3.2.3 Cholera

Question 1

What is the cause of cholera?

Answer 1

Bacterium - Vibrio cholerae

Question 2

Describe the physical appearance of Vibrio cholerae

Answer 2

• Curved, rod-shaped bacterium
• Has a flagellum

Question 3

Name 4 ways cholera is transmitted

Answer 3

1. Drinking water that hasn’t been purified
2. Untreated sewage leaching into water courses
3. Contaminated food
4. Eating other organisms (e.g. shell fish) that have fed on untreated sewage

Question 4

Name 3 precautions to prevent the transmission of cholera

Answer 4

• Effective water / sewage treatment
• Improved hygiene
• Vaccination
• Prevent water contamination
• Quarantining of affected area

Question 5

Name two symptoms of cholera

Answer 5

• Diarrhoea
• Dehydration

Question 6

Describe how cholera bacterium causes disease (6 steps)

Answer 6

1. In small intestine: bacteria uses its flagella to go through mucus lining of intestine
2. Produce toxin protein which binds to specific receptors on cell membrane
3. Toxic protein causes ion channels to open & chloride ions move into lumen
4. Loss of ions from epithelial cells = concentration gradient → ions diffuse into epithelial cells from surrounding tissues & blood
5. ↓Ψw in lumen = water move by osmosis from blood/tissues into lumen down Ψw gradient
6. Less water reabsorbed = symptoms of cholera

Question 7

Why does the cholera toxin (exotoxin) only affects the small intestine?

Answer 7

• Exotoxin specific to epithelial cells in small intestine
• Only binds to these specific receptors on membrane
• ∵ they’re complementary shape of exotoxin

Question 8

Name 3 causes of diarrhoea

Answer 8

• Damage to epithelial cells lining intestine
• Loss of microvilli due to toxins
• Excessive secretion of water due to toxins

Question 9

What is just drinking water ineffective to cure cholera?

Answer 9

• Water is not being absorbed from intestine
• Doesn’t replace electrolytes (ions) that are being lost from epithelial cells of intestine

Question 10

Name 5 things a rehydration solution contains

Answer 10

• Water
• Sodium
• Potassium
• Glucose
• Other electrolytes

Question 11

Why does a rehydration solution contain sodium?

Answer 11

To replace sodium ions lost from epithelium of intestine

Question 12

Why does a rehydration solution contain water?

Answer 12

To rehydrate tissues

Question 13

Why does a rehydration solution contain potassium?

Answer 13

Replace lost potassium ions and stimulate appetite

Question 14

Why does a rehydration solution contain glucose?

Answer 14

To stimulate uptake of sodium ions i.e. make use of the sodium-glucose carrier proteins

& provide energy

Question 15

Why does a rehydration solution contain electrolytes?

Answer 15

Help prevent electrolyte imbalance

Question 16

How should the rehydration solution be taken?

Answer 16

Regularly and in large amounts, throughout illness

Question 17

Explain how an oral rehydration solution replaces water lost by diarrhoea (4)

Answer 17

• Increase uptake of sodium ions/glucose
• By (sodium-glucose) co-transport carrier proteins
• Lowers water potential in cell/tissue
• Water moves out of intestine/into cells by osmosis