GCSE AQA Core Biology

The nervous system is what lets you react to what goes on around you. A stimulus is a change in your environment which you may need to react to. There are five sense organs :

• Eyes = Light receptors
• Ears = Sound and Balance receptors
• Nose = Smell receptors, sensitive to chemical stimuli
• Tongue = Taste receptors, sensitive to chemical stimuli
•  Skin = Sensitive to touch , pressure and temperature change

The central nervous system (CNS):

The CNS is where all the information from sense organs is sent and where reflexes and actions are coordinated. The CNS consists of the spinal cord and the brain only. 

Sensory neurones transmit the information (as electrical impulses) very quickly to the CNS. Instructions from the CNS are sent to the effectors (via motor neurones) which respond accordingly

The brain can decide how to respond to a stimulus very quickly. However, sometimes the reaction time is too slow to prevent the body from injury and therefore the body has reflex actions. 

Reflexes are automatic responses to certain stimuli. For example, The eyes reaction to having a bright light shone in it, is a reflex. The pupil contracts , to prevent the eye from damage. 

The passage of information in a reflex is called a reflex arc ( from receptor to effector ) 

• The neurones in reflex arcs go through the spinal cord or through an unconscious part of the brain
• A stimulus is detected by receptors, an impulse is sent along the sensory neurone to the CNS.
• In the CNS, the message is passed on to a relay neurone.
• A relay neurone relay the impulse to a motor neurone.
• The impulse goes from the motor neurone to the effector and the effector reacts accordingly. 

Synapses: The connection between two neurones is called a synapse. The nerve signal is transferred by chemicals which diffuse across the gap. These chemicals then set of a new electrical signal in the next neurone. 

The monthly release of an egg from a woman's ovaries and the build - up of the protective lining in the womb is called the menstrual cycle 

• STAGE 1 = Day 1, bleeding starts and continues for four days 
• STAGE 2 = Day 4 to Day 14, the lining of the womb builds up again 
• STAGE 3 = Day 14, a egg is developed and then released 
• STAGE 4 = Day 14 to day 28 (around 14 days) , if there is no fertilized egg then the lining breaks down again and the cycle starts again. 

Hormones control different stages:

FSH : produced by the pituitary gland, causes and egg to mature and stimulates the production of Oestrogen 

Oestrogen : produced by the ovaries, stimulates the production of LH and inhibits the release of FSH

LH : produced by the pituitary gland and stimulates the release of an egg 

Hormones can be used to artificially change how fertile a woman is. Hormones can be used to reduce fertility: 

• Oestrogen can be taken in the form of a pill as a oral contraceptive. If the pill id taken every day, then Oestrogen levels remain high enough to inhibit the production of FSH and after a while egg development and production stops. 
• Advantages: Over 99% effective, reduces the risk of some cancers
• Disadvantage: isn't 100% effective, can cause side effects such as headaches, nausea and irregular periods and fluid retention, doesn't protect against STD's 

Hormones can increase fertility: 

• some women's levels of FSH are too low for them to be able to mature eggs in their ovaries , so FSH can be taken to stimulate egg production 
• Advantages: helps allot of women get pregnant
• Disadvantages: doesn't always work, can be expensive and can result in multiple pregnancies. 

Homeostasis is how the body maintains a constant internal environment.

The body's cells are bathed in fluid. To keep the cells working properly, this fluid must be kept at the right level.

• Body levels that need to be controlled include: Ion content, Water content, Sugar content and temperature. 
• Ion content is regulated by the kidneys, if there are too many then the excess ions need to be removed. They can be lost in sweat or in urine. 
• Water is lost through the skin in sweat, via the lungs in breath and via the kidneys as urine. On a cold day, you don't sweat much, you'll produce more urine and the urine will be more diluted. 
• Body temperature is controlled by the brain. enzymes work best at a certain temperature. In the body, they work best at around 37 C  so, the body tries to maintain this temperature. A part of the brain acts as your own personal thermostat, its sensitive to the blood temperature in the brain and receives messages from the skin about skin temperature.    
• Blood sugar levels are controlled as well, the normal metabolism of cells removes glucose from the blood. The more exercise the more glucose is removed. To maintain the right level, the body uses Insulin. Diabetes type 1 is where the  body doesn't produce enough insulin. 

For good health, Your diet must provide the energy you need . The different food groups have different uses in the body, you need the right balance of foods as well.

