforests are protected.

Species are becoming extinct more rapidly now than at any other time in recorded history, except for the MASS EXTINCTION events seen in fossil record. It is though that human activity is driving species to extinction as they are hunted, and their habitats are broken up by roads or destroyed for building and farmland. Many species have become extinct without even being identified or classified.

Climate change, which is likely to lead to rising temperatures and more extreme events such as floods, droughts and storms will also accelerate the rate of extinctions, as habitats change more quickly than species can adapt to the changes. 

In order to record and monitor species accurately across the globe, scientists need to make sure they are all referring to the same species by the same name. A worldwide agreed system of classification helps to do this. Species that share characteristics specific to that group are put together. Some of these characteristics are visible, such as whether or not the organism has a skeleton, or what type of flower a plant has. Other groupings may depend on more detailed study of the organism, for example looking for similarities in DNA may help scientists decide to which group a species belongs.

There are different levels of classification that become more and more detailed as the levels progress from Kingdom to species. 

Kingdom > Phylum > Class > Order > Family > Genus > Species

(the order from biggest to smallest classifications).

Sustainability is finding a way of meeting our needs now without stopping future generations from meeting their needs. For example, the way we farm the land must leave it in a state that allows it to produce the same amount of crops in the future. With so many humans now living on Earth, ways must be found of limiting our impact on wildlife, habitats and environment that we all share and rely upon.

To increase our own contribution to sustainability we can reduce what we use, for example by choosing items with less packaging, re-using things that we have used before or that others no longer have a use for, and recycling rather than throwing away.

One important aspect of sustainability is the proptection of the environment. By maintaining important habitats for wildlife, we ca conserve a variety of different species and maintain biodiversity. Biodiversity is important for a number of reasons. One of these reasons is that the loss or extinction of only a few species can have a big impact on the whole ecosystem, causing it to break down and stop functioning as it previously did.

To ensure sustainability, we need to maintain ecosystems. Maintaining BIODIVERSITY is an important aspect of this. 

A widespread cause of the loss of biodiversity is INTENSIVE CROP PRODUCTION. Intensive crop production involves the large-scale planting of one type of crop, called monoculture. Often hedgerows and other areas of vegetation at the sides of the field are removed in order to increase the space for the crops. Farming in this way enables the farmer to make use of machinery available to plant, maintain and harvest the crop, and maximises yield and profit. Such farming methods have negative effects on BIODIVERSTY and are not sustainable. 

When a large area of only one crop is grown as a monoculture, the land will support very few other species. The application of pesticides and weed killers further reduces the numbers and diversity of other organisms that the farmland can support.

Scientists have identified the negative impacts that intensive crop production has had on biodiversity on farmland. They have worked to find ways to increase the biodiversity on farmed land, and some of these strategies have been very effective.

Beetle banks at the sides and within the crop provide a habitat for beetles that PREDATE on aphids that would otherwise damage the crop. As well as increasing the biodiversity, this can also lead to a reduction in the amount of pesticide that needs to be used. Farmers are also being encouraged to maintain hedgerows to support biodiversity on their farms.

Advances in science and technology can have unexpected effects. Before about 1950, for example, disposable nappies did not exist. Parents would use folded squares of absorbent cloth as nappies on their babies, and these cloth nappies would be soaked in disinfectant and washed daily. Modern disposable nappies with self sticking tapes at the sides were first available in the 1970s. They made life easier for millions of parents around the world and they are soft and comfortable for babies. They contain a super-absorbant polymer to make sure they do not leak.

But disposable nappies have a significant disadvantage. They create huge amounts of waste that does not easily decompose. Eight million disposable nappies are thrown out everyday. It has been estimated that a disposable nappy could take 500 years to break down in a landfill site. Modern washable nappies are now available that are easy to use and comfortable for babies. But there is debate about whether they are actually better for the environment than disposable nappies, as so much energy is needed to wash and dry them in modern machines.

The use of BIODEGRADEABLE packaging has also become popular for some products including plastic carrier bags. This biodegradeable materials, however, breaks down to release carbon dioxide. In landfill sites, this decomposition process ca take a long time. Also, those that are biodegradeable still use energy in their manufacture and in the transport needed to get them to their place of use. Cutting down or omitting packaging is more sustainable than reducing waste.

There are a number of ways to improve sustainability when products are manufactured. The most sustainable products are produced with little energy, using locally available materials and create little pollution in their manufacture. If transporting the ingredients or the final product can be avoided, this increases the sustainability of a product. The way that products are packaged and the packaging materials used have a big impact. Minimal packaging, or the re-using of packaging, increases the sustainability of a product.

When looking at the sustainability of an item, it is important to consider the whole LIFE CYCLE of the product, from manufacture to disposal. 

Something that is very sustainable in manufacture could need a lot of energy in its disposal, which would reduce its overall sustainability.

The life cycle assessment of a product tracks its environmental impact from sourcing the raw materials, through manufacture, transport to distribution centres, usage and then disposal.

Sourcing materials > Manufacture > Transportation > Usage > Disposal.