Transport Across Membranes

Question 1

What is a cell membrane made out of?

Answer 1

Phospholipids bilayer

The hydrophilic heads and hydrophobic tails separate the two environments from the external and internal sides of a cell.

Question 2

What are the main components in a cell membrane? And give their functions

Answer 2

Phospholipid bilayer- separates internal and external environments

Protein channels- transports charged ions across the membrane

Protein carriers- transports small molecules across the membrane

Cholesterol- regulates fluidity of the membrane

Cytoskeleton filaments- provides mechanical strength to the membrane

Glycolipids- antigens for self recognition

Glycoproteins- antigens for self recognition

Question 3

What are the main functions of the plasma membranes?

Answer 3

Partially permeable barriers:
Allows small molecules to diffuse through and lipid soluble molecules to diffuse through. Contains channel and carrier proteins for the non polar or charged molecules which may be too big to move through

Regulation of substances in and out of the cells

Regulation of metabolic pathways

Antigens - self recognition

Cell signalling

Question 4

What is the purpose of a membrane within cells?

Not cell surface/plasma membrane

Answer 4

Separate organelle contents from the cytoplasm of a cell

Question 5

Why is the cell membrane described as fluid mosaic?

Answer 5

Cell membranes are aqueous and have cholesterol to regulate the fluidity of the membrane (hence fluid part)

Then phospholipids are all aligned adjacent to one another creating a mosaic pattern

Question 6

What happens to phospholipids when the temperature decreases?

Answer 6

Saturated fatty acids become compressed so the fluidity decreases however cholesterol and the unsaturated fatty acids make the membrane more fluid to maintain their normal fluidity.

Question 7

What happens to phospholipids when the temperature increases

Answer 7

More kinetic energy and therefore the membrane becomes more fluid
But
Cholesterol resists these changes and maintains the normal fluidity levels

Question 8

What happens to the proteins in a cell membrane when the temperature is increased?

Answer 8

The tertiary structure of the proteins change and the proteins denature

Cytoskeleton threads are proteins that hold the membrane in place and therefore if they denature, the cells membrane deforms causing the cell to die.

Question 9

What kind of solvents would destroy cell membranes?

Answer 9

Acetone and ethanol

Question 10

What is a passive process?

Answer 10

A process which does not require metabolic energy from ATP

Question 11

What is diffusion?

Answer 11

The passive movement of molecules from an area of higher concentration to and area of lower concentration.

Question 12

What is facilitated diffusion?

Answer 12

Diffusion of molecules across a partially permeable membrane through carrier or channel proteins from an area of higher concentration to an area of lower concentration

Question 13

What is osmosis?

Answer 13

Movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane

Question 14

Define turgid?

Answer 14

A plant cell fully filled with water

Question 15

Define plasmolysed?

Answer 15

Plant cell whose cell membrane has pulled away from the cell wall due to a loss of water

Question 16

Define flaccid

Answer 16

A plant cell that is limp due to a reduction of pressure against the cell wall

Question 17

Define crenation

Answer 17

Lysis of an animal cell due to influx of water

Question 18

What factors affect the rate of diffusion?

Answer 18

Temperature
Diffusion distance
Size of diffusion molecule
Surface area
Concentration gradient

Question 19

What is water potential?

Answer 19

A measure of the tendency of water molecules to diffuse from one region to another

Question 20

What is active transport?

Answer 20

Movement of molecules against the concentration gradient from an area of lower concentration to an area of higher concentration which requires energy from ATP

Also requires channel/ carrier proteins

Question 21

How does ATP help in the transport of molecules across a membrane?

Answer 21

The hydrolysis of ATP releases energy to slightly change the shape of carrier proteins enabling a specific molecule to bind to it and be taken into a cell.

Question 22

What is endocytosis?

Answer 22

Movement of molecules in to a cell

Question 23

What is exocytosis?

Answer 23

Movement of molecules out of a cell

Question 24

What is pinocytosis?

Answer 24

Where a Pinocyte engulfs a particle that is a liquid

Question 25

What is phagocytosis?

Answer 25

When a phagocyte engulfs a small cell or particle such as bacteria