Biology modules 1 2 and 3

B1, B2, B3

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B1 - Genes, Chromosomes and DNA

Most cells in the body have a nucleus which contains genetic material. This material is arranged into chromosomes. The human cell nucleus contains 23 pairs of chromosomes. Each chromosome is one long molecule of coiled up DNA. A gene is a short length of a chromosome. Genes control the development of different characteristics such as hair colour. Genes can exist in different versions. Each version gives a different form of a characteristic like blue or brown eyes. The different versions of the same gene are called alleles.

Each gene is a code for making a certain protein which are building blocks for cells. Having different versions of proteins means that we end up with different characteristics. 1) some proteins are structural proteins. These are things like hair, skin, blood + the cytoplasm in our cells. Collagen is a structural protein that's found in tendons, bones + cartilage. 2) the others are functional proteins. Enzymes are proteins that help with digestion by breaking down food molecules. Amylase is a digestive enzyme that breaks down starch to maltose.

An organisms genotype is all the genes it has. The characteristics are phenotype. Some characteristics like dimples are controlled by only genes. Others such as scars are only environmental factors. Some are caused by both such as weight.

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B1 - Genes and Variation

Sex cells are different from normal cells because they contain 23 single chromosomes, one chromosome from each pair. When sperm fertilises the egg the 23 chromosomes in the sperm combine with 23 in the egg. The fertilised egg has 23 pairs of chromosomes. The 2 chromosomes in a pair always carry same genes + each gene is in the same place on the 2 chromosomes. Because the 2 chromosomes in a pair come from different parents, they may have different alleles.

Children get some alleles from each parent, so most children look a bit like both parents. They won't be exactly like either one because they haven't got all the same alleles. Every child has a unique combination of alleles.

2 chromosomes in a pair are never identical because they have different alleles. When they go into 2 different sex cells each of the cells gets different alleles. Each of the 23 chromosome pairs separates independently. So there are millions of different chromosome combinations. This means all sex cells produced by one individual will all be genetically different. When a woman releases an egg it can be fertilised by any one of millions of different sperm released by her partner. This means the chances of 2 siblings being identical are minuscule. They tend to look alike but there's always a difference.

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B1 - Inheritance and Genetic Diagrams

When you've got 2 copies of a gene usually only one of them can be expressed in the phenotype. If you're homozygous for a trait, you have 2 alleles the same for that gene. If you're heterozygous, you have 2 different alleles for that gene. Alleles can be dominant or recessive. If you have 2 dominant alleles for a gene or 1 dominant + 1 recessive allele, only the characteristics caused by the dominant allele are shown. To show the recessive characteristics, both alleles have to be recessive. In genetic diagrams, letters represent alleles. Dominant alleles are a capital letter.

A crazy hamster must have bb. However a normal hamster could be BB or Bb because the dominant allele(B) overrules the other. The genetic diagram below shows what can happen:

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B1 - Genetic Diagrams and Sex Chromosomes

You can work out a genetic cross by using punnett squares:


There are 23 pairs of chromosomes in every human body cell. The 23rd pair are labelled XY(sex chromosomes). They decide if you're male or female. All men have an X and Y chromosome(XY) The Y chromosome causes male characteristics. All women have 2 X chromosomes(XX). The Y chromosome carries a gene that makes an embryo turn into a male. The gene that makes an embryo into a male causes a protein to be produced. This protein causes the development of testes(instead of ovaries). Testes produces male sex hormones making the male reproductive system develop. In females the protein isn't produced so the embryo develops ovaries + the rest of the female reproductive system.

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B1 - Genetic Disorders

Some disorders are inherited - one or both parents carry a faulty allele + pass it to the child. Cystic fibrosis + huntington's disease are cause by a faulty allele of a single gene.

Most defective alleles that are responsible for genetic disorders are recessive. Cystic fibrosis is a genetic disorder of the cell membranes caused by a faulty recessive allele. Symptoms:thick sticky mucus, breathing difficulty, chest infection, digestion difficulties. The allele causing cystic fibrosis is a recessive allele. This means people with 1 copy of the allele won't show the symptoms of the disorder.

