AQA GCSE Biology Unit 1

  • Created by: sathu
  • Created on: 19-02-13 19:16

Balanced Diet

A balanced diet contains the correct balance of different food groups and the right amount of energy. 

A balanced diet should include different foods containing: carbohydrate, fat, protein, fibre, water, vitamins and minerals. 

Carbohydrate is needed for releasing energy.

Fat is needed for releasing energy and keeping warm.

Protein is needed for growth, cell repair and cell replacement. 

Fibre is needed to keep everything moving smoothly through the digestive system.

Water is needed to keep the skin hydrated and to keep the person alive. 

Vitamins and minerals are needed to generally keep everything healthy like skin and bone. 

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Healthy Lifestyle

Malnourished is when a person has an unbalanced diet. People who are underweight or overweight are malnourished. 

Deficieny diseases are diseases caused by lack of nutrients. For example, scurvy is a deficiency disease caused by lack of vitamin C. 

To stay healthy people should :

  • eat less animal products
  • eat more veg, fruhit and whole meal 
  • eat less salt
  • exercise regularly.

Having a balanced diet and regular exercise reduces the chances of getting health problems such as arthritis, stroke, type 2 diabetes, some kinds of cancer, high blood pressure and heart diseases. 

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Factors Affecting Health

Eating too much can lead to obesity which is a common disorder in developed countries like the UK. 

Obesity can be caused by hormonal problems but usually it's caused by a bad diet, overeating and lack of exercise.

Obesity can cause various future health problems like:

  • High blood pressure and heart diseases.
  • Arthritis
  • Type 2 Diabetes
  • Some kinds of cancer

Too much saturated fat can increase blood cholesterol level which will build inside blood vessels. This will cause a clot and if the vessels like arteries were completely blocked there can be heart attack and other health problems.

Too much salt can cause high blood pressure and heart problems.  

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Exercise Affecting Health

Lack of exercise also can get people health problems. 

Exercise increases the amount of energy used by th body and decreases the amount stored.

Due to this if a person regularly exercise they are less likely to be obese since people only put on weight if the amount of energy they take in is less than the amount they use. 

Sometimes people can be fit but malnourished. Some people may be slim and exercise regularly but they have an unbalanced diet causing them to lack in nutrients. 

As well as a balanced diet, exercise is vital in keeping a healthy lifestyle. 

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Eating too little and Inheritage Affecting Health

Eating too much can cause health problems like obesity but eating too little is also bad. 

People suffer from malnutrition particularly in developing countries. 

The effects of malnutrition are: 

  • Slow growth (in children)
  • Fatigue
  • Poor resistance to infections
  • Irregular periods in women

Sometimes inherited factors can also affect your health. 

Some people's cholesterol level are genetically high therefore they are more likely to get heart attacks and otehr problems associated with high cholesterol. 

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Cholesterol is a fatty substance made in the liver. It is carried around in your bloodstream attached to a protein. This fat-protein combination is called lipoprotein. 

Cholesterol is need to build cell membranes and some are needed to make hormones.

However, too much cholesterol is bad since it can lead to cholesterol being made in the blood vessels such as arteries. This could cause the artery to clot and get completely blocked. This is how heart attack take place. 

Unsaturated fat contains HDL (high density lipoprotein) which carries cholesterol from the cells to the liver. This reduces the amount cholesterol in the blood vessels therefore preventing heart attacks. 

Saturated fat contains LDL (Low density lipoprotein) which carries cholesterol from the liver to the cells. This increases the amount of cholesterol in the blood vessels therefore increaseing the chances of heart attacks. 

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Cholesterol - Food and Drugs

Vegetable oil contains a high level of mono unsaturated and poly unsaturated fat, these can help increase the HDL compared to the LDL level. 

But animal fats like butter, lard or meat can have a high level of saturated fat. 

Drugs like statins can be used to reduce the cholesterol level but has side effects, it can damage the liver and cause stomach pain, nausea and headaches. 

Some food are better then others therefore to stay healthy people should each a suitable amount of food with the suitable amount of nutrients which is a balanced diet. 

