4.3 COMMUNICABLE DISEASES Flashcards
What is a pathogen?
A pathogen is a microorganism that causes disease.
- to cause disease, a pathogen must travel from host to host, get into tissues, reproduce and cause damage (symptoms)
- transmission of pathogens can be by vectors, physical contact, droplet infections or indirect contact
What are the types of pathogen?
The types of pathogen is bacteria, fungi, viruses, protoctista
How do you calculate the number of bacteria divisions?
Calculate the number of bacteria divisions:
2^n - where n = number of divisions
e.g 4 hours/20 minutes = 12 divisions
2^12 = 4096
How does bacteria cause diease?
Bacteria causes disease by producing toxins and causing symptoms by cell damage. They can also damage cell membranes, enzymes or genetic material.
What are the shapes of bacteria?
Shapes of bacteria:
- cocci (spherical) = have less surface area per volume than bacilli or spirillum, and thus can survive in dryer environments
- bacilli (rod shaped) and vibrio (curved) = have a greater SA:V ratio and can take up nutrients from dilute solutions more efficiently
- spirilli (spiral) = spiral cells, move with corkscrew motion, meet less resistance from surrounding water
What is the structure of a virus?
Virus structure:
- very simple structures made up of 3 components
= nucleic acid
= protein coat
= lipid envelope
- non-living as they cannot replicate by themselves = manipulate their host cells to replicate them
-a bacteriophage is a virus that infects bacterial cells
How is a bacteriophage made?
Bacteriophage production:
- lysogenic phase
1. the phage attaches to the host cell and injects its DNA into the cytoplasm
2. the phage DNA integrates itself into the bacterial chromosome becoming a prophage
3. the prophage remains latent and is replicated every time the host cell divides
- lytic phase
4. at a trigger the phage DNA is expressed to make phage proteins, which assemble into phage capsids
5. the bacterial cell bursts (lysis), releasing hundreds of phage particles
How does a virus cause disease?
Virus causes disease:
1. virus attaches to host cell and the two membranes fuse, releasing the capsid into the cytoplasm
2. the viral enzyme reverse transcriptase synthesises ds DNA from the ss RNA. the DNA is incorporated into the host’s nuclear DNA where it is called a provirus
3. the provirus remains latent for years and is replicated every time the host cell divides
4. at a trigger the viral DNA is expressed to make viral proteins, which assemble in virus capsids
5. the virus particles are released by budding, collecting their lipid envelope from the host cell membrane
How do fungi cause disease?
How fungi cause disease:
- some produce toxins which effect host cells
- some digest living cells (parasitic) and destroy cells
- fungal infections stop parts of plants photosynthesising and can quickly kill plants
- when fungi reproduce they produce spores which spread rapidly through crop plants
How to protoctists transmit diease?
Protoctists:
- eukaryotes
- small percentage act as pathogens
- protists which cause disease are parasitic
- may need a vector to transfer them to their host (e.g malaria)
- may enter body through water (e.g aemobic dysentary)
What is a disease?
A disease is a condition that has a negative effect on part/all of the body.
What is health?
Health is mental and physical well-being.
What is an infectious disease?
An infectious disease can spread between organisms and is transmitted between organisms.
What is a vector?
A vector is an organism that carries a pathogen between hosts.
What is an epidemic?
An epidemic is a fast spreading disease that is spread nationally and causes casualities.
What is a pandemic?
A pandemic is a fast spreading disease that is spread globally and causes casualties.
What is indirect transmission?
Indirect transmission is where diseases are spread through shared surfaces.
What is direct transmission?
Direct transmission is where diseases are spread via exchanging bodily fluids and physical contact.
What is tuberculosis?
Tuberculosis is a bacterial disease that infects animals. It is common in overcrowded places and is carried in the air (droplet transmission), or can be caught by eating or drinking produce from infected cattle. It causes appetite loss, fatigue, a productive cough, coughing blood, paleness and night sweats. It can be treated by taking antibiotics for months. 10% of those infected get ‘full blown TB’ which negatively impacts their ability to work.
What is meningitis?
Meningitis is a bacterial disease that infects animals. It is spread via close contact and sharing bodily fluids. It causes a rash from sepsis and can be treated by taking a course of antibiotics. 25% people infected are left with permanent health issues and 10% die.
What is ring rot?
Ring rot is a bacterial disease that infects tubers and fruit in plants. It is spread by contact of vegetables/plants and is spread through the soil. It causes damage to plants and there is no treatment but to leave fields infected clear of crop for two years, which negatively impacts farmers.
