Diffusion Flashcards – AQA GCSE Biology - Foundation (8461)

What two conditions allow a substance to diffuse across a cell membrane?

A concentration gradient exists, and the membrane permits the substance to pass.

What role does diffusion of gases and dissolved solutes play in organisms?

It helps organisms obtain substances they need and remove substances they produce.

In what direction does net diffusion occur across a cell membrane?

From higher to lower concentration, rather than in a direction determined by the cell.

How does the steepness of the concentration gradient affect diffusion?

A steeper gradient produces a greater net movement of particles from higher to lower concentration.

Why does a higher temperature increase the rate of diffusion?

Particles have more kinetic energy and move faster.

Why does a larger membrane surface area increase the rate of diffusion?

More particles can cross the membrane at the same time.

How does gas exchange occur between alveolar air and blood?

By diffusion across the alveolar and capillary walls.

In which directions do oxygen and carbon dioxide diffuse during alveolar gas exchange?

Oxygen: alveolar air → blood. Carbon dioxide: blood → alveolar air.

How do numerous alveoli help gas exchange?

They provide a large surface area for diffusion.

How does the thin alveolar epithelium help gas exchange?

It gives a short diffusion distance between air and blood.

What role does the moist alveolar surface play in gas exchange?

It allows gases to dissolve before diffusing.

How does a rich capillary supply help alveolar gas exchange?

It helps maintain concentration gradients.

How does ventilation help maintain concentration gradients in the alveoli?

It replenishes alveolar air.

How does an organism’s external surface area relative to its volume change as it gets larger?

It becomes smaller.

Why may exchange across the body surface alone fail to meet a larger organism’s internal cells’ needs?

There is less surface area relative to volume, and substances must travel farther to reach internal cells.

How can a thin or flattened body shape help an organism exchange substances?

It increases surface area relative to volume and shortens diffusion distances.

What feature of specialised exchange surfaces helps larger organisms exchange substances?

They have a large surface area.

What is the role of transport systems in exchange in larger organisms?

They move substances between exchange surfaces and cells throughout the body.