Movement of Substances Into and Out of Cells

Question 1

What is diffusion?

Answer 1

The net movement of particles down a concentration gradient (from a higher concentration to a lower concentration), which occurs as a result of the random movement of particles

Diffusion often occurs across partially permeable membranes

Question 2

What is osmosis?

Answer 2

The net movement of water molecules down a concentration gradient (from a higher concentration to a lower concentration) through a partially permeable membrane, such as the cell membrane

Question 3

What is active transport?

Answer 3

• The net movement of molecules and substances against a concentration gradient (from lower concentration to higher concentration
• It requires energy from cellular respiration, as molecules do not naturally move this way

Question 4

How does active transport happen and work?

Answer 4

Carrier proteins in the cell membrane pick up specific molecules and take them through the cell membrane up the concentration gradient

Question 5

How does size influence surface area to volume ratio?

Answer 5

The bigger the organism, the smaller the surface area to volume ratio will be

Question 6

How does surface area to volume ratio influence movement into and out of cells?

Answer 6

• The higher the surface area to volume ratio, the higher the rate of diffusion as there is more space for molecules to move across
• Cells adapted for diffusion will have a high surface area to volume ratio

Question 7

How does diffusion distance influence movement into and out of cells?

Answer 7

• The shorter the required diffusion distance, the faster the rate of diffusion will be
• Cells adapted for diffusion will have low diffusion distances like thin cell walls (for plants)

Question 8

How does temperature influence movement into and out of cells?

Answer 8

• The higher the temperature, the faster will molecules will move, meaning the rate of movement will be higher
• This is because more collisions against the cell membrane will be made due to their higher kinetic energy

Question 9

How does concentration gradient influence movement into and out of cells?

Answer 9

• The greater the difference in concentration on each side of the membrane, the faster movement across it will occur
• This is because more random collisions will occur on the side with a higher concentration

Question 10

Outline an investigation on osmosis and concentration gradient

Answer 10

• Put equal sized cylinders of potatoes in solutions with different sucrose concentrations
• Wait a few hours, then weigh them
• The amount that they lose or gain is influenced purely by water potential of outside to inside the potato, as the skin is semi-permeable
• So they could gain or lose weight, depending on the how much water they lose via osmosis affected by the water potential gradient changed by the concentration of sucrose solution

Question 11

Outline an investigation on diffusion and temperature

Answer 11

• Put two equally sized cubes of beetroot in test tubes of water
• Allow different temperatures for each test tube
• Wait 10 minutes, than record the colour of the water each beetroot is in
• The higher the temperature, the more beet-root coloured the water will be