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Fighting Diseases - Pathogens

Pathogens are microorganisms that causes infectious diseases.

There are two main types of microorganisms which are bacteria and virus. 

Bacteria is a small cell that can reproduce rapidly inside a body. It can make a person ill by damaging the cells or producing toxins. 

Viruses are much smaller than bacterias, are not cells. It injects itself into a cell and reproduces using the cells' machineries. Then the viruses replicates into more copies ad eventually burst out of the cell. This cell damage causes the person to feel ill. 

Bacteria have a cell membrane, cell wall,flagella , DNA strand and plasma DNA. 

Viruses only have a DNA strand and a protein coat. 

Bacteria causes diseases like cholera, boils, MRSA, typhoid and tuberculosis.

Viruses causes diseases like warts, herps, polio, flu, mumps, measles, rubella and small pox. 

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Fighting Diseases - Defence System

Skin plus hair and mucus in you respiratory tract prevents alot of pathogens from getting inside your body. 

Platelets help blood clot quickly to seal wounds which prevents microbes from entering through cuts. 

If microbes get through then the immune system activates. White blood cells kill in 3 different ways: 

  • Consuming: Engulfs them and digest them by secreting enzymes. 
  • Producing antibodies: Produces proteins called antibodies when they come across a foreign antigen. The antibodies produced are specified for that antigen. If the same antigen comes again antibodies would be produced more rapidly - person is now naturally immuned. 
  • Producing antitoxins: Produces antitoxins to neutralise toxins produced by bacteria.

Antigens are molecules that pathogens have. 

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Fighting Diseases - Vaccination

A vaccine contains a dead or inactive pathogen with antigens. This antigen would initiate the immune system so that white blood cells would rush in. The blood cells will produce antibodies that are appropriate for the antigens to destroy the pathogen. After the antibodies have identified the pathogen and killed it, the person is immuned to the disease.

If a living pathogen that's the same arrive then the white blood cells would immediately recognize it and produce the right antibodies. The pathogen would be killed rapidly before it can damage any cell. 

Some vaccines wear off over time so booster injections may be needed to increase the level of antibodies. 

Pros: Have helped control lots of infectious diseases that were once common. Also prevent epidemics of the disease. 

Cons: Doesn't always work so won't give immunity and sometimes might cause bad reactions but bad reactions are very rare. 

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Fighting Diseases - Drugs

There are drugs called painkillers that relieve symptoms like aspirin but don't actually cure the disease.

There are drugs called antibiotics that actually kill or prevent the growth of bacterias.

But antibiotics don't destroy viruses. Viruses reproduce using your own cells so it is difficult to develop drugs that destroy just the virus without damaging the body's cell.

However, bacterias can mutate and become resistant to antibiotics. If you have an infection and the bacteria is resistant to antibiotics then it would be difficult to cure the infection. This resistant strain could cause a serious infection like MRSA.

To slow down the rate of developement doctors would have to avoid over prescribing antibiotics.

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The Nervous System

The  nervous system allows you to react to what is going around you. 

Sense organs detect stimuli. 

There are 5 different sense organs: 

  • Ears
  • Eyes
  • Nose
  • Tongue 
  • Skin

All theses sense organs contain different receptors. 

Receptors are group of cells which are sensitive to a stimulus. They convert a stimulus energy into electrical impulses. 

A stimulus can be light, sound, pain, change in temperature, pressure, chemical or change in position. 

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The five sense organs contain different receptors. 

Eyes: have light receptors - sensitive to light. These cells have a nucleus, cytoplasm and cell membrane. 

Ears: sound receptors - sensitive to sound. Also balance receptors sensitive to changes in position. 

Nose: Smell receptors- sensitive to chemical stimuli. 

Tongue: taste receptors - sensitive to bitter, salt, sweet, and sour plus the taste of savoury things like monosodium glutamate which is a chemical stimuli. 

Skin: Sensitive to touch, pressure, pain and temperature change. 

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The Neurones

Nerves are group of neurones. 

