transport across cell membranes

Question 1

What is diffusion?

Answer 1

The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.

Question 2

What factors affect diffusion?

Answer 2

• Temperature
• Concentration difference

Question 3

How does temperature affect diffusion?

Answer 3

The higher the temperature the higher the rate of diffusion. This is because the particles have more kinetic energy and move at higher speeds.

Question 4

How does concentration difference affect diffusion?

Answer 4

The greater the difference in concentration between two regions the faster the rate of diffusion, this is because the overall movement from the higher concentration to lower concentration will be larger.

Question 5

What does diffusion across membranes involves particles passing through?

Answer 5

The phospholipid bilayer.

Question 6

What does the membrane allow to diffuse across and what does the hydrophobic interior repel?

Answer 6

Allows - Non- polar molecules e.g oxygen
Doesn’t allow - positive or negative ions

Question 7

What are membranes described as in terms of permeability?

Answer 7

partially permeable

Question 8

What affects the rate at which molecules or ions diffuse across a membrane?

Answer 8

• Surface area
• Thickness of membrane

Question 9

How can surface area affect diffusion?

Answer 9

The larger the area of an exchange surface, the higher the rate of diffusion.

Question 10

How can the thickness of membrane affect diffusion?

Answer 10

The thinner the exchange surface, the higher the rate of diffusion.

Question 11

What is facilitated diffusion?

Answer 11

Diffusion across a membrane through protein channels.

Question 12

As most protein channels are specific to one molecule or ion what is known as?

Answer 12

Selectively permeable

Question 13

What does the rate of facilitated diffusion depend on which simple diffusion doesn’t depend on?

Answer 13

The number of protein channels present. The more protein channels, the higher the rates of diffusion.

Question 14

What type of process is active transport?

Answer 14

Active process -> requires energy

Question 15

What is active transport?

Answer 15

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration, up a concentration gradient.

Question 16

What is the metabolic energy for active transport supplied from?

Answer 16

ATP

Question 17

Which types of proteins are involved in active transport and what do they do?

Answer 17

Carrier proteins span the membranes and acts as “pumps”

Question 18

What is the process of active transport?

Answer 18

1- The molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell.
2- On the outside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
3- Binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up the inside of the cell.
4 - The molecule or ion is released to the inside of the cell.
5- The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
6- The carrier protein returns to its original shape.

Question 19

What is the process of active transport known as?

Answer 19

Selective - Specific substances are transported by specific carrier proteins

Question 20

What is bulk transport?

Answer 20

• Another form of active transport
• Large molecules such as enzymes, hormones, and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of cell by bulk transport.

Question 21

What is endocytosis?

Answer 21

• The bulk transport of material into cells.

Question 22

What are the two types of endocytosis?

Answer 22

Phagocytosis - For solids
Pinocytosis - For liquids

Question 23

What is the process for endocytosis?

Answer 23

• The cell-surface membrane first invaginate (bends inward) when it comes into contact with the material to be transported.
• The membrane enfolds the material until eventually the membrane fuses, forming a vesicle. The vesicle pinches off and moves into the cytoplasm to transfer the material for further processing within the cell.

Question 24

Process of exocytosis.

Answer 24

-Vesicles usually formed by the Golgi apparatus move towards and fuse with the cell surface membrane.
-The contents of the vesicle are then released outside of the cell.

Question 25

What is osmosis?

Answer 25

The diffusion of water across a partially permeable membrane.

Question 26

what type of process is osmosis?

Answer 26

Passive process - doesn’t require energy.

Question 27

What is water potential?

Answer 27

The pressure exerted by water molecules as they collide with a membrane or container.

Question 28

What is the net movement like in water in terms of water potential?

Answer 28

There will be net movement of water from the solution with the higher water potential ( less concentrated) to the solution with the lower water potential ( more concentrated). This will continue until the water potential is equal on both sides of the membrane (equilibrium).

Question 29

What is the effect of osmosis in animal cells of placed in solution with higher water potential than cytoplasm?

Answer 29

• Water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell.
• Due to the animal cell-surface being thin and not having cell walls it cannot stretch and the cell will burst.

Question 30

What is it known as when the animal cell bursts due to osmosis?

Answer 30

Cytolysis

Question 31

What is the effect on animal cells for osmosis if it is placed in a solution that has a lower potential than cytoplasm?

Answer 31

• It will lose water to the solution by osmosis down a water potential. This will cause a reduction in the volume of the cell and the cell-surface membrane to crenation.

Question 32

How does animals try to prevent water loss by osmosis?

Answer 32

• Multicellular animals usually make sure their cells are continuously surrounded by aqueous solutions with equal water potential (isotonic).

Question 33

What is the effect of osmosis on plant cells?

Answer 33

• When water enters by osmosis the increased hydrostatic pressure pushes the membrane against the rigid cell walls.
• Pressure against the wall is called turgor. As the turgor pressure increases it resists the entry of further water and cell is said to be turgid.
• When plant cells are placed in a solution with a lower water potential than their own, water is lost from cells by osmosis.

Question 34

What happens when there is a reduction to in the volume of the cytoplasm in a plant cell due to osmosis?

Answer 34

Cell- surface membrane is eventually pulled away from cell wall- cell is said to be plasmolysed.