Life Process Research Paper
Life Processes
Mrs.Nerg/Gren
Living things have certain life processes in common. There are seven things that they need to do to count as being alive. The phrase MRS GREN is a way to remember them
M Movement All living things move, even plants
R Respiration Getting energy from food
S Sensitivity Detecting changes in the surroundings
G Growth All living things grow
R Reproduction Making more living things of the same type
E Excretion Getting rid of waste
N Nutrition Taking in and using food
It can be easy to tell if something is living or not. A teddy bear might look like a bear, but it can't do any of the seven things it needs to be able to do to count as being alive.
What about a car? A car can move, it gets energy from …show more content…
petrol (like nutrition), it might have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust pipe (excretion). But it can't grow or make baby cars. So a car is not alive.
Respiration
Respiration is a chemical reaction that happens in all living cells. It is the way that energy is released from glucose, for our cells to use to keep us functioning.
Remember that respiration is not the same as breathing (which is properly called ventilation).
Aerobic respiration
The glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is needed for it to work.
Here is the word equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water (+ energy)
(Energy is released in the reaction. We show it in brackets in the equation because energy is not a substance.)
Now we will look at how glucose and oxygen get to the cells so that respiration can take place and how we get rid of the carbon dioxide.
Glucose from food to cells
Glucose is a type of carbohydrate, obtained through digestion of the food we eat. Digestion breaks food down into small molecules. These can be absorbed across the wall of the small intestine into the bloodstream.
Glucose is carried round the body dissolved in blood plasma, the pale yellow liquid part of our blood. The dissolved glucose can diffuse into the cells of the body from the capillaries. Once in the cell glucose can be used in respiration.
Oxygen from the air to cells
When we breathe in oxygen enters the small air sacs, called alveoli, in the lungs. Oxygen diffuses from there into the bloodstream.
Oxygen is not carried in the plasma, but is carried by the red blood cells. These contain a red substance called haemoglobin, which joins onto oxygen and carries it around the body in the blood, then lets it go when necessary. Like glucose, oxygen can diffuse into cells from the capillaries.
Red blood cells carry oxygen around the body
Carbon dioxide from cells to the air
The carbon dioxide produced during respiration diffuses out of the cells and into the blood plasma. The blood carries it to the lungs. It then diffuses across the walls of the alveoli and into the air, ready to be exhaled.
Respiratory system and ventilation
The respiratory system
The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we don't need. It contains these parts: lungs tubes leading from the lungs to the mouth and nose various structures in the chest that allow air to move in and out of the lungs Ventilation
Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. Take care - this is called breathing or ventilation, not respiration. When we breathe in, we inhale. When we breathe out, we exhale.
Air passes between the lungs and the outside of the body through the windpipe, called the trachea. The trachea divides into two bronchi, with one bronchus for each lung.
Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.
Gas Exchange
We need to get oxygen from the air into the blood, and we need to remove waste carbon dioxide from the blood into the air. Moving gases like this is called gas exchange. The alveoli are adapted to make gas exchange in lungs happen easily and efficiently.
Here are some features of the alveoli that allow this: they give the lungs a really big surface area they have moist, thin walls (just one cell thick) they have a lot of tiny blood vessels called capillaries.
The gases move by diffusion from where they have a high concentration to where they have a low concentration: Oxygen diffuses from the air in the alveoli into the blood. Carbon dioxide diffuses from the blood into the air in the alveoli.
Some water vapour is also lost from the surface of the alveoli into the lungs - we can see this condensing when we breathe out on cold days.
Movement
Why do we need a skeleton?
Our skeleton is made of more than 200 bones. Calcium and other minerals make the bone strong but slightly flexible. Bone is a living tissue with a blood supply. It is constantly being dissolved and laid down, and it can repair itself if a bone is broken. Exercise and a balanced diet are important for a healthy skeleton.
The skeleton has three main functions: to support the body to protect some of the vital organs of the body to help the body move.
Support
The skeleton supports the body. For example, without a backbone we would not be able to stay upright.
Protection
Here are some examples of what the skeleton protects: the skull protects the brain the ribcage protects the heart and lungs the backbone protects the spinal cord.
Movement
Some bones in the skeleton are joined rigidly together and cannot move against each other. Bones in the skull are joined like this. Other bones are joined to each other by flexible joints. Muscles are needed to move bones attached by joints.
Joints
Basic structure
If two bones just moved against each other, they would eventually wear away. This can happen in people who have a disease called arthritis. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by synovial fluid. Tough ligaments join the two bones in the joint and stop it falling apart.
The diagram shows the main features of a joint.
Movement
Different types of joint allow different types of movement. Hinge joints allow simple movement, the same as a door opening and closing. Knee and elbow joints are hinge joints. Ball and socket joints allow movement in more directions. Hip and shoulder joints are ball and socket joints.
The bones cannot move on their own - they need muscles for this to happen.
Antagonistic Pair
Muscles work by getting shorter. We say that they contract, and the process is called contraction.
Muscles are attached to bones by strong tendons. When a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint.
Muscles can only pull and cannot push. This would be a problem if a joint was controlled by just one muscle. As soon as the muscle had contracted and pulled on a bone, that would be it, with no way to move the bone back again. The problem is solved by having muscles in pairs, called antagonistic muscles.
Biceps and triceps
The elbow joint lets our forearm move up or down. It is controlled by two muscles, the biceps on the front of the upper arm, and the triceps on the back of the upper arm. The biceps and the triceps are antagonistic muscles. when the biceps muscle contracts, the forearm moves up when the triceps muscle contracts, the forearm moves down.
This solves the problem. To lift the forearm, the biceps contracts and the triceps relaxes. To lower the forearm again, the triceps contracts and the biceps relaxes.
Cells to System
Cells are very small. They are the basic building blocks of all animals and plants.
Animal and Plant cells
Animal cells usually have an irregular shape, and plant cells usually have a regular shape
Cells are made up of different parts. It is easier to explain what these parts are by using diagrams like the ones below.
Animal cells and plant cells both contain: cell membrane, cytoplasm, nucleus
Plant cells also contain these parts, not found in animal cells: chloroplasts, vacuole, cell wall
The table summarises the functions of these parts.
Part Function Found in
Cell membrane Controls what substances can get into and out of the cell. Plant and animal cells
Cytoplasm Jelly-like substance, where chemical reactions happen. In plant cells there's a thin lining, whereas in animal cells most of the cell is cytoplasm. Plant and animal cells
Nucleus Controls what happens inside the cell. Carries genetic information.
