B5 communicable diseases

Question 1

What are communicable diseases?

Answer 1

Infectious diseases caused by pathogens that can be passed from person to person

Question 2

What 3 factors can lead to good/ill health?

Answer 2

diet stress and life situations

Question 3

Differences between bacteria and viruses

Answer 3

A virus is non-living and cannot be treated by antibiotics, they do not have a cell wall. Viruses are generally smaller and require a host to survive. A bacteria can be affected by antibiotics and can survive outside of a host. Bacteria can be free-living and do not require a host to reproduce. Viruses cause disease in every organism but can only infect living things.

Question 4

How do bacteria and viruses reproduce?

Answer 4

Bacteria split into two (binary fission) and they produce toxins that harm cells and tissue
Viruses infect cells and reproduce inside of the damaged cell.

Question 5

How are pathogens spread?

Answer 5

By air: they are spread from one organism to another via the air and droplet infection where they travel in droplets and are expelled from the body (eg cough) and infect other organisms.
Direct contact: happens a lot in plants, some diseases can enter through open wounds and sexual contact.
Water: water can harbour pathogens and so can food so they have to be cooked or cleaned to consume.

Question 6

Bacteria culturing.

Answer 6

They need to grow in a culture medium, allows a liquid or gel to provide all the nutrients needed for bacteria to grow successfully. These must include: carbohydrates for energy, nitrogen for
protein synthesis, plus other minerals.

Agar plates are created by pouring hot molten agar into sterile
Petri dishes, which are then allowed to set. Bacteria can be spread onto the plates, and allowed to form
individual colonies of the specific bacterium.
Then you sterilise hands, surface petri dish and put an inoculating loop over a flame to sterilise it. When it has cooled use the loop and get the bacteria culture and move it in a zigzag shape across the jelly while keeping the lid partially over. Then seal it with two pieces of tape but leave oxygen to get in and store it upside down to stop condensation and place it in an incubator for the best temperature for the bacteria to grow.

Question 7

What are the factors that affect bacterial growth?

Answer 7

temperature nutrients pH and oxygen levels.

Question 8

What is the formula to calculate the number of bacteria in a population?

Answer 8

bacteria at the end of growth period= bacteria at the start of the growth period x 2^number of divisions

Question 9

How to prevent bacterial growth?

Answer 9

raising or dropping temperature, uv light,chemicals such as disinfectants that kill on the surfaces, antiseptics that stop infections on the skin and antibiotics which stop bacteria IN the body

Question 10

What did semmelweis discover?

Answer 10

Semmelweis realised the death rate among women giving birth in hospital was higher than among those giving birth at home. He believed this was because doctors often delivered babies after dissecting dead bodies. He then asked doctors to wash their hands and equipment in disinfectant and that stopped the death rate as the disease was spread from dead bodies to the mothers.

Question 11

What is vaccination and how does it work?

Answer 11

Pathogens are microbes that cause diseases. Vaccines allow a dead or altered form of the disease causing pathogen to be introduced into the body without causing the disease. The pathogens that are introduced contain a specific
antigen. The antigen causes the body’s immune system, specifically the lymphocytes, to produce complementary antibodies, which target and attach to the antigen.

An altered form of a pathogen which cannot cause disease is injected into someone.
This causes lymphocytes to make and then release complementary antibodies to the specific antigen that was injected.
The antibodies attach to and clump the antigens together.
Phagocytes engulf the antigens to remove them from the body.
Some of the lymphocytes remain in the bloodstream as memory cells which can produce the specific antibody for the antigen.
If the body is infected by the real pathogen, the memory cells release antibodies to fight off the pathogen and quickly destroy it.

Question 12

Problems with antibiotics

Answer 12

Commonly prescribed antibiotics are becoming less effective due to a number of reasons:

overuse of antibiotics
failing to complete the fully prescribed course by a doctor
use of antibiotics in farming

Question 13

What happens when the patient doesn’t fully complete the antibiotic course?

Answer 13

Patients should always fully complete the prescribed course of antibiotics, every time they are taken. This ensures all bacteria are killed, and so none survive which can subsequently mutate and produce resistant strains. Patients begin to feel well after a few days of taking the medicine, and stop taking them. This is potentially very harmful, as random mutations can occur which can lead to antibiotic resistance. The resistant bacteria reproduce quickly, and the resistance spreads.

Question 14

How to prevent antibiotic resistance?

Answer 14

Only take antibiotics when necessary.
Treat specific bacteria with specific antibiotics.
High hospital hygiene levels, including regular hand washing by staff and visitors.
Patients who are infected with antibiotic resistant strains of bacteria should be isolated from other patients

Question 15

How was penicillin discovered?

Answer 15

The first antibiotic - penicillin - was discovered in 1928 by Alexander Fleming. He noticed that some bacteria he had left in a petri dish had been killed by naturally occurring Penicillium mould.

Since the discovery of penicillin, many other antibiotics have been discovered or developed. Most antibiotics used in medicine have been altered chemically to make them more effective and safer for humans.

Question 16

What are viral diseases?

