GCSE Biology : Infection and response

Communicable diseases and pathogens - and what cells can be pathogenic

communicable diseases are spread from person to person, they are infectious - they are spread by pathogens.

pathogens are microorganisms that cause infectious diseases

these include bacteria, viruses, protists, fungi

how do bacteria make us ill ?

once inside the human body bacteria reproduce very quickly (20 min - if there are enough nutrients and a stable temperature)

bacteria can then release harmful chemicals called toxins which damage tissues and make us feel ill

bacteria can be killed using antibiotics

how do viruses make us feel ill ?

they cannot reproduce by themselves, they can only reproduce inside a host cell - they are not living and have no living sub cellular structures

the virus invades the host cell, the virus then reproduces inside the host cell

this is damaging to the cell as when the virus leaves it, it can cause the cell to burst open and die

how are pathogens spread ?

spread in the air e.g. water droplets (influenza)

spread directly in water e.g. cholera

direct contact e.g. HIV from sharing infected needles and sexual contact

how to reduce the spread of pathogens ?

BASIC HYGIENE Washing hands before eating can reduce spread of pathogens

providing people with clean drinking water e.g. cl in UK water kills microbes

reduce direct contact between induviduals e.g. using a condom during sex reduce spread of pathogens

in the case of some highly infectious diseases, patients may be isolated - reduces spread of pathogens

vaccination reduces the spread of pathogens

viruses overview

viruses are examples of a pathogen but are not living

they are MGs that cause infectious diseases

they cannot be killed by antibiotics

measles - viral, symptoms, spread

highly infectious disease and first symptom is often a fever

around 3 days the patient develops a red skin rash

measles virus is spread in water droplets when an infected person coughs or sneezes, it then passes into a different person when these droplets are inhaled

measles is a serious disease. In some cases, complications can develop and these can cause damage to the breathing system and brain

because of this most children are vaccinated against measles when they are very young

HIV - viral, symptoms,

first symptom is a flu like illness but often disappears after 1 or 2 wks - at this stage the virus is attacking the cells of the patients immune system, over time the immune system becomes severely damaged

At some point, the patients immune system becomes so badly damaged that it cannot fight off other infections that other people could easily deal with - also is unable to fight off cancer cells (AIDS).

when AIDS is reached the pateint can now easily contract other infections such as TB or cancer - frequently at this stage the disease is fatal

treatment and spread for HIV

antiretroviral drugs stop the virus from multiplying inside the patient so the virus doesn't damage the patients immune system - patients who take these drugs do not go on to develop AIDS and they can lead a normal life expectancy. These drugs are not a cure of HIV or AIDS , the patients must take these drugs for the rest of their life

HIV is spread by sexual contact or exchange of body fluids

such as blood which occurs when drug users share needles.

Salmonella

Salmonella food poisoning is spread by bacteria ingested in food,

or on food prepared in unhygienic conditions.

In the UK, poultry are

vaccinated against Salmonella to control the spread. Fever, abdominal

cramps, vomiting and diarrhoea are caused by the bacteria and the

toxins they secrete.

Gonorrhoea

Gonorrhoea is a sexually transmitted disease (STD) with symptoms of

a thick yellow or green discharge from the vagina or penis and pain on

urinating.

It is caused by a bacterium and was easily treated with the

antibiotic penicillin until many resistant strains appeared. Gonorrhoea

is spread by sexual contact.

The spread can be controlled by treatment

with antibiotics or the use of a barrier method of contraception such as a

condom.

malaria - protist disease

malaria cannot pass directly from one person to another, only by vectors like mosquitoes

The malarial protist has a life cycle that includes the mosquito. Malaria

causes recurrent episodes of fever and can be fatal.

