Movement of substances into and out of Cells

Question 1

Define diffusion

Answer 1

The net movement of molecules from an
area of high concentration to an area of
low concentration down their
concentration gradient.

Question 2

How does temperature affect the rate of

diffusion?

Answer 2

As the temperature increases, so does
the rate of diffusion as the particles have
more kinetic energy and move faster.

Question 3

How does the concentration gradient

affect the rate of diffusion?

Answer 3

The greater the concentration gradient
(the difference between the two areas),
the faster the rate of diffusion.

Question 4

How does the surface area of the membrane affect the rate of diffusion?

Answer 4

As the surface area increases so does
the rate of diffusion as there is more
space for the particles to move through.

Question 5

Define osmosis

Answer 5

The net movement of water molecules from a high water potential to a low water potential down their water potential gradient across a partially permeable
membrane.

Question 6

Define active transport

Answer 6

The movement of molecules from a low concentration to a high concentration against their concentration gradient
using energy.

Question 7

Is diffusion an active or passive process?

Answer 7

Passive - no energy is required

Question 8

What is the general size of molecules that can diffuse across partially permeable membranes?

Answer 8

Small - oxygen, amino acids, glucose + water

but not starch or proteins

Question 9

Why can single celled organisms rely on diffusion?

Answer 9

• have a relatively large surface to volume ratio

- and low metabolic demands

Question 10

Why can’t multi celled organisms rely on diffusion?

Answer 10

• surface area to volume ratio too small

- many metabolic demands

Question 11

Adaptations of diffusion in humans

Answer 11

• alveoli in lungs
• villi in small intestine
• root hair cells in plants

Question 12

Is osmosis an active or passive process?

Answer 12

Passive - it does not require energy from respiration

Question 13

Define isotonic

Answer 13

If there is no net movement of a substance the solution can be described as isotonic

Question 14

Define hypertonic

Answer 14

If the concentration of sugar is higher in the external environment than in the internal, water moves out and the solution is said to be hypertonic to the cell

Question 15

Define hypotonic

Answer 15

If the concentration of sugar is lower in the external environment than in the internal, water moves into the cell and the solution is said to be hypotonic to the cell

Question 16

Define shrivelled

Answer 16

If the external solution is more concentrated (lower water potential), excess water will
LEAVE the cell causing it to become shrivelled.

Question 17

Define turgid

Answer 17

If the external solution is more dilute, water will move INTO the cell and into the vacuole,
causing it to swell, resulting in high pressure. The cell is described as turgid

Question 18

Define plasmolysed

Answer 18

If the external solution is less dilute, water will move OUT of the cell, and the cell will become soft. Eventually the cell membrane will move away from the cell wall, and the cell will die. This is called plasmolysis

Question 19

Define flaccid

Answer 19

If a plant cell is surrounded by a solution that contains a lower concentration of water molecules than the solution inside the plant cell, water will LEAVE the cell by osmosis and the plant cell will become flaccid

Question 20

Does active require energy and if so where does it get its energy from?

Answer 20

Yes - cellular respiration

Question 21

Active transport examples

Answer 21

• root hair cells take up water and minerals from the soil where they are usually in higher concentration in the plant cells than in the soil. This means that it is travelling against the concentration gradient

Question 22

Active transport concentration gradient

Answer 22

Low to high

Question 23

Describe a practical to investigate diffusion in non-living systems

Answer 23

1) Cut a 1cm3 cube of agar made of sodium hydroxide and phenolphthalein indicator
2) Place cube in solution of hydrochloric acid
3) Remove the cube and wash with water to stop further reaction
4) Cut the cube in half and measure the distance that the acid has caused agar to become
colourless from outside inwards
5) Repeat the experiment two more times and calculate the mean
6) Repeat with different concentrations of hydrochloric acid

Question 24

Describe a practical to investigate osmosis

Answer 24

1) Place different sucrose solutions including 0% for a control, in different boiling tubes
2) Dry potato strips on a paper towel and measure the masses
3) Place each potato strip into each sucrose solution for 20 minutes and record how the mass
changed
4) Repeat tests at each solution several times with potato strips of similar masses

Question 25

What are the main biologically important groups of inorganic molecule

Answer 25

• water
• oxygen
• nitrogen
• carbon dioxide