Disease Flashcards
Pathogen
A microorganism that causes disease
How do bacteria cause disease?
Once in host cell, they can multiply rapidly. Presence causes disease by damaging cells or releasing toxins.
In plants, bacteria often live in vascular tissues causing them to blacken.
How do fungi cause disease?
Fungus lives in the skin of an animal and its hyphae, which forms a mycelium, grows under skin surface. Fungus can send out reproductive hyphae which grow to skin surface and release spores.
In plants fungus lives in vascular tissue to gain nutrients. Hyphae release extracelullar enzymes to digest surrounding tissue.
How do viruses cause disease?
Viruses invade cells and take over genetic machinery and other organelles. They cause the genetic machinery to make more copies of the virus and the host cell will burst to release many viruses that will infect healthy cells.
How do protoctista cause disease?
Enter host cell and feed on the contents as they grow
Diseases caused by bacteria
Tuberculosis
Bacterial meningitis
Ring rot (plants)
Diseases caused by viruses
HIV
Influenza
Tobacco mosaic virus
Disease caused by fungi
Black sigatoka ( bananas)
Blight (tomatoes and potatoes)
Ringworm (cattle)
Athlete’s foot
Diseases caused by protoctista
Malaria
Means of transmission of pathogenic organisms
Direct physical contact such as touching an infected person or surface
Faecal-oral transmission - eating/drinking contaminated food/water
Droplet infection - pathogen is carried inn droplets in the air
Transmission by spores
How to prevent transmission
Hygiene - wash hands regularly, sterilising surgical instruments
washing food, careful preparation of food
using and disposing of tissues, covering mouth to sneeze
use masks
Social factors that affect transmission
Overcrowding Poor ventilation Poor health Poor diet Homelessness Being around people who have migrated from a place where a disease is more common
Transmission of malaria
An uninfected person is bitten by a female Anopheles mosquito
Plasmodium migrates to the liver
Plasmodium migrates to blood
The person has malaria and gametes of plasmodium are in their blood
A female Anopheles mosquito sucks the blood and plasmodium develops and migrates to the mosquitos salivary gland
Another person is bitten
Physical plant defences against pathogens
Cellulose cell wall - acts as physical barrier and contain chemical defences that can be activated
Lignin thickening of cell walls - waterproof and almost completely indigestible
Waxy cuticles - prevent water collecting on the surface and pathogens can’t survive without water
Bark - contains a variety of chemical defences
Stomatal closure - when pathogens are detected, guard cells will close the stomata
Callose - a large polysaccharide that is deposited in the sieve tubes and blocks the flow in the sieve tube. This prevents spread of pathogen around the plant
Tylose formation - a swelling that fills the xylem vessels so that the vessel can no longer carry water. This prevents the spread of the pathogen. Tylose contains chemicals that are toxic to pathogens.
Active plant defences
Cell walls become thickened and strengthened with extra cellulose
Deposition of callose to strengthen cell wall and block plasmodesmata
Oxidative bursts that produce highly oxidative molecules capable of damaging cells of invading organisms
Increase in the production of chemicals
Plant chemicals against pathogens
Terpenoids - antibacterial and antifungal properties, may also create scent
Phenols - antibiotic and antifungal properties. Tannins in bark inhibit attack by insects
Alkaloids - nitrogen containing compounds give a bitter taste to inhibit herbivores feeding. They also inhibit or activate enzymes. Some inhibit protein synthesis
Defensive proteins - cysteine rich and have antimicrobial activity. Act on plasma membranes inhibiting ion channels
Hydrolytic enzymes - break down chitin in fungal cell walls, hydrolyse glycosidic bonds in glucans and degrade bacterial cell walls.
Necrosis
Deliberate cell death. By killing cells surrounding infection, pathogens have limited access to water and nutrients so prevent it spreading around the plant
Canker
A sunken necrotic lesion in the woody tissue, causes death of the cambium tissue.
Primary defences against disease
The skin Blood clotting and skin repair Mucous membranes Coughing and sneezing Inflammation Eyes protected by tears Wax in ear canal
How does the skin act as a primary defence?
The outer layer of skin (the epidermis) consists of keritinocytes which are produced by mitosis at the base of the epidermis. The cells migrate to the surface and dry out and the cytoplasm is replaced by keratin. By the time the cells reach the surface, they are dead and act as an effective barrier to pathogens.
How does blood clotting act as a primary defence?
Involves calcium ions and at least 12 clotting factors many of which are released from platelets of the damaged tissue. The factors activate an enzyme cascade. Once a clot forms, it drys out to form a scab which shrinks as it dries, drawing the sides together. This makes a temporary seal as the kin repairs.
The first stage is the deposition of fribrous collagen under the scab. Stem cells in the epidermis divide by mitosis and these cells migrate to surface to form new skin. New blood vessels grow to supply oxygen and nutrients. Tissues contract to draw edges of cut together.
How do mucous membranes act as a primary defence against disease?
Mucus is secreted from goblet cells which are in the epithelial layer. In airway, mucus lines passages and traps pathogens in the air. Ciliated cells waft the mucus along to the top of the trachea where it is swallowed down the oesophagus and killed by the stomach acid
How does coughing and sneezing act as a primary defence against disease?
Areas prone to attack are sensitive and respond to irritation caused by microorganisms by coughing, sneezing or vomiting. The sudden expulsion of air will carry the microorganism with it.
How does inflammation act as a primary defence against disease?
The presence of microorganisms is detected by mast cells which release histamine, a cell signalling substance. Histamine causes vasodilation and makes capillary walls more permeable to white blood cells and some proteins. Blood plasma and phagocytes leave blood and enter tissue fluid leading to increased production of tissue fluid causing swelling.
