Topic 2 Movement of Substances (from 2.15)

Question 1

What is diffusion?

Answer 1

• net movement of particles down a concentration gradient, from an area of high to low concentration
• occurs until concentrations are equal

Question 2

By what process do oxygen molecules move into a cell?

Answer 2

Diffusion

• conc of oxygen molecules greater outside cell than inside
• diffuse into cell

Question 3

By what process does carbon dioxide move into the leaf?

Answer 3

Diffusion

• carbon dioxide diffuses into the leaf via stoma and oxygen diffuses out

Question 4

By what process does oxygen move from lungs to bloodstream?

Answer 4

Diffusion

Carbon dioxide diffuses out of blood stream

Question 5

What are the factors affecting the rate of diffusion?

Answer 5

1) increasing surface area to volume ratio (more area for substances to travel across)
2) decreasing diffusion pathway (less distance for substances to travel)
3) increasing concentration gradient (greater concentration difference in either side of a membrane)
4) increasing temp (particles gain more kinetic energy and move faster)

Question 6

What is active transport?

Answer 6

Movement of substances from area of low concentration outside a cell to high concentration inside cell

• using energy

Question 7

How do mineral ions move from the soil into a root hair cell?

Answer 7

Via active transport

Move from low concentration to high concentration

Question 8

What is osmosis?

Answer 8

Movement of water molecules from region of HIGH WATER POTENTIAL to LOW WATER POTENTIAL across a partially permeable membrane

Question 9

What is a partially/semi permeable membrane?

Answer 9

• contains tiny holes which only allow small soluble substances to pass through freely

Examples of small molecules:
OXYGEN, CARBON DIOXIDE, WATER MOLECULES

Large insoluble molecules (GLUCOSE, SALT) cannot diffuse across + have to be carried across membrane by carrier proteins (these need energy)

Question 10

What is the water potential of pure water?

Answer 10

0

It is the highest water potential you can get, anything that is not pure water is lower

Question 11

What type of cell wall are plants surrounded by?

Answer 11

• strong cellulose cell wall
• outer structure keeps shape of cell
• can resist changes of pressure inside cell
• water can move in and out via osmosis

Question 12

What has happened when a cell is turgid?

Answer 12

1. Higher water potential outside cell
2. Higher water potential outside cell compared to water potential inside cell
3. Cell absorbs water via osmosis
4. Cell swells up + cytoplasm pushes against cell wall -> internal pressure = turgid
5. Plant is upright

Question 13

What has happened if the cell is flaccid?

Answer 13

1. Where water potential = same inside + out

2. Cell membrane has slightly come away from cell wall

Question 14

What has happened if the cell is plasmolyzed?

Answer 14

1. Higher water potential inside cell
2. Lower water potential outside cell
3. Cell loses water via osmosis
4. Cell membrane moves away from cell wall

(Plant wilts and dies)

Question 15

What happens when animal cells are placed in distilled water and why?

Answer 15

• do not have cell wall
• will gain water by osmosis
• swell and burst

Question 16

What happens when animal cells are in a solution with lower water potential than them?

Answer 16

• lose water by osmosis
• become crenated (shrivelled up)
• don’t have a cell wall to keep structure

Question 17

How would you investigate the effects of osmosis on potato tissue?

Answer 17

C. The concentration of sucrose solutions, between 0, 0.2, 0.4, 0.6, 0.8, 1.0 moles

O. Use a cork borer to cut 5 potato cylinders, from potatoes that are same type and age, trim so that all are same length with scalpel, blot them to remove excess water (use same method each time)

R. Repeat the experiment at least three times at each concentration and find an average for reliability

M. Measure and record the mass of each cylinder with a balance before placing in a tube and covering with sucrose solution, place a bung over each tube,then after 40 minutes, blot the chips to remove excess water and re weigh

M. Calculate the percentage change in mass for each potato chip and calculate mean percentage change

Question 18

What are the limitations of potato experiment?

Answer 18

• slight differences in dimensions of chips - multiple potato chips at each concentration and find an average
• test smaller intervals concentrations around point line crosses the x axis so that value where concentration is equal inside and outside cell is more exact

Question 19

How would you investigate the process of osmosis in a non living system?

Answer 19

1. Tie one end of a visking tube with piece of string
2. Pour sucrose solution into visking tube
3. Insert capillary tube into one end of visking tubing .
4. Mark initial water level in visking tubing
5. Use clamp stand to fix position of tube, and place visking tubing into a beaker of distilled water
6. Leave for half an hour
7. Notice the difference in solution level in the visking tube

Question 20

What is the result in the visking tube practical?

Answer 20

The solution moves up the tube

• > water moves via osmosis from high potential outside tube to low potential inside tube (visking tubing has small holes like pp membrane)
• greater volume of water therefore dye rises up tube

Question 21

Why didn’t the sucrose solution move out of the visking tubing into the beaker of water/

Answer 21

• sucrose molecules too big

Pp membrane = visking tubing