B3C3P3 Revision

B3 - Variation Variation in a species can be caused by genetic variation (e.g. Eye colour) or Environmental Variation (e.g. Hair dye). Lots of evidence has been collected towards Evolution (e.g. Fossil records) which suggests that creatures have slowly changed over millions of years. Evolution was first proposed by Charles Darwin. Some people do not believe the evidence for Evolution and have their own theories, e.g. Religious ideas about creation. Scientists continue to look for evidence.

Selective Breeding Farmers have used selective breeding for many years – taking the strongest, tallest, bushiest plants and breeding them together to make the species stronger. Natural selection is where the fittest/strongest/tallest survive and pass on their genes, e.g. The fastest antelope escape the lions and so survive to reproduce so the offspring are more likely to be fast runners too.

Mutations When genes are copied during reproduction, mistakes can be made. These mistakes produce differences in a species and sometimes they can be harmful and sometimes beneficial.

Where did life come from? Scientists are still gathering evidence. There are 2 main theories:- 1. Life started elsewhere in the solar system and came here on a meteorite. 2.Life started at the bottom of the oceans There are also religious theories.

Senses Parts of your body communicate with each other in one of two ways:- 1. Nerve cells (neurons) carry electrical impulses and have a fast response time 2. Hormones are carried in the blood, e.g. Adrenalin is made to make your muscles work harder when you are scared. Hormones are slower to respond than nerves but last longer.

Nervous System A receptor in your skin detects a stimulus. A nerve impulse is sent to your central nervous system which coordinates all the information and decides how to respond. A nerve impulse is sent to the appropriate muscle to make it move.

Extinction Many animals have become extinct and humans have to work hard to save others. Humans can easily destroy habitats or food sources of endangered species.

C3 – Food Matters Farmers have to grow crops against many challenges:- Pests like weeds which can block light and insects which can eat plants, fungi and viruses which can damage crops. Should they use Pesticides which can harm the natural food chain by killing off one whole part of it? Keeping the right chemical nutrients in the soil (fertilizers needed but these could damage the environment when they get washed into the soil and affect natural ecosystems)

The Nitrogen Cycle

Organic Farming Organic farmers do not use pesticides and chemical fertilizers. They try to use traditional methods to grow crops such as: Use animal manure not fertilizer Rotate their crops as different crops take different nutrients from the soil Use natural predators to control pests, not chemical pesticides These measures make organic food more expensive but it is sustainable. There is not enough evidence yet to say whether Organic Food is healthier than food produced by Intensive Farming.

Preserving and Processing Food Preservatives are added to food to make them last longer. Antioxidants stop oxygen in the air from making food go off. Food additives such as Colouring, Flavouring and Sweeteners help to make the food more attractive and tasty for consumers. Emulsifiers help to mix ingredients that would normally separate such as oil and water. Stabilizers help to stop these ingredients from separating again.

Digestion Your body needs Carbohydrates, Fats, Minerals, Vitamins, Proteins and Water to survive. Fibre in food helps your body to push food through the digestive system. Quite a lots of food has long chain polymer molecules which cannot be absorbed into your bloodstream. Your digestive system breaks the long chains into smaller ones which can pass through your gut wall into your blood, ready to be used by your body.

Excretion Your body cannot store amino acids so they are broken down in your liver to produce a toxic chemical called urea which your kidneys filter out of your blood and add water to make urine.

Diet and Diabetes In the western world, processed foods have become easily available. These contain simple carbohydrates which get into your blood quickly, leaving you hungry for more. This has led to a large rise in obesity in the population in the last few years. Obesity increases the risk of heart diseases. Diabetes occurs when the pancreas is not producing enough insulin so the amount of glucose in your blood remains high. Type 1 diabetes is more common in young people. Type 2 diabetes can start to occur during life and is slightly different to Type 1 – the pancreas is still producing insulin but the cells in the body no longer respond normally to the insulin. Being overweight is a risk factor for developing Type 2 diabetes, along with genetics and age.

