Infection and Response GCSE Biology AQA

4.3 Specification

Communicable disease

A disease caused by a pathogen which can be passed between animals or plants eg. flu.

Pathogen

Microorganism that can cause infection disease
Fungi
Virus
Protist
Bacteria

Toxin

Harmful chemicals produced by pathogens

Bacterial Infections

Can do damage to outside the cell 

Tuberculosis - fever, tiredness, coughing blood

Tetanus - lock jaw, muscle rigidity, spasms 

Scarlet fever - sunburn like rash, high temperature, chills, vomiting, white coating on tongue 

Bacterial Cell

Cytoplasm

Nucleotide DNA 

Ribosomes (site of protein synthesis)

Flagella for motion - not always there 

Slime capsule (mucus layer) - not always there 

Cell wall and Cell membrane 

Plasmids (small rings of DNA)

Mesosome - cell membrane collapses into cell (area of many cell reactions)

How Bacteria Causes Disease

Once inside the body, they divide rapidly by binary fission. They kill cells and produce harmful toxins.

Virus Cells 

Must get inside of body cell to infect 

Genetic material free flowing inside cytoplasm (RNA or DNA)

Protein Coat 

Keys (proteins) on the outside that can attach to only specific cells in the body

Sometimes secrete Toxins

Smaller than bacteria

Replicates rapidly inside host cells, damaging cells

Do not classify as a living organism

Viral Infections

Measles - Flat red spots over chest and face

Chicken pox - Fever

Hepatitis B

Tobacco Mosaic Virus 

Fungi Cells 

Cell membrane

Food storage granules (starch)

Vacuoles

Mitochondria

Cytoplasm

Cell Wall

Nucleus

Ribosomes

Can be unicellular or multicellular 

Gives out digestive enzymes on the surface they live on - break down complex carbohydrates and sucks them up to fuel cells 

Fungal Infections

Athletes Foot

Ringworm

Thrush

Target spot (plant)

Protists

Diverse collection of Eukaryotic organisms

most are unicellular 

Group includes algae and protozoa 

Plasmodium type of protist - Malaria f

Ways Pathogens Can Be Spread

By air - flu, tuberculosis and the common cold are spread by droplet infection.
By water - fungal spores in water spread plant diseases.
By direct contact - common in plant diseases and sexually transmitted infections.

Ways to Reduce the Spread of Pathogens

Hygiene - handwashing
Reducing contact with infected individuals - quarantine.
Removing vectors - use of pesticides and insecticides
Vaccination.

Importance of Preventing Viral Disease Spread

Scientists have not yet developed cures for many viral diseases.

Measles

A serious viral disease that can cause blindness and brain damage.

The main symptoms are a fever and a red skin rash.

Spread by Inhalation of Droplets from sneezes and coughs

HIV/AIDS

HIV is a virus which attacks and damages the immune system until it can no longer function properly (unless successfully controlled with antiretroviral drugs)
Causes flu-like illness 
AIDS is the condition resulting from a long-term HIV infection. There is no cure or vaccine for HIV/AIDS.
Spread by sexual contact or other exchange of body fluids 

Preventing the Spread of HIV/AIDS

Use of condoms.
Screening of blood for transfusions.
Not sharing needles.
Bottle-feeding by HIV-positive mothers.
Use of antiretroviral drugs to prevent the development of AIDS.

Tobacco Mosaic Virus (TMV)

A plant pathogen which causes leaf discolouration when cells are damaged.
Affected areas cannot photosynthesise, reducing the crop yield.
As there is no treatment, farmers grow TMV-resistant crop strains to avoid infection.

How Tobacco Mosaic Virus is Spread

Contact between infected and healthy plants.
Insects may act as vectors which transfer the virus between different plants.

Salmonella

A type of bacteria found in raw meat, poultry and eggs. If they enter the body via food poisoning, they can affect natural gut bacteria.

Symptoms of Salmonella Food Poisoning

Fever.
Abdominal cramping.
Vomiting.
Diarrhoea.
May be fatal in very young or elderly populations due the risk of dehydration.

Limiting the Spread of Salmonella

Vaccinating animals intended for consumption.
Keep raw meat away from cooked meat.
Disinfect hands and surfaces after contact with raw meat.
Thoroughly cook meat.

Gonorrhoea

A sexually transmitted bacterial infection caused by unprotected sex with an infected individual.
Early symptoms include yellow/green discharge from genitals and painful urination, although it may be symptomless.

Its spread can be controlled through the use of antibiotics (no longer penicillin as many strains are resistant) and using condoms.

Rose Black Spot

A fungal disease which causes purple or black spots to develop on rose leaves.
It reduces the area of the leaf which is available for photosynthesis and causes leaves to turn yellow and drop prematurely.
Spread by water or wind and can be treated by using fungicides and destroying affected leaves 

Malaria 

A protist disease that is spread by mosquito bites 
Malaria causes recurrent episodes of fever and can be fatal
Spread can be controlled by preventing mosquitos from breeding and by using mosquito nets to avoid being bitten 

Reducing the Spread of Malaria

Using insecticides.
Using insect nets to avoid bites.
Prevent mosquito breeding by removing stagnant water.
Antimalarial drugs.