In exams don't call the nucleus the 'brain' of the cell. That is not a good description and will not get you marks. Plant and animal cells
Chloroplast Where photosynthesis happens – chloroplasts contain a green substance called chlorophyll. Plant cells only
Vacuole Contains a liquid called cell sap, which keeps the cell firm. Plant cells only
Cell wall Made of a tough substance called cellulose, which supports the cell. Plant cells only
Cells and their functions
Humans are multi-cellular animals. That means we are made of lots of cells, not just one cell. The cells in many multi-cellular animals and plants are specialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism.
Specialised cells
You should be able to work out special features of a cell from a drawing, if you are told what the cell can do. The tables below show examples of some specialised animal and plant cells, with their functions and special features
Type of animal cell Function Special features
Red blood cells To carry oxygen Large surface area, for oxygen to pass through Contains haemoglobin, which joins with oxygen
Nerve cells To carry nerve impulses to different parts of the body Long Connections at each end Can carry electrical signals
Female reproductive cell (egg cell) To join with male cell, and then to provide food for the new cell that's been formed Large Contains lots of cytoplasm
Male reproductive cell (sperm cell) To reach female cell, and join with it Long tail for swimming Head for getting into the female cell
Type of plant cell Function Special features
Root hair cell
To absorb water and minerals Large surface area
Leaf cell
To absorb sunlight for photosynthesis Large surface area Lots of chloroplasts
Cells, tissues, organs and systems
Tissues
Animal cells and plant cells can form tissues, like muscle tissue. A living tissue is made from a group of cells with a similar structure and function, which all work together to do a particular job. Here are some examples of tissues: muscle the lining of the intestine the lining of the lungs phloem (tubes that carry dissolved sugar around a plant) root hair tissue (for plants to take up water and minerals from the soil)
Organs
An organ is made from a group of different tissues, which all work together to do a particular job. Here are some examples of organs: heart lung stomach brain leaf root
Organ systems
An organ system is made from a group of different organs, which all work together to do a particular job. Here are some examples of organ systems: circulatory system respiratory system digestive system nervous system reproductive system
Reproduction
Male reproductive system
The male reproductive system contains these parts: testes (pronounced "test-eez") glands sperm ducts urethra penis.
Testes
The two testes (one of them is called a testis) are contained in a bag of skin called the scrotum. They have two functions: to produce millions of male sex cells called sperm to make male sex hormones, which affect the way a man's body develops.
Sperm duct and glands
The sperm pass through the sperm ducts, and mix with fluids produced by the glands. The fluids provide the sperm cells with nutrients. The mixture of sperm and fluids is called semen.
Penis and urethra
The penis has two functions: to pass urine out of the man's body to pass semen into the vagina of a woman during sexual intercourse.
The urethra is the tube inside the penis that can carry urine or semen. A ring of muscle makes sure that there is no chance of urine and semen getting mixed up.
Female Reproductive System
The female reproductive system contains these parts: ovaries egg tubes uterus (pronounced "yoo-ter-russ") cervix vagina.
Ovaries
The two ovaries contain hundreds of undeveloped female sex cells called egg cells or ova. Women have these cells in their bodies from birth - whereas men produce new sperm continually.
Egg tubes
Each ovary is connected to the uterus by an egg tube. This is sometimes called an oviduct or Fallopian tube. The egg tube is lined with cilia, which are tiny hairs on cells. Every month, an egg develops and becomes mature, and is released from an ovary. The cilia waft the egg along inside the egg tube and into the uterus.
Uterus and cervix
The uterus is also called the womb. It is a muscular bag with a soft lining. The uterus is where a baby develops until its birth.
The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in place while the woman is pregnant.
Vagina
The vagina is a muscular tube that leads from the cervix to the outside of the woman's body. A man's penis goes into the woman's vagina during sexual intercourse. The opening to the vagina has folds of skin called labia that meet to form a vulva. The urethra also opens into the vulva, but it is separate from the vagina, and is used for passing urine from the body.
The menstrual cycle
The female reproductive system includes a cycle of events called the menstrual cycle. It lasts about 28 days, but it can be slightly less or more than this. The cycle stops while a woman is pregnant. These are the main features of the menstrual cycle. The start of the cycle, day 1, is when bleeding from the vagina begins. This is caused by the loss of the lining of the uterus, with a little blood. This is called menstruation or having a period. By the end of about day 5, the loss of blood stops. The lining of the uterus begins to re-grow and an egg cell starts to mature in one of the ovaries. At about day 14, the mature egg cell is released from the ovary. This is called ovulation. The egg cell travels through the egg tube towards the uterus. If the egg cell does not meet with a sperm cell, the lining of the uterus begins to break down and the cycle repeats.
If the egg cell meets and joins with a sperm cell, it is fertilised. It attaches to the lining of the uterus and the woman becomes pregnant.
Fertilisation and foetal development
Fertilisation
During sexual intercourse the man's penis releases semen into the woman's vagina. Sperm cells travel in semen from the penis and into the top of the vagina. They enter the uterus through the cervix and travel to the egg tubes. If a sperm cell meets with an egg cell there, fertilisation can happen. Fertilisation happens when an egg cell meets with a sperm cell and joins with it.
The fertilised egg divides to form a ball of cells called an embryo. This attaches to the lining of the uterus and begins to develop into a foetus (pronounced "fee-tuss") and finally a baby.
Development of the foetus
The foetus relies upon its mother as it develops. These are some of the things it needs: protection oxygen nutrients (food and water).
It also needs its waste substances removing.
The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion.
The placenta is responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord.
The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies: oxygen and nutrients diffuse across the placenta from the mother to the foetus waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother.
Birth
After nine months the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract, pushing the baby out of the mother's body.
Puberty
The reproductive system of a child is not mature and needs to change as a boy or girl develops into an adult, so that the system is fully working. These changes begin between the ages of ten and fifteen. The time when the changes happen is called puberty.
The changes happen because of sex hormones produced by the testes in boys and by the ovaries in girls. Some changes happen in boys and girls, while others just happen in boys or girls.
Here are some changes that happen to both boys and girls: underarm hair grows pubic hair grows body smell gets stronger. emotional changes growth rate increases
The time when the physical changes and emotional changes happen is called adolescence.
Boys
Here are some changes that happen only to boys: voice breaks (gets deeper) testes and penis get bigger testes start to produce sperm cells shoulders get wider hair grows on face and chest.
Girls
Here are some changes that happen only to girls: breasts develop ovaries start to release egg cells (periods start) hips get wider.
Diet, Drugs and Health
Nutrients
There are seven different nutrients: carbohydrates proteins fats minerals vitamins fibre water
Some foods are particularly rich in certain nutrients. The table shows why we need each nutrient, and some good sources of each.
