2d: Movement of substances into and out of cells

Question 1

Define diffusion

Answer 1

The net movement (more particles moving in one direction than another) of molecules from an area of their high concentration to an area of their lower concentration.

Question 2

Define osmosis

Answer 2

The net movement of water molecules from a region of their high concentration to a region of their lower concentration across a partially permeable membrane.

Question 3

Define active transport

Answer 3

The transfer of molecules across a cell membrane, against their concentration gradient (from low to high) using energy from cell respiration.

Question 4

By what means can substances move into and out of cells?

Answer 4

Diffusion, Osmosis and Active Transport

Question 5

What does the term turgid mean?

Answer 5

When a plant cell is full of water, to the point of bursting; however the cell wall prevents it from bursting. This swollen cell now helps to support the plant’s overall structure.

Question 6

Outline the factors that affect the rate of movement of substances into and out of cells

Answer 6

Surface area to volume ratio - the rate of diffusion increases as surface area increases. However, since the volume of an organism increases faster than the surface area, larger organisms have smaller SA:V . Therefore small single-celled organisms can acquire most of what they need by simple diffusion, while larger organisms require specialised exchange surfaces.
Temperature - An increase in temperature means the kinetic energy of the molecules is higher and they are moving more rapidly. Therefore their movement across the membrane is also quicker.
Concentration Gradient - The greater the difference in concentration between the inside and outside of the cell, the greater the concentration gradient, and the faster the movement of substances occurs.