Infection and response - biology

What does it mean if a scientist is culturing microorganisms?

They are growing large numbers of microorganisms so the bacteria can be seen as a whole

Why do scientists culture microorganisms?

so they can find out what nutrients they need to grown and investigate which chemicals are best at killing them

What 4 things do microorganisms need to grown and why?

1. Nutrients - respiration

2. Warmth - optimum enzyme activity

3. Moisture - chemical reactions take place in solution

4. Oxygen - respiration

2 types of culture mediums to grow microorganisms

1. on hot agar jelly that sets in a petri dish

2. in sterile nutrient broth solution

Why must scientists work aseptically?

To prevent the microorganisms escaping or becoming contaminated with an unwanted microorganism

To prevent the growth of pathogenic microorganisms

What is meant by the term inoculation and what apparatus is used?

Inoculation is when you introduce a microorganism into a larger organism to encourage it’s growth there - for experiments, research or immunisation

Inoculation loop that has been sterilised dipped into a suspension of bacteria then streaked across surface of agar jelly OR pipette and a spreader

Why do microorganisms need to be incubated for several days and at what temp at school?

To ensure they grown and reproduce

At 25oC at school because it reduces the risk of growing pathogens that could be harmful

What is a communicable disease?

A disease that is caused by pathogens and can spread from person to person or person to animal

What is a pathogen?

A microorganism that causes infectious disease

What are the 4 types of pathogen?

Bacteria, viruses, fungi, protists

Where in our bodies do bacteria reproduce and how do they make us feel ill?

Reproduce outside our cells and produce toxins which damage cells/tissues, making us feel ill

Where in our bodies do viruses reproduce and how do they make us feel ill?

Reproduce inside our cells. Copies of virus burst out of our cells, killing the cells and destroying tissues

What are the 6 ways in which disease can be transmitted

Waterborne, airborne, vectors, direct contact, sexual contact, placental transfer

Measles

Virus - airborne, inhalation of droplets from coughs and sneezes - blindness, brain damage, fever, red skin rash - no treatment - isolation to stop the spread, vaccination

HIV/AIDS

Virus - sexual contact and exchange of bodily fluids, placental transfer - no cure or vaccine but anti-retroviral drugs - use protection, don’t share needles, HIV positive mothers should bottle feed, screening blood used for transfusions

Malaria

Protist - mosquito vector - recurrent fever and shaking - a combination of drugs - insecticide to kill vectors, mosquito nets, anti-malarial drugs

Salmonella

Bacteria - direct contact (eating undercooked food) - develops within 8-72 hours of eating infected food, fever, abdominal cramps, vomiting, diarrhoea - antibiotics, keep water in take high to prevent dehydration - poultry vaccinated against disease, keep raw chicken away from cooked food, wash hands and surface, cook chicken well

Gonorrhoea

Bacteria - sexual contact - thick yellow/green discharge, pain on urination, ectopic pregnancies, long term pelvic pain, infertility - antibiotics - all sexual partners of infected person must take antibiotics, use contraception

How do the bronchi protect against disease?

They secrete mucus that traps pathogens. The cilia then wafts the mucus up to the back of the throat where it’s swallowed

How does the stomach protect against disease?

Produces hydrochloric acid which destroys microorganisms in swallowed mucus

How does the skin protect against disease?

Acts as a barrier that prevents pathogens reaching tissues below - if skin breaks, platelets form a clot that dries into a scab to prevent the entry of pathogens into the blood - antimicrobial secretions from the skin destroy bacterial pathogens

What do pathogens have on their cell membranes?

Antigens - specific proteins that identify them

What are lymphocytes?

White blood cells that produce antibodies that bond to specific antigens on the pathogens

Explain the specificity of lymphocytes, antibodies and antigens

Specific antibodies bind to their complementary antigen; it will either destroy the pathogen directly or label it for phagocytes to engulf - each lymphocyte produces a different type of antibody that only binds to specific type of pathogen as the chapes are complementary

What is the problem with lymphocytes being so specific?

When a pathogen enters the body, the correct lymphocyte must come into contact with the pathogen - this can take a while so person suffers the symptoms

Other than antibodies, what else do lymphocytes make?

Antitoxins which bind to toxins made by bacteria and neutralise them

Explain vaccination

When your body is exposed to a pathogen for the first time you become ill. This is because your lymphocytes do not produce a high enough concentration of antibodies quickly enough. However, after a first infection your immune system makes memory cells which remember how to produce the antibodies more quickly and at higher concentrations. This means the second time you are infected you are immune. Vaccination involves injection with a dead of inactivated form of a pathogen into the blood. This causes your body to make memory cells making you immune to the disease. Your lymphocytes learn to produce an antibody which has a complementary shape to bind to the antigen on the pathogen. If the pathogen enters again, your memory cells can quickly make lots of correct antibodies so you kill the pathogen before it causes symptoms/makes you ill

What is herd immunity and how is it achieved?