Nutrient Use in the body Good sources
Carbohydrate To provide energy Cereals, bread, pasta, rice and potatoes
Protein For growth and repair Fish, meat, eggs, beans, pulses and dairy products
Fat To provide energy. Also to store energy in the body and insulate it against the cold. Butter, oil and nuts
Minerals Needed in small amounts to maintain health Salt, milk (for calcium) and liver (for iron)
Vitamins Needed in small amounts to maintain health Dairy foods, fruit, vegetables
Fibre To provide roughage to help to keep the food moving through the gut Vegetables, bran
Water Needed for cells and body fluids Fruit juice, milk, water
Effects of a Poor diet
If you have too little of a particular nutrient, we say that you have a deficiency in that nutrient. For example, fibre is needed to keep food moving through the intestines easily, and people who have a fibre deficiency in their diet may get constipation.
Mineral deficiencies
People with iron deficiency may get anaemia and have too few red blood cells. People with iodine deficiency may get a swelling in the neck called a goitre (pronounced "goy-ter").
Vitamin deficiencies
Although we only need small amounts of the different vitamins in our diet, we become ill if we don't get enough. For example, vitamin A deficiency can cause blindness. Vitamin C deficiency causes scurvy, which makes the gums bleed, and vitamin D deficiency causes rickets, which makes the legs bow outwards in growing children.
Too thin, too fat
Food is a store of chemical energy. If you look on the side of food packets you will see the food's energy content. This is usually measured in kilojoules, kJ. If we eat too little food, we will use up our store of fat and become too thin. If we eat too much food, especially foods rich in sugar and fat, we will increase our store of fat and become too fat.
It is important to balance the amount of food we eat with who we are and what we do. The amount of energy we need from our food depends on our age, our height and how much exercise we get.
For example, a one-year old baby needs 3850 kJ each day to continue to grow, whereas an adult Olympic swimmer in training needs 15,600 kJ each day. Someone who sits at a desk all day will need less food than their twin who climbs ladders all day to wash windows.
Digestive System
When you eat a piece of bread, you don't wake up next day to discover it growing out of your arm! The food we eat has to be broken down into other substances that our bodies can use. This is called digestion. Without digestion, we could not absorb food into our bodies and use it.
Digestion happens in the digestive system, which begins at the mouth and ends at the anus.
After we swallow, our food passes through these organs in turn: oesophagus or gullet stomach small intestine large intestine.
Stages of digestion Food is digested in the mouth, stomach and small intestine. Digested food is absorbed into the bloodstream in the small intestine. Excess water is absorbed back into the body in the large intestine. Any undigested food passes out of the anus as faeces (pronounced "fee-seez") when we go to the toilet.
Liver and pancreas
The liver and the pancreas play important part in digestion. The liver produces bile, which helps the digestion of fat. The pancreas produces chemicals called digestive enzymes.
Digestion and enzymes
Our teeth break food down into small pieces when we chew. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body. Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are needed so that this break-down happens quickly enough to be useful.
Enzymes
Take care - enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients: carbohydrase or amylase enzymes break down starch into sugar protease enzymes break down proteins into amino acids lipase enzymes break down fats into fatty acids and glycerol.
Carbohydrates
Carbohydrates are digested in the mouth, stomach and small intestine. Carbohydrase enzymes break down starch into sugars.
The saliva in your mouth contains amylase, which is another starch digesting enzyme. If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet.
Proteins
Proteins are digested in the stomach and small intestine. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful micro-organisms that may be in the food.
Fats
Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on.
Things that are not digested
Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down, so they are not digested.
Digestive enzymes cannot break down fibre, which is why it cannot be absorbed by the body.
Absorption and egestion
These are the processes that happen in the digestive system: ingestion (eating) → digestion (breaking down) → absorption → egestion
We've already looked at how foods are broken down by enzymes in digestion. Now we will look at how the products of digestion are absorbed into the body.
Absorption
Digested food molecules are absorbed in the small intestine. This means that they pass through the wall of the small intestine and into our bloodstream. Once in the bloodstream, the digested food molecules are carried around the body to where they are needed.
Only small, soluble substances can pass across the wall of the small intestine.
Large insoluble substances cannot pass through.
The inside wall of the small intestine needs to be thin, with a really big surface area. This allows absorption to happen quickly and efficiently. If the small intestine had a thick wall and a small surface area, a lot of digested food might pass out of the body before it had a chance to be absorbed.
To get a big surface area, the inside wall of the small intestine is lined with tiny villi (one of them is called a villus). These stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.
Egestion
Excess water is absorbed back into the body in the large intestine. What is left then is undigested food. This is stored in the rectum, the lower part of the large intestine, until we are ready to go to the toilet. It then comes out of the rectum through the anus as faeces. This process is called egestion.
Smoking and Health
Smoking is very harmful to health. It causes around 80 per cent of deaths from lung cancer, bronchitis and emphysema in the UK, and almost a fifth of UK deaths from heart disease.
Tobacco smoke contains many harmful substances. These include: tar
nicotine carbon monoxide
A normal lung and a lung from a smoker:
Tar
Tar causes cancer of the lungs, mouth and throat. It coats the surface of the breathing tubes and the alveoli. This causes coughing and damages the alveoli, making it more difficult for gas exchange to happen.
Smoke
Cells in the lining of the breathing tubes produce sticky mucus to trap dirt and microbes. Cells with tiny hair-like parts, called cilia, normally move the mucus out of the lungs.
Hot smoke and tar from smoking damages the cilia. So smokers cough to move the mucus and are more likely to get bronchitis.
Nicotine
Nicotine is addictive - it causes a smoker to want more cigarettes. Nicotine also increases the heart rate and blood pressure, and makes blood vessels narrower than normal. This can lead to heart disease.
Carbon monoxide
Carbon monoxide is a gas that takes the place of oxygen in red blood cells. This reduces the amount of oxygen that the blood can carry. This means that the circulatory system has to work harder, causing heart disease.
Drugs and Health
Drugs are substances that have effects on the body. Medicines are drugs that help people suffering from pain or disease. Recreational drugs are taken for pleasure.
Some recreational drugs are legal, such as tobacco, alcohol and caffeine. Most other recreational drugs are illegal, such as cannabis, ecstasy and heroin.
Problems with drug use
Recreational drugs can be classified as depressants or stimulants. Most recreational drugs can be addictive.
All drugs can damage the liver, because it is the liver that breaks drugs down in the body. Any drug that is misused can cause damage to the body, as well as personal and social problems. Injecting any drug with a needle and syringe that someone else has used may lead to a number of diseases from infected blood, including HIV and hepatitis.
Depressants
Depressants slow down messages in the brain and along the nerves. Alcohol is a depressant. It is found in beer, wines and spirits such as vodka.
Other depressants include cannabis, heroin and solvents (eg glue and aerosols).
