4.1 Communicable diseases Flashcards
Define pathogen.
A microorganism that causes disease.
What is the organism in which a pathogen lives called?
Host.
What are the four types of pathogen?
- Bacteria
- Fungi
- Viruses
- Protoctista
What kingdom does bacteria belong to?
Prokaryotae
How is bacteria harmful to their host?
Bacteria can reproduce rapidly- in the right conditions, some bacteria can reproduce every 20 minutes.
Once in the host, their presence can cause disease by damaging cells or by releasing waste products and/ or toxins that are toxic to the host.
How is fungi harmful to animals?
In animals, there are common fungal infections where fungus lives in the skin of the animal, and where its hyphae, which forms mycelium, grow under the skin surface, the fungus can send out reproductive hyphae, which grows to the surface of the skin to release spores. This causes redness and irritation.
How is fungus harmful to plants?
The fungus often lives in the vascular tissue, where it can gain nutrients. the hyphae release extracellular enzymes, such as cellulases, to digest the surrounding tissue, which causes decay. Leaves will become molted in colour, curl up and shrivel, before dying. Fruit and storage organs (such as tubers) will turn black and decay)
What is cellulases and where is it found?
Cellulase is an enzyme that digests cellulose. This is an example of on of the extracellular enzymes fungi hyphae release in plants.
How are viruses harmful to their host?
Viruses invade cells and take over the genetic machinery and other organelles of the cell. They then cause the cell the manufacture more copies of the virus. The host cell eventually bursts, releasing many new viruses which will infect healthy cells.
How are protoctista harmful to their host?
Protoctista cause damage by entering host cells and feeding of their contents as they grow.
What are some examples of a disease caused by bacteria?
- Tuberculosis
- Bacterial meningitis
- Ring rot
What are some examples of a disease caused by a virus?
- HIV/AIDS
- Influenza
- Tobacco mosaic virus
What are some examples of a disease caused by a fungus?
- Black sigatoka (in bananas)
- Ringworm
- Athletes foot
What are some examples of a disease caused by protoctista?
- Malaria
- Blight
Define direct transmission.
Passing a pathogen from host to new host, with no intermediary.
Define indirect transmission.
Passing a pathogen from host to new host, via a vector.
Define vector.
An organism that carries a pathogen from one host to another.
What are 4 ways a pathogen can be directly transmitted?
- Direct physical contact
- Faecal-oral transmission
- Droplet infection
- Transmission by spores
How can we reduce direct physic contact spread of pathogens?
- Wash hands
- cleaning and disinfecting cuts and abrasions
- Sterilising surgical instruments
- Using condoms
How can we reduce faecal-oral transmission spread of pathogens?
- Treatment of water and drinking water
- Thorough washing of all fresh food
- Careful preparation and thorough cooking of food
How can we reduce droplet infection spread of pathogens?
- Catch it - bin it - kill it
- Cover your mouth when sneezing or coughing
- Use a tissue and dispose of it correctly
How can we reduce transmission by pores spread of pathogens?
- Use of a mask
- Washing skin after contact with soil
What social social factors can affect transmission of pathogens?
- Overcrowding
- Poor ventilation
- Poor health
- Poor diet
- Homelessness
- living or working with people who has migrated from areas where a disease is more common.
What is the plasmodium parasite?
Plasmodium parasite causes malaria.
How can pathogens infect plants?
- Many pathogens are present in the soil and will infect the plant by entering the roots- especially if these have been damaged as a result of replanting, burrowing animals or movement caused by a storm.
- Many fungi produce spores as means of sexual or asexual reproduction. The spores may be carried by the wind- airborne transmission- these can enter by the plants stomata.
What do pathogens do once it has entered the plant?
- Once inside the plant , it may infect all the vascular tissue- this allows the pathogen to be distributed throughout the plant. Pathogens infect leaves, then, when they shed, they carry the pathogen back to the soil where it can grow and infect other plants.
- Pathogens can also enter the fruit and and seeds, and will then be distributed with the seeds- so all the offspring will be infected.
How can pathogens be indirectly transmitted to plants?
Indirect transmission is often a result of an insect attack.
Spores or bacteria become attached to a burrowing insect which attacks an infected plant. When the insect attacks another plant, the pathogen is transmitted to the uninfected plant. The insect acts as a vector.
Why is transmission of pathogens in warmer climates more rapid?
Many protoctista, bacteria and fungi can grow and reproduce quicker in warm and moist conditions. As a result, there is a greater variety of diseases to be found in warmer climates, and animals or plants are more likely to be infected.
Why is global warming a threat to Europe in terms of pathogens?
Pathogens reproduce quicker in warm and moist conditions and in cooler climates, these pathogens may be damaged or killed by the cold. This is a threat because as winters get warmer, soon it will not be cold enough to kill these pathogens and more pathogens will be around and there will be a greater variety of them.
What is callose?
Callose is a large polysaccharide deposit that blocks phloem sieve tubes.
What does a plant have instead of an immune system?
- Passive defences
- Active defences
Define passive defences. What does this consist of?
These are defences present before infection, their role is to prevent entry and spread of the pathogen.