Huntington's disease is caused by a dominant allele. This causes tremors, clumsiness, memory loss, mood changes + poor concentration. There's no cure. If you inherit 1 allele you will automatically get the disease. If one parent has the disorder there is a 50% chance the child will inherit the disorder. The carrier parent will be a sufferer as the allele is dominant. The disease has a late onset. Symptoms don't appear until after the age of 40 by which time the allele is already passed onto the children maybe grandchildren.

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B1 - Genetic Testing

Embryos produced in IVF can be tested for genetic disorders(pre-implantation genetic diagnosis). When embryos are tested only healthy ones are implanted into the womb, embryos with the disorder are discarded. Children + adults can be checked to see if they carry alleles for disorders. They can also be tested before drugs are prescribed for them. This can show how the drug will affect an individual.

The results of the testing may not be 100% accurate. There are often errors due to samples getting contaminated or misinterpretation of results. Healthy people can be told they have the disorder(false positive result) or people with it can be told they don't(false negative). Tests during pregnancy aren't 100% safe, + can cause miscarriage. Some people may prefer not to know if family members also have it but it may not be fair on future children couples may have. Is it fair to put pressure on couples with the disorder who want children? Parents may have to terminate a pregnancy if they cant cope with a sick or disabled child. If the result becomes available to others it may cause discrimination. Employers may not want to give a job to someone who is more likely to get ill. Insurance companies may refuse to give life insurance to people with the 'wrong' alleles.

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B1 - Clones

Sexual reproduction produces offspring that are genetically different. Bacteria, some plants + some animals can reproduce asexually to form clones. These are genetically identical organisms which have the same genes + alleles of the genes. Because clones have the same alleles, any differences must be due to the environment e.g. if you're better nourished than your clone as a child, you would probably be taller than your clone even though the alleles are identical.

i)Asexual reproduction means there is one parent + offspring are genetically identical to each other + the parent. Most bacteria reproduce like this, they divide into 2 meaning they multiply very quickly. Many plants also reproduce asexually - some produce horizontal stems(runners) that move from the base plant to form clones at the tips. Others produce underground fleshy structures(bulbs). The grow to form a new identical plant. Few animals do this. Female greenfly lay eggs which develop to more identical females. ii) Identical twins are clones. A single egg is firtilised by a sperm and an embryo develops as normal. It sometimes splits in 2 + 2 separate embryos form.

Scientists can make animal clones in the lab. The nucleus of an egg is removed. A nucleus from an adult donor cell is inserted in its place. Cell is stimulated so it divides. The embryo produced is genetically identical to the donor cell.

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B1 - Stem Cells

Most cells in the body are specialised for a job. Most cells in multi-cellular organisms become specialised during the early development of the organism. Some cells are unspecialised. They develop into different types of cells depending on the instructions they're given. These cells are STEM CELLS. Embryonic stem cells are unspecialised cells found in early embryos. They are removed from the embryo then the embryo is destroyed. They're exciting to doctors because they have potential to turn into any kind of cell. All types of different cell found in an organism have to come from those few cells in the early embryo. Adult stem cells are unspecialised cells found in adult animals. They maintain + repair old + damaged tissues + can specialise into many cell types but not all. These can be safely removed from adult patients.

Medicine use adult stem cells to cure disease. People with blood diseases like sickle cell anaemia can have bone marrow transplants. Bone marrow contains adult stem cells that can turn into new blood cells to replace the faulty old ones. Embryonic stem cells could be used to replace faulty cells in sick people. You can make beating heart muscle cells for people with heart disease, insulin producing cells for diabetics. These treatments are being researched though so they may not be available for a while yet.

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B2 - Microorganisms and Disease - Part 1

The effects an infection has on the body like a fever are called symptoms. Different microorganisms cause different symptoms but all damage the body's cells in one way or another. Some microorganisms damage cells directly. Malaria parasites invade red blood cells + multiply inside them making the cells burst open. Many infectious microorganisms produce poisons that damage cells. Some bacteria produce proteins that damage the material holding the cells together. This helps the bacteria invade the body more deeply. Other microorganisms produce toxins that poison cells causing fever or inflammation. Some strains of Escherichia coli cause diarrhoea by secreting toxic substances.