Here are some of the typical effects depressants have on the body: feelings of well-being lowered inhibition slowed thinking slowed muscular activity a distorted view of the world, or hallucinations
Some of the long-term effects of depressants on the body include damage to the liver, brain and heart. They can also have the following effects: alcohol can cause weight gain solvent abuse causes a rash around the nose and mouth cannabis causes loss of memory and concentration, as well as an increased risk of mental illness.
Stimulants
Stimulants speed up messages in the brain and along the nerves. This makes you feel more alert. Caffeine is a stimulant and is found in cola drinks, coffee and tea. It makes you feel more energetic and alert, but it can also cause insomnia (difficulty in sleeping), headaches and nervousness.
Cocaine, ecstasy and amphetamines are all illegal stimulants. They make you feel more energetic and confident, but they can damage the liver and heart. They can also cause loss of memory and concentration, and bring an increased risk of mental illness.
Deseases
Many living things are so small that they can only be seen through a microscope. These living things are called microorganisms or microbes. There are three main types of microbe: fungi bacteria viruses
Fungi
Mushrooms and toadstools are fungi, but these are made of lots of cells, so they are not microbes. Yeasts are single-celled fungi, so they are microbes. Fungi are usually the biggest type of microbe. If there is just one of them, we call it a fungus.
Bacteria Bacteria are usually smaller than fungi. If there is just one of them, we call it a bacterium. Bacteria have many different shapes. Some have 'tails' (called flagella) that let them swim.
Viruses
Viruses are the smallest type of microbe. As a virus can only reproduce inside a cell, some people are not convinced that viruses are really living things.
Differences between fungi, bacteria and viruses
The table shows some of the similarities and differences between the three types of microbe.
Useful of not?
Feature Fungi Bacteria Viruses
Cell membrane ✔ ✔ ✗
Cell wall ✔
(hard) ✔
(soft) ✗
(protein coat)
Cell nucleus ✔ ✗
(circle) ✗
(strand)
People often use the word germ instead of microbe, so you might think that microbes are all harmful. But some are useful to us.
Useful microbes
Yeast cells are useful to bakers and brewers. Yeast cells can change sugar into carbon dioxide gas and alcohol. This is useful to bakers because the gas helps the bread rise, and it is useful to brewers because it adds the alcohol needed for their drinks.
Bacteria are also useful to us. For example, certain bacteria cause the changes needed in milk to make yogurt and cheese out of it.
Harmful microbes
Many microbes can cause diseases. For example here are some diseases caused by fungi: athlete's foot thrush
Here are some diseases caused by bacteria: tuberculosis, TB (affects the lungs) salmonella (causes food poisoning) whooping cough (affects the lungs)
Here are some diseases caused by viruses: chicken pox (affects skin and nerves) common cold influenza, flu measles (affects skin and lungs) mumps (affects salivary glands) rubella, german measles
Microbes cause disease when they are able to reproduce in the body. They produce harmful substances called toxins, and damage tissues and organs. We say that someone who has harmful disease-causing microbes in them is infected.
Spreading Microbes
Many harmful microbes can pass from one person to another. Diseases caused by such microbes are said to be infectious diseases. Here are some ways that harmful microbes can be spread: in air through contact with animals through contaminated food through touch in water
Air
Droplets containing microbes fly into the air when people sneeze or cough. The microbes they contain get into other people if breathed in.
Chicken pox, colds, flu, measles and tuberculosis are spread like this.
Animals
Animals may carry harmful microbes. The microbes can get into a person who is scratched or bitten by such an animal. Malaria is a tropical disease spread by a tiny fly called a mosquito.
Food
Food can have harmful microbes in and on it. The microbes get into the body when the food is eaten, causing food poisoning. Thorough cooking kills most microbes, but they can survive under-cooking. Careless handling of food increases the risk from harmful microbes.
Touch
Microbes can be passed from one person to another when people touch each other, or when they touch something an infected person has handled. Athlete's food is spread like this.
Bacteria on the skin can be killed by antiseptics, and bacteria on surfaces can be killed by disinfectants. Washing your hands reduces the chance of spreading microbes.
Water
Water can have harmful microbes in it. The microbes get into the body when the water is swallowed. Cholera is a disease caused by a bacterium that spreads like this. Thorough boiling or adding chlorine to the water can reduce the chance of spreading microbes in this way.
Defence against microbes
Natural barriers
The body has natural barriers to stop harmful microbes getting inside the body. Here are some of them: acid in the stomach kills many microbes sticky mucus in the lungs traps microbes, and then cilia sweep it out of the lungs the skin stops microbes from getting into the body scabs form on the skin if you get a cut, stopping microbes from getting into your body tears contain substances that kill bacteria
The immune system
The body has an immune system that kills microbes if they get past the natural barriers. White blood cells are very important in the immune system. There are different sorts of these cells, but they can do two main jobs. Some white blood cells can engulf microbes and kill them. Some white blood cells can make substances called antibodies that stick to microbes.
Microbes have chemicals called antigens. Different microbes have different antigens. White blood cells have chemicals called antibodies.
White blood cells can stick to microbes if they have the right antibody to match the antigen on the microbe. When this happens the microbes can be killed, or clumped together to make it easier for other white blood cells to kill them.
Antibiotics and immunisation
Antibiotics
Antibiotics are medicines used by doctors when harmful microbes have made you ill. They are substances that harm bacteria. Some antibiotics stop the bacteria reproducing and others kill the bacteria directly.
Antibiotics are helpful to treat diseases caused by bacteria, such as tuberculosis and food poisoning. They do not harm viruses, so antibiotics cannot treat diseases such as colds and flu, which are caused by viruses.
! Antibiotics only work against bacteria, not viruses
Immunisation
Immunity
When you are infected by a microbe, it takes time for your body to start fighting the infection. It does this by making enough white blood cells with the correct antibody. During this time, you continue to feel unwell.
You begin to recover when enough antibodies have been produced. After the microbes have been killed, the amount of antibodies goes down again. But some of the white blood cells that produce the correct antibody remain in your blood.
After a second infection by the same microbe, your body makes the correct antibodies much faster, because of the white blood cells that remain from when you had the first infection. The microbe doesn't get a chance to make you ill this time, and we say that you are immune to the microbe and the disease it causes.
Check your understanding of this by studying the animation.
Vaccination
Immunisation is a process that doctors use to make people immune from certain illnesses, even before they have been infected. It involves you receiving an injection containing a vaccine.
Vaccines contain a dead or weak form of the disease-causing microbe, or some of its antigens. In response to the vaccine your immune system produces white blood cells with the correct antibody to kill the microbe, so you become immune without falling ill.
You are likely to have been immunised against several microbes, viruses and bacteria, including the ones that cause diphtheria, whooping cough, polio, tetanus, meningitis, measles, mumps and tuberculosis. Girls are also immunised against rubella.
! Vaccination works against diseases caused by both bacteria and viruses.
