GCSE AQA Biology - Infection and response

Pathogens

Microorganisms that enter the body and cause disease

4 Pathogens

Bacteria, viruses, protists and fungi

Communicable diseases

Diseases that can easily be spread

How do bacteria make you feel ill?

By producing toxins that damage your cells and tissues.

How do viruses make you feel ill?

By replicating themselves inside of your cells until the cell bursts, causing damage the cell.

What are the three ways pathogens can be spread?

• Water

• Air

• Direct contact

Three viral diseases

• Measles

• HIV

• TMV (Tobacco mosaic virus)

How is measles spread?

By inhalation of droplets from an infected person’s sneeze or cough

What are the symptoms of measles?

A red skin rash, a fever and even fatal complications.

How do we protect against measles?

By vaccinating people from a young age.

How is HIV spread?

By sexual contact or exchanging bodily fluids (blood when sharing needles)

What are the initial symptoms of HIV?

Flu-like symptoms.

What does HIV do to the body?

It attacks the body’s immune cells.

How can we control HIV from attacking immune cells?

By using antiretroviral drugs.

What is AIDS?

The late stage of HIV infection, in which the body’s immune system becomes so badly damaged it cannot deal with other infections or cancers.

What does TMV affect?

Many species of plants including tomatoes.

What is the symptom of TMV?

A ‘mosaic’ pattern of discolouration on the leaf, showing it can’t photosynthesise as well and grow properly.

What is an example of a fungal disease?

Rose black spot

What are the symptoms of rose black spot?

Leaves develop purple or black spots, turn yellow and drop off early.

What is the effect of rose black spot?

Causes the rate of photosynthesis to fall and reduces the rate of growth.

How is rose black spot spread?

By water or by wind.

How can gardeners treat rose black spot?

By using fungicides and removing and destroying the affected leaves.

What disease is caused by a protist?

Malaria

How are malarial protists spread?

By mosquitos (vectors) picking up the protist when they feed on infected animals, and inserting the protist into other animals when they feed on them.

How can we control the spread of malaria?

• Preventing vectors from breeding

• Using insecticides and mosquito nets

What are two bacterial diseases?

• Salmonella

• Gonorrhoea

What are the 4 symptoms of salmonella?

Fever, stomach cramps, vomiting and diarrhoea

How is salmonella spread?

By food poisoning from eating food that’s been contaminated with salmonella bacteria.

How can we control spread of salmonella?

• Vaccinating poultry against salmonella

• Prepare food in hygienic conditions

How is Gonorrhoea spread?

By unprotected sexual contact

What are the symptoms of gonorrhoea?

Pain when urinating and a thick yellow discharge from the vagina or the penis.

How can we prevent the spread of gonorrhoea?

• Treating people with antibiotics

• Using barrier methods of contraception

What are the 4 ways we can reduce and prevent the spread of disease?

• Being hygienic

• Destroying vectors

• Isolating infected individuals

• Vaccination

What are 4 non-specific defense systems of the human body?

• Skin

• Nose

• Trachea and bronchi

• stomach

How does the skin defend against infection?

It acts as a physical barrier to pathogens and secretes antimicrobial substances which kill pathogens.

How does the nose defend against infection?

Hairs and mucus in the nose trap pathogens before they can reach the lungs.

How do the trachea and bronchi defend against infection?

They secrete mucus to trap pathogens, and cilia waft pathogens and mucus upwards.

How does the stomach defend against infection?

It produces hydrochloric acid to kill any pathogens.

What are the 3 functions of white blood cells?

• Consume pathogens (phagocytosis)

• Produce antibodies

• Produce antitoxins

Phagocytosis

White blood cells engulf foreign cells and digest them.

Antigens

Unique molecules on the surface of cells or pathogens.

What will some types of white blood cells do when they come across a foreign antigen?

They will produce antibodies specific to the antigen which lock onto the antigen of the invading pathogen so they can be found and destroyed by other white blood cells.

How do some white blood cells counteract toxins?

By producing antitoxins

How do vaccines work?

• The body produces antibodies to respond to antigens on small amount of dead or inactive pathogens.

• This means that if the same type of pathogen reappears, the white blood cells can quickly produce antibodies to respond to it.