Bacteria reproduce by making copies of themselves by using a source of nutrients for energy. They also need warm moist conditions so the chemical reactions inside them can take place. For humans there a lots of places in the body you can find these conditions, so few bacteria can quickly become a large colony inside the body. Vurises need other cells to reproduce + use parts of other cells to make copies of themselves. Certian viruses can easily reproduce inside the body as there are lots of the right kind of cells for them to use.

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B2 - Microorganisms and Disease - Part 2

Microorganisms reproduce by making copies of themselves. The copies + the original microorganisms can then go on to reproduce + make more copies. If you start with 1 microorganism that reproduces in 30 minutes, after that time you'd have 2 microorganisms. After 60 minutes you'd have 4 microorganisms, after 90 minutes 8 + so on.

To work out the size of a microorganism population after a certain amount of time you need to know:

  • The number of microorganisms before reproduction starts.
  • How long it takes for 1 microorganism to reproduce.
  • How long the microorganisms are left to reproduce for.

The bottom 2 points need to be in the same unit of time e.g. minutes or hours.

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B2 - The Immune System

The immune system deals with any infectious microorganisms that enter the body. An immune response always involves white blood cells. Anything that gets into the body should be picked up straight away by a certain type of white blood cell. These are able to detect things that are foreign to the body(microorganisms). They then engulf the microbes + digest them. These white blood cells are non-specific + attack things not meant to be there.

A different group of white blood cells attack specific microorganisms. These have receptors that recognise particular antigens. Antigens are substances that trigger immune responses. They're usually protein molecules on the surface of a MO cell. Some white blood cells produce antibodies, these are proteins that are specific to a particular antigen. Different MO's have different antigens, so a different antibody is needed to recognise each one. Antibodies latch onto invading MO's + either mark it so the other white blood cells engulf + digest it. Or they bind to + neutralise viruses or toxins. Or some can even attach to bacteria + kill them directly. Once the right white blood cell recognises the antigens on a MO it divides to make identical cells. They make lots of the right antibody to fight the infection. Some blood cells stay in the blood after the infection has been fought off(memory cells). These reproduce very quickly if the same antigen enters the body for a 2nd time. The memory cells produce loads of antibodies which kill the MO's before you're ill. This is immunity.

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B2 - Vaccination

When you're infected with a new MO, it takes white blood cells a few days to get their numbers up + make the right antibodies. By that time you can become ill. Immunisation is injecting dead/inactive MO's. These carry the same antigens so your body produces antibodies to attack them even though the MO is harmless. The body also produces memory cells that recognise the antigens of MO's + stay in the blood. If live MO's of the same type appear after that, memory cells rapidly mass-produce antibodies + kill them off. This means you can get rid of the disease causing MO's before they make you sick.

To prevent outbreaks of diseases(epidemics) a large % of the population need to be vaccinated. If a large number aren't vaccinated diseases can spread quickly + lots of people will be ill at the same time. If most people are vaccinated people who aren't vaccinated are unlikely to catch it because there are fewer people to pass it on.

Vaccines + drugs are never 100% safe for everyone. People can have side affects but can be more serious for some than others. 1 in 4 children who have meningitis vaccination get a painful swelling at the site of injection and 1 in 50 have fever. Genetic differences mean people react differently. Anaesthetic drugs stop people feeling pain, genetic differences mean the length of time this stays for is different.

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B2 - Antimicrobials

These are chemicals that inhibit the growth of MO's or kill them without damaging your own body cells. They're used to clear up infections that your immune system has trouble with. Antibiotics are an antimicrobial that kill bacteria. Antibiotics don't kill viruses, like flus + colds.

MO develop random mutations in their DNA. This can change the MO's characteristics. Sometime the organisms is less affected by a particular antimicrobial. For the MO, the ability to resist antimicrobials is an advantage. It can survive even if the host is being treated against it. It has time to reproduce lots + live longer. The leads to the gene for resistance being passed on to offspring(natural selection). This is how it spreads + becomes common over time. It's a problem for people who get infected with these MO's because you cant easily kill them with antimicrobials. Sometimes drug companies come up with new antimicrobials but superbugs that are resistant to most known antimicrobials are becoming more common.

