Biological membranes

Question 1

What is the role of membranes within cells.

Answer 1

In mitochondria as folded cristae
Chloroplasts membranes have thylakoids

Question 1

What is the role of membranes

Answer 1

To spectate cell components from its external environment
Regulate transport of materials in and out cell
Site of chemical reactions
Has antigens
Involved in cell communication and signalling

Question 2

Describe the fluid mosaic model

Answer 2

Membrane consists of a phospholipid bilayer which consists of phospholipid molecules with hydrophilic heads and hydrophobic tails. Proteins float among the lipids creating a mosaic pattern and the lipids can move providing it with fluidity

Question 3

What are carrier proteins?

Answer 3

Change their shape to carry specific molecules across the membrane

Question 4

What are channel proteins?

Answer 4

These have pores which act as channels to allow ions which have an electrical charge

Question 5

How do small molecules pass through

Answer 5

Can simply diffuse through the cell membrane or dissolve in the lipid bilayer and pass through

Question 6

What is simple diffusion?

Answer 6

The movement of molecules from an area of high concentration to an area of low concentration

Question 7

What molecules pass through simple diffusion?

Answer 7

Oxygen and carbon dioxide

Question 8

How does temperature affect rate of diffusion?

Answer 8

Increased temperature increases the level of kinetic energy which increases diffusion

Question 9

How does distance affect rate of diffusion?

Answer 9

A thicker membrane reduces the rate of diffusuion

Question 10

How does surface area affect rate of diffusion?

Answer 10

A larger surface area means there is a higher rate of diffusion

Question 11

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

Answer 11

Smaller molecules mean there is a faster rate of diffusion

Question 12

How does concentration gradient affect rate of diffusion?

Answer 12

The steeper the concentration higher the rate of diffusion on down gradient

Question 13

What is facilitated diffusion

Answer 13

Movement of molecules from an area of high concentration to area of low concentration across partially permeable membrane via proteins channels or carriers

Question 14

What is osmosis

Answer 14

Passage of water molecules down their water potential gradient across a partially permeable membrane

Question 15

What is water potential?

Answer 15

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

Question 16

What is the highest water potential

Answer 16

0 pure water with no solute

Question 17

what is a lower water potential?

Answer 17

• 10 which is dilute with a small amount of solute

Question 18

what is a very low water potential?

Answer 18

• 500 which is concentrated and has large amount of solute dissolved

Question 19

what is the water potetntial in cells

Answer 19

lower than pure water as there are solutes in the vacuole and cytoplasms

Question 20

what. happens when animals cells are placed into a solution of higher water potential?

Answer 20

water moves down ny osmosis into the cell and the cell may start to swell and burst this is called cytolysis

Question 21

what happens when plant cells are placed into a solution of higher water potential

Answer 21

the strong cellulose wall will prevent bursting and it becomes tugged and swells

Question 22

what happens when an animal cell is placed in a lower water potential

Answer 22

the water leaves the cell by osmosis and the cells shrivel and cdenale

Question 23

what happens when a plant cell is placed in a lower water potential ?

Answer 23

the cytoplasm of the plant cell shrinks and the membrane pulls away from the cellulose cell wall so becomes plasmolyse and placid

Question 24

what is endocytosis?

Answer 24

when large particles enter a cell. a segment of the plasma membrane surrounds and encloses the particles and brings it into the cel enclosed in a vesicle. ATP is needed to provide energy to form the vesicles and move them suing more proteins across the cytoskeleton

Question 25

what is exocytosis?

Answer 25

large molecules exported out of cells. a membrane bound vesicles which contains the substance to be secreted is moved towards the cell surface membrane. the vesicle then fuses with the cell surface membrane and then opens to release the contents

Question 26

how does reduced temperature affect membrane structure and permeability?

Answer 26

• saturated fatty acids care compressed
• instructed fatty acids from links when compressed which pushes adjacent molecules away and maintains fluidity
• cholesterol prevent molecules packing too close

Question 27

how does increasing temperature affect membrane structure and permeability?

Answer 27

• phospholipids have more kinetic energy to move and increase fluidity
• increased permeability
• high temperatures however cause the atoms within molecules to vibrate and breaks the hydrogen and ionic bonds within proteins, this causes the tertiary structure to change and the shape changes irreversibly.
• cytoskeleton may denature which claimed plasma membrane to become more permeable as holes from

Question 28

how do solvents affect membranes?

Answer 28

organi solvents like acetone and ethanol damage cell membranes as they dissolve lipids