A revision summary of OCR A level Biology Communicable disease, prevention & Immune 4.1.1.
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Transmission
Communicable disease – illness from infection of pathogens in host Animal Plant
Pathogen – a disease causing organism with takes nutrition from & damages
Direct Direct contact (kissing) Direct contact
host
Inoculation (break in skin)
Pathogen Structure Function Example Ingestion (contamination)
Bacteria prokaryotes, no ➗every 20mins by binary Humans - Spores
membrane- fission tuberculosis
bound Antigens produce toxins which & bacterial Indirec Fomites (inanimate Soil contamination
organelles. damage cells (stop cell meningitis t objects) Vectors (wind, water)
Cocci division) Droplet (salvia, mucus)
(spherical), Gram +ve =cell wall purple- Plants - Vectors (animal)
Bacillus (rod), blue Ring rot Factor Over-crowding Variety of crops
Vibro (curved), Gram -ve =cell wall red s Poor nutrition Over-crowding
Spirilli (Spiral) Immune strength Mineral nutrition
Virus No cellular 1. attaches to specific host Humans - Climate change Damp, warm conditions
structure – cell HIV/ AIDS, Hygiene/ waste disposal Climate change
cannot respire, 2. injects RNA/ DNA influenza
ATP, replicate 3. Viral DNA enters host DNA Plant defence (non-specific)
Genetic or viral RNA is synthesised Plants - Passive (present all the Chemical defences
material by cell HIV (retrovirus) Tobacco time)
surrounded by 1. Reverse transcriptase Mosaic Waxy cuticle prevent pathogens growing
protein makes DNA from RNA virus Cellulose lignified cell wall – on surface
2. DNA polymerase makes 2- impermeable & hard chew Sticky resin secreted by bark
stranded DNA Closed stomata VOCs - chemicals that
3. Attached to host DNA Bark encourage growth of
4. Can synthesise new Casparian strip harmless competing
viruses. microorganisms
Protocti Eukaryotic, Spread through vectors. Humans - Active mechanisms (activated when pathogens invade)
sta single-celled, Take over cells & break open Malaria Callose deposition - stops spread of pathogen.
Digest & use cell contents as 1. Callose (1,3 + 1,6 bond) synthesised & deposited between
they reproduce. Plants - cell wall & plasmodesmata, acting as barriers to stop
potato spread.
blight. 2. Lignin added making thicker & stronger
Fungi Eukaryotic, Saprophytic feeders – Humans - - Blocks sieve blates sealing off infected cells.
chitin cell wall, release digestive enzymes cattle - Stronger walls makes it harder for pathogen to enter.
vacuoles, onto dead organic matter & ringworm, Chemicals released during cell signalling
hyphae absorb nutrients. athletes’ Salicylic acid – migrates to uninfected areas & activates d
Parasitic – feed off living foot Ethylene –stimulate other leaves to react.
matter - Can disrupt pathogen cell membrane
Plants - - Secrete enzymes to break down pathogen cell wall
Black
sigatoka
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