When a large enough proportion of the population are vaccinated which means that vaccinated individuals cannot catch the disease and therefore cannot spread it to other people. It therefore protects unvaccinated people

What happens if you breath in the flu virus but have had the latest vaccine?

The memory cells recognise the antigens so produce antibodies faster and at a higher concentration. The antibodies then kill the pathogen before it makes you ill

Name some painkillers

aspirin, ibuprofen, paracetamol, morphine, codeine

What do painkillers do?

Relieve your symptoms but don’t kill your pathogen or cure you any faster

From where do we originally obtain drugs such as antibiotics?

From plants or microorganisms such as moulds

Why do microorganisms, including bacteria, produce chemicals that kill bacteria?

To reduce competition, specifically for glucose

From which plant is aspirin obtained?

From a compound found in the bark of willow trees - it relieves pain and has anti-inflammatory properties and thins the blood

From which plant is digitalis obtained?

foxgloves- helps strengthen the heartbeat

What is the source of must drugs these days?

synthesised by chemists in the lab and modified to increase effectiveness

Why is it so important to test drugs before they’re used?

To make sure they’re safe and not too toxic or have unacceptable side effects

Must prevent/cure the disease or make you feel better

Preclinical trials

Scientists target a particular disease and make lots of possible drugs, which they test in the lab on cells, tissues or whole organs for toxicity and efficacy. Scientists then test those drugs that are safe and effective on live animals in the lab for toxicity efficacy, possible dosage and side effects in whole organisms; these organisms are used as models to predict how the drugs may behave in humans

Clinical trials

Scientists give a very low dose of a drugs that has passed the preclinical trial to healthy volunteers to check for side effects. If the drug is safe, scientists give it to a small number of patients to see if it actually treats the disease and to check for side effects. If the drug is safe and effective, scientist then carry out bigger clinical double-blind trials with more patients and higher doses to find the optimum dose.

After clinical trials

If the drugs passes clinical trials, the scientists’ method and results are scrutinised in the process of peer review to help to prevent false claims. If the results are valid, they are published in a scientific journal and the drug may be prescribed by doctors; the drug’s safety is monitored for as long as it is used.

toxicity meaning

How poisonous something is

efficacy meaning

ability to do their job and achieve the desired results

dosage meaning

the size and frequency of a drug given to patient

side effects meaning

additional bad effects aside from the intended ones

double-blind trial meaning

used to see how effective a new drug is; patients with the target disease agree to take part in the trial; patients are randomly allocated to 1 or 2 groups; some are given the new medicine, other are given a placebo; neither the doctor or patient know who’s in which group until the trial’s complete; the patient’s health is monitored carefully throughout

placebo meaning

doesn’t contain the new drug - drug already used or a sugar pill

control group meaning

for comparison to the treatment group

randomised meaning

patients are randomly allocated to the control and treatment groups

How long does it take and how much does it cost to bring a new drug to use?

up to 12 years, around £1.7 billion

What are antibiotics?

Antibiotics are medicine that can work inside our body to kill bacterial pathogens. They damage bacterial cells without harming your own cells

How are antibiotics administered?

Can be taken using a pill or a syrup or if very ill, straight into the bloodstream, intravenously

Describe the specificity of antibiotics

Some can kill a wide range of bacteria, others only work against specific bacteria - correct antibiotics must be selected to destroy the bacteria

Describe how we can test the effectiveness of different antibiotics on a particular bacterium in a school laboratory

Inoculate agar jelly in a petri dish with pipette and spreader. Place patches of different antibiotics in different places around. Incubate then measure the diameter of the zone of inhibition then calculate the area. The larger the zone, the more effective the antibiotic is

Percentage decrease calculation

(final - original / original) x 100

Who first discovered antibiotics and when?

Alexander Fleming - 1928

How did Fleming discover penicillin

He was growing bacteria and left the lids off his culture plates causing them to grow mould over time. However, some spots of mould had clear rings in the jelly around them. This was a substance that killed the bacteria which was called penicillin after the Penicillium mould it produced

Which 2 scientists extracted penicillin and produced it on an industrial scale?

Ernst Chain and Howard Florey

Describe the problem of antibiotic resistance

Strains of bacteria that are resistant to antibiotics are evolving meaning that antibiotics used to kill a particular bacteria no longer have an effect so they can’t cure a disease. Some types of bacteria are resistant to all known antibodies. Antibiotic resistance means, unless we don’t discover new antibiotics soon, we may no longer be able to cure bacterial diseases causing an increase in death from disease we can currently cure

What is exacerbating the problem of antibiotic resistance?

People are taking them when they are not needed - some aren’t finishing their course - used in farming which speeds up process

Why is it more difficult to develop drugs to cure viral disease?

Viruses reproduce inside the cells so it is hard to kill the viruses without damaging the cells and tissues of your body as well

What are antigens?

proteins on the surface of pathogens or cell that enable the immune system to identify the cell/pathogen

What are antibodies?

Proteins created by lymphocytes that bond to the complimentary and specific antigen to help destroy pathogens or label them for phagocytes

What are monoclonal antibodies?

