Transport in Cells

Diffusion

The movement of molecules from a region of higher concentration to a region of lower concentration, down the concentration gradient.

Resolution

The degree at which a piece of equipment can measure to.

Systematic error

A consistent repeated error.

Random error

Unpredictable errors that are not repeated.

Osmosis

The passive movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane.

High water potential

Low concentration of solutes.

Low water potential

High concentration of solutes.

Hypotonic

High water potential

Hypertonic

Low water potential

What happens to the cell mass when the cell has a LWP?

The cell mass will increase because the water is moving into the cell via osmosis.

What happens to the cell mass when the cell has a HWP?

The cell mass will decrease because the water is moving out of the cell via osmosis.

Turgid

Has a larger mass than it did previously.

Flaccid

Has a lower mass than it did previously, is de-hydrated

Plasmolysed

Extremely de-hydrated

What will happen to the mass of a piece of potato, when placed in a strong sugar concentrated solution and left for 24 hours?

The solution is hypertonic to the cell. Therefore, the water inside the potato will move out of the cell via osmosis. The mass of the potato will decrease, becoming flaccid.

Percentage change

(Change in mass/original)*100

Active transport

Substances that are absorbed against the concentration gradient, from low to high concentration.

What does active transport require?

It requires energy.

High SA: Volume ratio

= efficient transfers of substances

Low SA: Volume ratio

= inefficient transfers of substances

Why is SA:V ratio important?

In cells, gases need to diffuse into and out of the cell, if a cell has a large surface area compared to its volume, it will be very efficient when diffusing gases.