You need: Carbohydrates and fats  to keep warm and provide energy. Protein for growth, cell repair and cell replacement. Fibre to keep the digestive system clean. Vitamins and minerals to keep skin, bones and everything healthy.

People whose diet is badly out of balance are said to be malnourished.

You need energy to fuel the chemical reactions in the body that keep you alive. These reactions are called your metabolism and the speed at which they occur is your metabolic rate. There are slight variations in the resting metabolic rate of different people. For example, muscle needs more energy than fat, which means people with a higher proportion of muscle to fat in their bodies tend to have a higher metabolic rate.

The larger you are, the more energy your body need s to be supplied with. Men tend to have a higher metabolic rate than women because they are slightly bigger and tend to have more muscle. Regular exercise can boost your resting metabolic rate because it builds muscle. The temperature can also effect your metabolic rate, when it is cold more energy is need to produce heat. This increase the metabolic rate     

Health problems due to the wrong kind of diet are different in different parts of the world.

In developed countries: Obesity is a serious problem. Hormonal problems can lead to obesity, through the usual cause is a bad diet, overeating and a lack of exercise. Health problems that can arise as a result of obesity include : arthritis, diabetes, high blood pressure and heart disease. It can even increase the risk of some types of cancer.

In developing countries: people can suffer from a lack of food. This can be a lack of one or more specific types of food (malnutrition) or not enough food of any sort (starvation).  Problems commonly include slow growth, fatigue, poor resistance to infection and irregular periods in women.

If scientists are to decide on the best way to tackle these problems, they need to know as much as possible about them. The first step is to collect some accurate data. The problem with getting the data depends on what data your trying to get. e.g With malnutrition , people suffering may not reach medical aid and if in that particular are there is a large scale emergency, the staff may not have the time to keep proper records. 

With obesity, allot of people do not seek medical assistance. Surveys can be done, but the data will not be accurate unless the sample isn't biased and on how the data is collected.    

Cholesterol is a fatty substance that's essential for good health. It's found in every cell in the body. A high cholesterol level in the blood causes increased risk of various problems - like coronary heart disease. This is due to blood vessels getting clogged with fatty cholesterol deposits. This reduces blood flow to the heart, which can lead to angina (chest pain) or a heart attack. The liver controls the amount of cholesterol in the body. It makes mew cholesterol and removes it from the blood so that it can be eliminated from the body. The amount the liver makes depends on your diet and inherited factors.  Cholesterol is transported around the body in the blood by lipoproteins. These can be high density lipoproteins (HDL's) and low density lipoproteins (LDL's). LDL's carry cholesterol from the liver to the body cells and are known as the one which are bad for you. HDL's carry cholesterol from the body to the liver, so are known as the ones which are good for you. But there must be a balance between the two in the body. Ideally, you want more HDL's than LDL's in the blood. 

Saturated fats ( with no C=C double bonds) raise cholesterol. Polyunsaturated fats (with more than one C=C double bonds) lower cholesterol by increasing removal from the body.Monounsaturated fats (with exactly  one C=C double bonds) were seen as neutral but may help to lower cholesterol. 

Another risk factor of heart disease is high blood pressure (hypertension). Too much salt may cause hypertension 

Drugs alter what goes on chemically in your body. Many drugs are derived from natural substances found in plants e.g Heroin was found as opium, a chemical in a species of poppy. Chemical changes caused by drugs can lead to the body becoming addicted to the drug. If the drug isn't taken, an addict can suffer physical withdrawal symptoms. New drugs are constantly being developed. Before they can give it to the general public, they have to go through testing procedure. 

• STAGE 1= computer models are often used in the early stages - these simulate a human's response to a drug
• STAGE 2= Drugs are developed further by testing on human tissues in the lab. 
• STAGE 3= Drugs are further developed and then tested on animals 
• STAGE 4= Drug is tested on human volunteers in a clinical trail, this should determine wether there are side effects. 

An example of a drug that was not tested thoroughly enough is Thalidomide - a drug developed in the 1950's. Thalidomide was a type of sleeping pill and was tested for that use. It was later found to be effective in relieving morning sickness in pregnant women. Thalidomide hadn't been tested on pregnant women, so wasn't known that it could pass through the placenta and stunt the growth of the fetuses arms and legs. The drug was banned but has been recently re introduced as a treatment for leprosy, AIDS and some cancers 

Drugs are also used recreationally. Some of there are legal, other illegal. And some are more harmful than others. But two drugs that have a massive impact on people and society are both legal.  

