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4.1 Communicable Diseases - Coggle Diagram
4.1 Communicable Diseases
Animal Pathogens and Defences
Pathogens
Communicable (or infectious) diseases are those that can be passed from one organism to another. They are caused by microorganisms known as pathogens.
There are 4 types of pathogens
Bacteria - Produce toxins that damage body cells
Viruses - Use host cells to replicate before bursting out and destroying cells.
Protoctists (protists) - Take over cells and break them open.
Fungi - Digest living cells to destroy them. Some also produce toxins.
Modes of Transmission
Direct Transmission
Pathogens can be transferred directly from one organism to another.
This transfer can take place in several ways. Direct contact - Skin-to skin contact, kissing, or sexual intercourse.
Airborne droplets - Coughing or sneezing tiny droplets of mucus or saliva onto someone.
Indirect Transmission
Communicable diseases can also be passed from one organism to another using an intermediate (e.g. water or another organism).
This transfer can take place in several ways:
Food and drinking water - Ingestion of contaminated food or water can cause disease.
Vectors - These transmit pathogens from one host to another (e.g. mosquitoes transmit malaria).
Contaminated objects - Pathogens from infected individuals can live on objects for a short time and infect others.
The risk of communicable disease is increased by certain factors:
Living conditions - Overcrowded areas increase the risk of direct transmission.
Climate - For example, warmer temperatures allow mosquitoes to breed and transmit malaria.
Social factors - For example, a lack of health education and healthcare systems increase the risk of communicable disease.
Examples of Communicable Diseases
Tuberculosis (TB)
Pathogen: Bacterium
Organisms affected: Humans, cows, pigs, and badgers
Effect on the body: Damages the lungs and suppresses the immune system
Mode of transmission: Airborne droplets, Contaminated food and drink
Bacterial Meningitis
Pathogen: Bacterium
Organisms affected: Young children and teenagers
Effect on the body: Damages membranes of the brain and can cause blood poisoning
Mode of transmission: Airborne droplets
HIV/ AIDS
Pathogen: Virus
Organisms affected: Humans and non-human primates
Effect on the body: Gradually destroys the immune system
Mode of transmission: Exchange of bodily fluids
Influenza
Pathogen: Virus
Organisms affected: Mammals including humans, pigs, and birds
Effect on the body: Kills ciliated epithelial cells in the gas exchange system
Mode of transmission: Airborne droplets, Contaminated objects
Athlete's Foot
Pathogen: Fungus
Organisms affected: Humans
Effect on the body: Causes cracking and scaling of skin between the toes
Mode of transmission: Contaminated objects
Ringworm
Pathogen: Fungus
Organisms affected: Mammals including cattle, dogs, cats, and humans
Effect on the body: Causes a circular, red rash
Mode of transmission: Direct contact
Malaria
Pathogen: Protoctist
Organisms affected: Humans, other mammals, reptiles, and birds
Effect on the body: Damages the red blood cells, liver, and brain
Mode of transmission: Vector (Anopheles mosquito)
Plant Diseases and Defences
Modes of Transmission
Direct transmission - This involves the direct contact of a healthy plant with any part of an infected plant.
Indirect transmission - This can take place via soil contamination when infected plants leave pathogens or spores in the soil ready to infect other plants. It also takes place using vectors.
Examples of vectors
Wind - Bacterial, viral, or fungal spores are carried by the wind to uninfected plants.
Water - Spores can travel on the surface of water to reach uninfected plants.
Animals - Insects and birds can carry pathogens or spores from one plant to another.
Humans - Pathogens and spores can be transmitted by handling plants, clothing, farming tools and practices.
The risk of communicable disease is increased by certain factors
Crop variety - Some crops are more susceptible to disease than others.
Overcrowding - This increases the likelihood of direct contact.
Mineral nutrition - Poor nutrition reduces resistance of plants.
Climate change - Increased rainfall and wind increase the spread of disease.
Plant Defences
Physical Defences
Waxy cuticles - Leaves and stems are covered in a waxy cuticle which provides a physical barrier against pathogens.
Cell walls - Plant cells are surrounded by cell walls that form a physical barrier against pathogens.
Production of callose - When plants are attacked by pathogens they produce a polysaccharide called callose. This is deposited between the cell wall and the cell-surface membrane to make it harder for pathogens to enter cells.
Chemical Defences
Insect repellents - These reduce the number of insects feeding on plants to prevent them from transmitting pathogens.
Insecticides - These kill insects to prevent them from transmitting pathogens.
Antibacterial substances - Chemicals such as antibiotics are produced to kill bacteria or inhibit their growth.
Toxins - Some plants produce chemicals that break down into cyanide (a toxic chemical) when the plant cells are attacked.
Examples of Plant Diseases
Ring Rot
Pathogen: Bacterium
Plants Affected: Potatoes, tomatoes, and aubergines
Effect on the Plant: Damages the leaves, tubers, and fruit
Tobacco Mosaic Virus
Pathogen: Virus
Plants Affected: Many plant species including tobacco, tomato, and pepper plants
Effect on the Plant: Damages the leaves, flowers, and fruit
Black Sigatoka
Pathogen: Fungus
Plants Affected: Banana plants
Effect on the Plant: Attacks and destroys the leaves, turning them black
Potato/ Tomato Blight
Pathogen: Protist
Plants Affected: Potatoes and tomatoes
Effect on the Plant: Destroys leaves, tubers, and fruit
Non- specific Animal Defences
Two types of defence mechanisms
Non-specific defences - These act quickly to defend the body, but respond in the same way for all pathogens. E.g. physical and chemical barriers and phagocytosis
Specific defences - These are slower to defend the body, but produce a specific response for each pathogen. E.g. Cellular Response and Humoral Response
Physical and Chemical Barriers
Skin
The skin acts as a physical barrier to block pathogens from entering the body.
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It also acts as a chemical barrier by producing sebum, an oily, antimicrobial substance that lowers pH to inhibit the growth of pathogens
Mucous Membranes
Parts of the ears, nose, throat, and digestive tract are lined by mucous membranes.
These membranes secrete mucus to trap pathogens and use lysozymes to destroy them.
Expulsive Reflexes
Coughing and sneezing are methods for expelling foreign objects (or pathogens) from the gas exchange system.
Vomiting and diarrhoea expel the contents of the gut along with any pathogens present.
Blood Clotting
Prevents excessive bleeding when blood vessels are injured.
Process
Damage to blood vessel wall which exposes collagen and releases clotting factors.
Platelets bind to collagen and release clotting factors.
3, Inactive thrombokinase in the blood is converted to active thrombokinase, which is an enzyme.
Active thrombokinase along with Ca 2+ ions convert Prothrombin to active thrombin, which is an enzyme
Active thrombin converts soluble fibrinogen in the plasma into insoluble fibrin.
Clotting factors form a temporary platelet plug.
Insoluble fibrin fibres attach to platelets to from a plug.
The platelet plug and fibres attached form a clot that traps red blood cells and platelets
Inflammation
Inflammation consists of swelling, heat, redness, and pain at the site of infections or wounds.
Process
Micro-organisms in the tissue is detected by mast cells which release a cell signalling substance called histamine.
Blood vessel walls become more permeable so that they start to leak tissue fluid, causing swelling and isolating any pathogens in the damaged tissue. This is called vasodilation.
When blood vessels become more permeable blood plasma and phagocytic white blood cells leave the blood and enter tissue fluid. This causes an increase in the production of tissue fluid, this causes the swelling (odema)
Excess tissue fluid is drained into the lymphatic system where lymphocytes are stored.
Antigens
Specific Immune System
Preventing Disease
Treating Disease