Biology Infection and Response
L1 - Communicable disease
What is the meaning of healthy?
The state of physical and mental well-being, not just the absence of disease
What is a pathogen?
Any microorganism that can produce disease
What is pathogenicity?
How pathogenic a microorganism is
Give the 4 types of pathogens
Bacterial
Prokaryote
Unicellular
Produces toxins (e.g. salmonella)
Virus
Not cells
They enter cells and duplicate - bursting the cell releasing the virus (e.g. measels)
Protists
Eukaryotic
Unicellular
Transferred by vectors (e.g. malaria)
Fungi
Eukaryotic
Multicellular or single cellular (e.g. athletes foot)
What is a communicable disease?
DIseases that can easily spread
How can pathogens spread?
Air
Sneezing/coughing
Contact with people
Contact with objects
Poorly prepared food
Animals
Lack of hygiene
Water
Vector (e.g. mosquito)
What can you do to prevent disease?
Hygiene - wash hands/cover mouth
Disinfectant - kill bacteria on surfaces
Vaccination – create immunity
Isolation - keep effected organism away from others
Wear a mask – prevent/slow the spread of airborne particles
Destroy vectors – (e.g kill mosquitos)
What are examples of physical/chemical barriers in the body?
Skin – acts as a barrier to pathogens
Hair - traps particles that contain pathogens (nose, ears and eyelashes)
Mucus – traps pathogens (nose, throat)
Stomach – contains hydrochloric acid to kill off foreign invaders
If a pathogen is able to overcome these defences, what system does the body use to protect itself?
The immune system
What is the malaria life cycle?
Malaria parasites reproduce asexually in the human liver and red blood cells
But, when the mosquito feeds again, the drop in temperature can cause sexual reproduction in the RBC now in the mosquito
This creates variation in the parasites which makes malaria difficult to vaccinate against
Why are viruses so hard to kill? (3 marks)
The parasites reproduce quickly and are hidden within human cells, and they are unable to be killed by antibiotics.
There is also variation in the parasites which means it can be difficult for the white blood cells/vaccinations to target them
(frequently mutating)
What might bacteria produce?
Poisons (toxins) that damage tissues and make us feel ill
VIRUSES
Recall: symptoms, how it is spread and the prevention/treatment
Measles
Symptoms
Red rash
Fever
Spread
Droplets through sneezing/coughing
Prevention/treatment
Vaccination
HIV/AIDS
Symptoms
Flu like symptoms
Attacks immune system
→ may become AIDS
Spread
Sexual contact
Sharing needles
Prevention/treatment
Antiretroviral drugs
Tobacco mosaic virus (TMV)
Symptoms
Mosaic pattern on the leaves
The colour changes means plants are unable to photosynthesise
Spread
Direct contact
Vectors/insects
Prevention/treatment
Remove plant and burn soil
FUNGI
Recall: symptoms, how it is spread and the prevention/treatment
Rose Black Spot
Symptoms
Black spots on leaves of plant - meaning photosynthesis unable to occur
Spread
Water source
Wind
Prevention/treatment
Fungicides
Burn the affected plants
BACTERIA
Recall: symptoms, how it is spread and the prevention/treatment
Salmonella toxins
Symptoms
Stomach cramps
Vomiting
Diarrhoea
Spread
Uncooked food
Poor food hygiene
Prevention/treatment
Wash food/hands
Antibiotics
Gonorrhoea
Symptoms
Pain when urinating
Yellow/green discharge
Spread
Sexual contact (unprotected)
Prevention/treatment
Contraception
Antibiotics
PROTISTS
Recall: symptoms, how it is spread and the prevention/treatment
Malaria
Symptoms
Fever
Tired
Spread
Vector (mosquito) inserts protist into animal when feeding
Prevention/treatment
Mosquito nets
Insecticides
L2 - WBCs and Vaccinations
What is a non-communicable disease
DIseases of long duration and generally get worse over time (not contagious)
What are some examples of NCDs?
Asthma
Cancer
Type 1/2 diabetes
CHD
What are phagocytes and what do they do?
