Diffusion and Osmosis

Question 1

Define Diffusion

Answer 1

Diffusion is the process by which molecules in a fluid spread from areas of high concentration to areas of low concentration down a concentration gradient, as a result of their random movement

Question 2

Examples of diffusion in cells

Answer 2

1. CO2
2. O2
3. Waste/Urea
4. Glucose/Amino Acids/Nutrients

Question 3

Rate of Diffusion based on -

1. Temperature
2. Diffusion Distance
3. Concentration Gradient
4. Surface Area

Answer 3

1. The higher the temperature, the more kinetic energy of diffusing molecules, the faster the rate of
   diffusion
2. The shorter the diffusion distance, the faster rate of diffusion
3. The steeper the concentration gradient, the faster the diffusion
4. The larger the surface area available for diffusion, the faster the rate of diffusion

Question 4

Define Osmosis

Answer 4

Diffusion of water molecules from a region of high water potential to a region of low water potential, through a partially permeable membrane

Question 5

Animal Cell in an Isotonic Solution

Answer 5

1. An isotonic solution has the same water potential as the cell
2. The cell remains the same size
3. The net movement of water molecules by osmosis between the animal cell and the solution is 0
4. The animal cell is in dynamic equilibrium with the isotonic solution

Question 6

Animal Cell in a Hypotonic Solution

Answer 6

1. A hypotonic solution has a higher water potential than the cell
2. Water moves from the solution into the cell, down the water potential gradient, by osmosis through the semi permeable cell membrane
3. The volume of the cytoplasm will increase
4. The cell will swell up and may burst (cytolysis)

Question 7

Animal Cell in a Hypertonic Solution

Answer 7

1. A hypertonic solution has a lower water potential than the cell
2. Water moves from the cell into the solution, down the water potential gradient, by osmosis through the semi permeable cell membrane
3. The volume of the cytoplasm will decrease
4. The cell shrinks and is plasmolyzed.

Question 8

Plant Cell in an Isotonic Solution

Answer 8

1. An isotonic solution has the same water potential as the cell
2. The cell remains the same size
3. The net movement of water molecules by osmosis between the plant cell and the solution is 0
4. The plant cell is in dynamic equilibrium with the isotonic solution

Question 9

Plant Cell in a Hypotonic Solution

Answer 9

1. A hypotonic solution has a higher water potential than the cell
2. Water moves from the solution into the cell, down the water potential gradient, by osmosis through the semi permeable cell membrane
3. The volume of the cytoplasm will increase
4. The plant cell becomes turgid

Question 10

Plant Cell in a Hypertonic Solution

Answer 10

1. A hypertonic solution has a lower water potential than the cell
2. Water moves from the cell into the solution, down the water potential gradient, by osmosis through the semi permeable cell membrane
3. The volume of the cytoplasm will decrease
4. The plant cell becomes flaccid and then plasmolyzed.

Question 11

What is a Turgid Cell

Answer 11

1. Cytoplasm increases in volume and presses out
   against the cell membrane
2. Cell wall resists and pushes back (prevents cell from
   bursting)
3. Cell is swollen and called turgid
4. Turgid cells help plants to stay erect.

Question 12

What is a Flaccid Cell

Answer 12

1. Cytoplasm loses water and stops pushing against the
   cell wall
2. Flaccid cells cause wilting

Question 13

What is a Plasmolyzed Cell

Answer 13

1. Cytoplasm and vacuole completely shrunk
2. Cell membrane tears/peels away from cell wall
3. Cell membrane is damaged – this may destroy the cell

Question 14

Define Active Transport

Answer 14

The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Question 15

Describe the Process of Active Transport

Answer 15

1. Active transport involves transport proteins located on the cell membrane
2. These proteins pick up ions from a region of lower concentration outside the cell and then change shape which enables these ions to be transported into the cell
3. ATP (Adenosine Triphosphate) produced in aerobic respiration is required for this change of shape in the transport proteins

Question 16

Give Examples of Active Transport

Answer 16

1. Uptake of nitrates by root hair cells from the soil
2. Glucose is actively transported from the lumen of the small intestine into the cells of the villi
3. Active transport of glucose out of kidney tubules into blood capillaries