En anglais

Keeping the gradient steep for every breather

Science · Organisms & Life Processes · ages 16-18

Name ______________________ Date ____________

Which sequence explains airflow into mammalian lungs during inhalation?
- Lungs expand, lung pressure falls, and air enters
- Lungs expand, lung pressure rises, and air enters
- Lungs contract, lung pressure falls, and air enters
What is ventilation's main contribution to gas exchange?
- Renewing air or water to maintain gas gradients
- Making every exchange barrier thicker during use
- Reducing the exchange area available to both gases
During quiet exhalation, air leaves because lung pressure is lower than atmospheric pressure.
Circle one: True False
Why can countercurrent flow extract more oxygen than parallel flow in an otherwise comparable fish-gill model?
- It keeps blood still while water moves along the lamella
- It lets water and blood mix directly inside the lamella
- It maintains an uptake gradient along the lamella
Why do lungs with a large exchange area still need ventilation?
- A large area prevents gases crossing until air is renewed
- Without renewal, gas gradients fall as exchange proceeds
- A large area makes barrier thickness increase unless air moves
How can many active insects increase airflow through their tracheal system?
- Body movements create pressure changes that move air
- Blood pumps air through every branching tracheal tube
- Open spiracles drive bulk airflow even when pressures are equal
At one point on a gill lamella, water has oxygen partial pressure 6 and adjacent blood has 4, in matching units. This local gradient favours oxygen entering blood.
Circle one: True False
At a breathing pause with open airways, lung and atmospheric total pressures are equal. Oxygen partial pressure is still higher in alveolar air than in blood. A student says both airflow and oxygen diffusion must stop. Which correction fits?
- Both continue because the oxygen gradient also drives bulk airflow
- Both stop because equal total pressures remove every gas gradient
- Bulk airflow stops; oxygen can still diffuse into blood

Answer key

For grown-ups. Fold this page away before handing over the rest.

Keeping the gradient steep for every breather W1-mt_Thd06O06Vr-s1

Lungs expand, lung pressure falls, and air enters · Expansion lowers lung pressure below atmospheric pressure. Air then flows into the lungs.
Renewing air or water to maintain gas gradients · Renewing the medium helps maintain gradients as oxygen enters the animal and carbon dioxide leaves it.
False · During outward airflow, lung pressure is above atmospheric pressure. Air flows from higher to lower total pressure.
It maintains an uptake gradient along the lamella · Opposite flows maintain favourable local oxygen partial-pressure differences. In parallel flow, the partial pressures approach each other and the gradient declines.
Without renewal, gas gradients fall as exchange proceeds · Area alone cannot maintain gradients. Oxygen uptake and carbon dioxide release alter nearby air unless it is renewed.
Body movements create pressure changes that move air · Body movements compress and expand parts of the tracheal system, producing pressure differences. Open spiracles permit airflow but do not drive it when pressures are equal.
True · Water has higher oxygen partial pressure than adjacent blood, so net oxygen diffusion at this point is into blood.
Bulk airflow stops; oxygen can still diffuse into blood · Equal total pressures remove the driving difference for bulk airflow. The stated oxygen partial-pressure difference still favours diffusion into blood.