The more antibiotics are used, the bigger antibiotic-resistance becomes. People should only use them if needed. You also should take all antibiotics doctors prescribe you, if you don't this increases the risk of antibiotic resistant bacteria emerging.

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B2 - Drug Trials

New drugs are always developed to help fight diseases. These are often developed using human cells grown in the lab. You can measure the effect the drug has on human cells. It can't create the whole system or organism, so the drugs still aren't 100% safe and they may not definitely work. All new drugs must be tested on at least 2 different species of live mammal before given to humans. Many mammals are given these drugs as they have systems similar to humans.

Drugs are tested on humans in clinical trials. First it is tested for safety on healthy volunteers, if the results are good they are tested on people suffering that illness. That would be a test of both safety + effectiveness. Placebos are used in human drug trials. These are fake treatments where you don't use the real drug. You can compare the group given the drug + the one given the placebo to see whats actually working.

Blind trial - patients don't know they've been given the drug because patients who know they're being treated may feel better for psychological reasons. Double Blind - even scientists don't know who has the drug so they aren;t subconsciously influenced by their knowledge. Open Label - patients and scientists know who has the drug. Human drug trials usually last a long time so you can get the full effect + see any long term side effects.

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B2 - The Circulatory System

Blood is circulated around the body in blood vessels, + carries oxygen + nutrients to the body cells. Waste substances like carbon dioxide are carried away from cells. The heart is a pumping organ + keeps blood flowing through vessels. It's a double pump, right side pumps deoxygenated blood to lungs to collect oxygen + remove carbon dioxide. Left side pumps oxygenated blood around body. The heart's made of muscle cells that keep it beating continually. These need their own blood supply to deliver nutrients + oxygen needed to keep the heart beating. Blood's supplied to heart by 2 coronary arteries which branch from the base of the aorta.

Arteries - carry blood away from heart to body cells. Comes out the heart at high pressure so artery walls need to be strong + elastic. Veins - carry blood to heart. Blood is at lower pressure in veins so walls aren't as thick. They have bigger lumen than arteries to help blood flow easier, and have valves to keep blood flowing in the right direction. Capillaries - tiny branches of arteries. Carry blood really close to every cell in the body to exchange substances with them. Permeable walls so substances can diffuse in + out. Supply nutrients + oxygen + take away wastes like carbon dioxide. Their walls are only 1 cell thick. This increases the rate of diffusion by decreasing the distance over which it happens.

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B2 - Heart Rate and Blood Pressure

Heart rate is the number of times your heart beats in 1 minute, measured in BPM. Pulse rate is number of times an artery pulsates in 1 minute. The pulsation of an artery is caused by blood being pumped through it by a heart beat.

When your heart muscle contracts, blood's forced out of the heart, increasing your blood pressure. When the heart relaxes it fills with blood + blood pressure decreases. You can measure blood pressure by taking a reading of the pressure of the blood against the walls of an artery. Blood pressure measurements have 2 values. It may be written as "135 over 85", the higher value is the pressure of the blood when the heart contracts, + the lower value is the pressure of blood when the heart relaxes.

High blood pressure increases the risk of heart disease. The inner lining of an artery is usually smooth + unbroken, but high blood pressure can damage it. Fatty deposits can build up in damaged areas of arteries, these deposits restrict blood flow + cause blood pressure in arteries to increase. If a fatty deposit breaks through the inner lining of an artery completely a blood clot may form around it. The blood clot could block the artery completely or break away + block a different artery. If a coronary artery becomes completely blocked an area of the heart muscle will be cut off from it's blood supply receiving no oxygen causing heart attack.

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B2 - Heart Disease

Heart disease can be linked to lifestyle factors like how much you eat + how much exercise you do. Some people are more at risk due to their genes.

Poor Diet - cholesterol makes up most of fatty deposits that form in damaged arteries. If the cholesterol level is high the risk of heart disease is increased. It is linked to eating foods high in saturated fat. High in salt also increases the chance + increases blood pressure. Smoking - Carbon monoxide + nicotine increase heart disease. Carbon monoxide reduces amount of oxygen the heart gets leading to a heart attack. Nicotine increases heart rate increasing blood pressure. Stress - people are stressed when under pressure. Blood pressure can increase. Misuse of Illegal drugs - Ecstasy + cannabis increase blood pressure. High Alcohol intake - increases blood pressure. Regular exercise reduces risk of heart disease because it burns fat + strengthens heart muscles.

