Diffusion and Osmosis

Question 1

What is diffusion?

Answer 1

• Diffusion is the net movement of particles in a gas or liquid from an area of high concentration to an area of low concentration, resulting from the random movement of the particles.
• This explains how molecules of water, oxygen and carbon dioxide can enter and leave cells through the cell membrane. If the plant cell is using up carbon dioxide, there’s a lower concentration of it inside the cell, so carbon dioxide outside will enter by diffusion.

Question 2

Leaves are adapted to increase the rate of diffusion of carbon dioxide and oxygen by having:

Answer 2

• (Usually) a large surface area
• Specialised openings called stomata, which are spaced out.
• Gaps between the spongy mesophyll cells

Question 3

The rate of diffusion is not a fixed quantity. The rate can be increased by having:

Answer 3

• A shorter distance for the molecules to travel
• A steeper concentration gradient (a greater difference in concentration between the two areas)
• A greater surface area for the molecules to diffuse from, or into.

Question 4

What does osmosis a type of?

Answer 4

Osmosis is a type of diffusion; it depends on the presence of a partially-permeable membrane that allows the passage of water molecules but not large molecules like glucose.

Question 5

What is osmosis?

Answer 5

Osmosis is the movement of water across a partially permeable membrane from area of high water concentration (a dilute solution) to an area of low water concentration (a concentrated solution).

Question 6

What is osmosis a consequence of?

Answer 6

Osmosis is a consequence of the random movement of water molecules, which is not restricted by a partially-permeable membrane. The net movement of water molecules will be from an area where there are many to one where there are few.

Question 7

How does the intake of water affect plant cells?

Answer 7

• The entry of water into plant cells increase the pressure pushing on the cell wall, which is rigid and not elastic. This turgor pressure supports the cell, stopping it, and the whole plant, from collapsing. When too much water leaves the cell, it loses this pressure and the plants wilt.
• A plant cell full of water is said to be turgid. When the cell loses water the cell contents shrink and becomes plasmolysed and the cell is called flaccid.

Question 8

How does the intake of water affect animal cells?

Answer 8

• Animal cells also reacts to Intake and loss of water due to osmosis. They will also shrink and collapse when they lose too much water, and swell up when too much water enters.
• Since animal cells lack a supporting cell wall, when too much water enters, they will swell up and burst (lysis). When too much water leaves an animal cell it shows crenation by shrinking into a scalloped shape.