Summary
OCR A A-level Biology Module 4 Notes Summary COMPLETE
Concise notes with diagrams and key words highlighted, sticking to the OCR A Biology specification
[Show more]
Seller
Follow
Content preview
A Level BiologyCOMMUNICABLE DISEASES OCR A Module 4
• Communicable diseases → diseases that can spread between organisms
Bacterial diseases Protoctist diseases
• Tuberculosis (TB) → affects animals including • Malaria → affects animals including humans
humans → spread by a vector (mosquitos)
→ spread via infected droplets • Potato (or tomato) late blight
• Ring rot → affects potatoes and tomatoes → affects potatoes (or tomatoes)
→ spread through direct contact → produces spores during reproduction that
are spread in the air to other hosts
Viral diseases Fungal diseases
• HIV/AIDS → affects humans • Black sigatoka → affects bananas
→ spread through sexual contact → spread via spores
• Influenza → affects animals including humans • Athlete’s foot → affects humans
→ spread through infected droplets → spread by direct and indirect
• Tobacco mosaic virus → affects plants #A
*
contact
→ spread by direct contact
"
i
Ni
Viruses are acellular. They have genetic
material (RNA or DNA) but no organelles or
nucleus. They cannot replicate without a The HIV
host cell. a
=
virus
Transmission
• Direct transmission → directly from one organism to another
→ e.g. through infected droplets (not plants), sexual contact, touch
• Indirect transmission → from one organism to another via an intermediate
→ e.g. through a vector, spores, through the air or food
• Climate affects transmission e.g. having the ideal temperature for a vector to survive and reproduce
• Living conditions affect transmission → overcrowding makes transmission easier
→ poor hygiene practises e.g. not washing hands
• Social factors affect transmission → lack of sexual education and hygiene education
→ lack of good healthcare facilities and poor drug or vaccine
availability
• Measures to decrease transmission → mask wearing and improving ventilation
→ meeting less people
→ destroying vectors
→ quarantine of infected individuals
→ increasing hygiene practises e.g. hand washing
→ restrict travel
A vector is an organism
which carries a pathogen Make sure to consider which
without getting symptoms measures would be effective
of the disease. for each type of transmission.
Page 1 of 1 © Dr Zoë Huggett
, A Level Biology
PRIMARY DEFENCES OCR A Module 4
Plant defences against pathogens
• Cell walls act as a physical barrier to pathogens → callose can be deposited between the cell wall and
plasma membrane which acts as an extra barrier
• Waxy cuticles are a physical barrier
• Production of toxic antimicrobial chemicals
→ e.g. production of chitinases to break down chitin cell walls of fungi
→ e.g. phytoalexins inhibit growth and reproduction of bacteria and fungi
• Leaf drop → some plants will lose leaves to prevent pathogens from spreading around the plant
Animal primary non-specific defences
• Skin → physical barrier
→ produces antimicrobial chemicals which lower the pH
• Blood clotting → blood clots are a mesh of protein fibres, platelets, and erythrocytes
→ platelets release a substance which results in a soluble plasma protein (fibrinogen)
being converted into an insoluble protein (fibrin) which can trap erythrocytes and
platelets to form a clot
→ blood clots are a physical barrier at wounds
• Wound repair → skin can be repaired by skin cell division and collagen fibres
• Inflammation → mast cells (a type of white blood cell) release histamine
→ histamine increases blood flow through vasodilation, and increases permeability of
the capillaries
→ more white blood cells can enter the affected area
• Expulsive reflexes → coughing and sneezing expels pathogens from the respiratory tract
• Mucous membranes → found at openings to the body e.g. the trachea
→ can contain goblet cells which secrete mucus
→ mucus traps pathogens and contains lysozyme
Page 1 of 1 © Dr Zoë Huggett
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller abdurrahmaanhasan. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £7.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
52510 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now