Epidemiology studies the patterns of diseases + factors that affect them. The can help identify lifestyle risk factors. You can study a group with heart disease + look for similarities in their lifestyle like smoking/poor diet. They also involve large scale genetics studies. You could map the genetic makeup of a group then see if there are any genetic similarities between people who have heart disease.

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B2 - Homeostasis The Basics

Homeostasis is about balancing inputs with outputs to maintain a constant internal environment. The conditions in the body need to be kept steady even when external environmental things change. Your cells need the right conditions to function properly. There are automatic control systems in the body that regulate the internal environment. Including nervous + hormonal communication systems. All your automatic control systems are made up of 3 main components which maintain a steady condition - receptors, processing centres + effectors.

Your automatic control systems keep your internal environment stable using negative feedback. When the level of something gets too high or too low your body uses negative feedback to bring it to normal.

Receptor - detects the change in environment. Processing centre - receives information + coordinates a response. Effector - produces a response which counteracts the change.

This system is automatic.

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B2 - Controlling Water Content 1

Water level in cells is important, your body needs to maintain the concentration of its contents at the correct level for cell activity. Inputs - water gained from drinks, food + respiration. Outputs - water lost through sweating, breathing, in faeces + urine.

Kidneys balance the levels of water, waste + other chemicals in the body. They filter small molecules from the blood(water, sugar, salt + waste). They reabsorb all the sugar, + as much salt + water as the body requires. This is controlled by the hormone ADH. Whatever isn't reabsorbed forms urine which is excreted by kidneys + stored in bladder.

Kidneys produce dilute or concentrated urine. The concentration depends on the concentration of blood plasma which varies with external temp, exercise level + intakes of fluids + salt.

External temp - this affects the amount you sweat. Sweating causes water loss. When its hot kidneys reabsorb more water into blood. Meaning concentrated urine is produced. Exercise - You sweat to cool down having same effect as heat, a concentrated small volume of urine. Fluid+Salt intake - not drinking or too much salt produces concentrated urine. Drinking lots produces lots of dilute urine.

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B2 - Controlling Water Content 2

Concentration of urine is controlled by the hormone anti-diuretic hormone(ADH). It's released into the blood stream by the pituitary gland. The brain monitors the water content of the blood + instructs the pituitary gland to release ADH into the blood according to how much is needed. Water regulation is controlled by negative feedback.

Receptor in brain detects the water content level > Processing centre in brain receives the information + coordinates response > Pituitary gland releases right amount of ADH so kidneys reabsorb right amount of water(less ADH less water).

ADH is regulated by negative feedback, but some drugs interfere with natural state of affairs which affects your urine.

Drinking alcohol results in larger amount of dilute urine. It suppresses the production of ADH so kidneys reabsorb less water. More water passes out the body as urine causing dehydration.

Ecstasy results in a smaller amount of concentrated urine. Causes production of ADH to increase so kidneys reabsorb more water. Less water passes out the body as urine.

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B3 - Adaptation and Variation

A species is a group of organisms that can breed together to produce fertile offspring.

Animals + plants adapt to their environment. Adaptations make individuals of a species more likely to survive + produce offspring, so the whole species is more likely to exist in its environment. Cactus - they have a round shape so also a small surface area compared to their volume to reduce water loss. Thick waxy layer(cuticle) + leaves reduced to spines to reduce water loss. Store water in thick stem to use to survive when not much around. Shallow extensive roots, ensuring water is absorbed quickly. Fish - gills extract oxygen from water for respiration. Tail fins with large surface area to propel through water. Other fins used for stability. Streamlined so they can move with little resistance. A swim bladder so they can ajust the amount of has in the swim bladder to change depth in the water without using energy.

There are variations within one species, some of this is genetic so can be passed onto offspring. One cause of genetic variation is when genes change. These are mutations, causes by outside factors like radiation or chemicals, + by mistakes. If mutations occur in body cells they have little or no effect but can lead to cancer. If they occure in sex cells there's more effect because it will be passed on to all cells of the offspring. This causes offspring to develop new characteristics, some harmful but some help them to survive.