Neurones transmit the electrical impulses very quickly to and from the CNS. 

There are three main neurones:

  • sensory neurones - carry signals from receptors to the central nervous system.
  • relay neurones - carry signals from sensory neurones to motor neurones. 
  • motor neurones - carry signals from CNS to the effector.

The effector is a gland or muscle which responds to the stimuli. 

Glands secrete hormones to respond and muscles contract in response. 

So the genuine series would be:

Stimuli -  receptor - sensory neurone - relay neurone - motor neurone - effector - response

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Synapses and Reflexes

Synapse is a gap between two neurones. 

A chemical called neurotransmitter is transferred through the synapse which diffuses across the gap. 

These chemicals then set off a new electrical impulse on the next neurone.

Reflexs are automatic responses to certain stimuli since they reduce the chances of being injured.

The reflex arc is the information travelled through the receptor to effector.

In a reflex arc the neurones go through the spinal cord or through an unconcious part of the brain. 

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Hormones - Definition

Hormones are secreted by glands. These hormones are chemicals released directly into the blood. They are carried in the blood plasm to other parts of the body but only to particular cells called target cells. 

Hormones control things in organs and cells that need constant adjustment. 

Hormones travel through your body at the speed of blood. 

They tend to have relatively long lasting effects. 

Definition for hormone: Chemical messengers that travel through the blood to activate target cells. 

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Hormones - Different hormones in the body

Hormones are secreted in many different glands. 

The pituitray gland produces various hormones like FSH, LH and growth hormones. 

The thyroid gland produces thyroxin which controls metabolism

The pancreas secretes insulin to control blood glucose level and digestive enzymes.

The adrenal gland secretes andrenalin which is the fight or flight hormone. When people are angry this hormone is secreted. It increases heart beat and breating rate as well as diverts blood (e.g from gut to the limb muscle). 

Females have ovaries which secretes oestrogen and progesterone which is needed for the menustrual cycle. 

Males have testis which secrete testestrone. 

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Hormones- Hormones and Nerves

Hormones and nerves do similar jobs but there are various differences. 


  • give very fast action.
  • Act for a very short time.
  • Act on a precise area. 


  • give slower action.
  • Act for a long time.
  • Act in a more general way. 
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The Menstrual Cycle - Stages

The menustral cycle is the monthly release of an egg from a woman's ovaries, and the build up or break down of the uterus lining. 

There are four stages in the menustral cycle. 

Stage 1: When the bleeding starts so the uterus break down for like 4 days. 

Stage 2: The lining of the uterus builds up again from day 4 to day 14, it completes full of blood vessels ready to recieve a fertilised egg.

Stage 3: An egg is released from the ovary at day 14.

Stage 4: The wall is then maintained for 14 days up til 28 day.  If no egg is fertilised the uterus lining will begin to break down causing the whole cycle to start again. 

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The Menstrual Cycle - Hormones

FSH (Follicle-stimulating hormone) : 

  • Secreted by the pituitary gland.
  • Causes and egg to mature in one of the ovaries.
  • Stimulates the ovaries to produce oestrogen. 


  • Produced in the ovaries.
  • Causes pituitary to secrete LH.
  • Inbits further release of FSH.

LH (Luteinsing hormone) : 

  • Produced by pituitary gland.
  • Stimulates release of the egg. 

Progesterone is also a hormone that maintains the uterus lining after the egg is fertilised. It is produced in the ovaries. 

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Controlling fertility - Reducing fertility

Oestregon can be used to prevent the release of an egg - so it can be uses as a way of contraception  since it inhibits the production of FSH but if taken for a long period it could completely stop the production.

Progesterone stimulates the making of thick cervical mucus, which prevents sperm getting through and reaching the egg. The pill is an oral contraceptive, the first version was made in the 1950s. Pills with oestrogen and progesterone is called combined oral contraceptive pill. 


  • 99% effective at preventing pregnancy.
  • reduces risk of getting some types of cancer. 


  • Isn't 100% effective.  
  • Can cause side effects
  • Doesn't protect against STDs. 
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Controlling fertility - Increasing fertility

Some women have low production of FSH which means their egg cannot get matured and released for pregnancy. 