The spread

of malaria is controlled by preventing the vectors, mosquitos, from

breeding (e.g. draining and spraying still water with insecticide where they breed) and by using mosquito nets to avoid being bitten.

non specific defence system and limitation

the job of the non specific defence system is to prevent pathogens from entering the human body

but even with all these systems, pathogens can still enter the human body and still cause really bad disease so to protect us, there is also an immune system

skin as a non specific defence system

skin forms a protective layer covering the body, the outer layer of the skin consists of dead cells and is difficult for pathogens to penetrate - skin also produces and oily substance called sebum which can kill bacteria

sometimes the skin is damaged and that could allow pathogens to enter the body, to stop this, the skin scabs over

nose and trachea and bronchi

areas in the body that are not covered by skin present openings where pathogens could enter

nose contains hairs and mucus which can trap pathogens before entering the breathing system but sometimes pathogens could still pass through the nose and go to the breathing system

to stop this is the trachea and bronchi are covered with tiny hairs called cilia. They are covered in mucus which can trap pathogens. The cillia now waft the mucus upwards towards the throat where it is swallowed into the stomach

stomach as a non specific defence system

there are lots of diff. pathogens that can be present on food, to protect the rest of the digestive system the stomach contains HCL which kills pathogens before they go further down the digestive sys.

need of immune system

non specific defence systems stop pathogens from entering the body,

however sometimes the pathogens can invade the body

and enter the bloodstream,

once inside the body pathogens can multiple and damage healthy tissue e.g. by releasing toxins

to protect us from invasive pathogens, the body also has the immune system

function of immune system

destroys pathogens and any toxins they produce

protects us incase the same type of pathogen invades us again in the future

Phagocytosis (white blood cells) - immune system

phagocytes ingest and destroy pathogens, the WBC detects chemicals released from the pathogen and moves towards it and then ingests the pathogen and uses enzymes to destroy it

antibodies from lymphocytes - immune system

antibodies are protein molecules produced by white blood cells, antibodies stick to pathogens which triggers the pathogens to be destroyed

they are extremely specific to each type of pathogen

they can remain in the blood for a long time, this means that they can protect us incase we ever get infected again by the same pathogen

white blood cells producing antitoxins

certain types of bacteria can release toxins

WBCs can produce chemicals called antitoxins which bind to toxin molecules and prevent them from damaging cells

Tobacco Mosaic Virus (TMV)

widespread plant infection, infects a number of different plants including tomatoes.

TMV causes the leaves to discolour in a mosaic pattern and because of this discolouration the rate of photosynthesis is reduced ∴ growth of the plant is also reduced

Rose black spot RSB - fungal

purple or black spots develop on leaves,

which often turn yellow and drop early.

It affects the growth of

the plant as photosynthesis is reduced BC of leaf spots.

It is spread in the environment

by water or wind.

Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.

vaccination

Vaccination involves introducing small quantities of dead or inactive

forms of a pathogen into the body to stimulate the white blood cells

to produce antibodies.

at the same time the WBC divides by mitosis to produce lots of copies of itself which can stay in the body for decades

because the pathogen is dead or inactive, it cannot cause infection in the body

If the same pathogen re-enters the body the

white blood cells respond quickly to produce lots of the correct antibodies,

preventing infection.

Herd immunity

it is important that a very large number of people are vaccinated against pathogens but there are always some people who do not get vaccinated e.g. new immigrants or ppl who missed

if enough ppl are vaccinated then this also protects unvaccinated people bc the unvaccinated person cannot catch the disease bc no-one around them can pass it on

antibiotics (what they do) and resistance

Antibiotics, such as penicillin, are medicines that help to

cure bacterial disease by killing infective bacteria inside

the body without harming body cells . It is important that specific bacteria should be

treated by specific antibiotics.

The use of antibiotics has greatly reduced deaths from

infectious bacterial diseases. However, the emergence of

strains resistant to antibiotics is of great concern.

antibiotic resistance

Several years ago, doctors discovered that certain antibiotics were no longer effective against certain bacteria because they had been overused.

The bacteria had no longer evolved so that they were no longer killed by the antibiotic

possible that bacterial diseases in the future will be very hard to treat

antibiotics facts

doctors always use specific antibiotics to treat specific bacteria

Antibiotics cannot kill viral pathogens.

Painkillers and other medicines are used to treat the

symptoms of disease but do not kill pathogens.

It is difficult to develop drugs that kill viruses without also

damaging the body's tissues because viruses live and reproduce inside human cells

aspirin, penicillin, digitalis

Traditionally drugs were extracted from plants and microorganisms.

• The heart drug digitalis originates from foxgloves.

• The painkiller aspirin originates from willow.

• Penicillin was discovered by Alexander Fleming from the Penicillium

mould.

