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B1a 1

Co-ordination and Control


Responding to change


Reflex actions


The menstrual cycle


Controlling fertility artificially


Controlling conditions

B1a 1.1 Responding to Change • • • •

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It is the nervous system that enables you to react to your surroundings and coordinates your behaviour The nervous system carries electrical signals, or impulses, at fast speeds that allow you to react to surroundings very quickly Controlling many of your body’s processes are chemical substances called hormones, which are made and released, or secreted, by special glands Any changes in the surroundings are called stimuli and are picked up by specialised cells called receptors. These are usually clustered together in special sense organs, such as your eyes and skin Once a sensory receptor picks up a stimulus, the information is sent as an electrical impulse along special cells called neurones, which are collected in bundles called nerves. The impulse travels until it reaches the central nervous system (CNS), made up of the brain and spinal cord The cells which carry impulses from sense organs to the CNS are sensory neurones The brain processes the information it is given and sends impulses out along special cells, which carry impulses from the CNS to the rest of your body. These cells are called motor neurones and they carry impulses to make the right bits of your body – the effector neurones respond Effector organs are muscles or glands. Your muscles respond to the arrival of impulses by contracting. Your glands respond by secreting chemical substances The way the nervous system works can be summarises by: receptor → sensory neurone → co-ordinator (CNS) → motor neurone → effector

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B1a 1.2 Reflex Actions • • •

Automatic responses in your body happen when, for example, you touch something hot or sharp and pull your hand away quickly before you even feel the pain. These automatic responses are called reflexes Reflexes help all animals avoid danger because they happen so fast Three types of neurone are involved in reflex actions: - sensory neurones - motor neurones - relay neurones, which connect the two above neurone types An impulse passes from the sensory receptor along the sensory neurone, to the CNS. It then passes along a relay neurone, usually in the spinal cord, and straight back along the motor neurone. From there the impulse arrives at the effector organ, usually a muscle for a reflex. We call this the reflex arc Your nerves are not joint together directly, but instead have junctions between them called synapses. The impulses have to cross this gap, but cannot leap it, so a chemical message is released, which crosses the synapse and releases an electrical impulse that travels along the relay neurone Most reflex actions can be shown as: stimulus → receptor → co-ordinator → effector → response

B1a 1.3 The Menstrual Cycle • • •

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Hormones control the activity of individual cells, and this is the case in a woman’s menstrual cycle The levels of hormones released by the brain and ovaries affect a woman’s body The average length of the menstrual cycle is about 28 days: - A new egg matures for around 12 days - After maturing for about 14 days, the egg is released, this is known as ovulation - The lining of the womb stays thick for several days after release - If the egg is fertilised by sperm, pregnancy takes place and the lining of the womb protects the developing embryo and provides food - If the egg is not fertilised, the dead egg and womb lining are shed, this is the monthly bleed, or the period All of these changed happen because of hormones, made and secreted by the pituitary gland (a pea-sized gland in the brain) and the ovaries The hormones also stimulate the ovaries to produce the female sex hormone, called oestrogen Also released from the pituitary gland, is a hormone called FSH which makes eggs mature in the ovaries and stimulates the ovaries to produce oestrogen Oestrogen stimulates the lining of the womb to build up ready for pregnancy, and stimulates the pituitary gland to make another hormone, called LH LH stimulates the release of a mature egg in the middle of the menstrual cycle

B1a 1.4 Controlling Fertility Artificially • •

The contraceptive pill can be taken to control fertility – oral contraceptives The pill contains many female hormones, mainly oestrogen, which affect the ovaries and prevent eggs being matured and the ovaries from releasing them – because without mature eggs, you can’t get pregnant People who want to get pregnant but can’t can now use science to do so – eggs can be removed from the body and fertilised with sperm outside the body, and reinserted

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B1a 1.5 Controlling Conditions •

