BIODIVERSITY, EVOLUTION

AND DISEASE

BIOLOGY NOTES

MODULE 4

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INDEXTOPIC 1: COMMUNICABLE DISEASES, DISEASE PREVENTION

& THE IMMUNE SYSTEM . . . . . . . . . . . . . . . . . . . . 51. The Different Pathogens that Cause Diseases in Plants and Animals . . . . . . . . . . . . . 52. The Means of Transmission of Animal & Plant Communicable Pathogens . . . . . . . . . . 73. Plant Defences Against Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84. The Primary Non-specific Defences Against Pathogens in Animals . . . . . . . . . . . . . . . 95. The Structure & Mode of Action of Phagocytes . . . . . . . . . . . . . . . . . . . . . . . . . 116. B and T lymphocytes in The Specific Immune Response . . . . . . . . . . . . . . . . . . . . 127. The Structure & General Functions of Antibodies . . . . . . . . . . . . . . . . . . . . . . . . 148. Active, Passive, Natural and Artificial immunity . . . . . . . . . . . . . . . . . . . . . . . . . 169. Autoimmune Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1610. Vaccination & The Prevention of Epidemics . . . . . . . . . . . . . . . . . . . . . . . . . . 1611. Possible Sources of Medicines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1712.The Benefits & Risks of Using Antibiotics to Manage Bacterial Infection . . . . . . . . . . 18

TOPIC 2: BIODIVERSITY . . . . . . . . . . . . . . . . . . . . . . . . . 211.Biodiversity at Different Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.Sampling and Measuring the Biodiversity of a Habitat . . . . . . . . . . . . . . . . . . . . . 223.How Genetic Biodiversity is Assessed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.The Factors Affecting Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255. Reasons to Maintain Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266. In Situ and Ex Situ Methods of Maintaining Biodiversity . . . . . . . . . . . . . . . . . . . . 277. International & Local Conservation Agreements Made to Protect Species & Habitats . . . 29

TOPIC 3: CLASSIFICATION AND EVOLUTION . . . . . . . . . . . . 311. The Biological Classification of Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312.The Evidence for The Theory of Evolution by Natural Selection . . . . . . . . . . . . . . . . 333.The Different Types of Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354. The Different Types of Adaptations of Organisms to Their Environment . . . . . . . . . . 375. Natural Selection and its Effect on the Characteristics of a Population Over Time . . . . . 376.Evolution and its Implications for Human Populations . . . . . . . . . . . . . . . . . . . . . 39

TOPIC 1

Communicable Diseases, Disease Prevention & The Immune System

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Communicable Diseases, Disease Prevention & The Immune System

1 The Different Pathogens that Cause Diseases in Plants and Animals

Disease can be caused by an enormous range of harmful pathogens.

Pathogen = a microorganism that causes disease.

Bacteria

• Can rapidly multiply in the right conditions • Cause disease by damaging cells or producing toxins that are harmful • Eg tuberculosis, bacterial meningitis, ring rot (plants)

Viruses

• Invade cells and take over the protein-synthesising organelles • Infect the cells with new DNA • Host cells eventually burst and release new copies of the viral DNA • Eg HIV/AIDS, influenza, tobacco mosaic virus (plants)

Fungi

• In animals, cause redness and irritation • This is due to hyphae released from the fungus • Eg black sigatoka (bananas), ringworm (cattle), athlete’s foot

Protoctista

• Feed on cell contents as they grow • Eg malaria, potato blight

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Cause Transmission Global ImpactTuberculosis • Bacterial

• Mycobacterium tuberculosis

• Divides slowly (every 20 hours)

• Can survive for 6 months outside body

• Sufferer cough, catapulting droplets of saliva into air

• Saliva contain tuberculi bacilli

• High speed • Reach over 1-2m • 1 sneeze can have up to 40,000 droplets

• worldwide • 1% of world newly infected each year

• 8.8 million cases • 34% new cases occur in S.E. Asia

• 1.6 million deaths

HIV/AIDS • Virus

• Human immunodeficiency

• Attacks and destroys immune cells weakens immune system

• Open to range of opportunistic diseases

• Secondary infection

• Exchange of bodily fluids

• Sharing of hypodermic needles

• Across placenta during child birth

• From mother to baby during breast feeding

• Use of unsterilized surgical equipment

• Worldwide

• 45 million sufferers

• 5 million new infections annually

• 30 million have died

• Rapidly rising in China

Malaria • Eukaryotic organism

• Plasmodium falciparum

• Spreads by vector

• Malarial parasites live in red blood

• Feed on hemoglobin

• Mosquito will suck parasitical gametes into its stomach

• Gametes fuse to form zygotes in mosquito stomach

• Plasmodium develops and moves to salivary glands

• Mosquito bites person, injecting saliva

• Plasmodium enters person

• Migrates to liver

• Multiplies and passes into blood

• Cycle repeats

• Kills 3 million annually

• 300 million affected worldwide

• limited to regions where anopheles mosquito can live

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2 The Means of Transmission of Animal & Plant Communicable Pathogens

The most common means of transmission can be identified as five groups:

• Droplet transmission ○ E.g. through sneezing - pathogen is contained within mucus ○ Type of direct transmission

• Physical contact ○ Common for skin diseases like ringworm, a fungal disease in cattle, which is spread by an infected animal brushing against an uninfected animal

○ Direct transmission • Faecal-oral transmission

○ E.g. E. coli ○ Transmitted by consumption of food or water with traces of faeces from infected animal ○ Direct transmission

• Transmission by spores ○ Spores are a resistant form of the pathogen ○ They can resist extremes of temperature, pH, and even strong disinfectants ○ E.g. anthrax ○ Direct transmission

• Vector transmission ○ E.g. malaria ○ The pathogen is carried from one host to another via a vector ○ With malaria the vector is female mosquitoes ○ The pathogen cannot be spread directly from one host to another ○ Indirect transmission

Some environmental factors can also contribute to the spread of disease.

Climate

• Some vectors only live in hot climates, e.g. mosquitos carrying malaria • Many viruses, protoctists and bacteria survive better in warm climates • Very cold climates can kill pathogens

Environment

• Cramped and crowded environments are conducive to spread of disease ○ Droplet infection rate likely to be higher ○ Contact infection also much higher

• Dirty environments harbour pathogens ○ E.g. using human sewage to fertilise crops is sometimes done in parts of the world ○ This is likely to cause the spread of faecal-oral pathogen spread

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