Communicable Diseases Flashcards
What is a pathogen
A microorganism that causes disease
What is the body that the pathogen lives in called
- The host
- Pathogen is fed by taking nutrition from the host but also caused damage in the process - can be considerable
What are the key features of bacteria
- belong to the Kingdom Prokaryotae
- smaller than eukaryotes but reproduce rapidly
- in right conditions can reproduce every 20 minutes
- can cause disease by damaging cells or by releasing waste products and/or toxins that are toxic to the host
- In plants bacteria often live in vascular tissue and caused blackening and death of tissue
What are the key features of fungi In humans
- Can cause variety of diseases in both plants and animals
- Common fungal infections where the fungus lives in the skin of an animal and where its hyphae which forms a mycelium grows under the skin surface
- The fungus can send out specialised reproductive hyphae which grows to the surface of the skin to release spores
- This causes redness and irritation
What are the key features of fungi in plants
-Fungus often lives in vascular tissue where it can gain nutrients
-hyphae releases extracellular enzymes such as cellulases to digest the surrounding tissue which causes decay
-Leaves often become mottled in colour curl up and shrivel before dying
-Fruit and storage organs such as tubers (potatoes) will turn black and decay

What are the key features of viruses
-Causes many diseases in plants and animals
-viruses invade cells and take over the genetic machinery and other organelles of the cell
- they then cause the cell to manufacture more copies of the virus
-The host cell eventually bursts releasing many new viruses which will infect healthy cells

What are the key features of Protoctista
- Number of diseases caused by animal like protoctists
- organisms usually cause harm by entering host cells and feeding on content as they grow
- malarial parasite plasmadomium Has immature forms that feed on the haemoglobin inside red blood cells
Name some diseases caused by bacteria
-tuberculosis
A disease that affects many parts of the body killing the cells and tissues the lungs are most often affected
-Ring rot (in plants)
Ring of decay and vascular tissue of the potato tuber or tomato accompanied by leaf wilting
Name some diseases caused by a virus
-HIV/AIDS
Attack cells in the immune system and compromises the immune response
-tobacco mosaic virus
Causes mottling and discolouration of leaves
Name some diseases caused by fungus
-ringworm (cattle)
Growth of fungus in skin with spore cases erupting through skin to cause a rash
-Black sigatoka (bananas)
Causes leaf spots on banana plants reducing yield
Name some diseases caused by protoctistan
-malaria
Parasite in the blood that causes headache and fever may progress to coma and death
-Blight (tomatoes and potatoes)
Affects both leaves and potato tubers
What is a pathogens life-cycle
- Travel from one host to another (transmission)
- entering the hosts tissues
- reproducing
- leaving for host tissues
What is direct transmission
Passing a pathogen from host to host with no intermediary
What are some examples of direct transmission
-Direct physical contact i.e. touching a person who is infected
Wash hands regularly and keep hygienic to avoid
-faceal (oral transmission) by eating or drinking food contaminated by pathogen
Wash all fresh food when cooking
-droplet infection (pathogen carried by water in the air)
Cover your mouth when coughing or sneezing
-transmission by spores (carried by air or side on surfaces or in soil)
Washing skin after contact with soil
What are some other factors that affect transmission including social factors
- overcrowding -many people living and sleeping together in one house
- Poor ventilation
- Poor health -particularly if a person has HID/AIDS as they are more like to catch other disease 
- Poor diet
- homelessness
- Living or working with people who have migrated from areas for a disease is common
What is indirect transmission
Passing a pathogen from host to new host via a vector
What is a vector
An organism that carries a pathogen from one house to another i.e. a mosquito
Outline the process of someone getting malaria indirectly
1) A person with malaria
2)Gametes of plasmodium in blood
3) female mosquito sucks blood
4)plasmodium Develops and migrate to mosquitoes salivary glands
5) An uninfected person is bitten
6)plamodium migrates to liver
7) Then migrates to blood
What are some examples of direct transmission in plants
- pathogen is present in the soil will infect plants by entering roots (especially if they have been damaged as a result of re-planting/burrowing animals/ movement caused by a storm)
- airborne transmission - Fungi produce spores as a means of sexual/asexual reproduction these may be carried in the wind
- once pathogen is inside plant it will affect vascular tissue - Pathogens in leaves are distributed when it leaves a shed and carry pathogen back to the soil where it can grow and infect another plant
-Can also enter fruit and seeds and will then be distributed with the seeds so many or all offspring are infected

