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

How does a single-celled organism exchange gases with its surroundings?

By diffusion directly across its cell surface membrane.

In which directions do oxygen and carbon dioxide diffuse in a single-celled organism when their concentration gradients favour exchange?

Oxygen diffuses into the cell; carbon dioxide diffuses out.

What two features allow gas exchange across a single-celled organism’s surface to meet its needs without a specialised system?

A large surface area relative to volume and short diffusion distances due to its small size.

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 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 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 do villi and microvilli aid absorption in the small intestine?

They provide a large surface area for absorption.

How does the thickness of the small intestine’s surface epithelium aid absorption?

It is one cell thick, giving substances a short distance to cross.

How does the capillary supply of a villus aid absorption?

It carries absorbed substances away, helping maintain concentration gradients.

What is the role of lacteals in intestinal villi?

They absorb products of fat digestion.

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

They bear many lamellae.

How do lamellae provide a short diffusion path?

They are thin.

Where do water and blood flow in the gills?

Water flows over the lamellae; blood flows through their capillaries.

In which directions do oxygen and carbon dioxide diffuse at the gills?

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

What maintains water flow over the gills?

Ventilation.

What is the role of the blood supply in gas exchange at the gills?

It carries gases to and from the gills.

How does the direction of blood flow relative to water flow help oxygen exchange at the gills?

They flow in opposite directions, helping maintain an oxygen concentration gradient along the lamellae.

How do root hair cell projections help exchange with the soil?

They provide a large surface area for exchange.

How do thin root hair cell walls help substances enter the cell?

They provide a short path into the cell.

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

Osmosis.

How can root hair cells absorb mineral ions when their concentration is lower in the soil than in the cells?

By active transport.

Where do water and mineral ions go after being absorbed by roots?

They move through the root to the plant’s transport tissues.

How do carbon dioxide and oxygen move during gas exchange in a leaf?

Carbon dioxide diffuses through stomatal pores and air spaces to photosynthesising cells; oxygen can diffuse out.

How does a broad leaf help gas exchange?

It provides a large surface area.

How does a leaf’s thin structure help gas exchange?

It gives gases a short diffusion path.

How do air spaces within a leaf help gas exchange?

They expose a large area of moist cell surfaces to gases, allowing diffusion between the air and cells.

What controls the opening and closing of stomata?

Guard cells.