Passive defenses consist of physical barriers and chemicals.
What are some examples of physical defences?
- Cellulose cell wall
- Lignin thickening of cell walls
- Waxy cuticle
- Bark
- Stomata closure
- Callose
- Tylose
How does cellulose cell wall act as a physical defence in plants?
This acts as a physical barrier. It also contains a variety of chemical defences that can be activated when a pathogen is detected.
How does lignin thickening of cell walls act as a physical defence in plants?
Lignin is waterproof and almost completely indigestible.
How does waxy cuticles act as a physical defence in plants?
These prevent water collecting on the cell surfaces. Since pathogens collect in water and need water to survive, the absence of water is a passive defence.
How does bark act as a physical defence in plants?
Most bark contains a variety of chemical defences that work against pathogenetic organisms.
How does stomata closure act as a physical defence in plants?
Stomata are possible points for entry for pathogens. Stomata aperture is controlled by guard cells. When pathogens are detected, the guard cells will close the stomata in that part of the plant.
How does callose act as a physical defence in plants?
Callose is deposited in the sieve tubes at the end of a growing season. It is deposited around the sieve plates and blocks the flow in the sieve plates and blocks the sieve tube. This can prevent a pathogen spreading around the plant.
What is a tylose formation?
A tylose is a balloon- like swelling or projection that fills a xylem vessel.
How does tylose formation act as a physical defence in plants?
When a tylose is fully formed, it plugs the xylem vessel and the vessel can no longer carry water. Blocking the xylem vessels prevent the spread of pathogens through the heartwood. The tylose contains high concentration of chemicals such as terpenes that are toxic to pathogens.
How does chemical defences act as a passive defence in plants?
Plant tissues contain a variety of chemicals that have antipathogenic properties. these include terpenoids, phenols, alkaloids and hydrolytic enzymes.
some chemicals such as terpenes in tyloses and tannins in bark, are present before an infection.
Why are many antipathogenic chemicals only produces as an active defence?
The production of chemicals requires a lot of energy, many chemicals are not produced until the plant detects an infection.
How can a plant detect a a pathogen has infected them?
When pathogens attack, specific chemicals in their cell walls can be detected by plant cells. These chemicals include specific proteins and glycolipids.
What is active defences in plants?
When a plant has detected a pathogen has invaded, the plant responds by strengthening the physical defences and producing defensive chemicals.
What does active defences include?
- Cell walls become thickened and strengthened with additional cellulose.
- Deposition of callose between the plant wall and cell membrane near the invading pathogen. It also strengthens the cell wall and blocks plasmodesmata.
- Oxidative bursts the provide highly reactive oxidative molecules capable of damaging the cells of invading pathogens.
- Increase of production of chemicals
- Necrosis
- Canker
What is necrosis?
A way a plant does active defences.
Deliberate cell suicide. A few cells are sacrificed to save the rest of the plant. By killing cells surrounding the infection, the plant can limit the pathogen’s access to water and nutrients and can therefore stop it spreading further around the plant. Necrosis is bought about by intracellular enzymes that are activated by injury. These enzymes destroy damaged cells and produce brown spots on leaves or dieback.
What is a canker?
A sunken neurotic lesion in the woody tissue such as in the main stem or branch. It causes death of the cambium tissue in the bark and is an active defence in plants.
What is inflammation?
Swelling and redness of the tissue caused by an infection.
What is a mucus membrane?
specialised epithelial tissue that is covered by mucus.
What is an organism primary defences?
Defences that prevent pathogens entering the body. These defences are non-specific, as they will prevent entry of any pathogen.
What is the main primary defence?
The skin.
How is the skin a primary defence?
The body is covered in skin, preventing the entry of pathogens.
What is the outer layer of skin called? What are the cells its made up of called?
The epidermis- it consists of layers of cells.
Most of these cells are celled keratinocytes.
How is the skin made?
Keratinocytes are produced by mitosis at the base of the epidermis. They then migrate out to the skin surface. As they migrate, they dry out and the cytoplasm is replaced by the protein keratin. This process is called keratinisation, it takes about 30 days. By the time the cells reach the surface, they’re no longer alive. The keratinised layer of dead cells act as an effective barrier to pathogens. Eventually, the dead cells slough off.
What is the process of the cytoplasm of keratinocytes being replaced by keratin called?
Keratinisation
What happens if the skin is damaged?
The body must prevent excess blood loss by forming a clot, making a temporary seal to prevent infection, and replacing the skin.
What does blood clotting involve?
Calcium ions and at least 12 factors- known as clotting factors. Many of the clotting factors are released from the platletes from the damaged tissue. These factors activate an enzyme cascade.
What happens once the clot has formed to repair the skin?
The clot dries out and forms a scab- the scab shrinks as it dries, drawing the sides of the cut together. This makes a temporary seal, under which the skin is repaired.
What happens after a scab has formed?
Firstly fibrous collagen is deposited under the scab. Then, stem cells in the epidermis divide by mitosis to form new cells, which migrate to the edges of the cut and differentiate to form new skin. New blood vessels grow to supply oxygen and nutrients to the new tissues. The tissues contract to help draw the edges of the cut together so that a repair can be completed. as the new skin is completed, the scab will be released.