About 70% of WBCs are phagocytes
They engulf and destroy unwanted microorganisms that enter the blood
This is called phagocytosis
They are part of the immune system
Why are antibodies produced?
Specific antibodies are produced to neutralise pathogens
What do antibodies do?
Enhance phagocytosis
Can stick pathogens together (so phagocytes can come and engulf them)
Release anti-toxins to neutralise toxins
What are the adaptations of antibodies?
Irregular shape to squeeze through the blood vessel and reach the site of infection
Large surface area to engulf more pathogens
Multi-lobed nucleus to squeeze through the blood vessels
Why are antitoxins produced?
They are produced to counteract toxins released by pathogens
What are lymphocytes and what do they do?
They produce antibodies which cover pathogens, alerting the phagocytes and telling them where to engulf/produce antibodies to help destroy all types of pathogens
What are antigens?
They are substances that our immune system detects as being foreign, such as the cell wall of a bacteria
What are antibodies?
Small proteins made by our own white blood cells, that can lock onto the foreign antigens and then act as signals to tell the white blood cells to destroy them. Each antibody is specific to a pathogen. If it can bind to a particular antigen, it won’t be able to bind to any others
How do vaccinations prevent illness in an individual?
If we have already been infected with the (weakened) pathogen, our immune system knows which of the antibodies can bind to the particular pathogen
It starts producing loads of antibodies and it remembers this for next time, so that if we were attacked with that pathogen sometime in the future, our body will start producing so many antibodies so quickly, that it will destroy all the pathogens before they get the chance to develop
This is what it means to be ‘immune’ to a disease
What happens during a second exposure to the same pathogen?
A second exposure causes the white blood cells to respond quickly in order to produce relevant antibodies
This prevents infection
How can the spread of pathogens be reduced?
By immunising a large proportion of the population
What are the stages of vaccination? (long)
Dead or weak pathogen is introduced (injected) into organism carrying antigens:
Injection can be in the arm or a spray in the nose
You can use a virus that affects a different animal (species) to get a weak pathogen (such as cow pox)
Microbes need to be grown at a low temperature to weaken (not 37C)
Irradiate the microbe/pathogen
Antigen = antibody generator (makes antibodies)
Pathogens have small molecules on their surface called antigens
Every single cell has them (eukaryotic and prokaryotic)
These can lead to the production of antibodies
Our own immune systems know not to target our cells but if they come across another antigen they will target it and make antibodies
This stimulates white blood cell growth (immune response)
These white blood cells produces the correct antibodies
Antibodies information is stored (memory cells) and reproduced rapidly if infection occurs again (immunity, antibodies kill the pathogens)
What does immunity mean?
When a person's body is not prone to a disease because they have a resistance to it
What is herd immunity?
The protection given to a population against an outbreak of a specific disease when a very high percentage of the population have been vaccinated against it
What are the pros and cons of vaccinations?
Pros Cons
Helps control the majority of communicable diseases from occuring
Doesn’t always work - sometimes immunity is not gained
Stops large outbreaks of diseases from spreading
Bad reaction to the vaccine (very rare)
Bacteria vs. Virus
Bacteria:
Bigger than viruses
Live almost anywhere
Made of cells
Many don't cause infection
Multiplies by division (some as quickly as every 20 minutes)
Can be useful for things such as digestion
Weak immunity in the digestive system means the balance may be disturbed
Fever, fatigue, general malaise
Antibiotics are only effective against bacteria
Virus:
Smallest of microbes (x10 smaller than bacteria)
Able to attack any living organism
Not cells
Need a host cell to take over, and uses an organism as a host
Invades a cell of the body and uses parts of the cell to multiply itself, creating hundreds of new viruses
Can only multiply inside cells, destroying them
Cannot survive outside the body of the host for more than a few seconds or minutes
Infections often go away by themselves
Antibiotics are not effective
Describe and explain the differences in antibody production after vaccination compared with after infection? (4 marks)
When you are first vaccinated against measles, your body has a primary immune response, producing antibodies to kill the pathogens, making you immune and making memory cells
We can see from the graph that there is a small increase in the number of antibodies after the vaccination takes place and after some time it drops again, but not to 0 (this could take many years.