What are aphids?

Insects/Vector that inject into plants and drink sugar from phloem - breed very quickly and cause wilting

Detection of plant diseases

Stunted Growth

Spots on leaves

Areas of decay (rot)

Growths 

Malformed stems or leaves

Discolouration 

Presence of pests 

Identification 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

Effects of Nitrate Deficiencies

Nitrate combines with glucose to make amino acids to build proteins.
Lack of Nitrate causes less protein production and protein synthesis, leading to stunted growth

Effects of Magnesium deficiencies

Causes chlorosis as Magnesium is used to make chlorophyll - less produced therefore leaves lose their bright green colour.
Chlorophyll needed for photosynthesis therefore less photosynthesis
Less glucose will be produced (by product of photosynthesis) therefore less respiration will happen and less energy will be release
This will cause less protein synthesis and cell production to happen, leading to stunted growth.

Plant Physical Barriers

Tough Waxy cuticle on leaves
Layers of Dead cells around stems + bark on trees
Cellulose cell walls
Leaf Walls
Callus Formation (synthesised + deposited between cell walls + cell membrane preventing spread of pathogen to adjacent cells)

Plant Chemical defences

Poison to stop animals from eating
Antibacterial Chemicals to get rid of pathogenic microorganism (lysosomes)
insect Repellents (Citronella from lemon grass plants, Pine resin from pine trees)

Plant Mechanical Adaptations

Thorns and hairs deter animals
Leaves which droop or curl when touched
Mimicry to trick animals 

How the Skin Prevents Pathogen Entry

Acts as a physical barrier.
Scab formation after skin is cut/wounded.
Antimicrobial secretions which can kill pathogens.

How the Respiratory System Prevents Pathogen Entry

Nose - has hairs and mucus which trap pathogens.
Trachea and bronchi - have mucus that traps pathogens.
Ciliated cells move mucus to the mouth so it can be swallowed - Pathogens trapped in mucus are killed in stomach acid (Chemical Defence)

Mechanical Defence - cilia 

How the Stomach Prevents Pathogen Infection

Secretes hydrochloric acid - kills any pathogens present.

Bacteria in Gut - Biological Defence 

Specific Defence

Distinguishes between pathogens - defends against specific Pathogens instead of defending against all (Non specific) 

Phagocytosis

White blood cells (phagocytes) ingest and destroy pathogens so they cannot infect more cells.

Lysosome in lysozyme which is an enzyme in White blood cells - they break the pathogen down

B Memory Cells 

White blood cells have receptors on their surfaces that attach to antigens on the pathogen
B- Naive cells Attaching to the antigen triggers the white blood cell to reproduce

Once pathogen is cleared, B naive cells produce B memory cells that can react more aggressively if the same pathogen is encountered again

Receptors are specific to only one type of pathogen so each type of white blood cell works against only type type of pathogen

Antibody Production

White blood cells (B-Naive cells) have receptors which attach to antigens on pathogen
Anitbodies are then produced in the same shape as receptor by B plasma cells which attaches to antigen on pathogen and kills it
In the case of a second infection, the correct antibodies (from b memory cells) can be produced rapidly, preventing the person getting the same disease again.

Antitoxin Production

Antitoxins bind to toxins released by pathogens and neutralise them.
Protein produced by lymphocytes to neutralise toxins

Vaccination

Contains a dead or inactivated form of the pathogen which stimulates white blood cells to produce complementary antibodies to the pathogen.
In the case of a second infection, memory cells can rapidly produce the correct antibodies and prevent illness.

Herd Immunity

If a sufficiently high proportion of a population are immune to a disease (especially through vaccination), the spread of this disease will be limited.

Advantages of Vaccinations

They have eradicated many deadly diseases eg. smallpox.
Many epidemics can be prevented by vaccinations.
Herd immunity protects those who cannot have vaccinations.

Disadvantages of Vaccinations

Not guaranteed to work - might not protect against multiple strains of a pathogen. May be side effects or adverse reactions.

Vaccination for Whooping Cough in pregnant women 

Pregnant women are given the vaccine

Dead/weak bacteria in vaccine would be detected by white blood cells which would then produce antibodies to kill the pathogen

These antibodies would transfer to the fetus via the placenta, making the baby immune to whooping cough for the next 3 months of their lives until they are old enough to be vaccinated

Drugs Used to Cure Some Bacterial Diseases

Antibiotics - they can kill bacterial pathogens inside the body.

Digitalis discovery 

Heart drug digitalis originates from foxgloves 

Aspirin discovery 

Painkiller aspirin originates from willow 
Willow bark contains salicin which body converts to salicylic acid 

Penicillin discovery 

Alexander Fleming discovered penicillin from penicillium mould 

How Antibiotics Work

Antibiotics eg. penicillin kill bacterial pathogens inside the body, but do not kill human cells - can break down chemicals in bacteria cell membranes and can stop bacteria from making new proteins or DNA

Why Antibiotics Can't Treat Viral Diseases + Anitbiotic Resistance

Viruses live inside human cells therefore difficult to kill without killing human cells
One or more bacteria mutate so they are more resistant to antibiotic - other bacterias die leaving all the resistance ones that will reproduce very quickly causing all bacterias to be antibiotic

Antibiotic Resistance

Antibiotic resistance occurs when mutations lead to individual bacteria being resistant to an antibiotic.
These bacteria are able to survive, reproduce and pass on their alleles, leading to a greater proportion of antibiotic-resistant bacteria.
This is concerning as some types of bacteria are becoming resistant to all known antibiotics, so the diseases that they cause cannot be cured.

