B4d

Question 1

What is diffusion?

Answer 1

• net movement of particles from an area of higher concentration to an area of lower concentration
• occurs in both liquids and gases, as individual particles in the substances are free to move about randomly
• the simplest type is when gases diffuse through each other, like air and perfume

Question 2

How does diffuse occur through cell membranes?

Answer 2

• only very small molecules can diffuse through the cell membrane, e.g. simple sugars, water or ions (big molecules like starch and proteins can’t pass through)
• the process is the same as diffusion in the air
• the particles move randomly so the movement can go both ways, but if there are a lot more particles on one side of the membrane, the overall movement will be from that side

Question 3

What does the rate of diffuse depend on?

Answer 3

• distance: substances diffuse more quickly when there is less distance to travel
• concentration gradient (difference): substances diffuse faster if there is a big difference in concentration. Lots more particles on one side, means there are more to move across
• surface area: the more available for molecules to move across, the faster they can get from one side to the other

Question 4

How do plants carry out both photosynthesis and respiration?

Answer 4

• photosynthesis only happens during the day
• plants respire all the time
• during the day plants make more oxygen by photosynthesis than they use in respiration
• so in daylight, they release oxygen and take in carbon dioxide
• at night plants only respire, so they take in oxygen and release carbon dioxide

Question 5

What does diffusion do in photosynthesis?

Answer 5

• during photosynthesis there is hardly any carbon dioxide left inside the leaf
• more carbon dioxide move into the leaf by diffusion (from an area of high concentration to an area of low concentration)
• at the same time oxygen is being made as a waste product
• some is used in respiration and the rest diffuse out of the leaf (from an area of high concentration to low)

Question 6

What does diffusion do in respiration of a plant?

Answer 6

• carbon dioxide diffuses out

- oxygen diffuses in