Diffusion

Question 1

What are the 3 different ways ions and molecules pass through the cell membrane?

Answer 1

Diffusion
Carrier mediated transport
Vesicular transport

Question 2

What is passive transport?

Answer 2

transport that occurs without the input of energy from the cell

Question 3

Give examples of a passive process

Answer 3

Facilitated diffusion, osmosis and diffusion

Question 4

What are active processes?

Answer 4

Transport that uses energy from the cell is needed to for the transportation to occur

Question 5

Give examples of an active process

Answer 5

Vesicular transport

Active transport

Question 6

What is diffusion?

Answer 6

The passive movement of molecules or particles from a region of high concentration to a region of low concentration, to reach equilibrium over the available space

Question 7

Can substances soluble in lipids (eg. Alcohol, steroids and fatty acids) diffuse through a membrane?

Answer 7

Yes they can through the lipid part of the membrane. Oxygen and CO2 can also diffuse through.

Question 8

How do water soluble substances/molecules enter or leave the cell, through diffusion?

Answer 8

They can go through a membrane channel if they are small enough to fit.

Eg. Water, sodium, calcium, chloride ions etc…

Glucose is too large

Question 9

What is osmosis?

Answer 9

Passive movement of water through a selectively semi-permeable membrane, from a region of high water concentration (low solute) to an region of low water concentration (high solute), to reach equilibrium.

Question 10

What is carrier mediated transport?

Answer 10

Molecules being transported through a carrier, like enzymes they are specific so they only bind to a specific molecule and they get saturated, increasing the concentration doesn’t make it faster

Question 11

What are two types of carrier mediated transport?

Answer 11

Facilitated diffusion

Active transport

Question 12

Describe what occurs in facilitated diffusion through a carrier protein

Answer 12

For example:
Glucose attaches to a binding site on the carrier, the carrier changes shape, and the molecule is released on the other side of the membranes.

Question 13

Describe the process of active transport in a carrier mediated transporter?

Answer 13

Requires ATP to act as a ‘credit card’ to transport molecules against the concentration gradient. The molecule ‘pays’ the protein by giving it ‘ATP money’ on which then it is allowed passage out of the cell.

Question 14

Describe the process of facilitated diffusion through a channel protein

Answer 14

They form narrow passageways through which small ions can diffuse through rapidly from a high ion concentration to a lower ion concentration.

Only specific ions of a specific shape and size can pass through, a particular channel.

Question 15

What is vesicular transport?

Answer 15

Movement of substances across the cell membrane in vesicles

Question 16

What is endocytosis in vesicular transport?

Answer 16

Taking liquids or solids into the cell

Question 17

What is pinocytosis?

Answer 17

Cell drinking

Vesicles contains liquid particles

Question 18

What is phagocytosis?

Answer 18

Cell eating

Vesicles contains solid particles

Question 19

How does endocytosis occur?

Answer 19

The cell membrane folds around a droplet of liquid or solid particle until the droplet is completely enclosed. The vesicles formed then pinches off and is suspended in the cells cytoplasm.

Question 20

What is exocytosis?

Answer 20

Contents inside the vesicle, in the cell are passed OUT of the cell

Question 21

How does exocytosis occur?

Answer 21

Vesicles in the cell migrate to the cell membrane and fuses with it where it will then ‘expel’ its contents into the extracellular fluid

Question 22

Explain diffusion into the cell

Answer 22

Before diffusion, high concentration of water molecules are outside the cell than inside where a low concentration is.

After diffusion, concentration of water molecules is the same outside and inside the cell

Question 23

What does osmosis do to the cell?

Answer 23

Concentration of the solution that surrounds a cell will affect the state of the cell

Question 24

What are the three possible concentrations of solution during osmosis?

Answer 24

Isotonic
Hypertonic
Hypotonic

Question 25

What is an isotonic solution?

Answer 25

A solution in the extracellular fluid has the same concentration than to the intracellular fluid.

Question 26

What happens to the cell when it is in an isotonic solution?

Answer 26

There is no change to the cell size.

The amount of water transported into the cell equal to the amount of water transported out the cell

Question 27

What is a hypertonic solution?

Answer 27

A solution of high concentration of water in the intracellular fluid then the extracellular

Intracellular contains dilute solution of salt compared to a concentration solution of salt outside

Eg. Cell placed in salt water

Question 28

What occurs to an animal cell when placed into a hypertonic solution?

Answer 28

Water moves out of the cell as the cell has more concentration of water than the extracellular, as of this the cell shrinks or crenate.

Question 29

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

Answer 29

Water will leave the cell, as the cell contains a higher concentration of water than the extracellular fluid because of this the cytoplasm shrinks and plasmoyse, and the cell becomes flaccid.

Question 30

What is a hypotonic solution?

Answer 30

A solution of low concentration of water in the intracellular than the extracellular.

Water moves from the more diluted solution of salt in the extracellular into the more concentrated solution of salt in the intracellular

Eg. Cell placed in distilled water

Question 31

What happens to an animal cell when placed in a hypotonic solution?

Answer 31

Water enters the cell, as the cell has less concentration of water than the extracellular, the cell swells and may burst or lyse.

Question 32

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

Answer 32

Water enters the cell, as there is less concentration in the cell than the extracellular, the cell swells a bit and becomes turgid due to the cell wall preventing the cell from bursting.

Question 33

What are the 6 factors affecting the rate of diffusion?

Answer 33

Concentration gradient
Size of particles
Membrane thickness
Surface area 
Distance
Temperature

Question 34

How does concentration gradient affect the rate of diffusion?

Answer 34

The greater the difference in concentration of a substance in 2 areas, the faster the rate of diffusion

Question 35

How does the size of particles affect the rate of diffusion?

Answer 35

Small particles tend to diffuse faster than larger particles.

Question 36

How does membrane thickness affect the rate of diffusion?

Answer 36

Diffusion takes place more quickly through a thin membrane because there is only a short diffusion pathway.

Question 37

How does surface area affect the rate of diffusion?

Answer 37

Diffusion is quicker if the membrane has a large surface area.

Question 38

How does distance affect the rate of diffusion?

Answer 38

The shorter the distance between two regions, the faster the rate.

Question 39

How does temperature affect the rate of diffusion?

Answer 39

An increase in temperature increases the rate of diffusion because the particles will have greater kinetic energy.

Question 40

How does Volume and Surface Area ratio of a membrane affect the rate diffusion?

Answer 40

As organisms get bigger, Surface area:Volume ratio of a cell gets smaller.
So as organisms get bigger, the more difficult it is form them to exchange materials with the surroundings (diffusion)

Question 41

Why are cells small?

Answer 41

They are small as,
A cell increasing in size reaches a point where the inward movement of essential substances and outward movement of wastes across the surface are by diffusion is not as fast and doesn’t come to the service of increasing volume of the cell.