FSH hormones and LH hormones can be injected to increases the level of hormone and cause the egg to mature and get released. 


  • Helps alot of women to get pregnant.


  • Doesn't always work.
  • Too many eggs may mature resulting in unexpected mutiple pregnancies. 
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Controlling fertility - IVF

IVF is in-vitro fertility which is basically test tube babies.Involves collecting eggs from the woman's ovary and fertilising them using the man's sperms on a petri dish in a lab. These will then grow into embryos. 

After the embryos have grown into small group of cells, one or two of them are transferred in to the woman's womb to increases the chance of pregnancy. 

FSH and LH is given before the collection of egg to stimulate the egg production (so more than one egg can be collected).


  • Can give a couple a child.


  • Some women have strong reactions like abdominal pain, vomiting and dehydration.
  • Reports of increases risk of cancer due to hormonal treatment (not completely proven).
  • Multiple births which is risky for mother and baby (higher risk of miscarriage, still birth).  
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Plant hormones - Auxin and Phototropism

Auxin is a plant hormone that controls growth near the tips of shoots and roots.

It controls the growth of a plant in response to light (phototropism), gravity (gravitropism or geotropism) and moisture (hydrotropism).

Auxin is produced in the tips and moves backwards to stimulate cell elongation process which occurs in the cells just behind the tips.

Extra auxins promotes growth in the shoots but inhibits growth in roots.

 When a shoot is exposed to light, more auxin accumulates on the side that's in the shade. This makes the cells elongate faster on the shaded side causing the shoot to bend towards light. 

This is called phototropism. 

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Plant hormones - Gravitropism and Hydrotropism

Shoots that are sideways grow upwards due to gravity. More auxins accumulates on the bottom so the cells will elongate faster on the bottom. This causes the shoot to bend upwards away from gravity.

Roots that are sideways also have more auxins accumulated on the bottom. But the side with the extra auxin in the root would inhibit cell elongation. Therefore the root would bend downwards towards gravity. 

This is called gravitropism.

When roots have an uneven amount of moisture on both sides of the roots more auxin would be produced on the side with more moisture. This inhibits growth on that side so the root would bend towards moisture. 

This is called hydrotropism. 

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Plant hormones - Uses in Agriculture

Plant hormones can be extracted or artifical versions can be made. 

Selective weedkillers are made from plant hormones. They are used to kill broad leaves in weeds. This will only affect the broad leaved plants. They disrupt their normal growth patterns which soon kills them, but leave the crop untouched. 

Plant cuttings won't always grow in soil. If you add rooting powder which usually contain auxin, they'll produce roots rapidly and start growing as new plants. This helps growers to produce lots of clones of a really good plant very quickly. 

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Homeostasis are the functions in the body that keeps your internal environment constant. Bodily levels that needs to controlled are ion content, water content, sugar content and temperature. 

Ions level is regulated by the kidney. Ions are in food and absorbed into the blood. Excess ion should be removed. Ions can be lost in sweat and kidneys remove excess ion by urine. 

The body needs to constantly balance the intake of water against the water going out. Water can be taken from food, drinks.It can be lost by sweating, the lungs in breath and kidneys as urine/faeces. 

Body temperature is controlled by brain. All enzymes work best at 37 degrees - the body maintains it like that. There's a part of the brain that acts as a personal thermostat, it detects blood temperature and receives message from the skin about the skin temperature.

Blood sugar level needs to be controlled by a hormone called insulin. 

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Drug alters what goes in your body. Drugs can interfere with chemical reactions in your body, sometimes in a good way and sometimes in a bad way. 

Some of the chemical changes caused by drugs could cause your body to become addicted to it. 

When your addicted, if you suddenly stop taking the drug you would suffer from withdrawal symptoms which can sometimes be very unpleasant. 

