Biology QWC's

Eutrophication is when excess Fertilisers (Nitrates) or waste sewage runs into lakes/streams/rivers from the soil by the rain.

The increase in nutrients encourages microsopic plants to grow (algae,) these plants will cover the surface of the water blocking the sunlight from the plants that live deeper in the water.

The plants at the bottem of the water die due to the fact they can't photosynethesis and the algae have short lives, so bacteria decompose the all decaying plants.

Bacteria respire alot of oxygen, so the oxygen level in the water falls rapidly. This then causes the fish to die due to the lack of oxygen in the water.

The scientist who came up with the ideas of the Theory of Evolution and Natural Selection was Charles Darwin. Evolution is random & usually happens by accident.

First there is always variation (difference in the individuals in a species) due to a mutation in a gene or a change in DNA. This means that a different protein is being made.

This variation is an advantage as it lead to the organims adapting to it's environment and the survival of the fittest. The organisms that survive pass on their benifical mutation to their offspring which will lead to evolution.

The organisms that survive and pass on the gene are selected for Natural Selection, while the ones who die are selected against Natural Selection & may die out and become extinct.

Examples of this happening is with the Peppered Moth and the Warfarin resistance in rats.

Nitrogen in the air are fixed by Nitrogen-fixing-bacteria and converted into Nitrates. These Nitrates are absorbed by the soil and then absorbed by the plants.

The plants are then eaten by animals and the Nitrates become proteins for growth.

When the animals & plants decay the protein and urea are decomposed by bacteria/microbes and converted into ammonium compounds with the enzyme, urease.

Then Nitrifying bacteria convert the ammonium compounds back into Nitrates in the soil.

Also De-nitrifying bacteria work against the Nitrogen cycle by converting the Nitrates into Nitrogen in the air.

Everything with life on this planet is carbon-based & there is a fixed supply on this planet.

For life to survive, it is essential that this carbon is recycled. This is done by the carbon cycle.

The carbon (dioxide) in the atmsphere is extracted and converted into glucose for the green plants in a process called photosynethesis. The plants can then respire the carbon dioxide back into the air or be fed on by animals and the carbon transferred to the animals. Also the animals can respire the carbon dioxide into the air.

Both the animals & plants will die which will provides materials for micro-organisms to feed on, & they resprie carbon dioxide back into the air.

Finally the combustion of fossil fuels will lead to an increase in carbon dioxide which can lead to global warming.

Decay is the break down of material through the action of miro-organisms (bacteria & fungi.) The material decayed maybe waste from organisms, dead bodies of plants or animals, or material from living organisms which humans use for food.

Decay is good as-

• waste & dead are broken down, & so don't build up in the environment
• the nurients in the waste & dead are released back into the environment. If decay is prevented then important chemicals can be locked into dead material. This has happened with the formation of fossil fuels, which were formed in conditions which prevented decay.

Decay can be inconvenient as -

• the micro-organisms use up oxygen & respire carbon dioxide, this is can sometimes deprive other organisms of the oxygen they need
• decay of food is a nuisance to humans

Useful materials that are released by decay (carbon, nitrogen & phosphorus) can be taken up by other organisms. This results in nutrient cycles. In a stable community, the process which remove materials are balnced by others which return materials.

Negative Feedback will control the systems tht keep such conditions constant (keep the body in homeostasis.)

An example of Negative Feedback is how it controls the blood sugar levels in the body.

The levels of glucose in the blood is monitored by the pancreas. Negative Feedback is when; if the blood sugar levels rise, the pancreas will release insulin (hormone) which will convert glucose to glycogen which is stored in the liver, the levels return to normal.

Howver if the blood sugar levels fall, the pancreas will produce another hormone called glucagon which will convert glycogen to glucose; which is then released into the bloodstream increasing blood sugar levels.

Genetic Modification is transfering a gene from one organism to another organism, for example placing the herbicide resistant gene in the soya bean plant.

To do this the herbicide resistant gene is cut out of the DNA. The DNA of the soya bean is cut & the herbicide resistant gene is transferred into the soya bean DNA using enzymes.

The soya bean is now resistant to herbicide so it will not be kiled by herbicide & this means you can get a higher yeild because there is less competition from other plants.

Different organisms can affect a population due to the relations between the predator and its prey, this can be shown in Predator-Prey graphs.

The predator is the organism that hunts and kills other organisms, which is what the prey is. For example; the predator would be the fox and the prey would be the rabbit.

If the population of the prey (rabbit) increases then the population of the predator (fox) will rise as well as there is more food for it to eat. When there is too many predators, the population of the prey will deacrease as they are being hunted. Then this will cause the predator to decrease as there is no prey to eat.

Intensive farming is using chemical & animals indoors to try and produce the highest yeild.

Fertilisers will introduce more nutrients making a bigger yeild, however it causes eutrophication.

Pesticides & insecticides kill insects so there will be more yeild, but it causes a reduction in biodiversity and bioaccumulation which is the build up of chemicals in the food chain.

Herbicides will stop competion between the crop and the weeds by killing the weeds & making a bigger yeild of the crop, but this too causes a loss in biodiversity & bioaccumulation.

Battery Farming is keeping the animals indoor so they grow quicker as less energy is lost in keeping the animals warm, however this is cruel and disease and pollution can spread quicker.

Disease control will kill the diseases so the animals don't fall ill but it does cause pollution

The sun is the ultimate source of energy and all food chains. It prodives light energy for the plants & the plants produces chemical energy (glucose) from the light, and therefore are the producers of every food chain.

Herbivores are the primary consumers and they eat the plants. Carnivores are the secondary and tertiary consumers and they eat the animals.

There is never more than 4 of 5 different energy levels in a food chain because a lot of enery is wasted when animals respire, move, use energy to keep warm and energy is lost into the waste of the animals.