Food Safety In the UK, the Food Standards agency monitors all food production and has introduced clear labelling that manufacturers must use. The Precautionary Principle – if there is not quite enough evidence to confirm that there is a definite risk from a food or a chemical in food, but a risk is suspected, then the risk should still be acted upon.

P3 – Radioactive Materials Nuclear Power produces about 20% of the UK’s electricity. A radioactive fuel gives off heat in a reactor. This heats water to make steam which spins turbines which then spin generators to produce electricity. Nuclear Power does not burn fossil fuels so is seen as a ‘clean’ way of producing electricity. The main problem with nuclear power is that the waste fuel will remain radioactive for millions of years and has to be buried. Other people are worried about the safety in Nuclear Power stations – there have been a couple of major accidents in the past which have released radioactive material into the environment and killed people and wildlife, e.g. Chernobyl in 1986.

Radioactivity is natural! There is ionizing radiation all around us. Even your body is slightly radioactive! However, there are some highly radioactive sources such as Radon Gas which is found naturally in the ground in some areas of the UK. Scientists calculate your dose of radiation from various sources so you can make a decision once you know the Risks. There is no such thing as a safe dose or zero risk – the ionizing radiation coming from just one radon atom might cause one of your body’s cells to mutate and become cancerous.

Alpha Radiation Radon gives off Alpha Radiation which is the most harmful type because it is highly ionizing. This means that if it is absorbed into your body it will cause most harm to your cells. But the good news... Alpha Radiation only travels a short distance in air (a few cms) and absorbed by almost all materials, even clothes or paper, so it is easy to stop.

Medical Radiation Doctors may give you a scan where they deliberately inject a radioactive material into your body that gives out gamma or beta radiation (alpha would be too dangerous). The radioactive material goes around your body and doctors use a scanner on the outside to pick up the alpha or beta radiation as it travels through your flesh. Doctors can see of you have blockages or tumours by looking at how the radioactive material has travelled through your body. There is a risk of doing this because you are putting radioactive material into your body but the benefits outweigh the risks, e.g. Doctors may discover a cancerous tumour which they can treat before it gets too large, thus saving your life.

Three types of ionizing radiation Alpha are most ionizing but are easily stopped Beta are weakly ionizing but stopped by thin aluminium Gamma is very weakly ionizing but are hardest to stop, even with thick lead. These can be used to sterilise medical equipment.

Radioactive Isotopes Atoms exist in different states called isotopes. These are different because each isotope contains different numbers of neutrons, e.g. Carbon-12 and Carbon-13 and Carbon 14:- Count the number of electrons, protons and neutrons in each.

Carbon 14 is radioactive Carbon 14 is unstable. At any random time its NUCLEUS can decay and give out radiation (this is why it is called Nuclear Radiation). A tiny amount of the carbon in your body is Carbon 14 which is why your body is slightly radioactive.

Nuclear Fission Nuclear Power stations produce energy when large nuclei of uranium are split apart. This energy heats water which makes steam to turn turbines and generators to make electricity. The control rods in the reactor control how fast the reaction goes by absorbing the neutrons as they are made so that the reaction does not get out of hand.

Half Life Nuclear material decays predictably. Over a certain length of time called the HALF LIFE, half of the radioactive atoms decay. Look at this graph – it takes 2 days for the amount of counts per minute to halve from 80 to 40, or from 40 to 20, or from 20 to 10 or from 10 to 5 – it is always 2 days. The half life of this material is 2 days. Radioactive Waste from power stations can have a half life of millions of years and has to be buried underground. Radioactive isotopes used in medicine have a half life of hours or days so the radiation rapidly disappears to reduce the risk.

A nuclear future? We need to burn less fossil fuels as they harm the environment and are running out. The UK government has just decided to build more Nuclear Power Stations in the next 50 years but people are worried about where they will be sited and where the waste will be buried. Difficult decisions need to be made as the country’s electricity supply needs to be maintained but most people are concerned about the risks associated with Nuclear Power and the Radioactive wastes it produces.