Advantages of vaccines

Control communicable diseases and prevent large outbreaks

How does herd immunity protect unvaccinated individuals?

The spread of the disease is significantly reduced when most people are vaccinated, making it harder for the pathogen to infect unvaccinated individuals.

Disadvantages of vaccines

They don’t always work, and you can sometimes have a bad reaction.

Painkillers

Relieve pain and reduce symptoms, but don’t actually kill pathogens.

Antibiotics

Kill bacteria

How can bacteria become resistant to antibiotics?

If not all bacteria are killed by antibiotics, some can survive and randomly mutate to subsequently produce antibiotic resistant strains.

What are the 3 reasons antibiotics are becoming less effective?

• Overuse

• Failing to complete the course of treatment

• High use in agriculture

How can aspirin be used?

As a pain killer and to lower fever.

What was aspirin developed from?

Willow

How can digitalis be used?

To treat heart conditions.

What was aspirin developed from?

Foxgloves

What was penicillin discovered from?

The penicillium mould

Who discovered penicillin?

Alexander Flemming

How are most drugs developed today?

Synthesised by chemists in a lab.

What are new drugs tested for?

Toxicity, efficacy and dosage.

What happens in the first part of pre-clinical trial?

Drugs are tested on computer models and human cells and tissues in the lab, allowing efficacy and possible side effects to be tested.

What happens in the second part of pre-clinical trial?

Drugs are tested on live animals, allowing efficacy, toxicity and dosage to be tested.

What happens in the clinical trials?

Drugs are tested on healthy volunteers to ensure they are safe, and are then tested on people with the illness.

How are placebos used in clinical trials?

• Patients are either given the new drug or a placebo

• This allows the doctors to see the difference the drug makes

The placebo effect

When the patient expects the treatment to work, so feels better despite the treatment not doing anything.

Double-blind trial

Neither the patient nor the doctor knows whether the patient is getting the drug or the placebo, preventing any subconscious influence the doctor may give be knowing.

Monoclonal antibodies

Antibodies produced from lots of clones of a single white blood cell.

How are monoclonal antibodies made? (4)

• A mouse is injected with the chosen antigen

• B-lymphocytes produced by the mouse are taken

• A B-lymphocyte is fused with a tumour cell, creating a hybridoma

• The hybridoma divides to produce lots of clones that produce the monoclonal antibody

Why are monoclonal antibodies useful?

They can bind to any antigen you want, so can target a specific cell or chemical in the body.

What is HCG?

A hormone found in the urine of women during pregnancy.

How are monoclonal antibodies used in pregnancy tests?

• Monoclonal antibodies are attached to the end of the test strip which a woman urinates onto.

• If the woman is pregnant, HGC will bind to the monoclonal antibodies.

• There will be a colour change to indicate the pregnancy

How can monoclonal antibodies be used to treat cancer?

Monoclonal antibodies can carry an anti-cancer drug which stops cancer cells when they bind to antigens on cancer cells.

What can monoclonal antibodies be used for in the lab? (3)

• To measure levels of hormones and other chemicals in the blood

• To detect pathogens in the blood

• To locate specific molecules on a cell or tissue

Disadvantage of monoclonal antibodies

• Can cause side effects - fever, vomiting and low blood pressure

What do plants need nitrates for?

To make proteins for growth

What does a lack of nitrates cause?

Stunted growth

What do plants need magnesium ions for?

To make chlorophyll for photosynthesis

What does magnesium deficiency cause?

The plant suffers from chlorosis and yellow leaves, limiting healthy growth.

What are the physical barriers to pathogens of plants?

• Waxy cuticle

• Cell walls surrounding plant cells

• Layers of dead cells around stems (e.g. bark on trees)

What are the chemical defenses plants have against pathogens?

• Some produce antibacterial chemicals

• Others produce poison to deter herbivores

What are the mechanical defenses plants have against pathogens?

• Thorns and hairs deter animals

• Leaves that droop when touched

• Mimicry to trick animals

7 signs of plant disease

• Stunted growth

• spots on leaves

• areas of decay

• growths

• malformed stems or leaves

• discolouration

• pests

How you make identification of plant diseases?

• Reference to a gardening manual or website

• Test the infected plant for pathogens in a lab

• Use test kits containing monoclonal antibodies