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Your body’s internal environment (i.e. the conditions inside your body) is very important. Organs cannot work properly if it keeps changing, so many of the processes taking place inside your body try to keep things as constant as possible. This balancing act is known as homeostasis Water especially can move in an out of the body, but we can consume water via food and drink Temperature is another factor we need to control, as it is vital that we keep it at 37oC for it is at this temperature that enzymes work best. If your body temperature rises or decreases just a few degrees, processes in cells will stop happening and you will die We also need to control blood sugar levels The pancreas keep the glucose concentration in our blood constant for us

B1a 2 Healthy Eating 2.1

diet and exercise


weight problems


fast food

B1a 2.1 Diet and Exercise • •

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A healthy diet contains: carbohydrates, proteins, fats, vitamins, minerals, fibre and water When a diet is unbalanced, a person becomes malnourished and you will end up with deficiency diseases if you don’t consume enough vitamins or minerals (e.g. Scurvy is the disease caused by a lack of Vitamin C) Younger people need more energy than older people Males need more energy than women of the same age – unless they are pregnant The rate at which the chemical reactions in the cells of the body happen varies a great deal between people. This rate is known as the metabolic rate, and the proportion of muscle to fat in your body affects this rate. Other factors which affect metabolic rate include the amount of activity you do, as exercise increases your metabolic rate for a short time after you’ve even finished exercising, and some scientists think you can inherit metabolic properties from your parents

B1a 2.2 Weight Problems •

Your BMI or body/mass index compares your height and weight in this formula: weight BMI = (height)2

The average BMI is between 20 and 30, but if yours is under 18.5 or over 35 then your health is at risk Excess energy is stored as fat, and too much fat can make you obese You can lose weight by eating less, especially less energy-rich foods, such as chips Increasing your exercise periods will also help you to lose weight In some parts of the world, there is a major lack of food, and people suffer from starvation, where you become so thin, and you muscles begin to wear away. In developed countries, this problem happens if people have the mental disorder anorexia (loss of appetite) nervosa

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B1a 2.3 Fast Food • • • •

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The amount of, and type of, fat you have in your body also affects you cholesterol levels Cholesterol is a substance made in the liver, which is transported around the body in blood. It is needed to make cell membranes, sex hormones and other hormones High levels of cholesterol increase your risk of getting heart disease It isn’t only the overall level of cholesterol in your body, there are two completely different types of lipoproteins to take into account - low density lipoproteins (LDLs) are known as ‘bad’ cholesterol, and raised levels of these increase your risk of heart problems - high density lipoproteins (HDLs) are known as ‘good’ cholesterol, and they reduce your risk of getting heart disease A good balance of HDLs and LDLs is important for a healthy heart There are three main types of fat which affect your cholesterol: - saturated fats increase blood cholesterol levels, and are found in animal fats, like milk, butter and cheese - mono-unsaturated fats have two useful effects. They reduce your overall cholesterol levels and improve the balance between HDLs and LDLs. These fats are found in foods like olive oil, peanuts and some margarines - polyunsaturated fats are even better at reducing cholesterol levels and balancing LDLs and HDLs, and are found in foods such as sunflower oil and oily fish Salt is needed, like fat, in your body to allow the nervous system to work

B1a 3

Drug Abuse




legal and illegal drugs




smoking and your health

B1a 3.1 Drugs • • • • • •

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A drug is defined as a substance in which alters the way the body works. It can affect your body, your mind or both Most drugs, both recreational and medicinal originally come from natural substances, often plants Caffeine, nicotine and alcohol (the chemical ethanol) are all legal drugs in the UK Other drugs, such as cocaine, ecstasy and heroin are illegal Which drugs are legal and which are not vary between different countries You can get addicted to drugs; because some drugs change the chemical processes in your body making you so addicted. This is when you become dependent on them, and cannot manage without it properly. When an addict tries to stop taking or using a drug, they suffer from withdrawal symptoms, which include sweating, pains, headaching and cravings for their drug People often take recreational drugs because they make them feel good about themselves There is no drug without any risks attached Cannabis has a label as a ‘safe’ drug, but this is proven not to be the case

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B1a 3.2 Legal and Illegal Drugs • •