When you are infected for the first time with the virus, you body activates the memory cells and makes lots of antibodies really fast, killing the pathogens a lot quicker.
The graph shows a rapid increase in the number of antibodies made because your body remembers that it needs to get rid of the pathogens by producing large amounts of antibodies.
L3 - Drugs
Where are drugs from?
Plants
Aspirin (painkiller) is found in willow and digitalis (a heart drug) is found in foxgloves
Mould
Alexander Flemming found that mould could prevent bacterial growth
Synthetic
Produced by large pharmaceutical companies (most made this way)
Why is it difficult to develop drugs to kill viruses without damaging the body tissue? (3 marks)
You do not know which cells to target
You cannot target the virus without targeting the cells
Because a virus multiplies inside the body cells
This evades detecting from white blood cells
Meaning it can damage healthy cells because to kill the virus you would also need to kill the cell
What are the two types of drugs?
Painkiller
What are the functions?
To reduce pain
Does not tackle the cause of the problem
Example?
Paracetamol
Aspirin
Antibiotic
What are the functions?
To slow down/ stop the growth of bacteria
Will not harm your cells
How do antibiotics work?
Antibiotics damage the bacterial cells but do not damage the host cells
They have the ability to cure some bacterial diseases that would have previously killed many people
Example?
Amoxocillin
Penicillin
How does antibiotic resistance happen?
A mutation occurs
Allowing some bacteria to survive
The new mutated gene is resistant to the antibiotic
This resistant gene is passed onto offspring via asexual reproduction/mitosis/binary fission
How do you prevent antibiotic resistance?
Do not overprescribe antibiotics
Finish the full course when ill
What are the problems with antibiotics?
Commonly prescribed antibiotics are becoming less effective because:
overuse of antibiotics
failing to complete the fully prescribed course by a doctor
use of antibiotics in farming
L4 - Drug Development
What are the 3 main stages of drug development?
Preclinical testing - lab tests using human cells and tissue
Still preclinical testing - live animal testing for:
efficacy (does the drug work)
toxicity (is it harmful)
dosage (how much do you need?)
Clinical trials:
Tested on healthy humans first (low dose to find out if it is toxic to humans)
Next on people with the illness to find the optimum dose
Finally double blind trials to avoid the placebo effect
What is a double blind trial?
The doctor and patient are not aware if the pill taken is the actual drug or a placebo (sugar/saline solution)
What is a peer review?
Results of testing and trials are published only after scrutiny by peer review (publishing paper in a scientific journal)
What is the placebo effect?
A beneficial effect produced by a placebo drug or treatment, which cannot be attributed to the properties of the placebo itself, and must therefore be due to the patient's belief in that treatment
Why are some people given a placebo during a drug trial?
Placebos are given to make sure that the drug is actually effective and not just working due to the patient's belief that they have been given medicine to help.
This is done alongside the real drug in order to get fair results from the trial.
Often the doctor does not know either, so neither can be influenced.
(As a control, to see/compare the effects of the treatment (vs. No treatment)
What are the pros of animal testing?
It doesn't harm humans
Saves human lives
Not toxic before being given to humans
Similar to humans
Reduces harmful effects for humans
Helps to understand drug use on whole organism
What are the cons of animal testing?
Can be harmful to animals
May not be accurate (could still be toxic on humans)
Cruel and inhumane
Not identical to humans
Alternative tests now available
L5 - Monoclonal Antibodies
What is a B lymphocyte?
A (white blood cell) lymphocyte from the bone marrow that produces antibodies (but doesn’t divide rapidly)
What properties of cancer cells might we want to use?
Cancer cells do not produce antibodies, but do rapidly divide
How might we utilise these properties to produce more antibodies?
By combining the two cells we can create a cell that produces antibodies and divides rapidly
How are monoclonal antibodies produced? (6 marks)
Inject mice with the antigen targeted to stimulate B lymphocyte cells
Correct B lymphocytes are extracted from mice, that produce a particular antibody
A tumour cell is then fused with the B lymphocytes to form a hybridoma
The hybridoma is then cloned many times and used to produce the correct antibodies
The monoclonal antibodies are then separated, purified and ready for use
What is a hybridoma?