Preventing Antibiotic Resistance

Avoid overuse and unnecessary use of antibiotics - eg. antibiotics are often used for viral infections. Finish antibiotic courses - to ensure all bacteria is killed.

Effect of Painkillers on Infectious Diseases

Painkillers can only treat the symptoms but do not kill pathogens.

Qualities of a Good Medicine/Drug

Effective. Safe. Stable. Able to be taken in and removed easily.

Single-Blind vs. Double-Blind Trial

In a single-blind trial, only the doctor knows whether the patient is receiving the drug or the placebo. In a double-blind trial, neither the patient nor the doctor knows. Double-blind trials help remove bias on the part of the doctor.

Peer Review

Where the results of drug trials are checked over by scientists knowledgeable in this field.

Why are mice usually tested on 

Reproduce Fast

Mammals - similar cell structures

Not endangered

Docile

Cheap to buy and keep 

Small 

Can inbreed - fewer genetic differences and controlling more variables 

Drug Testing Stage 1

Laboratory - Animals or tissues used in a lab to find out the level of toxicity and to find out if drug works
3 - 5 years 

Drug Testing Stage 2

Phase 1 Clinical - Low doses are tested on a small group of healthy people to evaluate its safety, and identify side-effects

Drug Testing Stage 3

Phase 2 Clinical - Tested on a larger group of people to see if its effective, to further evaluate its safety and to determine the optimum dose - dose that is most effective with fewest side effects

Drug Testing Stage 4

Phase 3 Clinical - Tested on a large group of people to confirm its effectiveness and monitor side effects
10 years from Phase 1 to 3

Why Healthy Volunteers First? 

Less likely to get seriously ill from bad drug

Sick volunteers may already be on other drugs

Sick Volunteers may have symptoms that mask side effects 

Sick volunteers may be immunocompromised 

What is a placebo?

Used as it doesn’t contain any of actual drugs and used as control and compare effects between psych and actual drug e.g sugar tablet or saline solution

Monoclonal antibodies (mAbs)

Antibodies that are clones from one parent cell and are specific to one type of antigen.

Production of Monoclonal Antibodies

Specific antigen (salmonella enterica) injected into a mouse Mouse recognises salmonella as foreign and B lymphocytes start producing antibodies specific for Salmonella enterica then extracted from mouse’s spleen
Purify lymphocytes and Identify the lymphocytes with the right antibodies

B-lymphocytes fuse with myeloma (cancer) cells to form hybridoma cells. - is able to divide quickly due to cancerous properties and creates clones of itself - Monoclonal antibodies collected and purified.

Uses of Monoclonal Antibodies

Detection of pathogens, location of cancer cells and blood clots, treatment of cancer, and use in pregnancy test kits.

Zones on Pregnancy Test

3 zones: Reaction, Test and Control

How does Pregnancy Tests test if women are Pregnant

Reaction zone 1 - Mobile monoclonal antibodies complementary to the HGC hormone (produced in early stages of pregancy) with enzyme attached to it which activates dye in a chemical in test and control zones
If there is HCG present, it binds to mAbs which move through with liquid urine to the Test zone
Test Zone 2 - There are immobile mAbs complementary to HCG which bind with HCG which is also bound to the mobile mAbs with enzyme from Reaction Zone
The mobile mAbs stay in that zone and the enzyme activates the chemical with dye and produces a line (positive test)
Control Zone 3 - Excess mobile mAbs move onto the Control - one which has the same chemical dye which activated by enzymes and binds to immobilised antibodies and creates a line to show test is working

Advantages of using monoclonal antibodies to test for pathogens

Specific to one particular antigen, very accurate, and provides quick results.

Why monoclonal antibodies can be used to target cancer cells

Cancer cells have specific antigens called ‘tumour markers’ on their membranes, and mAbs are specific to one type of antigen so can be targeted to ‘tumour markers’ without damaging other cells.

How monoclonal antibodies can be used to diagnose cancer

mAbs tagged to a radioactive substance are injected, bind to ‘tumour markers’ on cancer cells, and emitted radiation is detected to determine cancer cell location.

How monoclonal antibodies can be used to target drugs to cancer cells

mAbs attached to an anti-cancer drug are injected, bind to ‘tumour markers’ on cancer cells, and the anti-cancer drug destroys cancer cells.

Why monoclonal antibody cancer treatments are favored

mAbs only target cancer cells, reducing damage to normal cells.

How monoclonal antibodies can be used to locate blood clots

mAbs tagged to a radioactive substance target and bind to specific proteins in blood clots, and radiation emitted is detected to identify the location of blood clots.