What is an example of indirect transmission in plants 
- occurs as a result of insect attack
- Spores/bacteria become attached to burrowing insect (i.e. beetle) which attacks an infected plant
- when beetle attacks another plant the pathogen is transmitted to the uninfected plant
-Beetle acting as a vector i.e. fungus that causes Dutch elm disease is carried by a beetle
How does climate affects disease
- pathogens can grow and reproduce more rapidly in warm and moist conditions
- tend to be more common in warmer climates than cooler climates
Why are different organisms attracted to plants
They manufacture sugar in photosynthesis and convert the sugars to a wide variety of compounds i.e. protein/oils
-They represent a rich source of nutrients for many organisms
How do plants dedect pathogens
- a wide range of structural/chemical/protein based defenses which can detect invading organisms and prevent them from causing extensive damage
- Includes both active and passive defenses
What are passive defences
Defences present before infection and role is to prevent entry and spread of pathogen
Include physical barriers and chemicals

What are the physical defences in plants
- cellulose cell wall
- lignin thickening of cell walls
- Waxy cuticles
- bark
- stomatal closure
- callose
- Tylose formation
How does the cellulose cell wall act as a physical defence in plants
Not only acts as a physical barrier but most plant cell walls contain variety of chemical defences that could be activated from packaging is detected
How does lignin thickening of cell walls act as a physical defence in plants
lignin is waterproof and almost completely indigestible
How do the waxy cuticles acts as a physical defence
- Prevent water collecting on the cell surfaces
- Since pathogen is collected in water And need water to survive the absence of water is a passive defence
How is bark physical defence in plants
Most bark contains a variety of chemical defences that works against pathogenic organisms
How does stomatal closure act as a physical defences in plants
- stomata are possible points of entry for pathogens
- stomatal aperture is controlled by the guard cells
- when pathogenic organisms are detected in that part of the plant
How is Callose a physical defence in plants
- large polysaccharide that is deposited in sieve tubes at the end of growing season
- Deposited around the sieve plates and blocks the flow in the sieve tubes
- This can prevent a pathogen spreading around the plant
How is tylose formation a physical defence in plants
- A tylose is a balloon like swelling/projection that fills the xylem vessel
- When fully formed it blocks the vessel and the vessel can no longer carry water
- Blocking xylem vessels then prevents spread of pathogens through heartwood
- Also contains a high concentration of chemicals such as terpenes that are toxic to pathogens
How do chemical defences protect the plant from pathogens
- tissues contain a variety of chemicals that have anti-pathogenic properties including terpenoids/phenols/alkaloids/hydrolytic enzymes
- Some of these chemicals such as terpenes in tyloses and tannins in bark are present before infection
However the production of chemicals requires a lot of energy so many chemicals are not produced until the plant detects an infection
What are active defences in plants
- when pathogens attack, specific chemicals in their cell wall can be detected by plant cells
- chemicals include specific proteins and glycolipids
- plabt responds by fortifying the defences already present
- This includes increasing physical defences and producing defensive chemicals
What are the active defences in plants 
- cell walls become thickened and strengthened with additional cellulose
- deposition of callose between the plant cell wall and cell membrane near invading pathogen- Callose deposits are polysaccharide polymers that impede Cellular penetration at the site of infection it’s strengthens the cell wall and blocks plasmodesmata
- oxidative burst that produce highly reactive oxygen molecules capable of damaging the cells of invading organisms
- an increase in production of chemicals
- necrosis
- canker
What is the action points of terpenoids in plant cells
- Range of essential oils that have antibacterial and antifungal properties
- Also create sent for example the menthols and menthones produced by mint plants
What is the action point of Phenols in plant cells
- have antibiotic and antifungal properties
- tannins found in bark Inhibit attack by insects these compounds bind to salivary proteins and digestive enzymes such as trypsin and chymotrypsin deactivating enzymes
- Insects that ingest high amounts of tannins do not grow and will eventually die this helps prevent transmission of pathogens
What is the action point of alkaloids in plant cells
- Nitrogen containing compounds such as caffeine/nicotine/cocaine give bitter taste to inhibit herbervores feeding
- also acts on a variety of metabolic reactions via inhibiting for activating enzyme action
- Some alkaloids inhibit protein synthesis -if plants can reduce grazing by large animals then it will suffer less damage that can allow pathogens to enter plant
What is the action point of defensive proteins (defensins) in plants cells
- small cytosine rich proteins that have broad antimicrobial activity
- Acts upon molecules in plasma membrane of pathogen possibly inhibiting action of ion transport channels
What is the action points of hydrolytic enzymes plant cells
- found in spaces between cells
- these include chitinases (Which breakdown the chitin found in fungal cells walls) glucanases (Which hydrolyses the glycosidic bonds in glucans). And lysosomes (capable of degrading bacterial cell walls)
What are the chemicals used in active defences in plants cells
- terpenoids
- phenols
- alkaloids
- defensive proteins (defensins)
- Hydrolytic enzymes
What is necrosis
-Deliberate cell suicide
-Few cells are sacrificed to save the rest of the plant
-by killing cells surrounding infection stops pathogens access to water and nutrients and stop spreading further around Plant
-brought about by intracellular enzymes that are activated by injury -Enzymes destroy damaged cells and produce brown spots on leaves/dieback