Mrs.Nerg/Gren
Living things have certain life processes in common. There are seven things that they need to do to count as being alive. The phrase MRS GREN is a way to remember them
M Movement All living things move, even plants
R Respiration Getting energy from food
S Sensitivity Detecting changes in the surroundings
G Growth All living things grow
R Reproduction Making more living things of the same type
E Excretion Getting rid of waste
N Nutrition Taking in and using food
It can be easy to tell if something is living or not. A teddy bear might look like a bear, but it can't do any of the seven things it needs to be able to do to count as being alive.
What about a car? A car can move, it gets energy from …show more content…
petrol (like nutrition), it might have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust pipe (excretion). But it can't grow or make baby cars. So a car is not alive.
Respiration
Respiration is a chemical reaction that happens in all living cells. It is the way that energy is released from glucose, for our cells to use to keep us functioning.
Remember that respiration is not the same as breathing (which is properly called ventilation).
Aerobic respiration
The glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is needed for it to work.
Here is the word equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water (+ energy)
(Energy is released in the reaction. We show it in brackets in the equation because energy is not a substance.)
Now we will look at how glucose and oxygen get to the cells so that respiration can take place and how we get rid of the carbon dioxide.
Glucose from food to cells
Glucose is a type of carbohydrate, obtained through digestion of the food we eat. Digestion breaks food down into small molecules. These can be absorbed across the wall of the small intestine into the bloodstream.
Glucose is carried round the body dissolved in blood plasma, the pale yellow liquid part of our blood. The dissolved glucose can diffuse into the cells of the body from the capillaries. Once in the cell glucose can be used in respiration.
Oxygen from the air to cells
When we breathe in oxygen enters the small air sacs, called alveoli, in the lungs. Oxygen diffuses from there into the bloodstream.
Oxygen is not carried in the plasma, but is carried by the red blood cells. These contain a red substance called haemoglobin, which joins onto oxygen and carries it around the body in the blood, then lets it go when necessary. Like glucose, oxygen can diffuse into cells from the capillaries.
Red blood cells carry oxygen around the body
Carbon dioxide from cells to the air
The carbon dioxide produced during respiration diffuses out of the cells and into the blood plasma. The blood carries it to the lungs. It then diffuses across the walls of the alveoli and into the air, ready to be exhaled.
Respiratory system and ventilation
The respiratory system
The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we don't need. It contains these parts: lungs tubes leading from the lungs to the mouth and nose various structures in the chest that allow air to move in and out of the lungs Ventilation
Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. Take care - this is called breathing or ventilation, not respiration. When we breathe in, we inhale. When we breathe out, we exhale.
Air passes between the lungs and the outside of the body through the windpipe, called the trachea. The trachea divides into two bronchi, with one bronchus for each lung.
Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.
Gas Exchange
We need to get oxygen from the air into the blood, and we need to remove waste carbon dioxide from the blood into the air. Moving gases like this is called gas exchange. The alveoli are adapted to make gas exchange in lungs happen easily and efficiently.
Here are some features of the alveoli that allow this: they give the lungs a really big surface area they have moist, thin walls (just one cell thick) they have a lot of tiny blood vessels called capillaries.
The gases move by diffusion from where they have a high concentration to where they have a low concentration: Oxygen diffuses from the air in the alveoli into the blood. Carbon dioxide diffuses from the blood into the air in the alveoli.
Some water vapour is also lost from the surface of the alveoli into the lungs - we can see this condensing when we breathe out on cold days.
Movement
Why do we need a skeleton?
Our skeleton is made of more than 200 bones. Calcium and other minerals make the bone strong but slightly flexible. Bone is a living tissue with a blood supply. It is constantly being dissolved and laid down, and it can repair itself if a bone is broken. Exercise and a balanced diet are important for a healthy skeleton.
The skeleton has three main functions: to support the body to protect some of the vital organs of the body to help the body move.
Support
The skeleton supports the body. For example, without a backbone we would not be able to stay upright.
Protection
Here are some examples of what the skeleton protects: the skull protects the brain the ribcage protects the heart and lungs the backbone protects the spinal cord.
Movement
Some bones in the skeleton are joined rigidly together and cannot move against each other. Bones in the skull are joined like this. Other bones are joined to each other by flexible joints. Muscles are needed to move bones attached by joints.
Joints
Basic structure
If two bones just moved against each other, they would eventually wear away. This can happen in people who have a disease called arthritis. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by synovial fluid. Tough ligaments join the two bones in the joint and stop it falling apart.
The diagram shows the main features of a joint.
Movement
Different types of joint allow different types of movement. Hinge joints allow simple movement, the same as a door opening and closing. Knee and elbow joints are hinge joints. Ball and socket joints allow movement in more directions. Hip and shoulder joints are ball and socket joints.
The bones cannot move on their own - they need muscles for this to happen.
Antagonistic Pair
Muscles work by getting shorter. We say that they contract, and the process is called contraction.
Muscles are attached to bones by strong tendons. When a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint.
Muscles can only pull and cannot push. This would be a problem if a joint was controlled by just one muscle. As soon as the muscle had contracted and pulled on a bone, that would be it, with no way to move the bone back again. The problem is solved by having muscles in pairs, called antagonistic muscles.
Biceps and triceps
The elbow joint lets our forearm move up or down. It is controlled by two muscles, the biceps on the front of the upper arm, and the triceps on the back of the upper arm. The biceps and the triceps are antagonistic muscles. when the biceps muscle contracts, the forearm moves up when the triceps muscle contracts, the forearm moves down.
This solves the problem. To lift the forearm, the biceps contracts and the triceps relaxes. To lower the forearm again, the triceps contracts and the biceps relaxes.
Cells to System
Cells are very small. They are the basic building blocks of all animals and plants.
Animal and Plant cells
Animal cells usually have an irregular shape, and plant cells usually have a regular shape
Cells are made up of different parts. It is easier to explain what these parts are by using diagrams like the ones below.
Animal cells and plant cells both contain: cell membrane, cytoplasm, nucleus
Plant cells also contain these parts, not found in animal cells: chloroplasts, vacuole, cell wall
The table summarises the functions of these parts.
Part Function Found in
Cell membrane Controls what substances can get into and out of the cell. Plant and animal cells
Cytoplasm Jelly-like substance, where chemical reactions happen. In plant cells there's a thin lining, whereas in animal cells most of the cell is cytoplasm. Plant and animal cells
Nucleus Controls what happens inside the cell. Carries genetic information.
