6.3 Defense Against Infectious Disease The human body has structures and processes that resist the continuous threat of invasion by pathogens.

Q: What is a pathogen?

Bacteria Prokaryotes (no real nucleus) Divide by binary fission Can cause: Food poisoning (e.g. Salmonella) Ear and eye infections Cholera, diarrhea _II_Conjunctivitis.JPG

The 1918 flu epidemic killed between 50 and 130 million people. Viruses Acellular (non-living?) Need a ‘host’ cell to carry out functions of life, including reproduction Can have DNA or RNA Mutate, evolve and recombine quickly Cause: Flu, HIV/AIDS, smallpox, measles, common cold, herpes, ebola

Fungi Eukaryotes, reproduce with spores Cause: Athlete’s foot, mould, ringworm Allergic reactions and respiratory problems Image from:

Protozoa Simple parasites Cause: Malaria Leishmaniasis Toxoplasmosis Leishmaniasis image from:

The skin and mucous membranes form a primary defence against pathogens that cause infectious disease. Q: What parts of the body have mucous membranes? Q: List two characteristics of mucous membranes that help them defend against pathogens.

Cuts in the skin are sealed by blood clotting. Q: In numbered steps, explain how clotting occurs. Clotting factors are released from platelets. An enzyme called thrombin is produced. Thrombin converts soluble fibrinogen to insoluble fibrin. Fibrin forms a mesh that traps red blood cells. The gel, if exposed to air, hardens into a scab.

Application: Causes and consequences of blood clot formation in coronary arteries. CAUSES Well known factors correlated with an increased risk of blood clot formation in coronary arteries. Smoking High blood cholesterol concentration High blood pressure Diabetes Obesity Lack of exercise CONSEQUENCES If the coronary arteries become blocked by a blood clot: Part of the heart is deprived of O 2 and nutrients Cardiac muscle cells can not produce ATP Contractions become irregular and uncoordinated Fibrillation Heart does not pump blood effectively Review atherosclerosis

Ingestion of pathogens by phago (“eating”) cytic (“cell”) white blood cells gives non-specific immunity to diseases. Q: Draw the process of phagocytosis. Why is this “non-specific immunity”? Chemotaxis (movement in response to chemicals) attracts the phagocytes to the area of invasion as response to: proteins produced by the pathogen phospholipids released by damaged cells The phagocyte attaches to the pathogen’s cell surface proteins and then engulfs it. The fluid nature of the plasma membrane allows this to happen. A phagosome forms. This is a vesicle that contains the pathogen. Lysosomes – vesicles of digestive enzymes – deposit the enzymes into the phagosome. The digestive enzymes break down the pathogen and the waste products are expelled from the cell by exocytosis. Q: Why do infected wounds become pus-filled?

Phagocytic Leucocytes card sort game: order the images & outline the processes Images from:

Q: What is a lymphocyte?

Q: What is an antibody? Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity.

Some lymphocytes act as memory cells and can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered.

Q: Why does it take a couple of days for your body to be able to fight off a disease?

Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells. Q: List four processes in prokaryotes that are blocked by antibiotics.

Viruses lack a metabolism and cannot therefore be treated with antibiotics.

Antibiotics are ineffective against viruses! Analyse the graph below. Over time, outline what has happened to: The number of new approved antibiotics The diversity of new approved antibiotics

Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance.

Q: List three measures that can be taken to reduce the development of antibiotic resistance in bacteria.

Nature of science: Risks associated with scientific research— Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocol on testing. Application: Florey and Chain’s experiments to test penicillin on bacterial infections in mice. They tested the drug on humans after only a very brief period of animal testing…. How brief? 8 mice. There could have been severe side effects. The samples they were using were not pure. The patients they used were all at the point of death and several were cured. Penicillin was introduced more quickly than it should have been, in time for the D-Day invasion and the number of soldier deaths was greatly reduced.

Application: An understanding of immunity has led to the development of vaccinations.

Application: Effects of HIV on the immune system (a reduction in the number of active lymphocytes and a loss of the ability to produce antibodies, leading to the development of AIDS) and methods of transmission.