There are three type of drugs:

  • Medicinal - antibiotics, paracetomal.  
  • Recreational - legal or illegal, like alcohol, cannabis. 
  • Performance enhancing - steroids, improves person's performance in sport. 
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Drugs - Performance Enhancing Drugs

Performance enhancing drugs have health and ethical impacts. Some athletes take these drugs to make them perform better in sport. 

There are drugs like anabolic steroids that increases muscle size and stimulants that increases heart rate. But these drugs do have side effects like steroids can cause high blood pressure. 

Some drugs are banned by law but all are banned by sporting bodies. 

There ethical problems against drugs:

  • Unfair
  • Athletes not aware of serious health risks.

For drugs:

  • Athlete's own decision if it's worth taking.
  • Drug free is not fair either becuase some have more sport equipmenets and facilities then others. 
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Drugs - Claims about Effect of drugs

Claims about the efffects of drugs need to be looked at critically. 


  • Precribed drugs to lower risk of heart and circulatory diseases.
  • Proven to lower cholesterol level and significantly lower risk of heart disease in diabetics. 
  • Original research by government scientist - no connection to manufacturers. Sample was big - 6000 patients. 


  • Illegal drug.
  • Scientist investigated whether chemical in smoke causes mental health problems.
  • Result vary and open to different interpretations.
  • Not enough definite scientific evidence so need more - no one's sure. 
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Drugs - Testing Medicinal Drugs

New drugs are constantly being developed but need to go through thorough testing procedures. 

Stage 1: 

  • Drugs need to be tested on human cells and tissue in lab.
  • Cannot test drugs that affect whole/multiple body systems like drugs for blood pressure. 

Stage 2:

  • Tested on live animals to see whether it works, not toxic and the best dosage.
  • Law in Britain states drug must be tested on two diffferent live animals. 
  • Some people think it's cruel but others think it is the safest way to test it. 
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Drugs - Testing Medicinal Drugs Stage 3

Stage 3:

  • Drugs is tested on human volunteers in a clinical trial.
  • First tested on healthy volunteers to see there's no harmful side effects. Very low dose is given at the start and then gradually increased.
  • Then tested on patients with that illness. The optimum dose which is most effective with few side effects is found.

Next double blind randomized controlled trial is given:

  • There would be two groups of patients. One given the real drug and the other is given placebos - this is for doctors to see the actual difference the drug makes. 
  • Clinical trials are blind - patients don't know if they are getting the drug or the placebo. 
  • Often doctors don't know either. This is so doctors monitoring patients and analysing results aren't subconsciously influenced by their knowledge.
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Drugs - Recreational Drugs

Recreational drugs are taken for fun but have risk. 

Illegal drugs are often in two different classes - soft and hard. Hard drugs are usually seriously addictive and generally more harmful.

These drugs are taken for stress relief, relaxation and for enjoyment.

Studies link cannabis to hard drug as:

  • Is a stepping stone - creates desire for hard drugs.
  • Is a gateway - brings people into contact with drug dealers. 
  • Is genetic - some generally take drugs, so cannabis user will also try other drugs. 
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Drugs - Legal Drugs have More Impact than Illegal

Tobacco and alcohol are both legal recreationa drugs. 

Tobacco (smoking) :

  • Causes diseases of the heart, blood vessel and lungs.
  • Causes cancer.
  • Nicotine in cigarettes is addictive. 


  • Affects nervous system and slow down reaction. 
  • Too much causes impaired judgement, poor coordination and unconsciousness. 
  • Excess causes liver disease and brain damage also addictive.

Tobacco and alcohol have bigger impact than illegal drugs since so many people take them. 

Treating people related to smoking and treating alcoholics and the damage caused by them is expensive. 

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Adaptation is when organisms have particular characteristics that helps them to survive in their environment.

For example, dessert animals like camels have adapted to keep cool and save water:

  • Having large surface area compared to volume - this helps lose more body heat. 
  • Lose less water by producing small amount of concentrated urine. 
  • Make very little sweat .
  • Thin layers of body fat and a thin coat to them lose heat.
  • A sandy colour as good camouflage - avoid predators and sneak up on preys. 