Most new drugs are synthesised by chemists in the pharmaceutical

industry. However, the starting point may still be a chemical extracted

from a plant.

why drugs need to be tested and in what aspects ?

all new drug no matter where they come from have to be tested and trialled to check if they are safe or effective

firstly the toxicity of the drug must be checked (whether safe for humans)

need to check its (efficacy)effectiveness

need to check the best dosage of the drug

the first stage of drug testing which is pre clinical testing

then clinical testing

not carried out on humans bc the drug could be extremely toxic, instead preclinical testing is carried out on cells, tissues, or animals

once preclinical testing is carried out, the drug passes on to clinical testing :

Clinical trials use healthy volunteers and patients.

• Very low doses of the drug are given at the start of the clinical trial.

• If the drug is found to be safe, further clinical trials are carried out to find the optimum dose (best dose to treat the disease with the fewest side effects) for the drug

placebos for double blind testing in clinical trials

a tablet or injection with no active drug in it, some patients will get better if you give them a placebo because they think they are being treated so they believe that they are going to get better

double blind trial test

the test group receives the active drug. the placebo/control group receives a placebo drug with no active ingredient

in the double blind trial, neither the patients nor the doctors know which ppl are receiving the active or placebo drug

this is to stop bias incase the doctors paying closer attention to ppl receiving the active drug

lymphocytes, antigens

Antibodies are produced by WBCs called lymphocytes,

lymphocytes produce antibodies against anything that the body detects as foreign

scientists call foreign objects that trigger immune responses antigens

scientists can use mice to trigger lymphocytes to produce antibodies which can be rlly useful

how are monoclonal antibodies made

They are produced by stimulating mouse lymphocytes to make a

particular antibody (against a specific antigen).

The lymphocytes are combined with a particular kind

of tumour cell to make a cell called a hybridoma cell bc lymphocytes cannot easily undergo mitosis and divide.

The hybridoma

cell can both divide and make the antibody

. a single hybridoma cell producing the wanted antibody

is cloned to produce many identical cells that all produce the identical

antibody.

A large amount of the antibody can be collected and purified.

monoclonal antibodies are produced from a single clone of hybridoma cells.

this means that monoclonal antibodies are specific to one binding site on one protein antigen.

the benefit of this is that monoclonal antibodies can target specific chemicals or specific cells in the body and they have a large number of uses

MC antibodies in use

for diagnosis such as in pregnancy tests

• in laboratories to measure the levels of hormones and other

chemicals in blood, or to detect pathogens

• in research to locate or identify specific molecules in a cell or tissue

by binding to them with a fluorescent dye

• to treat some diseases: for cancer the monoclonal antibody can be

bound to a radioactive substance, a toxic drug or a chemical which

stops cells growing and dividing. It delivers the substance to the

cancer cells without harming other cells in the body.

Monoclonal antibodies create more side effects than expected.

They

are not yet as widely used as everyone hoped when they were first developed.

how can plant disease be detected

• stunted growth

• spots on leaves

• areas of decay (rot)

• growths

• malformed stems or leaves

• discolouration

• the presence of pests.

plants can also be attacked by insects such as aphids which extract nutrients like sugars from the plant stunting its growth - they are not pathogens bc they don't cause disease, but they can be vectors of diseases

How to identify different types of plant disease

reference to a gardening manual or website

• taking infected plants to a laboratory to identify the pathogen

• using testing kits that contain monoclonal antibodies.

plant ion deficiency diseases

stunted growth caused by nitrate deficiency because nitrate ions are needed for protein synthesis ∴ growth

• chlorosis caused by magnesium deficiency as magnesium ions are needed to make chlorophyll which gives leaves green colour

Physical plant defence responses

all plants have a cellulose cell wall

leaves are covered with a thin oily layer called the waxy cuticle

Layers of dead cells around stems (bark on trees) which fall off and replaced with fresh bark underneath - barrier to entry by MGs

these defence responses make it difficult for MGs such as bacteria to penetrate from attack

chemical plant defence responses

• Antibacterial chemicals which are released and kill bacteria

• Poisons to deter herbivores from grazing on the plant

mechanical plant defence responses

sharp thorns directly protect a plant from being eaten by a herbivore

other plants have hairs which irritate the mouth of herbivores, making the plant difficult to eat

Leaves which droop or curl when touched which might scare herbivores as they are not used to plants like that

Mimicry to trick animals e.g. stinging nettle like leaves with no sting to trick herbivores