Chapter 3: Movement Into & Out of Cells

Question 1

Define Diffusion [2]

Answer 1

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down the concentration gradient, as a result of their random movement.

Question 2

Where does the energy from diffusion come from? [1]

Answer 2

The energy from diffusion comes from the kinetic energy of random movement of molecules and ions.

Question 3

Examples of diffusion in cells [4]

Answer 3

Carbon Dioxide
Oxygen
Wastes / Urea
Glucose / Amino acids / Nutrients

Question 4

Factors affecting rate of diffusion [4+4]

Answer 4

Surface area: larger the surface area, higher the rate of diffusion
Temperature: higher the temperature, higher the rate of diffusion
Concentration gradient: steeper the gradient, higher the rate of diffusion
Diffusion distance: shorter the distance, higher the rate of diffusion

Question 5

Define Osmosis [2]

Answer 5

Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.

Question 6

Explain the process of dialysis tubing [4]

Answer 6

Diffusion is used to clean the blood through dialysis tubing. If the kidneys stop working, unwanted substances build up in the blood, some of them being toxic. To help remove these substances, the patient is attached to a dialysis machine. The blood from their vein flows into the machine. A liquid known as dialysis flows past his blood with a very thin membrane separating them. The toxic substances in his blood diffuse through the membrane into the dialysis fluid which flows away. The now clean blood flows back into their body.

Question 7

What are the 3 types of solutions [3+3]

Answer 7

Hypotonic: more water concentration than solute concentration
Isotonic: equal water and solute concentration
Hypertonic: less water concentration than solute concentration

Question 8

What happens to a plant cell when placed in a hypotonic solution? [3]

Answer 8

1. The plant cell has a lower water potential compared to the hypotonic solution
2. Water enters the cell by osmosis [endosmosis] down the water potential gradient across the partially permeable cell membrane
3. The plant cell becomes turgid

Question 9

What happens to a plant cell when placed in an isotonic solution? [3]

Answer 9

1. The water potential of the plant cell is equal to that of the isotonic solution
2. The net movement of water molecules by osmosis between the plant cell and the solution is zero
3. The plant cell is in dynamic equilibrium with the isotonic solution

Question 10

What happens to a plant cell when placed in a hypertonic solution? [3]

Answer 10

1. The plant cell has a higher water potential compared to the hypertonic solution.
2. Water leaves the cell by osmosis [exosmosis] down the water potential gradient across the partially permeable cell membrane
3. The plant cell becomes flaccid
4. The plant cell becomes flaccid and then plasmolyzed

Question 11

Define a turgid cell [4]

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

Define a flaccid cell [2]

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 [3]

Answer 13

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

Question 14

What happens when an animal cell is put in an hypotonic solution? [2]

Answer 14

1. In hypotonic solutions, there is a net movement of water from the solution into the body.
2. A cell placed into a hypotonic solution will swell and expand until it eventually burst

Question 15

What happens when an animal cell is put in an hypertonic solution? [2]

Answer 15

1. Concentrated solution outside the cell
2. More dilute solution inside the cell
3. Osmosis takes place and water diffuses out of the cell through the partially permeable membrane

Question 16

What happens when an animal cell is put in an isotonic solution? [1]

Answer 16

Nothing happens

Question 17

How is a plant cell supported? [1]

Answer 17

Plants are supported by the pressure of water inside the cells pressing outwards on the cell wall

Question 18

Define active transport [1]

Answer 18

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

Question 19

What is the importance of active transport [1]

Answer 19

A process for movement of molecules or ions
across membranes, including ion uptake by root
hairs

Question 20

How does active transport take place? [3]

Answer 20

1. Involves transport proteins which are located on the cell membrane
2. These proteins pick up ions from a region of lower concentration outside the cell and change shape, enabling the ions to be transported into the cell
3. ATP produced in aerobic respiration is required for this change in shape in the transport of proteins

Question 21

Describe how root hair cells are adapted for the absorption of ions [3]

Answer 21

Large surface area and thin cell walls. Many mitochondria for respiration to release energy required for active transport. Proteins for active transport take ions in the soil from lower concentration to the roots which have a higher concentration.

Question 22

What moves substances during active transport? [1]

Answer 22

Protein carriers move molecules or ions across a membrane during active transport