Also Arctic animals have adapted to reduce heat loss:

  • Small surface area compared to volume - compact body shape, reduces heat loss. 
  • Thick layer of blubber (fat) for insulation and acts as energy store when food is scarce.
  • Thick hairy coats keep body heat in and greasy fur sheds water (prevents cooling due to evaporation. 
  • White fur for camouflage - avoid predators and sneak up on preys. 
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Not only animals adapt but plant do as well to having little water:

  • Plants lose water vapour from the surface of their leaves (cacti have spines instead of leaves - to reduce heat loss).
  • Small surface area compared to volume.
  • Water storage tissues like cacti stores water in its thick stem.
  • Maximise water absorbtion by having shallow but extenive roots or deep root.
  • Detering predators : Have armour - e.g. roses have thorns and tortoises have shells.
  • Poison - e,g, bees and poison ivy. 
  • Warning colours to scare - e.g. wasps.

Microbes also have adapations: 

  • Survive high temperature - proteins don't break down easily.
  • No light - chemosythesis which make sugars for food, they have more adaptations. 
  • Some microbes are known as extremophiles - live in extreme conditions.
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These are resources plants compete for to survive :

  • Light
  • Space
  • Water 
  • Minerals from the spoil

These are resources animals compete for to survive:

  • Space (territory)
  • Mates
  • Food
  • Water
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Environmental Change

Environment in which plants and animals live changes all the time. 

Environment can be changed by living factors like:

  • A change in the occurence of infectious diseases.
  • A change in the number of predators.
  • A change in the number of prey or availability of food sources.
  • A change in the number or types of competitors.

Environment can also be changed by non-living factors:

  • A change in average temperature.
  • A change in average rainfall.
  • A change in the level of air or water pollution. 

Environmental changes can affect populations:

  • Population size increases
  • Population size decreases.
  • Population distribution changes. 
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Environmental Change - Living indicators

Environmental changes can be measured using living indicators. Some living organisms are very sensitive to changes in their environment. 

Living organisms like :

  • Lichens are sensitive to the concentration of sulfur dioxide in the atmosphere. The number and type of lichen at a particular location will indicate how clean the air is (e.g. the air is clean if there's lots of lichens).
  • Some invertebrate animals like mayfly larvae are good indicators for water pollution. They're very sensitive to the concentration of dissolved oxygen in water. If there's mayfly larvae then the water is clean.
  • Other invertebrate species have adapted to live in polluted conditions like rat-tailed maggots and sludge worms indicate a very high level of water pollution. 
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Environmental Change - Non - Living indicators

Scientists use different equiptments to collect date about the environment like:

  • Satellites- measures the temperature of the sea surface and amount of snow and ice cover. This is modern, accurate instrument that gives us a global coverage. 
  • Automatic weather stations - tells the atmospheric temperature at various locations, contain thermometers very sensitive and accurate.
  • Rain gauges - measures rainfall and can use to find out average rainfall changes year on year.
  • Dissolved oxygen meters - measures concentration of dissolved oxygen in water to discover how the level of water pollution is changing. 
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Pyramids of Biomass

 This is the pyramid of biomass. Each level is called trophic level. Biomass is the total weight of animal in each level. The bottom bar would always be the producer. Then it's primary, secondary and so on consumers. 

Pyramid of number is basically the number of each in the trophic level. 

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Pyramid of Biomass - Energy Transfer

Energy from sun is the source of energy for all life on earth. 

Green plants and algae use only small percentage from the sun to make energy for photosynthesis. This energy is stored in the substance which make up the cells of the plant and then works its way uup the food chain. 

How is energy lost through the food chain?

  • Respiration - movement and heat.
  • Some materials that make up the organisms are inedible - bones, teeth.
  • Waste material - urine and faeces. 

Most of the biomass is lost and so does not  become biomass in next level up. 

This explains why there are usually not more than five or four trophic levels. Since alot of energy is lost at each stage eventually there's not enough to support another organism. 

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Pyramid of Biomass - Decay

Plants take elements like carbon, nitrogen, oxygen and hydrogen from the soil or air. They turn these elements into complex compunds like fat, protein and carbohydrate. 