A combination of a lymphocyte and cancer cell that have been fused together for certain characteristics called a hybridoma
Uses of monoclonal antibodies?
In pregnancy tests to detect the presence of specific hormones
In research to locate/identify specific molecules in a cell or tissue by binding to them with a fluorescent dye
To treat some diseases e.g. cancer
→ for cancer the monoclonal antibody can be bound to a radioactive substance, toxic drug or a chemical which stops cells growing and diving → it delivers the substance to the cancer cells without harming other cells in the body
How do pregnancy tests use monoclonal antibodies? (3 marks)
(HCG) is produced when pregnant
Small amounts of this hormone is passed out in the urine
Monoclonal antibodies in the pregnancy test bind with the HCG to produce a colour change (positive result)
If the top line is blue but not the bottom, that means that the test is not working
How can they be used to treat disease?
What are the advantages of monoclonal antibodies?
Used to treat a wide range of conditions
Healthy cells are not affected
Only bind to specific cells that need treatment
What are the disadvantages of monoclonal antibodies?
Attaching monoclonal antibodies to drugs is difficult
Not widely used of 100% successful
Some side effects created when using mice cells in hybridoma
Expensive
L6 - Plant Disease and Infection
What are aphids?
Aphids are insects that have a stylet to penetrate the phloem vessel to feed off the plants sugar-rich phloem sap
This prevents the plant from using the products of photsynthesis for respiration, growth, etc.
They also act as vectors, carrying viruses, bacteria and fungal diseases from one plant to another
How do you control aphids?
Chemical pesticides - kill aphids
Biological pest control - releasing insects like ladybirds that feed on aphids
How are nitrate ions in soil important to plants and what may the deficiency cause?
Plants use nitrate ions to convert sugars into proteins
The proteins are needed for growth during protein synthesis
Nitrate deficiency will result in a lack of proteins, stunting growth
How are magnesium ions in soil important to plants and what may the deficiency cause?
Plants use magnesium ions to make chlorophyll used for photosynthesis
Magnesium deficiency will result in the leaves turning yellow (no chlorophyll)
No glucose made, no respiration, slowing growth due to lack of photosynthesis
Known as chlorosis
What can be used to replace a lack of ions?
Fertiliser
What are some ways to spot plant diseases and what are the solutions?
Stunted growth (fertiliser)
Spots on the leaves (antifungal treatment (rose black spot))
Area of decay or rotting (removing/separate area)
Malformed stems or leaves (removing/separate area)
Discoloration - yellow leaves (fertiliser)
Visible aphids (chemical/biological pest control)
How have plants adapted to prevent being eaten? (physical barriers)
Thorns, spines and prickles warning herbivores
Cellulose builds cell walls to strengthen the plant cell
Trichomes (sharp hair-like structures) used against insects
Waxy cuticle on leaves thickens, acting as a pathogen barrier
Lignin in tree bark is a dead layer of cells that act as a barrier, and is highly impermeable to pathogens
Leaf fall - diseased leaves fall from the tree to prevent spread
Some fruits (such as kiwi and pineapple) and plants produce raphides (needle-shaped crystals)
-> This creates small wounds in the animal's mouth, creating entry points for toxins
How have plants adapted to prevent being eaten? (chemical barriers)
Produce antibacterial chemicals
Oil released to prevent aphids attaching
Mint and hazel produced from plants act as antiseptics
Poison is produced to kill the attacking organism
Trichomes dispense chemical irritants
If a tomato plant is under attack it releases a compound to nearby tomato plants, getting them to release insect repellent
Stinging nettles and foxgloves have poisons to stop the herbivores from eating them, causing pain and inflammation when touched
Cotton plants release 10-12 chemicals into the air, summoning wasps which will come and inject the caterpillars with eggs
How have plants adapted to prevent being eaten? (other methods)
Mimicry - some plants mimic unhealthy plants to avoid being eaten or mimic insects
Curling up - mimosa plant shoots electrical signals through leaflet to base causing cells to release charge, shrivelling and pulling the leaflet closed
- > shrunken leaves look less appealing to animals