What is HIV/AIDS?
AIDS is a viral disease caused by HIV that infects animals. It is spread through sexual contact/sharing bodily fluids. It targets t-helper cells so the body is less able to deal with other infections. It can be treated with retroviral drugs. In the last 10 years death from AIDS has decreased and in 2021 38.4 million people were infected.
What is influenza?
Influenza is a viral disease that infects animals. It is spread via droplet transmission and touching infected surfaces. It causes respiratory issues, fever, headache, fatigue and pains. It can be treated/prevented with the flu vaccine. Avian flu is a strain that effects birds and can cause farmers to lose income.
What is tobacco mosaic virus?
Tobacco mosaic virus is a viral disease that infects plants. It is spread via direct contact of plants, workers can also spread. It causes decolourisation/damage to leaves, flowers, fruit and may stunt growth. There is no treatment for TMV and it causes total crop loss for farmers.
What is malaria?
Malaria is a protoctist disease that infects animals. It is spread through a vector (mosquitos, sharing needles). It causes lots of fever, headache, sweating, chills and vomiting. There is no treatment but anti-malarial drugs can be taken as a preventative. 50% of the world’s population is in malaria risk areas, 627,000 deaths in one year.
What is potato/tomato late blight?
Potato/tomato late blight is a protoctist disease that infects plants. It is spread through spores in the wind and infects all parts of the plant, hyphae from spores spread through tissue. It can be treated/prevented by using chemical sprays and choosing resistant species to plant. Impacts large crops and aided the Irish potato famine.
What is black sigatota?
Black sigatota is a fungal disease that infects plants. It is spread through spores in the air or water. Hyphae from spores spread through roots and causes them to go black. Treatment is to use resistant bananas and use hangicides. It causes 50% less yield of bananas.
What is ring worm?
Ring worm is a fungal disease that infects animals. It is spread by skin to skin contact and causes a raised, crusty scab. It is treated with anti-fungal cream and does not cause any lasting impact.
What is athletes foot?
.
How do plants recognise an attack by a disease?
Plants recognising an attack:
- receptors respond to molecules from pathogens or chemicals released that attack the cell wall
- the cells will then release signalling molecules
- these switch on genes in the nucleus
- this triggers cellular responses such as producing chemicals, sending alarm signals and strengthening the cell wall
What physical defences do plants have against disease?
Physical defences:
- cellulose cell wall = acts as a physical barriers and lignin thickens cell walls making them waterproof and indigestible
- waxy cuticle = prevents water from collecting on the surface (pathogens need water)
- guard cells = close stomata
- callose = large polysaccharide that is deposited in sieve at the end of the growing season, blocks the flow so that pathogens can’t spread
What chemical defences do plants have against disease?
Chemical defences:
- insect repellants = pine resin (antibacterial), citronella from lemongrass (masks attractive scents)
- insecticides = pyrethins made by chrysanthemums and are a neurotoxin, caffeine which is toxic to insects and fungi by preventing enzymes that are required from working in an insects nervous system
- antibacterial compounds including antibiotics = phenols (antiseptics made in many plants), antibacterial gossypol produced by cotton, defensins (proteins that disrupt bacterial and fungal membranes), lysosomes that break down bacterial cell walls
- antifungal compounds = phenols, antifungal gossypol, defensins, saponins (chemicals in many cell membranes that interfere with fungal cell membranes), chitinases that break down chitin in fungal cell walls
- anti-oomycetes = glucanases (enzymes that break down glucans (polymer in the cell walls of oomycetes/water moulds))
- general toxins = some plants make chemicals that can be broken down to form cyanide compounds when the plant cell is attacked
Is callose made from alpha or beta glucose and which carbons would you find the bonds?
Callose is made from beta glucose and has 1,3 and 1,6 bonds.
Initially callose is synthesised and deposited between the cell wall and cell membrane in cells next to infected cells.
What is the purpose of this?
Callose is synthesised and deposited between the cell wall and cell membrane in cells next to infected cells to act as barriers and prevent pathogens entering the plam as around the site or infection.
When is lignin added and what is it’s purpose (callose)?
Lignin is added when large amounts of callose is in the cell walls after the initial attack. This makes the mechanical barrier to invasion even thicker and stronger.
What is the purpose of callose in plasmodesmata?
Callose in plasmodesmata is deposited between infected cells and neighbours, sealing them off from healthy cells and helps prevent pathogens from spreading.
