3. Movement Into and Out of Cells

Question 1

Describe Diffusion

Answer 1

The net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement

Question 2

Where is the source of energy in diffusion?

Answer 2

The energy for diffusion comes from the kinetic energy of random movement of molecules and ions (that they naturally have; allowing them to collide, spread out, and eventually distribute evenly)

Question 3

Which process is used for substances to move into and out of cells?

Answer 3

Some substances move into and out of cells by diffusion through the cell membrane which is a partially permeable membrane

Question 4

Describe the importance of diffusion of gases and solutes in living organisms

Question 5

State and describe the factors that affect Diffusion

Answer 5

1. Surface area (↑, D↑)
   - More space for particles to enter
2. Distance (↓, D↑)
   - A thick layer of cell membrane consists particles inside of it which slows down the particles that has to diffuse
3. Concentration gradient (↑, D↑)
   - On the side with the higher concentration, more random collisions against the membrane occurs
4. Temperature (↑, D↑)
   - As more energy is provided, results in more collisions against the cell membrane

Question 6

Describe Osmosis

Answer 6

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 7

How does water molecules diffuse through partially permeable membrane?

Answer 7

By osmosis

Question 8

How does water move into and out of cells?

Answer 8

• By osmosis through the cell membrane (which is partially permeable, meaning it allows small molecules (like water) through but not larger molecules (like solute molecules))

Question 9

Investigate osmosis using materials such as dialysis tubing

experiment

Answer 9

1. Fill a section of dialysis tubing with concentrated sucrose solution
2. Suspend the tubing in a boiling tube of water for a set period of time
3. Note whether the water level outside the tubing decreases as water moves into the tubing via osmosis

Question 10

Describe the effects on plant tissues of immersing them in solutions of different concentrations

Answer 10

If the plant tissue gains mass:
- Net osmosis into the plant tissue from the solution

If plant tissue loses mass:
- Net osmosis out of the plant tissue and to the solution

If there is no overall change in mass:
- No net osmosis as the concentration in both the plant tissue and the solution surrounding it must be equal

Question 11

Explain the effects on plant cells of immersing them in solutions of different concentrations by using the terms: turgid, turgor pressure, plasmolysis, flaccid

Answer 11

1. During osmosis water molecules push the cell membrane against the cell wall, increasing the turgor pressure in the cells which makes them turgid
2. When plant cells are placed in a concentrated solution water molecules will move out of the plant
3. If plant cells become flaccid it can negatively affect the plant’s ability to support itself
4. If looked at underneath the microscope, the plant cells might be plasmolyse

Question 12

Explain the importance of water potential and osmosis in the uptake of water in plants

Answer 12

1. Water moves by osmosis into the plant’s roots through the root hair cell
2. Absorption of water by guard cells opens the stomata for gas exchange
   - (Structure of) plants are supported by the pressure of water inside the cells pressing outwards on the cell wall
   - Osmosis provides water in processes such as photosynthesis and transpiration in plants

Question 13

Explain the importance of water potential and osmosis in loss of water by organisms

Answer 13

• As animal cells do not have a supporting cell wall and vacuole, the results on the cell are more severe
• If an animal cell is placed into a strong sugar solution, it will lose water by osmosis and become crenated (shrivelled up)
• If an animal cell is placed into distilled water, it will gain water by osmosis and will continue to do so until the cell membrane bursts

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 (i.e. against a concentration gradient), using energy from aerobic respiration (synthesised by mitochondria)

Question 15

Explain the importance of active transport

process for movement of molecules or ions across membranes e.g.

Answer 15

Its a process for movement of molecules or ions across membranes, including:
1) Ion uptake by root hairs
2) Uptake of glucose by villi of the small intestine and by kidney tubules in the nephron

Question 16

Why do protein carriers move molecules or ions across a membrane during active transport?

Answer 16

As the molecules are unable to move by themselves against the concentration gradient without support from protein carriers

Question 17

How do protein carriers move molecules or ions across a membrane during active transport?

Answer 17

1. Combines with carrier protein molecules in the cell membrane
2. Transports substances across membranes (using energy from respiration to change shape and move the substance)
3. Substance released into cell

Question 18

State the differences between Diffusion and Active Transport

Answer 18

1. Active transport requires energy input unlike diffusion
2. Diffusion follows the concentration gradient (high → low) however active transport goes against it (low → high)
3. Active transport needs support from carrier proteins in order to move molecules or ions across a membrane