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The most common drugs around are everyday drugs, such as caffeine Many drugs used for medicinal purposes have no or little effect on your nervous system, whereas all drugs which people use for pleasure affect your brain and nervous system, and these are the changes people enjoy taking drugs for People might take drugs to help them cope with everyday life, such as alcohol, nicotine and caffeine. Few people who take these drugs would consider themselves addicts, but they also affect your brain Some recreational drugs are far more harmful than others, but they are all dangerous Legal recreational drugs include ethanol (alcoholic drinks), nicotine (cigarette smoke) and caffeine (coffee, tea and cola) Illegal recreational drugs include cannabis, cocaine, heroin, ecstasy and LSD Drugs can also be used for sporting purposes, as some drugs can enhance sporting performance

B1a 3.3 Alcohol • • • • • •

Alcohol is part of social life for some people In small amounts, alcohol (containing the drug nicotine) is harmless, but large consumptions and binging on alcohol can be extremely harmful Alcohol is poisonous but the liver can usually break it down, and get rid of it before permanent damage is done to your health Alcohol can also affect your mind: when drunk, you make foolish decisions Some people drink heavily for many years becoming alcoholics Alcoholics may develop cirrhosis of the liver, which destroys your liver tissue, or they can get liver cancer which spreads far quicker and can be fatal. Also, alcohol in extremely large quantities can be harmful to the brain, making it soft and pulpy and stopping it from working, causing death Alcohol is linked to many other problems, the most common of which being drinkdriving. Driving under the influence is a top killer in the UK today. Also linked to alcohol is domestic violence

B1a 3.4 Smoking and Your Health •

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Nicotine is the addictive substance found in tobacco smoke, and it makes people feel calm, contented and able to cope. The number you need to smoke to get these effects tends to increase, so the number you smoke daily increases over the years Tar is the sticky black chemical in tobacco smoke that builds up in your lungs, turning them from pink to grey, and it makes smokers much more likely to develop bronchitis. The build-up of tar in your lungs can also lead to the delicate air sacs in the lungs breaking down, called emphysema, making the lungs less efficient Tar is also a major carcinogen (a cancer-causing substance) Carbon monoxide is another substance found in cigarette smoke, which is a very poisonous gas, picked up by your red blood cells. Carbon monoxide in cigarette smoke affects pregnant women in particular. During pregnancy, a woman needs oxygen, not just for her own cells, but for her developing foetus as well Mums who smoke when pregnant have an increased risk of having: - a premature birth (born too early, will struggle to survive) - a baby with a low birth mass (more at risk of developing problems) - a stillbirth (where the baby is born dead)

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B1a 4 Controlling infectious diseases 4.1



defence mechanisms


using drugs to treat diseases


changing pathogens and mutation


developing new medicines


pathogen immunity

B1a 4.1 Pathogens • • • • • • •

An infectious disease is caused by a microorganism entering and attacking your body. They are infectious because people can pass them between one another Microorganisms which cause disease are called pathogens Common pathogens are bacteria and viruses A bacterium is a tiny single cell, made up of cytoplasm surrounded by a membrane and a cell wall. The genetic information in bacteria cells is not held in the nucleus Not all bacteria are harmful Viruses are even smaller than bacteria, and are made up of a protein coat containing the genetic material Bacteria and viruses cause disease by multiplying very rapidly: - Bacteria simply split in two and often produce toxins (poisons) affecting your body - Viruses take over your cells as they reproduce, destroying cells in the process Ignaz Semmelweiss page 63

B1a 4.2 Defence Mechanisms •

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There are several ways in which people spread pathogens: - droplet infection, often when people talk or sneeze tiny droplets full of pathogens are expelled from your breathing system - direct contact, through direct contact of the skin, such as impetigo and certain sexually transmitted diseases, e.g. genital herpes - contamination infection, eating and drinking contaminating goods, e.g. raw meat - through a break in skin, some pathogens can enter your body through cuts and scratches and needle punctures, e.g. HIV/AIDS or hepatitis Your body has its own defence mechanisms, for example when you cut yourself, you bleed, but the platelets quickly form a clot which dries into a scab Your breathing system in particular is vulnerable, as every time you breathe you draw in thousands of pathogens from the air – although your breathing organs produce mucus, a sticky substance, to trap the pathogens If a pathogen gets into your body past these defence mechanisms, your second line of defence are the white blood cells of your immune system. The white blood cells help in a number of ways (see table on next page): - some produce antibodies which target bacteria or viruses - some produce antitoxins which counteract the toxins released by pathogens - some white blood cells ingest (take in) the pathogens and destroy them