Tobacco: Tobacco smoke contains carbon monoxide which stops the blood from carrying as much oxygen. In pregnant women, Is can deprive the fetus of oxygen leading to the baby being born underweight. Tobacco smoke also contains carcinogens which are chemical which can cause cancer. Smoking can cause disease of the heart and blood vessels which could lead to a heart attack or a stroke. It can damage the lungs leading to disease such as emphysema and bronchitis. The tar in cigarettes damages cilia in your lungs and wind pipe. These hairs, along with mucus, catch a load of dust and bacteria before they reach the lungs. When they are damage, chest infections are more likely. Smoking tobacco is addictive due to the nicotine.

Alcohol: Reduces the activity of the nervous system - slowing your reactions, it makes you feel less inhibited, leads to impaired judgment, poor balance and coordination, lack of self-control, unconsciousness and even a coma. It also cause dehydration which can damage the brain cells, and can also cause severe liver damage.  Alcohol is linked with way more than half of murders , stabbing, domestic violence, divorces and child abuse.  

Alcohol and tobacco have bigger impact in the UK than illegal drugs, as so many people use them.

Illegal drugs are often divided into two main classes : Soft and hard drugs 

Hard drugs e.g heroin or cocaine are seriously addictive and are more harmfull 

Why people use them : Enjoyment, Relaxation or stress relief, to me inspired. There many be factors in the user's personal life that influences them to take drugs.

Almost all hard drug users try cannabis first. The link between cannabis and hard drugs isn't clear but some people se the drug as a steeping stone ( the effects of cannabis create a desire to try harder drugs), a gateway ( Cannabis use brings people into contact with drug dealers) and some people think it just down to the individual, that some people are simply more likely to take drugs generally. 

As lung cancer and Smoking are linked, stop smoking products are now big business. The main products available are : Nicotine gum and patches, Acupuncture and Hypnosis. 

It's sometimes difficult to figure out if health claims or adverts are true or not. 

Advertisers aren't allow to make claims that are untrue, It's illegal . But, They do make claims that could be misleading or difficult to prove or disprove. Some advertisers will make vague claims that don't really say what the product does. Some might call a product low fat, but that could suggest that other types of the product are high in fat, when that isn't true. 

What to look for to find reliable products: 

• Is the report a scientific study, published in a reputable journal ?
• Was it written by a qualified person (not connected with the food producers)?
• Was the sample of people asked/tested large enough to give reliable results 
• Have there been other studies which found similar results ?

When pathogens enter the body they cause disease. There are two main types of pathogen: Bacteria and Viruses. They multiply quickly inside your body. 

Bacteria - Bacteria are very small cells which can reproduce rapidly. They make you feel ill by doing two things : damaging your cells and producing toxins. Some bacteria is useful in the right place e.g digestive system 

Viruses - Viruses are not cells. They are tiny and they can replicate themselves by invading your cells and using the cells to produce many copies  of themselves. The cell damage is what makes you feel ill. 

Skin, hairs and mucus in the respiratory system stop disease from getting inside. To prevent microorganisms getting into the body through cuts platelets help the blood to clot to seal wounds.  If something does get in, your immune system kicks in and white blood cells are the most important feature of the immune system.  When they come across a microbe they have three ways of attack. 

• consuming them - the cells engulf the microbe  and digest it
• produce anti bodies - anti bodies lock on to the antigens and kill them. antibodies are specific to that type of antigen. If the same antigen enters the body again then the white blood cells can quickly produce antibodies to kill it. The person has become immune and will not get ill. 

Dealing with disease come in three basic ways - prevention, dealing with the symptoms and curing. 

Immunization ( prevention) - It takes your white blood cells a few days to learn how to deal with a virus, by this time you could be very ill.  Immunization involves injecting dead on inactive microorganisms. These carry antigens, which cause your body to produce antibodies to attack them - even through the microorganisms is harmless. If the live microorganisms of the same type appear after that, the white blood cells can rapidly mass- produce antibodies to kill off the pathogen. Vaccinations wear off over time. So, boster injections can be given to increase levels of antibodies again. 

Relieve symptoms - pain killers e.g aspirin are drugs that relieve pain, they don't actually tackle the cause of the disease. Cold remedies relieve cold symptoms, they don't cure the cold. 

Curing- Antibiotics kill or harm bacteria causing the problem without harm your own body cells. Antibiotics don't kill viruses because viruses use body cells to reproduce, it's difficult to harm the virus without destroying the body's cells .  There are some antiviral drugs available but they are reserved for serious viral illnesses such as AIDS and hepatitis. 

