Chapter 6: Infection and Response Flashcards
What is the definition of a disease?
An abnormal condition that affects all or part of an organism and results in specific symptoms, and is not a direct result of physical injury
What are communicable diseases?
Diseases that can be passed between organisms
What is a pathogen?
Microscopic organisms that cause disease
What are the 4 main types of pathogen?
Viruses (not living), bacteria and protists (prokaryotes), and fungi (eukaryotes)
What are the 3 basic shapes of bacteria?
Spheres, rods and spirals
How do bacteria reproduce?
By splitting in half (binary fission)
How do bacteria damage the body?
By producing toxins, which are capable of destroying tissue
How do antibiotics kill bacteria?
They exploit the fact that bacterial cells are different from human cells. Penicillin weakens bacterial cell walls causing bacteria to burst. Other antibiotics alter bacterial enzymes, and others prevent bacteria from reproducing
How long is the average bacterium?
1 to 5 micrometers (1/1000mm)
How do viruses reproduce?
Viruses are not actually living, and reproduce by taking over cells, injecting them with RNA, and using turning them into virus-creating machines until the cell bursts and dies
How do viruses damage the body?
When a virus enters a cell, the cell effectively dies, meaning that large amounts of tissue can be destroyed by viruses
Why are viruses non-living?
They do not respire, excrete, move, grow or respond to their environment. It also has no nucleus (just RNA with a protein jacket)
Why are antibiotics ineffective against viruses?
They are hidden within their host cells
How large are viruses?
0.01 to 0.1 micrometers (1/1000mm) in length
Name 5 ways pathogens can be transmitted
Contaminated food/water, airborne droplets, animal vectors, direct contact, sex
Name some methods of preventing the spread of pathogens
Sneezing into tissues, washing hands before eating, sterilizing food/water, killing vectors, using condoms
What is a control variable?
Any other variable that may affect the outcome. If at all possible, these need to be kept constant during the experiment
What is a dependent variable?
An outcome variable that is measured each time the independent variable is changed
What is an independent variable?
The variable that is deliberately changed by the experimenter
Name some of the body’s first-line defenses against pathogens
Saliva contains enzymes that break down bacterial cell walls, skin acts as a barrier, stomach acid destroys bacteria, mucus traps bacteria, hair follicles produce antiseptic oil, scabs keep bacteria out
How do we know that handwashing is effective?
Because Ignaz Semmelweis showed maternity wards in which doctors washed their hands had lower infant mortality rates than wards where they didn’t
Explain the non-specific immune system
White blood cells known as phagocytes engulf and destroy pathogens (which release antigens that they can detect)
Explain how the specific (also known as acquired) immune system fights off an infection
During infection, white blood cells known as lymphocytes produce Y-shaped antibodies that fit specific antigens. The antibodies then bind to the surface antigens on the pathogen and clump viruses together, allowing them to be more easily destroyed by phagocytes. After the infection, some lymphocytes stay behind and become memory cells
What is a memory cell?
Memory cells are long-lived lymphocytes that are capable of producing the right antibodies to fight a disease that has already occurred
How does vaccination work?
A small quantity of a dead, inactivated or genetically modified pathogen is injected into the bloodstream. Crucially, these pathogens must have the same antigens as the real pathogen. After the injection, phagocytes start engulfing the pathogen and lymphocytes produce antibodies and antitoxins. If you were to later get infected with a real version of the pathogen, memory lymphocytes would be able to respond by producing antibodies and antitoxins fast enough for you to not get sick
How does herd immunity work?
A large percentage of the population become immune to a disease, meaning those who cannot be vaccinated do not become infected
What are antitoxins?
Special types of antibody that bind to and neutralise bacterial toxins
What’s the difference between a T cell and a B cell?
While they are both lymphocytes, B-cells produce antibodies, T cells produce cytokines and kill infected cells
How does antibiotic resistance happen?
Antibiotics kill all but the strongest bacteria, which survive and reproduce
