Defence: 1st Line
What is the body’s first line of defence against pathogens?
Skin and mucous membranes (physical and chemical barriers).
Which immune cells engulf and digest invading pathogens?
Phagocytes, such as macrophages and neutrophils.
A student moves from direct sunlight into shade. Which source of heat gain is reduced?
Radiation from the Sun.
What is the process of maintaining stable internal conditions called?
Homeostasis.
What is heat transfer through direct contact called?
Conduction.
What substance in tears helps destroy some bacteria?
Lysozyme, an enzyme that breaks down bacterial cell walls.
What is the body’s general response that can cause redness, warmth, swelling, and pain?
Inflammation
A person sits on cold tiles after exercising. Which heat-transfer mechanism cools the areas touching the floor?
Conduction
Which part of the brain helps regulate body temperature?
The hypothalamus.
What is heat transfer through the movement of air or water called?
Convection
How does mucus protect the respiratory system?
It traps pathogens and particles so they can be removed.
Why can a fever help the body fight an infection?
A controlled rise in body temperature can support immune responses and inhibit some pathogens.
Why might two students exercising in the same hot environment respond differently?
Differences in hydration, acclimatization, exertion, health, clothing, and cooling capacity affect their responses.
Why is sweating less effective on a very humid day?
Humid air slows evaporation, reducing evaporative cooling.
How does energy from the Sun reach and warm your skin?
Radiation.
A student gets a cut while playing football. Which defence has been broken?
The first line of defence: the skin barrier.
A splinter introduces bacteria beneath the skin. Why might the area become red and swollen?
Inflammation increases blood flow and helps immune cells reach the injured area.
A runner becomes dizzy, confused, and collapses in extreme heat. Why is this more serious than ordinary sweating?
Confusion and collapse suggest a potentially life-threatening heat illness, including possible heatstroke, requiring emergency medical attention.
How does negative feedback help regulate body temperature when a person becomes too hot?
The body detects rising temperature and activates responses such as sweating and increased skin blood flow to promote cooling.
You touch a metal railing that has been heated by the Sun. Identify the two heat-transfer mechanisms involved.
Radiation heats the railing; conduction transfers heat from the railing to your hand.
Why is intact skin more effective at preventing infection than an open wound?
Intact skin blocks entry; a wound bypasses the barrier, allowing pathogens into tissues.
Why is the second line of defence called nonspecific?
It responds broadly to threats rather than targeting one specific antigen.
A person exercises intensely in extreme heat and humidity while dehydrated. Explain how physical, chemical, and homeostatic limits can interact.
Heat gain and reduced evaporation cause overheating; dehydration reduces cooling and circulation; rising temperature can impair cellular and enzyme function, potentially causing organ failure.
Why can severe overheating affect both enzymes and organ function?
Excessive heat can disrupt protein function and cellular processes, while dehydration and circulatory strain impair oxygen and nutrient delivery.
A fan blows air over sweaty skin. Explain two mechanisms that can cool the body.
Convection removes heat when the air is cooler than the skin, and evaporation of sweat removes thermal energy.