The treatment of disease has changed in the last 200 years quite dramatically.

Ignaz Semmelweiss - was a doctor working at a hospital in the 1840's. He saw that women were dying in huge number after child birth from a disease called puerperal fever. He believed  that doctors were spreading disease on unwashed hands. He told the doctors to wash there hands in an antiseptic solution before entering the ward and the death rate dropped from 12% to 2%. Because, the existence of bacteria and the link between them and disease wasn't discovered for another 20 years, Semmelweiss couldn't prove why his idea worked and when he left the hospital and his methods were droped and the death rate rose again.

Vaccinations have changed the way we fight disease. We can now prevent it from occurring in the first place. Vaccination have helped control lots of infectious diseases that were once common in the UK e.g polio, measles, whooping cough, rubella, mumps, tetanus.

If an out break does occur, vaccines can slow down or stop the spread. Vaccines don't always work and can in some cases not give you immunity but a bad reaction.   

Animals and plants survive in many different environments,from extreme heat to cold polar regions, they are able to survive because they have adapted to their environment.

Desert animals: animals that live in hot,dry conditions need to keep cool and use water efficiently.  

• They have large surface areas in comparison on volume, this helps them lose more body heat 
• They lose less water and produce small amounts of concentrated urine. They also sweat very little.
• They have very thin layers of body fat 
•  Tend to be a sandy colour,so they can camouflage

Arctic animals : animals that live in really cold conditions need to keep warm.

• They keep their surface area to a minimum by being compact
• They have a thick layer of blubber for insulation, which also acts as an energy store for when food is scarce
• Tend to have white fur, so they can camouflage with the ice and snow
• They have big feet, to help spread their weight so they don't crack thin ice or sink into the snow 

Often different organisms have adapted to suit the same environment and use the same resources. They have to compete with each other for survival. A population is a group of organisms of one species that live in a particular environment. The size of the population will do up and down depending on these three main factors:  

• Competition: Organisms compete with other species (and members of their own species) for the same resources. Plants compete for light, water and nutrients. Animals compete for space, food, water and mates 
• Disease: Infectious diseases can kill off many members of a population but organisms that are fit and healthy stand the best chance of survival 
• Predation: If an organism gets eaten its population will decrease  

Competition for resources can affect the location, size and distribution of population. Organisms live where they find the resources they need to survive. Competition for the same resources means that a habitat will only be able to support a certain number of organisms. If the amount of resources in an area decreases, the size of a population will decrease. Competition affects how far apart members of  a population are in a habitat. Not many resources = lots of space need by each organism. Lots of resources = organisms need less space.  

Not all people are identical. There are reasons for this.

Organisms of the same species have differences. These differences are called variation within a species - and there are two types of variation: genetic variation and environmental variation. 

Different genes cause gene variation : All plants and animals have characteristics that are in some ways similar to their parents. an organism's characteristics are determined by the genes inherit from their parents. Some characteristics are determined only by genes w.g a plants flower colour. In animals these include eye colour, blood group and inherited disorders e.g haemophilia or cystic fibrosis

Characteristics are also influenced by environment : The environment that organisms live and grow in also cause differences between members of the same species - this is called environmental variation. Environmental variation covers a wide range of differences - from losing your toes to getting a suntan to having yellow leaves. any difference that has been caused by the conditions something  lives in is a environmental variation. 

• Most cells in the body have a nucleus and the nucleus contains genetic material.
• The human cell nucleus contains 23 pairs of chromosomes 
• Chromosomes carry genes. Different genes control different  characteristics e.g eye or hair colour
•  A gene is a short  of a chromosome which is a long length of DNA
• Genes can exist in different versions, each version gives different characteristics , like blue or brown eyes. The different versions of the same gene are called alleles instead of genes .
• The DNA is coiled up to form the arms of the chromosome 

Cells can reproduce to make new cells, it happens i two different ways :

• Asexual reproduction : this produces genetically identical cells. A ordinary cell cam make a new cell by simply dividing in two the new cell has exactly the same genetic information as the parent. In asexual reproduction there is only one parent and the parent and the offspring are clones. 
• X shaped chromosomes have two identical halves, so each chromosome splits down the middle to form two identical sets of half chromosomes and a membrane forms around the set and the DNA replicates itself to form identical cells with complete sets of X shaped chromosomes.
• This is how all plants and animals grown and produce replacement cells. Some organisms produce offspring using asexual reproduction e.g bacteria and some plants
• Sexual reproduction : Genetic information is taken from two organisms and is combined to produce offspring which are genetically different to either parent. In sexual reproduction, the mother and father produce gametes ( e.g sperm and egg cells ) In humans, each gamete has 23 chromosomes -half the amount in normal cells ). The egg and the sperm fuse together to form a cell with the full number of chromosomes ( half from the mother, half from the father )

