Chapter 5 Biological Membranes

Question 1

Describe the structure of the Fluid Mosaic Model

Answer 1

Phospholipids form a continuous bilayer that is ‘fluid’ as the phospholipids are constantly moving
Cholesterol molecules are present within the bilayer
Protein molecules are present within the the bilayer or attached to the outside of the bilayer

Question 2

Describe the structure of the Phospholipid bilayer

Answer 2

Phospholipids contain polar hydrophilic head that arrange themselves on the outside of the membrane, facing the aqueous solution and hydrophobic non polar tails which form the inner core of the bilayer.
The hydrophobic centre acts as a barrier to prevent water soluble substances such as ions from move through it.
However, fat- soluble substances are able to dissolve in the bilayer and pass through.

Question 3

What is the function of cholesterol in plasma membranes?

Question 4

Describe the process of cell signalling

Answer 4

A cell releases a messenger molecules (eg, hormone) which travels to another cell

Question 5

What is diffusion?

Answer 5

Net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient. (Molecules will diffuse both ways, however the net movement will be to the area of low concentration)
Passive process

Question 6

What molecules are able to diffuse through the membrane?

Answer 6

Small, non polar molecules such as Carbon dioxide and oxygen can diffuse between the spaces of phospholipids.
Water can also diffuse across the membranes via osmosis.

Question 7

What factors affects the rate of diffusion?

Answer 7

Concentration gradient
Thickness of the exchange surface
Surface area
Temperature

Question 8

How does concentration affect the rate of diffusion?

Answer 8

The higher the concentration, the faster the rate of diffusion

Question 9

How does the thickness of the exchange surface affect the rate of diffusion?

Answer 9

The thinner the exchange surface (shorter the distance that particles have to travel) the faster the rate of diffusion

Question 10

How does surface area affect the rate of diffusion?

Answer 10

The larger the surface area of a cell membrane the faster the rate of diffusion

Question 11

How does temperature affect the rate of diffusion?

Answer 11

The higher the temperature, the faster the rate of diffusion because molecules have more kinetic energy

Question 12

Describe an experiment to investigate the factors that affect the arteries of diffusion

Answer 12

1- Make up agar jelly with phenolphthalein and dilute sodium hydroxide
2- Fill a beaker with dilute hydrochloric acid, using a scalpel cut cubes from the jelly and put the, into the acid
3- Leaving the cubes in means they will eventually turn colourless as the acid difusss into the agar jelly neutralising the Sodium hydroxide

Surface area
Cut jelly cubes into different sizes and work out volume to surface area, time now long it takes for cube to turn colourless when paced into the same concentration of HCl
Temperature
Put tubes of HCl of same cconetrationa jd volume into water bath pf varying temperature
Pit equal sizes of cubes into the test tubes and time how long it takes to go colourless

Concentration gradient
Different concentrations of HCL
Put equal sized cubes of agar jelly into each test tube and time how long it takes for one to turn colourless

Question 13

WHAT is facilitated diffusion?

Answer 13

Movement of larger molecules, ions and polar molecules down a concentration gradient through channel or carrier protein s
Passive

Question 14

What do carrier proteins carry

Answer 14

Large molecules

Question 15

How does a carrier protein work?

Answer 15

A large molecule attaches to the carrier protein in the membrane
Protein chnages shape
Releasing molecule onto opposite side

Question 16

What do channel proteins carry

Answer 16

Charged particles - ions and polar modules

Question 17

How do channel proteins work

Answer 17

Form pores in the membrane that allow charged particles to move down the concentration gradient.

Question 18

Hat is active transports

Answer 18

Used energy to move molecules and ions against a concentration gradient involving carrier proteins

Question 19

Ow does active transport work

Answer 19

Molecules attached to the carrier proteins, the protein chnages chape moving the molecule across the membrane and releasing onto other side
ATP is used to move the solute against concentration gradient

Question 20

Describe the process of endocytosis

Answer 20

Large molecules (proteins, lipids, carbohydrates, white blood cells ) move in by this process
A section of a plasma membrane of a cell surrounds substance
Membrane pinches off to form a vesicle inside the cell
ATP is used in this process active

Question 21

Describe the process of exocytosis

Answer 21

Vesicles pinch off from sacs of Golgi apparatus and move toward plasma membrane
Vesicles fuse with plasma membrane and release contents outside cell
Some substances like Membrane proteins are not rerelease outside ceel, but inserted into plasma membrane
ATP is used for energy

Question 22

What is osmosis

Answer 22

Difussion of water molecules across partially permeable membrane down a water potential gradient, form an area of high water potential to an area of low water potential
(Less negative ro more negative)

Question 23

What is water potential

Answer 23

Likelihood of water molecules to diffuse into out of of cell

Question 24

What is an isotonic solution

Answer 24

Solutions with the same water potential as the cell (water still moving in and out however no net movement.)

Question 25

What is hypotonic solution.

Answer 25

Solutions with higher water potential than the cell

Question 26

What is hyper tonic solution

Answer 26

Solutions with lower water potential than the cell

Question 27

How does hypotonic solution affect animal cells

Answer 27

Net movement of water molecules into the cell- cell burst

Question 28

How does isotonic solutions affect animal cells

Answer 28

Wateer molecules pass into and out of the cells in equal amounts - cell stays same

Question 29

How does hypertonic solutions affect animal cells

Answer 29

Net movement of water out of cell causes shell to shrink

Question 30

How does hypotonic solutions affect plant cells

Answer 30

Net movement of water into cell, vacuole swells and vacuole and cytoplasm push again cell wall
Turgid

Question 31

How does isotonic solutions affect plant cells

Answer 31

Water molecules move into nd out of cell in equal amounts - cell ramens same

Question 32

How does hypertonic solutions affect plant cells

Answer 32

Net movemt of water is out of cell so cell becomes flaccid
Ceytoplasm and vacuole move away from cell wall plasmolysis

Question 33

Describe an investigation to measure water potential an

Answer 33

Putting potato cylinders into different concentrations of sucrose
Prepare concentrations of sucrose
Use cork borer to cut potatoes to same size- 18 cylinders
Divide the chips into groups of three and use mass balanace to measure mass of each group
Place one group in each solution
Leave Chios fro 20 minutes or more
Remove chips and pat dry with paper towel
Weigh mass gain of each group and record results
Calculate % chnage of mass for each group
Plot result on graph