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B3 - Natural Selection > "Survival of the fittest"

Living things show genetic variation. Resources they need to survive are limited, so individuals must compete for them to survive. Some varieties of a particular species have better chances of survival. They will have an increased chance of reproducing + passing on their genes. A greater proportion of individuals in the next generation will have characteristics that help them to survive. Over generations the species becomes better able to survive. The best features are naturally selected.

E.g. All the rabbits once had short ears + managed OK. One day a rabbit with big ears was born + had better hearing, meaning it got away from predators quicker. This rabbit reproduced lots of rabbits with big ears. All the others died because they couldn't hear as well so only big eared ones were left.

Selective breeding is where humans choose what gets selected. Humans can deliberately choose a feature they want to appear in the next generation and only breeding from animals or plants that have it. Selective breeding may promote features that dont help survival.

E.g. a breeder may choose to only breed from cows that produce the most milk so the future generation will produce more milk than the previous. This doesn't help the cow survive, it helps the farmer make more money.

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B3 - Evolution

Life on earth began about 3500mil years ago. There are a lot of species that have become extinct. The very first living things were simple, life then evolved + became more complex + varied. All living things that exist now + have ever existed evolved from the simple early life forms.

Different mutations create different new features in the two groups of organisms. Natural selection works on new features so if they are a benefit they spread through each of the populations. Environmental changes play a part. Fossil records + DNA provide evidence for evolution. There is evidence in the fossile record which shows species getting more complex as time goes on. DNA controls the characteristics of living things. It mutates + changes over time. All living things have similarities in their DNA, the more closely related 2 species are the more similar their DNA is.

Charles Darwin proposed the theory of evolution by natural selection, by making observations + applying creative thought to his findings. But Lamarck argued if a characteristic was used a lot by an animal it would become more developed. He thought the characteristics could be passed on to offspring. Like if a rabbit did lots of running + had big leg muscles, its offspring would too. People realised characteristics don't have a genetic basis so can't be passed to offspring.

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B3 - Biodiversity and Classification

Biodiversity: number of different species on earth - range of different types of organisms(plants,animals,microorganisms) - genetic variation between organisms of same species. The more plants available the more resources there are to develop new food crops. New medicines are discovered using chemicals produced by living things. Gigitalis(drug for heart disease) was discovered in foxglove. When a living organism becomes extinct, the chemicals it produces are not longer available.

The rate of exinction is increasing. There is a correlation between the growth of the world's population and number of species extinctions. This suggests alot is due to human activity. Humans cause extinction directly by hunting (Tasmanian wolf). Humans have cause it indirectly by destroying habitats or introducing new species which others can't compete with.

Classification is organising organisms into groups. There are 5 kingdoms, bacteria, fungi, algae, plants + animals. Each kingdom is divided into more groups until you get to a species. As you go down the groups, the number of types of organisms inside decreases but the number of things they have in common increases. Classifications shows evolutionary relationships between different organisms.

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B3 - Interactions Between Organisms

The environment provides factors essential for life: Light - plants us to make food. Food - for animals. Oxygen - animals + plants. Water - for all living organisms. If any of these are in short supply the species have to compete for it. If there isn't enough some won't survive. This will limit the size of population in that habitat. Organisms depend on other organisms for food, this is interdependence.

The interdependence of living things in a habitat means major change in the habitat can have serious effects.

The fossil record contains many species that don't exist any more. Like all different species of dinosaurs + mammoths are extinct with only fossils to say they existed at all. Rapid change in environment can cause a species to become extinct. 3 changes that can cause this: The environmental conditions change + the species can't adapt to the change. A new species is introduced which is a competitor, disease organism or predator of that species. An organism in its food web that it is reliant on becomes extinct.

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B3 - Energy in an Ecosystem

Energy from the sun is the energy source for all life on earth. Plants use a small % of light energy for photosynthesis. The light energy is converted into chemicals which make up plants cells. Energy's transformed between organisms in an ecosystem when animals eat plants + animals. Energy is transferred when decay organisms feed on dead organisms + waste materials. Energy is lost at each stage, much is used for staying alive(respiration). Most energy is lost to surroundings as heat. Its also lost at each stage of the food chain as waste products + uneaten parts of organisms (bones).

