DISEASE HOW ARE DISEASES SPREAD?

DISEASE HOW ARE DISEASES SPREAD?

Starter: How is your body like a castle?

Our skin is like the castle walls but microbes can enter through gaps in the defences

AIM Can use simple physical models to show how white blood cells engulf microbes. Can describe how microbes can get into the body and some of the body defenses which help to prevent this. Can explain how white blood cells defend the body against invading microbes.

MICROBES CAN CAUSE DISEASE The diseases caused by microbes, and their severity, depend on the type of microbe: bacteria food poisoning sore throats tuberculosis (TB) tetanus cholera typhoid bacterial meningitis virus influenza (flu) mumps chickenpox smallpox polio HIV / AIDS viral meningitis fungi fungal sinusitis athlete s foot onychomycosis (causes discoloured toe nails)

DO YOU KNOW. How can microbes and disease be spread? Where on your body can microbes infect?

HOW DOES DISEASE SPREAD?

Why do people do this? What are they trying to stop?

An agar plate showing a mixture of microbes growing after exposure to a dirty hand.

Bacteria on skin magnified thousands of times Our skin is coated in microbes, but it stops them getting inside. The surface layers are dead and are continually replaced from below as they rub off. So how do they get in?

Life at your fingertips Clean skin has less than 10 000 bacteria per cm 2 and that s not many. 200 million would fit in that space.

A microbe desert It s like 4 people sitting in Wembley Stadium.

Defenses Bacteria reproduce fast if they get inside us, so we need good defenses. How could microbes get into Will s body? What defenses does Will have? *Label the diagram to show how microbes could enter the body

TASK Label the diagram showing what defences the body has to stop microbes getting in

HOW DO MICROBES ENTER THE BODY? Microbes can enter the body in many different places: eyes nose genitals skin ears mouth cuts

Defenses Stomach acid destroys most of the microbes in food but a few may get through if you swallow enough contaminated food.

Defenses Clots form fast to cover cuts..but a few microbes can dissolve their way in.

Defenses Mucus traps microbes in your lungs, and cilia sweep them out but some microbes get past them.

THE BODY S DEFENCES

These defences are not perfect we need a second line of defence.

Destroying invaders These microbes got in through Will s cut. Left unchecked they will reproduce rapidly and fill his blood and tissues with toxins. How can Will s immune system stop them?

Destroying invaders It looks yellow on the image, but this is a white blood cell. What is it doing?

Destroying invaders Once the bacteria are inside the white blood cell, enzymes destroy them. The white cells eventually die and get broken down. The broken down cells ooze out of wounds as pus.

White blood cells killing bacteria

WHAT DO WHITE BLOOD CELLS DO? If harmful microbes enter the body the immune system produces white blood cells to help defend it from microbes. Some white blood cells can destroy microbes by engulfing them. bacteria antigen white blood cell Some white blood cells are able to produce chemicals called antibodies. These pair with matching antigens on the surfaces of microbes and so help the white blood cells to engulf microbes.

ENGULFING MICROBES - WHAT S THE ORDER?

ENGULFING MICROBES - WHAT HAPPENS?

Destroying invaders Other types of white blood cells defend the body in different ways. They make chemicals called antibodies which stick to microbes and make them easier to destroy. They work against both bacteria and viruses. This is the body s third line of defence.

White blood cells produce antibodies

Destroying invaders These Y-shaped particles are models of antibodies. Some antibodies destroy bacteria others just make it easier for white cells to engulf them. Each type of microbe needs a different antibody, so they aren t made in advance. When a new microbe invades the body, it takes a couple of days to make them.

Destroying invaders Once a white blood cell has made antibodies, it never forgets its target. If that microbe returns, it makes antibodies straight away. So the microbes are destroyed before they can reproduce and cause disease...which makes you immune to that disease.

PREVENTING THE SPREAD OF DISEASE There are several methods that can help reduce the spread of disease: l l l l l disinfecting surfaces disinfecting skin using antiseptics sterilizing equipment using food preservatives in food personal hygiene. The spread of disease can also be reduced by vaccinating the population and using antibiotics.

WHAT ARE ANTIBIOTICS? Antibiotics are chemicals used to treat bacterial infections. These chemicals kill or stop the growth of bacteria. However, some types of bacteria are no longer affected by certain antibiotics this is called antibiotic resistance. This can be a problem as without effective antibiotics some people might not be able to fight the infection themselves.

WHAT ARE VACCINES? Vaccines can protect people from diseases, such as measles. Vaccines contain dead or weakened strains of the harmful microbe that causes the disease. This stimulates the immune system. If the person comes into contact with the microbe again the immune system can destroy it quickly and effectively. Why is it important that everyone is vaccinated?

WHY DO WE NEED TO HAVE VACCINATIONS?

Destroying invaders Paul is beginning to feel ill. Bacteria have infected his throat. He is under a lot of stress and it has weakened his immunity.

Destroying invaders Explain what is happening in each part of the graph.

Destroying invaders What would help Paul get better quicker?

Destroying invaders Why doesn t Paul notice the second infection?

Destroying invaders Asha has AIDs. She gets a lot of infections and feels tired all the time. This white cell used to help Asha make antibodies..but HIV particles have stopped it working..so her immune system cannot protect her.

White blood cell HIV In HIV sufferers white blood cells are infected and destroyed. This stops their immune system from working properly.

Lucky or unlucky? You are a microbe. You want to get into Will s body. Are you lucky or unlucky?

Lucky or unlucky? You re with a group of salmonella bacteria in the middle of a burger. What happens next?

Lucky or unlucky? You re are a cold virus. You drifted into Will s nose as he breathed. What happens next?

Lucky or unlucky? You are a tetanus bacterium in the mud on Will s football. He has a cut on his finger and he has just picked up the football. What happens next?

Support I can use simple physical models to show how white blood cells engulf microbes. Support I can describe how microbes can get into the body and some of the body defenses which help to prevent this. Developing I can explain how white blood cells defend the body against invading microbes. Independent I can use models presented as graphs to explain why it takes time to recover from the infection. Applying I can make connections between bacterial reproduction and antibody manufacture to explain immunity to further infection by a microbe.

PRODUCING ANTIBODIES You re going down Step 1: The white blood cell sees the antigen (microbe) Step 2: The cell produces antibodies to fit the antigen Step 3: The antibodies fit onto the antigens and cause them to clump Step 4: The antigens are eaten by the white blood cells

MATCHING MICROBES AND ANTIBODIES

MULTIPLE-CHOICE QUIZ