COMMUNICABLE DISEASES
L1 pathogens notes
Communicable - Caused by an organism that infects another by pathogens.
diseases - Pathogens; bacteria, viruses, fungi, Protoctista
- Often infectious and passed on from organism to organism easily.
Damage to - Viruses – take over cellular metabolism, viral genetic material into genetic material of
tissues host cell which makes more virus and bursts the cell to destroy.
- Protista – take over cell and digest insides to reproduce inside and burst.
- Fungi – digest and destroy living cells.
Producing - Most pathogens produce toxin which is poisonous.
toxins - Toxin damages cells plasma membrane or inactivating enzymes.
- Some fungi produce toxins.
Bacteria - Most common organism for infection
- Not all cause disease
- Prokaryotic cells with no membrane bound organelles.
- Shapes; rod, spherical, comma, spiraled, corkscrew
tuberculosis - Airborne bacteria; mycobacterium tuberculosis affecting respiratory system.
- Antibiotics help but there are resistant strains emerging.
- Macrophages (leucocytes) engulf bacteria by phagocytosis.
- Tissue called tubercle forms around infected site and heals after 3-8 weeks.
- Bacteria can survive in macrophages until immune system weakens.
- Rapid reproduction results in destroying of lung tissue.
- Coughing, shortness of breath, loss if appetite, weight loss, fever, night sweats and
extreme fatigue.
- Fever and night sweats; neutrophils and macrophages releasing fever causing
substances part of response and increase body temperature.
viruses - Non-living infectious agents
- Sort section of RNA surrounded by protein and inserts own RNA into DNA of cell.
- Infected cell reproduces with viral RNA.
- All viruses are pathogens.
bacteriophages - Virus affecting bacteria.
- Viruses insert genome into host cell, so it is away from medicine and immune
responses.
- Virus replicates and the external proteins are self-proteins – so if medicine attacks these
proteins it would affect healthy cells.
- Can change external proteins quickly so medicine and vaccines are irrelevant.
Protista - Eukaryotic cells
- Single or multicellular
- Very few are pathogens affecting organisms
- Often require a vector
Fungi - Unicellular or multicellular
- Eukaryotic
- Made of chitin
- Made up of mycelium of hyphae (Moulds)
- Reproduce and spreads via spores
- Mainly affect plants
- Saprophytic – release digestive enzymes onto dead organic matter and absorbs
nutrients leaving it Moulding
- In plants they affect the leaves mostly preventing photosynthesis
- Release many spores that spread onto other organisms.
- Some are parasitic – live off of living organic matter.
, L2 transmission notes
Mechanism, of disease - Damage cells
- Produce toxins;
- Exotoxins – secreted by living normal pathogen.
- Endotoxin – released when pathogen is damaged.
Methods of disease spread - Direct transmission – direct contact, inoculation (introducing pathogen to
organism directly), ingestion.
- Indirect transmission – fomites, droplet infection, vectors
- Direct contact – exchange of bodily fluids, skin to skin contact and micro-
organism from faces.
- Inoculation – break in skin, bites, puncture wounds or sharing needles.
- Ingestion – contaminated food or water
- Fomites – inanimate objects carrying pathogens such as bedding, socks,
cosmetics.
- Droplet – saliva and mucus spreading through talking, coughing or
sneezing.
- Vectors – transmit from one host organism to another.
Factors affecting - Use of traditional medicine
transmission of disease - Climate change
(animals) - Overcrowded living
- Poor waste disposal
- Bad immune system
- Poor nutrition
- Lack of helpers or socio-economic factors.
Spreading disease in plants - Direct contact – any contact between healthy and contaminated
- Soil contamination – infected plants leave pathogens in soil and can be
passed on.
- Vectors – wind, water, animals and humans.
L3 Plant defences notes
Plant health is important. - Crop damage means loss of money, you don’t sell and lose money or trying
to maintain damaged plants – you end up losing money.
Passive and active defences - Passive – defences present before infection, they prevent entry and spread
of pathogen e.g., physical and chemical barriers.
- Active defence's – fortification of defences when pathogens are detected.
Recognising an attack - Plants don’t have an immune system but use cell signalling to initiate
defence measures and communicate to other cells.
Primary defences – physical - Cell wall – cellulose and lignin
barriers - Leaf cuticle – wax stops moisture building up and keeps it dry as pathogens
require water
- Stomata – prevents droplet pathogens and spores entering leaf
- Bark – contains chemical where production of chemical increases when
plant is under attack
Strengthening cell walls - Rapid, unspecific response to invasion by pathogen
with callose - Callose is synthesised and deposited between cell wall and membrane and
at plasmodesmata preventing spread of pathogen to other cells
- Further thickening and deposition of lignin increases effectiveness of
barrier
- Also blocks sieve plates in phloem, seals infected cells and prevent spread
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