In exams don't call the nucleus the 'brain' of the cell. That is not a good description and will not get you marks. Plant and animal cells
Chloroplast Where photosynthesis happens – chloroplasts contain a green substance called chlorophyll. Plant cells only
Vacuole Contains a liquid called cell sap, which keeps the cell firm. Plant cells only
Cell wall Made of a tough substance called cellulose, which supports the cell. Plant cells only
Cells and their functions
Humans are multi-cellular animals. That means we are made of lots of cells, not just one cell. The cells in many multi-cellular animals and plants are specialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism.
Specialised cells
You should be able to work out special features of a cell from a drawing, if you are told what the cell can do. The tables below show examples of some specialised animal and plant cells, with their functions and special features
Type of animal cell Function Special features
Red blood cells To carry oxygen Large surface area, for oxygen to pass through Contains haemoglobin, which joins with oxygen
Nerve cells To carry nerve impulses to different parts of the body Long Connections at each end Can carry electrical signals
Female reproductive cell (egg cell) To join with male cell, and then to provide food for the new cell that's been formed Large Contains lots of cytoplasm
Male reproductive cell (sperm cell) To reach female cell, and join with it Long tail for swimming Head for getting into the female cell
Type of plant cell Function Special features
Root hair cell
To absorb water and minerals Large surface area
Leaf cell
To absorb sunlight for photosynthesis Large surface area Lots of chloroplasts
Cells, tissues, organs and systems
Tissues
Animal cells and plant cells can form tissues, like muscle tissue. A living tissue is made from a group of cells with a similar structure and function, which all work together to do a particular job. Here are some examples of tissues: muscle the lining of the intestine the lining of the lungs phloem (tubes that carry dissolved sugar around a plant) root hair tissue (for plants to take up water and minerals from the soil)
Organs
An organ is made from a group of different tissues, which all work together to do a particular job. Here are some examples of organs: heart lung stomach brain leaf root
Organ systems
An organ system is made from a group of different organs, which all work together to do a particular job. Here are some examples of organ systems: circulatory system respiratory system digestive system nervous system reproductive system
Reproduction
Male reproductive system
The male reproductive system contains these parts: testes (pronounced "test-eez") glands sperm ducts urethra penis.
Testes
The two testes (one of them is called a testis) are contained in a bag of skin called the scrotum. They have two functions: to produce millions of male sex cells called sperm to make male sex hormones, which affect the way a man's body develops.
Sperm duct and glands
The sperm pass through the sperm ducts, and mix with fluids produced by the glands. The fluids provide the sperm cells with nutrients. The mixture of sperm and fluids is called semen.
Penis and urethra
The penis has two functions: to pass urine out of the man's body to pass semen into the vagina of a woman during sexual intercourse.
The urethra is the tube inside the penis that can carry urine or semen. A ring of muscle makes sure that there is no chance of urine and semen getting mixed up.
Female Reproductive System
The female reproductive system contains these parts: ovaries egg tubes uterus (pronounced "yoo-ter-russ") cervix vagina.
Ovaries
The two ovaries contain hundreds of undeveloped female sex cells called egg cells or ova. Women have these cells in their bodies from birth - whereas men produce new sperm continually.
Egg tubes
Each ovary is connected to the uterus by an egg tube. This is sometimes called an oviduct or Fallopian tube. The egg tube is lined with cilia, which are tiny hairs on cells. Every month, an egg develops and becomes mature, and is released from an ovary. The cilia waft the egg along inside the egg tube and into the uterus.
Uterus and cervix
The uterus is also called the womb. It is a muscular bag with a soft lining. The uterus is where a baby develops until its birth.
The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in place while the woman is pregnant.
Vagina
The vagina is a muscular tube that leads from the cervix to the outside of the woman's body. A man's penis goes into the woman's vagina during sexual intercourse. The opening to the vagina has folds of skin called labia that meet to form a vulva. The urethra also opens into the vulva, but it is separate from the vagina, and is used for passing urine from the body.
The menstrual cycle
The female reproductive system includes a cycle of events called the menstrual cycle. It lasts about 28 days, but it can be slightly less or more than this. The cycle stops while a woman is pregnant. These are the main features of the menstrual cycle. The start of the cycle, day 1, is when bleeding from the vagina begins. This is caused by the loss of the lining of the uterus, with a little blood. This is called menstruation or having a period. By the end of about day 5, the loss of blood stops. The lining of the uterus begins to re-grow and an egg cell starts to mature in one of the ovaries. At about day 14, the mature egg cell is released from the ovary. This is called ovulation. The egg cell travels through the egg tube towards the uterus. If the egg cell does not meet with a sperm cell, the lining of the uterus begins to break down and the cycle repeats.
If the egg cell meets and joins with a sperm cell, it is fertilised. It attaches to the lining of the uterus and the woman becomes pregnant.
Fertilisation and foetal development
Fertilisation
During sexual intercourse the man's penis releases semen into the woman's vagina. Sperm cells travel in semen from the penis and into the top of the vagina. They enter the uterus through the cervix and travel to the egg tubes. If a sperm cell meets with an egg cell there, fertilisation can happen. Fertilisation happens when an egg cell meets with a sperm cell and joins with it.
The fertilised egg divides to form a ball of cells called an embryo. This attaches to the lining of the uterus and begins to develop into a foetus (pronounced "fee-tuss") and finally a baby.
Development of the foetus
The foetus relies upon its mother as it develops. These are some of the things it needs: protection oxygen nutrients (food and water).
It also needs its waste substances removing.
The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion.
The placenta is responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord.
The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies: oxygen and nutrients diffuse across the placenta from the mother to the foetus waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother.
Birth
After nine months the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract, pushing the baby out of the mother's body.
Puberty
The reproductive system of a child is not mature and needs to change as a boy or girl develops into an adult, so that the system is fully working. These changes begin between the ages of ten and fifteen. The time when the changes happen is called puberty.
The changes happen because of sex hormones produced by the testes in boys and by the ovaries in girls. Some changes happen in boys and girls, while others just happen in boys or girls.
Here are some changes that happen to both boys and girls: underarm hair grows pubic hair grows body smell gets stronger. emotional changes growth rate increases
The time when the physical changes and emotional changes happen is called adolescence.
Boys
Here are some changes that happen only to boys: voice breaks (gets deeper) testes and penis get bigger testes start to produce sperm cells shoulders get wider hair grows on face and chest.
Girls
Here are some changes that happen only to girls: breasts develop ovaries start to release egg cells (periods start) hips get wider.
Diet, Drugs and Health
Nutrients
There are seven different nutrients: carbohydrates proteins fats minerals vitamins fibre water
Some foods are particularly rich in certain nutrients. The table shows why we need each nutrient, and some good sources of each.
