Chapter 2: Movement of substances

Question 1

Concentration Gradient

Answer 1

• difference in concentration between 2 regions

Question 2

Diffusion

Answer 2

• the net movement of particles from a region where they are of higher concentration to a region where they are of lower concentration, down a concentration gradient

Question 3

Factors that affect the rate of diffusion

Answer 3

1. Diffusion distance
2. Surface area-to-volume ratio
3. Concentration gradient

Question 4

Relationship between diffusion and concentration gradient

Answer 4

• the steeper the concentration gradient, the faster the rate of diffusion
• diffusion only stops when concentration of the substance is the same in both regions (dynamic equilibrium)
• diffusion cannot happen if pores of permeable membrane is smaller than size of particle

Question 5

Relationship between diffusion distance and diffusion

Answer 5

• diffusion distance is the distance through which a substance diffuses through
• the shorter the diffusion distance, lesser time is needed for the substance to travel, & hence the rate of diffusion is higher

Question 6

Relationship between surface area-to-volume ratio and diffusion

Answer 6

• the greater the surface area-to-volume ratio, the higher the rate of diffusion

Question 7

Osmosis

Answer 7

• the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

Question 8

Types of osmosis

Answer 8

1. Endomosis: Movement of water from surroundings into cell
2. Exomosis: movement of water out of the cells into the surroundings

Question 9

Water Potential

Answer 9

• the measure of the tendency of water molecules to move from one place to another
• a dilute solution has a higher water potential then a concentrated solution

Question 10

Types of membrane

Answer 10

1. Permeable: Allows all molecules to pass through it
2. Partially permeable: Only certain molecules can pass through it
3. Impermeable: Does not allow any molecules to pass through

Question 11

Types of solutions

Answer 11

1. Hypotonic: Low in concentration and high in water potential
2. Hypertonic: High in concentration and low in water potential
3. Isotonic: Water potential and concentration is the same in cell and environment

Question 12

Factors that affect osomosis

Answer 12

1. Water potential gradient
2. Distance over which water molecules need to move
3. Surface area-to-volume ratio

Question 13

What happens if plant cell is placed in solution with high water potential?

Answer 13

1. Cell sap has lower water potential then solution
2. Water molecules enter the cell through the partially permeable membrane via osmosis
3. The cell expands and swells and becomes turgid
4. As water molecules enter the cell, the vacuole increases in size & pushes the cytoplasm against the cell wall. The cell does not burst since it is protected by inelastic cell wall.

Question 14

What is turgor

Answer 14

The turgidity of cell with water is called turgor

Question 15

What is turgor pressure

Answer 15

The pressure exerted by water in vacuole

Question 16

What happens if animal cell is placed in solution with high water potential

Answer 16

1. Cell sap has lower water potential then solution
2. By osmosis, water molecules enter the cell through the partially permeable cell surface membrane
3. The cell swells and expands and bursts since it does not have a cell wall to protect it

Question 17

What happens if plant cell is placed in solution with low water potential

Answer 17

1. Cell sap has higher water potential than solution
2. Water molecules from vacuole and cytoplasm leave cell through partially permeable cell membrane
3. Cell decreases in size and becomes flaccid and limp
4. As cell loses water, vacuole decreases in size. Cytoplasm shrinks away from cell wall and the cell is said to be plasmolysed

Question 18

Plasmolysis

Answer 18

• the shrinkage of cytoplasm & cell membrane away from the cell wall
• the cell is said to be plasmolysed
• a plasmolysed cell can be restored to original state by placing in solution with higher water potential

Question 19

What happens if animal cell is placed in solution with low water potential

Answer 19

1. Cell sap has higher water potential than solution
2. Water molecules from vacuole and cytoplasm leave cell through partially permeable cell membrane
3. Cell shrinks and spikes appear on cell. This process is called crenation. An animal cell will become dehydrated and eventually die when placed in solution with lower water potential

Question 20

Why is turgor important in plants

Answer 20

• helps maintain the shape of the soft tissues in plants
• stems and leaves of non-woody and herbaceous plants are able to remain firm and erect due to turgor pressure within their cells
• when there is a higher rate of water loss by cells, they lose their turgidity and plant wilts
• movement of certain parts of plant is cause of turgor

Question 21

Why can’t cells be plasmolysed

Answer 21

• causes cells to become flaccid/limp. Cells will be killed if they remain plasmolysed for too long
• inability for roots to absorb water, tgt with continued evaporation of water from leaves causes plant to wilt. The plant will die unless sufficient water is added to dilute salt solution

Question 22

Active transport

Answer 22

• process whereby energy is used to move particles of a substance across a membrane against its concentration gradient, from a region of lower concentration to region of higher concentration
• only occurs in living cells since they respire
• requires cell membrane and energy from respiration