Chapter 7 Set 6

Question 1

List the 8 external defences of the body.

Answer 1

• Skin
• Mucous Membranes
• Hairs
• Cilia
• Acids
• Lysozymes
• Cerumen
• Flushing action of body fluids

Question 2

Describe Skin as an external defence.

Answer 2

Skin:
Effective barrier covering outside of body
Stops entry of microorganisms if unbroken
Normal bacteria also provide protection – stop pathogenic bacteria from settling in.
Secretes oily sebum – has substances that kill some bacteria
Sweat can also prevent micro-organism growth

Question 3

Describe Mucous Membranes as an external defence.

Answer 3

Mucous Membranes
Eg in mouth, nose, conjunctiva, reproductive tract etc
Line body cavities that open to exterior
Secrete mucus – interferes with micro-organism entry

Question 4

Describe Hairs and Cilia as an external defence.

Answer 4

Hairs
In nasal cavity, ears, eyelashes
Trap pathogens for processing and removal

Cilia – tiny hairs with beating motion – sweeps mucus and pathogens towards entrance
Trachea
Nasal cavity
Other air passages

Question 5

Describe Acids as an external defence.

Answer 5

Acids
Kill bacteria and other micro-organisms
Eg stomach acid, acidic vaginal secretions, sweat

Question 6

Describe Lysozyme as an external defence.

Answer 6

Lysozyme
Enzyme that kills bacteria
Contained in tears, saliva, sweat, nasal secretions, tissue fluid

Question 7

Describe Cerumen as an external defence.

Answer 7

Cerumen
Ear wax
Slightly acidic, contains lysozyme
Protects ear canal from infection

Question 8

Describe flushing actions as an external defence.

Answer 8

Flushing action of body fluids
Helps keep free of pathogens

Question 9

What are the 4 main protective reflexes?

Answer 9

Sneezing
Coughing
Vomiting
Diarrhoea

Question 10

Describe Sneezing as a protective reflex

Answer 10

Triggered by irritation of nasal cavity
Expels dust, dirt, mucus, and pathogens from mouth (not as much from the nose, despite what you think you know!)

Question 11

Describe Coughing as a protective reflex

Answer 11

Irritation of lower respiratory tract
Air forced from lungs, taking mucus and pathogens up trachea and out

Question 12

Describe Vomiting as a protective reflex

Answer 12

Contraction of muscles of abdomen and diaphragm
Expels pathogens from stomach

Question 13

Describe Diarrhoea as a protective reflex

Answer 13

Irritation of intestinal wall causes fluid to accumulate in intestines, plus explosive contractions of smooth muscle in intestinal wall.

Question 14

What are 5 examples of assisting the body’s external defences?

Answer 14

Self-isolating when unwell.
Wearing a mask to prevent spread of respiratory disease when you are sick
Maintaining environmental hygiene – wiping surfaces, regular cleaning
Wearing condoms to prevent sexually transmitted disease
Mosquito nets to prevent mosquito-borne diseases eg malaria