Diffusion

Question 1

What is diffusion?

Answer 1

The movement of substances in and out of cells across cell membranes
The spreading out of particles of any substance in solution or gas resulting in a net movement from an area of higher concentration to an area of lower concentration

Question 2

What is the most significant forms of diffusion in the body

Answer 2

1. Oxygen And carbon dioxide in the gas exchange - the oxygen moves from the air in the lungs into red blood cells then down concentration gradient into cells, carbon dioxide moves from cells into red blood cells and into air in lungs and out - gas exchange
2. Waste products like urea from cells move into blood plasma for excretion in the kidney
3. Simple sugars like glucose

Question 3

What factors affect rate of diffusion?

Answer 3

Difference in concentration - concentration gradient
Temperature - higher = quicker
Surface area of membrane - single cell organism bias high ration of surface area to volume, allowing movement in and out of cells
Size of particles - smaller particles can move faster

Question 4

How do multi cellular organisms work?

Answer 4

The surfaces and organ systems are specialised for exchanging materials
Small intestine
Lungs
Gills
Roots and leaves
All adapted together to exchange material

Question 5

How is the effectiveness of the exchange surface is increased by?

Answer 5

Larger surface area
A thin membrane to provide short diffusion path
In animals having an efficient blood supply
In animals for gas exchange being ventilated

Question 6

How does diffusion work?

Answer 6

It takes place because of random movement of particles

The motion of particles causes to them to bump into each other and this moves them around

Question 7

Explain how diffusion works in nerve impulses?

Answer 7

1. A synapse is a junction between two neurones across which electrical signals must pass
2. Neurotransmitter molecules diffuse towards neurotransmitter receptors

Question 8

Explain diffusion in the placenta?

Answer 8

Placenta develops the uterus during pregnancy
Umbilical cord connects placenta to the foetus
Blood passes to mother from placenta which is high in CO2 and waste but low in O2 and nutrients
Placental villi increase surface area for diffusion
Blood passes from mother high in O2 and nutrients and low in CO2 and waste
Placenta cannot be stopped by harmful substances like alcohol and some viruses

Question 9

How does cell size affect rate of diffusion and why?

Answer 9

Smaller cells means quicker diffusion because

1. Greater surface area to volume ratio
2. Shorter diffusion distance
3. Maybe thinner cell walls than larger cells