These elements are returned to the world through waste materials or death. Thesematerials decay because it's broken down or digested by microorganisms and get put back into the soil. 

Microbes work best when it's warm, moist and there's plenty of oxygen.  Compot bins recreate thees ideal conditions.

All the important element are therefore recycled.

In a stable community the materials taken out of the soil and used are balanced by those that are put back in. There's a constant cycle happening. 

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The Carbon Cycle

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The Carbon Cycle - Information

CO2 is removed from the atmosphere by plants for photosynthesis. It's used to make carbohydrates, fats and proteins. Some of the carbon is returned through respiration and some through the food chain. 

Some carbon returns to the atmosphere when animals respire.

When plants and animals die other animals called detritus feeders and microbes feed on their remains. When the organisms repisre CO2 is returned.

Animal waste is broken down by detritus feedders and microbes. Compounds in the waste are taken up by plants which is put back into the food chain.

Some useful plant and animal products like wood and fossil fuels are burnt (combustion) which releases CO2.

So carbon is constantly being cycled.  

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Variation is the characteristics that are obtained by offsprings genetically and environmentally.

Genetic characteristics that do not depend on environmental characteristics are blood group, eye colour and inherited disorders. Theses characteristics are pass on by their parents. These genes are passed from gametes which are sex cells.

Characteristics that are environmentally affected are like health, skills and intelligence. 

Most variation is determined by a mixture of genetic adn environmental factors. 

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Genes, Chromosomes and DNA


The first picture is a cell.

The second picture is the chromosome inside the nucleus of the cell.

The third picture is the DNA that is in the chromosome. 

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Genes, Chromosomes and DNA

Most cells in your body have a nucleus. This section contains your genetic material in the form of characteristics. 

There are 23 pairs of chromosomes in a human body. 

Chromosomes carry genes which determine your characteristics and control the development of it. 

A gene is a short length of the chromosome which is quite a long length of DNA.

The DNA is coiled up to form the arms of the chromosome.

There can be different versions of genes like blue or brown eyes. These are called alleles.  

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Reproduction - Sexual Reproduction

Sexual reproduction is when the genes from two organisms are combined to form the offspring which are genetically different to either parent.

In sexual reproduction gametes are produced by mother and father like egg and sperm in animals.

In humans each gametes contain 23 chromosomes. 

During fertilisation the egg and the sperm cell fuse together to form a cell with the full number of chromosomes. 

Because there are two parentx the offspring contain a mixture of their parents' genes therefore making them differentiate from either of them. 

This mixture of genetic material produces variation in the offspring. 

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Reproduction - Asexual Reproduction

An ordinary cell can reproduce by simply dividing into two therefore making an exact copy with the same genetic information. This is called asexual reproduction. 

This is how all animals and plants grow and produce replacement cells.

Some organisms also produce offspring asexually like bacteria and certain plants. 

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Cloning - Tissue culture and Embryo Transplant

Plants can be cloned from cuttings by tissue culture:

  • Gardeners can take cuttings from good parent plants and then plant them to produce genetically identical copies (clones) of the parent plant. 
  • These plants can be produced quickly and cheaply. 

Tissue culture is where a few plant cells are put in a growth medium with hormones. These plants can grow very quickly, in very little space and grown all year.

Embryo transplants can be used to clone animals:

  • Sperm cell and egg cell can be taken out and then use the sperm cell to artificially fertilise the egg cell. 
  • The embryo that develops would split many times before any cell becomes specialised. 
  • These cloned embryo is ikmplanted into the cows to grow the embryo into calves. 
  • Hundreds of ideal offspring can be produced every year. 
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Cloning - Adult cell cloning

Adult cell clonging is taking an unfertilised egg and removing its genetic material. A complete set of chromosomes from an adult body cell is inserted into the empty egg cell.

The egg cell is then stimuated by an electric shock which makes it divide like a normal embryo. 

When the embryo is a ball of cells it is implanted into an adult female to grow the emrbyo into a genetically identical copy of the original adult body cell. 