Nutrient Use in the body Good sources
Carbohydrate To provide energy Cereals, bread, pasta, rice and potatoes
Protein For growth and repair Fish, meat, eggs, beans, pulses and dairy products
Fat To provide energy. Also to store energy in the body and insulate it against the cold. Butter, oil and nuts
Minerals Needed in small amounts to maintain health Salt, milk (for calcium) and liver (for iron)
Vitamins Needed in small amounts to maintain health Dairy foods, fruit, vegetables
Fibre To provide roughage to help to keep the food moving through the gut Vegetables, bran
Water Needed for cells and body fluids Fruit juice, milk, water
Effects of a Poor diet
If you have too little of a particular nutrient, we say that you have a deficiency in that nutrient. For example, fibre is needed to keep food moving through the intestines easily, and people who have a fibre deficiency in their diet may get constipation.
Mineral deficiencies
People with iron deficiency may get anaemia and have too few red blood cells. People with iodine deficiency may get a swelling in the neck called a goitre (pronounced "goy-ter").
Vitamin deficiencies
Although we only need small amounts of the different vitamins in our diet, we become ill if we don't get enough. For example, vitamin A deficiency can cause blindness. Vitamin C deficiency causes scurvy, which makes the gums bleed, and vitamin D deficiency causes rickets, which makes the legs bow outwards in growing children.
Too thin, too fat
Food is a store of chemical energy. If you look on the side of food packets you will see the food's energy content. This is usually measured in kilojoules, kJ. If we eat too little food, we will use up our store of fat and become too thin. If we eat too much food, especially foods rich in sugar and fat, we will increase our store of fat and become too fat.
It is important to balance the amount of food we eat with who we are and what we do. The amount of energy we need from our food depends on our age, our height and how much exercise we get.
For example, a one-year old baby needs 3850 kJ each day to continue to grow, whereas an adult Olympic swimmer in training needs 15,600 kJ each day. Someone who sits at a desk all day will need less food than their twin who climbs ladders all day to wash windows.
Digestive System
When you eat a piece of bread, you don't wake up next day to discover it growing out of your arm! The food we eat has to be broken down into other substances that our bodies can use. This is called digestion. Without digestion, we could not absorb food into our bodies and use it.
Digestion happens in the digestive system, which begins at the mouth and ends at the anus.
After we swallow, our food passes through these organs in turn: oesophagus or gullet stomach small intestine large intestine.
Stages of digestion Food is digested in the mouth, stomach and small intestine. Digested food is absorbed into the bloodstream in the small intestine. Excess water is absorbed back into the body in the large intestine. Any undigested food passes out of the anus as faeces (pronounced "fee-seez") when we go to the toilet.
Liver and pancreas
The liver and the pancreas play important part in digestion. The liver produces bile, which helps the digestion of fat. The pancreas produces chemicals called digestive enzymes.
Digestion and enzymes
Our teeth break food down into small pieces when we chew. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body. Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are needed so that this break-down happens quickly enough to be useful.
Enzymes
Take care - enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients: carbohydrase or amylase enzymes break down starch into sugar protease enzymes break down proteins into amino acids lipase enzymes break down fats into fatty acids and glycerol.
Carbohydrates
Carbohydrates are digested in the mouth, stomach and small intestine. Carbohydrase enzymes break down starch into sugars.
The saliva in your mouth contains amylase, which is another starch digesting enzyme. If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet.
Proteins
Proteins are digested in the stomach and small intestine. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful micro-organisms that may be in the food.
Fats
Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on.
Things that are not digested
Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down, so they are not digested.
Digestive enzymes cannot break down fibre, which is why it cannot be absorbed by the body.
Absorption and egestion
These are the processes that happen in the digestive system: ingestion (eating) → digestion (breaking down) → absorption → egestion
We've already looked at how foods are broken down by enzymes in digestion. Now we will look at how the products of digestion are absorbed into the body.
Absorption
Digested food molecules are absorbed in the small intestine. This means that they pass through the wall of the small intestine and into our bloodstream. Once in the bloodstream, the digested food molecules are carried around the body to where they are needed.
Only small, soluble substances can pass across the wall of the small intestine.
Large insoluble substances cannot pass through.
The inside wall of the small intestine needs to be thin, with a really big surface area. This allows absorption to happen quickly and efficiently. If the small intestine had a thick wall and a small surface area, a lot of digested food might pass out of the body before it had a chance to be absorbed.
To get a big surface area, the inside wall of the small intestine is lined with tiny villi (one of them is called a villus). These stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.
Egestion
Excess water is absorbed back into the body in the large intestine. What is left then is undigested food. This is stored in the rectum, the lower part of the large intestine, until we are ready to go to the toilet. It then comes out of the rectum through the anus as faeces. This process is called egestion.
Smoking and Health
Smoking is very harmful to health. It causes around 80 per cent of deaths from lung cancer, bronchitis and emphysema in the UK, and almost a fifth of UK deaths from heart disease.
Tobacco smoke contains many harmful substances. These include: tar
nicotine carbon monoxide
A normal lung and a lung from a smoker:
Tar
Tar causes cancer of the lungs, mouth and throat. It coats the surface of the breathing tubes and the alveoli. This causes coughing and damages the alveoli, making it more difficult for gas exchange to happen.
Smoke
Cells in the lining of the breathing tubes produce sticky mucus to trap dirt and microbes. Cells with tiny hair-like parts, called cilia, normally move the mucus out of the lungs.
Hot smoke and tar from smoking damages the cilia. So smokers cough to move the mucus and are more likely to get bronchitis.
Nicotine
Nicotine is addictive - it causes a smoker to want more cigarettes. Nicotine also increases the heart rate and blood pressure, and makes blood vessels narrower than normal. This can lead to heart disease.
Carbon monoxide
Carbon monoxide is a gas that takes the place of oxygen in red blood cells. This reduces the amount of oxygen that the blood can carry. This means that the circulatory system has to work harder, causing heart disease.
Drugs and Health
Drugs are substances that have effects on the body. Medicines are drugs that help people suffering from pain or disease. Recreational drugs are taken for pleasure.
Some recreational drugs are legal, such as tobacco, alcohol and caffeine. Most other recreational drugs are illegal, such as cannabis, ecstasy and heroin.
Problems with drug use
Recreational drugs can be classified as depressants or stimulants. Most recreational drugs can be addictive.
All drugs can damage the liver, because it is the liver that breaks drugs down in the body. Any drug that is misused can cause damage to the body, as well as personal and social problems. Injecting any drug with a needle and syringe that someone else has used may lead to a number of diseases from infected blood, including HIV and hepatitis.
Depressants
Depressants slow down messages in the brain and along the nerves. Alcohol is a depressant. It is found in beer, wines and spirits such as vodka.
Other depressants include cannabis, heroin and solvents (eg glue and aerosols).