Answer 16

Viruses are not alive because they do not complete all of the seven life processes: Movement, Respiration, Sensitivity, Nutrition, Excretion, Reproduction and Growth.

We say ‘strains’ of virus and not species. They are made of a relatively short length of genetic material
DNA which is surrounded by a protein coat.

The life cycle of a virus is the same as other
pathogens. They can often survive outside a host for long periods of time. When they have infected a suitable host cell or cells, they replicate themselves within the cell thousands of times. They do not divide and reproduce, but replicate their DNA and protein coats. These are then assembled into new virus particles. The host cell or cells then burst and other nearby cells can be infected with the virus. This process can be as quick as twelve hours in the case of the Norovirus or several days for Ebola.

Viral infections cannot be treated by
antibiotics.

Question 17

What is HIV and AIDS

Answer 17

HIV stands for human immunodeficiency virus. This infection is transmitted by body fluids, often during unprotected sex, but also through cuts and injecting drugs using shared needles. Immediately after infection, people often suffer mild flu-like symptoms. These pass and for a period of time infected people might not know they are infected.

AIDS
stands for acquired immune deficiency syndrome. Months or years after the infection of the HIV virus, it becomes active and starts to attack the patient’s immune system. HIV at this point has become AIDS.

There is no cure for HIV/AIDS although many scientists are trying to find one. Currently, infected people are given
antiviral drugs, which can slow the development of AIDS.

Question 18

What is salmonella?

Answer 18

Salmonella is a
genus
of bacteria that causes food poisoning. This often means abdominal cramps, vomiting and
diarrhoea. It is often found in unhygienic kitchens, undercooked foods such as meat, eggs and poultry, or the same foods that have not been reheated properly. To prevent the spread of salmonella in the UK, all poultry are
vaccinated against it. Cooking food thoroughly, after preparing it in hygienic conditions, is the best way to avoid illness.

Question 19

An example of a protist disease and a fungal disease

Answer 19

Protist:Malaria
is spread by mosquitos which carry the Plasmodium protist. These are often found in areas with higher temperatures like Africa, Asia, and South and Central America, but not the UK. Mosquitos suck blood containing the protists from an infected person. They pass the protist, to other people they suck blood from. The mosquitos do not become ill and are called ‘vectors’ because they transmit the disease.The symptoms of malaria include a fever, sweats and chills, headaches, vomiting and diarrhoea. Of the 200 million people infected each year, up to half die from this disease. There is no vaccination for malaria. Infection can only be prevented by stopping individuals from being bitten. People sleep under mosquito nets and wear insect repellent to avoid bites. Antimalarial drugs are also taken, which treat the symptoms and can prevent infection.

Fungal:Rose black spot is caused by a fungus which infects roses. It infects leaves and causes black or purple spots on the leaves. The rest of the leaves often turn yellow and can drop off the plant. This reduces that plant’s ability to
photosynthesise
and reduces growth. It can be transmitted in air or water, as well as through direct contact by gardeners. It is treatable using
fungicides
and by removing and destroying infected leaves.

Question 20

Non specific human defences against pathogens

Answer 20

The skin covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed it immediately begins to heal itself, often by forming a scab, which prevents infection as the skin acts as a physical barrier. Parts of the body that do not have skin have developed other ways to prevent infection. For example, the eyes produce tears, which contain
enzymes
, and these are chemical barriers.

The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce
mucus
. This traps pathogens before they can enter the lungs. When the nose is blown, mucus is removed and any pathogens are trapped within it

The
trachea
runs from the nose towards the lungs. The cells that line the trachea also have hairs called
cilia
, which are much smaller than those in the nose. These are called
ciliated cells
. The ciliated cells waft their hairs and move mucus and pathogens upwards towards the throat where it is swallowed into your
stomach
. Other cells called
goblet cells
create the mucus in order to trap pathogens. The production of mucus in your airways is a physical barrier.

Stomach acid is part of the body’s non-specific first line of defence. It is hydrochloric acid and while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water. Stomach acid is a chemical barrier against infection.

Question 21

What is the immune system and phagocytes/lymphocytes?

Answer 21

If pathogens pass the non-specific first line of defence they will cause an infection. However, the body has a second line of defence to stop or minimise this infection. This is called the
immune system. As a part of this there are two types of white blood cell called
phagocytes and lymphocytes.
Phagocytes surround any pathogens in the blood and engulf them. They are attracted to pathogens and bind to them.

The phagocytes membrane surrounds the pathogen and enzymes found inside the cell break down the pathogen in order to destroy it. As phagocytes do this to all pathogens that they encounter, they are called ‘non-specific’.

Lymphocytes are another type of white blood cell. They recognise proteins on the surface of pathogens called antigens. Lymphocytes detect that these are foreign not naturally occurring within your body and produce
antibodies. This can take a few days, during which time you may feel ill. The antibodies cause pathogens to stick together and make it easier for phagocytes to engulf them.

Some pathogens produce
toxins which make you feel ill. Lymphocytes can also produce antitoxins to neutralise these toxins. Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, thus the lymphocytes that produce them are called ‘specific’.