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B1a 4.3 Using Drugs to Treat Disease When we have infectious diseases, we take medicines, but often they don’t destroy pathogens, they simply ease the pain, e.g. aspirin • Drugs which do kill disease-causing bacteria are called antibiotics • Alexander Fleming discovered penicillin after he came back from a holiday to discover that the mould growing on his plates had killed the bacteria growing on them • It was Ernst Chain and Howard Florey who first put penicillin into practice Antibiotics work by killing the bacteria whilst inside your body, and can be used to cure diseases such as plague and TB Antibiotics have no effect whatsoever on viruses, as viral pathogens work inside your body’s cells, making it hard to find treatments which will kill the virus and leave your cells in tact •

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B1a 4.4 Changing Pathogens and Mutation • • •

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Not all bacteria are killed when you take an antibiotic. The ones that remain have naturally mutated and so are not affected by the antibiotic If antibiotics do not kill a bacteria, they are resistant to that antibiotic MRSA came about due to resistance of antibiotics – where these resistant bacteria are carried around hospitals easily by doctors and nurses travelling from patient to patient An outbreak of a disease which affects people on a major scale is an epidemic, usually affecting a single country A pandemic can affect several countries The flu pandemic between 1918 and 1919 killed between 20 and 40 million people, and this came about from cell mutation

B1a 4.5 Developing New Medicines •

When developing new medicines, scientists must keep in mind that they should be: - effective, as in it will cure the disease or prevent the disease - safe, it should not be toxic (poisonous) and there shouldn’t be any unacceptable side effects - stable, it should be able to be used for quite some time and stored for some time - successfully taken into and removed from your body, the medicine must be able to reach the desired destination and your body must be able to remove it once it has done its work

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B1a 4.6 Pathogen immunity •

Every cell has unique proteins on its surface called antigens, and antigens on the microorganism which get inside your body differ from those on your cells, which is how your immure system recognises they are different Your white blood cells appear to ‘remember’ the pathogens they destroy and so can make the antibodies again very quickly should they encounter that particular pathogen again – this is called being immune to a disease Immunisation can happen through vaccination, where a tiny amount of the disease you are being immunised against is injected into your body, so that your shite blood cells can make the appropriate antibodies No medicines are risk-free, including medical vaccines

B1b B1b 5 Adaptation to Environment 5.1

adaptation in animals


adaptation in plants


competition in animals


competition in plants

B1b 5.1 Adaptation in Animals • • • • • •

Living creatures have special features, or adaptations, which help them to survive in certain conditions Animals have adapted to live in extreme climates. The amount of heat you lose is closely linked to your surface area : volume ratio (SA:Vol) Some animals have fat layers which provide warmth as well as a food supply Some animals are camouflaged to protect them from predators Certain creatures have adapted to live in dry and hot climates, such as large ears Other adaptation examples include a camel’s feet. The size of them is so important because it stops them from sinking into the sand

B1b 5.2 Adaptation in Plants • • • •

There are some plants which live in desert conditions which need to prevent water loss, and they do this by controlling the SA:Vol as well as curling their leaves Controlling the transpiration stream is important in plants Many plants store water in their tissues to prevent water loss. Plants which store water in their fleshy leaves are called succulents Plants like cacti have adapted by having vicious thorns. Other plants avoid being eaten by having poisonous chemicals and unpleasant tastes

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B1b 5.3 Competition in Animals • •