Here are some of the typical effects depressants have on the body: feelings of well-being lowered inhibition slowed thinking slowed muscular activity a distorted view of the world, or hallucinations
Some of the long-term effects of depressants on the body include damage to the liver, brain and heart. They can also have the following effects: alcohol can cause weight gain solvent abuse causes a rash around the nose and mouth cannabis causes loss of memory and concentration, as well as an increased risk of mental illness.
Stimulants
Stimulants speed up messages in the brain and along the nerves. This makes you feel more alert. Caffeine is a stimulant and is found in cola drinks, coffee and tea. It makes you feel more energetic and alert, but it can also cause insomnia (difficulty in sleeping), headaches and nervousness.
Cocaine, ecstasy and amphetamines are all illegal stimulants. They make you feel more energetic and confident, but they can damage the liver and heart. They can also cause loss of memory and concentration, and bring an increased risk of mental illness.
Deseases
Many living things are so small that they can only be seen through a microscope. These living things are called microorganisms or microbes. There are three main types of microbe: fungi bacteria viruses
Fungi
Mushrooms and toadstools are fungi, but these are made of lots of cells, so they are not microbes. Yeasts are single-celled fungi, so they are microbes. Fungi are usually the biggest type of microbe. If there is just one of them, we call it a fungus.
Bacteria Bacteria are usually smaller than fungi. If there is just one of them, we call it a bacterium. Bacteria have many different shapes. Some have 'tails' (called flagella) that let them swim.
Viruses
Viruses are the smallest type of microbe. As a virus can only reproduce inside a cell, some people are not convinced that viruses are really living things.
Differences between fungi, bacteria and viruses
The table shows some of the similarities and differences between the three types of microbe.
Useful of not?
Feature Fungi Bacteria Viruses
Cell membrane ✔ ✔ ✗
Cell wall ✔
(hard) ✔
(soft) ✗
(protein coat)
Cell nucleus ✔ ✗
(circle) ✗
(strand)
People often use the word germ instead of microbe, so you might think that microbes are all harmful. But some are useful to us.
Useful microbes
Yeast cells are useful to bakers and brewers. Yeast cells can change sugar into carbon dioxide gas and alcohol. This is useful to bakers because the gas helps the bread rise, and it is useful to brewers because it adds the alcohol needed for their drinks.
Bacteria are also useful to us. For example, certain bacteria cause the changes needed in milk to make yogurt and cheese out of it.
Harmful microbes
Many microbes can cause diseases. For example here are some diseases caused by fungi: athlete's foot thrush
Here are some diseases caused by bacteria: tuberculosis, TB (affects the lungs) salmonella (causes food poisoning) whooping cough (affects the lungs)
Here are some diseases caused by viruses: chicken pox (affects skin and nerves) common cold influenza, flu measles (affects skin and lungs) mumps (affects salivary glands) rubella, german measles
Microbes cause disease when they are able to reproduce in the body. They produce harmful substances called toxins, and damage tissues and organs. We say that someone who has harmful disease-causing microbes in them is infected.
Spreading Microbes
Many harmful microbes can pass from one person to another. Diseases caused by such microbes are said to be infectious diseases. Here are some ways that harmful microbes can be spread: in air through contact with animals through contaminated food through touch in water
Air
Droplets containing microbes fly into the air when people sneeze or cough. The microbes they contain get into other people if breathed in.
Chicken pox, colds, flu, measles and tuberculosis are spread like this.
Animals
Animals may carry harmful microbes. The microbes can get into a person who is scratched or bitten by such an animal. Malaria is a tropical disease spread by a tiny fly called a mosquito.
Food
Food can have harmful microbes in and on it. The microbes get into the body when the food is eaten, causing food poisoning. Thorough cooking kills most microbes, but they can survive under-cooking. Careless handling of food increases the risk from harmful microbes.
Touch
Microbes can be passed from one person to another when people touch each other, or when they touch something an infected person has handled. Athlete's food is spread like this.
Bacteria on the skin can be killed by antiseptics, and bacteria on surfaces can be killed by disinfectants. Washing your hands reduces the chance of spreading microbes.
Water
Water can have harmful microbes in it. The microbes get into the body when the water is swallowed. Cholera is a disease caused by a bacterium that spreads like this. Thorough boiling or adding chlorine to the water can reduce the chance of spreading microbes in this way.
Defence against microbes
Natural barriers
The body has natural barriers to stop harmful microbes getting inside the body. Here are some of them: acid in the stomach kills many microbes sticky mucus in the lungs traps microbes, and then cilia sweep it out of the lungs the skin stops microbes from getting into the body scabs form on the skin if you get a cut, stopping microbes from getting into your body tears contain substances that kill bacteria
The immune system
The body has an immune system that kills microbes if they get past the natural barriers. White blood cells are very important in the immune system. There are different sorts of these cells, but they can do two main jobs. Some white blood cells can engulf microbes and kill them. Some white blood cells can make substances called antibodies that stick to microbes.
Microbes have chemicals called antigens. Different microbes have different antigens. White blood cells have chemicals called antibodies.
White blood cells can stick to microbes if they have the right antibody to match the antigen on the microbe. When this happens the microbes can be killed, or clumped together to make it easier for other white blood cells to kill them.
Antibiotics and immunisation
Antibiotics
Antibiotics are medicines used by doctors when harmful microbes have made you ill. They are substances that harm bacteria. Some antibiotics stop the bacteria reproducing and others kill the bacteria directly.
Antibiotics are helpful to treat diseases caused by bacteria, such as tuberculosis and food poisoning. They do not harm viruses, so antibiotics cannot treat diseases such as colds and flu, which are caused by viruses.
! Antibiotics only work against bacteria, not viruses
Immunisation
Immunity
When you are infected by a microbe, it takes time for your body to start fighting the infection. It does this by making enough white blood cells with the correct antibody. During this time, you continue to feel unwell.
You begin to recover when enough antibodies have been produced. After the microbes have been killed, the amount of antibodies goes down again. But some of the white blood cells that produce the correct antibody remain in your blood.
After a second infection by the same microbe, your body makes the correct antibodies much faster, because of the white blood cells that remain from when you had the first infection. The microbe doesn't get a chance to make you ill this time, and we say that you are immune to the microbe and the disease it causes.
Check your understanding of this by studying the animation.
Vaccination
Immunisation is a process that doctors use to make people immune from certain illnesses, even before they have been infected. It involves you receiving an injection containing a vaccine.
Vaccines contain a dead or weak form of the disease-causing microbe, or some of its antigens. In response to the vaccine your immune system produces white blood cells with the correct antibody to kill the microbe, so you become immune without falling ill.
You are likely to have been immunised against several microbes, viruses and bacteria, including the ones that cause diphtheria, whooping cough, polio, tetanus, meningitis, measles, mumps and tuberculosis. Girls are also immunised against rubella.
! Vaccination works against diseases caused by both bacteria and viruses.