Identical antibodies produced in a laboratory that have a variety of uses including detecting and treating diseases

How are monoclonal antibodies produced?

A mouse is injected with the antigen. The mouse produces lymphocytes that produce antibodies. The specific lymphocytes are removed from the spleen and fused with a tumour cell to form a hybridoma cells, which can both die and make the specific antibody. The hybridoma cells are cloned (forced to divide by mitosis) to make millions of cells that will all produce the specific antibodies

What are the general uses of monoclonal antibodies?

1. detecting the presence, absence or levels of hormones, chemicals or pathogens in the blood, urine or saliva

2. locating specific molecules in a cell or tissue

3. treating diseases such as cancer

How are monoclonal antibodies used in pregnancy tests?

A hormone called human chorionic gonadotrophin (HCG) is present in the early stages of pregnancy and small amounts pass out in the urine. If the hormone is present, monoclonal antibodies that are complementary to this hormone bind to it, causing a coloured line to form on the test strip

How are monoclonal antibodies used in COVID 19 lateral flow tests?

If the virus is present, the monoclonal antibodies that are specific to the virus’ antigens bind to them, causing a coloured line to form on the test strip

How are monoclonal antibodies used to locate specific molecules in cells or tissues?

A fluorescent dye or marker is attached to monoclonal antibodies that are complementary to the specific molecule. The monoclonal antibodies bind to the specific molecule in the cell or tissue and fluoresce, so you can see which cells/tissues contain the specific molecules using UV light

How are monoclonal antibodies used in treating cancer?

Monoclonal antibodies bind to specific complementary antigens found only on the cancer cells and either signal to phagocytes to engulf and destroy the cancer cells OR prevent growth-stimulating molecules from binding to the cancer cells and stop them from dividing by mitosis, so a tumour can’t grow OR are attached to radioactive substances or toxic chemicals that kill the cancer directly

What are some advantages of using monoclonal antibodies?

• only bind to the specific disease/ damaged cells that need treatment

• don’t damage healthy cells

• specificity means can treat wide range of disease

What are some disadvantages of using monoclonal antibodies?

• not yet as widely used or successful as hoped

• ethical issues around using mouse

• created more side effects than expected

• can trigger immune response in humans if from mouse

• difficult to produce correct monoclonal antibodies and attaching them to drugs

• currently very expensive

• time-consuming to produce

Tobacco mosaic virus

Virus - direct contact - yellowing of leaves so reduced chlorophyll so less photosynthesis so less glucose for respiration so stunted growth and death - no treatment - remove and destroy infected leaves by burning

Rose black spot

Fungus - airborne and waterborne - black spots on leaves and yellowing of leaves so less chlorophyll so less PHS, leaves drop early so less PHS so reduced plant growth - apply fungicide - removed and destroy infected leaves by burning

why do herbivores and pathogens attack plants?

to access the rich nutrients such as sugars and amino acids that the plants contain

How can you detect diseases in plants (the signs)?

discolouration of leaves, leaves drop early, stunted growth, spots on leaves, areas of decay, growths, malformed stems or leaves, presence of pests

How can you determine which disease a plant has?

1. compare plant to photos in gardening manual or website

2. take plants to plant biology laboratory and have them identify the disease

What type of pathogens can plants be infected by?

virus, bacteria, fungus

Example of insect pest that affects plants

Aphids use mouth parts to extract sugars and amino acids from the phloem - reduced rate of respiration so less energy released for processes such as protein synthesis. They also act as vectors as they transmit the pathogen from one plant to another

Magnesium deficiency

chlorosis (yellowing) - magnesium is found in chlorophyll molecules so lack of magnesium means lack of chlorophyll so leaves turn yellowed - reduced photosynthesis, lack of glucose for respiration. Fertiliser containing magnesium ions can be added to soil as treatment

Nitrate deficiency

Stunted growth and chlorosis - nitrate is needed for making compounds important in plant growth. Nitrogen is needed to make amino acids, to make proteins so can’t grow. Nitrogen is needed to make chlorophyl so lack causes yellowing of leaves. Fertiliser containing nitrate ions in soil will help with growth

What are the 3 ways in which plants defend against pathogens and herbivores?

Chemical defences, physical defences, mechanical defences

State 3 physical defences that plants use to resist invasion by pathogens

Thick cellulose cell wall, tough waxy cuticle on leaves, layers of dead cells around stems e.g. bark on trees that fell off

State 2 chemical defences that plants use to defend against pathogens and herbivores and list examples of each

Antibacterial chemicals, including antibodies AND poisons that deter herbivores, e.g. castor oil beans producing risin

Why is ripe fruit more susceptible to plant disease than unripe fruit?

Contains more sugars so more attractive - produces fewer chemical defenses

State 3 mechanical adaptations that plants use to deter herbivores

1. Thorns and hairs e.g. acacia trees

2. leaves that droop or curl - makes the plant look unhealthy or dead

3. mimicry to trick animals into thinking it’d be dangerous to eat the plant