Topic 3: Infection and Response

Question 1

Pathogens are…?

Answer 1

microorganisms that enter the body and cause disease

Both animals and people can be affected.

Question 2

Bacteria are…?

Answer 2

very small cells (1/100th the size of your body’s cells) which can reproduce rapidly inside your body. Make you feel ill by producing toxins that damage your cells and tissues.

Question 3

Viruses are…?

Answer 3

NOT CELLS
Tiny (1/100th a bacterium)
Live inside your cells and replicate themselves rapidly using the cells’ machinery to produce many copies of themselves and burst out, releasing all the new viruses.
This cell damage will make you feel ill

Question 4

Protists are…?

Answer 4

EUKARYOTES and most are single-celled

Some are parasites - living on or inside other organisms and can cause damage - transferred by a VECTOR

Question 5

Some Fungi are…?

Answer 5

single-celled. Others have a body made up of hyphae. These hyphae can grow and penetrate human skin and the surfaces of plants, causing disease. They can also produce spores, which can be spread to other plants and animals.

Question 6

How can pathogens be spread?

Answer 6

Through air
touch
SHaring of bodily fluids (sex, sharing needles etc)
Food
Water
Animals

Question 7

Measles

Answer 7

VIRUS
The Measles Virus is spread by droplet infection.
It causes fever and a rash and can be fatal.
There is no cure
Isolation of patients and vaccination prevents the spread of the disease.

Question 8

HIV?

Answer 8

VIRAL
HIV initially causes a flu-like illness.
Unless it is successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells.
Late-stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers.
HIV is spread by sexual contact or by the exchange of bodily fluids, such as blood — occurring when drug users share needles, it can be also be passed from mother to child through breastmilk.

Question 9

TMV?

Answer 9

VIRUS
The Tobacco Mosaic Virus was the first virus ever to be isolated.
The virus causes a distinctive ‘mosaic’ pattern of discolouration on the leaves at the virus destroys the cells.
It is spread by contact and vectors.
It damages leaves, reduces photosynthesis and can seriously reduce the yield of a crop.
There is no treatment.
Spread is prevented by field hygiene and pest control.

Question 10

Fungal diseases?

Answer 10

Fungal diseases are caused by fungi and, although there are relatively few that affect people, can be devastating to plants.

Rose Black Spot is a fungal disease spread in the environment by wind and water.
It damages leaves so they drop off, affecting growth as photosynthesis is reduced.
Spread is controlled by removing affected leaves and chemical sprays - but are not very effective.

Question 11

Diseases by protists?

Answer 11

Protists (a type of single-celled organism) can cause a range of diseases in both animals and plants. They are relatively rare pathogens but the diseases they cause are often very serious and damaging to those infected.

Malaria is caused by parasitic protists and is spread by the bite of female mosquitos.
It damages blood and liver cells causing fevers and shaking.
Malaria can be fatal.
Some drugs are effective if given early, but the protists are becoming more resistant.
Spread is reduced by preventing the vectors from breeding and by using mosquito nets to prevent people from being bitten.

Question 12

Plant Diseases and symptoms?

Answer 12

Plants can be infected by a range of viral, bacterial and fungal pathogens as well as insect pests.

Plants can be damaged by a range of ion deficiency conditions.

Plant diseases can be detected by a range of symptoms and identified in a number of ways, including gardening manuals involving laboratory tests, some involving monoclonal (forming a clone asexually from a single cell or individual) antibodies.

Some symptoms of a disease in a plant:
Stunted growth (eg nitrate deficiency)
spots on leaves (eg rose black spot0
areas of decay or rotting (eg rose black spot, blights on potatoes)
growths (eg crown galls caused by bacterial infection)
malformed stems and leaves (eg due to aphid/nematode infestation)
discolouration (eg yellowing or chlorosis in magnesium deficiency, mosaic patterns caused by TMV)
presence of visible pests (eg aphids/caterpillars)

Question 13

Plant defence responses?

Answer 13

Plants have developed many defences against their common pathogens.
Including signalling systems that allow damaged cells to warn other cells within the plant that they are under attack.
Some plants cam even signal to other plants around them, allowing them to get their defences in place.
Physical plant defences against invasion include:
cellulose cell walls
tough waxy cuticles
layers of bark (or dead leaves) which fall off.
Chemical plant defences include antibacterial chemicals and poisons to deter herbivores
Many plants have mechanical adaptations against herbivores such as thorns and hairs, leaves that droop or curl when touched, and mimicry (imitation) to trick animals.

Question 14

Salmonella?

Answer 14

Salmonella - food poisoning BACTERIAL
fever, stomach cramps, vomiting and diarrhoea
Caused by toxins the bacteria produce
By eating food that’s been contaminated with the bacteria or by being prepared in unhygienic conditions
In the UK, most poultry is given a vaccination against salmonella

Question 15

Gonorrhoea?