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Animals best adapted to their environment are most likely to succeed in competition Animals compete for many things, including water, territory and mates. Animals which eat a wide range of plants are most likely to survive, as picky eaters will die of starvation if their food supply runs out Animals try to avoid competition with others as best as they can The best adapted creatures are those who find it easier to find food and a mate, and these are the most likely to succeed in competition Although it is hard to avoid competition, many animals attempt to do so by setting up a territory, but this can also encourage disputes

B1b 5.4 Competition in Plants • • •

Plants compete for light, water and nutrients from the soil A successful competitor in plants is one which avoids competing with its own seedlings Some plants might ‘mark their territory’ by using mini explosions to disperse their seedlings

B1b B1b 6 Variation and Inheritance 6.1



different methods of reproduction




genetic engineering

B1b 6.1 Inheritance •

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Animals inherit characteristics from the parents, as a result of their genetic information passed onto you in the sex cells (gametes) from which you developed. This genetic information determines what you will look like Inside the nucleus of all your cells there are chromosomes made up of DNA (deoxyribose nucleic acid). This is where the genetic information is actually stored Each of your chromosomes contains thousands of genes joined together. These are the units of inheritance

B1b 6.2 Different Methods of Reproduction • • • •

There are two types of reproduction: asexual reproduction and sexual reproduction Asexual reproduction involves one parent and the offspring are clones, where the genetic material of the offspring is identical to that of the parent Asexual reproduction is common in the smallest animals, plants and bacteria With sexual reproduction, a male sex cell and a female sex cell must join, one from each parent. If you are the result of sexual reproduction, you will inherit genetic information from both parents, having some characteristics from different parents. In animals, the involved sex cells are called the ova (eggs – single ovum) and sperm The joining of two different genetic materials ensures variation in the offspring, unlike the clones produced in asexual reproduction – which is better for competition survival

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B1b 6.3 Cloning •

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Plants can be cloned via cutting, which simply involves taking a small piece of the plant, and if it is grown under the right conditions, new roots and shoots should develop Many growers now use hormone rooting powders to encourage the cuttings Tissue culture can also now be used, which is a more modern way of cloning plants • Cloning animals involves a very different process: 1 Divide each cell into several individual cells 2 Each cell grows into an identical embryo in the lab 3 Transfer the embryos into their host mothers, which have been given hormones to get them ready for pregnancy 4 Identical cloned calves are born. They are not biologically related to their mothers

B1b 6.4 Genetic Engineering •

We can change organisms and give them characteristics that we want them to have by genetic engineering or genetic modification. To do this, we take a small piece of DNA, a gene, from one organism, and transfer it to the genetic material of a completely different organism. An example of this is genetically modifying cells to make insulin go into someone else’s body. People with diabetes need supply of the hormone insulin Genetic engineering can also help us medically in other ways. For example, if there is a mistake in your genetic information, you are said to have a genetic disease, and many people hope that genetic engineering can fix this The big drawback with genetic modification is that no one really knows for sure what the long-term effects are in using it

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B1b B1b 7 Evolution 7.1

the origins of life on our planet earth


different evolution theories


natural selection



B1b 7.1 The Origins of Life on our Planet Earth •

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Millions of species roam the planet, but scientists believe around 4 billion species have existed here at some stage, some of which have gone completely, others leaving living relatives, other still standing strong Fossils are the remains of plants or animals from many thousands or millions of years ago which are found in rocks Fossils can be formed in a number of ways: - Most were formed when harder parts of the animal or plant were replaced by other minerals over long periods of time - Some are formed when animals or plants do not decay when dead, often because the temperature is too low for decay to happen

B1b 7.2 Different Evolution Theories • •

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The theories of evolution tell us quite simply that different species have evolved since simple life forms that once existed on our planet Jean-Baptiste Lamarck was a French biologist brought around the idea of a ‘fountain of life’ and his theory was that everything had evolved from primitive worms. This theory was named inheritance of acquired characteristics Lamarck’s theory had no evidence supporting it, and as a result fell Our most modern theory began with the work of Charles Darwin, who explains that all living organisms have evolved from simpler life forms. This evolution has come about by a process of natural selection The fossil record shows us how species have evolved over time

