1. Cell Biology (transport of substances & required practical 3: potato practical)

Question 1

What is diffusion?

Answer 1

Diffusion is the net movement of particles from an area of high concentration to low concentration.

Question 2

When will diffusion stop?

Answer 2

Diffusion will stop when equilibrium has been reached.

Question 3

What does going along the concentration gradient mean?

Answer 3

It means that particles spread from an area of high concentration to low concentration.

Question 4

What is equilibrium?

Answer 4

When the same amount of particles are on both sides of the room

Question 5

What factors affect the rate of diffusion?

Answer 5

1. Temperature - the particles gain more kinetic energy so they move at a faster rate.
2. The concentration gradient - the steeper the gradient the faster the rate of diffusion
3. The surface area to volume ratio - diffusion happens quicker in an object with a larger SA to smaller volume

Question 6

What can make the process of diffusion quicker?

Answer 6

The smaller the length of diffusion pathway, the faster the rate of diffusion

Question 7

What is the equation for diffusion?

Answer 7

Rate of diffusion = surface area x concentration gradient / length of diffusion pathway

Question 8

What is Osmosis?

Answer 8

Osmosis is the general net movement of water particles from a high concentration to a low concentration across a partially permeable membrane.

Question 9

What is a concentration gradient?

Answer 9

The difference in concentration between 2 sets of things

Question 10

What is a partially permeable membrane?

Answer 10

A material which will only allow certain things through

Question 11

What is the word and symbol for water potential?

Answer 11

Water potential = phi (a Greek letter)

The symbol looks like a trident. Or a ‘w’ with a line in the middle.

Question 12

How does diffusion, osmosis and active transport move on the concentration gradient?

Answer 12

Diffusion = along (down) the concentration gradient, from high conc to low conc.
Osmosis = along (down) the concentration gradient, from high conc to low conc.
Active transport = against (up) the concentration gradient, from low conc to high conc, requiring more energy.

Question 13

What is Osmosis?

Answer 13

Osmosis is the net movement of water particles from a high concentration to a low concentration across a partially permeable membrane.

Question 14

What is Active transport?

Answer 14

Active transport is the movement of particles from a low concentration to a high concentration, against the concentration gradient, using energy

Question 15

Where is active transport used?

Answer 15

1. Root hair cells use active transport to absorb minerals and ions from the soil
2. The small intestine absorbs nutrients via active transport

Question 16

Can osmosis also be refferred to as diffusion?

Answer 16

Yes, it’s just the diffusion of water molecules

Question 17

What are the steps for the potato practical?

Answer 17

1. Cut up the potato into identical cylinders and get some beakers.
2. One beaker should have distilled water and the other beakers should be concentrated with sugar going up until 1mol/dm cubed.
3. Measure the initial mass of each potato cylinder, record it, and place potatoes in the beakers.
4. After 24hrs take them out and gently dry them to remove excess water and then measure mass
5. potato that has increased in mass has drawn water in and potato that has decreased in mass has drawn water out.
6. repeat the experiment 3 times and calculate the mean and percentage change.

Question 18

What happened if a potato’s mass increased?

Answer 18

Water was drawn into the potato by osmosis

Question 19

What happened if the potato’s mass decreased?

Answer 19

Water was drawn out of the potato by osmosis

Question 20

What is the IV, DV and CV of this experiment?

Answer 20

IV - concentration of solutions in each beaker
DV - mass
CV - the volume of the solutions

Question 21

What would you expect to happen to the potato’s mass in a concentrated solution?

Answer 21

• The potato’s mass to decrease
• Because there is more water in the potato then in the solution

Question 22

What would you expect to happen to the potato’s mass in pure water?

Answer 22

• The mass to increase
• Because there is more water outside the potato then inside

Question 23

What is this practical observing?

Answer 23

How sugar solutions effect plant tissue

Question 24

Where is diffusion said to move?

Answer 24

down the concentration gradient