Why do we need mucous membranes?
Certain substances must enter our blood (e.g.oxygen, nutrients from food) the exchange surfaces where this occurs must be thinner and are less protected from pathogens. The air and food we take in from our environment may harbour microorganisms, Therefore, the airways, lungs and digestive system are at risk of infection.
These areas are protected by mucous membranes.
What are cilia?
Tiny, hair like organelles that can move.
What are primary defences?
- The skin
- Blood clotting and skin repair
- Mucous membrane
- Coughing and sneezing
- Inflammation
- Eyes protected by antibodies and enzymes in tear fluid
- Ear canal is lined with wax, which traps pathogens
- Female reproductive system is protected by a mucus plug in the cervix and by maintaining acidic conditions in the vagina.
How is the airways protected by mucous membranes?
Mucous lines the passages and traps any pathogens that could be in the air. Cilia move mucous up to the top of the trachea, where it can enter the oesophagus. It is swallowed and passes down the digestive system. Most pathogens in the digestive system are killed by the acidity of the stomach (what can have a pH 1-2). This denatures the pathogens enzymes.
What do ciliated epithelial cells do in mucous membranes?
They move in a coordinated fashion to waft the layer of mucous along.
Where are mucous membranes found?
- Gut
- Airway
- Genital areas
- Anus
- Ears
- Nose
How does coughing and sneezing act as a primary defence?
Areas that are prone to attack from pathogens are sensitive- this means they respond to irritation that may be caused by the presence of microorganisms or the toxins they may release. These reflexes include coughing, sneezing and vomiting. In a cough or sneeze, the sudden explosion of air will carry with it the microorganisms causing the irritation.
What are mast cells?
Specialised cells that detect can detect the presence of microorganisms. They release a cell signalling substance called histamine.
What does histamine do?
Histamine is released by mast cells as a response to the presence of microorganisms.
The main effect of histamine is vasodilation, which makes the capillary walls more permeable to white blood cells and some proteins. Blood plasma and phagocytic white blood cells leave the blood and enter the tissue fluid. This leads to an increased production of tissue fluid, which causes swelling. Excess tissue fluid is drained into the lymphatic system where lymphocytes are stored. This can lead to pathogens coming into contact with the lymphocytes and initiating specific immune response.
Why is it important blood clots don’t form in vessels?
Clots could disrupt blood flow, could cause reduced flow to vital organs, could reduce delivery of oxygen, causing heart attack or stroke.
How is thrombin activated by the removal of some amino acids from prothrombin?
A short chain of amino acids could be blocking the active site; removal of this short chain would expose the active site.
What is an expulsive reflex?
A sneeze or a cough, which expels air and pathogens quickly.
How is inflammation caused?
Dilation of arterioles leading to infected area, increased leakiness of capillaries, more tissue fluid produced.
How does smoking lead to increased lung infections?
Cilia are paralysed due ti the tar inhaled and mucus is not removed; pathogens collect in mucus and reproduce.
What is the clotting cascade?
A series of enzyme controlled reactions in the blood that leads to the formation of a blood clot.
What does the clotting cascade form a blood clot?
Blood platelets in a damaged vessel release a chemical called thromboplastin, which triggers the clotting cascade.
Thromboplastin triggers an enzyme to catalyse the conversion of the protein prothrombin into an enzyme called thrombin.
The enzyme thrombin catalyses the conversion of soluble fibrinogen (found in the blood) into insoluble fibrin, forming a mesh.
The mesh taps more platelets and red blood cells forming a blood clot.
As more platelets are trapped, they restart the process and keep the blood clot forming and growing.
What does terpenoids do in plants?
Terpenoids are a type of chemical released as a defence that have antibacterial and antifungal properties.
What do phenols do in plants?
Phenols are a type of chemical released by plants as a type of defence that have antibacterial and antifungal properties. Some of them act as chemical deterrents against herbivores and pathogens.
What do alkaloids do in plants? include examples of alkaloids.
Alkaloids give a bitter taste to inhibit herbivores from feeding of the plant as a way of defence.
They also act of a variety of metabolic reactions via inhibiting or activating some enzyme action. e.g. some alkaloids will inhibit protein synthesis.
Examples include nitrogen-containing compounds such as caffeine, nicotine, cocaine, morphine.
What do defensive proteins do in plants? What are they?
Defensive proteins are small cytosine-rich proteins that was a broad anti-microbial activity.
They act upon molecules in the plasma membrane of pathogens, inhibiting the action of ion transporting molecules.
What do hydraulic enzymes do in plans? Give some examples.
Found between cells, they degrade bacterial walls.
Examples include chitinases, glucanases and lyzosomes.
What is an antigen-presenting cell?
A cell that isolates the antigen from a pathogen and places it on the plasma membrane so that it can be recognised by other cells in the immune system.
How does agglutinins work?
Because each antibody has two identical binding sites, it is able to ‘crosslink’ pathogens by binding on one pathogen with one binding site and then an antigen on another pathogen with it’s other binding site. When many antibodies perform this crosslinking they clump together (agglutinate) pathogens.
