Diffusion Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Higher

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.

What does the small intestine absorb into the body?

Soluble products of digestion.

How do villi and microvilli adapt the small intestine for absorption?

Villi line the small intestine, and microvilli cover their cells, providing a large surface area for absorption.

How does the epithelial layer of a villus help absorption?

It is thin, giving substances a short distance to cross.

How does the rich capillary supply of a villus help maintain concentration gradients for diffusion?

Blood carries absorbed substances away, helping maintain the gradients.

In which directions do oxygen and carbon dioxide diffuse across fish gills?

Oxygen diffuses from water into blood; carbon dioxide diffuses from blood into water.

How do gill filaments provide a large surface area for gas exchange?

They bear many lamellae.

How do thin gill exchange surfaces aid gas exchange?

They give gases a short diffusion path.

How does a rich blood supply help maintain concentration gradients at fish gills?

It carries oxygen away and brings carbon dioxide to the gills.

What is the role of water flow over fish gills?

It ventilates the exchange surface.

How does a root hair cell’s long, thin projection aid uptake from the soil?

It increases the surface area in contact with the soil.

How does a root hair cell’s thin cell wall aid uptake?

It provides a short path for uptake.

By what process does water enter root hair cells from the soil?

Osmosis.

How can root hair cells take up mineral ions against a concentration gradient?

By active transport.

What route do gases take between the air and mesophyll cells in a leaf?

Through stomata and internal air spaces to or from the moist mesophyll cell surfaces.

How does a broad leaf aid gas exchange?

It provides a large surface area.

How does a thin leaf aid gas exchange?

It gives gases a short diffusion path.

During photosynthesis, which gases diffuse into and out of a leaf?

Carbon dioxide diffuses in; oxygen diffuses out.

What controls the opening of stomata?

Guard cells.

How can water vapour leave a leaf?

Through its stomata.