B1b 7.3 Natural Selection • • • •

Scientists use the process of natural selection to explain today’s variety of life Whether it be from competition or adaptation for survival, natural selection determines which species will survive and continue to breed Natural selection is essentially survival of the fittest A good example is a rabbit. With all-round eyesight, extremely sharp hearing and the longest legs, they will be the ones most likely to escape a fox’s clutches, and these useful genes will be passed onto their babies Good characteristics can come about from mutations in genes, which sometimes are good and sometimes are bad – good ones will improve an animal’s chance in natural selection The main points of natural selection can be summarised by saying: mutation → variation → adaptation → survival → genes passes onto next generation

B1b 7.4 Extinction •

Of the 4 billion species estimated to have existed in the past, only a few million live on today, the rest all died out – they became extinct

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The term extinction means the permanent loss of all members of a species from the face of the Earth A species may become extinct for several reasons. One is environmental factors. For example, an organism best suited for hot climates won’t survive well in a cold place – they will be too cold, find it hard to eat and be too cold to breed. Environmental changes are the most common causes of extinction throughout history Another reason is because of other organisms. When a new predator turns up, it can wipe out unsuspecting prey animals very quickly, because the prey animals have no adaptations to avoid it. Other organisms, i.e. microorganisms, can spread diseases to the point of extinction The other main reason is through competition, also caused by other organisms

B1b B1b 8 How people Affect the Planet 8.1

the effects of the new population explosion


acid rain and the environment


global warming and earth


sustainable development


the future of our planet - in our hands

B1b 8.1 The Effects of the New Population Explosion • • •

One thousand years ago, there were around 500 million people on this planet. Now there are over 6 billion people The ever-growing population has such a bad effect on our land and natural resources The growing population also means a vast increase in waste, both human bodily and rubbish from packaging, uneaten scraps and disposable goods. This large dumping of waste makes the land unavailable for anything else and can cause serious pollution, which is exceptionally bad for the planet’s atmosphere

B1b 8.2 Acid Rain and the Environment •

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When fossil fuels are burned, carbon dioxide is released into the atmosphere as a waste product. But this is not the only waste, sulphur impurities react with oxygen gas to form sulphur dioxide gas. These gases pollute the air, and have devastating effects All waste gases produced from burning fuel can cause serious breathing problems Sulphur dioxide and nitrogen oxide gases dissolve in the rain and react with oxygen in the air to make the rain acidic – acid rain Acid rain can ruin buildings, homes, statues and habitats for animals and plants

B1b 8.3 Global Warming and Earth •

Normally the Earth radiates back much of the heat energy it absorbs from the Sun, keeping the surface temperature acceptable for life. Now carbon dioxide and methane are building up in the atmosphere, acting like a greenhouse around Earth The greenhouse gases absorb much of the energy which is radiated away. It can’t escape out into space. As a result, the Earth and its surrounding atmosphere are warmer than they should otherwise be – this greenhouse effect plays a part in global warming

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B1b 8.4 Sustainable Development • •

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We aim to improve the quality of our lives without risking the future of generations to come, and this is sustainable development An example of sustainable development is the replanting of trees as they are felled for wood and paper, which not only provide a good resource for wood and paper, but also continue to play home to animals’ and plants’ habitats We can improve our planet by all switching to energy-efficient light bulbs in order to help reduce carbon dioxide levels in the atmosphere We all need to make our houses more energy-efficient

B1b 8.5 The Future of Our Planet – In Our Hands •

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In the UK, we have two types of land: brown field sites and green field sites. We are able to build on both of these. When we build on a green field site, we build on a new piece of land. Brow field sites are places that have already been built on, so if we build on them, it may be refurbishments or it may be destroyed and rebuilt Similar to green field sites are green belts, which we are not allowed to build on Similar to green belts are SSSIs (Sites of Special Scientific Interest), which may have a unique or particularly interesting landscape, or be home to rare species of plants or animals and need protecting The idea of protected areas may benefit the atmosphere from pollution, as well as the actual areas themselves

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Core Biology Revision Guide