Answer 15

BACTERIAL
An STD - having unprotected sex
pain when urinating
Thick yellowy-green discharge from the vagina or penis
Originally treated with penicillin but is now tricky as strains of the disease have become resistant to it
Treated with antibiotics and should use barrier methods of contraception (condoms)

Question 16

Reducing the spread of diseases?

Answer 16

Being hygienic
Destroying vectors
Isolating infected individuals
Vaccination

Question 17

Human defences?

Answer 17

The skin acts as a barrier and it also secretes antimicrobial substances which kill bacteria
Hairs and mucus in your nose trap particles that could contain pathogens
The trachea and bronchi secrete mucus to trap pathogens - are also lined with cilia - hair like structures that waft the mucus up to the back of the throat to be swallowed
The stomach produces hydrochloric acid that kills pathogens that make it that far from the mouth.

Question 18

The white blood cells and pathogens?

Answer 18

1. They consume the pathogens - by engulfing the foreign cells and digesting them - PHAGOCYTOSIS
2. Producing antibodies - When WBCs come across foreign antigen (unique molecules on the surface of pathogens) they will start to proteins called antibodies to lock onto invading cells so they can be found and destroyed by other WBCs.
   The antibodies produced are unique to that specific antigen.
   Antibodies are then produced rapidly and carried around the body to find all similar bacteria or viruses.
   If the person is infected with the same pathogen again, the WBCs will rapidly produce the antibodies to kill it - the person is naturally immune to that pathogen and won’t get ill.
3. Producing antitoxins - To counteract the toxins produced by invading bacteria.

Question 19

Vaccination?

Answer 19

These involve injecting small amounts of dead or inactive pathogens. These carry antigens, which cause your body to produce antibodies to attack them - even though the pathogen is harmless. Eg = MMR vaccine = Measles, Mumps and Rubella

Question 20

Pros and cons of vaccination

Answer 20

Herd immunity - If a large proportion of the population is immune to a disease, the spread of the pathogen in the population is very much reduced and the disease may even disappear

They don’t always work
You can have a bad reaction to a vaccine - swelling/fever/seizures.

Question 21

Drugs to cure/relieve symptoms?

Answer 21

Painkillers- drugs that relieve pain, but don’t actually tackle the cause of the disease or kill pathogens - purely relieving symptoms
Antibiotics - penicillin - actually kill the bacteria causing the problem without killing your cells. Different antibiotics kill different types of bacteria
BUT antibiotics don’t destroy viruses. They reproduce using your body’s cells, making it very hard to develop drugs that do not damage the bodies cells.

Question 22

Resistant Bacteria?

Answer 22

Bacteria can mutate - sometimes these mutations cause them to be resistant to an antibiotic
If you have an infection, some bacteria might be resistant to antibiotics, so when you treat the infection, only the non-resistant strains will be killed. Meaning that the non-resistant bacteria will survive and reproduce and the resistant strain will increase.
It could cause serious infection that cannot be treated with antibiotics.
eg. MRSA (meticillin-resistant Staphylococcus aureus) causes serious wound infections and cannot be treated by powerful antibiotic meticillin.
To slow down the rate of development of resistant strains, it’s important for doctors to avoid over-prescribing antibiotics and that you finish the whole course when you have to take them.

Question 23

Drugs that came from plants?

Answer 23

Aspirin = painkiller and to lower fever = From a chemical found in willow
Digitalis = heart conditions = From a chemical found in foxglove

Question 24

Drugs that came from microorganisms?

Answer 24

Alexander Flemming cleared out some Petri dishes containing bacteria. He noticed that one of them containing bacteria had mould on it, and the area around the mould was free of bacteria
He found that the mould (Penicillium notatum) on the Petri-dish was producing a substance that killed the bacteria = penicillin

Question 25

Three main stages in testing drugs?

Answer 25

1. • Preclinical testing where the drugs are tested on human cells and tissues in the lab. However, you cannot use human cells and tissues to test drugs affecting whole or multiple body systems.
2. • The next step in preclinical testing is to test on animals. To test for efficacy (whether the drug works and gives the desired effect) to find out about its toxicity (if it’s toxic) and the best dosage to be given.
     UK law states each new drug should be tested on two different live mammals. SOme think animal testing is cruel and barbaric, whereas others think that it’s pointless as animals are so different from humans.
3. Now human volunteers.
   Healthy volunteers - to ensure it has no harmful effect when the body is working normally and to find the optimum dose
   Patients are put into two groups - one given the placebo and one given the new drug
   Blind trial - where the doctor knows which one is which
   Double-blind trial - where the doctor doesn’t know which is which - only someone not involved in the trial

After all of this, the trials are rigorously peer-reviewed by other scientists to prevent false claims.

Question 26

Monoclonal antibodies are…?

Answer 26

Produced from lots of clones of a single white blood cell. Meaning that all the antibodies are identical and will only target one specific protein antigen.