The numbers show the amount of energy available to the next stage of a food chain. 80000kJ is available to greenfly. Energy lost at 1st stage = 80000kJ - 10000kJ = 70000kJ lost.

Efficiency at 1st stage = 10000kJ ÷ 80000kJ x 100 = 12.5% efficient.

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B3 - The Carbon Cycle


1) theres one arrow going down, the whole cycle is powered by photosynthesis. 2) In photosynthesis plants conver carbon from carbon dioxide into sugars. Plants incorporate this into carbohydrates, fats + proteins. 3) Eating passes the carbon compounds in the plants along to animals in a food chain or web. 4) Plant + animal respiration whilst the organisms are alive release carbon dioxide into the air. 5) Plants + animals eventually die + decompose. 6) When they decompose they're broken down by microorganisms. The decomposers release carbon dioxide into the air by respiration as they break down the material. 7) Combustion of fossil fuels release carbon dioxide into the air.

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B3 - The Nitrogen Cycle

The atmosphere contains 78% nitrogen gas. This is unreactive so can't be used directly by plants or animals. Nitrogen is needed to make proteins for growth. Plants get nitrogen from soil but it needs to be turned into nitrates. Animals only get proteins by eating plants. Nitrogen fixation is the process of turning nitrogen into nitrogen compounds in the soil which plants can use. Lightning - the energy in a bolt of lightning is enough to make nitrogen react with oxygen in the air to give nitrates. Nitrogen fixing bacteria - in roots + soil. Decomposers break down proteins in dead plants + animals, + urea in excreted animal waste into ammonia. Ammonia is turned into nitrates by nitrifying bacteria found in soil.

Decomposers - decompose proteins + urea + turn them into ammonia.

Nitrifying bacteria - turn ammonia in decaying matter into nitrates(nitrification)

Nitrogen fixing bacteria - turn atmospheric nitrogen into nitrogen compounds for plants.

Denitrifying bacteria - turn nitrates into nitrogen gas. No benefit to living organisms.

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B3 - Measuring Environmental Change

Temperature - this varies all the time, however measurements taken using instruments over a long period of time could indicate the climate is changing. Nitrate level - can be used as an indicator of environmental change in water. An increase in nitrate levels can be caused by sewage/fertilisers entering the water. Carbon dioxide level - can measure environmental change in the air. An increase could be caused by humans(burning fossil fuels) . Increased levels increase the rate of global warming.

Lichen - Air pollution measured by looking at lichen which are sensitive to sulfur dioxide in the atmosphere. Number + type of lichen at a location will indicate how clean the air is. The more there are the more clean it is.

Mayfly Nymphs - If raw sewage is released into a river the bacterial population in water increases + uses up oxygen. The nymphs are a good indicator for water pollution because they're sensitive to the level of oxygen in water. The more mayfly nymphs, the cleaner the water.

Phytoplankton - population increases when levels of nitrates + phosphates in water increase, this is called algal bloom. Adding fertilisers or sewage to water causes an increase in nitrates + phosphates so algal blooms can indicate water pollution.

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B3 - Sustainability

Damage done to the environment can be repaired. This means it won't be the same for future generations. We're placing more pressure on the planet's limited resources such as fossil fuels. We need to plan carefully so we don't mess up the future. SUSTAINABILITY MEANS MEETING THE NEEDS OF TODAYS POPULATION WITHOUT HARMING THE ENVIRONMENT SO THE FUTURE GENERATIONS CAN MEET THEIR OWN NEEDS. Maintaining biodiversity is part of sustainability. Loss of biodiversity means the future generations wont be able to get the things we do today.

Packaging is usually thrown away. The resources that have gone into making the packaging material aren't re-used so are not available for the future. Energy has been used to make packaging + to produce energy. Most waste is thrown in landfill sites using up space + damaging environment.

Sustainability is improved by: using renewable materials, use paper/card instead of plastic because more trees can be planted. Use less energy by recycling materials as making things with recycled objects uses less energy. Create less pollution by using biodegradable products like wood.

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