Chapter 6: Infection and Response

Question 1

What is the definition of a disease?

Answer 1

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

Question 2

What are communicable diseases?

Answer 2

Diseases that can be passed between organisms

Question 3

What is a pathogen?

Answer 3

Microscopic organisms that cause disease

Question 4

What are the 4 main types of pathogen?

Answer 4

Viruses (not living), bacteria and protists (prokaryotes), and fungi (eukaryotes)

Question 5

What are the 3 basic shapes of bacteria?

Answer 5

Spheres, rods and spirals

Question 6

How do bacteria reproduce?

Answer 6

By splitting in half (binary fission)

Question 7

How do bacteria damage the body?

Answer 7

By producing toxins, which are capable of destroying tissue

Question 8

How do antibiotics kill bacteria?

Answer 8

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

Question 9

How long is the average bacterium?

Answer 9

1 to 5 micrometers (1/1000mm)

Question 10

How do viruses reproduce?

Answer 10

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

Question 11

How do viruses damage the body?

Answer 11

When a virus enters a cell, the cell effectively dies, meaning that large amounts of tissue can be destroyed by viruses

Question 12

Why are viruses non-living?

Answer 12

They do not respire, excrete, move, grow or respond to their environment. It also has no nucleus (just RNA with a protein jacket)

Question 13

Why are antibiotics ineffective against viruses?

Answer 13

They are hidden within their host cells

Question 14

How large are viruses?

Answer 14

0.01 to 0.1 micrometers (1/1000mm) in length

Question 15

Name 5 ways pathogens can be transmitted

Answer 15

Contaminated food/water, airborne droplets, animal vectors, direct contact, sex

Question 16

Name some methods of preventing the spread of pathogens

Answer 16

Sneezing into tissues, washing hands before eating, sterilizing food/water, killing vectors, using condoms

Question 17

What is a control variable?

Answer 17

Any other variable that may affect the outcome. If at all possible, these need to be kept constant during the experiment

Question 18

What is a dependent variable?

Answer 18

An outcome variable that is measured each time the independent variable is changed

Question 19

What is an independent variable?

Answer 19

The variable that is deliberately changed by the experimenter

Question 20

Name some of the body’s first-line defenses against pathogens

Answer 20

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

Question 21

How do we know that handwashing is effective?

Answer 21

Because Ignaz Semmelweis showed maternity wards in which doctors washed their hands had lower infant mortality rates than wards where they didn’t

Question 22

Explain the non-specific immune system

Answer 22

White blood cells known as phagocytes engulf and destroy pathogens (which release antigens that they can detect)

Question 23

Explain how the specific (also known as acquired) immune system fights off an infection

Answer 23

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

Question 24

What is a memory cell?

Answer 24

Memory cells are long-lived lymphocytes that are capable of producing the right antibodies to fight a disease that has already occurred

Question 25

How does vaccination work?

Answer 25

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

Question 26

How does herd immunity work?

Answer 26

A large percentage of the population become immune to a disease, meaning those who cannot be vaccinated do not become infected

Question 27

What are antitoxins?

Answer 27

Special types of antibody that bind to and neutralise bacterial toxins

Question 28

What’s the difference between a T cell and a B cell?

Answer 28

While they are both lymphocytes, B-cells produce antibodies, T cells produce cytokines and kill infected cells

Question 29

How does antibiotic resistance happen?

Answer 29

Antibiotics kill all but the strongest bacteria, which survive and reproduce