We use asexual reproduction to clone plants and animals in different ways:

• Cuttings - Gardeners can take cuttings from good parent plants, then plant them to produce genetically identical copies. These plant can be produced quickly and cheaply 
• Tissue culture - a few plant cells are put in a growth medium with hormones , then grow into new plants, clones of the parent plant. Advantages of this are that you can make new plants very quickly, with very little space and you can grow all year
• Embryo Transplants - Farmers can produce cloned offspring with prize cows, using embryo transplants. Sperm cells are taken from the male and eggs from the female. Sperm cell are used to artificially fertilize an egg. The embryo that develops is then split multiple times before any cells become specialized. These can then be implanted into lots of  cows where they grow. The advantage of this is hundreds of ideal offspring can be created every year, the disadvantage is that the gene pool is reduced. 
• Adult cell cloning - This is the method that was used to create Dolly the sheep. She was created by the cell of an adult sheep being taken, then inserted into an empty egg cell which eventually grew into a sheep that was a clone of the previous sheep. This method could be used to cure human disease but some people think that it is unethical. Fusion clone will avoid this problem as no cell are destroyed in the process and the cell isn't genetically identical.   

Scientists can now add, remove or change an organism's genes to alter its characteristics. This is new science with exciting possibilities but there might be dangers as well.

Gene splicing - A useful gene is cut from one organism using enzymes. Enzymes are then used to cut another organisms chromosome , then insert the useful gene. Scientist use this method to do all sorts of things e.g the human insulin gene can be inserted into bacteria to produce human insulin.               Genetic modification - This method can be used to transfer usfel genes into animals and plants at the very early stages of development. This has useful applications. Genetically modified (GM) plants have  been developed that are resistant to viruses and herbicides and to also have long lives. Genes can also be inserted into animal embryos to have more useful characteristics. e.d sheep can be made to produce drugs in their milk to treat human diseases. Genetic disorders like cystic fibrosis are caused by faulty genes. scientists are trying to cure this by inserting working genes into sufferers. This is called gene therapy. However, some people strongly believe that we shouldn't change peoples genes because it isnt natural or because there are worries that changing someone's genes could cause unplanned problems that could get passed on to future generations.

Pros an cons of GM crops - Pros, GM could provide plants with more nutrients  and provide a bigger yield. Cons, transplanted genes could get out into the environment e.g the herbicide resistance strain being picked up by weeds, producing a new super weed. It could also reduce biodiversity  

However, despite how little we know about how life started, we know much more about how it progressed. 

Fossils form in rocks as minerals replace slowly decaying tissue and show features like shell skeletons, soft tissue and foot prints. They chow what was on earth millions of years ago. We also know the layers of rock where fossils are found were made at different times. This means, it is possible to tell how long ago a particular species lived. From studying the similarities and differences between fossils in differently ages rocks, we can see how species have evolved over billions of years. Unfortunately , very few organisms turn into fossils when they die. This creates gaps in the fossil record , which means there are many species that no one will ever know about.

The fossil record contains many different species that don't exist anymore - these species are said to be extinct. There are three main reasons why animals become extinct: 1. The environment changes too quickly e.g habitat is destroyed 2. A new predator or disease kills them all 3. They can't compete with another species for food  

An organism's DNA can change (or mutate) through everyday wear and tear. Most of the time mutation have no effect. If the mutation happens within a gene and it's passed on to the nest generation it can cause new characteristics. These mutations can give the organism a better chance of survival. These useful mutations can help a species adapt to an environment and may lead to the evolution of a completely new species.

Charles Darwin came up with the idea of natural selection. He noticed that species tend to be well- adapted to the environment they live in. He argued that organisms that are better adapted have a better chance of survival and are more likely to breed and pass on their genes to the next generation. If an organism is born with a useful characteristic, that characteristic has a good chance of being passed on. Where as if a mutation leads to a disadvantage, the organism may well die before it can breed. Good characteristics are accumulated and the bad are lost.  

