Food chains and food webs

In an ecosystem, feeding patterns are not usually simple. For example, mice will eat fruit and small insects as well as grass seed. The owl will also eat other prey. In any community of plants and animals, complex patterns will emerge. Many food chains will exist and some of these will be interlinked. These interlinked food chains are described as a food web.A food web for a simple pond community is shown in Fig. 3.

Fig. 3

Food production and ecosystems

Food production often involves the careful management of ecosystems.For example, in taking fish from the sea or from rivers, we must ensure that stocks do not fall below acceptable levels. Otherwise, the fish population may not be able to maintain its numbers and this would disrupt the network of food chains and food webs. Similar situations arise when we kill other wild animals, such as deer or pheasants, for food.

Food production may also involve the creation of artificial ecosystems.Examples of this are fish farms, arable farms, dairy farms and market gardens. In these examples, the ecosystems are not in balance. Very often there are far more animals or plants per hectare than would normally be the case and any predators are held at bay. This might involve fencing in animals or destroying the insects that feed on the plants. These artificial ecosystems place additional demands on farmers and gardeners. They need to:

• provide adequate supplies of food,

• provide adequate supplies of water,

• remove waste products such as manure and dead plants,

• prevent diseases in their animals and plants.

A healthier plant

Politicians around the world are meeting to discuss ways in which to safeguard our environment. The message is clear. Leaders in industry must find alternatives to create energy, other than traditional burning of 1…..such as coal. The laws governing the disposal of 2….. must be rigorously enforced. Governments must support projects to reduce our dependency on oil, and 3….. must decrease – our rainforests must be protected, not destroyed.

Many farming methods are also detrimental to our environment. Firstly, there is the 4….. of pesticides on local 5….. .If insects are killed to boost crop production, other creatures in the food chain risk elimination too. Secondly, these chemicals pollute the produce and the soil that crops grow in. If more farmers could be persuaded to use less intensive methods, 6….. farming methods for example, and consumers be persuaded to pay higher prices to support this move, agricultural dependency on poisonous chemicals would decrease dramatically.

As individuals, we can all help in a very particular way by 7….. materials such as glass, cans and paper. Collection bins such as 8….. and waste paper containers are becoming a more common sight, making it easier and more convenient to sort recyclable household waste for reprocessing.

Reducing our dependency on natural resources, and on petrol in particular, is vital. The increasing volume of traffic on our roads is one of the main contributors to the 9….. which is causing our planet to get warmer. We must all take responsibility for the alarming 10….. that this is having on the environment we live in.

Louis Pasteur

Pasteur (1822-1895) began his scientific career as a chemist, but it is because of his applications of germ theory to the prevention of disease that he became known as 'The Father of Microbiology'. Pasteur did not create germ theory, but he proved it to be correct. Once he had achieved this, he set about finding ways to prevent germs, the microorganisms present in the air, from infecting food and people.

He completed his famous experiment proving that microorganisms were present in the air while working for a wine company. He was trying to discover why wine sometimes went bad as it was being made. Once he had found the cause -microorganisms - he began to develop the process which carries his name - pasteurisation. It was perfectly possible to kill all the microorganisms in food by boiling it, a process known as sterilisation, but this damaged the taste and the quality of the food. Pasteur's process killed not all, but most, of the microorganisms, with the result that the food needed to be kept cool and eaten or drunk within a limited time. Most importantly, the quality of the food was not harmed by the process. Much of the food we eat today is pasteurised.

His next achievement was to build on the discovery of the British scientist Edward Jenner. Many years earlier, Jenner had discovered a way of giving people resistance to the deadly disease smallpox, by injecting them with a similar disease that was found among cows. The process became known as vaccination. Pasteur applied germ theory to his work and looked at samples of blood taken from healthy and infected animals. He grew bacteria in his laboratory and used it to infect animals. By chance, some of these germs failed to grow well in his laboratory; these weak germs were then used to infect some chickens. Although the chickens suffered at first, they made a complete recovery and could not be infected again. In this way, he discovered a way of increasing resistance to disease. Pasteur developed vaccines for many serious diseases including cholera and anthrax. At that time, these illnesses were certain death for anyone who caught them.

Pasteur's discoveries revolutionised work on infectious diseases. Pasteur's vaccines were different from Jenner's in one important way. Jenner found a weak form of smallpox and transferred it to humans. Pasteur weakened the disease in a laboratory and immunised people with that weakened form. His success allowed a colleague to develop the first vaccine for rabies, which Pasteur used to save the life of a nine-year-old boy. By this act, Pasteur's position as a hero was assured.

Thanks to the work of Pasteur, we now live longer, our food stays fresh longer and we are less likely to die of disease. Indeed, smallpox is no longer found anywhere in the world, due to a huge vaccination programme carried out in the 20^th century. This could never have happened without the scientific achievements of The Father of Microbiology.

Gregor Mendel

1. Gregor Mendel was born on 20^th July, 1822, and died on 6^th January, 1884. He was a biologist and botanist whose scientific research showed that inheritance proceeds according to certain scientific laws.

2. Mendel was a brilliant student and his family encouraged himto study, but they were very poor so Mendel entered a monastery in 1843. There he taught Mathematics, Physics and Greek to high school students. Eight years later, in 1851, the monastery sent him to the University of Vienna where he was able to continue his education. In 1853, he returned to the monastery and began teaching and researching again.

3. Mendel's theories of heredity based on his work with pea plants are well known to students of Biology. But his findings were so different from the accepted views on heredity at the time that his work was ignored until long after his death. His paper, Experiments in Plant Hybridisation, in which he described how traits were inherited, has become one of the most influential publications in the history of science.

4. Mendel was the first person to trace the characteristics of successive generations of an organism. In Mendel's day, a number of hypotheses had been suggested to explain heredity. The most popular one was the so-called blending theory. According to this theory, inherited traits blended from generation to generation. For instance, a red rose crossed with a white rose would, over time, produce a pink rose. Another theory put forward by Charles Darwin was called pangenesis. This stated that there were hereditary particles in our bodies, and that these partieles were affected by our actions. The altered partieles could be inherited by the next generation. These theories were disproved by Mendel.

5. The first thing he noticed when he began his experiments was that traits were inherited in research is being used to improve the way we live certain numerical ratios. This observation led him to come up with the idea of the dominance of genes and he tested itin peas. For seven years he crossed thousands of plants to prove the Laws of Inheritance. From his experiments, Mendel developed the basic laws of heredity. Those laws are the following: that traits do not combine, but are passed whole from generation to generation (which disproved the blending theory and Darwin's theory); each member of the parental generation passes on only half of its hereditary information to each offspring (with certain traits dominant over others); and different offspring of the same parents receive different sets of hereditary information.

6. Mendel's research formed the beginnings of the modern science of genetics. Genetic theory has had a huge impact on our lives. Many diseases, for example haemophilia, are known to be inherited, and family histories can be traced to determine the probability of passing on a hereditary disease. Scientists can now design plants that are easier to grow, or which can produce more food. This practical side of the results of Mendel's research is being used to improve the way we live.