This technique was used to created Dolly - the famous cloned sheep. 

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Cloning - Issues

There are many issues in cloning:

  • Cloning gets you alot of ideal off spring but reduces gene pool - fewer different alleles in a population. If new disease appear in closely related population they could be wiped out - no allele giving resistance to the diseases. 
  • Animala cloning could lead to greater understanding of development of emrbyo, ageing anad ageing related disorders. 
  • Help preserve endangered species. 
  • Clones are not as healthy as normal offsprings. 
  • People worry about human being cloned. If was allowed could cause unsuccessful cloning like severe disability. 
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Genetic Engineering - How it works?

Scientists can now change an organism's genes to alter its characteristics which is called genetic engineering. However, there are some dangers associated with it. 

The basic idea is to copy a useful gene from one organism's chromosome into the cells of another. 

A useful gene is cut using enzymes.

Enzymes are used to cut another organism's chromosome then used to insert the useful gene. 

This method is used to do sort of things like the human insulin gene can be inserted into bacteria to produce human insulin. 

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Genetic Engineering - Organisms and Controversy

The previous method can be used to transfer useful genes into animals and plants at the very early stages of their developement after fertilisation. This means they'll develop useful characteristics like:

  • Genetically modified crops have ahd their genes modified to make them resistant to viruses, insects or herbicides (chemicals used to kill weeds). 
  • Sheep have been genetically engineered to produce substances like drugs in their milk that can be used to treat human diseases.
  • Genetic disorders are caused by faulty genes. Gene therapy is used to treat these disorders by inserting working genes. 

Genetic engineering is good to solve many problems like treating diseases, more efficient food production. 

But genetic engineering could cause accidentally created unplanned problems which can be passed on to future generations. 

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Genetic Engineering - GM Crops Pros and Cons

Genetic engineering pros:

  • GM crops can be engineered to contain missing nutrients that's missing which can be useful for developing countries who don't get enough nutrients from their food. 
  • GM crops are being grown already elsewhere in the world often without any problems.

Genetic engineering cons:

  • Some say GM crops affect the number of weeds and flowers (so the insects) that live in and around the crops - reducing farmland biodiversity. 
  • Some say GM is not safe - worried it might develop allergies, although probably no risk. 
  • Transplanted gene may get out into the natural environment. E.g. the herbicide resistance gene may be picked up by weeds creating new super weed variety.
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Evolution - Evolutionary and Ecological

Studying differences and similarities in organsims help understand how all living things are related (evolutionary relationships) and how they interact with each other (ecological relationships). 


  • Species with similiar characteristics have similiar genes becuase they share a recent common ancestor, so they're closely related. Often look very alike in similiar types of habitat. 
  • Genetically different species - may look alike, adapted to live in same habitat. Closely related but evolved from different ancestors. 
  • Evolutionary tree with more recent common ancestor has the more closely related two species. 


  • Organisms with similiar characteristics in same habitat - may be competing. 
  • Differences in same habitat can show predator to prey relationships. 
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Evolution - Natural Selection and Mutation

Charles Darwin came up with the idea of natural selection. 

Individuals with chaaracteristics that make them better adapted have a better chance of surviving and so breed successfully. 

So the genes responsible for survival are more likely to pass onto the next generation. 

Evolution can occur due to mutation:

Mutatation is a change in an organism's DNA. 

Mutation can be beneficial by producing useful characteristics. This may give a better chance of surviving and reproducing. Over time the beneficial mutation will accumulate into a population e.g. some species of bacteria have become resistant to antibiotics due to a mutation. 

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More Evolution

Not everyone agreed with Darwin. At that time Darwin's idea was very controversial at the time for:

  • it was against religious beliefs about how life on Earth developed.
  • couldn't give a good explanation since at that time he didn't know anything about genes or mutations. 
  • not enough evidence to convince many scientists, not many other studies were done. 

Different scientific hypothesis:

  • Lamarck argued if a characteristic was used a lot then would develope over time like rabbit leg would get longer over time.
  • Also believed acquired characteristics would be passed on to the next generation. 
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