Not everyone agreed with Darwin's theory because : It went against religious beliefs ( Darwin gradually persuaded people with scientific evidence.) There were different theories at the time as well as Darwin's e.g Lamarck who argued that if a characteristic was used a lot it developed and would be passed on. Darwin also didn't have a good explanation to why theses mutations occurred ( he didn't know of the existence of genes or mutations) 

We have an impact on the world around us and the more humans, the bigger the impact. There are six billion people in the world. the population of the world is currently rising very quickly and its not slowing down . This is mostly due to modern medince and farming methods which have reduced the number of people dying from disease or hunger. This is great for us humans but it means we're having great effect on the environment we live in. 

When the earth's population was much smaller the effect on the environment were small and local. Now, our actions can have a more widespread effect. Our rapidly increasing population puts pressure on the environment, as we take the resources we need to survive. People around the world are also demanding a higher standard of living. We use more raw materials and more energy for manufacturing processes. Unfortunately, many raw materials are being used up quicker than they can be replaced, so are in danger of running out.

We are also producing more waste and unless this waste is handled properly, more harmful pollution will be caused. This affects water, land and air. Water: sewage and toxic chemicals can pollute lakes, rivers and oceans, affecting the plants and animals that rely on them to survive. Land: we use toxic chemicals for farming e.g pesticides and herbicides. We also bury nuclear waste underground and we dump household waste into landfill sites. Air: Smoke and gases released into the atmosphere can pollute the air e.g sulfur dioxide can cause acid rain     

We need the greenhouse effect, since it makes the earth a suitable temperature for living on. But unfortunately it's starting to trap more heat than is necessary.

The temperature of the earth is a balance between the heat it gets from the Sun and the heat it radiates back out into space.  Gases in the atmosphere naturally act like an insulating layer. They absorb most of the heat that would normally be radiated out into space . There are several different gases in the atmosphere which help keep the heat in. They're called Greenhouse gases. The main ones are Carbon dioxide and Methane. The levels of these two gases are rising quire sharply. There is evidence that the earth is gradually heating up, because of the increasing levels of greenhouse gases - This is global warming , and it may cause climate change. 

Human activity : Humans release carbon dioxide into the atmosphere all the time as apart of our everyday lives. In car exhausts, industrial processes and as we burn fossil fuels. People around the world are also cutting down trees which affects the levels of CO2 as CO2 is released when the wood is burnt, when microorganisms feed of bits of dead wood they release CO2 and there is also less photosynthesis so less CO2 is taken out of the atmosphere.

The Earth is getting warmer, so, Scientists are trying to work out what the effects of global warming might be. 

The consequences of Global warming:

• Sea gets warmer and expands causing the sea level to rise. This would be an issue for low - lying places like the Netherlands, East Anglia and the Maldives - they would be flooded. 
• Ice caps melt causes sea level to rise further and the cold fresh water from the ice could cause problems for Britain as it would disrupt ocean currents and the warm currents flowing towards Britain would stop making the island colder. 
• More extreme weather and changes in weather patterns. Changes in weather patterns could also affect food production, places could become too dry or too wet to grow some foods. 
• Increase in ocean temperature, could cause and increase in hurricanes

To find out how out climate is changing, scientists are collecting data about the environment. Satellites are being used to monitor snow and ice cover,  temperature of the seas surface, speed of ocean currents and atmospheric temperatures. All this data is only useful if it covers a wide enough area and a long enough time scale.   

There is a growing feeling that if we carry on behaving as we are, we may end up causing problems for future generations. Human activities can damage the environment e.g pollution. Some of the damage cannot be repaired e.g destruction of rain forests. We are also placing greater pressure on our planet's limited resources e.g oil. This means we need to plan carefully to make sure our activities do not  leave problems for future generations - This is the idea behind sustainable development. 

SUSTAINABLE DEVELOPMENT = meeting the needs of todays population without harming the ability of future generations to meet their own needs 

Reduction in biodiversity: Biodiversity is the variety of different species present in an area. Ecosystems, such as tropical rain forests, can contain a huge number of species, so when a habitat is destroyed there is a risk of many species becoming extinct - Bio diversity is reduced. Due to biodiversity being reduced, There are a number of loss opportunities: useful products that we will never know about because the organisms that created them have become extinct. Newly discovered plants and animals are a great sorce of new foods, clothing and medicines. Also, loss of one or more species from an ecosystem unbalances it.        Human impact on an area is measured by monitoring indicator species e.g lichen population indicate levels of pollution as they are sensitive to sulfur dioxide.