What is a canker
- The parts of the plant where the cells have died after necrosis
- it’s a sunken necrotic lesion in the body tissue such as the main stem/branch
- causes death of the Cambian tissue in the bark 
What are primary defences
prevent pathogens entering the body
Non-specific as will prevent the entry of any pathogen
How is the skin a primary defence against disease
- main primary defence
- Outer layer of the skin is called the epidermis and consists of layers of cells
- most of the cells are called keratinocytes
- these are produced by mitosis at the base of the epidermis
- they then migrate out to surface of the skin
- as they migrate they dry out and the cytoplasm is replaced by the protein keratin
- this process is called keratinisation and takes about 30 days
- by the time cells reach the surface they are no longer alive
- keratinised layer of dead cells act as an effective barrier to pathogens
- Eventually dead cells slough off
Why is blood clotting and skin repair important
- abrasion/lacerations damage the skin an open body to infection
- When it occurs what do you must prevent excess blood loss by forming a clot making a temporary seal to prevent infection and repair the skin
What are the first stages in the Blood clotting and skin repair process
- blood clotting is a complex process as it is important to prevent clots forming in blood vessels where they are not needed
- involves calcium ions and at least 12 factors known as clotting factors
- many of the clotting factors are released from platelets and from the damaged tissue
- These factors activate an enzyme cascade
What are the second stages of the blood clotting and skin repair process once the clot has formed
- once clot has formed it begins to dry out and form a scab
- scab shrinks as it dries drawing the sides of the cut together
- this makes a temporary seal under which the skin is repaired
- first stage is the deposition of fibrous collagen under the scab
- Stem cells in the epidermis then divide by mitosis to form new cells which migrate to the edge of the cut and differentiate to form new skin
- New blood vessels great to supply oxygen and nutrients to new tissues
- The tissues contract to help draw the edges of a cut together so that the repair can be completed
- As the new skin is completed the scab will be released
Describe the steps in the enzyme cascade
1) Blood vessel is damaged collagen becomes exposed and releases clotting factors platelets bind to collegen and Release clotting factors
2) these cause inactive thrombinkase to be converted to active thrombinkase (an enzyme)
3) this enzyme along with calcium ions then catalyse the conversion of prorthrombin in thr bloood to active thrombin (an enzyme)
4)This enzyme thing catalyses the conversion of soluble fibrogen in plasma to insoluble fibrin
5) these fibres attach to platelet plug and a temporary platelet plug is formed
6) The red blood cells and platelets are trapped and a clot is formed

What does an active enzyme become
Phosphorylated
Why are mucous membranes needed
- certain substances such as oxygen and nutrients in our food must enter our blood
- Exchange services where this occurs are thinner and less well protected from pathogens
- food and air we breathe in a harbour micro organisms
- Airways lungs and digestive system are at risk of infection
- So protected by mucus membranes
How do mucous membranes work (goblet cells)
-epithelial layer contains mucus secreting cells called goblet cells
- There are also extra mucus secreting glands under the epithelium
- In airways the mucus lines the passages and traps any pathogens that may be in the air 
How do you mucous membranes work (ciliated cells)
- cilia are tiny hair-like organelles that can move
- They move in a coordinated fashion to waft the layer of mucus along
- they move the mucus up to the top of the trachea where it can enter the oesaphugus
- It is swallowed and passes down the digestive system
- Most packages in digestive system are killed by the acidity of the stomach which can be pH 1-2 debatures pathogens enzymes
Where are mucus membranes also found
- gut
- genital areas
- anus
- ears
- nose
